Most Important NDT Interview Question & Answer | Magnetic Particle Testing | Interview Q&A NDT | NDT

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MPI
Questions (1) What is meant by magnetic particle test?
Magnetic particle testing is a non-destructive process used to detect surface and subsurface discontinuities in ferromagnetic materials like nickel, cobalt, iron and their alloys.
Questions (2) Explain the steps in Magnetic Particle Testing?
Preclean the specimen.
Induce a magnetic field in the specimen.
Apply magnetic particles to the specimen's surface.
View the surface, looking for particle groupings that are caused by defects.
Demagnetize and clean the specimen.
Questions (3) What is dry magnetic particle inspection?
In this magnetic particle testing technique, dry particles are dusted onto the surface of the test object as the item is magnetized. Dry particle inspection is well suited for the inspections conducted on rough surfaces. Dry particle inspection is also used to detect shallow subsurface cracks.
Questions (4) What is the maximum depth that magnetic particles can detect a discontinuity?
1/4 inch (Approx 6 to 7 mm)
Questions (5) What is the principle of MPT?
Principle of MPT is as follows: When the workpiece to be inspected is magnetized, magnetic flux is induced. If there is a flaw on the surface, magnetic flux leaks into the air at the position of the flaw. Then magnetic particles (Wet or dry) are applied to the surface (Principle: Magnetic Flux leakage)
Questions (6) Can you do MPI on stainless steel?
Stainless steel is simply not magnetic enough. Stainless steel can't be inspected by magnetic particle testing as we aren't able to induce a magnetic field on the stainless steel. Due to this, the material remains non-magnetic.
But Only austenitic stainless steels that are not capable of magnetization, Ferritic stainless steels are actually magnetic.
Questions (7) What is the lifting power of yoke during calibration?
The magnetizing power of yokes shall be verified prior to use each day the yoke is used. Alternating current electromagnetic yoke shall have a lifting power of at least 10 lb (4.5 kg) at the maximum pole spacing, with contact similar to what will be used during the examination.
Direct current or permanent magnetic yoke shall have a lifting power of at least 40 lb (18 kg) at the maximum pole spacing.
Questions (8)What is Minimum and maximum prod spacing during Prod MPT?


Maximum prod spacing shall be 8 in. (200 mm), prod spacings of less than 3 in. (75 mm) are usually not practical due to banding of the particles around the prods.
Questions (9) How much Particle Settling volume is required during wet MPT ?
For fluorescent particles the required settling volume is from 0.1 mL to 0.4 mL in a 100-mL bath sample.
For Non Fluorescent particles, the value is 1.2 mL to 2.4 mL.
Questions (10) What is the code & acceptance criteria for magnetic particle inspection?
MPT Shall be done as per ASME Boiler and pressure vessel code, Section
Article- 7.
Acceptance shall be in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, Appendix 8 (Video in the Channel playlist)
Questions (11) What is the use of pie gauge in magnetic particle testing?
The Pie Gauge is a tool for quickly verifying the direction of magnetic flux on a surface. It is made from eight ferrous segments, braised into a single piece, providing a star pattern of non-ferrous discontinuities.
Questions (12) How much Light intensity is required for MPT?
The minimum light intensity shall be 100 fc (1076 Ix) for visible (Colour contrast) particles,
For Fluorescent particles, UV-A lights shall achieve a minimum of 1000 µW/cm² on the surface of the part being examined throughout the examination. It shall be performed in a darkened area with a maximum ambient white light level of2 fc 21.5 lx)
Questions (13) What is demagnetization? How to do it?
The removal of Cesidual magnetism by simultaneously or alternately reducing the strength and reversing the direction of a magnetic field.
Generally two methods are used for demagnetization:
(i) The part is placed in the field of an AC coil and withdrawn slowly to about 1.2 to 2 m away. Small parts should be kept close to the I.D. of the coil.
(ii) Part is subjected to a reversing, diminishing DC or HWAC current.