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Mail Inbox - November 2011

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Written by Administrator
Saturday, 22 October 2011 12:18

A too high fluorescent background brightness?

November 2011

A more-than-thirty year friend of ours, who has been a Level 3 trainee with us as instructors, in the ‘80s, Claude BOURIGEAUD, a consultant engineer in ASSISTEC-CB, sent us the underneath question:
"Which criteria make it possible to claim that the fluorescent background is too high?

A Non-Compliance Report (NCR) has been issued by a NADCAP auditor on this topic, up to now failing to give us “true criteria"; he presented us with subjective criteria only.
Can someone shed some light on it? (UV light, for a better understanding?)
Thank you. Sincerely yours."

Our answer is a bit … subjective:
“Indeed, this is a … sensitive topic! Pratt and Whitney does not accept any background, when General Electric prefers to have some, a "proof" the part has not been overwashed.

The background level is also very dependent upon the surface roughness and the material. Further, there are also kinds of affinity between some penetrants and some materials. This had been tested in one of our laboratories: the same screws, same batch number, made of the same material, with the same characteristics, taken out of the same container: they retain different penetrants differently, partly according to the viscosity (but not for all the penetrants!), partly according to the brand or the formula of the penetrant.

An "excessive" background is always only a qualitative criterion: every person may "see" it differently, may "interpret" it differently. Further, cast iron will always display some background. If the auditor is accustomed to check only machined parts, or if on the same part, there are both machined surfaces and unmachined ones, obviously, this makes a difference.
The TAM panel, also known as the PSM-5®, makes it easier to detect “an excessive background level” (meaning: more than usual) when the result is compared to the reference picture of this same panel. A background level may only be assessed by comparison, not as a figure.

The criterion that may help to claim there is a too high background level is the ratio:

Indications of discontinuities fluorescent brightness
—————————————————————————
Background fluorescent brightness

That should be high enough to allow for an easy detection of the indications. It is called contrast.
This is a point presented in one of our conferences(1).

As you may have noticed in several of the papers published on our website, we recommend that the auditees do not comply with the "diktat of auditors".

Thus, in one of our Editorials (2):
"Our own opinion is that auditors should stick to the relevant specifications, where the person under audit is aware of the requirements and prepared to answer questions related to them. The auditor should not be allowed to invent questions that cannot be answered from the specifications, and the auditor has no business imposing criteria or procedures that are not in the specification. Blindsiding a person under audit serves no useful purpose and expense for the auditee.
The more auditors "invent" new questions not written in the applicable specification, the more means they have to issue non-conformance reports (NCR), the more they multiply audits, hence significant additional revenues for auditors and audits bodies. Auditees must have in mind that, if they are requested to show records of some process not written in the applicable document, they can, and they must, ask the question: "please, show me the paragraph in which this is required”. Further, after an audit, an auditee may report to the auditing body if he or she thinks that the auditor has been “unfair” during the audit."

In your case, the auditor shall show the auditee where this requirement is stated in the applicable specification(s). Should the auditor be unable to do that, his requirement is null and void.

Claude Bourigeaud sent us a reply:
"Thank you for your answers and explanations. This confirms me in the opinion I had on this topic. I fully agree with you on how to answer the problem and on the way to react when faced to overzealous auditors, quick to write NCRs!
However, what about the signal/noise ratio: I had thought it would be OK, but far too expensive for a small company. The PSM-5® panel is useful to control under-and overwashing, but does not match the surface of the parts. Nevertheless, it is better than nothing.
Once again, thank you for your answers."

References

(1) Patrick DUBOSC and Pierre CHEMIN, Un niveau plus élevé d’UV-A en cabine peut-il permettre de contrebalancer un niveau élevé de lumière visible ?’’ (Editor’s note: ‘‘Is increasing UV-A irradiance the right answer to a high luminance in the inspection booth?"), COFREND Congress, Dunkirk (France), May 24-27, 2011.

(2) Patrick DUBOSC and Pierre CHEMIN, Don’t let auditors cross the lines! - Editorial - December 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/edito/edito-2010/82-decembre-2010-ne-laissez-pas-les-auditeurs-franchir-les-limites-

Last Updated ( Saturday, 22 October 2011 12:48 )