The auditor and the units

The following story is true - as all the examples we give are!

Do our American friends have a feeling against SI units (units used in the Système International, the International System of units)? (*)

We could think so, when we read the American specifications ... and when we see how sometimes they "understand" the powers of 10. They are prone to use a capital M for "micro" (10^-6) when in the SI a capital M comes for "mega" (10⁶). That means a trillion times (10¹²) less or more!!!

Since something as 30 years kinematic viscosity unit is the m²/s (please our American friends, note that the SI abbreviation for "second" is "s" and not "sec"!!), while American specifications ask for a figure in cSt (centistokes). This unit is obsolete since then, and it is even forbidden in Europe to use it for that reason.

It happens that the figure in cSt and in mm²/s are exactly the same: a 5 cSt kinematic viscosity, or a 5mm²/s kinematic viscosity, it is exactly the same thing.

One of us met a problem some years ago with a European Level 3 PT; this problem longed for more than 3 weeks. This man measured viscosity of a penetrant we thought as a possible replacement for the one he was using. He found a result lower than the one stated on the certificate supplied by us. He made only one test, and concluded we were not a reliable supplier.

We asked several questions:

• Why did the lab carry out only one measurement? We do 5 measurements, delete the highest and lowest figures, and take the average of the remaining 3 to give a figure.

• Which method was used?

• Which temperature was used? How was it stabilised? (viscosity varies rapidly even with a difference of 1°C, 2°F) We stabilise our equipment at +/-1/100°C.

• The applicable specification states a temperature of 38°C +/-3°C (100°F +/-6°F).

• Why your lab would be "better" than ours? Why the "wrong figure" must be the one from our lab?

After 3 weeks of more or less friendly exchanges, the situation was blocked for a while (at least one week) because this Level 3, working after American specifications, wanted that kinematic viscosity figures be written in cSt, while our certificates showed mm²/s. He was stubborn on that! However, we were more stubborn than he was: we said it was not possible for us to issue illegal certificates.

- "But my current supplier does supply me with cSt figures".

- "OK, Sir, your supplier does as he wants, but we stand by our position: no illegal certificate will be issued".

Some time later, we had a better understanding of the situation: this Level 3 was well entrenched with his then current supplier, and tried to find ANY point against the new would-be supplier!

Reference

(*) Pierre CHEMIN and Patrick DUBOSC, MT/PT units: Follow the rules: stop the mess, DPCNewsletter N°026, July 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/dpc-news/2010/149-dpcnews-026-unites-de-mesure-et-grandeurs-physiques

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.