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Colour contrast penetrant without any developer

Written by Administrator
Saturday, 02 July 2011 11:28

This is a very specific case.

In 1978 (yes, 1978!), a subcontractor of a French car manufacturer phones us, stating that he has a 10,000 brake master cylinder batch of dubious quality. Some of them may be broken. It is a one-time problem; the subcontractor knows where the problem comes from. It has been fixed, but there is a need to inspect 10,000 parts! No investment, no complex equipment accepted: once again, it is a once-in-a-life problem.

450 km (280 miles) later, we see the parts. Very well machined, no dead-end surface. Finally, a very easy-to-solve problem, at least for someone knowing Penetrant Testing a bit!

During PT training courses, when excess of penetrant removal is the topic, the trainer points out that, if a solvent remover is to be used, this shall be done carefully, using a lightly moistened rag, and never, NEVER, spraying the solvent remover on the part, or immersing the part in the solvent remover.

Nevertheless, immersion in the solvent remover is the method we recommended then - and it worked perfectly!

Using a colour contrast penetrant, you MUST spray a non-aqueous wet developer so as to get the white contrasting surface. We recommended NOT TO USE ANY DEVELOPER!

By the hell, everything is against the basics of penetrant testing, and you seem sure it works! How is this possible?

Remember: no equipment to buy - so, no fluorescent penetrant with its UV-A source.

10,000 parts to be inspected by people who knew NOTHING about penetrant testing. Better, to use whatever they had on site.

At these times, a product which our young engineers have never seen was largely used as degreaser: T-111, 1,1,1-trichloroethane. This chemical has been banned since...many years because it is a major cause for ozone-layer depletion (OLD). It is the reference for that, with an OLD effect figure of 1 by definition.

T-111 evaporates very quickly, is not so hazardous for human health, does not dissolves or attack many plastics.

For the absence of the developer, in fact some tests carried out on faulty parts which had been found by a visual inspection showed that the red penetrant bleeding from the crack was very easy to detect against the very clear machined surface.

Therefore, we established the following inspection process:
• Dip parts in T-111 for degreasing (parts were already very clean) (tank N°1)
• Take the parts out. Let dry for about one minute.
• Dip the parts in red-dye penetrant for one minute.
• Let drain for one minute.
• Dip the parts for 10 seconds in T-111 (tank N°2)
• Let T-111 evaporate (10 seconds). No developer.
• Inspect within one minute.
If the part is faulty, a very thin, very clear, unambiguous red linear indication appears.

T-111 in N°2 tank had to be replaced when about 5 baskets of parts had been processed.

Very unusual indeed ... but really efficient in that occurrence!

In the '60s a UK Company had a motto: "For every surface treatment problem, there is a product xxxxxx" (trademark we do not display).

Engineers and Commercial people in this Company had made a "translation": "With every surface treatment product xxxxxx (trademark we do not display), there is a problem".

This anecdote is there only to remind everyone that problems met in workshops may be due to the suppliers/manufacturers as well as to the users.

Our idea in these documents is NOT to target anyone, but on the contrary to bring to your knowledge some interesting cases which may prevent you to duplicate the same mistakes while performing Penetrant Testing (PT) or Magnetic Testing (MT).

All the ministories you will read are TRUE. We think they will be helpful:
• First as examples of specific technical --or non-technical-- requirements or peculiar problems.
• Second to let you see that the problems do not always come where you think they should come from.
• Third so that users feel free to ask for help from people (the experts) who may know more than they do.

Last Updated ( Saturday, 02 July 2011 11:38 )