Grinding and Liquid Penetrant examination

[monirri]

Hi. I was told in my Liquid penetrant course that surfaces should not be grinded prior to testing, cause that would cause litlle round indications to hide. Now i am working in the pipeline industry, and a quality control engineer with far more experience tells my, afeter I finish the LP test, that the final weld should be grinded so that spaces between welding passes won´t hide real indications. You know, that would mean that the joint should be "blended" to be smoother, cause wipers don´t always reach that spaces, so penetrant remains, and it looks red. That would be bad for joints, specially if the final pass is ugly. What is the best point of view? It is necessary to clean toroughly with the wiper again and again?

 

[DVWE]

What type of material are you testing? Carbon, stainless, nickel?

 

[monirri]

Carbon, for oil.

 

[Mr168]

You're going to have some very angry management if they're wasting time grinding off the cap passes of every weld for the sake of a PT exam.

A cap pass that is bad enough to where a level II or level III PT test personnel can't tell the difference between a relevant and a non-relevant indication probably shouldn't make it pass the visual inspection stage anyways. If you're talking about looking red AFTER the PT has already been performed, just spray the joint directly with your solvent to clean it, rather than wiping it down.

 

[DVWE]

monirri,

If you are doing PT on carbon steel, I am assuming it is a customer specific requirement. Typically, final PT is performed after all weld dressing (grinding, machining, etc). A light blend grind is acceptable only if you are having trouble interpreting an indication.

 

[jbeckhou]

PT testing could not be done correctly without dressing the weld. Why not MP the weld?

Petrotrim Services

http://www.petrotrim.com