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* Unit –IIpart 2

*LIQUID PENETRATE INSPECTION-CONTINUED…

*By:Zoha NasirAssistant professorJIT, Barabanki

05/01/2023 Jahangirabad institute of technology 2*Penetrant

Penetrants are carefully formulated to produce the level of sensitivity desired by the inspector. The penetrant must possess a number of important characteristics:Spread easily over the surface of the material being inspected to provide

complete and even coverage.Be drawn into surface breaking defects by capillary action.Remain in the defect but remove easily from the surface of the part.Remain fluid so it can be drawn back to the surface of the part through the

drying and developing steps.Be highly visible or fluoresce brightly to produce easy to see indications.Not be harmful to the material being tested or the inspector.

05/01/2023 Jahangirabad institute of technology 3*Types Of Penetrant

Penetrant materials come in two basic types:Type 1 - Fluorescent Penetrants: they contain a dye or several dyes

that fluoresce when exposed to ultraviolet radiation.

Type 2 - Visible Penetrants: they contain a red dye that provides high contrast against the white developer background

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Fluorescent penetrant systems are more sensitive than visible penetrant systems because the eye is drawn to the glow of the fluorescing indication.

However, visible penetrants do not require a darkened area and an ultraviolet light in order to make an inspection.

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Penetrants are then classified by the method:

Method A - Water Washable: penetrants can be removed from the part by rinsing with water alone. These penetrants contain an emulsifying agent (detergent) that makes it possible to wash the penetrant from the part surface with water alone. Water washable penetrants are sometimes referred to as self-emulsifying systems.

Method B - Post- Emulsifiable, Lipophilic: the penetrant is oil soluble and interacts with the oil-based emulsifier to make removal possible.

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Method C - Solvent Removable: they require the use of a solvent to remove the penetrant from the part.

Method D - Post- Emulsifiable, Hydrophilic: they use an emulsifier that is a water soluble detergent which lifts the excess penetrant from the surface of the part with a water wash.

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Penetrants are then classified based on the strength or detectability of the indication that is produced for a number of very small and tight fatigue cracks.

Level ½ - Ultra Low SensitivityLevel 1 - Low SensitivityLevel 2 - Medium SensitivityLevel 3 - High SensitivityLevel 4 - Ultra-High Sensitivity

05/01/2023 Jahangirabad institute of technology 8*Developer

The role of the developer is to pull the trapped penetrant material out of defects and spread it out on the surface of the part so it can be seen by an inspector.

Developers used with visible penetrants create a white background so there is a greater degree of contrast between the indication and the surrounding background.

On the other hand, developers used with fluorescent penetrants both reflect and refract the incident ultraviolet light, allowing more of it to interact with the penetrant, causing more efficient fluorescence.

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According to standards, developers are classified based on the method that the developer is applied (as a dry powder, or dissolved or suspended in a liquid carrier). The six standard forms of developers are:

Form a - Dry PowderForm b - Water SolubleForm c - Water SuspendableForm d – Non aqueous Type 1: Fluorescent (Solvent Based)Form e – Non aqueous Type 2: Visible Dye (Solvent Based)Form f - Special Applications

05/01/2023 Jahangirabad institute of technology 10*Zyglo Testing

It is a zyglo fluorescent penetration process.Zyglo is the trademark of MAGNAFLUX corporation for

fluorescent penetration process.It is a modern testing processIt is accurate and quick process for locating surface flaws as-Shrinkage cracksPorosityCold shutsFatigue cracks etc…

05/01/2023 Jahangirabad institute of technology 11*Magnetic Particle Inspection

INTRODUCTION:Magnetism is the ability of matter to attract other matter to itself. Objects

that possess the property of magnetism are said to be magnetic or magnetized and magnetic lines of force can be found in and around the objects.

A magnetic pole is a point where the a magnetic line of force exits or enters a material.

Magnetic field lines:• Form complete loops.• Do not cross.• Follow the path of least resistance.• All have the same strength.• Have a direction such that cause poles to attract or repel.

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(a) (b) (c)

(a)Magnetic lines of force around a bar magnet(b)Opposite poles attracting(c)Similar poles repelling

05/01/2023 Jahangirabad institute of technology 13* How Does Magnetic Particle

Inspection Work?

A ferromagnetic test specimen is magnetized with a strong magnetic field created by a magnet or special equipment.

If the specimen has a discontinuity, the discontinuity will interrupt the magnetic field flowing through the specimen and a leakage field will occur.

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Finely milled iron particles coated with a dye pigment are applied to the test specimen.

These particles are attracted to leakage fields and will cluster to form an indication directly over the discontinuity.

This indication can be visually detected under proper lighting conditions.

05/01/2023 Jahangirabad institute of technology 15*Basic Procedure

Basic steps involved:

Component pre-cleaning.Introduction of magnetic field.Application of magnetic media.Interpretation of magnetic particle indications.

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*Pre Cleaning

When inspecting a test part with the magnetic particle method it is essential for the particles to have an unimpeded path for migration to both strong and weak leakage fields alike.

The part’s surface should be clean and dry before inspection.

Contaminants such as oil, grease, or scale may not only prevent particles from being attracted to leakage fields, they may also interfere with interpretation of indications.

05/01/2023 Jahangirabad institute of technology 17*Introduction Of Magnetic

Field

The required magnetic field can be introduced into a component in a number of different ways.

Using a permanent magnet or an electromagnet that contacts the test piece.

Flowing an electrical current through the specimen.Flowing an electrical current through a coil of wire around the

part or through a central conductor running near the part.

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*Application Of Magnetic Media

MPI can be performed using either dry particles, or particles suspended in a liquid.

With the dry method, the particles are lightly dusted on to the surface.

With the wet method, the part is flooded with a solution carrying the particles. The dry method is more portable.

The wet method is generally more sensitive since the liquid carrier gives the magnetic particles additional mobility.

05/01/2023 Jahangirabad institute of technology 19*Dry Magnetic Media

Magnetic particles come in a variety of colors. A color that produces a high level of contrast against the background should be used.

05/01/2023 Jahangirabad institute of technology 20*Wet Magnetic Media

Wet particles are typically supplied as visible or fluorescent. Visible particles are viewed under normal white light and; fluorescent particles are viewed under black lights.

05/01/2023 Jahangirabad institute of technology 21*Interpretation Of Indications

After applying the magnetic field, indications that form must interpreted.

This process requires that the inspector distinguish between relevant and non relevant indications.

The following series of images depict relevant indications produced from a variety of components inspected with the magnetic particle method.