handout liquid penetrant test level ii - rev. 3 - 28 august 2009

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TRAINING HAND OUT

LIQUID PENETRANT TESTING General

Editor: Wing Hendroprasetyo, M.Eng. ASNT NDT Level III (ID No. 144934)

NDE CENTER DEPARTMENT OF NAVAL ARCHITECTURE AND SHIPBUILDING ENGINEERING FACULTY OF MARINE TECHNOLOGY SEPULUH NOPEMBER INSTITUTE OF TECHNOLOGY (ITS) – SURABAYA

Kampus ITS Keputih, Sukolilo Surabaya 60111 Telp./Fax. 031 591 4533 Mobile 0816 542 8017

Rev. 3, ‐ 28 August 2009

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CONTENTS page

CHAPTER ONE 5

Introduction 5

Basic Principles 7

The Nature of Discontinuity 8

Surface Conditioning 9

History 10

Commercially Available Liquid Penetrant Materials 11

Chapter One Review 15

CHAPTER TWO 16

Introduction 16

Surface Preparation 16

Detergent Cleaning 17

Vapor Degreasing 17

Steam Cleaning 17

Solvent Cleaning 17

Rust and Scale Remover 18

Paint Removal 18

Etching 18

Ultrasonic Cleaning 18

Mechanical Cleaning 18

Stationary Penetrant Test Equipment 20

Portable Penetrant Test Equipment 21

Black Light Equipment 22

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Penetrant Material Combinations 23

Penetrant Testing Materials 24

Safety Precaution 26

Chapter Two Review 29

CHAPTER THREE 28

Introduction 28

Cleaning 28

Penetrant Application 29

Penetration (Dwell) Time 31

Penetrant Testing Processes 33

Leak-through Technique 37

Filtered Particle Technique 37

Fixing and Recording Indications 38

Chapter Three Review 39

CHAPTER FOUR 40

Introduction 40

Post-emulsifiable Penetrant (PE Penetrant) 40

Lipophilic Method 43

Hydrophilic Method 44

Developers Application 45

Dry Developers 45

Wet Developers 46

Guidelines to Choose Developer 48

Chapter Four Review 49

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CHAPTER FIVE 50

Introduction 50

Inspection 50

Interpretation and Evaluation of Indications 50

Typical Indications in Penetrant Inspection 51

False Indications 51

Nonrelevant Indications 52

True Indications 52

Depth Determination of Penetrant Discontinuities 56

Post Cleaning 56

Quality Control of Penetrant Process Variables 56

Aluminum Test Block 56

Sensitivity Test 57

Meniscus Test 57

Ceramic Block Test 58

Water Content Test 58

Viscosity Test 58

Fluorescent Penetrant Fade Test 59

Water Washability Test 59

Developer Test 59

Portable Equipment 59

Lighting 60

Chapter Five Review 61

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CHAPTER SIX 62

Introduction 62

Categories of Discontinuities 62

The Origins of Discontinuities 63

Casting Discontinuities 64

Processing Discontinuities 66

Working the Billet 66

Forging Discontinuities 68

Service Discontinuities 73

Chapter Six Review 75

CHAPTER SEVEN 76

Introduction 76

Identification and Comparison of Discontinuities 76

Training and Certification 77

Chapter Seven Review 79

CHAPTER EIGHT 80

Introduction 80

Controlling Liquid Penetrant Tests 80

Standards 80

Specifications 80

Written Practice 82

Sample Specification – Penetrant Testing Process 83

Chapter Eight Review 90

REFERENCES 93

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CHAPTER ONE

INTRODUCTION

Liquid penetrant testing is a nondestructive means of locating surface discontinuities based on capillarity or capillary action. Capillary action is responsible for both penetrant entry and exit from discontinuities.

In the liquid penetrant method, the liquid is applied to the surface of the specimen and sufficient time is allowed for penetration of surface discontinuities. If the discontinuity is small or narrow as in a crack or pinhole, capillary assist the penetration.

PENDAHULUAN

Pengujian cairan penetrant merupakan pengujian tanpa merusak untuk menemukan diskontinuitas permukaan berdasarkan prinsip kapilaritas. Kapilaritas bertanggung jawab terhadap masuk dan keluarnya cairan penetrant dari dan ke dalam diskontinuitas.

Pada metoda cairan penetrant, cairan diaplikasikan di atas permukaan spesimen dan diberikan waktu yang cukup untuk menyusup ke dalam diskontinuitas. Jika diskontinuitasnya kecil dan sempit seperti pada retak atau lubang jarum, kapilaritas membantu penetrasi.

After sufficient time has passed for the penetrant to enter the discontinuity, the surface of the part is cleaned. Capillary action is again employed to act as blotter to draw penetrant from the discontinuity.

Setelah waktu mencukupi bagi penetrant untuk memasuki diskontinuitas, permukaan spesimen kemudian dibersihkan. Gaya kapiler sekali lagi bekerja sebagai penghisap yang menarik penetrant keluar dari dalam diskontinuitas.

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Liquid penetrant inspection is a physical-chemical process. Application and reaction of the penetrant (chemical) is dependent upon the nature of the test article and the discontinuity it contains (physical).

The ability of penetrant to spread over a solid surface is referred to as the wetting ability. The wetting ability and contact angle between solid-liquid are inversely proportional. The higher the wetting ability, the smaller the contact angle. The contact angle determines the wetting ability.

Penetrating capability of a liquid penetrant is controlled by:

• Surface tension.

• Contact angle.

Pemeriksaan penetrant merupakan proses fisika-kimia. Aplikasi dan reaksi cairan penetrant (kimia) tergantung pada sifat artikel yang diuji dan diskontinuitas yang terdapat padanya (fisika).

Kemampuan penetrant untuk menyebar di atas pemukaan benda padat disebut kemampu-basahan (wetting ability). Wetting ability dan sudut kontak (contact angle) antara benda cair dan padat adalah berbanding terbalik secara proporsional. Sudut kontak menentukan wetting ability.

Kemampuan penyusupan cairan penetran dikendalikan oleh:

• Tegangan permukaan.

• Sudut kontak.

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BASIC PRINCIPLES

To insure visibility, the liquid penetrant contains either a colored dye easily seen in white light, or a fluorescent dye visible under black (ultraviolet) light.

A penetrant examination consists of the following basic steps, regardless of the material tested:

• Step 1: The test object or spot is thoroughly cleaned and dried.

• Step 2: The penetrant is applied. Dwell time is allowed to penetrate discontinuities.

• Step 3: The excess surface penetrant is removed.

• Step 4: Developer is applied

• Step 5: Indications are evaluated and accepted or rejected.

• Step 6: After the penetrant test, the test object or spot is postcleaned.

PRINSIP-PRINSIP DASAR

Agar dapat terlihat, cairan penetrant diberi pewarna merah yang dapat dilihat dengan cahaya biasa atau pewarna fluorescent yang dapat dilihat dengan cahaya ultraviolet.

Pengujian penetrant terdiri dari tahapan-tahapan berikut tanpa mempertimbangkan material yang diuji:

• Langkah 1: Pembersihan dan pengeringan benda atau lokasi yang diperiksa.

• Langkah 2: Aplikasi penetrant. Dibiarkan beberapa lama agar menyusup ke dalam diskontinuitas.

• Langkah 3: Pembersihan penetrant sisa di permukaan.

• Langkah 4: Aplikasi developer

• Langkah 5: Evaluasi indikasi, diterima atau ditolak.

• Langkah 6: Pembersihan benda atau lokasi setelah selesai diuji.

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THE NATURE OF DISCONTINUITY

Discontinuities that are subsurface in one stage of production could be open to the surface at another stage, such as after grinding or machining.

Nonmetallic inclusions and porosity in the ingot may cause stringers, seams, forging laps, cold shuts, and the like as the billet or slabs is processed in the manner shown below.

SIFAT DISCONTINUITAS

Diskontinuitas yang terletak dibawah permukaan pada satu tahapan produksi dapat terbuka ke permukaan pada tahapan lainnya seperti akibat penggerindaan dan permesinan.

Inklusi nonlogam dan porositas dalam ingot dapat menyebabkan stringers, seams, lipatan tempa, cold shuts, dan sejenisnya saat billet atau slab diproses dengan cara seperti di bawah ini.

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SURFACE CONDITIONING

Anything that could block the penetrant from entering the discontinuity must be removed.

A list of contaminants that must be removed would include DIRT, GREASE, RUST, SCALE, ACIDS, and even WATER. The cleaning solvent used must be volatile (readily vaporized) so that it easily evaporates out of the discontinuity and does not dilute the penetrant.

Surface preparation by mechanical cleaning such as wire brushing, abrasive blasting, emery cloths, and metal scraping are not generally recommended, but there are times when they must be used.

When they are used, discontinuities that are open to the surface may be closed as ilustrated below.

PENGKONDISIAN PERMUKAAN

Semua kotoran yang menghalangi penetrant untuk memasuki diskontinuitas harus dibersihkan.

Jenis kotoran yang harus dibersihkan meliputi DEBU, GEMUK, KARAT, KERAK, ASAM, bahkan AIR. Solvent yang digunakan untuk pembersih harus mudah menguap sehingga cepat keluar dari dalam dikontinuitas dan tidak mengencerkan penetrant.

Pembersihan permukaan secara mekanis seperti memakai sikat baja, abrasive blasting, kertas gosok, dan alat sekrap umumnya tidak direkomendasikan, namun ada kalanya cara-cara tersebut harus digunakan.

Apabila digunakan cara-cara di atas, diskontinuitas yang membuka ke permukaan dapat tertutupi seperti gambar di bawah ini.

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HISTORY

Historically, penetrant inspection was called “oil and whiting” method. The oil and whiting method used in the railroad industry, i.e. locomotive parts, etc. (axles, crank pins and couplers), in the early 1900s was the first recognized use of the principles of penetrants to detect cracks.

The oil and whiting method used dirty or dark-colored lubricating oil that was thinned with kerosene followed by the application of a whiting or chalk coating, which absorbed oil from the cracks revealing their locations.

By the 1940s, fluorescent or visible dye was added to the oil used to penetrate test objects.

Following is stages of oil and whiting method.

SEJARAH PENGUJIAN PENETRANT

Menurut sejarahnya, pemeriksaan penetrant dulunya disebut metoda “minyak dan kapur”. Pada awal tahun 1900an, metoda ini digunakan dalam industri perkeretaapian untuk memeriksa kompo-nen lokomotip (batang torsi, batang penggerak, dan coupler, dll.), yang merupakan awal mula dike-nalnya prinsip penetrant untuk mendeteksi retak.

Metoda minyak dan kapur memakai minyak lumas hitam yang diencerkan dengan minyak tanah, diikuti dengan aplikasi bubuk kapur di atasnya yang akan menyerap minyak dari dalam retak sehingga dapat diketahui lokasinya.

Pada tahun 1940an, zat pewarna merah dan fluorescent dicampurkan ke dalam oli yang digunakan untuk pemeriksaan.

Berikut adalah tahapan metoda pengujian minyak dan kapur.

Experience showed that temperature and soak time were important.

This started the practice of written instructions to provide standard, uniform results. The use of written procedures has evolved, giving the ability for design engineers and manufacturers to get the same high standard results from any properly trained and certified liquid penetrant testing technician.

Pengalaman mengajarkan pentingnya mempertim-bangkan suhu dan waktu celup.

Hal tersebut memicu diterapkannya penggunaan instruksi tertulis agar hasil pengujian menjadi standard dan seragam. Pemakaian prosedur tertulis diharapkan menjadikan pemeriksaan penetrant akan memberikan hasil dengan standard tinggi jika dikerjakan oleh teknisi yang terlatih.

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Table 1.1. Basic liquid penetrant classification system.

COMMERCIALLY AVAILABLE LIQUID PENETRANT MATERIALS

The liquid penetrants used in nondestructive testing can be categorized by the type of dye they contain.

1. Visible dye penetrants contain a colored (usually red) dye.

2. Fluorescent penetrants contain a fluorescent dye

3. Dual sensitivity penetrants contain a combination of visible and fluorescent dyes.

Penetrants can be further categorized by the processes used to remove the excess penetrant from the specimen.

1. Water-washable penetrants, are either self-emulsifying or removable with plain water.

2. Post-emulsifiable penetrants require a separate emulsifier to make the penetrant water washable.

3. Solvent-removable penetrants must be removed with a solvent which is typical when using visible dye in pressurized spray cans.

The basic liquid penetrant classification system is shown in Table 1.1.

MATERIAL CAIRAN PENETRANT YANG TERSEDIA DI PASARAN

Cairan penetrant yang dipakai di dalam NDT dapat dikagorikan berdasarkan jenis zat pewarna yang ditambahkan.

1. Visible dye penetrants mengandung zat pewarna merah.

2. Fluorescent penetrants mengandung zat pewarna fluorescent (hijau-kuning).

3. Dual sensitivity penetrants, mengandung kombinasi kedua zat pewarna, visible dan fluorescent.

Penetrant dikelompokkan lebih lanjut berdasarkan proses pembersihan sisa penetrant dari permu-kaan spesimen.

1. Water-washable penetrants, mengandung zat pengemulsi atau dapat dibilas dengan air.

2. Post-emulsifiable penetrants, memerlukan pengemulsi terpisah untuk menjadikan penetrant dapat dibilas dengan air.

3. Solvent removable penerants, harus dibersihkan dengan solvent khusus jika menggunakan penetrant visible dalam kaleng bertekanan.

Sistem klasifikasi cairan penetrant dapat dilihat dalam Tabel 1.1.

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The flowchart below illustrates the processing sequence with visible and fluorescent penetrants.

Diagram alir berikut memperlihatkan urutan proses dengan penetran visible dan fluorescent.

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Dual sensitivity penetrants would follow a processing sequence similar to that shown below.

Dual sensitivity penetrants mengikuti urutan proses yang diperlihatkan diagram alir di bawah ini.

The selection of the best process depends upon:

1. Sensitivity required. 2. Number of articles to be tested. 3. Surface condition of part being

inspected. 4. Configuration of test specimen. 5. Availability of water, electricity,

compressed air, suitable testing area, etc.

Pemilihan proses terbaik ditentukan oleh:

1. Sensitivitas yang disyaratkan. 2. Jumlah artikel yang diuji. 3. Kondisi permukaan komponen yang

diperiksa. 4. Konfigurasi benda uji. 5. Ketersediaan air, listrik, udara bertekanan,

lokasi pengujian yang sesuai, dll.

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Penetrant testing is succesfully used on most any materials, including metallic and nonmetallic objects.

Metallic materials include aluminum, magne-sium, titanium, cast iron, stainless steel, powdered metal products, copper, brass, and bronze, as well as most other common alloys.

Nonmetallic materials include ceramics, plastic, molded rubber, composites, and glass.

Penetrant testing is limited by its inability to test materials with discontinuities that are NOT OPEN to the surface or having extremely porous surface.

List below indicates the penetrant systems, ranging from the most sensitive and expensive to the least one.

1. Post-emulsified – fluorescent. 2. Solvent-removable – fluorescent. 3. Water-washable – fluorescent. 4. Post-emulsified – visible. 5. Solvent-removable – visible. 6. Water-washable – visible.

Pengujian penetrant secara memuaskan dapat diplikasikan pada kebanyakan material, termasuk material logam dan nonlogam.

Material logam termasuk aluminium, magnesium, titanium, besi cor, stainless steel, produk serbuk logam, paduan tembaga, kuningan, perunggu, juga paduan-paduan lainnya.

Material nonlogam termasuk keramik, plastik, karet, komposit, dan kaca.

Pengujian penetrant tidak dapat diaplikasikan untuk menemukan diskontinuitas yang TIDAK MEMBUKA ke permukaan dan permukaan material yang berpori.

Daftar berikut menunjukkan tingkat sensitivitas sistem penetrant, dari mulai yang paling senfitif dan paling mahal.

1. Post-emulsified – fluorescent. 2. Solvent-removable – fluorescent. 3. Water-washable – fluorescent. 4. Post-emulsified – visible. 5. Solvent-removable – visible. 6. Water-washable – visible.

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CHAPTER ONE REVIEW

_______ 1. Nonmetallic inclusions and porosity in the steel ingot are commonly found using liquid penetrant inspection techniques.

_______ 2. Type II penetrants, according to our test, are those containing a fluorescent dye.

_______ 3. Because of the capillary action of penetrants, this process of inspection works well on parts with very porous surfaces.

_______ 4. When doing a liquid penetrant test, the configuration of the specimen has little effect on the effectiveness of the test.

_______ 5. Liquid penetrant inspection can be used only on metals such as aluminum and steel.

_______ 6. The penetrant inspection method is used only on the finished product.

_______ 7. Oil and whiting are the names of the two men who invented the penetrant test method.

_______ 8. The first important step in penetrant testing is surface preparation.

_______ 9. One of the most common contaminants in the penetrant method is water.

_______ 10. The most common method of surface preparation for penetrant testing is sandblasting.

_______ 11. Chemical etching Is sometimes used to remove smeared metal from a surface to open discontinuilies.

_______ 12. Some subsurface defects can be tested with the highly sensitive Type II penetrants.

_______ 13. Blow holes and gas porosity may be detected with the penetrant method.

_______ 14. Solvent cleaning is a common method of surface cleaning parts before penetrant testing.

_______ 15. The one major limitation to penetrant testing is that the part must be metallic.

_______ 16. Grease and rust would usually be considered a contaminant on the surface of a test piece.

_______ 17. To locate a defect with penetrant testing, the defect must be open to the surface.

_______ 18. It is considered advantageous for a liquid penetrant material to have low tension and high capillarity.

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CHAPTER TWO

INTRODUCTION

This chapter discusses the equipment and material required to perform the various penetrant test and the required PRE and POST test cleaning.

SURFACE PREPARATION

As discussed in Chapter 1, there are SIX basic steps required for a penetrant test. Surface preparation is entered on the flow diagram below as step one.

PENDAHULUAN

Bab ini mendiskusikan peralatan dan bahan yang diperlukan untuk melakukan pengujian penetrant serta pembersihan material SEBELUM dan SESUDAH pengujian.

PENYIAPAN PERMUKAAN

Telah disampaikan dalam Bab 1 bahwa ada ENAM langkah dasar pengujian penetrant. Penyiapan permukaan dimasukkan sebagai langkah pertama dalam diagram alir berikut.

Surface preparation, including proper cleaning is essential to liquid penetrant testing for TWO reasons:

1. If the specimen is not physically and chemically clean and dry, penetrant testing may be ineffective.

2. If all tracess of penetrant materials are not removed after the test, they may have a harmful effect on the specimen after the test object is placed in service (chlorine and sulfur may affect some alloys).

Selection of the cleaning process breaks down to the following basic factors.

• Type of contaminant.

• Composition of the base material.

• Degree of cleanliness required.

• Availability of cleaning equipment.

• Cost and time factors.

Unless the cleaning methods and chemicals are known to be compatible with the penetrant, a final cleaning should be done with the solvent recommended by the manufacturer.

Pembersihan permukaan sangat penting dalam pengujian cairan penetrant karena DUA alasan:

1. Jika spesimen tidak bersih secara fisika dan kimia, pengujian penetrant menjadi tidak efektip.

2. Jika semua bekas material penetrant tidak dibersihkan setelah pengujian, maka akan merusak spesimen setelah benda tersebut terpasang (klorin dan sulfur dapat merusak beberapa jenis paduan).

Pemilihan proses pembersihan ditentukan oleh faktor berikut.

• Jenis kotoran yang dibersihkan.

• Komposisi logam induk.

• Tingkat kebersihan yang disyaratkan.

• Ketersediaan peralatan pembersih.

• Faktor-faktor biaya dan waktu.

Jika kompatibilitas antara metoda pembersihan, cairan pembersih dan penetrant tidak diketahui, pembersihan akhir sebaiknya dilakukan dengan solvent yang direkomendasikan oleh pabrik penetrant.

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DETERGENT CLEANING

Immersion tanks and detergent solution may be used as an effective method for removing surface soils, particularly when employed as a hot tank process.

However, since the solutions used may be either acidic or alkaline in nature, precautions must be taken to ensure that the selected detergent is noncorrosive to the article being cleaned.

When thoroughly rinsed and dried, detergent cleaning leaves a test surface that is physically and chemically clean.

VAPOR DEGREASING

Vapor degreasing is effective in the removal of oil, grease, and similar organic contaminants. This method does not remove solid contami-nants such as varnish, paint, scale, or oxide.

However, this method is considered as the most effective means of precleaning a test item prior to a penetrant test

Safety and environmental concerns have virtually eliminated vapor degreasing. The chlo-rinated solvents employed (methyl chloroform), if acidic, can be harmful to certain materials such as nickel, stainless steel, and titanium.

STEAM CLEANING

Steam cleaning is an excellent method of cleaning large articles, or portions of large articles that cannot be washed with detergents. It removes inorganic soils as well as many organic contaminants, but it may not reach to the bottom of deep discontinuities. A follow-up solvent soak is often recommended.

SOLVENT CLEANING

Solvent cleaning may use immersion tank, or the solvent may be sprayed, brushed, or wiped on and wiped off. Solvent cleaning is the process most commonly used for spot inspections.

Solvent cleaners should only be used to remove organic contaminants, and are not recommended for removing rust and scale, welding flux or spatter. Typical solvents are kerosene, paint thinner, alcohol, benzol, and trichloroethylene.

PEMBERSIHAN DENGAN DETERJEN

Tangki perendam dan larutan deterjen dapat dipakai sebagai metoda yang efektip untuk membersihkan kotoran permukaan, utamanya jika memakai proses tangki panas.

Namun demikian mengingat larutan yang dipakai dapat bersifat asam atau basa, harus diperhatikan agar deterjen yang dipilih tidak mengakibatkan korosi terhadap benda yang dibersihkan.

Bila dibilas dengan bersih dan dikeringkan, pembersih deterjen menghasilkan permukaan yang bersih secara fisika dan kimia.

PEMBERSIHAN DENGAN UAP SOLVENT

Uap solvent efektif untuk membersihkan minyak, gemuk, dan kontaminan organik sejenisnya. Metoda ini tidak menghilangkan kontaminan padat seperti pernis, cat, kerak, dan oksida.

Namun demikian, metoda ini dianggap sebagai cara yang paling efektip untuk membersihkan benda sebelum diuji penetrant.

Masalah keselamatan dan lingkungan telah melarang penggunaan metoda ini. Chlorinated solvent yang dipakai (methyl chloroform), jika bersifat asam dapat merusak material seperti nickel, stainless steel, dan titanium.

PEMBERSIHAN DENGAN UAP AIR

Pembersihan dengan uap air merupakan cara yang unggul untuk membersihkan benda beruku-ran besar yang tidak dapat dicuci dengan deterjen. Cara ini menghilangkan kotoran organik dan inorganik, namun tidak dapat mencapai dasar diskontinuitas yang dalam. Pencelupan ke dalam solvent setelahnya seringkali direkomendasikan.

PEMBERSIHAN DENGAN SOLVENT

Cara ini dilakukan dengan pencelupan, penyemprotan, penyikatan, atau pengusapan. Pembersihan dengan solvent merupakan proses yang umum digunakan untuk pemeriksaan setempat.

Solvent pembersih hanya untuk menghilangkan kotoran organik dan tidak diremomendasikan untuk menghilangkan karat dan kerak, flux pengelasan, atau percikan las. Cairan solvent contohnya minyak tanah, thinner cat, alkohol, benzol, dan trichloroethylene.

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RUST AND SURFACE SCALE REMOVER

Rust removers (descaling solutions, either alkaline or acid), pickling solutions (acid), and sometimes wire brushing are used to remove rust and surface scale. Wire brushing is accomplished with a minimum of pressure to avoid closing surface discontinuities or filing them with smeared metal.

PAINT REMOVAL

Dissolving type hot tank paint strippers and bond release or solvent paint strippers may be used to remove paint in precleaning.

ETCHING

Etching is normally required on soft metallic materials (such as aluminum and magnesium), materials that tend to smear (such as titanium), and materials which have been mechanically process-ed by machining, grinding, or similar procedure. Etching is accomplished with either an acid or an alkaline solution to open up grinding burrs and remove metal from surface discontinuities.

ULTRASONIC CLEANING

Ultrasonic cleaning equipment is useful in the cleaning of large quantities of small test objects. Ultrasonic cleaning is often combined with a solvent or detergent bath to improve cleaning efficiency and reduce cleaning time.

The method works best with water and deter-gent cleaning when contaminants to be removed are inorganic, and with solvents when contaminants are organic.

MECHANICAL CLEANING

Cleaning processes that are not generally recommended include abrasive blasting (shot, sand, grit, or pressure), liquid honing, emery cloth, wire brushes, and metal scrapers, but there are times when they must be used.

These processes tend to close discontinuities by peening or cold working the surface of the specimen.

PENGHILANG KARAT DAN KERAK PERMUKAAN

Penghilang karat dan kerak (larutan penghilang kerak, basa atau asam), larutan pickling (asam), dan kadang kala sikat baja digunakan untuk menghilangkan karat dan kerak permukaan. Penyikatan dilakukan dengan tekanan rendah untuk mencegah penutupan atau pengisian diskontinuitas permukaan oleh gram.

PENGHILANG CAT

Pengelupas cat dan pelepas ikatan memakai tangki pelarut panas atau solvent pengelupas cat dapat dipakai untuk menghilangkan cat saat pembersihan awal.

ETSA

Etsa biasanya disyaratkan pada material logam lunak (seperti aluminium dan magnesium), material yang cenderung teroksidasi (seperti titanium), dan material yang telah diproses secara mekanis melalui permesinan, penggerindaan atau sejenis-nya. Etsa dilakukan dengan larutan asam atau basa untuk membuka bekas gerinda dan menghilangkan gram dari permukaan diskonti-nuitas.

PEMBERSIHAN ULTRASONIK

Peralatan ultrasonik dipakai untuk membersihkan benda berukuran kecil yang jumlahnya banyak. Pembersihan ultrasonik seringkali memakai bak berisi cairan solvent atau deterjen untuk mening-katkan efisiensi pembersihan dan menghemat waktu.

Campuran air dan deterjen merupakan yang terbaik untuk membersihkan kontaminan inorganik, sementara cairan solvent untuk membersihkan kontaminan organik.

PEMBERSIHAN SECARA MEKANIS

Proses pembersihan yang umumnya tidak direko-mendasikan adalah abrasive blasting (pelor, pasir, atau tekanan), cairan pengasah, ampelas, sikat baja dan penyekrapan. Namun ada kalanya cara-cara tersebut harus dilakukan.

Proses ini cenderung menutup diskontinuitas dengan cara pemukulan atau pengerjaan dingin pada permukaan spesimen.

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Table 2.1. Mechanical cleaning processes.

Table 2.2. Chemical cleaning processes.

When mechanical cleaning must be used, closed discontinuities can be reopened with a chemical etch that removes a very slight amount of material from the surface.

Saat pembersihan mekanis harus dilakukan, diskontinuitas yang menutup dapat dibuka kembali dengan pengetsaan yang akan menghilangkan lapisan tipis material dari permukaan.

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CHAPTER TWO REVIEW

_______ 1. Wire brushing Is a common and acceptable method of surface cleaning a test part that is to be penetrant inspected.

_______ 2. A good exhaust system is recommended when working with cleaning solvents.

_______ 3. Vapor degreasing is often used to remove oxidation, rust, and scale before a part is penetrant inspected.

_______ 4. Parts that have been painted usually cannot be inspected with penetrants because suitable paint removing techniques have not been developed.

_______ 5. Detergent cleaning is acceptable for postcleaning but should never be used for precleaning because it may affect the emulsifier during the penetrant test.

_______ 6. Etching is often effective in precleaning a part that has been machined to a specific tolerance by surface grinding.

_______ 7. Only visible dye penetrants are available in portable kits because fluorescent dyes will not function in pressurized spray cans.

_______ 8. Dry developers are usually only used with visible dye penetrants.

_______ 9. Emulsifiers and solvents are both commonly used in penetrant testing as postcleaners.

_______ 10. Wet developers should never be used when they will come into contact with gaseous or liquid oxygen because of the results caused by oxygen and water mixing.

_______ 11. Emulsifiers must have high penetrating characteristics to emulsify penetrants that lie in fillets and corners.

_______ 12. The black light used in fluorescent penetrant inspection is not hazardous to the human eyes if the correct filter is in place and not broken or cracked.

_______ 13. Penetrant materials are often placed in groupings that will assure a valid test with materials that are compatible with each other.

_______ 14. Nonaqueous developer refers to a powder that is applied dry.

_______ 15. Post-emulsifiable penetrants are usually soluble in water after the application of an emulsifier.

_______ 16. Water-washable penetrants are cornmonly used with either a visible or fluorescent dye.

_______ 17. Flashpoint refers to the lowest temperature at which vapors will ignite when exposed to flame.

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CHAPTER THREE

INTRODUCTION

This chapter discusses penetrant application. As discussed in Chapter 2, surface cleaning is the first step prior to the penetrant application.

CLEANING

The effectiveness of liquid penetrant testing is based upon the ability of the penetrant to enter surface discontinuities. All paint, carbon, oil, varnish, oxide, plating, water, dirt, and similr coating must be removed before application of penetrant.

Liquid penetrant placed on the surface of a specimen does not merely seep into discontinuities. It is pulled into them by capillary action. This is the reason one can cover the under surface of an item with a penetrant and still have a valid test.

PENDAHULUAN

Bab ini mendiskusikan aplikasi penetrant. Seperti dibahas dalam Bab 2, pembersihan permukaan adalah tahap pertama sebelum aplikasi penetrant.

PEMBERSIHAN

Efektifitas pengujian cairan penetrant bergantung pada kemampuan penetrant untuk menyusup ke dalam cacat permukaan. Semua cat, karbon, oli, pernis, oksida, lapisan, air, kotoran dan cat sejenisnya harus dihilangkan sebelum aplikasi penetrant.

Cairan penetrant di atas permukaan benda uji tidak semata-mata meresap ke dalam diskontinuitas. Penetrant tertarik ke dalamnya oleh gaya kapiler. Inilah mengapa permukaan bagian bawah dari suatu benda masih dapat diperiksa dengan penetrant dan memperoleh hasil yang valid.

The following are typical cleaning methods discussed earlier.

1. Detergent cleaning 2. Vapor degreasing 3. Steam cleaning 4. Solvent cleaning 5. Rust and surface scale remover 6. Paint removal 7. Etching 8. Ultrasonic cleaning 9. Mechanical cleaning

Berikut adalah metoda pembersihan permukaan seperti didiskusikan sebelumnya:

1. Pembersihan dengan deterjen 2. Pembersihan dengan uap solvent 3. Pembersihan dengan uap air 4. Pembersihan dengan solvent 5. Penghilang karat dan kerak permukaan 6. Penghilang cat 7. Etsa 8. Pembersihan ultrasonik 9. Pembersihan secara mekanis

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PENETRANT APPLICATION

Since penetrant application is step two in the process, let’s add it to the flow diagram.

APLIKASI PENETRANT

Aplikasi penetrant merupakan tahapan kedua dalam proses pemeriksaan.

Almost any liquid could be considered a penetrant, but modern penetrants must have:

1. The ability to hold a dye material in suspension.

2. The ability to spread the dye evenly over the surface.

3. The ability to carry the dye into any discontinuity open to the surface.

4. The ability to bring up the dye as it is “coaxed” back to the surface.

5. The ability, when desired, to be easily removed.

There are two types of dye used in modern penetrants:

1. Visible or color contrast – a brightly colored dye that is highly visible under normal lighting conditions.

2. Fluorescent or brightness contrast – an almost colorless dye which emits visible ligh rays when viewed under black light.

A dye with dual sensitivity, or dual-mode, or dual-response contains a combination of visible and fluorescent dyes.

The visible color is generally a bright red and the fluorescent color a bronze-orange or blue-green.

The combination permits penetrant tests to be made under visible light and question-able indications to be resolved under black light; hence the term dual response.

Hampir semua cairan dapat dianggap sebagai penetrant, namun penetrant moderen harus memiliki:

1. Kemampuan menahan zat pewarna dalam suspensi.

2. Kemampuan menyebarkan pewarna secara merata di atas permukaan benda.

3. Kemampuan membawa pewarna ke dalam diskontinuitas yang terbuka ke permukaan

4. Kemampuan membawa kembali pewarna ke permukaan.

5. Kemampuan, jika diinginkan, untuk dibersih-kan dengan mudah.

Ada dua jenis zat pewarna yang digunakan dalam penetrant moderen:

1. Visible atau color contrast – pewarna merah yang tampak jelas di bawah kondisi pencahayaan normal.

2. Fluorescent or brightness contrast – pewarna yang akan memancarkan cahaya tampak apabila dilihat dengan lampu ultraviolet.

Pewarna dengan sensitivitas ganda atau mode ganda atau respon ganda mengandung kombinasi pewarna visible dan fluorescent.

Pewarna visible umumnya merah menyala dan pewarna fluorescent berwarna kuning-perunggu atau biru-hijau.

Kombinasi ini memungkinkan pengujian penetrant dilakukan di bawah cahaya biasa dan indikasi yang meragukan diperiksa di bawah cahaya ultraviolet.

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Table 3.1. Liquid penetrant application terminology.

Penetrants, either fluorescent or visible can be applied by any one of the following means:

1. Spraying – usually using a conventional low pressure spray guns or from pressurized spray cans.

2. Brushing or swabbing – usually applied with rags, cotton waste, or brushes, when testing a small, specific area of the specimen.

3. Dipping or immersion – the article is generally lowered into a tank of penetrant, then raised and allowed to drain. This method is impractical when dealing with large articles, and is wasteful when only small areas of a large specimen are to be tested.

4. Flowing or drain-dwell – the penetrant is simply poured over the surface and allowing it to drain.

The terminology used in penetrant application is listed in Table 3.1.

Penetrant, baik fluorescent maupun visible dapat diaplikasikan dengan salah satu dari cara berikut:

1. Penyemprotan – biasanya menggunakan alat penyemprot bertekanan rendah atau dari kaleng semprot bertekanan.

2. Kuas atau kain – bisasanya diaplikasikan dengan kain lap, kapas, atau kuas, apabila menguji sebagian kecil/lokasi dari suatu benda.

3. Pencelupan – benda uji dibenamkan ke dalam tangki penetrant, lalu diangkat dan ditiriskan. Metoda ini tidak cocok untuk benda berukuran besar dan merupakan pemborosan apabila hanya daerah kecil saja yang diuji.

4. Penuangan – penetrant dituangkan di atas permukaan benda dan setelah itu ditiriskan.

Istilah yang digunakan dalam aplikasi penetrant dapat dilihat dalam Table 3.1.

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PENETRATION (DWELL) TIME

The period of time during which the penetrant is permitted to remain on the specimen is a vital part of the test. This time, known as dwell time, is directly related to the size and shape of the discontinuities anticipated since the dimensions of the discontinuities determine the rapidity with which penetration occurs.

Tight, crack-like discontinuities may require in excess of 30 minutes for penetration to an extent that an adequate indication can be expected. Gross discontinuities may be suitably penetrated in 3 to 5 minutes.

The temperature of the specimen and temperature of the penetrant can affect the required dwell time.

Warming the specimen accelerates penetration and shortens dwell time. However, care should be taken not to overheat the specimen since too much heat may cause evaporation of the penetrant from the discontinuity, and thereby reduce sensitivity.

Dwell times are based on the assumption that the penetrant will remain wet on the part surface. Additional penetrant may be applied during dwell time.

In each instance, dwell time is determined by the anticipated discontinuities and the penetrant manufacturer’s recommendations. Typical minimum penetration times are shown in Table 3.2.

WAKTU PENETRASI (WAKTU DIAM)

Jangka waktu dimana penetrant berada di atas permukaan benda uji merupakan bagian terpenting dari pengujian. Jangka waktu ini dikenal sebagai waktu diam, yang berhubungan langsung dengan ukuran dan bentuk diskontinuitas yang dicari mengingat ukuran diskontinuitas menentu-kan kecepatan terjadinya penetrasi.

Diskontinuitas yang rapat, seperti retakan memerlukan waktu penetrasi lebih dari 30 menit untuk terbentuknya indikasi. Diskontinuitas berukuran besar memerlukan waktu penetrasi antara 3 sampai 5 menit.

Suhu benda uji dan suhu cairan penetrant dapat mempengaruhi waktu diam yang disyaratkan.

Menghangatkan benda uji mempercepat penetrasi dan mempersingkat waktu diam. Namun demikian perlu diperhatikan agar tidak berlebihan memanaskan spesimen karena suhu yang terlalu tinggi menyebabkan penguapan penetrant dari dalam diskontinuitas, yang akhirnya akan mengurangi sensitivitas.

Waktu diam didasarkan pada asumsi bahwa penetrant tetap dalam kondisi basah pada permukaan benda. Penambahan penetrant selama waktu diam diperbolehkan.

Pada tiap kasus, waktu diam ditentukan oleh jenis diskontinuitas yang hendak dicari dan rekomendasi dari pabrik pembuat penetrant. Waktu penetrasi minimum untuk kasus tertentu diperlihatkan dalam Tabel 3.2.

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Table 3.2. Typical minimum penetration time.

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PENETRANT TESTING PROCESSES

We previously mentioned the two types of penetrants: visible and fluorescent. For both categories, there is a further breakdown.

1. Water-washable (visible or fluorescent). 2. Post-emulsifiable (visible or fluorescent). 3. Solvent-removable (visible or fluorescent).

Water-washable Penetrants (WW Penetrants)

WW penetrants have a built-in emulsifier, or what-so-called “self-emulsifying” penetrants. The penetrant is soluble in water and is easily removed by a water rinse.

Care must be taken to insure that the spray volume and force does not wash penetrant out of the discontinuity. A solid stream of water is not desirable. A coarse droplet size provides optimal removal. Water pressure should not exceed 40 psi.

The recommended temperature range for water rinse is 10oC - 38oC. Water temperatures above 38oC are not recommended because this may speed up the evaporation of the penetrant.

At angles of 80-90 degree, the spray droplets will rebound into oncoming spray, which diverts the droplets and reduce velocity. Generally, an angle of 45-75 degree is most effective.

The sketch below represents the steps in a water-washable penetrant test.

PROSES PENGUJIAN PENETRANT

Telah disebutkan sebelumnya ada dua jenis penetrant: visible dan fluorescent. Kedua jenis penetrant tersebut dapat dirinci menjadi:

1. Water-washable (visible atau fluorescent). 2. Post-emulsifiable (visible atau fluorescent). 3. Solvent-removable (visible atau fluorescent).

Water-washable Penetrants (WW Penetrants)

WW penetrant mengandung zat pengemulsi, atau dinamakan penetrant “self-emulsifying”. Penetrant ini larut dalam air dan mudah dibersihkan dengan bilasan air.

Harus diperhatikan agar volume dan kekuatan semprot tidak sampai membasuh penetrant dari dalam diskontinuitas. Aliran air yang pejal tidak diinginkan. Air dalam bentuk percikan kasar menghasilkan pembersihan yang optimal. Tekanan air tidak boleh melebihi 40 psi.

Suhu air pembilas yang direkomendasikan sebesar 10oC - 38oC. Suhu air melebihi 38oC tidak direko-mendasikan karena dapat mempercepat pengua-pan penetrant.

Pada sudut 80-90 derajat, titik-titik air akan memantul kembali dan menabrak titik air yang datang sehingga mengurangi kecepatan. Sudut semprot yang paling efektif adalah 45-75 derajat.

Gambar di bawah memperlihatkan langkah-langkah pengujian water-washable penetrant.

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Water-washable penetrants are usually preferred for use on articles with a rough surface or if they contain threads or keyways.

The built-in emulsifier provides the best penetrant removal from blind holes and other hard-to-reach locations, but has the disadvantage of poor reliability in detecting wide or shallow discontinuities.

Water-washable penetrant biasanya digunakan untuk memeriksa benda yang permukaannya kasar atau benda yang ada ulir atau alurnya.

Emulsifier yang ada di dalamnya mengakibatkan penetrant mudah dihilangkan dari lubang buntu dan lokasi yang sulit dijangkau, namun memiliki kelemahan dalam mendeteksi diskontinuitas yang lebar dan dangkal.

Post-emulsifiable Penetrants (PE Penetrants)

The penetrants employed in the PE process DO NOT contain an emulsifying agent. The penetrant is NOT soluble in water.

PE penetrants require a two-step removal process. Excess penetrant is removed by applying a separate emulsifier to make the penetrant water-washable. The emulsifier is usually applied by dipping/immersion, spraying, or flowing. The amount of dwell time in the emulsifier is in the range of one to four minutes in accordance with manufacturer recommendations and the type of defects expected.

The resultant penetrant-emulsifier mixture is removed by water rinse.

Solvent-removable Penetrants (SR Penetrants)

The solvent removable method employs post-emulsification-type penetrant. But instead of using an emulsifier and water wash, excess penetrant is removed by a solvent.

SR penetrants have the advantage of portability and can be used outdoors without using heavy complex equipment.

They are excellent for many maintenance inspection and for checking portions of larger structure.

Post-emulsifiable Penetrants (PE Penetrants)

Penetrant yang dipakai pada proses PE tidak mengandung zat pengemulsi. Penetrant ini tidak larut dalam air.

PE penetrant memerlukan dua langkah proses pembersihan. Sisa penetrant dibersihkan dengan aplikasi emulsifier secara terpisah sehingga penetrant dapat dibilas dengan air. Emulsifier biasanya diaplikasikan dengan pencelupan, penyemprotan, atau penuangan. Lamanya waktu diam untuk emulsifier adalah satu sampai empat menit mengacu pada rekomendasi pabrik pembuat dan jenis cacat yang dicari.

Hasil campuran antara penetrant dan emulsifier selanjutnya dapat dibilas dengan air.

Solvent-removable Penetrants (SR Penetrants)

Metoda solvent removable menggunakan penetrant jenis post-emulsification. Solvent digunakan untuk menghilangkan pentrant sisa yang ada di permukaan benda.

SR penetrant menguntungkan dari segi portabilitas dan dapat digunakan di luar tanpa menggunakan peralatan yang berat dan rumit.

Cara ini sangat memuaskan untuk pemeriksaan pemeliharaan dan untuk memeriksa bagian dari suatu struktur yang besar.

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Table 3.3. Process selection guide.

Penetrant is often applied from a pressurized spray can which makes the system very portable.

After the specified dwell time, the excess penetrant is first removed by wiping with absorbent towels and then cleaned with towels dampened with solvent.

Solvent is NEVER applied directly to the specimen as it might wash out or dilute the penetrant in the discontinuity.

Table 3.3 lists the preferred processes for various penetrant test problems.

Penetrant seringkali diaplikasikan dari kaleng semprot bertekanan yang membuat sistem ini sangat portabel.

Setelah waktu diam terpenuhi, penetrant sisa pada mulanya diseka dengan lap penyerap dan kemudian dibersihkan dengan lap yang dibasahi dengan solvent.

JANGAN PERNAH menyemprotkan solvent secara langsung ke permukaan benda karena akan melenyapkan penetrant dari dalam diskontinuitas.

Tabel 3.3 memperlihatkan macam-macam proses pengujian penetrant dan kegunaannya.

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1. Water-washable

2. Post-emulsifiable

3. Solvent-removable

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LEAK-THROUGH TECHNIQUE

The leak-through technique is well suited for finding leaks in such articles as tanks, piping, tubing and hollow castings. There is no knowledge concerning other quality characte-ristics of the specimen is obtained.

The sketch below illustrates the liquid penetrant leak-through test as used on a large plate section.

TEKNIK PEREMBESAN BOCORAN

Teknik perembesan bocoran sangat sesuai untuk mendeteksi kebocoran pada tangki, pipa, tube, dan cor-coran berongga. Tidak ada informasi lain yang diperoleh mengenai karakteristik kualitas benda.

Gambar di bawah memperlihatkan pengujian kebocoran dengan penetrant untuk memeriksa bagian dari suatu pelat.

FILTERED PARTICLE TECHNIQUE

Filtered particle testing uses small particles suspended in the penetrant liquid. In most instances these particles are fluorescent.

The size of the suspended particles varies and depends upon the porous nature of the inspection surface.

When testing a porous surface with filtered particles, all of the liquid penetrant will be absorbed. There will be no “excess” requiring removal. Where a discontinuity (such as a crack) is present, the increased area created by a crack (its walls, etc.) will cause more of the penetrant to be absorbed there than elsewhere.

The crack will “filter” the penetrant, leaving the fluorescent particles on the surface. Since more penetrant will be absorbed there, a greater buildup of particles will be found at the site of the crack. This particel buildup provides an indication of discontinuities open to the surface.

TEKNIK PARTIKEL TERSARING

Teknik ini menggunakan partikel berukuran kecil yang tersuspensi dalam cairan penetrant. Partikel yang dipakai biasanya fluorescent.

Ukuran partikel yang tersuspensi bervariasi, tergantung pada kondisi pori-pori permukaan benda yang diperiksa.

Saat menguji permukaan berpori dengan cara ini, semua cairan penetrant akan diserap. Tidak ada langkah pembersihan penetrant sisa pada teknik ini. Pada tempat dimana terdapat diskontinuitas (seperti retak), penambahan luasan akibat retak (dinding retak, dll.) akan mengakibatkan penetrant lebih banyak terserap di daerah tersebut.

Retak akan “menyaring” penetrant, meninggalkan jejak partikel fluorescent pada permukaan. Karena lebih banyak penetrant terserap di sana, pengumpulan partikel lebih banyak terjadi di daerah retak. Pengumpulan partikel ini menun-jukkan adanya diskontinuitas yang membuka ke permukaan.

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FIXING AND RECORDING INDICATIONS

Fixing and recording indications can be carried out by:

1. Photographs – digital photography provide excellent permanent records. In addition to photographs, video cassette recorders (VCRs) and closed-circuit television cameras (CCTVs) are used to record indications.

2. Special wax and plastic film developers have been developed to absorb and fix the penetrant indication to form a permanent record. a. Strippable lacquers are sprayed in

several coats over the indication and when dry can be “lifted” to provide a permanent record.

b. Special “fixers” are sprayed over the indication and when dry are lifted with transparent tape.

PEMELIHARAAN DAN PEREKAMAN INDIKASI

Pemeliharaan dan perekaman indikasi dapat dilakukan dengan:

1. Fotografi – foto digital merupakan cara terbaik untuk merekam indikasi. Disamping itu video kaset dan kamera CCTV juga dapat digunakan untuk merekam indikasi.

2. Lilin khusus dan lapisan plastik developers dikembangkan untuk menyerap dan mengawetkan indikasi penetrant dan membentuk rekaman permanen. a. Lapisan lak disemprotkan beberapa lapis

di atas indikasi, dan setelah kering dapat dikelupas untuk menghasilkan rekaman permanen.

b. Fixer khusus disemprotkan di atas indikasi dan setelah kering diangkat dengan pita transparan (isolasi).

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CHAPTER THREE REVIEW

_______ 1. A dual sensitivity penetrant contains a special dye that is visible in white light and will fluoresce without the use of a black light.

_______ 2. A part being penetrant inspected must stay immersed in the penetrant tank for the entire specified dwell time.

_______ 3. The liquid penetrant leak-through test refers to the ability of a penetrant to spread through the dry developer evenly.

_______ 4. Visible dye penetrants are usually considered to be less sensitive than fluorescent penetrants.

_______ 5. Water-washable penetrants have a built-in emulsifier that permits good results in penetrant removal from parts suspected of having wide or shallow discontinjuities.

_______ 6. Solvent-removable penetrants are available in both visible and fluorescent dye.

_______ 7. Excess post-emulsifiable penetrant is commonly removed by spraying the surface of the part with cleaner (solvent) and then wiping with a lint-free towel.

_______ 8. Water washable penetrant systems are usually very portable because the materials are commonly used in pressurized spray cans.

_______ 9. Warming the specimen to temperatures up to about 20o C tends to accelerate penetration and shortens dwell time.

_______ 10. For the dwell time to be accurate, the surface of the specimen must stay wet with penetrant for the entire time specified.

_______ 11. The typipal dwell time for most penetrant Inspections is about 20-30 minutes.

_________________________ 12. List two (2) of the commonly used methods of applying _________________________ penetrants to a specimen that is to be inspected.

_________________________ 13. List four (4) of the commonly used methods of _________________________ precleaning the specimen before penetrant inspection. _________________________ _________________________

_______ 14. If you were asked to examine 200 steel bolts, each 3/8 x 3 inches with rolled threads, which penetrant method would you choose?

(a) Post-emulsification (b) Water-washable

_______ 15. The filtered particle method of penetrant inspection used extra fine fluorescent particles that will not pass through a #120 sieve.

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CHAPTER FOUR

INTRODUCTION

This chapter discusses emulsification, penetrant removal, and developer application.

PENDAHULUAN

Bab ini mendiskusikan proses emulsifikasi, pembersihan penetrant, dan aplikasi developer.

POST EMULSIFIABLE PENETRANT (PE PENETRANT)

This type of penetrant emulsification is accomplished by dipping, spraying, or flowing, but NEVER by brushing. Brushing makes emulsification more difficult to control, besides the bristle of the brush may enter the discontinuity.

POST EMULSIFIABLE PENETRANT (PE PENETRANT)

Emulsifikasi penetrant jenis ini dilakukan dengan pencelupan, penyemprotan atau penuangan, namun TIDAK BOLEH diaplikasikan dengan kuas. Aplikasi dengan kuas menyulitkan pengontrolan emulsifikasi, disamping bulu-bulu kuas bisa masuk ke dalam diskontinuitas.

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The skecth below represents the steps in a post-emulsifiable penetrant test.

Gambar berikut menunjukkan langkah-langkah pengujian post-emulsifiable penetrant.

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The length of time the emulsifier is left to dwell before commencing the penetrant removal cycle is determined by the emulsifier used and the type of discontinuities suspected.

If too short an emulsification time is used, not all penetrant will be removed, which will cloud over discontinuities.

If too long a time is used, penetrant within the discontinuities will also become water soluble and be washed away with excess penetrant.

The PE penetrant makes the water wash less critical.

The sketches below compare the effects of water-washable and post emulsification penetrants.

Jangka waktu emulsifier dibiarkan di atas permukaan benda sebelum dilakukan pembersi-han penetrant ditentukan oleh jenis emulsifier dan diskontinuitas yang dicari.

Jika waktu emulsifikasi terlalu singkat, tidak semua penetrant akan tersapu, yang nantinya akan menghalangi munculnya diskontinuitas.

Jika waktu emulsifikasi terlalu panjang, penetrant di dalam diskontinuitas akan bereaksi dengan emulsifier dan akan tersapu oleh air.

PE penetrant membuat pembilasan dengan air menjadi tidak terlalu kritis.

Gambar di bawah ini membandingkan antara pemakaian WW dan PE penetrants.

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There are two types of emulsifiers used in the removal process — LIPOPHILIC (Method B) and HYDROPHILIC (Method D).

Lipophilic and hydrophilic processes have completely different mechanisms in converting the oil based penetrant into a mixture that can be washed.

LIPOPHILIC METHOD

Lipophilic emulsifier is applied by immersion to prevent mechanically mixing emulsifier into the penetrant. In some automatic installations, the emulsifier is applied as a fog or mist.

The mechanism of lipophilic emulsification is by DIFFUSION. Molecules of emulsifier enter into the penetrant layer while at the same time molecules of penetrant enter the emulsifier layer. The rate of diffusion increases with increased concentration and higher temperatures.

The three properties of lipophilic emulsifiers that control the washing characteristics are activity, viscosity and water tolerance.

If a penetrant is highly resistant to water, an emulsifier with a high activity is needed. High viscosity emulsifiers diffuse more slowly than low viscosity emulsifiers. Lipophilic emulsifier should tolerate 5% water by weight without gelling, separating or coagulating and still be capable of passing the penetrant removability test.

Method B emulsifiers are supplied in the ready-to-use form and do not require further mixing.

Terdapat dua jenis emulsifier yang digunakan dalam proses pembersihan – LIPOPHILIC (Metoda B) dan HYDROPHILIC (Metoda D).

Proses lipophylic dan hydrophilic memiliki mekanisme yang sangat berbeda dalam merubah penetrant berbahan dasar menjadi campuran yang bisa dibilas dengan air.

METODA LIPOPHILIC

Emulsifier lipophilic diaplikasikan dengan cara pencelupan untuk mencegah bercampurnya emul-sifier dengan penetrant. Pada instalasi otomatis, emulsifier diaplikasikan secara pengkabutan.

Mekanisme emulsifikasi lipophilic adalah dengan cara DIFUSI. Molekul emulsifier memasuki lapisan penetrant, sementara pada saat yang bersamaan molekul penetrant memasuki lapisan emulsifier. Laju difusi akan bertambah dengan peningkatan konsentrasi dan penambahan suhu.

Tiga sifat emulsifier lipophilic yang mengontrol karakteristik pembilasan adalah aktivitas, kekentalan, dan toleransi terhadap air.

Jika suatu penetrant memiliki ketahanan tinggi terhadap air, maka diperlukan emulsifier dengan aktivitas yang tinggi. Emulsifier dengan kekentalan tinggi berdifusi lebih lambat ketimbang emulsifier yang encer. Lipophilic emulsifier harus mampu mentolerir 5% air tanpa mengalami penggumpalan atau pembekuan dan mampu lulus uji pember-sihan penetrant.

Emulsifier metoda B dijual dalam bentuk siap pakai dan tidak memerlukan pencampuran lagi.

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HYDROPHILIC METHOD

Hydrophilic emulsifier is a water based solution and is a mixture of chemicals called surfactants. They are supplied as a concentrate and are mixed with water either before or during the removal process. The concentrate is required to contain a maximum of 5% water.

Hydrophilic emulsifier works based on the principle to peel the penetrant away or by dissolving droplets so they do not redeposit on the surface.

Because post-emulsifiable penetrant is incompatible with water, prerinsing before application of emulsifier is recommended. Prerinsing removes 60-80% of the surface layer of penetrant, which greatly reduces contamination of the emulsifier. It also provides an even layer of surface penetrant.

Hydrophilic emulsifier is applied either by immersion or spraying.

Immediately following the emulsification, a fresh water rinse of the entire part is required. This stops the action of any emulsifier remaining on the part.

METODA HYDROPHILIC

Emulsifier hydrophilic adalah larutan antara air dan zat kimia yang disebut surfactant. Dijual di pasaran dalam bentuk konsentrat dan harus dicampur dulu dengan air sebelum atau selama proses pembersihan. Konsentrat disyaratkan mengan-dung air maksimum sebesar 5%.

Emulsifier hydrophilic bekerja berdasar pada prinsip pengelupasan lapisan penetrant, atau dengan melarutkan penetrant sehingga tidak terdeposit kembali ke permukaan.

Karena post-emulsifiable penetrant tidak kompatibel dengan air, direkomendasikan untuk melakukan pembilasan awal sebelum aplikasi emulsifier. Pembilasan awal menghilangkan 60-80% lapisan penetrant di permukaan, sehingga banyak mengurangi terjadinya kontaminasi pada emulsifier. Pembilasan awal juga menghasilkan lapisan penetrant permukaan yang rata.

Emulsifier hydrophilic diaplikasikan dengan cara pencelupan atau penyemprotan.

Segera setelah proses emulsifikasi, disyaratkan untuk membilas seluruh bagian benda uji dengan air bersih. Langkah ini akan menghentikan aksi emulsifikasi yang masih tersisa di permukaan benda.

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DEVELOPERS APPLICATION

Some indications may be visible prior to the application of a developer, but this step will ensure that ALL discontinuities are visible to the naked eye.

APLIKASI DEVELOPER

Beberapa indikasi bisa saja nampak sebelum developer diaplikasikan, namun langkah ini akan memastikan bahwa SEMUA diskontinuitas akan tampak oleh mata telanjang.

Developing is accomplished when a highly absorbent powder is applied to the item being tested after excess penetrant is removed.

The penetrant is actually drawn out of the discontinuity by the strong capillary action of the developer.

Proses developing dilakukan dengan mengapli-kasikan serbuk berdaya serap tinggi ke permukaan benda uji setelah sisa penetrant dibersihkan.

Penetrant akan tertarik keluar dari diskontinuitas akibat gaya kapiler yang kuat dari serbuk developer.

As shown above, the image of the discontinuity in the developer will actually be larger than the actual size of the discontinuity.

There are two common types of developers in use today – dry and wet. Both use a white powder and the primary difference is in the method of application.

DRY DEVELOPERS

Dry developer is supplied as a fine-grained fluffy white powder.

Methods of application include the use of low air pressure, such as that from a rubber squeeze bulb or a spray gun. A soft brush may sometimes be used; or, since the developer is a very fine powder, articles may be simply dipped in the developer, raised, and the excess powder removed by gently blowing, shaking, or tapping the article.

Seperti diperlihatkan dalam gambar di atas, citra diskontinuitas pada developer tampak lebih luas ketimbang ukuran diskontinuitas sebenarnya.

Ada dua jenis developer yang dipakai saat ini – kering dan basah. Keduanya memakai serbuk putih dan perbedaan utamanya terletak pada metoda aplikasinya.

DEVELOPER KERING

Developer kering dijual dalam bentuk butiran halus, serbuk putih lembut.

Aplikasi dilakukan dengan dengan alat penyemprot bertekanan rendah. Kadangkala dipakai juga kuas halus; atau karena bentuknya yang sangat halus, benda uji dapat dibenamkan ke dalam tangki developer, diangkat, dan sisa developer di permukaan dihilangkan dengan cara meniup, menggoyang-goyang, atau mengetuk-ketuk benda uji.

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It is very necessary to have a dry surface prior to application of a dry powder.

A wet surface would result in an uneven layer of powder or, even worse, too thick a powder buildup. Discontinuity indications would be obscured.

Dry developer is usually used with fluorescent penetrant.

WET DEVELOPERS

Non-aqueous wet developer is held in suspension in a solvent base and is usually supplied in pressurized cans. Evaporation of the solvent carrier helps draw penetrant from discontinuities.

Nonaqueous wet developer is most often employed with solvent-removable penetrants and less often with water-washable or post-emulsifiable penetrants.

The nonaqueous wet developer is THE MOST SENSITIVE of all the developers in detecting fine discontinuities.

The best results are obtained when developer is applied as a thin and even film.

Like dry developer, nonaqueous developer is applied ONLY to dry test surfaces.

Permukaan benda uji harus benar-benar kering sebelum serbuk developer diaplikasikan.

Permukaan yang basah menghasilkan lapisan yang tidak merata, bahkan bisa terjadi peggum-palan serbuk. Indikasi diskontinuitas akan terhalangi.

Developer kering biasanya dipakai bersama dengan penetrant fluorescent.

DEVELOPER BASAH

Non-aqueous wet developer terikat dalam suatu suspensi solvent dan dikemas dalam kaleng semprot bertekanan. Penguapan solvent membantu menarik penetrant dari dalam diskontinuitas.

Nonaqueous wet developer paling sering diguna-kan bersama solvent-removable penetrant dan jarang dipakai bersama water-washable atau post-emulsifiable penetrants.

Nonaqueous wet merupakan jenis developer yang PALING SENSITIP dalam mendeteksi diskonti-nuitas halus.

Hasil terbaik diperoleh apabila developer diaplika-sikan dalam bentuk lapisan tipis dan rata.

Seperti halnya developer kering, nonaquous developer HANYA diaplikasikan pada permukaan yang benar-benar kering.

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Water-base wet developer

In water-base wet developer, the powder is mixed with water.

The developer comprises of two types: water-suspended and water-soluble developers.

1. In water-suspended developer, the developer particles are held in suspen-sion in water and require continuous agitation to keep them in suspension.

2. In water-soluble developer, the developer powder is dissolved in water and forms a solution. Once mixed, they remain mixed. Water-soluble developer provides the greater sensitivity in detecting fine discontinuities.

Water-suspended and water-soluble develo-pers are generally used with water-washable or post-emulsifiable penetrants and rarely with solvent-removable penetrants. They are applied while the test article is still wet from the water wash.

Methods of application include the following:

• Dipping (or immersing)

• Pouring (or flowing)

• Spraying

A short time is allowed for the water to evaporate, leaving a thin layer of white powder. The evaporation process is often hurried by the use of a recirculating hot-air dryer after the developer has been applied. If an oven is used, the temperature should not exceed about 100oC as this could evaporate penetrant in the discontinuity.

Water soluble developer is not recommended to be used with water washable penetrant.

Water-base wet developer

Pada water-base wet developer, serbuk developer dicampur dengan air.

Developer ini terdiri dari dua jenis: water-suspended dan water-soluble developers.

1. Pada water-suspended developer, partikel serbuk developer terikat dalam suspensi dengan air dan perlu diaduk terus-menerus agar tidak mengendap.

2. Pada water-soluble developer, serbuk developer larut dalam air dan membentuk suatu larutan yang tidak perlu diaduk lagi. Water-soluble developer menghasilkan sensitivitas yang lebih baik untuk mendeteksi diskontinuitas halus.

Water-suspended dan water-soluble developers umumnya digunakan dengan water-washable atau post-emulsifiable penetrants, dan jarang dengan solvent-removable penetrant. Mereka diaplikasikan saat permukaan benda uji masih dalam kondisi basah setelah pembilasan.

Metoda aplikasi water-base wet developer:

• Pencelupan

• Penuangan

• Penyemprotan

Beberapa saat diperlukan bagi air untuk menguap, meninggalkan lapisan tipis serbuk putih. Proses penguapan seringkali dipercepat dengan menggunakan oven setelah aplikasi developer. Jika digunakan oven untuk pengeringan, suhunya tidak boleh melebihi 100oC karena akan menguapkan penetrant di dalam diskontinuitas.

Water soluble developer tidak direkomendasikan untuk dipakai dengan water washable penetrant.

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GUIDELINES TO CHOOSE DEVELOPER

Now you might ask: What governs the choice of developer for a given situation? Here are some guidelines.

Water-Base Wet Developer Applications

• On very smooth surfaces where a dry developer will not adhere.

• When testing large numbers of small, irregularly-shaped articles (production testing).

• When wide, shallow discontinuities are sought, wet developer tends to leave a more even film of developer than does dry developer.

Nonaqueous Wet Developer Applications

• Applications on spot checks or when conducting tests in the field.

• On vertical surfaces, a uniform film of developer is more easily obtained.

• When greatest sensitivity is needed in revealing difficult-to-detect indications.

Dry Developer Applications

• On rough surfaces, dry developer gives far better results than wet developer.

• On sharp fillets, holes, and threaded articles where wet developers tend to leave too much developer.

• On very large articles where it might be difficult to apply wet developer.

Again, these are only guidelines. There will be exceptions. Some specifications permit the use of only one type of developer and, as mentioned earlier, there are some applications that do not require the use of a developer since the penetrant alone provides sufficient discontinuity indications through self-development.

PEDOMAN PEMILIHAN DEVELOPER

Sekarang anda mungkin bertanya: Apakah yang menentukan pemilihan developer untuk situasi tertentu? Berikut beberapa pedomannya.

Aplikasi Water-Base Wet Developer

• Pada permukaan sangat halus dimana developer kering tidak bisa menempel.

• Saat memeriksa sejumlah besar artikel berukuran kecil dan bentuknya tidak teratur (pengujian untuk produksi).

• Saat mencari diskontinuitas yang lebar dan dangkal, developer basah cenderung menghasilkan lapisan developer yang lebih rata ketimbang developer kering.

Aplikasi Nonaqueous Wet Developer

• Aplikasi untuk pemeriksaan setempat atau untuk pengujian di lapangan.

• Pada permukaan vertikal, lapisan developer yang merata lebih mudah diperoleh.

• Apabila diinginkan sensitivitas terbaik untuk mencari diskontinuitas yang sulit terdeteksi.

Aplikasi Developer Kering

• Pada permukaan kasar, developer kering memberikan hasil yang lebih baik dibandingkan developer basah.

• Pada sudut-sudut tajam, lubang, artikel berulir dimana developer basah cenderung meninggalkan lapisan yang terlalu tebal.

• Pada artikel berukuran besar dimana kesulitan mengaplikasikan developer basah.

Sekali lagi perlu disampaikan bahwa ini hanya sekedar pedoman. Beberapa spesifikasi mungkin hanya mengijinkan penggunaan satu jenis developer saja, dan seperti telah disebutkan sebelumnya, bahwa ada beberapa aplikasi yang tidak mensyaratkan penggunaan developer karena penetrant sendiri sudah menghasilkan indikasi diskontinuitas yang mencukupi melalui mekanisme self-development.

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CHAPTER FOUR REVIEW

_______ 1. When using a post-emulsified penetrant, if too long a time is used for emulsification, penetrant within the discontinuities will be washed away with the excess penetrant.

_______ 2. During the rinse cycle an emulsifier is added to a solvent-removable penetrant to make it water soluble.

_______ 3. Water washable penetrants have a built-in emulsifier.

_______ 4. Post-emulsification penetrants are commonly available in both visible and fluorescent dyes.

_______ 5. Post-emulsification penetrants usually require a two-step penetrant removal process.

_______ 6. The penetrant removal process with water washable penetrants is very critical because of the danger of over-wash.

_______ 7. Solvent-removable penetrants are commonly used because they will withstand a very forceful water wash without the danger of over-wash.

_______ 8. An advantage of the solvent –removable penetrant is that the excess penetrant is easily removed by dipping the part in a tank of solvent solution.

_______ 9. Wet developers are usually chosen over a dry developer for use on a smooth surface.

_______ 10. A major advantage of the dry developer over wet is that it will not leave the same amount of excess build-up in threads and fillets.

_______ 11. The emulsification time required to detect wide or shallow discontinuities is usually longer than for finding narrow and deep discontinuities.

_______ 12. To avoid over-wash when using water washable penetrants, the water spray nozzle is usually held at a 90° angle to the surface.

_______ 13. When using a water-washable penetrant, the part must be completely dried in an oven (not in excess of 225° F) before the wet developer can be applied.

_______ 14. A major advantage of a nonaqueous developer is that it can be applied to a part that is heated above 225° F without evaporation on the developer vehicle.

_______ 15. Solvent-removable fluorescent penetrants require the use of a rather time- consuming method of excess penetrant removal.

_______ 16. Post-emulsifiable visible dye penetrants commonly use both wet and dry developers.

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CHAPTER FIVE

INTRODUCTION

This chapter discusses the final step in the penetrant process inspection, evaluation, postcleaning, and material control.

PENDAHULUAN

Bab ini mendiskusikan langkah akhir dalam proses pemeriksaan penetrant, evaluasi, pembersihan akhir, dan pengendalian material.

INSPECTION

Proper lighting should be the first consideration in the inspection of an article.

1. If a fluorescent dye penetrant is used, a room or booth with dim light and a black light with proper intensity are required.

2. If a visible dye penetrant is used, adequate normal lighting is necessary.

INTERPRETATION AND EVALUATION OF INDICATIONS

The terms “interpretation” and “evaluation” are often confused by testing personnel. Actually, the terms refer to two entirely different steps in testing process.

After an indication is located, it is interpreted. During the interpretation, the cause of the bleedout and the severity of the indication must be determined. It is at this phase that the indication is classified as false, nonrelevant or relevant.

Evaluation follows interpretation. If during the evaluation phase it is determined that the discontinuity interferes with the serviceability of the part or it does not meet the acceptance and rejection criteria, the discontinuity is then classified as a DEFECT.

PEMERIKSAAN

Pencahayaan yang tepat harus dijadikan pertim-bangan pertama dalam pemeriksaan benda uji.

1. Jika dipakai fluorescent dye penetrant maka diperlukan ruangan gelap dan lampu ultraviolet dengan intensitas yang memadai.

2. Jika dipakai visible dye penetrant, diperlukan penerangan dengan cahaya biasa.

INTERPRETASI DAN EVALUASI INDIKASI

Istilah “interpretasi” dan “evaluasi” seringkali mem-bingungkan personel NDT. Sesungguhnya kedua istilah tersebut mengacu pada dua langkah yang sama sekali berbeda dalam proses pengujian.

Setelah indikasi diketahui lokasinya, selanjutnya diinterpretasi. Selama interpretasi, penyebab dan pengaruh indikasi terhadap artikel harus diten-tukan. Pada tahap ini indikasi tersebut diklasifikasikan sebagai palsu, tidak relevan atau relevan.

Evaluasi mengikuti interpretasi. Jika selama tahap evaluasi ditentukan bahwa diskontinuitas memba-hayakan pemakaian komponen, atau tidak meme-nuhi kriteria penerimaan dan penolakan, diskon-tinuitas tersebut selanjutnya diklasifikasikan sebagai CACAT.

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TYPICAL INDICATIONS IN PENETRANT INSPECTION

All indications found with the liquid penetrant method will be open-surface discontinuities, but the indications may or may not affect the usefulness of the article.

FALSE INDICATIONS

The most common sources of false indications are poor washing, poor processing conditions, lack of cleanliness in the inspection booth or other aspects of the penetrant process.

The operator can easily tell when a good rinse is obtained by using a black light during and after the fluorescent pentrant removal process.

To avoid false indications, care should be taken so that no outside contamination such as the following occurs:

1. Penetrant on operator’s hand. 2. Contamination of wet or dry developer. 3. Penetrant transfered to clean specimen

from other indications. 4. Penetrant spots on the inspection table.

JENIS INDIKASI PADA PEMERIKSAAN PENETRANT

Semua indikasi yang ditemukan dalam pengujian penetrant adalah diskontinuitas permukaan, namun indikasi tersebut mungkin saja atau tidak, mempengaruhi kegunaan benda uji.

INDIKASI PALSU

Penyebab indikasi palsu yang paling umum adalah pembersihan yang buruk, kondisi pemrosesan yang buruk, bilik pemeriksaan yang kurang bersih, atau aspek lain dari proses penetrant.

Operator dapat dengan mudah mengatakan jika pembilasan sudah dilakukan dengan benar dengan memakai lampu ultraviolet selama dan setelah proses pembersihan penetran fluorescent.

Untuk menghindari indikasi palsu, harus diperhati-kan agar tidak ada kontaminasi dari luar seperti berikut ini:

1. Jejak penetran di tangan operator. 2. Kontaminasi developer basah atau kering. 3. Penetran yang berpindah dari indikasi lain ke

spesimen yang bersih. 4. Jejak penetran di meja pemeriksaan.

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NONRELEVANT INDICATIONS

Nonrelevant indications are caused by surface irregularities or part configuration that in most cases are there by design.

They are caused by some features of assembly such as articles that are press-fitted, keyed, splined, or riveted. Nonrelevant indications could also include loose scale or rough surface on a forging, casting, or welding.

Nonrelevant indications are considered not detrimental to the serviceability of the part.

As with false indications the inspector must carefully examine these indications to ensure that they do not mask a relevant indication.

TRUE INDICATIONS

True indications are those caused by surface discontinuities that have been interpreted as not being false or nonrelevant.

True indications are subject to evaluation as to the cause and the effect they will have on the service life of the article.

It is important to note that all relevant indications are discontinuities, but not all discontinuities are defects.

True indications could be divided into SIX basic categories.

1. Continuous Line These indications are caused by cracks, cold shuts, forging laps, scratches, or die marks. Cracks usually appear as jagged lines; cold shuts as smooth, narrow, straight lines; and forging laps as smooth, wavy lines. Scratches and die marks appear in a variety of linear patterns but are readily recognizable when all penetrant traces are removed, since the bottom of the discontinuity is usually visible.

2. Intermitten Line These indications could be caused by any of the discontinuities mentioned above provided they were very tight or where the part had been peened, machined, or ground.

INDIKASI NONRELEVANT

Indikasi nonrelevant disebabkan karena ketidak-teraturan permukaan atau konfigurasi benda yang pada kebanyakan kasus akibat disain.

Indikasi nonrelevant disebabkan karena adanya press-fitted, alur, splined, atau kelingan. Termasuk juga dalam indikasi nonrelevant adalah kerak lepas dan pemukaan kasar pada benda tempa, benda cor dan pengelasan.

Indikasi nonrelevant dianggap tidak menggangu pemakaian komponen.

Sama halnya dengan indikasi palsu, inspektor harus memeriksa indikasi ini dengan hati-hati untuk memastikan agar jangan sampai menutupi indikasi relevant.

INDIKASI SEJATI

Indikasi sejati disebabkan karena diskontinuitas permukaan yang telah diinterpretasikan bukan sebagai indikasi palsu atau nonrelevant.

Indikasi sejati harus dievaluasi penyebab sampai pada pengaruh yang ditimbulkannya pada usia pakai komponen.

Penting dicatat bahwa semua indikasi relevant adalah diskontinuitas, namun tidak semua diskontinuitas adalah cacat.

Indikasi sejati dibagi menjadi ENAM katagori utama:

1. Garis Menerus Indikasi ini disebabkan karena retak, cold shuts, lipatan temp, goresan, atau tanda cetakan. Retakan biasanya tampak sebagai garis bergerigi; cold shut sebagai garis lurus, rapat, halus; lipatan tempa sebagai garis berombak yang halus. Goresan dan tanda cetakan kelihatan sebagai pola lurus yang bervariasi, namun mudah dikenali setelah jejak penetrant dibersihkan, karena dasar diskontinuitas ini biasanya tampak.

2. Garis Putus-putus Indikasi ini disebabkan karena diskontinuitas memerus dimana ada bagiannya yang tertutup rapat akibat terkena pukulan, permesinan, atau penggerindaan.

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3. Round Rounded indications usually are caused by porosity. Deep cracks may also appear as rounded indications, since they trap a large amount of penetrant that spreads when the developer is applied.

Any rounded indication that appears singularly in an isolated position usually indicates a discontinuity of depth that may or may not be round.

4. Small Dots Tiny round indications caused by the porous nature of the specimen, coarse grain structure, or microshrinkage.

5. Diffuse or weak These indications are difficult to interpret and often the part must be cleaned and retested. In many cases the diffused or weak indications turn to be false indications caused by an improper penetrant procedure.

6. Gross Gross indications are the result of ineffective penetrant removal or deep indications on the surface.

Skecthes below show typical true indications.

3. Bundaran Indikasi berbentuk bundar biasanya disebab-kan karena porosity. Retak dalam juga bisa kelihatan sebagai indikasi bundar karena banyaknya penetrant yang terperangkap di dalamnya yang menyebar saat developer diaplikasikan. Sembarang indikasi bundar yang muncul sendirian pada posisi menyendiri biasanya menunjukkan indikasi yang dalam dan belum tentu bentuk aslinya bundar.

4. Bintik-bintik Kecil Indikasi bundar kecil-kecil disebabkan kare-na sifat permukaan spesimen yang berpori, butiran kasar, atau penyusutan mikro.

5. Tersebar atau Samar Indikasi ini sulit diinterpretasi dan seringkali benda uji harus dibersihkan dan diuji ulang. Pada banyak kasus, indikasi yang tersebar atau samar berubah menjadi indikasi palsu yang disebabkan prosedur penetrant yang kurang benar.

6. Nyata Indikasi nyata adalah akibat pembersihan penetrant yang tidak efektip atau adanya indikasi yang dalam pada permukaan.

Gambar berikut adalah indikasi sejati.

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Visible dye indication of seam.

Visible dye indication of lamination.

Visible dye indication of forging lap.

Visible dye indications of unhealed porosity in aluminum plate.

Figures below illustrate typical liquid penetrant indications found in liquid penetrant testing.

Gambar dibawah ini memperlihatkan indikasi cairan penetrant pada pengujian penetrant.

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Visible dye indications of cracks in aluminum forging.

Visible dye indications of weldment shrink cracks.

Visible dye indication of forging burst.

Fluorescent indications of porosity.

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DEPTH DETERMINATION OF PENETRANT DISCONTINUITIES

The greater the depth of a discontinuity, the more penetrant it will holds and the larger and brighter the indication.

POSTCLEANING

After the specimen has been inspected, it is very important that it be thoroughly cleaned. A thorough postcleaning is necessary because penetrant and developer residue tend to attract moisture which may cause corrosion, or it can interfere with subsequent processing or usage.

Postcleaning usually will involved the same types of cleaning operations as were used in precleaning.

QUALITY CONTROL OF PENETRANT TEST MATERIALS

ALUMINUM TEST BLOCKS

They provide a good means of evaluating general purpose penetrants. They should be used for comparisons only and not for absolute evaluations.

These blocks are nonuniform, the depth and width of cracks are uncontrolled. The size of the blocks may vary but are about 5 x 8 cm by 10 mm thickness of 2024-T-3 aluminum alloy.

The blocks are heated to 510-525oC and quenched in cold water to provide an overall crack pattern. A groove approximately 1.5 mm deep by 2 mm wide may be cut across the center of the heat-affected zone on both faces of the block.

Because of the large cracking that often results in this block, it is used for comparing low and medium sensitivity fluorescent penetrant.

PENENTUAN KEDALAMAN DISKONTINUITAS PENETRANT

Makin dalam suatu diskontinuitas, makin banyak penetrant tertahan di dalamnya dan makin besar dan jelas indikasinya.

PEMBERSIHAN AKHIR

Setelah spesimen diperiksa, sangat penting untuk mencucinya dengan bersih. Pembersihan akhir yang menyeluruh perlu dilakukan karena sisa-sisa penetrant dan developer akan mengikat uap air dan mengakibatkan korosi, atau zat-zat tersebut dapat mengganggu proses atau penggunaan selanjutnya.

Pembersihan akhir biasanya melibatkan jenis proses pembersihan yang sama seperti pada pembersihan awal.

KENDALI MUTU UNTUK MATERIAL PENGUJIAN PENETRANT

BLOK UJI ALUMINIUM

Blok ini dipakai untuk mengevaluasi kegunaan umum dari penetrant. Blok ini hanya dipakai sebagai perbandingan saja, bukan untuk evaluasi mutlak.

Blok ini tidak seragam, kedalaman dan lebar retak tidak terkontrol. Ukuran blok bisa bervariasi tapi biasanya sekitar 5 x 8 cm dengan tebal 10 mm, terbuat dari paduan aluminium 2024-T-3.

Blok dipanaskan sampai suhu 510-525oC dan didinginkan cepat di air dingin untuk membuat pola retakan. Alur sedalam 1.5 mm dan lebar 2mm dibuat di tengah-tengah daerah pengaruh panas pada kedua sisi blok tersebut.

Karena jumlah retak yang banyak pada blok ini, maka blok ini seringkali dipakai untuk memban-dingkan sensitivitas penetrant fluorescent tingkat rendah dan medium.

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SENSITIVITY TEST

While there have been no simple quantitative tests developed for measuring penetrant sensitivity, a simple comparative test is usually adequate.

The penetrant to be tested is applied to one-half of the test block and the new or reference penetrant is applied to the remaining half.

The processing used—including dwell time, emulsification or removal, and developing—is that recommended by the penetrant manufacturer.

By visual observation it is determined if the old penetrant is contamined to the point where it must be discarded.

MENISCUS TEST

Provides a practical test for evaluating the dye concentration in thin-liquid films.

The test utilizes a flat glass platen and a convex lens. When a drop of solution is placed between the lens and platen, a colorless or nonfluorescent spot is formed around the point of contact. The resultant contact angle simply indicates the ability of a liquid to wet a surface.

The diameter of the remaining spot of colorless penetrant provides a measure of film thickness which can be used to compare the dye concentration of penetrant.

UJI SENSITIVITAS

Sementara belum ada uji kuantitatip sederhana untuk mengukur sensitivitas penetrant, uji perbandingan sederhana biasanya dianggap mencukupi.

Penetrant yang diuji diaplikasikan pada setengah blok uji, dan penetrant baru atau yang dijadikan referensi diaplikasikan pada setengah bagian lain.

Pemrosesan penetrant – termasuk waktu diam, emulsifikasi atau pembersihan, dan developing – dilakukan sesuai rekomendasi pabrik pembuat penetrant.

Melalui pengamatan visual, selanjutnya ditentukan apakah penetrant yang lama telah terkontaminasi dan harus dibuang.

UJI MENISKUS

Merupakan pengujian untuk mengevaluasi konsentrasi pewarna di dalam cairan.

Pengujian ini menggunakan kaca rata dan lensa cembung. Saat satu tetes larutan fluorescent diteteskan antara lensa dan kaca, maka akan terbentuk jejak di sekitar titik sentuh. Sudut kontak yang dihasilkan memperlihatkan kemampuan cairan untuk membasahi permukaan.

Diameter dari jejak penetrant pada lensa cembung menunjukkan ukuran ketebalan lapisan film yang dapat dipakai untuk membandingkan konsentrasi zat pewarna di dalam penetrant.

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Prolonged exposure of a film to ultraviolet light or accidental contamination by acids or alkalis will affect the dye concentration and therefore change the spot diameter.

Paparan dalam waktu lama di bawah cahaya ultraviolet atau kontaminasi akibat asam atau basa akan mempengaruhi konsentrasi pewarna dan akan mengubah diameter jejak pada lensa.

CERAMIC BLOCK TEST

Consists of an unglazed ceramic disc which has thousand of micropores and cracks on its surface.

A performance comparison can be made of two or more penetrant merely by noting the number of distribution of porosity indication and their brightness in a side-by-side compari-son test.

A small amount of a test penetrant is placed on one side and a reference penetrant is applied to the other side. After the correct dwell time, the two penetrants are compared.

A reduction in the number of apparent brightness of pore indications should be observed when comparing a fresh and old batch of penetrant.

WATER CONTENT TEST

The ASTM Standard D-95 describes a test where 100 ml of penetrant is placed in a boiling flask with a similar quantity of moisture-free xylene. The condensate is collected in a graduated tube to show percent of water by volume.

If percent of water exceeds manufacturer’s remommendation, the penetrant is discarded.

VISCOSITY TEST

A viscometer tube is used to measure the viscosity in centistoke to determine if the penetrant is within the range recommended by the manufacturer. A typical standard is ASTM D-445.

UJI BLOK KERAMIK

Terdiri dari piringan keramik buram yang mengan-dung ribuan pori dan retak berukuran sangat kecil pada permukaanya.

Perbandingan performance dapat dilakukan antara dua penetrant atau lebih yang diaplikasikan secara sebelah-menyebelah dengan memperhatikan jum-lah distribusi indikasi porositas dan kecemer-langannya.

Sejumlah kecil penetrant yang diuji ditempatkan pada satu sisi dan penetrant referensi ditempatkan pada sisi yang lain. Setelah waktu diam tertentu, kedua penetrant tersebut diperbandingkan.

Pengurangan jumlah dan tingkat kecemerlangan indikasi pori-pori selanjutnya diamati saat membandingkan antara penetrant yang lama dan baru.

UJI KADAR AIR

Standard ASTM D-95 menjelaskan pengujian ini, dimana 100 ml penetrant ditempatkan dalam gelas ukuran yang berisi xylene bebas air dengan volume yang sama. Uap pembakaran dikumpulkan dalam suatu tabung berjenjang untuk memperlihat-kan persentase air per volume.

Jika persentase air melebihi rekomendasi pabrik, penetrant harus dibuang.

UJI KEKENTALAN

Sebuah tabung ukuran kekentalan digunakan untuk mengukur kekentalan dalam centistoke untuk menentukan apakah penetrant masih di dalam rentang yang direkomendasikan oleh pabrik. Standar yang dipakai adalah ASTM D-445.

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FLUORESCENT PENETRANT FADE TEST

This test involves the use of the aluminum test blocks in a side-by-side comparison test.

The fluorescent penetrant is placed on both sides of the block and processed normally. One half of the block is then exposed to a standard black light for one hour, while the other side is covered with paper.

The fluorescent brilliance of the two sides is observed and if one side is noticeably less brilliant, the penetrant is discarded.

WATER WASHABILITY TEST

This test evaluates the efficiency of the emulsifier by comparing two different percentage blends of penetrant and emulsifier.

A special steel block is placed at a 75o angle and the two blends are allowed to flow separately down the block. After a five-minute waiting period, the block is washed and examined for traces of remaining penetrant.

DEVELOPER TEST

Dry developers are simply visually inspected to see that they are not lumpy or caked instead of fluffy and light.

Wet developers are often checked using a hydrometer to assure that the density of the powder in the vehicle is within the range that recommended by the manufacturer.

PORTABLE EQUIPMENT

The process control of portable equipment involves checking materials and associated equipment of the penetrant kit.

When ordering penetrant materials from the manufacturer, performance specifications should be requested in the purchase order. This establishes the necessary documentation to verify material performance. Aerosol cans are normally used in portable equipment; each can has a batch number on it.

Portable kits contain a cleaner. If the cleaner is used to preclean a part, it must be able to preclean the part without leaving a residue. Care should be taken to ensure that the cleaner used is not marked as a remover, which has a very slow evaporation rate and will leave an oil residue.

UJI KEPUDARAN PENETRAN FLUORESCENT

Pengujian ini memakai blok aluminium dengan perbandingan secara sebelah menyebelah.

Penetran fluorescent ditempatkan pada kedua sisi blok dan diproses seperti biasanya. Separuh bagian blok disinari cahaya ultraviolet selama satu jam, sedangkan separuh sisi yang lain ditutupi kertas.

Kecemerlangan fluorescent dari kedua sisi tersebut diamati dan dibandingkan, dan jika salah satu sisi tampak lebih pudar, penetrant harus dibuang.

UJI KEMAMPUCUCIAN DENGAN AIR

Pengujian ini mengevaluasi efisiensi emulsifier dengan membandingkan dua macam persentase campuran penetran dan emulsifier yang berbeda.

Blok baja khusus diposisikan pada sudut 75o dan dua macam campuran tadi dialirkan secara terpisah di atas blok. Setelah waktu tunggu selama lima menit, blok dicuci dan diperiksa mengenai keberadaan jejak penetran.

UJI DEVELOPER

Developer kering cukup diperiksa secara visual untuk melihat adanya gumpalan-gumpalan atau tidak ada yang lengket satu sama lain.

Developer basah seringkali diperiksa memakai hydrometer untuk menjamin bahwa massa jenis serbuk di dalam campuran masih dalam rentang yang direkomendasikan oleh pabrik pembuat.

PERALATAN PORTABEL

Pengontrolan proses untuk peralatan portabel meliputi pemeriksaan material dan peralatan yang ada hubungannya dengan paket penetran.

Saat memesan material penetran dari pemasok, spesifikasi performance sebaiknya dicantumkan dalam dokumen pembelian. Hal ini bermanfaat untuk mendokumentasikan performance material penetrant. Tiap kaleng semprot yang dipakai pada peralatan portabel, pada bagian bawahnya selalu terdapat nomer batch.

Paket portabel termasuk juga pembersih (cleaner). Jika cleaner dipakai sebagai pembersih awal maka harus mampu membersihkan benda tanpa meninggalkan sisa. Harus diperhatikan agar tidak memakai remover sebagai pembersih awal karena laju penguapannya rendah dan akan mening-galkan sisa minyak di permukaan.

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Most cleaners today are labeled cleaner/ remover. These cleaners do not leave a residue and can be used to preclean parts.

Developers now use a different liquid solvent as a vehicle, which does not evaporate as quickly. To prevent a loss of sensitivity and a possible masking of discontinuities, allow the developer to dry before applying more developer.

LIGHTING

Control of lighting is a key part of the process control.

The ultraviolet light in fluorescent penetrant portable kits must be checked for lens cleanliness and possible cracks. The ultraviolet light intensity must be checked against the applicable specification.

Ultraviolet lights from a 100 Watt mercury vapor lamp normally produce higher intensities than the 1000 μW/cm2 at a distance of 38 cm.

Daily checks of ultraviolet light intensity is a necessity for adequate process control. For systems used during multiple 8 h shifts, ultraviolet lights should be checked at the start of each shift.

The darkness of the fluorescent penetrant inspection area is important. Most specifi-cations require no more that 20 lux. (2 fc) of white light in the area.

In addition, inspectors must allow their eyes to adjust when first entering the darkened test area. Normally, 5 min is enough time for the eye to adapt to a dark environment. Tests should not start until the inspector’s eyes have adapted to the darkened conditions.

Kebanyakan cleaner yang ada saat ini diberi label sebagai cleaner/remover. Cleaner ini tidak mening-galkan sisa minyak dan bisa dipakai sebagai pembersih awal.

Developer yang ada saat ini memakai solvent cair yang berbeda-beda sebagai pengencer, sehingga tidak cepat menguap. Untuk mencegah hilangnya sensitivitas dan tertutupnya diskontinuitas, biarkan developer mengering dulu sebelum penyemprotan developer tambahan.

PENCAHAYAAN

Pengontrolan cahaya merupakan bagian kunci dari pengendalian proses.

Lampu ultraviolet pada paket portabel penetran fluorescent harus diperiksa kebersihan lensanya dan kemungkinan adanya retak. Intensitas cahaya ultraviolet harus diperiksa apakah sudah sesuai dengan spesifikasi yang berlaku.

Cahaya ultraviolet dari lampu mercury 100 Watt umumnya menghasilkan intensitas lebih dari 1000 μW/cm2 pada jarak 38 cm.

Pemeriksaan harian intensitas cahaya ultraviolet diperlukan untuk pengendalian proses yang benar. Untuk sistem shift yang digunakan selama kelipatan 8 jam, lampu ultraviolet harus diperiksa di awal mulainya shift.

Tingkat kegelapan ruangan pemeriksaan penetrant fluorescent perlu diperhatikan. Kebanyakan spesifikasi mensyaratkan intensitas cahaya tampak tidak lebih dari 20 lux (2 fc) dalam ruang pemeriksaan.

Sebagai tambahan, inspektor harus membiasakan matanya saat memasuki ruang gelap. Umumnya perlu waktu 5 menit bagi mata untuk beradaptasi dalam lingkungan gelap. Pengujian sebaiknya jangan dimulai hingga mata inspektor terbiasa dengan keadaan gelap.

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CHAPTER FIVE REVIEW

_______ 1. A typical false indication could be caused by an assembly that requires the components to be press-fitted.

_______ 2. Nonrelevant indications could be caused by the rough surface on a casting.

_______ 3. Postcleaning is necessary only when the part must be retested by the liquid penetrant method.

_______ 4. A typical true indication producing round indications is commonly caused by porosity.

_______ 5. Diffused or weak indications are often caused by subsurface discontinuities, and the part must be retested using a highly sensitive penetrant that will penetrate grain structure.

_______ 6. True indications are usually those that require evaluation to determine their effect on the service life of the part.

_______ 7. The aluminum test blocks used in penetrant evaluation are heated and quenched in water to produce a pattern of cracks on the surface.

_______ 8. The sensitivity tests used in penetrant inspection are relatively simple, nonquantitative, and require side-by-side visual observation.

_______ 9. The meniscus test utilizes a flat glass platen and convex lens to determine the dye concentration of a visible or fluorescent penetrant.

_______ 10. The ceramic block test uses an unfired ceramic disc to determine the dye concentration of a visibles or fluorescent penetrant.

_______ 11. A special steel block, placed at a 75° angle, is used to check the effectiveness of the emulsifier.

_______ 12. Dry developers are often checked with a hydrometer to insure that they are still light and fluffy and not settled into a dense mixture.

_______ 13. The fluorescent penetrant fade test usually makes use of the aluminum test blocks to perform the test.

_______ 14. The depth of a discontinuity can be compared by observing the relative size or brightness of the indication.

_______ 15. Penetrant that has been transferred to a clean article from the indication on another article can cause a false indication.

_______ 16. Nonrelevant indications often are actual surface discontinuities.

_______ 17. If a discontinuity is evaluated as being a true indication, the article should automatically be rejected.

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CHAPTER SIX

INTRODUCTION

This chapter discusses types of discontinuities that can be evaluated with the liquid penetrant method.

CATEGORIES OF DISCONTINUITIES

Discontinuities can be divided into THREE general categories: inherent, processing, and service.

1. Inherent. They are usually related to discontinuities found in the molten metal. Inherent wrought discontinuities relate to the melting and solidification of the original ingot before it is formed into slabs, blooms, and billets. Inherent cast discontinuities relate to the melting, casting, and solidification of a cast article. Usually caused by inherent variables such as inadequate feeding, gating, excessive pouring temperature, and entrapped gases.

2. Processing discontinuities. They are usually related to the various manufacturing processes such as machi-ning, forming, extruding, rolling, welding, heat treating, and plating.

3. Service discontinuities. They are related to the various service conditions such as stress corrosion, fatigue, and erosion.

REMEMBER, when you use the liquid penetrant method, you can find only those discontinuities which are open to the surface.

However, during the manufacturing process, many discontinuities that were subsurface can be made open to the surface by machining, grinding, and the like.

Remember that discontinuities are not necessarily defects. Any indication that is found by the inspector is called a discontinuity until it can be identified and evaluated as to the effect it will have on the service of the part.

PENDAHULUAN

Bab ini mendiskusikan jenis-jenis diskontinuitas yang dapat dievaluasi menggunakan metoda cairan penetrant.

KATAGORI DISKONTINUITAS

Diskontinuitas dapat dibagi menjadi TIGA katagori umum: bawaan, proses, dan servis.

1. Bawaan. Biasanya berhubungan dengan diskonti-nuitas yang ditemukan dalam logam cair. Diskontinuitas wrought bawaan berhubungan dengan peleburan dan pembekuan ingot sebelum dibentuk menjadi slabs, bloom, dan billet. Diskontinuitas tuangan bawaan berhubu-ngan dengan peleburan, pengecoran, dan pembekuan benda cor. Biasanya disebab-kan karena variabel bawaan seperti kurang pengisian, gating, suhu tuang berlebihan, dan gas yang terperangkap.

2. Diskontinuitas Proses. Biasanya berhubungan dengan aneka proses manufaktur seperti permesinan, pembentukan, extruding, pengerolan, pengelasan, laku panas, dan pelapisan.

3. Diskontinuitas Servis. Berhubungan dengan aneka kondisi pengoperasian seperti korosi tegangan, kelelahan, dan erosi.

INGAT, jika anda menggunakan metoda cairan penetran, anda hanya bisa menemukan diskonti-nuitas yang membuka ke permukaan.

Namun demikian, selama proses manufaktur, banyak diskontinuitas yang tadinya di bawah permukaan menjadi membuka ke permukaan karena permesinan, penggerindaan, dan sejenisnya.

Ingat bahwa diskontinuitas belum tentu cacat. Sembarang indikasi yang ditemukan oleh inspektor dinamakan sebagai diskontinuitas hingga dikenali dan dievaluasi pengaruhnya terhadap pengopera-sian komponen.

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THE ORIGINS OF DISCONTINUITIES

Listed below are some typical discontinuities that should be recognized when doing any type of nondestructive test.

Discontinuities trapped in the ingot during steel making process may cause aditional types of discontinuities as the steel is used in the manu-facture of an article.

There are FOUR main types of discontinuities found in ingots:

1. Porosity – caused by entrapped gas in the molten metal.

2. Nonmetallic inclusions – caused by impurities accidentally included in the molten metal.

3. Pipe – caused by shrinkage at the center of the ingot as the molten metal solidifies.

4. Segregations – occurs when the distribution of the various elements is not uniform throughout the ingot. This condition is called “banding” and is not usually significant.

ASAL-MUASAL DISKONTINUITAS

Di bawah ini adalah beberapa jenis diskontinuitas yang sebaiknya dikenali jika melakukan pengujian tanpa merusak.

Diskontinuitas yang terperangkap di dalam ingot selama proses pembuatan baja dapat menyebab-kan terjadinya jenis diskontinuitas lain saat baja tersebut dipakai memproduksi suatu artikel.

Ada EMPAT jenis diskontinuitas utama yang ditemukan di dalam ingot:

1. Porositas – disebabkan oleh gas-gas yang terperangkap di dalam logam cair.

2. Inklusi Nonlogam – disebabkan karena ketidakmurnian yang tanpa sengaja terjadi dalam logam cair.

3. Pipa – disebabkan karena penyusutan pada bagian tengah ingot selama pembekuan.

4. Segregasi – terjadi karena ketidakseragaman distribusi aneka elemen di dalam ingot. Kondisi ini dimanakan “banding” dan dianggap tidak begitu berarti.

The “hot top” is usually cropped off to remove most of the above discontinuities.

Bagian “hot top” biasanya dipotong untuk menghi-langkan sebagian besar diskontinuitas di atas.

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CASTING DISCONTINUITIES

Casting discontinuities occur when molten metal is poured into a mold and allowed to solidify.

A COLD SHUT is caused when molten metal is poured over solidified metal as shown below.

DISKONTINUITAS TUANGAN

Diskontinuitas tuangan terjadi saat logam cair dituangkan ke dalam cetakan dan dibiarkan membeku.

COLD SHUT disebabkan jika ada logam cair menumpuki logam yang sudah membeku.

When the metal is poured, it hits the mold too hard and spatters small drops of metal. When these drops of metal hit higher up on the mold, they stick and solidify. When the rising molten metal reaches and covers the solidified drops of metal, a crack-like discontinuity is formed.

HOT TEARS (SHRINKAGE CRACKS) occurs when there is unequal shrinkage between light and heavy sections as shown below.

Saat logam cair dituangkan dan membentur dinding cetakan terlalu keras akan terjadi percikan logam cair. Jika percikan ini mengenai dinding cetakan, dia akan lengket dan membeku. Apabila logam cair menutupi percikan beku tersebut, terbentuk diskontinuitas yang menyerupai retakan.

SOBEK PANAS (RETAK SUSUT) terjadi apabila terjadi penyusutan yang tidak merata antara bagian ringan dan berat seperti dalam gambar.

In a casting having light and heavy sections, the light sections, being smaller, solidify faster; they shrink faster pulling the heavier sections, which are hotter and not shrinking as fast, toward the light sections.

Pada benda cor, makin ringan suatu bagian maka makin cepat pembekuan dan penyusu-tannya, yang akan menarik bagian berat yang lebih panas dan lebih lambat penyusutannya dibandingkan bagian tipis.

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SHRINKAGE CAVITIES occur when there is insufficient molten metal to fill the space created by shrinkage, just as pipe is formed in an ingot.

RONGGA SUSUT terjadi jika volume logam cair tidak cukup mengisi rongga akibat penyusutan, sama seperti halnya pipe yang terbentuk di dalam ingot.

Shrinkage cavities can be eliminated, or the possibility of shrinkage cavities can be greatly reduced, by adding a feeder head or reservoir as shown above on the right.

MICROSHRINKAGE is usually many small subsurface holes that appear at the gate of the casting caused by premature blocking of the gate.

Microshrinkage can also occur when the molten metal must flow from a thin section into a thicker section of a casting.

BLOW HOLES are small holes at the surface of the casting caused by gas which comes from the mold itself. Many molds are made of sand, and when molten metal comes into contact with the mold, the water in the sand is released as steam.

POROSITY is caused by entrapped gas. Porosity is usually subsurface but can occur on the surface depending on the design of the mold.

WATER WASHABLE FLUORESCENT PENETRANT is best suited for the highest sensitivity in cast articles.

Rongga susut dapat dicegah atau dikurangi kemungkinan terjadinya dengan menambahkan corong pengisian seperti dalam gambar kanan atas.

SUSUT MIKRO biasanya berupa lubang-lubang kecil di bawah permukaan yang muncul pada gate akibat penyumbatan gate sebelum pengisian selesai seluruhnya.

Susut mikro dapat juga disebabkan ketika logam cair harus mengalir dari bagian tipis ke bagian yang lebih tebal di dalam cetakan.

LUBANG TIUP adalah lubang-lubang kecil pada permukaan benda cor akibat gas-gas yang berasal dari dinding cetakan. Banyak cetakan yang dibuat dari pasir dan saat logam cair bersentuhan dengannya kelembaban yang terkandung dalam pasir berubah menjadi uap air.

POROSITAS disebabkan karena gas-gas yang terperangkap. Porositas biasanya di bawah permukaan namun dapat pula terjadi di permukaan, tergantung pada disain cetakan.

WATER WASHABLE FLUORESCENT PENETRANT adalah jenis penetrant yang paling baik untuk memperoleh sensitivitas tertinggi pada benda-benda cor.

GATE (ENTRANCE FOR MOLTEN METAL)

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PROCESSING DISCONTINUITIES

Processing discontinuities are those found or produced by forming or fabrication operations including rolling, forging, welding, machining, grinding, and heat treating.

WORKING THE BILLETS

When an ingot is further processed into slabs, blooms, and billets, it is possible for the discontinuities to change size and shape.

As a billet is flattened and spread out, nonmetallic inclusions may cause a lamination. Pipe, and porosity could also cause laminations in the same manner as shown below.

DISKONTINUITAS PROSES

Diskontinuitas proses ditemukan atau dihasilkan saat pembentukan atau operasi fabrikasi, termasuk pengerolan, penempaan, pengelasan, permesinan, penggerindaan, dan perlakuan panas.

PENGERJAAN BILLET

Ketika ingot diproses lebih lanjut menjadi slabs, blooms, dan billets, diskontinuitas bisa berubah ukuran dan bentuk.

Saat billet diratakan dan digepengkan, inklusi nonlogam dapat menyebabkan laminasi. Pipa dan porositas juga dapat menyebabkan laminasi dengan cara yang sama seperti dalam gambar di bawah ini.

As a billet is rolled into bar stock, nonmetallic inclusions are squeezed out into longer and thinner discontinuities called stringers.

Saat billet dirol menjadi batang tongkat, inklusi nonlogam tertekan menjadi diskontinuitas yang panjang dan tipis dinamakan stringers.

A nonmetallic inclusion in bar stock extends in the direction of grain formation. As the billet is rolled smaller around and longer, the stringer also becomes smaller around and longer.

Inklusi nonlogam dalam batang tongkat menyebar ke arah pembentukan butiran. Saat billet dirol semakin kecil dan panjang, stringer juga menjadi lebih kecil dan panjang.

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As a billet is rolled into round bar stock, surface irregularities may cause SEAMS. Seams are caused by folding of metal due to improper rolling or by a crack in the billet as shown below.

Saat billet dirol menjadi batang tongkat, ketidak-teraturan permukaan bisa mengakibatkan seams. Seams terjadi akibat lipatan logam karena pengerolan yang salah atau karena retakan pada billet seperti dalam gambar berikut.

A seam could also occur when the billet is formed into a rectangular bar as shown below.

Seam juga bisa terjadi saat billet dibentuk menjadi batang kotak seperti berikut.

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FORGING DISCONTINUITIES

Forging discontinuities occur when metal is hammered or pressed into shape, usually while the metal is very hot.

A forged part gains strength due to the grain flow taking the shape of the die, and the process is shown below.

DISKONTINUITAS TEMPAAN

Diskontinuitas tempaan terjadi saat logam dipukul atau ditekan menjadi bentuk tertentu, biasanya ketika logam dalam kondisi sangat panas.

Benda tempa memperoleh kekuatan akibat aliran butiran yang berlangsung ke semua arah mengikuti bentuk cetakan seperti gambar.

A FORGING BURST is a rupture caused by forging at improper temperatures. Forging metal at too low temperature may cause burst. Burst may be either internal or open to the surface a shown below.

PECAH TEMPA adalah kepecahan yang disebab-kan karena suhu penempaan yang salah. Penem-paan logam pada suhu terlalu rendah mengaki-batkan kepecahan. Pecah tempa bisa di dalam, maupun membuka ke permukaan.

Improper temperatures caused these parts to break as the material was being shaped by forging. The metal was not hot enough and did not want to flow with the forging. When squeezed by the heavy forging press, the metal in the center simply ruptured.

Suhu tempa yang terlalu rendah mengakibatkan komponen di atas pecah saat ditempa. Logam tidak cukup panas sehingga tidak terjadi aliran saat ditempa. Saat ditekan pada waktu penempaan, logam akan pecah di bagian tengahnya.

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A FORGING LAP is caused by folding of metal on the surface of the forging, usually when some of the forging metal is squezeed out between the two dies that do not match.

LIPATAN TEMPA disebabkan lipatan logam pada permukaan benda tempa, terjadi karena logam terjepit antara cetakan bagian atas dan bawah yang tidak lurus.

Forging laps can also be caused by poor die design. As the metal is pressed into the cavity in this die, the metal is forced up at the bottom of the die and tends to fold over on itself, forming the forging lap shown on the right.

Lipatan tempa dapat juga disebabkan disain cetakan yang keliru. Saat logam ditekan di dalam rongga cetakan, logam dipaksa meme-nuhi cetakan dan cenderung terlipat ke arahnya sendiri membentuk lipatan tempa seperti dalam gambar kanan bawah.

For production testing of forgings, POSTEMUL-SIFIABLE FLUORESCENT PENETRANT is the recommended penetrant technique to obtain the best sensitivity.

Untuk pengujian produksi benda-benda tempa, POSTEMULSIFIABLE FLUORESCENT PENE-TRANT merupakan teknik yang direkomendasikan untuk memperoleh sensitivitas terbaik.

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GRINDING CRACK are a processing-type discontinuity caused by stresses which are built up from excess heat created between grinding wheel and metal.

Grinding cracks will usually occur at right angle to the rotation of the grinding wheel.

RETAK GERINDA adalah diskontinuitas proses, disebabkan karena tegangan yang terjadi akibat panas berlebih yang ditimbulkan antara mata gerinda dan logam.

Retak gerinda biasanya akan terjadi pada arah tegak lurus terhadap arah putar mata gerinda.

HEAT TREAT CRACKS are often caused by the stresses built up during heating and cooling. Unequal cooling between light and heavy sections may cause heat treat cracks.

Heat treat cracks have no specific direction and usually start at sharp corners which act as stress concentration points.

During inspection of heat treated parts, the first areas of concern will be:

• Any sharp area, such as corner, ridges, etc.

• Junction of light and heavy sections.

The photo below shows a part that has cracked from heat treatment. Notice that the crack cuts across the grain. Since heat treatment cracks have no specific direction, the crack might just as well have followed the grain.

RETAK LAKU PANAS seringkali disebabkan tega-ngan yang terjadi selama pemanasan dan pendi-nginan. Laju pendinginan yang tidak sama antara bagian ringan dan berat bisa menyebabkan retak.

Retak laku panas tidak mempunyai arah tertentu, dan biasanya bermula dari pojok-pojok tajam yang bertindak sebagai titik konsentrasi tegangan.

Selama pemeriksaan komponen yang dilaku panas, tempat pertama yang menjadi perhatian:

• Daerah tajam seperti pojok-pojok, permukaan kasar, takik, dll.

• Pertemuan antara bagian ringan dan berat.

Foto di bawah ini memperlihatkan komponen yang retak akibat perlakuan panas. Perhatikan bahwa retak tersebut melintang terhadap butiran logam. Karena retak laku panas tidak memiliki arah ter-tentu, arahnya bisa juga mengikuti butiran logam.

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WELDING DISCONTINUITIES below are types of processing discontinuities.

Crater cracks

DISKONTINUITAS PENGELASAN dibawah ini termasuk ke dalam diskontinuitas proses.

Retak kawah

Stress cracks Retak tegang

Porosity Porositas

Slag Inclusion Inklusi Slag

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Tungsten Inclusion Inklusi Tungsten

Lack of Penetration Kurang Penembusan

Lack of Fusion Kurang Peleburan

Undercut Undercut

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SERVICE DISCONTINUITIES

FATIGUE CRACKS are service-type disconti-nuities that are usually open to the surface where they start from concentration points.

Fatigue cracks occur crosswise to the direction of strees movement. The stress on the driven shaft below would have been clockwise – the direction of its rotation. The fatigue crack occured across the direction of stress movement.

DISKONTINUITAS SERVIS

RETAK FATIK merupakan diskontinuitas servis yang biasanya membuka ke permukaan dimana mulainya dari titik-titik konsentrasi tegangan.

Arah perambatan retak fatik melintang terhadap arah tegangan. Arah tegangan yang bekerja pada poros penggerak di bawah ini searah jarum jam – yaitu arah putaran poros. Retak fatik yang timbul arahnya melintang terhadap arah tegangan.

Fatigue cracks are possible only after the part is placed into service, but may be the result of porosity, inclusions, or other discontinuities in a highly stressed metal part.

Retak fatik hanya mungkin timbul setelah komponen menjalankan fungsinya, dan bisa disebabkan karena porositas, inklusi, atau diskontinuitas lain pada bagian logam yang konsentrasi tegangannya tinggi.

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CHAPTER SIX REVIEW

_______ 1. The general category of processing discontinuities relates to discontinuities caused during manufacturing processes such as welding, extruding, and heat treating.

_______ 2. During the steel-making process the top of the ingot is usually removed to help eliminate such discontinuities as pipe, porosity and nonmetallic inclusions.

_______ 3. When a billet is rolled into bar stock, a nonmetallic inclusion could be formed into a longer and thinner discontinuity called a stringer.

_______ 4. Porosity in a billet could cause a lamination if the metal were formed into a flat plate.

_______ 5. Seams are usually subsurface discontinuities caused by improper rolling of a billet into round stock.

_______ 6. During the rolling of a billet into round bar stock, the grain in the metal forms perpendicular to the direction of rolling.

_______ 7. In the forging operation, underheated metal will not allow the metal to flow properly and may cause "forging seams".

_______ 8. Forging bursts are considered subsurface discontinuities and can never be inspected with liquid penetrant techniques.

_______ 9. Cold shuts are common discontinuities found in the forging process and are caused by inadequate heating of the forged part.

_______ 10. Blow holes are subsurface discontinuities commonly found in cast parts.

_______ 11. Because cold metal occupies more space than hot metal, there is the danger of "hot tears" during the casting process.

_______ 12. Porosity is often caused by entrapped gas that is expanded during the heating and pressing in the forging process.

_______ 13. Microshrinkage is often found at the gate of a casting and is usually subsurface.

_______ 14. Grinding cracks are usually at right angles to the direction of grinding and are caused by the heat build-up between the grinding wheel and metal.

_______ 15. Heat treat cracks are often associated with stress concentration points on the part being heat treated.

_______ 16. Porosity may lead to a fatigue crack in a highly stressed part.

_______ 17. Crater cracks and tungsten inclusions are both associated with discontinuities formed during the welding process.

_______ 18. Lack of penetration and lack of fusion both refer to the same type of welding discontinuity.

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CHAPTER SEVEN

INTRODUCTION

It should be emphasized that liquid penetrant inspection is NOT the best method in all cases.

The selection of one testing method over another is based upon variables such as:

1. Type and origin of discontinuity. 2. Material manufacturing process. 3. Accessibility of article. 4. Level of acceptability desired. 5. Equipment available. 6. Cost.

IDENTIFICATION AND COMPARISON OF DISCONTINUITIES

Each of the specific discontinuities below are divided into three general categories: INHERENT, PROCESSING, and SERVICE.

Cold shut

Fillet crack

Grinding crack

Heat-affected zone cracking

Heat-treat crack

Shrinkage crack

Thread crack

Hydrogen flake

Lack of penetration

Lamination

Laps and seams

Laps and seams

Microshrinkage

Stress corrosion

Hot tears

Intergranular corrosion

PENDAHULUAN

Perlu ditekankan bahwa pemeriksaan cairan pene-tran BUKAN metoda terbaik untuk semua kasus.

Pemilihan satu metoda pengujian atas metoda lainnya didasarkan pada variabel-variabel seperti:

1. Jenis dan asal diskontinuitas. 2. Proses pembuatan material. 3. Akses ke artikel. 4. Tingkat keberterimaan yang diinginkan. 5. Ketersediaan peralatan. 6. Biaya.

PENGENALAN DAN PEMBANDINGAN DISKONTINUITAS

Tiap jenis diskontinuitas di bawah ini dibagi menjadi tiga katagori umum: BAWAAN, PROSES, dan SERVIS.

Cold shut

Retak fillet

Retak gerinda

Retak daerah pengaruh panas

Retak laku panas

Retak susut

Retak ulir

Hydrogen flake

Kurang penembusan

Laminasi

Lipatan dan lapisan

Lipatan dan lapisan

Susut mikro

Korosi tegangan

Sobek panas

Korosi batas butir

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TRAINING AND CERTIFICATION

It is important that the technician and super-visor be qualified in the liquid penetrant method before the technique is used and test results evaluated.

The American Society for Nondestructive Testing recommends the use of its document Recommended Practice No. SNT-TC-1A.

This document provides the employer with necessary guidelines to properly qualify and certify the NDT technician in all methods.

To comply with this document, the employer must establish a WRITTEN PRACTICE which describes in detail how the technician will be trained, examined, and certified.

The student is advised to study the 2006 Edition of SNT-TC-1A to determine the recommended number of hours of class-room instruction and months of experience necessary to be certified as a liquid penetrant testing technician.

Certification of NDT personnel is the responsi-bility of the employer and is usually at THREE levels. Level I – is qualified to properly perform

speci-fic calibrations, specific NDT, and specific evaluations for acceptance or rejection determinations according to written instructions and to record results. Should receive the necessary instruction and supervision from a certified NDT Level II or III individual.

Level II – is qualified to set up and calibrate equipment and to interpret and evaluate results with respect to applicable codes, standards, and specifications. Should be thoroughly familiar with the scope and limi-tations of the methods for which qualified. Should exercise assigned responsibility for on-the-job training and guidance of trainees and NDT Level I personnel. Should be able to organize and report the results of NDT tests.

PELATIHAN DAN SERTIFIKASI

Adalah penting bahwa teknisi dan pengawas dikualifikasi untuk metoda cairan penetran sebe-lum menggunakan teknik ini dan mengevaluasi hasil uji.

ASNT merekomendasikan penggunaan dokumen Recommended Practice No. SNT-TC-1A.

Dokumen tersebut memberikan pedoman bagi perusahaan dalam mengkualifikasi dan menser-tifikasi teknisi NDT untuk semua metoda.

Dalam rangka mengikuti dokumen tersebut, perusahaan harus menyusun sebuah WRITTEN PRACTICE yang menjelaskan secara detil, cara melatih, menguji dan mensertifiksi teknisi NDT.

Peserta disarankan untuk mempelajari dokumen SNT-TC-1A edisi 2006 untuk mengetahui jumlah jam pelajaran yang direkomendasikan dan pengalaman (dalam bulan) yang diperlukan dalam proses sertifikasi sebagai teknisi pengujian cairan penetrant.

Sertifikasi personil NDT merupakan tanggung jawab perusahaan dan biasanya dibagi menjadi TIGA level. Level I – memiliki kualifikasi untuk melakukan

kalibrasi, NDT, dan evaluasi tertentu untuk menentukan penerimaan atau penolakan dengan mengacu pada pedoman tertulis, dan untuk merekam hasil. Menerima perintah dan pengawasan seperlunya dari NDT level II atau III.

Level II – memiliki kualifikasi untuk mengatur dan mengkalibrasi peralatan dan mengiter-pretasi serta mengevaluasi hasil dengan mengacu pada code, standard, dan spesifikasi. Mengenal dengan baik lingkup dan batasan metoda dimana ia terkualifikasi. Melakukan tanggung jawab yang dibebankan untuk memberi-kan petunjuk kepada siswa dan NDT Level I. Mampu mengorganisir dan membuat laporan hasil pengujian NDT.

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Level III – Should be capable of developing, qualifying, and approving proce-dures, establishing and approving techniques, interpreting codes, stan-dards, specifications, and proce-dures; and designating the particular NDT methods, techniques, and procedures to be used. Should be capable of interpreting and eva-luating results in terms of existing codes, standards, and specifica-tions. Should have sufficient practical background in applicable materials, fabrication, and product technology to establish techniques and to assist in establishing acceptance criteria when none are otherwise available. Should have general familiarity with other appropriate NDT methods. Should be capable of training and examining NDT Level I and II personnel for certification in those methods.

The SNT-TC-1A document recommends that the level I and II NDT technician be examined in the following areas:

A. General examination. B. Specific examination. C. Practical examination.

ASNT provides a service to the industry by providing Level III examination in the basic and method areas. Because of the individual requirements of the many industries using NDT, the specific examination is still the responsibility of the employer.

Level III – mampu mengembangkan, mengkualifi-kasi, dan menyetujui prosedur, menyu-sun dan menyetujui teknik, menginter-pretasi code, standard, dan prosedur; dan menunjuk metoda NDT tertentu, teknik, dan prosedur yang akan diguna-kan. Mampu menginterpretasi dan mengevaluasi hasil sesuai code, standard, dan spesifikasi yang ada. Memiliki latar belakang kemampuan praktis yang mencukupi dalam aplikasi material, fabrikasi, dan teknologi produksi yang berlaku untuk menyusun teknik dan untuk membantu dalam menetapkan kriteria penerimaan dimana tidak tercakup dalam code, standard, atau spesifikasi yang ada. Memiliki pengetahuan tentang semua metoda NDT. Mampu mengadakan pelatihan dan pengujian terhadap personil NDT Level I dan II untuk disertifikasi pada metode NDT tertentu.

Dokumen nomer SNT-TC-1A merekomendasikan bahwa teknisi NDT Level I dan II diuji dalam bidang berikut:

A. Ujian General. B. Ujian Specific. C. Ujian Practical.

ASNT menyediakan layanan kepada industri dengan mengadakan ujian Level III dalam bidang basic dan method. Mengingat banyaknya persya-ratan industri pengguna NDT yang berbeda-beda, ujian specific masih merupakan tanggung jawab perusahaan.

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CHAPTER SEVEN REVIEW

_______ 1. The selection of one test method over another is usually the decision of the Level I technician performing the test.

_______ 2. ASNT provides a service for examining Level I, II, and III personnel in the General and Specific areas.

_______ 3. The responsibility of issuing a certificate to the NDT technician is always given to the employer if the SNT-TC-1A document is to be complied with.

_______ 4. If the SNT-TC-1A document is to be used as a recommended guideline, the Written Practice must be submitted to ASNT for approval.

_______ 5. If the SNT-TC-1A guidelines are to be followed, the Level III technician should have a knowledge of other commonly used methods of NDT eventhough certification is needed only in the liquid penetrant area.

_______ 6. A Level I technician performing a liquid penetrant test is permitted to accept or reject the part provided that written instructions or procedures are given to him by a level II or level III certified individual.

_______ 7. It is essential that every employer using the SNT-TC-1A document establish a Written Practice.

_______ 8. If an employer does not have a Level III technician in his company, he can retain the services of an outside agency to perform these functions.

_______ 9. To comply with the guidelines of SNT-TC-1A, all three levels of technicians must take a General, Practical, and Specific test if examinations are used to determine certification.

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CHAPTER EIGHT

INTRODUCTION

This chapter discusses test procedure for liquid penetrant test.

CONTROLLING LIQUID PENETRANT TESTS

The three types of written documents that control penetrant tests are standards, specifications, and written practices. Level II personnel are required to be able to interpret and prepare these documents.

STANDARDS

A standard is a reference document that controls and standardizes generally accepted practices for a nondestructive testing method. It defines criteria for equipment, penetrant materials, inspector qualifications, test require-ments, and written procedure requirements. ASTM E 165, Standard Test Method for Liquid Penetrant Examination are examples of standards.

Many standards require that penetrant tests be performed to written procedures. Quality and reliability can be affected if proper test techniques and procedures are not followed. In addition, written procedures establish test repeatability.

SPECIFICATIONS

A specification is written by a company for a specific process. The specification is a tool used by engineering, management, and purchasing for contractual documents. Normally, the specification will contain the following sections:

1. Reference documents, 2. Materials, 3. Equipment, 4. Personnel qualification, 5. Process control, and 6. Written procedure requirements.

A sample specification is contained in the last part of this chapter.

PENDAHULUAN

Bab ini mendiskusikan prosedur pengujian untuk cairan penetrant.

PENGENDALIAN UJI CAIRAN PENETRAN

Tiga jenis dokumen tertulis untuk mengendalikan pengujian penetrant adalah standard, spesifikasi, dan written practice. Personil level II disyaratkan agar mampu menginterpretasi dan menyiapkan dokumen-dokumen tersebut.

STANDARD

Standard adalah dokumen referensi yang mengen-dalikan dan menstandardkan kebiasaan yang umum diterima untuk melakukan metoda NDT. Standard mendefinisikan kriteria peralatan, material penetran, kualifikasi inspektor, persyaratan uji, dan persyaratan prosedur tertulis. ASTM E 165, Standard Test Method for Liquid Penetrant Examination merupakan contoh standard.

Banyak standard mensyaratkan agar pengujian penetran dilakukan dengan mengacu pada prose-dur tertulis. Kualitas dan keandalan dapat terpengaruh jika teknik dan prosedur yang benar tidak diikuti. Lagi pula, prosedur tertulis menjamin dilakukannya pengujian berulang-ulang.

SPESIFIKASI

Spesifikasi dibuat oleh perusahaan untuk proses tertentu. Spesifikasi adalah alat yang digunakan oleh bagian teknik, manajemen, dan pembelian untuk keperluan dokumen kontrak. Biasanya, spesifikasi akan mencantumkan bagian-bagian berikut ini:

1. Dokumen referensi, 2. Material, 3. Perlengkapan, 4. Kualifikasi personil, 5. Pengendalian proses, dan 6. Persyaratan prosedur tertulis.

Contoh spesifikasi dapat dilihat di bagian akhir bab ini.

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1. Reference Documents Section All the documents that are applicable to the penetrant specification are listed in the reference document section of the proce-dure. For example, the company may require that all penetrant practices meet the requirements of ASTM E 165, Standard Test Method for Liquid Penetrant Examination, so this standard would be listed as a source or reference document.

2. Materials Section The materials section establishes the penetrant materials that can be used to perform the procedure. It may include the type, technique, and sensitivity level of the penetrant. Acceptable developers are also included in this section, and any special cleaning materials may be noted.

3. Equipment Section The equipment required to apply, remove, dry, develop, and test the part is listed in this section. Any special equipment require-ments will also be noted.

4. Personnel Qualification Section The personnel qualification section is nor-mally written to an established industry document such as Recommended Practice No. SNT-TC-1A or CP-189.

5. Process Control Section The process control section specifies any tests that must be performed on the materials and the acceptable criteria for that test. In addition, this section contains any special requirements to be used, such as acceptable precleaning techniques or specific developers.

6. Written Procedure A prime contractor may establish the written procedure for a part or have the subcon-tractor submit a written procedure for approval. In either case, a written procedure is needed to perform a liquid penetrant test effectively.

1. Bagian Dokumen Referensi Semua dokumen yang berlaku untuk membuat spesifikasi penetran dimasukkan dalam daftar di bagian dokumen referensi dari prosedur tersebut. Contohnya, perusahaan mensya-ratkan bahwa semua pekerjaan penetran harus memenuhi ketentuan ASTM E 165, Standard Test Method for Liquid Penetrant Examination, sehingga standard ini akan dimasukkan dalam daftar sebagai sumber atau dokumen referensi.

2. Bagian Material Bagian material menetapkan material penetran yang dapat dipakai untuk menjalankan prosedur. Bagian ini menyebutkan jenis, teknik, dan tingkat sensitivitas penetrant. Developer yang diijinkan untuk dipakai juga disebutkan di dalam bagian ini, disamping itu jenis material pembersih khusus juga bisa dimasukkan.

3. Bagian Peralatan Peralatan yang disyaratkan pemakaiannya, untuk membersihkan, mengeringkan, mende-velop, dan menguji komponen dimasukkan da-lam daftar di bagian ini, termasuk persyaratan untuk peralatan khusus jika ada.

4. Bagian Kualifikasi Personil Bagian kualifikasi personil biasanya mengacu pada dokumen yang sudah ada seperti Recommended Practice No. SNT-TC-1A atau CP-189.

5. Bagian Pengendalian Proses Bagian pengendalian proses menetapkan jenis pengujian yang harus dilakukan pada material penetran dan kriteria keberterimaan untuk pengujian tersebut. Bagian ini juga menyebut-kan persyaratan khusus yang dipakai seperti teknik pembersihan awal yang diijinkan atau jenis developer khusus.

6. Prosedur Tertulis Kontraktor utama dapat membuat prosedur tertulis untuk suatu komponen atau meminta subkontraktor mengajukan prosedur tertulis untuk dimintakan persetujuan. Pada kedua kasus tersebut, prosedur tertulis diperlukan agar pelaksanaan pengujian penetran berjalan efektip.

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WRITTEN PRACTICE

Written practices provide specific guidance on the performance of the penetrant test. The depth or detail contained in a written practice will vary.

Some written practices are very specific and are written for one kind of test object, whereas others are general and cover many different parts. Often, company will require a subcontractor to provide written practice for a specific part. In this case, the written practice will be written to the company’s specification document.

A written practice should contain, at the minimum, the following:

1. Penetrant materials to be used, 2. Details of precleaning the part, 3. Complete processing parameters, 4. Inspection and evaluation requirements, 5. Specific information of part to be

inspected, 6. Acceptance/rejection criteria and 7. Postcleaning procedures.

Many times, inspection personnel will find that testing documentation is a combination of the specification and written practice. This is acceptable and, in some cases, can be a more cost effective way to control penetrant tests.

An example of a combined specification and written practice is the way one aircraft manufacturer combined the documents. The combined document was placed in the general section of the aircraft maintenance manual. Whenever a part in other areas of the manual required a penetrant test, the inspector was referred to this document. This simplified the process and was more cost effective.

WRITTEN PRACTICE

Written practice memberikan pedoman khusus terhadap pelaksanaan pengujian penetran. Detil yang tercantum dalam suatu written practice adalah bervariasi.

Beberapa written practice bisa sangat khusus dan ditulis untuk satu macam benda uji, sebaliknya yang lain bersifat umum dan mencakup banyak benda uji yang berbeda. Seringkali, perusahaan mensyaratkan subkontraktor menyediakan written practice untuk satu bagian khusus. Dalam hal ini written practice akan ditulis mengacu pada dokumen spesifikasi dari perusahaan tersebut.

Sebuah written practice sebaiknya memuat, paling tidak, hal-hal berikut ini:

1. Material penetran yang dipakai, 2. Detil pembersihan awal benda uji, 3. Parameter pemrosesan secara lengkap, 4. Persyaratan inspeksi dan evaluasi, 5. Informasi khusus mengenai benda yang

diperiksa, 6. Kriteria keberterimaan dan penolakan dan 7. Prosedur pembersihan akhir.

Acapkali, personil pemeriksaan akan menemukan bahwa dokumentasi pengujian adalah kombinasi antara spesifikasi dan written practice. Hal ini sah-sah saja dan, pada beberapa kasus, dapat menghemat biaya.

Contoh dari kombinasi antara spesifikasi dan written practice adalah cara dimana sebuah pabrik pesawat terbang meggabungkan dokumen. Dokumen gabungan diletakkan pada bagian umum dari manual perawatan pesawat. Apabila sebuah komponen di bagian lain dari manual tersebut mensyaratkan uji penetran, inspektor dapat mengacu pada dokumen ini. Hal tersebut menyederhanakan proses dan menghemat biaya.

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SAMPLE SPECIFICATION – PENETRANT TESTING PROCESS

XYZ Manufacturing, Inc.

1.0. Penetrant Testing Process Specification

1.1. Scope – This specification establishes the minimum requirements for penetrant inspection of nonporous materials. The penetrant inspection processes described in this specification are applicable to inprocess and final inspections.

2.0. Reference Documents

2.1. The following documents, of the issue in effect on the date of invitation for bids or request for proposal, forma part of this specification to the extent specified therein:

ANSI/NCSL — American National Standard for Calibration

Z540-1-1994

ASNT — Recommended Practice No. SNT-TC-IA

ASTM D 95 — Method of Test for Water in Petroleum Products

ASTM D 2512 — Test Method for Compatibility of Materials with Liquid Oxygen

ASTM E 1316 — Standard Terminology for Nondestructive Examinations

ASTM E 1417 — Standard Practice for Liquid Penetrant Examination

MIL-I-25135 — Inspection Materials, Penetrant

QPL-SAE-AMS-2644-3 — Qualified Products List of Products Qualified under SAE Aerospace Material Specification AMS 2644.

2.2. The referenced documents form a history of this specification to the extent specified herein. Unless otherwise indicated, the issue in effect on the date of invitation for bids or request for proposal shall apply.

3.0 Materials Section

3.1. Penetrant Materials

a. Use only materials listed or approved for listing by the Air Force in QPL-SAE-AMS-2644-3 for penetrant inspection.

b. The manufacturer of penetrant materials shall furnish the purchaser with recommended emulsifier dwell times, wet developer concentrations and mixing instructions.

c. The manufacturer shall provide material safety data sheets for each product.

d. The system concept for penetrant materials shall be used for all penetrant inspections.

4.0. Equipment Section

4.1. General — The penetrant equipment shall be constructed and arranged in a manner that will:

a. minimize water, dust and other contamination to the inspection materials and parts,

b. permit uniform, controlled operations and provide safe and adequate ventilation for the process and materials involved and

c. be suitable for the penetrant material in use.

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4.2. Certification and calibration of equipment.

a. All gages, meters and measurement equipment shall be calibrated per ANSI/NCSL Z540-1-1994.

b. Certify temperature and pressure instrumentation for the operating range to be used. Minimum accuracy of temperature gages is ± 2.8°C (± 5°F). Minimum accuracy of pressure gages is ± 35 kPa (± 5 psi).

c. SI units shall be used for measurement of ultraviolet light intensity.

d. Lux (lx) shall be used for measurement of visible light.

4.3. Removal Station.

a. The removal station shall be equipped with a water pressure gage, water temperature gage and spray nozzles that produce a coarse spray that is cone shaped or fan shaped.

b. Maximum water pressure allowed is 276 kPa (40 psi).

c. Water temperature shall be between 10 and 38°C (50 and 100°F).

d. Ultraviolet light intensity at the rinse station shall be 1000 μW/cm2 and a maximum of 100 lx of ambient white light at the parts surface.

4.4. Developer Station.

a. Dry developer stations shall be equipped with a system to inject dry air into the chamber and disperse the particles.

b. Aqueous suspendible developers shall be equipped with a system to keep the developer agitated and maintain the developer materials in suspension.

4.5. Dryer Station

a. Dryers shall be equipped with a temperature control and a monitoring device.

b. Thermostatic controlling devices shall be calibrated per 4.2.

c. Dryer temperatures shall not exceed 72°C (160°F) in the area of the component. Recommended dryer temperature is 49°C (120°F).

4.6. Inspection Station

a. The area shall be kept clean and free of contaminating products and clutter.

b. Ultraviolet lights used in the inspection station shall have a minimum intensity of 1000 μW/cm2 at the working surface of the part being inspected.

c. Ambient light in the inspection station during fluorescent penetrant inspection shall not exceed 20 lx.

d. White light used in the inspection station for interpretation and evaluation of visible penetrant indications shall have a minimum intensity of 1000 lx.

e. Inspection stations should be equipped with ventilation systems.

4.7. Portable Kits

a. Ultraviolet lights used in portable kits shall have a minimum intensity of 1000 μW/cm2 at the working surface of the part being inspected.

b. Portable kits shall maintain the system concept for penetrants and developers.

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5.0. Personnel Qualification Section

5.1. The training, qualification and certification of personnel performing penetrant operations and inspections for acceptance/rejection shall be in accordance with ASNT Recommended Practice No. SNT-TC-1A.

6.0. Process Control Section

6.1. Quality Checks

a. The following tests of penetrant materials used in open tanks shall be made, in accordance with AMS 2644, on a monthly basis:

1) penetrant intensity,

2) sensitivity,

3) water content (Method A only),

4) lipophilic emulsifier water content and

5) hydrophilic remover concentration.

b. Dry developers shall be checked daily for caking and penetrant contamination.

c. Wet developers shall be checked daily for penetrant contamination and wetting ability and weekly for concentration.

d. Ultraviolet light intensities shall be checked at the beginning of each shift and after bulb replacement.

e. Ambient light intensities shall be checked weekly.

f. White light inspection intensities shall be checked at the beginning of each shift and after bulb replacement.

g. System performance checks shall be made daily.

6.2. Process Limitations

a. Do not use form a or b developers with Type II penetrant systems.

b. Do not use Type II penetrants for final acceptance inspection of aerospace components except as specified on engineering drawings.

c. The use of developer is required for all inservice inspections.

d. When inspecting oxygen lines or tanks, penetrant materials should be tested for impact sensitivity before use per ASTM D 2512.

e. Final inspection of components shall not be performed until all operations that could expose or produce surface discontinuities have been performed.

6.3. Sequence of Operations for Penetrant Inspection

a. Penetrant inspection operations shall follow established and approved sequences.

b. Normal inspection sequence shall be:

1) precleaning,

2) penetrant application and dwell,

3) penetrant removal/wash,

4) dry and developer application depending on type developer used,

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5) developer dwell,

6) inspection and

7) postcleaning and protection.

6.4. Precleaning of Components

a. Clean all components to be penetrant tested in accordance with applicable process specifications.

b. Surfaces shall be free of any rust, scale, welding flux, burrs, feather edges, smeared material, spatter, grease, paint, carbon, plating, engine varnish, oily film, dirt and other contaminants that would mask discontinuities or produce nonrelevant indications.

c. Surfaces shall be cleaned by solvent or chemical means. Mechanical cleaning shall only be accomplished by abrasive blasting if the surface of the metal is not peened by the process and surface discontinuities sealed.

d. Etching of components shall only be accomplished per approved engineering data.

e. Components shall be thoroughly rinsed and dried after solvent, chemical or mechanical cleaning.

6.5. Penetrant Selection and Application

a. Unless indicated on engineering drawings, the following penetrants and sensitivities will be used for the components indicated in Table 1.

b. Method B or Method D will be used on aluminum alloys.

c. Temperature of the component, penetrant and ambient air shall be between 10 and 43°C (50 and 110°F) for penetrant application. Components shall not be preheated above the maximum temperature range.

d. Application of penetrant shall be applied by dipping, spraying, brushing, pouring or flowing.

e. Parts shall not remain immersed in penetrant during penetrant dwell time. Parts shall be rotated if necessary to avoid pooling of the penetrant. The penetrant on the surface of the component will not be allowed to dry.

6.6. Penetrant Dwell Time

a. Unless indicated on engineering drawings, the minimum penetrant dwell time shall be 15 min for discontinuities other than intergranular corrosion.

b. Minimum penetrant dwell time for intergranular corrosion shall be 1 h.

6.7. Penetrant Removal

a. General — Keep washing of components to a minimum. Components suspected of being overwashed shall be reprocessed. A small amount of background is acceptable. Type I penetrants shall be removed under ultraviolet light.

b. Method A, Water Washable Penetrant

1) A manual or automatic spray wash may be used.

2) Removal shall be as specified in 6.7f.

c. Method B, Postemulsifier, Lipophilic Penetrant

1) Emulsifier will be applied by dipping, pouring or flowing onto the component. Brushing or spraying shall not be used.

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2) Emulsifier dwell time shall be the minimum time required to render the penetrant water washable. Minimum time will be determined by experimentation on a test component.

Table 1. Penetrant selection

Type Sensitivity

Level Material/Component

I 1 Castings, other than precision.

I 2 All materials not otherwise covered by this table.

I 3 Aluminum alloys.

I 3 Method C for suspected localized damage or rework.

II N/A Ground handling or support equipment and tooling.

3) Maximum dwell time is 3 min for Type I penetrants and 30 s for Type H penetrants.

4) Emulsifier action shall be stopped by water immersion or quick water spray of the entire component.

5) Rinse of the component shall be performed as specified in 6.7f.

d. Method C, Solvent Removal

1) Type I and II penetrants shall be removed by first using a clean, dry, lint free cloth or towel to remove excess penetrant. The remaining background penetrant shall be removed, under appropriate lighting, by wiping with a clean, lint free cloth or towel dampened with solvent. Repeat until all excess penetrant is removed.

2) In no manner will penetrant be removed by spraying or flushing the surface of the component with solvent.

e. Method D, Postemulsifier,

Hydrophilic Penetrant

1) Prerinse the component with a water spray for the time necessary to remove the bulk of the excess penetrant. Water spray shall be in accordance with 6.7f. Maximum prerinse time is 90 s for any one area.

2) Hydrophilic remover may be applied by immersion, flowing or spraying. If a spray rinse is used, do not exceed recommended limits for remover concentration. Spray rinse parameters are in 6.7f.

3) Remover dwell time will be determined by experimenting on test components. The dwell time will be the minimum time necessary to produce an acceptable background. Dwell time will not exceed 2 min.

4) Final rinse will be performed as specified in 6.7f.

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f. Rinsing

1) Removal stations shall conform to 4.3.

2) Hydro air nozzles are permitted only with Type I, level 1 sensitivity penetrants. Maximum air pressure is 172 kPa (25 psi).

3) Rinse spray will be a coarse spray that is cone shaped or fan shaped. Spray nozzles will held about 30 cm (12 in.) from the part.

4) Rinse water contaminants that may leave residue on the component after drying are not acceptable. Filtering of water may be required.

g. Drying

1) Dry stations will conform to 4.5.

2) Components shall be removed from the dryer as soon as the surface is dry.

3) Maximum drying time, for circulating air dryers shall not exceed 30 min. Parts left in dryers for longer than 30 min shall be reprocessed.

4) Maximum drying time for room temperature drying is 1 h.

5) If required, parts will be rotated to avoid pooling of liquid during drying.

6) Components with thin cross sections shall not be mixed with components with thicker sections.

h. Developing

1) Components will be completely dried before application of dry or nonaqueous developer.

2) Developer dwell times will be half of the penetrant dwell time, but not less than 10 min for final inspection. Developer dwell time begins when developer is on the part and dry.

3) Dry developers may be applied by dipping, dusting or fogging. Excess dry developer may be removed by gently tapping component.

4) Aqueous soluble and suspendible developers may be applied by dipping, flowing and spraying. Brushing on is not acceptable. Dry parts immediately after excess developer has drained from the component.

5) Nonaqueous developers are applied by spraying. Containers shall be shaken or agitated sufficiently. Developer will be sprayed onto the component in a manner to produce a light uniform coating.

i. Inspection/Evaluation

1) Inspection of components may begin and it is recommended, as soon as developer is dry. However, final inspection of the component shall not be made until the developer dwell time has elapsed.

2) Inspection of components shall be accomplished in the proper and appropriate lighting conditions as specified in 4.6.

3) Inspectors working in darkened conditions shall allow at least 5 min for dark conditioning to occur before inspection components.

4) Inspect components completely. Magnifiers may be used to interpret or evaluate indications.

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5) Perform interpretation and evaluation of indications to determine if components meet specification requirements per engineering data.

6) Removal of an indication and application of nonaqueous developer is permitted only once.

7) Acceptance and rejection criteria per engineering data will be provided for each component inspected and included in the written procedure.

j. Postcleaning

1) Components will be postcleaned by either water wash or solvent to remove all penetrant materials.

2) Mild scrubbing may be used to remove wet developers.

3) Components will be dried after cleaning and protected as needed.

7.0. Written Procedure Requirement

7.1. Written procedures for components shall be in writing and approved by a Level III certified per 5.1 in penetrant testing.

7.2. Perform penetrant inspections according to a written procedure that meets the requirements of this specification. A general written practice for similar components is acceptable. All written procedures will contain at least the following information:

a. precleaning operations should include the materials and procedures to be used;

b. the type, technique and sensitivity of penetrant materials to be used;

c. detailed procedures on the application and dwell time of penetrants, the removal of the penetrant, drying parameters, developer and application technique, developer dwell time, inspection and evaluation requirements and postcleaning of components;

d. inspection and evaluation criteria will include areas of high interest on each component and acceptable and rejectable criteria based on engineering data. Allowable limits of mechanical evaluation should be included;

e. postcleaning operations should include the materials and procedures to be used; and

f. documentation requirements for each inspection.

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CHAPTER EIGHT REVIEW

_______ 1. For penetrant testing, the process specification establishes: a. a minimum degree requirement. b. an average degree requirement. c. a maximum degree requirement. d. an engineering specific degree requirement.

_______ 2. When are inservice quality test on penetrant materials in open tanks required? a. Quality tests are not required; they are recommended periodically according to

need. b. Whenever a complete changeover of materials is accomplished. c. Whenever requested in writing by the Quality Assurance Auditor. d. At least monthly.

_______ 3. In order to enhance the sensitivity of the process, which of the following may be done before application of the penetrant?

a. The penetrant may be preheated to 66 °C (150 °F). b. The parts may be preheated between 66 and 107 °C (150 and 225 °F). c. A more sensitive penetrant may be mixed with contaminated penetrant. d. Fluorescent penetrant can be charged by exposure to intense ultraviolet light. e. None of the above procedures are permitted.

_______ 4. Which reference document covers the calibration of equipment? a. ANSI/NCSL Z540-1-1994. b. SNT-TC-lA. c. ASTM E 1316. d. QPL-SAE-AMS-2644-3.

_______ 5. Allowable penetrant materials are restricted to those in: a. ANSI/NCSL Z540-1-1994. b. ASTM E 1316. c. ASTM E 1417. d. QPL-SAE-AMS-2644-3.

_______ 6. The minimum accuracy of a temperature gage is: a. ± 5 °F (± 2.8 °C). b. ± 10 T(±5.6 -C). c. ± 15 -F(±18.3 -C). d. Calibration is not required.

_______ 7. Material safety data sheets are provided by the: a. prime contractor. b. subcontractor. c. penetrant manufacturer. d. Federal government.

_______ 8. For small parts, a dryer is required when: a. aqueous wet developer is used. b. nonaqueous developer is used. c. dry developer is used. d. all of the above are used. e. only a and c are used.

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_______ 9. One component requiring penetrant testing is suspected of having stress corrosion cracking. According to the specification, the penetrant dwell time required is:

a. 10 min. b. 30 min. c. 1 h. d. 2 h.

_______ 10. According to the specification, which of the following reference documents is used for qualification of testing personnel?

a. ATA Specification 105. b. SNT-TC-1A. c. MIL-STD-410E. d. ISO 9712.

_______ 11. Your company has entered into a contract to produce components for XYZ Manufacturing. A requirement of the contract is to use this specification for penetrant testing of the components. The date of the contract is January 1, 1996; components were not produced and tested until June 1996. The Specification was originally approved for use in January 1980. It was superseded and revised in May 1985 as the B Revision, again in April 1992 as the C Revision and also in August 1996 as the D Revision. Which revision is in effect for the purpose of your company's contractual requirement?

a. The original January 1980 version. b. Revision B. c. Revision C. d. Revision D. e. Any of the above, according to your preference.

_______ 12. Emulsifier dwell time shall be: a. as recommended by the penetrant material manufacturer. b. as specified in Table 1 of the Specification. c. determined experimentally on each part. d. controlled by use of a stopwatch.

_______ 13. According to the specification, specifying acceptance criteria is the responsibility of:

a. the Level III. b. Quality assurance personnel. c. engineering personnel. d. the Federal government.

_______ 14. According to the specification, Type II penetrant can be used with: a. Form a developer. b. Form b developer. c. Form c developer. d. both a and b above. e. both b and c above.

_______ 15. According to the specification, Type II penetrants can be used for final acceptance inspection of aerospace components.

a. True b. False

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_______ 16. The system concept for penetrant materials is required for: a. water washable penetrants. b. postemulsifier penetrants. c. solvent removed penetrants. d. all penetrants. e. The system concept does not have to be used.

_______ 17. According to the specification, etching of components shall be accomplished:

a. per engineering data. b. according to MIL-STD-6869. c. according to the Level III. d. Etching of parts is not permitted.

_______ 18. The maximum lipophilic emulsifier dwell time for Type I penetrants is: a. 30 s. b. 1 min. c. 2 min. d. 3 min.

These last two questions are not related to the sample specification.

_______ 19. What is a common industrial technique of implementing a penetrant test requirement?

a. Use an established written standard. b. Use a process specification. c. Use a written practice. d. None of the above.

_______ 20. A subcontractor for a manufacturer would normally perform penetrant test to:

a. A process specification. b. An established standard. c. A written practice. d. None of the above.

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REFERENCES

ASNT, NDT Training Program – Liquid Penetrant Method, Columbus, 2nd Edition, 1979.

Badger, Duane, Liquid Penetrant Testing – Classroom Training Book, ASNT, Columbus, 2005.

Eick, Charles W., ASNT Level III Study Guide – Liquid Penetrant Testing Method, ASNT, Columbus, 2nd Edition, 2003.

Smilie, Robert W., Classroom Training Handbook, Nondestructive Testing – Liquid Penetrant, PH Diversified, Inc., South Harrisburg, 1998.

Smilie, Robert W., Programmed Instruction Handbook, Nondestructive Testing – Introduction, PH Diversified, Inc., South Harrisburg, 1995.

Smilie, Robert W., Programmed Instruction Handbook, Nondestructive Testing – Liquid Penetrant, PH Diversified, Inc., South Harrisburg, 1998.