What is the difference between MT and PT?
| Magnetic Particle Testing (MT/MPT) | Dye Penetrant Testing / Liquid Penetrant Testing (PT/LPT/DPT) |
| Can detect surface and sub-surface discontinuity | Can detect only surface discontinuities |
| Used on ferrous materials | Used on non-porous materials |
| Pre-cleaning is not a critical requirement | Pre-cleaning is a critical requirement |
| Instruments may require electricity | Instruments for testing don’t require electricity |
| MT is faster than PT | PT requires more time than MT |
How is penetrant testing performed?
Their are some step to follow while performing Liquid penetrate testing
Step 1 – Pre-cleaning of the Surface
The cleaning process must remove contaminants from the surface of part and defects, and must not mask any of defect.
Step 2 – application of penetrate
Many method of application of penetrate like spraying, brushing, dipping.
Step 3 – Dwell time
After application of penetrate we have to wait some time (10- 20 min known as dwell time. In this time, the penetrant liquid enters to the crack (normally is not visible). The penetrant liquid soaks inside of the defects/ imperfections by capillary action.
Step 4 – Removal of the Excess Penetrant Liquid
In this step penetrant liquid remove from the surface by rag or cloth No penetrate should be visible after cleaning. Then takes a clean rag and sprays some cleaner on a cloth and then cleans the surface one more time. This can be done two or three times to remove all penetrant liquid from the surface.
Step 5 – Application of Developer and development time
The developer spray can and agitates it and then sprays to the surface. Then he waits for 10 minutes. In this time, the defect will be visible, the developer material uses reverse capillary action and bleeds out the penetrant, and if there is a crack in the surface, you will see a penetrate line within the white color covered by developer material.
Step 6 – Evaluation / Interpretation
The ASNT Level II liquid penetrant inspector evaluates the test result based on the acceptance criteria indicated in the approved test procedure. Please note one indication might be considered imperfection and be rejected by one acceptance criteria and be accepted by another one. So it is imperative that the test be evaluated with right acceptance criteria.
Step 7 – Post-cleaning
We have to remove all chemical from material surface because chemical may harm test material
What materials can penetrant testing be used on?
Penetrant testing can be applied to both ferrous and non-ferrous materials, all metal and alloys non metal, it can be done only on non-porous materials (plastics, polymer, glassware or ceramics).
It is commonly used to detect defects in castings, forgings and weldments.
What materials can magnetic particle inspection be done on?
MT can be performed on ferrous materials as this material can sustain magnetism which is the basic principle of testing.
How can one get certified in penetrant testing?
You can apply to Spark Institute of Nondestructive Testing to get trained and certified in Penetrant Testing.