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DPCNews 025 - PT test panels

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Written by Administrator
Tuesday, 01 June 2010 11:21

PT test panels: Criteria for choosing ones for on-site use

June 2010

We are always delighted when readers send us emails to get answers to questions they cannot find the right answer to elsewhere.
Not only we are happy to answer them, but quite often such a request is an opportunity for us writing a new paper that should be of some interest for everyone!

Early April 2010 one of our regular readers asked a question about follow-up of on-site PT inspections.
Which test panels should he use : standardized ones, or others?

PT materials manufacturers use reference test blocks described in the ISO 3452-3:1998 standard to carry out type and batch tests according to the ISO 3452-2:2006 standard.

The ISO 3452-2:2006 standard requires using:
• The type 1 reference test blocks of the ISO 3452-3:1998 standard to carry out only the sensitivity (type and batch) testing.
• The type 2 reference test block of the ISO 3452-3:1998 standard to carry out only the washability (Method A penetrants only) batch testing.

This means that, as per the ISO 3452-3:1998 standard the type 2 reference test blocks shall not be used as a test panel to carry out sensitivity tests.

Contrary to the ISO 9934-2:2002 standard dealing with MT, the ISO 3452-2:2006 standard does not require on-site check of the materials performance with reference test blocks. 

But some primes ask their suppliers and service companies to check the performance of their PT process.

No problem when the prime gives its suppliers and service companies its own specifications comprising the test procedure and the acceptance criteria; provided that, as a minimum, the requirements are attainable and technically right!

On the other hand, a problem arises when the prime requires that its suppliers/service companies show the process is right without giving them any clue of what the prime is looking for.

Some suppliers/service companies face such a problem every day and are in a bad situation to overcome it.

What can a supplier/service company do to meet his customer’s implicit requirements?

First which test panels shall be used to check sensitivity?
• Standardized test panels: the type 1 reference test blocks of the ISO 3452-3:1998 standard.
• Non standardized test panels: the single-use bakelite test panels, the type 2 reference test block of the ISO 3452-3:1998 standard or the PSM-5® test panels ?

Our reader plans to use a test panel with 5 "imprints" of Brinell hardness balls of different sizes/pressures, i.e. the type 2 reference test block of the ISO 3452-3:1998 standard or the PSM-5® test panel.

He is to use colour contrast PT and he then wonders, accurately, that his prime, who has no knowledge whatever about PT inspection, would require the “highest sensitivity”, i.e. the on-site detection of the 5 star-burst indications. It is likely that, in on-site conditions, sensitivity cannot be as good as in lab conditions. This is a basic concern.

Our advice:

Though single-use bakelite test panels are not standardized, they are used by, among others:

• Companies and services companies which work for nuclear industry. A specification, at least in France, asks for some kind of on-site demonstration of performance of the PT materials. But these bakelite panels display large defects, and, further, using them this way is against the idea which led to their design, as described underneath.

• Railways companies maintenance workshop, at least in France, as a simple, sturdy and cheap means to check PT materials.

The truth is, these test panels were designed for the PT process lines in which the penetrant is applied by a pneumatic or electrostatic spraying technique. On many automatic process lines, the tin of penetrant has no low-level alarm - an incredible error! Therefore, even if there were no penetrant, robots would move one or several spray guns according to the program. In the inspection booth, obviously ... you may guess that all the parts will be cleared! Until somebody worries about not finding indications! To prevent this, on these lines, a bakelite panel should be attached to each jig/basket or each part if just a single part is processed at a time. Should the agent, in the inspection booth, detect no indication on the test panel, this may be due either to the test panel being defective – a very unlikely odd, as there are two notches on the same face of the test panel: it would mean that both notches are missing - or that no penetrant has been sprayed on the panel- and therefore probably no penetrant on the part either!  
This way of doing is quite common in aerospace industries as most of the automatic PT lines using spraying technique are seen there.

KEEP IN MIND THAT, WHATEVER ITS USE, A SINGLE-USE BAKELITE PANEL SHALL BE USED ONLY ONCE!!

The PSM-5® test panel is commonly used in aerospace industries as a way to meet NADCAP requirements (read underneath about the “NADCAP requirements”). It is tougher than the types 1 and 2 reference test blocks of the ISO 3452-3:1998 standard, and also, less costly. Its key performance factors are due to the induced defects, which are FAR SMALLER than those on the type 2 reference test block of the ISO 3452-3:1998 standard.

Type 1 reference test blocks of the ISO 3452-3:1998 standard are used much more currently in France than the type 2. In aerospace industries, they are put in the first basket of parts to be inspected and at the end of each shift or of each day to make users sure that all the parts were processed in accordance with the specified criteria. Indications are then compared to reference pictures; these reference pictures shall be visible under UV-A light and should be made by some PT materials suppliers which have specialized equipment/lighting/procedures to take pictures; better than asking professional photographers to do the job.

Laboratory conditions lead to constantly better results than on-site’s. That’s why we ask for doing the pictures in the REAL working conditions: comparing day-to-day pictures to the references is more meaningful.

As far as we know, no standard states the number of indications to be found with the type 2 reference test block of the ISO 3452-3:1998 standard or with the PSM-5® test panel. However we may remind you that Pratt and Whitney and General Electric require that at least three stars should be detected with a Level 2 fluorescent penetrant, 4 with a Level 3 fluorescent penetrant, and, as anticipated, 5 stars with a Level 4 fluorescent penetrant. Other primes follow these main primes, and this requirement is written in NADCAP questionnaires; we MUST remind you that NADCAP has no requirements per se, but records the requirements of this or that prime. None should say “NADCAP asks for this, NADCAP lay down that". If the NADCAP questionnaire asks for something, it is because at least one of the primes asks for it!

When using a colour-contrast penetrant on a PSM-5® test panel, we agree that finding 3 indications is a right figure. On the type 2 reference test block of the ISO 3452-3:1998 standard it would be possible to find the five indications!!! However we think just 3 is acceptable, especially for on-site tests.

Should a prime ask for 5 indications out of 5 on the PSM-5® test panel with colour contrast PT, you may guess its knowledge about PT is close to null!!

Cleaning of these PT test panel is a very important point, so important that this topic was dealt with in our DPCNewsletter N°010 of March 2009.

Nevertheless, even before speaking about on-site tests with PT reference test blocks, we think it wise to raise some questions.

• Why should you make these tests if only to check the MATERIALS?
If you buy materials from a renowned supplier, they are supplied with a certificate or declaration of conformity to specific standards/specifications, and they have been tested in the manufacturer/supplier laboratory as per a test program as described in these standards/specs. NO USER has the technical means to duplicate these tests, even the performance tests. Why not just endorse the figures displayed on the laboratory test report which should be supplied with every batch of materials?
When we buy a car, it shall be supplied in accordance with some regulations about noise, safety, consumption, pollution, etc. A certificate is supplied with the vehicle. The user trusts the manufacturer about the product conformity with the laid-down rules.
Let us think about more day-to-day products, such as the bottle of milk, mineral water, a stick of butter. For sure, these products do not come with a certificate of analyses for every batch. The user nevertheless is sure the supplier meets all the pertaining regulations. Moreover, if a consumer wants to test the product as thoroughly as the supplier did, he would spend a fortune!

• So, the on-site check, useful or not? It may help to VALIDATE A PROCESS. That’s the case with the bakelite panels which are put in baskets/jigs on automatic process lines. It does not give any clue about the performance of the materials, but makes the user confident that, if he does not see any indication on the part, this is not due to a flaw of the process, of the line.

Nevertheless the “right tool” shall be used.  It is useless to check on-site that the system is able to detect discontinuities of 1.5 µm wide and some millimeters long, using type 1 reference test blocks of the ISO 3452-3:1998 standard, while one looks for real discontinuities at least 100 times larger! This may lead, when working “near the limits of the process”, to state the test is unsatisfactory once every 2 or 3 times: unable to detect discontinuities which are 100 times smaller than the smallest due to be detected with a 100% probability of detection!!

• Another example: the ISO 3452-5:2008 standard displays the tests to be carried out on high temperature PT materials.
Penetrants designed for the 50°C-100°C (122-212°F) shall be tested at 50°C and 100°C. An auditor REQUIRED that “standard” penetrants, designed for the 10-50°C (50-122°F) range, be tested at 50°C, though this is not required in the ISO 3452-2:2006 standard nor in the ISO 3452-5:2008 standard.
Obviously these tests come at a cost, in time and in workforce to simply confirm that these standard penetrants may be used at 50°C, when most of them may be satisfactorily used even at 80°C (112°F). Penetrants designers always take a large safety margin, as they know that their materials may be used on very different sites: very hot deserts, very wet or very dry environment, low-temperature, etc.

We therefore recommend you work only with renowned suppliers. You may find some of them in Europe, in the USA, in Japan. When possible, use only materials listed in the Qualified Products List annexed to the SAE-AMS 2644 American specification. However, this list does not take into account some special materials (high-temperature, low-temperature, for example). Another reason thus to rely only on suppliers who have already proven their expertise!

Reference

• Patrick DUBOSC and Pierre CHEMIN, DPCNewsletter N°010, March 2009, Penetrant testing: test panels/parts cleaning on our Website
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info

• ISO 3452-3:1998 Non-destructive testing -- Penetrant testing -- Part 3: Reference test blocks, International Organization for Standardization, Geneva, Switzerland, 1998.

• ISO 3452-2:2006 Non-destructive testing -- Penetrant testing -- Part 2: Testing of penetrant materials, International Organization for Standardization, Geneva, Switzerland, 2006.

• ISO 9934-2:2002 Non-destructive testing -- Magnetic particle testing -- Part 2: Detection media, International Organization for Standardization, Geneva, Switzerland, 2002.

• SAE-AMS 2644E: Inspection Material, Penetrant, Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, Pennsylvania 15096, 2006.

• ISO 3452-5:2008 Non-destructive testing -- Penetrant testing -- Part 5: Penetrant testing at temperatures higher than 50 degrees C, International Organization for Standardization, Geneva, Switzerland, 2008.


We, Pierre CHEMIN and Patrick DUBOSC, welcome any comment, any idea. If you have some examples you would like to see discussed here, please give us all the useful indications. If you require confidentially, we would modify locations, names and some parameters to prevent any traceability.
Nevertheless, we are convinced that our site may be a kind of surge-valve: the topic is NOT to target this company, or that auditor; but it is always to make users think, to make them ask themselves, or others, the right questions.
We may also give advice, once again on a confidential basis if needed: please, feel free to ask questions, to document our data basis: about Material Safety Data Sheets (MSDS), about environment, a chemical name you don't understand, a Penetrant process you have heard about, etc.
We have plenty of examples, some being out of all the specifications/standards, which led to the discontinuities detection, when the "current, normal, processes" prevented discontinuity finding.