April 2009

The volatile organic compounds (VOC) and penetrant testing/magnetic testing (PT/MT)

Document updated in April, 2009

Why this updating?

One of our alert readers has just drawn our attention on the fact that the Directive n° 1999/13/CE of March 11, 1999 on the limitation of emissions of volatile organic compounds due to the use of organic solvents in certain activities and installations (OJ L L85 of. March 29, 1999), corrigendum OJ L 188 of July 21, 1999 and corrigendum OJ L 87 of April 8, 2000) was amended by the Directive n° 2004/42/CE of April 21, 2004 on the limitation of emissions of volatile organic compounds due to the use of organic solvents in certain paints and varnishes and vehicle refinishing products.

For your information, we use underneath the SI system for units. Equivalences in other units are given for a better understanding, the pressure unit, Pascal, abbreviation Pa, not being very familiar. Further it is a very small unit: the standard atmospheric pressure is 101,325 Pa.

1- What is a VOC?

By definition as per the European Directive 1999/13/CE of the Council of March 11,1999, in its Article 2, a VOC is a chemical containing at least one atom of carbon and at least one of any following element: oxygen, hydrogen, nitrogen, sulphur, etc. with the exception of carbon oxides and inorganic carbonates, and bicarbonates and any organic compound having a vapour pressure more than 0.01 kPa at 293.15 K (i.e. +20°C/68°F) or having a corresponding volatility in particular conditions of use.

As per article 2 of the Directive n° 2004/42/CE of April 21, 2004, a VOC is any organic compound having an initial boiling point less than or equal to 250°C (482°F) measured at a standard pressure of 101.3 kPa.

PT and MT materials manufacturers face now a huge task to update the material safety data sheets in which VOC contents should be indicated.

The users’ HSE (Hygiene, Safety, Environment) Departments involved in the VOC reduction according to the standard ISO 14001: 2004 ‘‘Environmental management systems -- Requirements with guidance for use’’ of November 2004 have to take into account the new material safety data sheets dealing with all the materials entering their factories to better control their VOC emissions.

2- Is volatile ... volatile?

A 0.01 kPa vapour pressure i.e. a 10 Pa pressure i.e. 1/10,000th of the standard atmospheric pressure is very low. As an example a very common hydrocarbon used as solvent, called "white spirit" in France and naphtha (petroleum), hydrodesulfurised heavy by chemists, CAS N° (its I.D. number) 64742-82-1 has a vapour pressure of 0.2 kPa at +20 °C (i.e. at 293.15 K).

This solvent is quite common in non water-based paints. Do you think it is volatile? A paint layer may require up to 24 hours before drying.

An other example, considering a hydrocarbon which is used in some penetrants and magnetic inks.

This hydrocarbon (CAS N°64742-48-8, EINECS N°265-149-8) has the following distillation range (ASTM D 86 Method):

- Initial point : 230 °C (446 °F)

- 50%  : 245 °C (473 °F)

- 65%  : 247 °C (477 °F)

- Final point  : 270 °C (518 °F)

Its vapour pressure is 0.002 kPa, i.e. 2 Pa at 20°C (i.e. at 293.15 K). So the Directive 1999/13/CE of March 11, 1999 was not applicable, but due to its boiling point lower than 250 °C (482 °F) at the standard pressure of 101.3 kPa, it is now classified as a volatile organic compound according to the Directive n° 2004/42/CE of April 21, 2004 and therefore it shall be taken into account.

The common sense says that a volatile liquid should evaporate within few minutes.

3- PT/MT requirements for volatile products

One of the most important steps in PT is the surface preparation before penetrant application. If ANYTHING is in the discontinuity when penetrant is applied by whatever means, odds are high that the penetrant either cannot enter at all or will enter in such a small quantity that the discontinuity will go undetected.

This surface preparation may require several operations (coating removal, oxide removal or descaling, etc.) but the last and final operation is ALWAYS: degrease.

Degreasing will be the subject of a specific paper of our site. But to sum up, degreasers shall:

- remove any pollutant from the surface AND FROM THE INSIDE OF THE DISCONTINUITIES.

- NOT LEAVE ANY TRACE IN THE DISCONTINUITIES WITHIN MINUTES.

In other words the degreasing agent shall evaporate quite rapidly: it shall be clean, so as not to leave any pollutant in the discontinuities, it shall evaporate rapidly so as to let no residue in the discontinuities.

Two other products shall evaporate rapidly if colour contrast penetrants are used: if a penetrant remover is needed instead of water, it must evaporate within a reasonable time-frame, say 3 to 5 minutes.

And the last product, the non-aqueous wet developer (NAWD) which must arrive on the surface a bit moistened to draw out the penetrant, but must also dry within 1 to 3 minutes. If it dries too slowly indications will become blurred and may even be undetectable after a while as contrast between the less and less red indication and the white background would dramatically lower.

Magnetic testing requirements are generally less stringent. Nevertheless if a white contrast-paint is to be used this additional step shall be short enough not to lengthen the entire inspection. That means this contrast-paint shall dry within very few minutes! Not only dry but not able to retain magnetic particles: really dry!

4- Technical requirements vs health and safety vs environment requirements

Do you think that a "degreaser" which evaporates completely after something as 18 hours is the product of choice before penetrant testing? NO, we are sure you agree.

Several years ago a test was carried out by a renowned PT/MT materials supplier. Several degreasers with very different formulae and technical characteristics were chosen, among QPL - SAE-AMS 2644 approved products, with additional products sold on the French market as "non-flammable degreasers for use previous to penetrant inspection".

This test gave very interesting results.

Why are all the approved degreasers classified as flammable or highly flammable?

Evaporation rate of flammable degreasers is directly linked to the flash point: the lower the flash point, the higher the evaporation rate and the vapour pressure at 20°C. This general rule has very few exceptions.

People who qualify PT materials know that the degreaser's volatility is a very important factor for a reliable PT process. And there is no secret formula: halogenated chemicals (chemicals containing fluorine and/or chlorine) are forbidden, for different reasons (mainly for metallurgical ones, at least that was the main reason for many years); fluorine and/or chlorine atoms generally make the molecules non flammable. So rapidly evaporating non halogenated chemicals are flammable (highly or not is not that important). If a "degreaser" is stated as "non flammable", its flash point is higher than 65 °C (149 °F); it is then free from flammable chemical labelling. Keep in mind that does not mean it cannot burn if there is a fire! For instance heating fuel or diesel gasoline are both "non flammable"!

Some suppliers, not really well aware of what is PT, are ready to supply users with "degreasers" very close to heating oil or diesel gasoline. Did you already try to "degrease" a surface with these chemicals???

When tested with renowned colour contrast penetrant/NAWD, these products, let to dry for 18 hours, led to a sensitivity which is about 35% of the 100% sensitivity got when using a qualified degreaser which dries within 1 to 5 minutes!

The "argument" for these non flammable "degreasers", safety first, is not the right one. When performing an NDT, whatever it is (PT, MT, UT, ET, etc.), the main point is "first detect the discontinuities, by using the least dangerous products/processes/equipments/procedures". It is not "use the least dangerous products/etc., and if we are lucky, we may detect some of the discontinuities".

5- Conclusion

The VOC concept is misleading: a product stated "by law" as volatile may be, by far, not volatile enough for our applications. This same remark is valid when Environment people want products with a low "volatile content". Sorry, but an organic degreaser -- the contrary of a water-based one-- is by definition 100% volatile! A NAWD is something as 75-90%, depending whether it is in bulk or in spray cans. A white contrast-paint packed in spray cans (also in 5 litre tin plate containers but drying so fast if the container is not quickly and thoroughly closed that suppliers generally prefer not to sell it in bulk to prevent complaints!) is something as 60 to 90% volatile!

Quite often Health, Safety and Environment (HSE) people ask for impossible combinations: the user wants a low odour, fast drying, halogen-free product. The HSE people ask for a low volatile content, non-flammable product, free from cancer-inducing, mutagen or endocrine disruptors. Though every requirement taken alone is highly legitimate, all together they lead to impossible tasks.

We have put on the site an MSDS of an oxygenated solvent that a lot of people would not want to use by reading the MSDS. But when they are told it is the water's MSDS ...

We, Pierre CHEMIN and Patrick DUBOSC, welcome any comment, any idea. If you have some examples you would like to see discussed here, please give us all the useful indications. If you require confidentially, we would modify locations, names and some parameters to prevent any traceability.
Nevertheless, we are convinced that our site may be a kind of surge-valve: the topic is NOT to target this company, or that auditor; but it is always to make users think, to make them ask themselves, or others, the right questions.

We may also give advice, once again on a confidential basis if needed: please, feel free to ask questions, to document our data basis: about Material Safety Data Sheets (MSDS), about environment, a chemical name you don't understand, a Penetrant process you have heard about, etc.
We have plenty of examples, some being out of all the specifications/standards, which led to the discontinuities detection, when the "current, normal, processes" prevented discontinuity finding.