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June 2013 - Penetrant testing and test panels: The "masters" and their future

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Written by Administrator
Sunday, 12 May 2013 10:38

Many specifications, in the aerospace industry, require that PT process lines be checked every shift, every day, every time they are put in service, etc.

This PT process line check, which is called the system performance(1) or penetrant system performance(2), shall be performed using test panels or any known defect standards. Any discrepancy in the appearance of the indications and/or of the background shall be a cause for concern.

First, in such a case, almost all the procedures require that the test panels be reprocessed. Generally, if the discrepancy is not confirmed by the second test … everything is considered as … OK!!!

Almost all the specifications require that a second set of test panels, the "masters," be available. If the discrepancy with the "daily" set of panels is confirmed, the "masters" set shall be used. When the "masters" give good results while "daily" panels give poor results, the "daily" panels shall be recalibrated by the manufacturer.
If the test panels cannot be recalibrated, they shall be discarded.
Usually, in this case, a brand-new  set of test panels is supplied to be used as the new "masters."
The old "masters" are used as the new "daily" test panels.

For decades, the results from the tests were compared to photographs … that were not, by far, the exact replica of the indications:
• The pictures might be in black-and-white,
• The pictures size might be smaller than panels,
• The indications on the photographs might be invisible under UV-A radiation.
Quite often, the three parameters were "available" at the same time!!!

We both have struggled over many years, for the following requirements to be stated:
• Colour pictures,
• Full-scale pictures,
• With indications on pictures visible under UV-A radiation.
This was not so easy to get when using photographs obtained from photographic films, but it was not impossible.

Since several years, thanks to the dramatic improvement to the quality of digital still cameras, of the computers, software printers and photo paper, it is easier (not easy, easier) to get the right, high-quality pictures, which can be used as reference photograph baselines(3).

Due to the revision of several specifications, which require that the pictures comply with the three latest points, and which require a recalibrating of the test panels, for instance, every three years, it seems likely that the requirement for a “masters” set (so-called, back-up) of panels will become superfluous and obsolete.

Fewer quality-assurance papers/computer files, fewer disputes with auditors … less test panels to buy … less test panels to supply, for the manufacturer … All in all, an alleviated burden … A rarity, in our world in which the simplest things become harder, because of not-always-useful applications of the principle of precaution, of more and more stringent requirements by the authorities [Federal Aviation Administration (FAA), or its equivalents all around the world].


Reference

(3) Patrick DUBOSC and Pierre CHEMIN, What is a reference picture? Editorial – November 2012: on our Website.


Normative references

(1) ISO 3452-1:2008, Non-destructive testing -- Penetrant testing -- Part 1: General principles, International Organization for Standardization, Geneva, Switzerland, 2008.

(2) ASTM E1417/E1417M, Standard Practice for Liquid Penetrant Testing, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959, USA, 2011.

Last Updated ( Sunday, 12 May 2013 10:48 )