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January-February 2014 : Again and again: Are penetrant testing and magnetic particle testing definitely obsolete NDT methods ?

Written by Dubosc
Monday, 13 January 2014 15:36

Though we have already written, and will write in the future, about this topic, we think it necessary to focus again on this media hype (it cannot be something less than media hype!):


A recently released article, in a French technical journal, may make NDT users believe that the future will be bright without PT and MT, "historical methods" as they are sometimes referred to.

The European REACh regulation, the European Directive 2013/35/EU(1) (2), the “high-tech” society that we have built, using scores of transducers, probes, sensors, mother-boards, computers, smart phones, which may also (as a complementary action only...) be used, a kind of “fear” of many people against everything that includes this awful word – chemical -...should lead to a dramatic decrease in the use of these two basic (at least, they seem so!) and old (that’s true!) NDT methods!

We have to remind, once again, our readers, that in the ‘70s, a person well-known in the – American – NDT world wrote that the manufacturers of this materials/equipment would have completely disappeared by the year 2,000. These methods would have been replaced by electronic means, automatic machines, etc., which would have no need of chemicals.
In fact, the year 2,000 has been tremendous for all the manufacturers of this materials/equipment. Indeed, year after year, during the 2,000 decade, their revenues were up by 12 to 15 %, every year, and by “only”...7 % the “bad years”. These figures almost duplicate the figures of the...Chinese economic growth during these same years. Not that bad!

Well, the results of the past do not foretell the future results. We agree!

PT and MT materials manufacturers have been able to anticipate the regulation changes. In other papers published on our Website, we have told about the water-based penetrants and magnetic inks...which cannot always or completely replace oil-based materials.
Penetrant Testing may be performed on thousands of very small parts, on huge parts (several metres long), on very complex-shape parts, everywhere in the world (except in water), at extreme temperatures (very high: up to 200 °C/392 °F, even higher; deep-freezing temperatures: down to -22 °C/-8 °F, even lower); using rope access on structures such as bridges, gas- or petrol- or chemical-tanks; etc. No need of battery-operated equipment, except, sometimes, for white light (which is anyway necessary with any other NDT method, if performed inside a pipe, for instance) or for UV-A/actinic blue light, when fluorescent techniques are used.

Magnetic particle testing may use hand-held, rather cheap electromagnets, and requires some materials, too. On the other hand, very powerful devices exist, which can handle very long, heavy, complex-shape parts, using, for instance, multidirectional techniques for parts magnetization purpose in a rather short time, while allowing for the detection of all surface-breaking discontinuities and many discontinuities just below the surface on ferromagnetic materials.

Most of the other NDT methods, said to be able to replace soon these two valuable methods, require:


  • Electronic equipment. Right, computer-controlled, programmable logic control (PLC) units, found in many current automated PT process lines and in magnetic benches, are also electronic equipment. However, many on-site PT inspections require only some spray cans, some rags, a good training...and a brain, to overcome any unanticipated situation.
  • Batteries and chargers. Right, there are battery-operated UV-A sources and hand-held electromagnets. The following accessories: luxmeters, radiometers, magnetic-field strength meters, require also batteries and chargers. However, many on-site inspections are carried out, the world over, without such accessories. This is not compliant to standards and many procedures? In some countries, better to do some inspections using any flux indicator and a chain made of paper clips (this latter for checking roughly the residual magnetization), than no inspection at all!
  • A calibration of the process to the specific material/shape of the part to be inspected,

Regarding the environment, some of the opponents to PT and MT consider these NDT methods as polluting, because they need using chemicals.
If we understand them, they would tend to make the whole NDT community believe that "only the theoretical chemistry does not pollute."
They simply forget that there are effective methods of effluent treatment.
It would be fair and square to say that

  • PT and MT may only require treatment effluent and/or waste management.
  • The operators shall comply with the safety instructions stated in the safety data sheets of the materials they use, especially if working in confined area or poorly ventilated atmosphere and even more so when using spray cans. These instructions also apply to people working nearby.

We have recently seen, and written about, some “manufacturers” who claim their materials are (in French) “bio”. In English, “bio” is translated by “organic”, be it for diet or cosmetics, for instance.

Further, many people make confusion between “organic” and “natural”.

Many are those who think that “natural” is always better than “petrochemical”, than “synthetic”, etc.

May we remind them that:

-    The botulinum toxin is one of the most powerful poisons; it is NATURAL,

-    The Belladona contains atropine, which can be deadly (DO NOT eat its berries),

-    The sea wasp (Chironex fleckeri), an Australian jellyfish, can kill an adult within three minutes. No antidote to this NATURAL deadly poison.

Obviously, these NATURAL chemicals are classified as toxic or very toxic. Many of the chemicals used in PT and MT materials are not classified, or are classified as an irritant, sometimes as harmful. NONE is classified as toxic!!!

Both of us have been for so long involved in these two NDT methods that we are, maybe, in a better position than many users, Level IIIs, or even some “manufacturers”, to see the bright future ahead for these two NDT methods.

However, it is the health, safety and the environment (HSE) constraints that led to looking for alternative techniques to penetrant testing and magnetic particle testing.
On not complex-shaped parts, such as wheel hubs, the active infrared thermography allowed to detect some defects that had not been detected by magnetic particle testing.

However, if the TOFD ("Time of Flight Diffraction" or "time of flight measurement of the diffracted wave") technique, coupled or not with the phased array technique, is regarded as an alternative technique to industrial radiographic testing (RT), it cannot compete in terms of reliability and probability of detection with:
- Penetrant testing for the detection of open-to-surface discontinuities,
- Magnetic particle testing for the detection of the surface-breaking or subsurface (under certain conditions, down to some millimetres deep) discontinuities.

Of course, quite often, these alternative techniques are not really suitable for the inspection of complex-shaped parts, or for the batch control of parts of different sizes and/or shapes. Then, penetrant testing and magnetic particles testing keep a distinctive advantage that makes them essential and irreplaceable.


(1)Pierre CHEMIN and Patrick DUBOSC, Low-frequency magnetic fields and exposure of users (follow-up, Editorial August 2013)

(2)Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents electromagnetic fields (20th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC) and repealing Directive 2004/40/EC. Official Journal of the European Union L 179/1 of 29.6.2013.

Last Updated ( Monday, 27 January 2014 20:17 )