Excessive background vs Insufficient background (Overwashing)

December 2011

Further to our Mail Inbox of November 2011, titled "A too high fluorescent background brightness?" (Which criteria make it possible to claim that the fluorescent background is too high?), in which one of our readers told us that a NADCAP auditor has issued a Non-Compliance Report (NCR) due to a too high background?

We have received the following comment from Bob Steffen, Process Engineering Metallurgist, Principal Fellow, an NDT Level 3 who has worked for 30+ years in the aerospace/defense industry:

"Greetings,
I want to compliment you on a great website and articles. These are valuable topics for discussion and improving the art of NonDestructive Testing. Thank you so much for your efforts!

Concerning Excessive background vs Insufficient background (Overwashing):
This is an auditor's question intended to test the confidence of the Level 3 and the rest of the penetrant inspection personnel. Of course the precise answer is impossible on the shop floor. In practice, this decision requires a subjective judgment - this is why we train and certify NDT personnel. In an audit situation, the L1 & L2 should be able to explain their "feel". The L3 should be able to answer with confidence concerning the theory and controls applicable to the types of parts they inspect and there are several reasonable ideas to tie together.

My outline of principles:
• The processing personnel (L1, L2, or L3) should be able to explain how they perform and observe water wash to control background.
• The evaluating personnel (L2 or L3) should be able to explain what they look for in the examination booth.
• The L3 should be able to explain that the daily sensitivity test panel shows that the material and process is behaving "normally" for their penetrant inspection facility.
• The L3 should be able to explain that the "practical test" parts and annual "performance review test" parts are intended to be representative of the types of parts processed by that facility and typical discontinuities encountered. The fact that the inspectors can locate the designated flaws during these practical tests is another element that confirms the background is not excessive, nor insufficient/overwashed.
• Having successfully accomplished this explanation, the auditor has no viable basis to issue a non-compliance report. After this point, the "kicking to the curb" begins’’. (Editor’note: for the non-American readers, it means, At this point the L3 realizes that no further reasoning will persuade this particular auditor and escalates the topic to upper management (“kicking” – moving this issue off the immediate agenda)."

Once again, we are happy to get news and comments from abroad readers. Always interesting also to learn day-to-day wording that no book mentions!