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September / October / November 2015 : Coffee and corrosion inhibitor

Written by Laurence
Saturday, 12 September 2015 00:24

A very interesting-- and funny! – story!

In the late '70s - yes, again, old times! - a French company manufacturing new complex parts for high-performance engines asked for a PT process line. Tests showed that a then Level V water-washable penetrant (equivalent to today's Level 2 of the SAE-AMS 2644 American specification) without developer would be the right choice.

During the very first days, thousands of parts showed rust spots. A meeting with metal specialists made us understand that the washing water was the cause for the problem: when drying in an oven, it let small drops ("the last drop phenomenon") in curved areas, though the oven was ventilated.

It was suggested to add a corrosion inhibitor to the washing water. A very simple, cheap one was tested and found satisfactory: such an additive shall have no influence at all on the fluorescent brightness, on washability, on fluorescent background increase.

Water was not recycled. It was treated in an activated-carbon filter before being sent to the sewers.

We recommended using a very small amount of this viscous liquid in water; the best way would be to have a pump controlled by the water flow. No water used, no additive injected. The rate was set at some mL per litre of water (0.4 oz/US gal).

Everything went smooth for more than two years.

On a Monday morning, 8 am, we get a phone call from the occupational doctor working in the company. Two hours before, when workers took coffee from the coffee-machine, they detected an awful taste. Coffee, and in fact, water from tap could not be drunk.

Maintenance people had to come late on the previous Sunday, as an incident on the water network on Saturday led to a break of water supply. The late Sunday on-site action made water supply returned to normal early on Monday morning.

So, what went wrong?

In fact, on the PT process line, instead of a pump controlled by the water-flow, a pump controlled by a timer had been installed! Cheaper it was.

The trouble is that this plant ran 7 days a week, 3 shifts a day. So water consumption on the PT process line was quite constant. Further, it was still a time when cooling machines with non-recycled water were very common. The Saturday incident stopped any "replacement water" in the network, while the timer-controlled pump continued to push, to perfuse the corrosion inhibitor in the pipes! When, finally, the water supply was restored, this inhibitor was well entrenched everywhere in the network. It dissolved in water, some of this water going to the coffee machines!

Fortunately, this inhibitor was not a danger for human health, especially as quantities taken by the workers had been very small! The taste alerted everyone.

This example shows that not following recommendation from an experienced supplier may lead to unanticipated consequences. This time, the damage was so low that there was no action against nobody-- as far as we know: maybe the "who" who chose a timer-controlled pump instead of the costlier flow-driven one had no salary increase at the end of the year!



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 Particle 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.

If you know of examples of some interest for others, please feel free to mail them to us. They will be displayed on our website as anonymously as those already published.

One's experience may help others. In addition, any interesting problem met during audits may also help: auditors, who sometimes face incredible situations and have hard times, as well as auditees may have very useful pieces of information.

We thank you in advance for any input.

Last Updated ( Saturday, 12 September 2015 00:27 )