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January 2011 - Penetrant testing stil shines, with new colours

Written by Administrator
Saturday, 01 January 2011 20:42

Penetrant Testing is not a “dead NDT method”, far from it, as you may have noticed while reading the many papers published, in French and in English, on our purely technical Website, dedicated to PT and MT, established April 2008.

Every month, it is improved by 3 to 6 new papers: editorial, Dpcnewsletter, technical paper, the "oldies but goodies" column and, also, the mail inbox.

So far 114 papers (also available in French) may be read and downloaded.

What is the current situation for PT?

Penetrant Testing is more present than ever in many industries.

Even if it does not draw attention of young engineers - not enough electronics, computing, in most of the PT inspections!
it is obvious that PT changes, day after day:
• Materials usable in conditions inconceivable one decade ago.
• Materials more in line with users’ hygiene and safety concerns.
• More environment-friendly materials.
• Better training and certification of the Level 1 operators, Level 2 inspectors and Levels 3.

Hence a better understanding of the physical parameters of this NDT method, and thus, of its specific requirements.

1- Technical evolution

If high temperatures PT materials, up to ca 200°C (390°F), have been marketed for more than 30 years, the very low temperature PT was considered few years ago only. Materials and propellants are now available for inspection in the -30°C (-22°F) range.

Penetrant testing at extreme temperatures has been endorsed by ISO standards in a way: time has come finally!

Water-based penetrants, mainly fluorescent, make it possible to check numerous non-metallic materials after thorough short-term and long-term compatibility tests.

Viewing conditions: it has to be said that blue and green are two very "trendy" colours in PT.

On the one hand, fluorescent PT inspection under blue light (centred on the 450 nm wavelength) is likely to be more and more used due to its usefulness in specific conditions; nevertheless, the “standard” inspection under UV-A radiation will stay as mandatory for a while.

On the other hand, a supplier recently gave examples of the results from using “green light” to increase the contrast of colour-contrast PT indications as seen by industrial vision equipment.

2- Hygiene and safety

Today materials are very users-friendly - or visitors/auditors friendly-- especially when used according to the safety rules and instructions. In fact, even with materials used 30 years ago, we never heard of chronic disease due to PT materials, when in these “ancient” times, some solvents and non-aqueous wet developers (NAWD) were based on chlorinated solvents classified as toxic nowadays.

True, the chemical without any risk does not exist. We suggest you read the Material Safety Data Sheet (MSDS) of an oxygenated solvent on our Website(*) (**). It will give you some idea of how to read material safety data sheets!

For an efficient PT inspection, using chemical ingredients, such as surface active agents, dyes, solvents (even in the water-based formulae) is a given. It is the duty of the user to choose only among renowned products, and to use them according to the labelling...and to the basic common sense.

3- More environment-friendly materials

Here again, improvements are dramatic: penetrants are less and less volatile. On the other hand, to be effective, the organic solvent removers MUST be very volatile, as the volatile solvent of non-aqueous wet developers shall be.

Surface active agents largely used in penetrants and emulsifiers are no more alkylphenols ethoxylates (APE) derivatives - at least, in Europe. Therefore, these chemicals are no longer thrown away in the rinsing/washing water.

Liquid effluents are often now treated either on site, or by specialized companies. PT effluents are not easy to treat - and many companies renowned in the water treatment area have been confounded by this technical point.

4- Better Training

Oh yes, a better training to the specific PT requirements, be it about the conformance to the requirements for the quality of the surface preparation before PT, for the contact time, for the excess penetrant removal technique, for drying, for the developer application, for the viewing conditions (illumination/irradiance, adaptation time of eyes to darkness), etc., can be only profitable to the quality. In addition, a better knowledge of the method by auditors cannot go against the quality of audits.  All of that adds to the improvement of PT inspections!

We then can avoid remarks by people who know almost nothing about time requirements of the different steps of a PT. Ever heard something as:

"The laws of physics make it necessary that the penetrant stays on the parts for 30 minutes? To decrease that down to 5 minutes, we just need to change these laws!" ???

5- Better understanding of cause for trouble

The PT process lines designers shall be able to resist to " ‘‘pressures’’ from some of their customers:

- "Why do we need two drying ovens, one after the degreasing step, the second one after the washing step? One is enough, we spare room, and it is cheaper!’’

- ‘‘The emulsifier tank releases unpleasant smells, because of bacteria growth? Problem solved if we use ‘‘bactericides!’’

- ‘‘The UV-A booth shall allow the inspector for easily going into and out, as he will bring in the baskets of parts to be inspected.’’

- “Increasing safety in the UV-A booth needs we have more visible light, and a parallel increase of UV-A irradiance.’’

All these claims lead to disputable results. Staff training, at any level, shall comprise these data. The trainers themselves shall be able to explain why these claims are not sustainable.

A conference in Moscow in June 2010 was titled: “Penetrant Testing in 2060”. We wish that many of you will be there to check PT advances!


(*) Patrick DUBOSC and Pierre CHEMIN, MSDS (Material Safety Data Sheet) how to decipher this important document? DPCNewsletter N°006, November 2008.

(**) Patrick DUBOSC and Pierre CHEMIN, The mysterious, dangerous solvent finally cleared!
DPCNewsletter N°007, December 2008.

Last Updated ( Thursday, 19 May 2011 15:21 )