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Penetrant Testing in 2060

Written by Administrator
Saturday, 17 September 2011 13:39

October 2011
(Updated in May 2011)

Paper presented under the title ‘‘Penetrant Testing and year 2060’’
at the 10th European Conference on Non-Destructive Testing
June 7-11, 2010, Moscow (Federation of Russia)

The first issue of this paper is also available on the following Website:

The text of the first issue of this paper is also available in Russian on request.

1- Introduction

The death of a major NDT method is heralded! In fact, since a famous paper in an American technical journal in 1970, the death of Penetrant Testing is postponed year after year, but it is still a going concern.

Penetrant Testing is by large the most widely used NDT method, and many are the NDT suppliers of other methods ready to step onto this turf! Even ready to replace it with Ultrasonic Testing (UT) or Eddy Current Testing (ET). Nevertheless, PT is still valid, valiant, invaluable and irreplaceable.

All the NDT methods have their own niche; none can replace any other one they use.

True some industries have seen along the years a dramatic decrease of the volumes of penetrant testing materials they use.

Just as an example: many years ago, car manufacturers' subcontractors had to check all their parts, even the non-critical ones, in a time when sampling was uncommon.

Imagine now that the prime did use again PT to check the same parts! That was the way of life! Double-check: a beloved time for penetrant materials suppliers! This time has gone!

PT, that is true, does not seem an "attractive" method for some people and is even labelled as a "minor method" by more and more people.

Penetrant Testing puts many people off:
• Using chemicals which may soil or stain hands, clothes, and further may be bad-smelling.
• Penetrant, solvent, developer used in bad conditions.
• Processing in dirty and badly- maintained installations.

Well, PT gives a bad impression to many. So easier, more pleasant, more comfortable to use an electronic equipment as in UT or ET!

And yet nothing can be done through electronics.

Is PT an NDT method for the future? Oh, yes!

• Every day new manual, half-automatic or fully automatic PT lines are commissioned.

• Every day new users perform a PT inspection for the first time.

2- The products

Performances of the penetrant testing materials currently available are at the level required by all the major industries including nuclear and aerospace ones.

Nevertheless, we may assume materials will change in the future.

The main points are hygiene, safety and environment improvement concerns.

Chemistry engineers have faced many challenges along the years. Here are some examples:

2.1- 1,1,1-trichloroethane

One of the most important challenges. In the '70s, it has been classified as an ozone layer depleting agent.

This non-flammable, low-toxicity solvent was then widely used, not only in NDT, but also in electronics, as THE dry-cleaning solvent of choice, etc.

For PT applications, it was the preferred solvent for degreasing parts before penetrant application; often the solvent used to remove the excess of penetrant from the surface when water could not be used; it was also the volatile solvent of some non-aqueous wet developers (NAWD).

This ubiquitous solvent could be replaced by trichloroethylene for degreasing before penetrant application. Trichloroethylene was used as a vapour-degreaser (except on austenitic steels, on nickel-based alloys and on titanium alloys). Everything seemed perfect...except that:

Trichloroethylene was classified as harmful, in the Council Directive 67/548/ECC dated June 27, 1967 but the Commission Directive 2001/59/EC of August 6, 2001 adapting to technical progress for the 28th time Council Directive 67/548/EEC, modified its classification. Trichloroethylene is therefore now labelled as:

• Toxic with the skull and crossbones symbol displayed.
Plus the following risk sentences:
• R 45 May cause cancer.
• R36/38 Irritating to eyes and skin.
• R52/53 Harmful to aquatic organisms, may cause long-term adverse effects in the aquatic environment.
• R67 Vapours may cause drowsiness and dizziness.
• R68 Possible risk of irreversible effects.

That is the reason why trichloroethylene can be used ONLY as a vapour degreaser in suitable installations meeting all the Hygiene and Safety requirements/standards/laws/regulations.

As for the developer solvent, almost all the manufacturers went to isopropanol (2-propanol) and/or acetone. Some use light hydrocarbons.

As for degreasing before penetrant application, the alternative is to use alkaline degreasers, which may be used on any metal including austenitic steels, nickel alloys and titanium alloys. Alkaline degreasers SHALL BE LOW IN SILICATES as these chemicals adhere to the surface and seal open-to-the-surface discontinuities. When supplied as liquid concentrates, they are easy to mix in water by agitation. On the other hand, powder alkaline degreasers are cheaper but, if poured too fast in water or without beater, they glue at the bottom of the tank giving a kind of cake almost impossible to mix.

Following alkaline degreasing parts should be dried for three hours at 125°C (257/260°F) to remove any moisture which could stay entrapped in discontinuities and would prevent penetrant from entering.

The alkaline degreaser line shall be well apart from the PT line to prevent any water from the degreasing line going into the PT line.

2.2- Chlorofluorohydrocarbons

Known by their acronym CFC they have been banned also due to their action on the ozone layer. They were the best choice as propellents for spray cans. Compressed gases or other liquefied gases are now used as replacement. This topic has been explained on our website (1).

2.3- Glycol ethers

Some glycol ethers of the "E" (for ethylene) series, especially the 2-ethoxyethanol and its derivatives and the 2-butoxyethanol, were used in penetrants by some manufacturers. One challenge was either to completely withdraw any glycol ether from formulas or to replace the "E" series by glycol ethers from the "P"(for propylene) series.

2.4- Endocrine-disrupting substances

At the very beginning of the 21st century the endocrine disrupting substances (EDS) have been another source for concerns: the main target is the nonylphenol ethoxylates (NPE) (2) (3) family and, in fact, the larger alkylphenol ethoxylates family. APE, the acronym for this family is a source of smile for our English-speaking friends.

The European Union has prevented use of NPE in detergents (except when cleaning liquids are recycled or burned) as they are toxic, using them "may have an immediate or long-term harmful effect on the environment or on biodiversity". This means that detergents or any chemical containing these substances even at high concentrations may be used as far as they or their effluents are either recycled or burnt ... This was misunderstood by users of large quantities of such chemicals when hastily reading the Directive.

NPE were used in many water-washable (WW) penetrants as well as in hydrophilic emulsifiers formulas. A large European manufacturer of aircraft engines required that "no product entering our plants shall contain APEs". All the plants had a four-month time-span to comply.

On PT lines, if they meet regulations requirements, liquid effluents are either treated and recycled or collected and burnt. As for the penetrant or used emulsifiers tanks the products are given for a - high! - fee to registered companies able to dispose of the chemicals as per local regulations.

Keep in mind that the Directive allows up to 0.1% of APE in untreated waste-water (which is well above the real figure measured in waste-water coming from rinsing and washing stations when taking into account the concentration of APE in penetrants and emulsifiers and the dilution due to the large volume of water used to remove the excess of penetrant: removing one litre of a Level 2 WW penetrant may require between 400 and 1000 litres of water while a Level 4 post-emulsifiable [PE] penetrant may require up to 4000 litres!).

Nowadays in Europe, most of the WW penetrants and the hydrophilic emulsifiers are free from these chemicals.

In the USA, well, in fact NPE sales are increasing. For our PT business the situation depends on manufacturers; some still have formulation comprising NPE or APE while others anticipate what could be a ban within a decade.

2.5- Volatile organic compounds (VOC)

Many companies in Europe want to be ISO 14001:2004 certified. ISO 14001:2004 standard is THE standard dealing with environment. Among many items, it requires that companies reduce their VOC emissions. Therefore knowing which products contain VOC is the first step.

In PT, several products are classified as VOC emitting: the solvents used as degreasers/removers, the solvent of non-aqueous wet developers (NAWD), but also, incredibly, many penetrants, due to the hydrocarbons which are the basis of their formulas! Keep in mind that a chemical is classified as "volatile" when its vapour pressure at 20°C (68°F) is equal to or more than 10 Pa, i.e ... 1/10,000th of the standard air pressure!

To lower solvents emissions, alkaline degreasing may seem as the right choice. Excess of penetrant may be removed using water instead of solvents. Developers could be either water-soluble or as a powder-suspension in water. All of these alternatives may be used in a workshop, at a pinch, depending on many other parameters. However, they cannot be used for many on-site inspections.

Liquefied petroleum gases (LPG) and dimethylether (DME) are used as propellents in spraycans. They are 100% VOC. One way to lower their emissions would be to use instead compressed gases such as carbon dioxide (CO2) or nitrogen. This topic has been dealt with in one of our papers (1).

2.6- The organic basis of penetrants' formulas

Is it possible to replace the hydrocarbons basis in penetrants' formula?

This topic has been dealt with in a paper (4) on our website.

There are hydrocarbons-free (or almost free) formulas; these penetrants maybe water based, but then the highest sensitivity achieved is Level 2.

2.7- REACH

REACH is the acronym for Registration, Evaluation, Authorisation and Restriction of CHemical Substances.

REACH (5) is a new European Union regulation enforced as of June 1st, 2007.

REACH is designed to improve protection of the human life and of the environment by a better and earlier knowledge of the characteristics of chemical substances. At the same time, this would enhance capability for invention and competitiveness of the European Chemical Industry. The more substances are registered, the more Europe at large will benefit from this regulation, step by step.

The REACH regulation makes the industry more accountable of handling risks due to chemicals and supplying safety information. Manufacturers and importers have to gather pieces of information about the physical, chemical, biological, etc. proprieties of the chemicals. This should allow users to use them safely. Pieces of information shall be registered in a central data basis managed by the European Chemicals Agency (ECHA) based in Helsinki (Finland). This Agency is the "focal point" of the system: manufacturers, users, National Agencies, M.Ds, etc. should find the right information.

REACH asks for a phased replacement of the most dangerous chemicals when safer substances exist.

As of Feb 11, 2009, ca 150,000 chemicals were registered by some 65,000 European companies.

2.8- Global harmonised system (GHS)

The EU regulation on classification, labelling and packaging of chemicals is based on the UN GHS and is now in use.

The UN GHS deals with classification and labelling of chemicals: dangerous products are clearly identified and users are warned through symbols and standardised sentences displayed on labels and Safety Data Sheets (SDS). On Dec 16, 2008, the European Parliament and the European Council approved a new regulation about classification, labelling and packaging (CLP) of substances and mixtures, which harmonise the European Union regulation and the UN GHS.

CLP is in force since Jan 20, 2009. Dec 1st, 2010 is the target date to classify substances as per the new regulation, while June 1st, 2015 is the target date for mixtures. At the end of a transitional time CLP regulation will replace all the previous documents about classification, labelling and packaging of substances (Directive 67/548/EEC) and of preparations (Directive 1999/45/EEC).

2.9 - Study analysis

PT as a whole will need thorough adjustments to meet the current and future requirements without impairing the method's performances; it will still be a major NDT method in 2060, we are confident!

3- Waste-water treatment

We anticipate few changes in this area:

• Waste-water from PT shall be treated as a separate waste from any other waste-water. Waste-water from PT may be recycled if it is adequately treated. If the recycled water contains even small amounts of surface-active agents (surfactants) and if it is used to wash off/rinse parts, there is a major risk that the penetrant be too much emulsified, hence a dramatic effect on the process sensitivity. Quite often, a waste-water treatment installation for PT effluents and the PT line are quite close together and are considered as an entity.

• Activated carbon filters are a good way of treating water. In fact, even when other treatment means are used the last step is an activated carbon filter. There are now many replaceable filters which ease maintenance.

Coalescence filters may be used on post-emulsifiable (PE) penetrants lines to put apart water and non-emulsified penetrants coming from the pre-wash step, previous to the hydrophilic emulsifier’s application.

Here are some other methods that some manufacturers have told of as "THE RIGHT ANSWER" to waste-water treatment.

3.1- Reverse osmosis

Reverse osmosis, as well as ultrafiltration and nanofiltration, uses membranes which are supposed to let clean water go through while stopping all the pollution. You already may anticipate that it is not that easy!

Osmosis is a pressure given by, say, pure water when in contact with water containing soluble chemicals. Clean water "wants to go" to the "dirty water" side to balance the concentration of the dissolved chemicals. It is what happens when a person is in a bath, in a pool. If the person stays for a long time, when he or she goes out, he or she may see the skin has swollen. In fact, the pure water of the pool has been attracted by the blood (which is mainly based on water and 8 g/L of salt): the pure water "wants" to dilute the blood. This is the osmotic pressure.

To purify water, to get clean water, what we want to do is to take out the water from the "dirty water" through a membrane which, ideally, would retain everything except water. To do that, it is necessary to "push" the dirty water through the membrane, to counterbalance the osmotic pressure. That is why this process is called "reverse osmosis".

Every membrane-based process will face the same problems: huge investment, small volumes of clean water available per day, clogging and/or chemical reaction of the membranes. Keep in mind that membranes are in contact with the waste-water which contains penetrant, even at low concentrations, 24 hours a day, and 7 days a week!

3.2- Ultrafiltration and nanofiltration

These two methods are very similar to reverse osmosis, except that they will let some "pollutants" go through the membranes. Therefore, an activated carbon filter is needed as the final step of treatment.

Organic membranes are not prone to clogging -- not too much, by the way. On the other hand, these membranes or the spacers or both react chemically and/or mechanically with the penetrants. Given for a 5-year lifetime membranes generally need to be replaced every year (this maintenance is not easy when spacers have swollen).

Mineral membranes are chemically resistant but are easily clogged. The clean water flow rate dramatically decreases. In no way the "rejuvenating process" as claimed by manufacturers (which needs using of strong acids or alkaline products, which cannot be thrown away in a river or to the sewers) is able to allow for a come back to the nominal flow rate. Once again, though the membranes have been chemically resistant, their lifetime is less than a year.

You may guess the costs are far higher than anticipated.

Another technical point: in these membranes processes powerful pumps are used; a large share of their mechanical power heats water in the installation. So the addition of: water + organic materials + heat + a small amount of oxygen leads to the development of anaerobic bacteria, which increase clogging, but above all produce hydrogen sulphide and thiols whose smelling is really offensive. Further, hydrogen sulphide is very soluble in water and is washed on the parts ... which may be corroded this way!

Membranes, be they for ultrafiltration, nanofiltration or reverse osmosis, are not the right solution from an economical and technical point of view.

3.3- Coagulation and flotation

Coagulation of emulsions, using chemicals such as aluminium chloride (AlCl3), has been in use for decades. Many such chemicals, also known as flocculents, are available. Other methods use flotation by air, or even by an electric current to help coagulation of all the pollutants which become solids. Solids are then filtered. For penetrant application, though not often used, this process gives very good results on some penetrants (it depends on the penetrant's formula). Water coming from filtration must get a final step through an activated carbon filter which lasts a long time, as it has very few pollutants to retain.

3.4- Mechanical compression of vapor (MCV). Biological process

MCV requires huge investments for small quantities of clean water per day.

Biological process (bacteria "eat" the organic molecules and produce mainly water and carbon dioxide) requires enriching the pollutants with phosphorus (as phosphoric acid), nitrogen and compressed air (to bring oxygen to the tank).

These two methods need to be used as planned. By experience we know that, due to the low daily volume of clean water given by these installations when compared with their size and their sophistication, users are prone to use the units beyond their capability...and, therefore, there is a dramatic lowering of the quality of the "clean water".

Furthermore, a biological unit shall run 24/24, 7/7: no weekends, no holidays (vacations, for our American friends).

3.5- Other methods

The other industrial methods are inefficient and have been given up: ozone, ferric perchloride or even hydrogen peroxide as oxidants; PTFE disks with baffles to use the tiny difference of density between water and non-emulsified chemicals; electrolysis has even been tested on waste-water from PT lines ... when penetrants materials give no ion in water!

Keep in mind that the process, which, as if by magic, comprises a dirty water tank, a clean water tank and in the middle a "black box" that no one checks or maintain and that produces no refuse does not exist!  Except for the biological method (which nevertheless produces refuse as "activated sludge" which cannot be thrown away as domestic refuse), a waste-water treatment installation condenses the pollutants ... Sooner or later this "concentrate" shall be disposed of!

4- Indications viewing

Automation in PT deals only with parts processing. Inspection is always carried out by a human being.

Almost all the "black box" systems have failed when trying to replace the human eyes (the sensors) connected to the human brain (the signal processor).

The first test was the Integrated Blade Inspection System (IBIS) designed in the USA in 1978 (6).

In Europe, the first prototype of an automatic viewing system was the AEOS® (7) designed in 1980. Lighting came from an helium-cadmium laser, swinging mirrors allowed for scanning the parts, photodiodes coupled with photomultiplier tubes detected the fluorescent indications and a PC (you may imagine its capability, as compared to today's machines!) was supposed to decide: "accept" or "reject".

In 1985, the Cherry Point (North Carolina, USA) US Navy Air Rework Facility (NARF) bought an automatic Fluorescent Penetrant Inspection (FPI) line comprising an automatic inspection booth to check turbines blades of the AV8-B (8), the American version of the vertical take-off and landing Harrier. Engines were the Rolls-Royce Pegasus 11-61 (F402-RR-408, as per the American jargon). A UV-A radiation source, a high sensitivity CCD still camera supplied data to a computer. The blades were then classified as per the dimensions and the location of the indications. Discontinuities down to 0.25 mm (0.01") were detected.

In the 2000 decade, an American company introduced a system comprising a video camera, a manually adjustable lens and suitable software program.

A French Maintenance, Repair and Overhaul (MRO) company carried out industrial tests. Results were good except that no handling equipment allowed for a quick, reliable handling while minimising the "blind surfaces". It was seen more as a laboratory equipment than an industrial one.

A suitable handling equipment, whatever the viewing system, should allow for:

• Taking every part after the development time has elapsed.

• Showing the automatic viewer sensor all the surfaces to be checked (this is very difficult when surfaces are complicated).

• Classifying the parts according to the results of inspection.

An improvement would be that such a system be able to check very different parts without any recalibration: MRO lines inspect so many kinds of parts!

We have been told this system is supplied to foundries, to car industry manufacturers, to railways industry. As far as we know it is not yet included in completely automatic FPI lines; it may be used primarily as a "filter" previous to human inspection: parts without any indication would go directly to the "accepted" line while those with any kind of indication would go to the inspection booth and be seen by a human inspector. We have no information about its would-be use in aerospace industry.

We are dubious about any automatic viewing, at least for the following reasons:

• What about the wipe-off (rebleed) technique ?

• How to discern between acceptable indications and indications probably due to a discontinuity? A very tiny indication may be a large discontinuity the top of which has been almost closed by a mechanical action. A human inspector could then use a fine sandpaper just to reopen the discontinuity.

• How to "feel" that an area with a background a bit stronger than usual on a casting is in fact an area of non-acceptable porosities?

5- How to make penetrants fluoresce

From the very first days of fluorescent penetrants, they have been designed to have the top of their response curve when excited by a UV-A radiation, at 365 nm. This wavelength is based on the physical effects of an electric arc in mercury vapour. Since the 1880s, this fluorescence effect was well known, though understood only in the 1930s when the theory of quanta was accepted.

Therefore, the "vapour-mercury bulb" as well as some luminescent tubes have been widely used as the source of 365 nm. During the 1990s, another source was marketed, based on very small bulbs in which xenon and traces of mercury give a high UV-A irradiance. For different technical reasons these bulbs failed to replace the ubiquitous vapour-mercury bulb.

The real breakthrough came with diodes able first to give 385 nm, then 370 nm, then 365 nm radiation. Nevertheless, these diodes did not give high UV-A irradiance. However, once again R and D by manufacturers was successful, and powerful 365/370 nm sources are available.

Then, another concern was talked of on a wide scale: UV-A radiation dangers for skin and eyes. Though this has been known for decades (both of us sent warnings around 1985), it suddenly appeared as if the major concern for inspectors safety in PT lines!

Penetrant manufacturers, helped by diodes manufacturers, soon understood that there was an escape way: try 405 nm, then 450 nm diodes i.e. diodes emitting in the violet or blue (respectively) range of the visible spectrum. The fluorescent dyes used in penetrants respond fairly well to these wavelengths. However, at least three drawbacks are facing this solution:

• No standard allows for using any source other than 365 nm ones to excite the dyes of the fluorescent penetrants.

• Violet or blue visible lights ... are visible! Further, they are detrimental to the ability of the inspectors' eyes to detect tiny green or yellow-green indications.

• The fluorescent brightness is lower than with 365 nm. For decades penetrants formula were optimised for 365 nm; and it is therefore easy to understand that these formulae do not have the best response to 450 nm (which seems to be the future standard).

How to counteract?

It is not so difficult ... if changing standards on such an "entrenched" data is easy!!! By experience, we know that years, many years, may be needed before such an important change is accepted. Moreover, during an "interim period" while both would be acceptable, auditors and auditees will have a ... funny time!!! Let us say this is only "policy", and not really a technical point.

The visible light that should not be visible: this is very easy. Inspectors shall wear suitable filtered goggles, as seen in the CSI/NCIS TV series!! (respectively: Criminal Scene Investigation and Navy Criminal Scene Investigation).

The fluorescent brightness drop is in fact the most important problem. Tests have shown that using the current fluorescent penetrants may lead to fluorescent brightness in the 60 to 80% when compared with the figure under 365 nm.

In-use penetrants, when monthly tested for fluorescent brightness, shall have more than 80, and sometimes more than 90% of the fluorescent brightness they had when new. That means in many cases, just by using a 450 nm source, the fluorescent brightness for an unused penetrant will be lower than acceptable for the same in-use penetrant!

The only way is for penetrants manufacturers to redesign formulas, to have them tested and approved by the USAF (at least for the aerospace industry). On the other hand, we are sure that, if the formula is optimised for use under 450 nm, it will then not be optimised for use under 365 nm!  That means it will be forbidden to mix "365" and "450" penetrants; that the PT lines shall be devoted either to 365 inspection or to 450 nm inspection, shall have the suitable penetrants AND the suitable sources, goggles, viewing conditions, irradiance meters, suitable radiometers either for UV-A radiation or for 450 nm radiation, suitable luxmeters, etc! A nightmare for auditees, a source of major non-compliance reports(NCR) issued by auditors, a source of additional revenue for auditing companies which will have to send again auditors to check that NCRs have been dealt with!

The new dyes/brighteners shall be chosen among non-harmful, non cancer-inducing chemicals. Not that easy for chemistry engineers!

The same question arises for fluorescent magnetic particles! If the 450 nm sources become the standard (which is likely), these particles will also need a formula adjustment. An additional problem for manufacturers, as the fluorescent dye (almost all the manufacturers use the same one nowadays) is different from any fluorescent dye used in PT!

6- How to apply penetrant materials

Materials may be very good, if improperly used, the process results are likely to be bad.

Many improvements are necessary to improve current performance.

As a first step, the surface preparation shall remove EVERYTHING that is not the basic metal without impairing neither its mechanical performances nor its fatigue strength. Mechanical processes of surface preparation are generally to be followed by chemical preparation. For instance vibro descaling had been seen as the right answer for turbine blades descaling until proof was given that some defects had not been detected due to metal smearing from this mechanical process.

Easy to understand that surface preparation is more easily achieved in workshop than on-site.

Penetrant application is generally the easiest step in the entire penetrant testing process.

Applying an emulsifier requires some precautions to be taken (9).

Dry powder application is by far the step where numerous improvements should be enforced. (10) (11) (12) (13).

Design of the handling equipment shall be such that the "contact surface" between parts and the equipment be minimised. Further, no surface of any part shall be hidden from products application.

Optimising and enforcing control parameters, PT lines maintenance, checking in-use materials quality/performances are on the same level as quality assurance audits and inspectors training to improve overall performance and reliability.

7- Standards/specifications

7.1- ISO standard 3452-2 revision

The 2006 revision of this standard "Non-destructive testing- Penetrant testing- Testing of penetrant materials" led to a standard which is now close to the SAE-AMS 2644 specification.

Some divergences are noticeable:

• Colour contrast penetrants are classified as Level 1 and Level 2 in the ISO 3452-2:2006 standard using the Type 1 reference blocks (50 and 30 µm) described in ISO 3452-3:1998 standard. The SAE-AMS 2644 specification has only a "pass" "do not pass" criteria on the old ASME aluminium test-block.

• The sensitivity of fluorescent penetrants is determined in ISO 3452-2:2006 standard comparing the "candidate" and the reference product on Type 1 test blocks (50, 30, 20 and 10 µm) as described in the ISO 3452-3:1998 standard.

• There is no Qualified Product List as an annex to the ISO 3452-2:2006 standard.

• No independent laboratory qualifies products.

7.2- The other ISO Standards

• ISO 3452-1:2008: is due to supersede EN 571-1:1997.

• ISO 3452-5: 2008

• ISO 3452-6: 2008

Therefore, there are now standards to help for PT at temperatures lower than 10°C (50°F) and over 50°C (122°F).

The ISO 12706:2009 has been published.

7.3- The SAE-AMS 2644 specification

At the end of 2007 US Air Force WRIGHT PATTERSON Research Laboratory asked every manufacturer to give it an updated list of the products then qualified, still manufactured and that the manufacturer would like to see in the next QPL annexed to the SAE-AMS 2644 specification. The products no longer manufactured would be deleted.

Further, the laboratory gave every manufacturer the new procedure due for service on Jan 1st, 2008. For instance, manufacturers would have to endorse all the costs incurred for qualification.

To begin with, the applicant fills in, signs a questionnaire for AFRL/RXSA department, and supplies it with a 16-chapter Materials and Safety Data Sheet (MSDS).

Then AFRL/RXSA checks the documents and accepts or not that the applicant goes on with the qualification process. If not explanations are given.

Laboratories of five penetrant materials manufacturer as well as an independent laboratory are qualified to carry out some tests.

Another independent laboratory is the only one approved to carry out tests for sensitivity of penetrants, washability of Type 1 (fluorescent) penetrants and bio resistance of water-soluble and developers in suspension in water.

All these laboratories are based in the USA.

Results from the qualified laboratories and data supplied by the applicant are compiled to have the product listed - or not - in the QPL. The applicant gets an official advice.

7.4- Our comments

Europe as well as the rest of the world is happy that the USA stays with the QPL.

As a matter of fact, the aircraft manufacturers require that PT products be listed in the QPL-SAE-AMS 2644; sometimes they issue their own QPL, which displays only some of the AMS QPL products!

The only independent laboratory, in charge of qualification tests (except for sensitivity, washing of Type 1 penetrants and bio resistance of water-based developers) is renowned. For the last three decades manufacturers of chemicals used for surface cleaning (such as: aircraft cleaning, paint removers, etc.) had to have their products tested by this laboratory after the applicable military specifications (MIL specs); if approved the products are listed in the relevant annex of the MIL spec provided that such QPL exists since most MIL specs have no QPL. The manufacturers also pay these tests costs.

Not a bad idea that an independent laboratory be in charge of all the sensitivity and removability tests of Type 1 penetrants. Sensitivity tests have always been carried out on specific series of test blocks (turbine blades with stress-corrosion induced cracks on the leading edge) that only the Wright Patterson laboratory was able to manufacture. We may guess that the reference blocks and their manufacturing process have been transferred to this laboratory.

The penetrants manufacturers have quite often faced troubles getting their penetrants approved for the sensitivity level they targeted. It seems it is one of the reasons for the Level 1/2. It occurred several times that a manufacturer hoped to gain the Level 3 qualification for a WW penetrant, but failed and got only the Level 2. There were even harsher disappointments.

Would it be possible that the ISO 3452-2:2006 standard goes farther to better match the SAE-AMS 2644 specification?

At least one European laboratory should be able to carry out qualification tests (as far it has all the suitable equipments and competent people) as per the ISO 3452-2:2006 standard using the Type 1 reference blocks described in standard 3452-3:1998 for the sensitivity test. Contrary to the SAE-AMS 2644 specification process it is then conceivable to "quantify" the data as Jean VAERMAN (†) (14) (15), from SNECMA, did several decades ago.

What was the process thought by Jean VAERMAN (†)? The four Type 1 panels are processed on a small fully automatic PT line in the laboratory. Then the panels are photographed under specific and reproducible conditions. When the film is processed indications are visible on the negative film itself as parallel lines. The films are scanned by a sensor in a direction perpendicular to the indications at several distances from the edge of the panels. Seven scans results are averaged. Some cracks may appear as dotted lines and preliminary tests led to this figure of seven scans to get reproducible results. Then the ratio of the number of detected flaws and the number of known flaws is calculated for each panel. Finally, the four ratios are averaged, leading to the sensitivity level of the penetrant: Level 2, 3 or 4. This process should be adapted using now digital still cameras.

Both the ISO 3452-2:2006 standard and the SAE-AMS 2644 specification use marketed degreasers, penetrants, emulsifiers and developers as references. This could be questionable if one imagines a reference product shows a light drift in performance along the years. However, no independent laboratory is able to design equivalent products. So better to use widely accepted, high quality, reliable commercial products from different suppliers (all American, as a matter of fact!!).

Another questionable point is that the defects of the ISO 3452-3:1998 Type 1 panels are artificial. Such cracks cannot be compared to real defects. Nevertheless, the SAE-AMS 2644 reference parts display also "artificial defects", though closer to real ones. Another point "against" real defects is that it is very difficult to manufacture reproducible parts.

A last questionable point: would a penetrant qualified, say, as a Level 3 when using cracks induced by stress-corrosion still be a Level 3 if another type of crack had been used for qualification? Every day penetrants qualified on stress-corrosion induced cracks are used to find cracks due to manufacturing/processing of parts.

Nobody says it is not right. However, nobody can suggest a better way to qualify products!

This point is debatable for the future.

8- Conclusion

Hygiene, Safety and Environment concerns and regulations will lead to a ban of some chemicals or to their use on a smaller scale.

Therefore penetrant materials manufacturers will have to redesign numerous products deleting use of chemicals which proved very useful and efficient for decades...but which will be considered as unacceptable.

Very likely UV-A will be replaced by 450 nm light for fluorescent inspection.

The ISO 3452-2:2006 standard and the SAE-AMS 2644 specification should come closer to each other. The American specification is aerospace-applications oriented while the ISO standard is more general. Using a modified "VAERMAN's method" for sensitivity qualification would be recommended.

Inspectors and users training as well as Quality Assurance audits will be irreplaceable for this method reliability.

NEVERTHELESS, THE UTMOST IMPORTANCE shall be given to the "new generation" of engineers, users, inspectors, auditors. Penetrant Testing will be a reliable method for many decades if, and only if:

• The basics of the method are fulfilled: as we have written on our website in an Editorial (16) dated June 2009:

"Manufacturing a yoghourt takes as long a time as it did a century ago.
Manufacturing good bread takes as long a time as it took several centuries ago.
Performing a good PT inspection requires as long a time as it did 40 or 50 years ago, even if penetrants sensitivity is by far much higher, even if viewing conditions are far better".

In this paper, we explain why. Please spare some minutes to have a look at it.


(1) Patrick DUBOSC and Pierre CHEMIN, Propellents for PT/MT spray cans, March and April 2009.
On our Website:

(2) Pierre CHEMIN, Changement de réglementation: une nouvelle ère pour les produits de ressuage (Editor’s note: "Change of regulation : a new era for PT materials"), in the April 2006 issue of the Contrôle-Essais-Mesures Journal (Editor’s note: A French journal dealing with inspection, testing and measurements, published by SOGI Communication, 103 Rue La Fayette, F-75841 Paris Cedex 10, France).

(3) Directive 2003/53/EC of the European parliament and of the council of 18 June 2003 amending for the 26th time Council Directive 76/769/EEC relating to restrictions on the marketing and use of certain dangerous substances and preparations (nonylphenol, nonylphenol ethoxylate and cement).

(4) Patrick DUBOSC and Pierre CHEMIN, Oil-free penetrants, May 2009 (updated in December 2010).
On our Website:

(5) Regulation (EC) N°1907/2006 of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) N°793/93 and Commission Regulation (EC) N 1488/94 as well as Council Directive 76/769/EEC and Commission Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC (L 396, Official Journal of the European Union, December 30, 2006).

(6) De Liberato, Tony J. Perkins, Steven W, Saplin, Steven K, Snyder, John G., Toussaint, Gregory J., Integrated Blade Inspection System (IBIS) Upgrade Study, Air Force Institute of technology Wright-Patterson AFB OH School of Engineering, December 1992.

(7) Pierre CHEMIN, Automatisation de la lecture des indications de défauts en ressuage et en magnétoscopie fluorescents sous rayonnement ultraviolet par un dispositif automatique à balayage électronique et optique, (Editor’s note: Automating the defects indications viewing in fluorescent under ultraviolet radiation PT and MT by an automatic electronic and optical scanning system.), National COFREND (French Confederation for Non-Destructive Testing), Congress on NDT, Paris (France), January 1982.

(8) Pierre CHEMIN, La lecture automatique des indications de défauts mis en évidence par ressuage fluorescent (Editor’s note: The automatic viewing of defect indications detected by fluorescent PT), N°143 bis of the Revue Pratique du Contrôle Industriel (Editor’s note: French Practical Journal of Industrial Inspection), March 1987.

(9) Patrick DUBOSC and Pierre CHEMIN, Post-emulsifiable penetrant testing: hydrophilic emulsifier, DPCNewsletter N°001, May 2008.
On our Website:

(10) Patrick DUBOSC and Pierre CHEMIN, Report and comment on ASNT Fall conference and quality testing show in Charleston, South Carolina, USA, november10/14, 2008, Dpcnewsletter N° 008, January 2009.
On our Website:

(11) Patrick DUBOSC and Pierre CHEMIN, Apply dry developer the right way, DPCNewsletter N°004, September 2008.
On our Website:

(12) Patrick DUBOSC, Dry powder application - The French Paradox, ASNT Fall Conference and Quality Testing 2002, San Diego, California, USA, November 4-8, 2002.

(13) Lisa BRASCHE, TNT supplement, Materials Evaluation of January 2008 issue.
Materials Evaluation, 1711 Arlingate Lane, PO Box 28518, Columbus, OH 43228-0518, USA, 2008.

(14) Jean VAERMAN (†) Fluorescent Penetrant Inspection Process. Automatic Method for Sensitivity Process, 11thWorld Conference on NDT, Las Vegas, USA, November 1985.

(15) Jean VAERMAN (†), Fluorescent Penetrant Inspection, Quantified Evolution of the Sensitivity Versus Process Deviations, 4th European Conference on Non-Destructive Testing, London, United Kingdom September 13-18, 1987.

(16) Patrick DUBOSC and Pierre CHEMIN, Yoghurt, bread, PT: for the attention of the PT young users, Editorial June 2009.
On our Website:


• EN 571-1:1997 Non-destructive testing - Penetrant testing – Part 1: General principles, Committee for Standardization, Brussels, Belgium, 1997.

• ISO 3059:2001 Non-destructive testing - Penetrant testing and magnetic particle testing - Viewing conditions, International Organization for Standardization, Geneva, Switzerland, 2001.

• ISO 14001:2004 Environmental management systems - Requirements with guidance for use, International Organization for Standardization, Geneva, Switzerland, 2004.

• SAE-AMS 2644E: Inspection Material, Penetrant, Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, Pennsylvania 15096, USA, 2006

• ISO 3452-2:2006 Non-destructive testing - Penetrant testing - Part 2: Testing of penetrant materials, International Organization for Standardization, Geneva, Switzerland, 2006.

• ISO 3452-3:1998 Non-destructive testing - Penetrant testing - Part 3: Reference test blocks, International Organization for Standardization, Geneva, Switzerland, 1998.

• ISO 3452-1:2008 Non-destructive testing - Penetrant testing - Part 1: General principles, International Organization for Standardization, Geneva, Switzerland, 2008.

• ISO 3452-5:2008 Non-destructive testing - Penetrant testing - Part 5: Penetrant testing at temperatures higher than 50 degrees C, International Organization for Standardization, Geneva, Switzerland, 2008.

• ISO 3452-6:2008 Non-destructive testing - Penetrant testing - Part 6: Penetrant testing at temperatures lower than 10 degrees C, International Organization for Standardization, Geneva, Switzerland, 2008.

• ISO 12706:2009 Non-destructive testing - Penetrant testing - Vocabulary, International Organization for Standardization, Geneva, Switzerland, 2009.

Last Updated ( Saturday, 14 January 2012 08:04 )