1. Dye penetrant test and Magnetic particle
Inspection
16BME153 (AMIN KAUSHAL)
16BME156 (PATEL PRASHANT)

2. Dye penetrant test (DPT)
• Dye penetrant inspection (DPI), also called liquid penetrant test (LPT).
• Is a widely applied and low-cost inspection method used to locate surface-breaking
defects in all non-porous materials (metals, plastics, or ceramics).
• The penetrant may be applied to all non-ferrous materials and ferrous materials.
 Principles :-
• DPI is based upon capillary action, where low surface tension fluid penetrates into
clean and dry surface-breaking discontinuities.

3.  Inspection steps
1. Pre-cleaning:
• The test surface is cleaned to remove any dirt, paint, oil,
grease.
• The end goal of this step is a clean surface where any
defects present are open to the surface, dry, and free of
contamination.
2. Application of Penetrant:
• The penetrant is then applied to the surface of the item
being tested.
• The penetrant is allowed "dwell time" to soak into any
flaws (generally 5 to 30 minutes).
• The dwell time mainly depends upon the penetrant being
used, material being tested and the size of flaws sought.

4. 3. Excess Penetrant Removal:
• The excess penetrant is then removed from the surface.
• The removal method is controlled by the type of
penetrant used. Water-washable, lint-free cloth.
• If excess penetrant is not properly removed, once the
developer is applied, it may leave a background in the
developed area that can mask indications or defects.
4. Application of Developer:
• After excess penetrant has been removed, a white
developer is applied to the sample.
• Several developer types are available, including: non-
aqueous wet developer, dry powder, water-suspendable,
and water-soluble.
• Choice of developer is governed by penetrant
compatibility (one can't use water-soluble or -
suspendable developer with water-washable penetrant),
and by inspection conditions.

5. 5. Inspection:
• The inspector will use visible light with adequate intensity for visible dye penetrant.
• Inspection of the test surface should take place after 10 to 30 minute development
time, depends of product kind.
• This time delay allows the blotting action to occur.
6. Post Cleaning:
• The test surface is often cleaned after
inspection and recording of defects,
Especially if post-inspection coating
processes are scheduled.

6.  Advantages
• The main advantages of DPI are the speed of the test and the low cost.
• Large areas and large volumes of parts/materials can be inspected rapidly.
• Parts with complex geometric shapes are routinely inspected.
• Indications are produced directly on the surface of the part and constitute a visual
representation of the flaw.

7.  Disadvantages:
• Only surface breaking defects can be detected.
• Only materials with a relatively nonporous surface can be inspected.
• Surface finish and roughness can affect inspection sensitivity.
• Multiple process operations must be performed and controlled.
• Post cleaning of acceptable parts or materials is required.
• Chemical handling and proper disposal is required.

8. Magnetic particle Inspection (MPI)
Magnetic particle Inspection (MPI) is a non-destructive testing (NDT) process for
detecting surface and slightly subsurface discontinuities in ferromagnetic
materials such asiron, nickel, cobalt, and some of their alloys.
This module is intended to present information on the widely used method of
magnetic particle inspection.
Magnetic particle inspection can detect both production discontinuities (seams,
laps, grinding cracks and quenching cracks) and in-service damage (fatigue and
overload cracks).

9.  Procedure of MPI:
• 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.

10. • 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.

11.  Applications:
• Can detect both surface and near sub-surface defects.
• Can inspect parts with irregular shapes easily.
• Precleaning of components is not as critical as it is for some other inspection
methods.
• Considered low cost compared to many other NDT methods.
• Is a very portable inspection method especially when used with battery powered
equipment.

12.  Limitations:
• Magnetic particle inspection methods will work only on ferromagnetic materials.
• Demagnetization following magnetic particle testing is often necessary.
• Exceedingly large currents sometimes are required for very large parts.
• Care is necessary to avoid local heating and burning of finished parts or surface at
the points of electric contact.