Computers and magnetic testing

Once again a story by a veteran!

Imagine our surprise when, some 30 years ago, while personal computers (PC) were still in their infancy, one of us got a phone call from a computer manufacturer: a full load of then very expensive PCs had fallen on the ground from a fork-lift truck while running. Nobody was hurt, but the entire load, which would be today valued at 100,000 € (ca 140,000 USD), crashed and had to be thrown away.

In fact, one of the forks had suddenly broken … with the consequences above-written.

We were asked whether some NDT means might be used to prevent a similar occurrence. Of course, we immediately understood that we were really in our business! Computers or not, the point of interest was the forks … and that is steel … that is easy to inspect with MT!

In France, a yearly mandatory inspection of forks went then as follows: a service company certified by the French government sent an inspector in a truck in which many heavy cast-iron weights would make it easy to perform a load resistance test. On every fork, depending on the maximum load allowed to this fork, the inspector would put one or several cast iron weights and look for a crack appearing in the curved area connecting the vertical and the horizontal branches of the fork. This area is where the strains are maximum when the fork is in use, and it is in this area that cracks, all perpendicular to the efforts, appear, one day. At the very beginning, a crack is so tight that it is not visible to the naked eye.

A mere magnetic testing, performed with a portable electromagnet and either a white contrast paint + black magnetic ink or a fluorescent magnetic ink, is able to alert the inspector within few seconds, even if the fork is not under stress! That means an inspector would reliably inspect far more many forks per day than using the visual inspection with different loads. Nevertheless, this MT inspection is not accepted as a replacement for the mandatory "weight-lifting" process.

However, any company using one forklift truck, or dozens of, has a cheap means to carry out, say, every six months, an inspection "for safety"; this inspection is not "legal" … but so useful!!! This could prevent some accidents. Thus, if a fork is seen with a small crack, such a test may allow for letting the fork in service, provided the frequency of the test is increased - exactly as for aircrafts: when a crack is found, very often, the equipment does not need to be put out of service immediately, but is put under increased scrutiny. Doing so, the equipment may be used safely for additional hundreds or thousands of hours/cycles, hence lowering the costs induced by a non-planned stop, dismantling, replacement.

Keep this in mind: many, many companies use forklift trucks. An electromagnet + the right MT product(s) + the suitable viewing conditions is a very cheap, convenient means for an increased safety. Further, the inspector needs not to be certified as far as he is trained enough by the supplier. This inspection is a very rare occurrence when:
• The location of the likely crack is well known.
• The direction of the crack is always the same.

MT inspection therefore is very easy, quick and efficient.

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.