equipment fabrication

8/3/2019 Equipment Fabrication

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I

OISD - 128Amended edition

FOR RESTRICTEDCIRULATION

No.

INSPECTIONOF

UNFIRED PRESSURE VESSELS

OISD - STANDARD-128First Edition, November 1988

Amended edition, August, 1999

OIL INDUSTRY SAFETY DIRECTORATE

Government of India

(Department of Petroleum & Natural Gas)


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OISD STD- 128First Edition, November, 1988Amended edition, August, 1999

FOR RESTRICTEDCIRCULATION

INSPECTIONOF

UNFIRED PRESSURE VESSELS

Prepared by

COMMITTEE ON INSPECTION

OF STATIC EQUIPMENT

OIL INDUSTRY SAFETY DIRECTORATE2

ndFloor, KAILASH BUILDING,

26, KASTURBA GANDHI MARG,NEW DELHI - 110 001.


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III

NOTE

OISD publications are prepared for use in the Oil and gasindustry under Ministry of Petroleum and Natural Gas. These are theproperty of Ministry of Petroleum and Natural Gas and shall not be

reproduced or copied and loaned or exhibited to others without writtenconsent from OISD.

Though every effort has been made to assure the accuracyand reliability of the data contained in these documents, OISD herebyexpressly disclaims any liability or responsibility for loss or damageresulting from their use.

These documents are intended only to supplement and not toreplace the prevailing statutory requirements.

Note 1 in superscript indicates themodification/changes/addition based on theamendments approved in the 17th Safety Councilmeeting held in July, 1999.


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IV

FOREWORD

The Oil Industry in India is nearly 100 years old. Due tovarious collaboration agreements, a variety of international codes,standards and practices have been in vogue. Standardisation indesign philosophies and operating and maintenance practices at anational level was hardly in existence. This, coupled with feed backfrom some serious accidents that occurred in the recent past in Indiaand abroad, emphasized the need for the industry to review theexisting state of art in designing, operating and maintaining oil andgas installations.

With this in view, the Ministry of Petroleum & Natural Gas, in1986, constituted a Safety Council assisted by Oil Industry SafetyDirectorate (OISD), staffed from within the industry, in formulating and

implementing a series of self regulatory measures aimed at removingobsolescence, standardising and upgrading the existing standards toensure safer operations. Accordingly, OISD constituted a number ofFunctional Committees comprising of experts nominated from theindustry to draw up standards and guidelines on various subjects.

The present document on Inspection of Unfired PressureVessels has been prepared by the Functional Committee onInspection of Static Equipment. This document is based on theaccumulated knowledge and experience of industry members and thevarious national and international codes and practices. It isrecognised that failure of internals of a pressure vessel may only affectits performance and at most times may not materially affect the safety

of the vessel. However, it is also recognised that failure of an internalcomponent may load to unit upsets which in turn could lead to a leakof hydrocarbons. Keeping this in view the Committee decided toinclude inspection of internals also as a part of this standard. Thisdocument is meant to be used as a supplement and not as areplacement for existing codes and practices. It is hoped that theprovisions of this document, when adopted may go a long way toimprove the safety and reduce accidents in the Oil and Gas Industry.Users are cautioned that no standard can be a substitute for thejudgment of a responsible qualified inspection Engineer. Suggestionsare invited from the users, after it is put into practice, to improve thedocument further.

This standard in no way supercedes the statutory regulationsof CCE, Factory Inspectorate or any other Govt. body which must befollowed as applicable.

Suggestions for amendments to this document should beaddressed to

The Co-ordinator,Committee on

Inspection of Static Equipment,Oil Industry Safety Directorate,

2ND

Floor, Kailash

26, KasturbaGandhi Road,New Delhi 110 001


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V

COMMITTEE

ON

INSPECTION OF STATIC EQUIPMENT

List of Members---------------------------------------------------------------------------------------------------------------------------------------

Name Designation & Position inOrganisation Committee

---------------------------------------------------------------------------------------------------------------------------------------

1. Sh. R.K. Sabharwal CMNM-IOC (R & P) Leader

2. Sh.A.S. Soni DGM (P)-ONGC Member

3. Sh.R.H. Vohra DGM-IOC (Mkt.) Member

4. Sh.D.P. Dhall CH INSP & AE MGR-BPC (REF) Member

5. Sh.P. Dasgupta SIPM-IOC ( R & P) Member

6. Sh.I.M. Advani MGR INSP-(PROJ) HPC (REF) Member

7. Sh.R.M.N. Marar Jt.Director OISD Member Co-ordinator.

---------------------------------------------------------------------------------------------------------------------------------------

In addition to the above, several other experts from industry contributed in the preparation, review and

finalisation of this document.


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VI

INSPECTION OF UNFIRED PRESSURE VESSELS

CONTENTS

SECTION PAGENO.

1.0 Introduction

2.0 Scope

3.0 Definition and Types of Pressure Vessels3.1 Pressure Vessel3.2 Types of Pressure Vessels

4.0 Role of Inspection

5.0 Inspection Tools

6.0 Inspection of New Pressure Vessels During Fabrication

7.0 Check List for Inspection of Pressure Vessels Prior to Erection andCommissioning.

8.0 Likely Locations of Metal Wastage8.1 Main Fractionating Towers of Crude Distillation Unit8.2 Crude Distillation Unit-Overhead Accumulators8.3 Dehydration, LP./HP. Separators8.4 Vacuum Distillation Columns8.5 Reactors in Reformers

8.6 Reactors in FCCU8.7 Regenerator in FCCU8.8 Orifice Chamber in FCCU8.9 Coke Chambers8.10 Bullets and Spheres8.11 Vessels in Low Temperature Service8.12 Ammonia Storage Vessels8.13 Columns & Vessels in Diethyl Amine & Monoethyl Amine Service

9.0 Frequency of Inspection

10.0 Inspection Procedures10.1 Inspection of Columns

10.1.1 External Inspection10.1.2 Internal Inspection10.1.3 Inspection of Lined Columns10.1.4 Inspection of Pressure Vessels in FCCU10.2 Inspection of Vessels10.2.1 External Inspection10.2.2 Internal Inspection10.2.3 Riveted Vessels10.3 Corrosion Coupons/Probes10.4 Safety Relief Devices

11.0 Retiring Thickness


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12.0 Inspection During Maintenance12.1 Weld Build Up12.2 Nozzles Replacement

12.3 Partial Replacement of Shell Plates and Domes12.3.1 Hydrostatic Test12.3.2 Pneumatic Testing12.4 Repair of Cladding and Striplining12.5 Repair of Painted and Rubberlined Areas13.0 Documentation

14.0 References

ANNEXURES

I Inspection Check List for Column in ServiceII Inspection of Welding

III Hydrogen Blisters-Inspection, Evaluation andRepair of Pressure Vessels


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INSPECTION OF UNFIRED PRESSURE VESSELS

1.O INTRODUCTION

The contents of a pressure vessel arealways under pressure. Any deterioration of thevessel could lead to a large release ofhydrocarbon vapour and consequent creationof a flammable atmosphere. Timely inspectionand Preventive Maintenance will go a long wayin ensuring safe operation of pressure vessels.

2.0 SCOPE

This standard covers the minimuminspection to be carried out during operationand maintenance of pressure vessels. Thestandard specifies frequency of inspection,inspection procedures, areas to be inspected inthe pressure vessels and inspection during andafter repairs. This standard also covers in brief,fabrication and pre-commissioning inspectionchecks.

3.0 DEFINITION AND TYPES OFPRESSURE VESSELS

3.1 PRESSURE VESSEL

A pressure vessel is defined as avessel designed to safely withstand an internalpressure in excess of 1.05 Kg/Sq.cm. Somevessels in a refinery may be subjected toexternal pressure caused by an internalvacuum or by a fluid pressure between anouter jacket and the vessel wall. Such vesselsare usually inspected in the same manner asvessels with internal pressure.

3.2 TYPES OF PRESSURE VESSELS

The following four types of pressurevessels are normally used in hydrocarbonservice:

i) Cylindrical vessels with flat, conical,toriconical, torispherical, semiellipsodial orhemispherical heads.

ii) Spheroids.iii) Spherical.iv) Jacketted Vessels

Cyllindrical vessels can be vertical orhorizontal and may be supported in differentways.

4.0 ROLE OF INSPECTION

The following are the activities of the inspectiondivision:

i) To inspect, measure and record thedeterioration of materials and to evaluatepresent physical condition of the pressurevessel for its soundness to continue inservice.

ii) To corelate the deterioration rate with

design life for further run.iii) To determine causes of deterioration and

to advise remedial measures.iv) To recommend/forecast short-term and

long-term repairs and replacements toensure further run length on the basis ofeconomics and safety.

v) To advise regarding equipment/componentreplacement so that procurement actioncould be initiated.

vi) To inspect while doing the repairs and toaccept after completion of repairs.

vii) To maintain uptodate maintenance &

inspection records and history of pressurevessels.

viii) To keep the concerned operating andmaintenance personnel fully informed as tothe condition of the various pressurevessels.

ix) To advise regarding schedules of pressurevessels inspection and also statutoryrequirement schedules.

5.0 INSPECTION TOOLS

Tools required for Pressure Vessels Inspectionare as follows:

i) Ultrasonic Thickness Gauge.ii) Ultrasonic Flaw Detector.iii) Radiography Equipment.iv) Magnetic Particle Testing Kit. (Wet

Fluorescent Type)v) Metallographic Equipment.

vi) Infra-red Scanner for Thermography.

vii) Dye Penetrant Kit.viii) Paint Thickness Gauge.


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ix) Shore Hardness Meter.x) Adhesion Testing Kit.xi) Holiday Detector.xii) Spark Tester.xiii) Pit Depth Gauge.xiv) ID & OD Gauges.

xv) Plumb & Bob.xvi) Magnet.xvii) Measuring Tape.xviii)Magnifying Glass.xix) Temp. Indicating Crayons.xx) Inspectors Hammer.xxi) Straight Edge.xxii) Safety Torch.

6.0 INSPECTION OF NEWPRESSURE VESSELS DURINGFABRICATION

Pressure vessels are designed as pervarious codes available like IS, BS, ASME etc.The design and consequently, inspection ofpressure vessels shall be as per any one codeonly and not by a combination of differentcodes since factor of safety used while arrivingat design stresses for different materials varywith codes. Inspection of the new pressurevessel at the time of fabrication is done as perthe inspection requirements of relevant code.

Inspection shall be carried out in the following

stages:

i) Study of the tender document and all thetechnical specifications.

ii) Identification and inspection of thematerials.

iii) Check bonding of cladded plates, whereverapplicable before and after forming.

iv) Approve the welding procedures inaccordance with tender specifications/code requirements.

v) Carry out welders performancequalification test as per the code.

vi) Check nozzle orientation, joints fitup andoverall dimensions as per the approveddrawings.

vii) Ensure that welding is carried out as peragreed welding sequence and weldingprocedure with approved electrodes andtested welders.

viii) Inspect the weld joints for proper qualityduring welding.

ix) Ensure proper post weld heat treatmentwhenever required.

x) Inspect weld joints by radiography as perthe code.

xi) Ensure proper heat treatment is carriedout for cold formed parts (like dishends,

tori cones etc.) as per relevant codes /

drawings.NOTE 1

xii) Ensure all internal attachments are welded

as per drawing.NOTE 1

xiii) Witness pneumatic tests of the liner welds

(lined nozzles) and reinforcement pads.NOTE 1

xiv) Inspect for ferrous contamination ofcorrosion overlay welding/flange facings

etc., as per code.NOTE 1

xv) Ensure proper welding of insulation bearing

nuts wherever applicable.NOTE 1

xvi) Ensure proper welding of refractory bearing

lugs/hexes etc. wherever applicable.NOTE 1

xvii) Ensure repairs and reinspection of

damaged parts, if any, are carried outbefore giving clearance for hydrostatictesting.

xviii)Check the procedure for various types oftesting.xix) Ensure all the tests are carried out strictly

as per the approved procedures.xx) Inspect quality of painting as specified in

the tender document.xxi) Check that vessel has been stamped as

per code.xxii) Prepare and certify the relevant

documents.

7.0 CHECK LIST FORINSPECTION OF PRESSUREVESSELS PRIOR TOERECTION ANDCOMMISSIONING.

The check list format shall contain the followinginformation.

Equipment No.PlantDutyPurchase Order No. & DateSerial No. & Type

ManufacturerMain DimensionsMaterial of ConstructionMax. Allow. working pressure/VacuumMax. Allow. Working TemperatureStress-relievedRadiographyHydrostatic Test PressureErection ContractorContractors InspectorCompanys InspectorDate of Inspection

CHECKLIST


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The following checks shall be madeprior to commissioning of new pressurevessels.

CHECKS REMARKS1. Check for proper

alignment of supports.2. Check nameplate

attachment.3. Check nameplate rating.4. Check foundation bolts

and shims.

CHECKS REMARKS

5. Inspect shell wall for outof roundness, bulges anddents.

6. Inspect visually, weldjoints.

7. Check alterations madeduring plant construction.

8. Check wall thickness ofshell and nozzles.

9. Check and testreinforcement plates andtest holes.

10. Check and test nozzles,facings, gaskets andbolts.

11. Check outside bolting and

stiffening rings.12. Check insulation and fire

proofing.13. Check insulation

protection.14. Check painting quality.15. Check internals.16. Check and test internal

lining of shell nozzles.17. Check for internal

cleanliness before finalboxing up.

18. Check whether design of

vessel and foundationallows vessel to behydrotested in situ.

19. Test shell hydrostatically,if any alteration has beenmade in the shell.

20. Check whether properrelief valve is installed.

21. Check that connectedpipings do not strain thevessel nozzles.

22. Check for verticality ofcolumns and tall vessels.

Note 1

8.0 LIKELY LOCATIONS OFMETAL WASTAGE

8.1 MAIN FRACTIONATING TOWERS OFCRUDE DISTILLATION UNIT

The fractionating column bottom andinternals are subjected to high temperaturecorrosion due to presence of sulphur whereascolumn top is prone to low temperature acidiccorrosion because of salts and H2S present inthe crude. The crude containing naphthenicacid also causes the corrosion of the columnshell, and the same is pronounced in thesections where temperature ranges from 200

oC

to 400oC. Severity of naphthenic acid attack is

higher where the turbulent conditions exist.The impingement plate particularly in the

columns where the feed nozzle is radial issubjected to severe erosion. Noticeablecorrosion or erosion is also generally observedwhere the steam impinges the shell. Thedislodging of the trays (particularly valve trays)is common due to steam surge.

Galvanic corrosion is also observed atthe location where cladded shells anduncladded shells join together. Where thelining is bulged, the parent metal is subjected tocorrosion. Liquid level corrosion is noticeablein the top tray downcomer collectors

particularly at the reflux collector trays.

8.2 CRUDE DISTILLATION UNIT-OVERHEAD ACCUMULATORS

Pronounced corrosion is generallynoticed at the interface level of water andhydrocarbons. Mostly the corrosion is noticedin the bottom portion of the accumulators,which are not internally protected.

8.3 DEHYDRATOR, LP/HP SEPARATORS

Dehydrators & LP/HP separators ofcrude stabilising units are likely to get corrodedin the bottom portion from 5 to 7 O clockposition due to presence of salt & water.

8.4 VACUUM DISTILLATION COLUMNS

The sections where the turbulentconditions exist like impingement plate/flashzone are subjected to corrosion erosion due tonaphthenic acid and sulphur in the crude.Columns, shells are also liable to corrodeopposite to impingement plate due to rebound

of fluid. Weldments and Heat Affected Zoneare also susceptible to corrosion.


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8.5 REACTORS IN REFORMERS

Generally the reactors are of low alloysteels like 2-1/4Cr-1 Mo or cladded withstainless steel. Due to this superior metallurgy

metal wastage is generally not observed.However, the following locations give indicationof deterioration/cracking.

i) Cracking of weldment of grid with shell atthe bottom..

ii) Baskets for collecting the catalyst dust arealso prone to corrosion.

iii) Liners installed in the big diameter nozzlesare susceptible to bulging due to failure ofweld joints at the end.

iv) Reactors made of low allow steel specially2-1/4Cr-1 Mo are prone to temper

embrittlement. (Temper embrittlement isdefined as a loss of ductility and notchtoughness due to post weld heat treatmentor high temperature service above 370

0C.)

8.6 REACTORS IN FCCU

The shell, riser O.D. and portion of thecyclone dipleg O.D. are severely attacked inthe riser extension type of installation. Wherethe grids are still used, erosion is found fairlyuniform over most of the grid when highvelocities are employed through cyclones.

Some erosion occurs to the wall of the plenumchambers and to the top head where smallplenums are in use. For those reactors withonly two cyclones, high swirl of catalyst throughthe nozzles cause severe erosion.

The refractory lining generally standsup quite well in reactor cyclones. Normalrepairs require some resurfacing of small areasor replacement of small localised sections.There are two kinds of valves at the bottom ofdipleg. The one mostly in use is the flappertype with counter weight. The other is the

trickle valve type, with the flapper plate hangingover the opening suspended by rings. Theflapper type of valves are subjected to erosion.

8.7 REGENERATOR IN FCCU

In the plate type of distribution grid,erosion to the grid plates is a commonphenomenon. Due to considerable vibrationand heat differentials cracking of the grid platecan also take place.

In pipe type of grid design where sealsare still in use, these seals may leak. Migration

of catalyst past the seal could destroy a pipegrid in a very short time.

The branches (pipe coming off eachlateral) experience metal loss, mainly to the topcircumference. Occasionally the steam coming

out of jet blowing directly into another branch,lateral or end plate creates erosion. Warpageof pipe grids can take place due to overheatingduring startup and during operation. Many 5%Cr. grids experience weld cracking.

The failure of refractory lining on theshell is another common problem. Duringoperation, it may cause hot spots on the shell.Erosion of cyclone dip legs, failure of cyclonewelds alongwith weld of cyclone supports mayalso take place.

8.8 ORIFICE CHAMBER IN FCCU

Erosion of the double disc sliding valvegates, erosion at the core near the inlet and atholes/sleeves in the grid plate are commonproblems. Bulging or cracking on the shelladjacent to the gridplate also may take place.The erosion problems in orifice chamber arecaused by the catalyst carryover from theRegenerator.

8.9 CHOKE CHAMBERS

Cracking of skirt and shell weld joints isquite common particularly in the cokechambers where the skirt is not of slotted type.In the coke chambers generally feed, strippingsteam and water quench nozzles are installedat the bottom. Due to thermal cyclic shockslower portion of the coke chamber gets bulged.At the advanced stages of bulging,circumferential welds which act as stiffenersget cracked in the axial direction. However, theeffect is pronounced just opposite the feedentry nozzle at an elevation of about 1 meter.The chambers where the feed enters from the

top, bulging is confined in the top portion. Theconical portion of the coke chamber where thefeed enters is also prone to cracking at theknuckle portion. Bottom flange to shell weld joint, weld joints of feed, water quench andsteam nozzles are also likely to crack underthermal cyclic conditions.

8.10 BULLETS AND SPHERE

The corrosion and scaling is generallyconfined to the bottom between 5 to 7 O clockpositions probably due to the presence ofcorrodents like H2S and water. LPG storagevessels are also prone to stress corrosion


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cracking. The circumferential weld joints belowthe equitorial plates in the LPG Horton spheresare more prone on such cracking.

8.11 VESSELS IN LOW TEMPERATURESERVICE

Vessels in low temperature service e.g.in KTU of refineries and propane circuit of LPGrecovery units of Gas Processing Plants areprone to external corrosion due to faultyinsulation, which causes condensation of thevessels. The severity of corrosion increases incase of corrosive atmosphere as in KTU.

In these vessels internal corrosion dueto moist So2 where condensation can takeplace, also occurs. Internals and shell areaffected due to this.

8.12 AMMONIA STORAGE VESSELS

Generally the storage vessels arefabricated from Carbon steel and Nickel steels.For the operating conditions prevailing atrefineries, material of construction used forAmmonia storage vessels in the refineries arecarbon steels. The weld joints of C.S. vesselsare prone to stress corrosion crackingparticularly in the vessels, which have not beenstress relieved initially or after fabricationrepairs.

8.13 COLUMNS & VESSELS IN DIETHYLAMINE OR MONOETHYL AMINESERVICE

The weld joints and heat affected zoneof the columns and vessels in DEA and MEAservice which have not been stress relieved arealso prone to cracking due to presence of H2Sor H2S and H2.

Further details about corrosion inpressure vessels are available in corrosion

Manual-OISD Publication No. 136.

9.0 FREQUENCY OF INSPECTION

i) All new vessels, regardless of service shallbe inspected within first 2 years ofoperation. Thereafter, the periods of futureinspection shall be scheduled on the basisof established corrosion rates, the type ofservice, remaining corrosion allowance andthe life expectancy.

ii) The frequency of inspection shall bedetermined based on history,corrosiveness of the fluid handled and

operating conditions. The periods betweeninspection shall be planned so thatminimum corrosion allowance remains forthe next run. In any case inspectionfrequencies as per statutory requirementsshall be strictly adhered to.

Internal inspection of all the columns,and vessels installed in battery area shouldbe done during scheduled turnarounds,unless inspection observations andcorrosion rates dictate otherwise. Otherpressure vessels installed in offsite shall beinternally inspected at the time when theseare due for hydrostatic test as per statutoryrequirements.

iii) The internal inspection of reactors isgenerally programmed when the catalyst is

dumped or topped up. However, it isrecommended that in-situ metallography becarried out once in 5 years or at the time ofreplacement of catalyst. The reactors shallbe inspected externally in every turnaroundand the internal, inspection shall be carriedout within 10 years.

10.0 INSPECTION PROCEDURES

Prior to initiating the inspection ofpressure vessels, the inspector should

familiarise himself with the complete previoushistory of the vessel, design parameters,service, original thickness, corrosion allowance,corrosion rate and vulnerable locations ofcorrosion.

10.1 INSPECTION OF COLUMNS

10.1.1 External Inspection

Most of the external inspection can bedone while the column is in operation. Thefollowing shall be checked during the external

inspection.

I) FOUNDATION AND SUPPORTS

a) Foundations

Foundations for pressure vessels aremostly constructed of steel reinforced concreteor of fireproofed structural steel. These shallbe checked for spalling cracking andsettlement. Settlement shall be checked till it

gets stabilisedNote 1

. If due to cracks, big gapshave been formed, steel should be checked for

external corrosion by removing the concrete atcracked locations.


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b) Skirts

Skirts shall be inspected for corrosion,distortion and cracking from outside as well asfrom inside. The weather proofing on the

extremities and fire proofing of structuralsupports shall be checked for water tightness.

The inside of the skirt is oftensubjected to corrosion. This is particularly truefor vessels operating under cryogenicconditions. Thickness measurements shallalso be done to assess the extent ofdeterioration. The condition of fire proofing onsupport beams and skirts shall be inspected forbulging and cracks. Very light taps with ahammer will indicate lack of bond between fireproofing and steel. Appearance of rust stains

on the surface of fire proofing is an indication ofmoisture ingress and presence of corrosion onthe metal underneath. If there is reason tosuspect that water or moisture has seepedthrough to the steel, pockets of insulationshould be removed to determine the extent ofcorrosion. however, inspection of the skirt afterremoval of fireproofing insulation shall be doneat an interval not greater than 5 years. Skirt toshell weld joint shall be checked for cracking.

c) Support of Horizontal Vessels

Horizontal vessels resting on concretesaddle supports where water can accumulateand cause external corrosion shall also beinspected. Horizontal vessels operating at hightemperatures shall be checked to ensure freethermal expansion.

ii) FOUNDATION/ANCHOR BOLTS

Foundation bolts shall be inspected forcorrosion and damage. The nuts on anchorbolts may be inspected to see that these areproperly tightened.

iii) LADDERS, STAIRWAYS,PLATFORMS AND STRUCTURALS

These shall be inspected visually forcorrosion, cracks, paint failure etc. Visualinspection shall be supplemented by hammertesting. Corrosion is most likely to occur atpoints where moisture can accumulate.Crevice corrosion may exist around the headsand nuts of bolts. Ladders shall be examinedfor free movement to take up expansion of thevessels.

iv) INSULATION AND PROTECTIVECOATINGS

Visual examination of insulation willreveal its condition. Insulation shielding shallalso be checked for quality and thickness. At

few locations samples may be removed todetermine condition of the insulation and of themetal underneath. Paint or protective coatingshall be examined for peeling or rusting .Insulation shielding should be intact. If at anytime insulation shielding/cladding is blown off ordamaged the same shall be put backimmediately after repairs to avoid corrosion.The insulation retaining rings shall be checkedto see that moisture is not trapped between therings and weldment. The pressure vesselsoperating at high temperature are insulatedfrom outside and the skirt is insulated from

outside as well as inside to reduce the thermalgradient between skirt and shell weld joint. Anydamage to this insulation is likely to cause thecracking of this joint. Hence the insulation shallbe inspected to ensure that the same is intact.

v) GROUND CONNECTIONS

Grounding connections shall bevisually examined to see that good electricalcontact is maintained. The cable shall beexamined for broken strands. Its resistanceshall be checked at intervals as outlined in

OISD standard-137 (Inspection of ElectricalEquipment).

vi) NOZZLES AND SMALLCONNECTIONS

The nozzles on a pressure vessel shallbe visually inspected and thickness surveyed.When vessel is out of service, carbon steelnozzles may be hammer tested. Smalldiameter nozzles (less than 50mm) are difficultto be thickness surveyed ultrasonically. Thethickness may be determined by taking

radiographs wherever possible. The tell-talehole in the reinforcement pad shall be checkedfor possible leaks.

Special attention should be given tonipples used for pressure and temperaturegauges etc. These nipples shall be checkedthoroughly in every shutdown. Test nipples ofthe lined nozzles shall be checked for anyleakage. Any leakage will indicate damage ofthe lining. If leakage is observed, pressuretesting through tell-tale hole and test-nipplesshall be done during internal inspection tolocate the leaks. Care shall be taken to keepthe plugs on the tell-tale holes loose.


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vii) EXTERNAL INSPECTION OF METALSURFACE

a) Visual Inspection

The external surface of the pressurevessel shall be inspected visually. The externalsurface may show signs of deterioration due toatmospheric corrosion, caustic embrittlement,hydrogen blistering, thermal fatigue andmechanical damage. If caustic is stored orused in a vessel it shall be checked for causticembrittlement. The areas around the nozzlesand in or adjacent to weld seams aresusceptible to this type of corrosion.

External corrosion takes place in humid

areas and in areas where corrosive chemicalvapours are present. External corrosion can bedetermined by visual inspection. Hydrogenblistering is more often found on the insiderather than outside but may be found at eitherplace depending upon the location of the voidwhich causes the condition. Blisters are foundmost easily by visual examination. The shellshould be checked for buckles and bulges.These can be found and measured by placinga straight edge against the shell.

b) Weld Joints

The weld joints and heat affectedzones (HAZ) shall be checked visually forcracks. In case of doubt it should be checkedby dye penetrant test.

c) Hot Spots on Lined Vessels

Hot spots, which might have developedon the outer surface due to the failure ofinternal linings of lined vessels, shall bechecked during operation. The areas, whichhave developed hot spots during service, shallalso be checked for mechanical damage suchas gouges and dents, leaks, cracks andoxidation of any external stiffeners.

d) Ultrasonic Inspection

Thickness measurement of the shelland domes may be taken from outside. Exactlocation of thickness measurement may bedecided after internal inspection only.

e) Vessels in High TemperatureService

Pressure vessel which operates onthermal cycle like coke chamber and at hightemperature like orifice chamber in FCCU shallbe thoroughly inspected from outside. In caseof coke chamber if the entry of feed is at thebottom, insulation of at least 2 to 3 courses all

around shall be removed. The skirt to shellweld joints shall be thoroughly checked forcracks. The bottom flange welding with theshell shall also be inspected. The weld joints,HAZ and shell of 2 to 3 courses shall bechecked for cracks and apparent bulging etc.Presence of suspected cracks should beconfirmed by using Dye Penetrant Kit. Weldingof the nozzles shall also be checked forcracking.

f) LPG vessels

LPG Bullets and spheres having fireproofing on the outside surface shall beexamined for cracks, spalling, bulging anddeterioration of fire proofing. Appearance ofrust stains on the surface of fire proofing is anindication of presence of corrosion of metalunderneath. If above indications are apparentthe fire proofing in suspected areas shall beremoved and the external surface shall beinspected for any corrosion.

10.1.2 Internal Inspection

Pressure vessels entry shall be madeonly with an applicable work permit as detailedin OISD-STD-105 on work permit systems.The area of the column to be inspectedinternally shall be decided based on the pasthistory of the equipment. Available past historyshall supplement the standard inspectionprocedure of the equipment. The inspection ofa column is divided into the top, feed andbottom zones. If installed equipment is beinginspected for the first time, then all traymanways shall be opened and the completeinspection shall be carried out. Internal

inspection can be divided into two parts.

i) PRELIMINARY INSPECTION

Prior to scheduled shutdown of the unitthe pressure vessel shall be examined from theoutside to detect any unusual condition duringoperation, such as leaks in nozzle weldsthrough tell-tale holes or gaskets, the conditionof the bolts and flanges, the apparent conditionof insulation and any other visible defects.During shutdown, before cleaning the columnfrom inside, preliminary internal inspection shallbe done. Observations regarding internaldislodging etc. shall be noted. Samples of


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deposits shall be collected for analysis.Preliminary inspection will also reveal the areashaving deposits, scales etc. requiring thoroughcleaning to detect metal wastage underneaththe deposits during detailed inspection. Afterthe preliminary inspection, clearance for

internal cleaning may be given.

ii) DETAILED INSPECTION

a) Top Zone

Top dome, shell and internals in thetop zone shall be visually inspected. Inspectionshall be done to locate corrosion, erosion,hydrogen, blistering, cracking, laminations or

mechanical damage. Special attention shall begiven to weld joints and surface conditions. Ifpits are noticed, depth of pits should bemeasured with depth gauge or pit gauge. Shellplates below the refux nozzle shall beinspected for any possible grooving. Refluxcollector shall be checked for thinning. Spoutsand counter spouts shall be checked byhammer testing for finding any possibledeterioration. The trays and valves shall bechecked for pitting and cracking. Thickness ofdome and shell near the shell and domewelding shall be taken in all four directions

(E,W,N and S). Thickness of the dome aroundthe nozzles shall be taken. Sample thicknessof column internals like downcomer,downcomer collectors and support platesshould be taken. Besides this, if at certainlocations of shell or dome, corrosion isobserved thickness shall be measured at theselocations to know the exact loss. Shell at thedowncomer collector level shall be checked forany possible liquid level corrosion in the form ofgrooving. Reference points should be markedon shell, dome and nozzles and same shouldbe monitored for thickness during every

inspection to determine rate of metal wastage.

b) Feed Zone

While inspecting the feed zone (flashzone), the impingement plate shall be checkedfor any corrosion, erosion and properattachment with shell. Shell plates shall beinspected near the impingement plate wherethere is a possibility of fluid impingement. Theinternals shall also be inspected. Thickness ofthe shell plates in four direction and theimpingement plate shall be taken. Samplethickness should also be taken on internals.

c) Bottom Zone

In the bottom zone, bottom dome andshell shall be inspected. Special care is to betaken at the area near the bottom drawoff. Ifpittings are observed, pit depth should be

measured. At steam injection points, the shellplate opposite to steam nozzles shall bethoroughly inspected for possible impingement.All the internal pipings etc. shall be inspected.Thickness and hammer testing whereverpossible should be carried out. All the nozzlesincluding the manhole nozzles and retractablespool piece shall be thickness surveyed. Incase of insulated column, insulation aroundnozzles should be broken to facilitate thicknesssurvey. Wherever, it is not possible toapproach the nozzle, ID measurements frominside shall be taken to determine thickness.

d) Columns in Hydrogen Service

Column in hydrogen service shall bethoroughly inspected for possible hydrogenblistering. Hydrogen blisters shall be inspectedand evaluated as outlined in Annexure III.

In catalytic Reactors andRegenerators, the supporting bars for internalequipment such as cyclones shall be closelyexamined for this type of attack. In these, thecatalyst and air distribution facilities are

particularly susceptible to erosion and shall beclosely examined for this type of attack.Welding of the grid supporting rings shall alsobe checked for cracking and damage. Out ofroundness or bulging may be evaluated bymeasuring the inside diameter of the vessel atthe cross section of maximum deformation andcomparing it with the original inside diameter.If the bulging is at intervals, the measurementcan be done by dropping a plumb line andtaking the measurements at selected intervals.This will also reveal the contour of the shell.

10.1.3 Inspection of Lined Columns

Austenitic stainless steel columns andcolumns lined with austentic SS plates shall bepassivated as per the procedure given NACERP-01-70 before opening them in order toprotect them against stress corrosion cracking.

i) STRIPLINED COLUMN

Procedure for inspection of striplinedcolumn is similar to the unlined column asexplained above with certain critical locationsas outlined below needing special attention.Strips shall be visually inspected. Special


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attentions shall be given to the weld joints andHAZ of welds, where cracking can take place.If cracks are suspected, dye penetrant testshould be carried out. The strips shall also beinspected for bulging. The striplining should bechecked by air and soap solution. The

pneumatic pressure should be around 0.2kg/sq. cm. but in no case should it exceed 0.2kg/sq. cm. The area where the striplining endsshall be checked carefully as corrosion maytake place due to galvanic action of stripliningand Carbon steel shell. Thickness on the CSportion shall be measured. Nozzle liner shouldbe tested by pressurising the area between theliner and nozzle by air through test nipple. Thepressure shall not exceed 0.5 kg/sq. cm. Aftertesting, the test nipple shall be kept open andcapped only when the plant/equipment iscommissioned. Otherwise bulging of the liner

may take place. Thickness of the strips shallbe measured at places to ascertain whetherstrips have been subjected to any corrosion.Thickness survey of the column shall be donefrom outside to check the parent materialthickness.

ii) CLADDED COLUMNS

Cladding shall be visually checked forany deterioration like corrosion/erosion, pitting,bulging etc. Thickness at designated locationsshall be measured to check the bonding of the

cladding metal with parent metal. The portionwhere the cladding ends, shall be checked forcorrosion which may take place due to galvanicaction. The weld joints and HAZ shall bechecked for cracks. Nozzle liners should bechecked in a similar way as explained in para(i) above.

iii) INSPECTION OF INTERNALLYPAINTED AREA

The temperature limitations of thepainting systems used inside the vessel should

be known. While shutting down a unit, waterflushing shall be resorted to instead of steamflushing. If steam flushing is necessary, careshould be taken that flushing steamtemperature should not go beyond 100

oC or as

recommended by the paint manufacturer. Thepainted surface shall be cleaned by waterwashing and then mopping with cotton or jute.Cleaning with wire brush shall not be resortedto. Man entry shall be by wearing soft-shoes orbare foot. Painting shall be visually inspectedand thickness should be measured with paintthickness gauge and the same shall becompared with original DFT of painting system.The paint should be checked for holidays

FRE/FRP linings shall be visually checked formechanical damage and cracks. Thickness ofthe pressure vessel shall be measured fromoutside (Inspection checklist for column isgiven in Annexure-I)

10.1.4 INSPECTION OF PRESSUREVESSELS IN FCCU

i) REACTORS

Shell of the Reactor shall be visuallyinspected and thickness surveyed.Thermowells shall be inspected for oxidation,cracking or distortion. Linings for the primary

cyclone shall be visually inspected at locationslike inlet horns, barrel and helix cones etc.Dipleg shall be inspected for perforations bylowering a light through the cyclones. Lining ofthe secondary cyclones shall be visuallyinspected at the locations like barrel, cone etc.Dipleg should be inspected forperforation/plugging by lowering a light throughthe cyclones after cutting a window in seal port.Aeration points in the secondary dipleg shall behammer tested. Grid holes shall be inspectedfor erosion and plugging. Condition of deflectorplate lining, grid cone lining and riser pipe shall

be checked.

In the stripping section, stripper shelland steam nozzle shall be inspected forerosion. Thickness measurements of strippershell shall be done. Condition of the lining inthe fixed and removable sections in feed riserpipe shall be checked. Inverted V-type bellowsat the expansion joint shall be inspected forperforation. Inspection of steam and catalystfeed injections piping and nozzles shall becarried out.

In the plenum chamber, shell shall beinspected for erosion and thicknessmeasurements shall be taken. Safety valveinlet nozzles and vapour outlet line shall beinspected for thinning and plugging.

In the anticoking chamber, peripheralholes shall be checked for plugging. Cyclonesupports should be hammer tested. Shell andweld joints between shell and bottom plateshall be inspected. Thickness measurementsof the shell should be made.

The internal lining of riser pipe shall beinspected with the help of a cage lowered from


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the reactor. The bud bayonet shall be removedand the condition of Y section shall be criticallyexamined for erosion and cracking. Whenever,dissimilar weld joints exist in the riser pipe,these should be checked for cracks. TheReaction and Regeneration stand pipes shall

be examined for failure of internal lining andmetal deterioration. The convolutions ofexpansion bellows shall be checked fordeposits. The slide valves shall be examinedfor erosion and proper operation.

ii) REGENERATOR

The shell lining shall be checked fordeterioration. Particular attention should begiven just near manway and in areas behindthe grid seal. Aeration connections,thermowells and trickle valves shall be

inspected.

Lining for primary cyclones shall bechecked. Special care should be taken in theareas at inlet horn, barrel, helix and cones.Diplegs shall be inspected for perforations.Hangers and supports, spray shields andsupport lugs for cyclones shall be inspected. Inthe secondary cyclones, barrel, cones anddipleg shall be inspected. Lining of the plenumchamber and stack above the plenum chambershall be inspected. Emergency steam spraysshall be inspected for oxidation. If the plenum

chamber is of SS material, the bimetal weld joint between chamber and shell shall beexamined from inside.

Grid plates shall be checked for bulgesand thickness. Grid seal shall be inspected forcracks or perforations. Overflow well and sealboxes shall be checked for erosion andperforations. Lining of the cone below gridshall be inspected. Auxiliary burner tips, airdoor and the pilot shall be inspected visually.Inspection of aux-burner dome and the lining ofthe dome on the inside shall be carried out.

Lugs and supports for the auxiliary burnerdome shall also be inspected.

iii) ORIFICE CHAMBER

The orifice chamber shell shall beinspected for erosion. The areas just after theDouble Disc Slide Valve (DDSV) shall beinspected critically. The holes/sleeves on thegrid plate shall also be examined for increaseddiameter due to erosion. The shell adjacent togrid plate should be examined for anydeformation, cracks or deterioration afterremoving the insulation at random from

outside. The discs of DDSV shall be examinedfor erosion and proper operation.

10.2 INSPECTION OF VESSELS

10.2.1 External Inspection

External inspection of the vessel iscarried out in a manner similar to the externalinspection of column. Various steps detailed inthe previous chapters shall be followed. Inaddition to above, attention should be given tometal surface in contact with concrete saddles.Vessels which are partially or completelyunderground are subject to soil corrosionwhere they are in contact with ground.Therefore, inspection of the external surfaceshould be done, after cleaning of the surface.

10.2.2 Internal Inspection

Normally there are no trays inside thevessels. Inspection of the vessel is donesimilar to internal inspection of the column.Care should be taken to inspect the liquid levelcorrosion. Nozzle weldings, internal stiffnersand area around them shall be checkedthoroughly from inside.

Pressure vessels which can not beinternally inspected due to mechanicalrestrictions shall be inspected using ultrasonic

equipments. In addition they shall be pressuretested as per statutory requirements.

All weld joints in Ammonia and LPGstorage vessels shall be checked internally bywet fluorescent magnetic particle examinationto detect cracks due to stress corrosioncracking, once in ten years, besides the normalinspection.

Similarly, for vessels in DEA/MEAservice spot checking of T-weld joints shall becarried out by radiography/ultrasonic testing. If

defects or cracks are detected 100% weld joints shall be checked byRadiography/Ultrasonic Testing.

i) CONCRETE, GUNITE ANDREFRACTORY LININGS

Concrete, Gunite and RefractoryLinings inside a pressure vessel shall bevisually checked for mechanical damage suchas spalling and cracks.

Particular attention should be given atlocations where hot spots have been noticedduring operation. Minor cracks and areas of


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porosity are more difficult to find. Lightscrapping will sometimes reveal suchconditions. Bulging which can be locatedvisually is usually accompanied by cracking inmost cases. If corrosion occurs behind aconcrete lining, the lining will lose its bond with

steel. The sound and feel of light hammertapping will usually make such loosenessevident. If corrosion behind a lining issuspected, small sections of the linings shall beremoved for shell inspection. This will alsopermit a cross sectional examination of thelining. In cases where bare metal has beenexposed because of lining failure, visualinspection shall be made of the exposed metal.Thickness of the shell shall be measured fromoutside.

ii) RUBBER LINED PRESSURE VESSEL

Some pressure vessels are rubber linedform inside for protection against corrosion.The rubber lining shall be inspected formechanical damage, holes, cracking, blistering,bonding etc. Holes in the lining is evidenced bybulging. A holiday detector should be used tothoroughly check the lining for leaks andholiday. Care must be taken so that the testvoltage does not approach a value that mightpuncture the lining. Standards are available forvalues of test voltages as per thickeness ofrubber lining. For inspecting rubber lined

vessels, IS-4682-Part-I shall be referred.Bonding of the rubber lining should be checkedultrasonically from the outside.

10.2.3 Riveted Vessels

Besides the internal and externalinspection as given earlier, Riveted vesselsshall be examined for tightness of rivets,soundness of caulking and seal welds andother conditions. For the insulated rivetedvessel, insulation should be removed from alljoints for checking at 18 months intervals.

10.3 CORROSION COUPONS/PROBES

Corrosion coupons are installed in thepressure vessels to evaluate accurately thecorrosion rate or to evaluate a new material inthe existing environment. While doing theinternal inspection the corrosion coupons ifinstalled should be taken out. Nature ofcorrosion attack on the corrosion coupons shallbe studied. The coupons are then thoroughlycleaned and weight loss in a specified length of

time shall be calculated. This gives thecorrosion rate and cleaned coupons are againinstalled for future evaluation. Corrosion

probes may be installed at vulnerable locationson the pressure vessels for onstreammonitoring of corrosion rates. Coupons andprobes can be either fixed or retractable type.

10.4 SAFETY RELIEF DEVICES

The safety valves and safety reliefvalves on the pressure vessels should berevisioned and tested. For details oninspection of pressure relieving devices OISD-Std-132 shall be referred.

11.0 RETIRING THICKNESS

Before determining the limiting or retiringthickness of any pressure vessel, it should bedetermined under which code it has been

manufactured. Retiring thickness shall becalculated as per applicable code as mostvessels are built with some excess thickness invessel walls and heads, over that required towithstand the internal operating pressure. Theexcess thickness may result from any one ormore of the following factors:

i) Excess thickness as a result of using anominal thickness of plate rather than theexact (smaller) value calculated.

ii) Excess thickness available as a result ofsetting minimum thickness of the plates for

construction purposes.iii) Excess thickness available as a result ofchange in vessel service, by reducingsafety valve setting or maximum metaltemperature or both.

Retiring thickness for many accessories ofpressure vessels are not covered in the ASMEcode; neither are the methods of calculatingsuch thickness. Some of these parts are trays,internal tray supports, valves, grid, baffles,ladders and platforms. For some of theequipment, there are generally accepted

methods of setting retiring thickness. Minimumthickness should be developed for all suchequipment. The results of possible failure ofsuch equipment. The results of possible failureof such equipment should be considered forsetting these limits. Safety and continuousefficient operation are the prime factorsaffecting retiring thickness for thesecomponents. Repair or replacement should becarried out when they have lost one half theiroriginal thickness. The retiring thickness fornozzles and internal pipings shall be calculatedby applicable codes or ANSI standards. Widely

scattered pits may be ignored provided:


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a) no pit depth is more than one half thevessel wall thickness exclusive of thecorrosion allowance.

b) the total area of the pits does not exceed45 square centimeters within any 20centimeter diameter circle, and

c) the sum of their dimensions along anystraight line within the circle does notexceed 5 centimeters.

As an alternative to the proceduresdescribed above, any thinning of componentsbelow minimum required wall thickness due tocorrosion or other wastage may be evaluatedto determine the adequacy for continuedservice by employing the design by analysismethods of the ASME code. Section VIII Divn.2 Appendix- 4.

12. INSPECTION DURINGMAINTENANCE

12.1 WELD BUILD UP

In pressure vessels where some of thesmall areas within rejection limit as specified in11.0 sub clause b, have thinned down andentire corrosion allowance has been eatenaway, repair by local weld filling may berequired to build up the thickness . The area tobe repaired should be marked at site and

should be cleaned thoroughly. The area isfilled with weld deposits, in a staggared mannerto avoid warping, with suitable electrodesmatching with the base part. After weld buildup, the area should be visually/dye penetrantinspected for cracks and defects. Thicknessspots are made at a few locations at the builtup area by grinding. Thickness shall then bemeasured ultrasonically to check whetherrequisite thickness has been obtained.Preheating and post weld heat treatmentwhenever required should be carried out as perthe code.

12.2 NOZZLE REPLACEMENT

Thinned and deteriorated nozzles shallbe replaced. Rejected nozzle shall be removedby gouging the welding. New nozzlesfabricated out of piping having thicknessequivalent to original nozzles are installed.Welding shall be carried out from inside as wellas outside with suitable electrodes matchingwith base metal and nozzle material.Preheating and post weld heat treatment of thewelding shall be carried out as per the

requirement of relevant code. The weld jointsshall be checked visually and also by dye

penetrant test. Defects, if found are repaired.The weld joints shall be checked for leaks bypressurising with air at a pressure 1.03 kg/cm2through the tell-tale hole provided in thereinforcing pad. Pressurising the entire columnto check the nozzle weld joints should be

avoided. In some cases where the area isaccessible from inside, a box may be providedaround the nozzle. The box is pressurised withwater to the test pressure of the column/vesselcalculated by applicable code. The weld jointsand HAZ are checked for possible leaks. If anydefect is found in the weld joints, these aregouged, rewelded and retested.

12.3 PARTIAL REPLACEMENT OF SHELLPLATES AND DOMES

Some portion of shell plates and

domes of pressure vessels may get thinneddue to corrosion or erosion. The thickness ofthe affected area may reach the retiringthickness. In such cases, partial replacementof shell plate or dome is carried out as weldrepair of the big area is not practically possible.The affected portion is cut and removed. Thenew plates matching with the metallurgy andthickness of the original plate is madeavailable.

The edge preparation shall be done asper the code requirement by grinding. The

prepared edges shall be checked for cracks,flaws and defects by magnifying glass and byusing dye penetrant kit. The welding procedureis developed for welding the old and new pieceas per the relevant code. The welding may beperformed either from inside or outside. Theroot run shall be thoroughly inspected forcracks and flaws. After completing the weldingfrom one side, the other side is chipped andgrounded. Before welding again, the groove ischecked for cracks and defects. Welding isthen completed from the other side. Completewelding shall be visually checked and

radiographed as per the applicable code.Detailed inspection of welding shall be done asoutlined in Annexure II.

Preheat and post weld heat treatmentshall be carried out as per the requirement ofrelevant code. In order to check whether postweld treatment has been carried out properly,hardness readings on the weldment and HAZshall be taken after PWHT. The hardnessreadings should be minimum as indentationmarks required during hardness measurementact as stress riser and this leads to stressconcentration. If post weld heat treatment isrequired it is recommended to carry out


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radiography before post weld heat treatmentalso. The defects in the welding are repairedby gouging and rewelding. In lieu ofradiography, ultrasonic inspection of weld jointsmay be carried out.

12.3.1 Hydrostatic Test

After satisfactory inspection andradiography, the column/vessel ishydrostatically tested at a pressure calculatedby applicable code. The pressure should beheld for a minimum of 30 minutes. Duringhydraulic testing the pressure gauge should beinstalled at the highest point. It isrecommended that two pressure gauges be

used. The range of the pressure gauge shouldbe 30% more than test pressure and calibratedpressure gauges shall be used. The areawhich has been repaired should be thoroughlychecked for leaks and signs of deformation.The pressure drop shall also be noted. Beforesubjecting the column/ vessels to hydrostatictest, the foundation/supporting structures of thepressure vessels should be checked for waterload. Austenitic SS pressure vessels shall bepressure tested using DM water or passivatingsolution. Hydrostatic testing of vessel operatedunder vacuum conditions shall be done as per

the relevant code.

12.3.2 Pneumatic Testing

When testing pneumatically, a soapsolution should be used as an aid to visualinspection. This soap solution is brushed overthe seams and joints on the vessel. The vesselis then examined for evidence of bubbles as anindication of leaks. Often a vessel whichoperates at a vaccum may be pressure tested.This is the preferable testing method whenfeasible, because it permits the location of any

leaks. When pressure testing is not feasible, avacuum vessel can be tested for leaks bycreating a vacuum by means of evacuators orvacuum pumps installed in the units. If thevacuum can be held for a specified time afterclosing of the evacuators or vacuum pumps, itis an indication that the vessel is free of leaks.

If the vacuum cannot be held, leaks arepresent but this method gives no indication oftheir location. A search, which may be difficult,must then be made to trace the leaks. It issuggested that pneumatic testing should beavoided as far possible and if at all is to be

carried out it should be done in accordancewith relevant code.

12.4 REPAIR OF CLADDING ANDSTRIPLINING

The bulged, cracked or heavily pittedcladding inside the pressure vessels shall berepaired. The deteriorated cladding is removedby cutting. The edges of the remainingcladding is sealed by welding, using properelectrodes as per cladding and shellmetallurgy. If the area of the damagedcladding is small, the area is weld overlavedusing suitable electrodes. The area is thenground smooth. The repaired portion shall bechecked visually and by using D.P. for defectsand cracks etc. The welding should be done ina staggerd manner to avoid distrotion of the

shell. When the damaged area is big, aftersealing the remaining cladding, striplining of thearea can be done. (Details of striplining andwelding procedure is given in Annexure - II).Bulged striplining is replaced by puncturing thelining to remove entrapped air. The bulgedportion of the lining is flattened by lighthammering and then welded. If the striplininghas cracked or heavily pitted the damagedlining should be removed and fresh lining put.The weld joints are checked for flaws andcracks by DP and visual examination. Whileremoving or puncturing the cladding/striplining,

necessary precautions should be taken ashydrocarbon may be entrapped in between thelining and shell.

12.5 REPAIR OF PAINTED ANDRUBBERLINED AREAS

If the painting in a small area of avessel has peeled off or has been damagedpatch painting repair can be done. Thedamaged areas shall be painted with originalpainting system with proper curing time etc. Ifthe area of damage is large, the area is shot

blasted to Swedish, standard Sa 2-1-/2 to cleanthe surface and original painting system isapplied with proper curing time. DFT ismeasured with paint thickness gauge. Ifinternal rubber lining of vessels has bulged orcracked in a small area, the deteriorated liningshall be removed and fresh rubber lining is putin that small area. New lining shall be checkedfor holes and flaws. Local curing should bedone to achieve hardness of 65+50A (shorehardness-A). When a large area of the rubberlining has cracked and bulged, the damagedlining is taken out. Bare metal is cleaned byshot blasting. New rubber lining is provided.Curing shall be done to achieve 65 + 50A


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(shore hardness A). The lining shall be visuallychecked for cracks, holiday and bulging. Theholidays shall be checked by using holidaydetector. For inspecting the rubber lining IS-4682-Part I shall be referred.

13.0 DOCUMENTATION

Observations of each inspection shallbe properly recorded. After determining thecorrosion rate and remaining corrosionallowance, repair and replacement of apressure vessel can be planned. The followingcards shall be used for proper documentationof the Inspection findings:

i) Data card (Ref. Form No. 1)ii) Index card (Ref. Form No. 2)iii) History card (Ref. Form No.3)iv) Data record card (Ref. Form No. 4)v) Development sketch (Ref. Figure 5 & 6)

14.0 REFERENCES

The following codes standards andpublication have either been referred or used inthe preparation of this standard, and the sameshall be read in conjunction with this standard.

i) API Guide for Inspection of RefineryEquipment - Chapter VI - Unfired PressureVessels.

ii) API Guide for Inspection of RefineryEquipment - Chapter V - Preparation ofEquipment for Safe Entry and Work.

iii) ASME - Pressure Vessel Code. SectionVIII Divn. I & II.

iv) Indian Standard for Unfired PressureVessels - IS-2825.

v) BS-5500-Specification for Unfired FusionWelded Pressure Vessels.

vi) API-510-Pressure Vessels, InspectionCode-Maintenance, Inspection, Rating,Repair & Alteration.

vii) IS-9964 Part-I, Preparation of Tank forSafe Entry and Work.

viii) IS-4682 part I, Code of practices for liningof vessels and equipment for chemicalprocesses-Rubber Lining.

ix) Pressure Vessel Inspection Safety Code-Part 12 Institute of Petroleum.


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FORM 1

VESSEL DATA CARD

INFORMATION WEIGHTS

DESIGN CODE_________________________ SHELL______________________________

MANUFACTURER_______________________ INTERNALS_________________________

MANUFACTURERS INSULATION_________________________ORDER NO.____________________________

DRG.NO.______________________________ EMPTY VESSEL______________________

JOB NO._______________________________ FULL OF WATER

DIMENSIONS OPERATING CAPACITY________________

TOTAL HEIGHT________________________ MATERIALS

HEIGHT BETWEEN TANGENTS__________SHELL_________________________________

DIAMETER___________________________ HEADS_____________________________

WALL THICKNESS____________________ SKIRT_______________________________

TYPE OF HEADS______________________ BASE PLATE_________________________

CORR. BENCH MARKS_________________ MANWAY NOZZLE______________________

CONDITIONS

DESIGN TEMPOC_____________________ OPERATION TEMP

OC_______________________

DESIGN PRESSURE KG/SQ.CM__________ OPERATING PRESSURE KG/SQ.CM____________

HYDROTEST PRESSURE KG/SQ.CM_____ CORROSION ALLOWANCE mm________________

STRESS RELIEVED____________________ RADIOGRAPHED____________________________

JOINT EFFICIENCY LONG SEAM________ HEAD_____________________________________


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FORM 4

DATA RECORD CARD

UNIT_________

INSP.

POINT

DESCRIPTION SIZE SCHDL ORG.

THICKN

RET

THICKN

THICKNESS

1986 1987 1988 1989 1990 1991


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UJ+


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ANNEXURE I

INSPECTION CHECK LIST FOR COLUMNS IN SERVICE

UNIT_______________ EQUIPMENT No_____________ DATE_______________

1. SERVICE

2. REASON FOR INSPECTION

I) Shutdownii) On-StreamII) Breakdown

3. INTERNAL INSPECTION

A. TOP ZONE

a) Scaling Natureb) Domec) Shelld) Weldinge) Nozzle Weldingf) Internals

g) Spouts and Counter Spouts

B. MIDDLE ZONE

a) Scaling Natureb) Shellc) Weldingd) Nozzle Weldinge) Internalf) Spouts and Counter Spouts

C. BOTTOM ZONE

a) Scaling Natureb) Shellc) Domed) Weldinge) Nozzle Weldingf) Steam Coils


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4. EXTERNAL INSPECTION

a) Foundation & Foundation Boltsb) Insulationc) External Corrosion

d) Ladder and Stair Casee) Nozzle Flangesf) Bosses and Nipplesg) Grounding Connectionsh) Testing Nipple of Liners on Nozzle

5. THICKNESS SURVEY OF COLUMN INCLUDING ALL NOZZLES YES/NO

6. CONDITION OF INTERNAL LINING, IF ANY

7. REPAIR, IF ANY

8. CORROSION COUPONS: YES / NO

9. REMARKS

INSPECTION ENGINEER


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ANNEXURE-II

INSPECTION OF WELDING

1. DUTIES OF WELDING INSPECTOR

The duties of a welding inspector usuallyinvolve the performance of a number ofoperations, including :

i) Interpretation of drawings andspecifications.

ii) Verification of the metal being welded.

iii) Verification of procedure and welderqualification.

iv) Checking application of approved weldingprocedures.

v) Verification of proper heat treatment.vi) Assuring acceptable quality of welds.vii) Preparation of records and reports.

2. INSPECTION PRIOR TO WELDING

i) The faces and edges of material should beexamined for laminations, blisters, scabsand seams.

ii) Heavy scale, oxide films, grease, paint, oiland moisture should be removed.

iii) The pieces to be welded should bechecked for size and shape. Warped, bentor otherwise damaged material should bedetected in the early stages of fabrication.

iv) Edge preparations, bevel angle, alignmentof parts and fit up should be checked. Thegroove surface should be smooth(equivalent to machined/filled/ground

surface). The root gap should be uniform.

v) Tacks to hold alignment of joint must bechecked for soundness. Tacks which areto be included in weld must be done byqualified welders in accordance with thewelding procedure and must be of thesame quality as root pass.

3. INSPECTION DURING WELDING

Visual inspection is employed to check detailsof the work while welding is in progress. Thedetails to be considered are:

i) Welding processii) Cleaning.iii) Preheat and interpass temperatures.iv) Joint preparation.v) Distortion control.vi) Filler Metal.vii) Interpass chipping, grinding or gouging.

The inspector should be thoroughly familiar

with the items involved in the qualified weldingprocedures. Compliance with all details of theprocedure should be verified. The root pass ismost important from the point of view of weldsoundness. The root pass may be checked bydye-penetrant testing. The inspection of rootpass offers another opportunity to inspect forplate laminations.

In the case of double-groove welds, slagform the root pass on the side of the plate mayfrom slag deposits on the other side. Suchdeposits should be chipped, ground or gouged

out prior to welding the opposite side. Whereslag removal is incomplete, it will remain in theroot of the finished welds. Emphasis should beplaced on the adequacy of the tack welds andclamps or braces used to maintain the rootopening to assure penetration and alignment.

4. INSPECTION AFTER WELDING

Visual examination is the first stage in theinspection of a finished weld. The followingquality factors should be checked:

i) Dimensional accuracy of the weldment(including distortion).

ii) Comformity to specification requirementsregarding extent, distribution, size, contourand continuity of the welds.

iii) Weld appearance, surface roughness, weldspatter etc.

iv) Surface flaws, such as cracks, porosity,unfilled craters and crater cracksparticularly at the end of welds,

undercutting, overlap, excessive weldreinforcement, excessive grinding etc.


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v) The areas where fitup lugs were attachedor where handling lugs, machining blocksor other temporary attachments werewelded on, must be checked carefully afterthe attachment is removed. The area mustbe ground smooth and any pits or tears

shall be filled in with weld metal groundsmooth Air hardening materials should bepreheated before any thermal cutting.

vi) Postweld heat treatment time, temperatureand heating/cooling rates. For groovewelds, the width of finished welds willfluctuate in accordance with the grooveangle, root face, root opening andpermissible tolerances. The height ofreinforcement should be consistent with thespecified requirements. Where notspecified the inspector may have to rely on

his judgement, guided by what heconsiders a good welding practice.

The finished weld, should be thoroughlycleaned of oxides and slag for its finalinspection.

After visual inspection the finished weld may beexamined by one or more than one of thefollowing techniques.

5. NON DESTRUCTIVE TESTS

i) DYE PENETRANT TESTING: Unlessotherwise specified, the extent of this testwill be 100% for all root runs for alloy steelwelds. Adequate precautions as specifiedin applicable code should be taken whileinterrupting the welding cycle.

ii) MAGNETIC PARTICLE TESTING

iii) RADIOGRAPHY: Unless otherwisespecified the extent of radiographicexamination will be as follows:

a) carbon and carbon molybdenum steels-10% of the welds.

b) alloy steel - 100% of the welds. The weld joint for radiography will be marked by theinspector.

Radiographic examination of weld joints of twodissimilar materials shall be considered as perthe higher metallurgy stipulations.

iv) ULTRASONIC TESTING.v) EDDY CURRENT TESTING.

vi) FERRITE DETERMINATION.vii) ULTRASONIC HARDNESS TESTING

Hardness testing by portable hardness testersmay be considered as NDT method. Hydraulictesting may be done to check for leaks throughwelds, cracks etc.

6. DESTRUCTIVE TESTS

i) Mechanical tests like tensile, bend, impact,hardness, drift, flattening tests etc.

ii) Chemical analysis, microscopicexamination, grain size determination etc.

The method and extent of examinations will begoverned by applicable code requirements.

7. REPAIR OF WELDS

i) No repair should be carried out withoutprior permission of the inspector.

ii) Weld discontiniuties which are beyondacceptable limits shall be removed from the

joint completely by the process of chippingand grinding.

iii) Where random radiography is specified,the first weld of each welder shall becompletely radiographed. In case of pipesize 150 mm dia and below, the first twowelds shall be completely radiographed.

iv) For each weld found unacceptable due to awelders fault two additional checks shouldbe carried out on welds performed by thesame welder.


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ANNEXURE-III

HYDROGEN BLISTERS-INSPECTION, EVALUATION ANDREAPIR OF PRESSURE VESSELS

1. INSPECTION

A. Visually inspect exterior and interior ofvessel to determine location of all hydrogenblisters.

B. Determine blister thickness by ultrasonicsurvey or by drilling.

C. Conduct magnetic particle inspection at theedge and crown of any blister 2 inches andgreater in diameter to locate cracks whichoriginate at, or have progressed near to thesurface.

D. In order to detect plate cracks (fissures),conduct magnetic particle inspection of theplate for a distance of 6 inches beyond thelimits of blisters 2 inches and greater indiameter appearing on the inside of thevessel. See Figure 1.

2. EVALUATION

A. If the blisters are clustered and originate atvarying depths, replace the plate.

B. If plate fissures are detected underParagraph II. F, replace the affected plate.

C. Hydrogen blisters vissible in the cylindricalsection of the shell, the crown of flangedand dished or eliptical heads, or in

hemispherical heads and those that areaway from seams of localised loading such

as support pads should be consideredacceptable.

D. Hydrogen blisters visible in and very nearhighly stressed areas such as headknuckles, openings, seam and seam junctures, and support pads should beconsidered unacceptable in pressurevessels.

1. Affected components should be repairedor replaced. Repair or replacementshould be approved by an appropriateinspector aided by material and designspecialists as required.

E. If the diameter of any blisters listed inparagraph III.C exceeds the thickness ofthe plate, and the vessel is operated belowthe metal transition temperature, thematerial should be replaced.

USE ASME Code, Section VIII Division 2,impact Test Exemption Curves for CarbonSteels.' as a measure of transition temperature.

3. REPAIRS

A. Cracked blisters on the outside surface ofvessels in hydrofluoric acid service andcracked blisters on either inside or outsidesurfaces of vessels in other services shallbe repaired as follows:

1. Drill 1/8" diameter holes at ends of eachcrown crack or edge crack to a depthequal to blister depth as determined bythickness measurement.

B. Relieve hydrogen pressure in uncrackedblisters 2 inches and larger in diameter bydrilling a 1/16 inch diameter hole in thecenter of the crown as follows:

1. Blisters showing on outside of vessels.a. Drill from outside.

2. Blisters showing on inside of vessel.a. Drill from inside.


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b. For vessels in hydrofluoric acid service,drill from outside.

3. Blisters showing on both inside and outsideof vessel.

a. Drill from inside.

b.For vessels in hydrofluoric acid service, drillfrom outside surface only.

D. Vessels in hydrofluoric acid service.

1. If blisters 2 inches and larger in diameteron the inside surface have crown or edgecracks, gouge out complete blister, fill withweld metal and grind smooth with platesurface.

2. If blisters on the outside surface arecracked, treat as in Paragraph III A.

D. Preheat, welding procedures, stress-relief,etc. should be in accordance with currentacceptable practice for the specific vesselmaterial.

E. Spheres and other vessels with tubular legs.

1. Hydrogen may diffuse through the vesselwall and become trapped inside tubularlegs that are welded to the vessel. Thiscan form an explosive mixture with air in

the legs.

2. Prior to any welding or cutting on or nearthe legs of a blistered vessel, the legsshould be purged of any explosive gasesas follows:

a) Drill 1/4" diameter holes at top andbottom of legs, with a non-sparkingdrill.

b) Flush with inert gas or with air from thebottom hole.

3. Other dead spaces of significant volumeshould be treated in a similar manner.

equipment fabrication

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