How to rejuvenate a colour contrast penetrant

In the '60s a British military aircraft engines manufacturer subcontracted some business to a French manufacturer.

In these old times some military engines casings were made of magnesium alloys castings.

To avoid any discrepancy in control a colour contrast penetrant, so-called "Bristol-type", had been standardised in the Bristol (UK) plant - hence the name! - and in the French plant.

In these old times colour contrast penetrant testing (PT) was quite often used in aerospace industry while fluorescent PT was thought of as too sensitive! Beginning '70s fluorescent PT was seen as the PT method of choice, instead of the colour contrast technique, for aerospace use.

Colour contrast penetrants were often used in large tanks, an unusual way of doing nowadays. Further no specification asked for a flash point (FP) figure, as is the 93°C (200°F) minimum as per the Pensky-Martens closed cup (PMCC) method required in the American SAE-AMS 2644E specification(1) (2).

This "Bristol-type" penetrant showed a PMCC flash point of only 41°C (106°F).

When used in a tank this penetrant was prone to have a high evaporation rate of its volatile materials, especially in Summer when parts still warm from trichloroethylene vapour-degreasing were immersed in the penetrant.

Indeed this penetrant comprised a somewhat volatile and flammable alcohol which, when evaporating, carried along it some of the aliphatic hydrocarbons whose FP PMCC was ca 70°C (158°F).

As already explained in a paper on our Website(*) this evaporation leads to an unbalanced formula of the penetrant with the underneath consequences:
• A higher viscosity, hence a higher penetrant consumption due to the higher drag-out from the parts.
• A higher background on the surface of the parts.

Operators counteracted this higher background by overwashing parts while this penetrant was not at all overwash resistant! This situation brought cases of non-detection of flaws, led to a lower sensitivity and a loss of confidence in the method reliability.

To avoid such inconveniences the penetrant manufacturer designed a "rejuvenating agent" for this penetrant which was called "Solvent Additive for Penetrant".

This additive was a mix of the alcohol and the hydrocarbons used as the basis of the formula. The alcohol/hydrocarbons ratio was calculated as a function of their respective evaporation rates.

Keep in mind that "rejuvenating" penetrants in tanks was then a common habit.

On a regular basis the user sent a sample of the in-use penetrant to the Technical Support Lab of the supplier/manufacturer.

This laboratory then distilled the sample following the required safety rules as the penetrant was flammable.

Knowing the volume of the in-use tank of penetrant and what was left of the alcohol and hydrocarbons in the penetrant the supplier/manufacturer then sent the user the right quantity of the additive to be poured in the tank.

Once the mix done the user used test panels to check the parameters of his "rejuvenated penetrant".

These test panels were stainless steel based. A layer of electrolytic hard-chromium on one side, 3 imprints from a Brinell hardness machine made by 3 different balls giving different diameters/pressures on the other side; these imprints broke the hard-chromium layer giving rise to 3 "star-like" cracks whose dimensions are stated underneath:

These dimensions are far greater than those found on the TAM panels (PSM-5) ®.

You may be somewhat surprised by this way of doing but it was by the rule book!

Nowadays penetrants used in tanks do not evaporate so fast, by large, and they do not need such an "adjustment". We may think that Quality Assurance would not clear such a way of doing as penetrant is so all-important for quality and reliability of Penetrant Testing.

References

(1) Patrick DUBOSC and Pierre CHEMIN: The Specifications which changed the penetrant materials, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/news/pt-texts/162-les-specifications-qui-ont-change-les-produits-de-ressuage

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

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.