Waste-water treatment and Penetrant Testing

July/August 2011

Further to the DPCNewsletter published last month in the ‘‘News’’ section, we have received the underneath e-mail from Alain CARTAILLAC MORETTI, Tech & sales dept Manager in the French PT/MT supplier Babb-Co/Sherwin-Babb-Co:

[Translated from French] ''Here is my comment on your “information” letter: Water treatment: PT, a polluting method.

Now that biodegradable materials certified according to the European OECD Test N°302B(1) are marketed, we can no longer say that PT is the main pollutant; one must keep in mind that, in the aerospace industry at large, many PT processes come after a previous step, surface preparation, often etching, used to remove a layer of few micrometers. This is even a mandatory step if the part went through a prior mechanical treatment. Then, PT is no longer the main culprit, when, more and more, etching processes and their polluting effects and environmental requirements are the main concern.”

To which we answer:
‘‘Thank you very much for your comment that we think of as relevant.

Etching, also known as pickling, is indeed an essential step before PT if the substrate has smeared, as already explained on our website(2). Though this stripping shall meet specific environmental requirements, it cannot be considered as pollutant, as long as its liquid and gaseous effluents are treated.

Surface preparation and PT shall be considered as different steps.
Indeed, some etchings carried out before PT are not done only for PT purposes.
For instance, after stainless steel welding, it is necessary to remove scale (oxides formed at high temperatures) and to passivate again stainless steel.
Similarly, in aircraft maintenance, oxides formed at high temperatures shall be removed in the hot section of aeroengines before repair and any inspection, regardless of the NDT method used.
Further, in maintenance at large, parts shall be cleaned before any inspection, whatever the method used: can any NDT method be carried out on a dirty part? Once again, this is an environmental requirement but effluents due to this mandatory cleaning are treated.’’

Reference

(1) OECD Guideline for testing of chemicals, Zahn-Wellens/EMPA Test, OECD Publishing.
Link:
http://browse.oecdbookshop.org/oecd/pdfs/free/97302b1e.pdf

(2) Pierre CHEMIN and Patrick DUBOSC, Some of the limits to industrial uses of PT, December 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/news/pt-texts/58-quelques-limites-du-champ-dapplications-industrielles-du-ressuage