PT inspection after Grinding a Weld Seam?
Mohamed Arbaoui
Dear Members,
I have a question since I'm a beginner in this domain.
After a weld inspection by PAUT, a crack was detected at a certain depth. I noticed that the welders grind down the weld surface until they reach the depth indicated by PAUT, and then apply a PT test.
My concern is: isn't there a risk that the grinding process may partially close or smear the crack surface, making it harder for the PT liquid to penetrate and properly reveal the defect?
If so, this could mean that PT might give a false result, and the crack would only be detected later when PAUT is reapplied after re-welding.
Am I misunderstanding the procedure? What is the best practice in this case?
sridhar cn
Your concern is valid. Grinding a weld surface
down to the depth indicated by PAUT before performing a Penetrant Test (PT) can
indeed
risk smearing or partially closing the crack surface. Grinding down to the PAUT-indicated crack depth before PT can cause smearing that
partially closes cracks, making PT less effective and potentially leading to false negatives.
To avoid this:
Use a low force (a lower grind pressure) and avoid overheating during final grinding to minimise smearing. Employing the bleed-back
technique (i.e., after applying developer in PT, wiping the area and reapplying developer can help reveal cracks if there is still an open path
to the surface. If the indication reappears, further light grinding may be needed to reopen cracks before performing the PT. Interpret PT
results with caution after grinding and confirm with ultrasonic methods if needed.
This combined approach ensures more reliable detection of weld cracks and reduces the risk of missing critical defects.
C Sridhar.
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