Insoluble particles in a colour contrast penetrant

End of the '60s.

The tests then carried out on penetrants were far less stringent than today's. Performance tests (somewhat different from the current sensitivity tests) were performed either on real cracked parts or on test panels with artificial defects.

Some companies used the "Aluminum Comparator" as described in the ASME code and in the Annex W of the obsolete AFNOR NF A 09-520 standard, quite easy to manufacture. Note that the "penetrant comparator", described in the Annex A (informative) of the ISO 3452-5 standard, "comprises two blocks to be used as a matched pair which are cut from one piece", this last one being identical to that of the ASME code and the above AFNOR(*) standard.

Only one company in France designed and manufactured, for its own use and its subcontractors', stainless steel test panels. A layer of electrolytic hard chromium on one side; on the other side 3 "prints" of Brinell hardness balls of different sizes/pressures led to 3 star-like cracks on the layered side. Refer to the picture for more information.

These home-made panels were not easy to manufacture and the "rejected" trash-can (dust-bin, for our UK readers) was filled far quicker than the "accepted" can! These panels could not be standardised.

In these old times, a lot of users had a "control on arrival" procedure for almost any raw material/chemical. Quality Assurance systems, "just-in-time" process were not in place.

Aerospace industry was then using colour contrast penetrants in tanks.

Along the drums of penetrant when delivered this company got a half-liter (1/2 quart) as sample for its control lab. Drums were sent to a waiting area; sending them to the warehouse or pouring them into the tank was forbidden until an "OK" notice from the lab.

It happened that, after a delivery, when the lab people tested the penetrant on the chromium-plated panel, during the penetration time, he saw small particles in the penetrant, never seen before! The manager, immediately notified, imagined these particles were dye pigments settling from the penetrant. He checked whether any unusually cold period occurred some days before. Obviously, the problem was due to the penetrant itself.

What did happen?

Manufacturing penetrants, either red dye or fluorescent ones, required a strict procedure to adhere to. Even when using liquid dyes (in these old times, dyes were supplied as powders) stirring all the raw materials needs some time. Then the penetrant (manufactured in huge vessels: 1,800 to 6,000 litres - 480 to 1,600 US gal - 400 to 1,320 imperial gal) shall stay still for, say, two days before being poured into drums through a suitable filter, only to prevent any insoluble particle going in the drums.

The problem may have been due to a "hurry-up" process: too many orders at the same time, customers who need a quick delivery, not enough product stored ...

A well-known story: not to follow a well-established procedure is generally the best way to induce problems!

(*) Editor’s note: AFNOR (Association Française de Normalisation) is the French national organization for standardization. Address: 11 rue Francis Pressensé, F-93571 La Plaine Saint-Denis Cedex (France).
Website: http.afnor.org

Reference

• ASME ASME's Boiler and Pressure Vessel Code (BPVC), West Caldwell, New Jersey, USA, 2010 Edition.

• AFNOR NF A 09-520 Standard, Non-destructive testing – Penetrant Testing – Check of penetrant properties, 1989.

• 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.

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.