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Regularly clean your PT materials tanks!

Written by Administrator
Saturday, 14 April 2012 15:43

End of the '70s: an unfortunate incident happened in a penetrant tank of a major aerospace company.

The 4,600 litres (1,200 US gal or 1,000 Imperial gal) tank contained a post-emulsifiable (PE) fluorescent penetrant listed at Group VIB in the QPL (Qualified Products List) of the MIL-I-25135C(1) specification, then in force. This specification has been later replaced by the SAE-AMS 2644 one.

Note that the Group VIB of the MIL-I-25135C specification used then would correspond to a penetrant classified as Type 1, Method D, Level 4 in the SAE-AMS 2664 specification or in the ISO 3452-2 standard.

Parts accidentally felt to the bottom of the tank.

The inspector had to check the process line using nickel-chrome test panels (10 and 20 µm), nowadays called Type 1 reference test blocks of the ISO 3452-3:1998 standard. The inspector was unable to see the cracks indications that he had seen perfectly the day before.
The Quality Assurance Manager was immediately notified. He decided to ban using this penetrant tank until further notice, and he called the manufacturer/supplier Technical Services.

This call focused on the fact that the tank, without any lid, had not been cleaned since a long time. As a consequence, when parts fell down, the mud accumulated on the bottom was put in suspension in the penetrant. This made it impossible to find the cracks on the reference test blocks.

The supplier recommended following this process:
• Let the tank still for several days, to allow for the settling of the sludge,
• The top layer of the clean and transparent penetrant was then to be pumped out of the tank and transferred to clean dry drums,
• The "cloudy" penetrant was to be pumped out of the tank and transferred to reconditioned drums for a further disposal by a suitable licensed facility.

On the tank bottom of the tank, sludge was found, as anticipated, along with cigarette butts, empty beer bottles (then, smoking and drinking alcohol in workshops was not yet forbidden) and other different items!

Sludge had been "produced" by all the solid and/or volatile particles/substances in suspension in the workshop air. Not only they gathered in the penetrant, but some particles may also be "glued" by some ingredients of the penetrant. As for cigarette butts, empty beer bottles and other items, this had more to do with unacceptable behaviour by some people.

The tank was then thoroughly cleaned and dried. The recovered clean and clear penetrant was poured back into the tank, while an add-on of brand new penetrant made it for the right level.

The inspector processed again the same test panels through the process line and easily saw that the cracks indications matched the reference pictures’ ones.

However, for almost a week this process line has been out of service, with easy to understand consequences on the output.

This is why we recommend to clean regularly thanks of penetrants, but also tanks of hydrophilic emulsifiers, the periodicity depending on the working conditions: for example, once a year, for penetrants, or more often (in foundries, especially), and on request for emulsifiers. Cleaning may be carried out during long week-ends or shutdown/holiday time. Further, operators shall be reminded that PT materials tanks are not dust-bins (trash-cans, for our American readers.) 


(1) Pierre CHEMIN and Patrick DUBOSC, The specifications which changed the penetrant materials, August 2008, document completed and updated in April 2012: On our Website.

Normative references

• American Military Specification MIL-I-25135C (ASG), Inspection Materials, Penetrants, Amendment of September 12, 1979.

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

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

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, 15 September 2012 15:25 )