Trends Affecting Penetrant Specifications and Standards: Beyond 2000

by Ronald G. Sherwin* and Patrick DuBosc⁺

The times they are a-changing. This old saying is not a news flash to most of us in NDT. "Back to Basics" has contained several articles on changes in technology, standards, codes, regulations, materials, etc. Here is another with an international flavor - and an ending paragraph containing some foreboding for the future. Frank A. Iddings Tutorial Projects Editor

 

Introduction
With the year 2000 approaching, it is valuable to assess trends affecting change in the specifications and standards governing inspection penetrants and their related products.

There are two major sets of trends. First are environmental trends involving the materials themselves: mostly their chemical composition, but also their disposal. Second are regulatory trends involving the materials’ manufacture and usage.

Driven mainly by environmental concerns, penetrant products are changing. Less environmentally hazardous or toxic materials are being used in conjunction with penetrant inspection. And there are increasing efforts to minimize the release of penetrant materials into the environment.

Meanwhile, there are conflicting trends concerning the regulation of penetrant manufacture and usage. In the United States the trend is towards decentralization, while in Europe the trend is towards centralization. At a global level, there is also a trend towards more widespread penetrant manufacture and usage, which, itself, has implications for maintaining penetrant inspection standards.

 

Environmental Issues
Best known among the environmental issues affecting penetrant usage is the elimination of 1.1.1-trichloroethane, a chlorinated solvent. The penetrant industry relied for many years on 1.1.1-trichloroethane as a precleaner (in both liquid and vapor applications), as a wipe-off remover, and as a carrier for nonaqueous, nonflammable developers.

 

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The penetrant industry should take steps to alleviate the regulatory confusion it faces.

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In the spirit of the 1990 Montreal Protocol, the US Congress passed the Clean Air Act, under which the US Environmental Protection Agency (EPA) banned the further production of most chlorinated solvents after December 31, 1995. Thus, 1.1.1-trichloroethane, identified as contributing to depletion of the earth’s ozone layer, is banned from further production.

In the penetrant industry, substitutes for 1.1.1-trichloroethane have been introduced. For the most part, they are aqueous, alkaline cleaners, often containing silicates. They typically are used at higher than ambient temperature; there are even means to convert vapor degreasers to alkali cleaning stations.

It is interesting to note that alkaline cleaners are essentially powders dissolved in water, and that water is one of the contaminants whose presence in penetrants must not exceed certain levels. There is irony in that a cleaning material used in one step in the penetrant inspection process contains water, which must not contaminate the material used in the next step.

Thus, penetrant users must guard against carrying water from the cleaning step into the penetrant application step, causing penetrant gel or separation. Users must also guard against water residue remaining in flaws to inhibit the entry of penetrant into the flaws. Most likely, penetrant users will be required to take extra precautions - and time - to ensure that newly cleaned parts are totally free of water prior to penetrant application.

In addition to the need to guard against introducing water into the inspection process, penetrant users need to be alert to another issue concerning aqueous alkali cleaners. This issue concerns the fact that evaporated, water-based alkali cleaners may leave silicate, or other residue, entrapped in flaws to inhibit penetrant entering those flaws.

Clearly, those responsible for establishing specifications and maintaining standards will have to deal with problems arising from substituting aqueous alkali cleaners for chlorinated solvents. Thus, banning 1.1.1-trichloroethane from the penetrant process has introduced other issues which penetrant users must confront.

Penetrant users face additional issues arising from environmental concerns. They stem from introducing penetrant oils and surfactants into the Earth’s water supply.

Despite whatever precautions may be taken, some penetrant material inevitably enters the water supply as unemulsified oils, arising, mainly, from the rinsing of excess post-emulsifiable penetrant from parts prior to the emulsification step, or as emulsions containing penetrant materials and surfactants. In either case, the effluent material will also contain organic dyes and brighteners.

Where more stringent environmental regulations prevail, the principal means for ameliorating the entry of penetrant materials into the water supply includes on-site filtering of penetrant effluent, as is often done in Europe. Or, it includes removing penetrant materials from sewage processed at public treatment facilities, as is often done in the United States.

In the United States there is increasing emphasis on recycling penetrant and penetrant rinse water. Equipment is being perfected which will permit the removal of emulsified and unemulsified penetrant from rinse water, allowing the rinse water to be re-used in the inspection process.

As recycling is perfected, one of the issues which the industry will face concerns the level of residue permissible in recycled water. This matter is particularly important if the rinse water contains traces of emulsifier which could result in the over emulsification of penetrant. Coupled to this should be concern for how much hydrolyzed penetrant can be allowed in recycled rinse water before the rinse water must be replaced.

While awareness of, and sensitivity to, the problems of penetrant materials entering the environment is increasing, there is very little uniformity in the evolution of regulations governing recycling or the disposal of penetrant effluent.

 

New Products
Another way in which environmental issues may affect inspection penetrant usage is in the development of new products. As new penetrant products are developed, it is foreseeable that they will have to be as environmentally harmless as possible.

Moreover, they will have to be non-toxic. Currently, under MIL-I-25135, the formulas for new penetrants are submitted to the Office of the United States Air Force’s Occupational and Environmental Health Laboratory, where their toxicity is evaluated. The Air Force must determine the products to be "non-toxic" in order for them to be placed on the "qualified products list." Confirming that new penetrant products are non-toxic will be a matter of concern to the penetrant industry should the United States Air Force no longer perform this function.

It is also possible that entirely new classes of penetrants may appear, such as products which substitute water for oil. If so, traditional approaches to dwell time, corrosion control, ambient inspection temperatures, and humidity, as well as water concentration, may require examination.

 

Regulatory Trends
Evolving regulatory trends are affecting penetrant manufacture and usage. Currently, there are two conflicting trends in the way governmental, or quasigovernmental, bodies intend to involve themselves in formulating penetrant specifications and standards. The first trend is marked by the US Government’s policy to place the making of specifications and standards in the hands of civilian agencies. The course of events seems to be leading towards a situation whereby individual penetrant manufacturers will have greater responsibility for making sure their materials meet specifications. At the same time, it appears that individual users will have greater latitude in interpreting penetrant usage standards.

Meanwhile, there is another trend emerging in Europe. Whereas European governments historically have not participated in writing penetrant regulations, with the emergence of the European Union the trend is towards greater centralization in writing penetrant performance specifications and usage standards.

 

Trends in US Regulations
The overriding trend involving regulations in the United States involves the government’s intention to hand off responsibility for maintaining penetrant regulations to civilian technical societies. Two societies are involved: the Society of Automotive Engineers (SAE), to be responsible for the specification concerning how penetrants perform, and the American Society for Testing and Materials (ASTM), to be responsible for the penetrant usage standard.

Performance Specifications
Traditionally, the specification on how penetrants are supposed to perform, and, therefore, to some degree, on how they are to be manufactured, has been governed by MIL-I-25135. The responsibility for maintaining MIL-I-25135 is being passed to the SAE, with potentially major implications for how penetrants are qualified under the replacement SAE specification. The SAE document intended to replace MIL-I-25135 is Aerospace Material Specification (AMS) 2644.

One of the key differences between MIL-I-25135 and the AMS specification is in how penetrant materials are deemed to meet performance specifications. Previously, penetrant manufacturers wishing to qualify products under MIL-I-25135 would submit product samples to the Materials Evaluation Laboratory at Wright-Patterson AFB. The lab would test the performance of the candidate product against a standard - the key variables being brightness, sensitivity, and washability. If a candidate product was determined to meet performance standards, it would be added to the military’s list of "qualified products." A penetrant manufacturer could then sell the product, certifying that it matched the performance characteristics of the sample product approved at Wright-Patterson Air Force Base.

Thus, an important step in introducing a penetrant product to the market would be having the product added to the qualified products list (QPL) maintained by the US Department of Defense. Once on the list, the product could be used by Department of Defense contractors and subcontractors, many of whom are major aerospace manufacturers.

However, being on the military’s QPL was merely the main starting point for qualifying a product in the general marketplace. After a penetrant manufacturer had successfully qualified a product for the military, the next step was convincing individual prime aerospace manufacturers to add the product to their own list of approved products, thereby approving the product for their own use, as well as for use by their subcontractors.

In practice the prime United States aerospace manufacturers have required that any products they approve must first be approved at Wright-Patterson AFB and placed on the QPL. Some prime manufacturers even go so far as to say that they will automatically accept any product that has been approved to the military specification.

Arguably the most significant difference between MIL-I-25135 and AMS 2644 arises from there no longer being a single, lead entity to be the custodian of penetrant regulations and to qualify new penetrant products. For the time being, even if the Materials Evaluation Laboratory will no longer be the key player in looking after penetrant regulations, the laboratory will remain the central authority in determining whether a product meets requisite performance standards.

Thus, in the short term, manufacturers will still submit their products to Wright-Patterson Air Force Base for approval and placement on the QPL. Although nobody knows whether, or when, the US Department of Defense might cease being the lead penetrant qualifying agent, it is conceivable that the Department of Defense will one day hand this task to another agency. Should this happen, the global effects on the penetrant industry would be profound.

One way to pass control for qualifying penetrants would be to make individual penetrant manufacturers responsible for testing their own products. Regardless of whether manufacturers tested new products in their own laboratories or used an outside laboratory, a risk would be that the evaluation standards would vary with individual manufacturers. Even worse, without central oversight, marginal penetrant manufacturers may allow their testing standards to diminish, thereby approving products which may not have been approved under the old regime. Thus, central oversight, at least so far as approving products is concerned, is an important element in preserving the actual, and perceived, integrity of the penetrant inspection process.

Usage Standards
Similarly, responsibility for maintaining the US military standard governing penetrant usage, i.e., MIL-STD-6866, is being passed to a civilian agency, ASTM. The new governing document will be ASTM E1417-95a. As with MIL-I-25135, the passing of responsibility for maintaining MIL-STD-6866 to a civilian agency potentially has implications for future penetrant usage.

There are at least two important ways in which the new ASTM E1417-95a could affect penetrant usage. The first stems from differences in the standards for testing the quality of in-use penetrants. Under MIL-STD-6866 penetrant system performance was to be tested on a daily basis, usually by such means as processing a test panel conforming to Pratt-Whitney’s drawing for its "TAM 146040 Test Panel."

Additionally, periodic laboratory tests were to be conducted to confirm continued fluorescent penetrant brightness (quarterly), penetrant sensitivity (monthly), penetrant removability (monthly), and emulsifier removability (weekly). While major penetrant users such as the prime aerospace manufacturers have conducted their own laboratory tests, smaller users have tended to send samples of their in-use penetrants to outside laboratories - usually those of the penetrant manufacturers- for testing and recertification.

Under ASTM E1417-95a the requirement for periodic testing and recertification is waived if daily performance tests are conducted at a penetrant user’s site. While this change alleviates testing and record keeping requirements, it begs the question of whether, in practice, the quality of in-use penetrant will be as carefully maintained as it was previously.

One danger is that with daily system checks operators may overlook gradual degradation in a system’s performance. It is possible that a system may shift gradually from performing acceptably to performing unacceptably without an operator’s perceiving the change. For this reason, at least, it is important to perform the periodic tests, as called for under MIL-STD-6866, and this is what the prime manufacturers are requiring. Whether that continues to be the case remains to be seen.

Another potential effect on penetrant usage arising from ASTM E1417-95a is that, without a centralized agent to resolve issues concerning usage standards and to disseminate information throughout the industry, procedures for using penetrants may vary locally more than they would otherwise. This, in itself, is not bad, insofar as users will be able to adapt usage standards to their local practices. However, inefficiencies could arise when individual users solve problems at their own level without information being shared throughout the industry. This can affect training as well, insofar as training programs will no longer be able to train technicians to observe a single standard, with the potential for leading to confusion regarding the qualifications of technicians nominally trained to a certain level.

The new ASTM E1417-95a is being prepared by the ASTM’S Subcommittee E07-03. The precise differences between it and MIL-STD-6866 are summarized in "Review of Penetrant Method Specifications," by Vilma Holmgren, Magnaflux, Glenview, IL.

 

Trends in Europe
Whereas the United States trend concerning penetrant regulations is towards decentralization, the European trend is the opposite: towards centralization. The move towards centralization is motivated by western Europe’s intention to unify under the aegis of the European Union.

French Tradition
Examining how penetrant regulations have developed in France is instructive, since the process gives some insight into how the procedure for developing regulations in the United States might evolve. In France, individual aerospace manufacturers have taken their lead from the specifications and standards heretofore developed at Wright-Patterson Air Force Base. Using MIL-I-25135, MIL-STD-6866, and the list of qualified products approved under MIL-I-25135, French aerospace manufacturers have issued their own quality control specifications and standards which echo those in the United States.

The regulations for penetrant usage issued by Dassault Aviation, Aérospatiale, and SNECMA are typical. The Dassault and Aérospatiale regulations refer specifically to MIL-I-25135 and QPL-25135, the AÀ rospatiale regulation even going so far as to say that products listed on QPL-25135-16 are a suitable substitute for any product of the same category approved by AÀ rospatiale (AÀ rospatiale, 1995; Dassault, 1993; SNECMA, 1995).

In addition to the regulations issued by individual manufacturers, another agency guiding French regulations is L’Association Fran¸ aise de Normalisation, or "AFNOR." AFNOR issues what are called Normes Fran¸ aises, one of which, NF A 09-521 (AFNOR, 1988), gives guidelines for determining the sensitivity of penetrant products, and for generally using those products. However, the document explicitly eschews identifying approved products, leaving the responsibility for approving and choosing products to individual major penetrant users.

Nominally, NF A 09-521 was prepared by a committee of more than forty members, although one suspects that, in a such a large group, certain members had a greater hand in the committee’s output than others. Regardless of how the committee’s work was distributed, the question arises of how efficient any committee composed of representatives from penetrant users and manufacturers might be, particularly when the representatives must make time for their committee tasks while carrying on their regular work.

Another question may also rise, particularly in the face of the emerging situation in the United States. It concerns whether a committee can keep pace with the need to alter penetrant regulations should factors affecting penetrant usage - such as the introduction of new products, or changes in environmental regulations - begin to change rapidly.

Also arising is a question concerning what guidelines will govern how French aerospace manufacturers will choose penetrant products should the United States Department of Defense no longer maintain its QPL. The answer to this question has implications for the penetrant industry at large.

Europe - Steps Towards Centralization
Movement towards European unification has stimulated centralizing responsibility for penetrant specifications and standards. The key player in this process is the Comité Européen de Normalisation (European Committee for Standardization), or CEN. The CEN members are Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. In practice, the CEN has taken over the function of the International Standards Organisation (ISO), at least so far as formulating penetrant regulations is concerned.

One of the CEN’s goals is to produce a document governing all aspects of penetrants, including physical properties, performance, usage, and in-use testing under a larger umbrella for NDT. The target document will be designated EN-471, "Non-Destructive Testing, Penetrant Testing." EN-471 is still in the process of being formulated.

One important aspect of the emerging EN-471 is its recognition of the need for an examining board to test penetrant products. The draft of EN-471, "Part 2 - Verification of Penetrant Testing Materials," says of the test to qualify penetrant materials that it "...has to be carried out by an examining board (control office) that has neither any relation to the manufacturer nor to the supplier and that is capable to execute the tests necessary...." The idea of having a neutral "examining board," has relevance not only in the European community but in the world at large.

 

Global Penetrant Manufacture and Usage
Traditionally, penetrant usage has been confined to Europe, North America, and certain Asian countries. However, as sophisticated manufacturing becomes more global, there is an increasing tendency for penetrants to be manufactured and used on a wider scale around the world.

This is particularly true in aircraft maintenance and manufacturing, where several countries have established regional aircraft overhaul facilities. It is also true in countries which are expanding native aircraft manufacturing, such as India, Brazil, or China.

Moreover, aircraft maintenance and manufacture are not the only industries where penetrant usage is more widespread. Penetrants are increasingly used around the world in such industries as construction (pipelines and bridges) and plant maintenance (petroleum and chemicals).

In response to these trends, penetrant manufacturers have formed partnerships whereby penetrants are manufactured locally and sold regionally. Where a parent penetrant company does not operate a local penetrant manufacturing facility, penetrants are manufactured and sold under license. In such cases, the parent company provides formulas, technical expertise, and, sometimes, a measure of quality control oversight. Ultimately, however, it is the local manufacturer who obtains raw materials and actually makes the product.

One achievement of which the penetrant industry should be proud is that penetrant products have maintained a consistently high level of quality, resulting in user confidence that penetrant products are reliable. Achieving a high standard of consistency, as manufacturers can attest, is not easy. It requires diligence to ensure that basic materials, such as oils and surfactants, obtained from major materials manufacturers, such as Dow Chemical or Elf-Atochem, are the same over time.

The globalization of penetrant manufacturing and usage may have implications for maintaining the reliability of penetrant products. As far as manufacturing is concerned, it will become increasingly difficult to maintain product consistency when penetrant products are manufactured locally. The major chemical manufacturers produce at different plants around the world what nominally are the same materials. However, those products can vary according to where they have been manufactured. Thus, widespread penetrant manufacturing requires ensuring that a product manufactured in one hemisphere is the same as its counterpart manufactured in another hemisphere.

Similarly, penetrant usage patterns and standards can vary: the standards for training technical personnel can vary, as can the diligence with which in-use products are tested and maintained.

Where the globalization of penetrant manufacturing and usage becomes particularly important is at the nexus of divergent trends in the formulation of regulations. If decentralization of the formulation of penetrant regulations prevails, it will place increasing responsibility for ensuring high standards in the production and usage of penetrant materials in the hands of those who have not, heretofore, performed these functions.

The problems inherent in this situation, should it materialize, will be compounded by the fact that parts manufacturers, as they receive less centralized guidance governing penetrant usage, are likely to issue their own increasingly divergent guidelines which will be difficult to enforce, and, when vague, will be difficult to interpret, particularly at more distant locations. A similar circumstance could arise on the production side as penetrant manufacturers become increasingly responsible for qualifying their own products and issuing guidelines for gaging the products’ performance at the local level.

In contrast is the situation that could arise from a more centralized system. Under increased centralization, there is the risk that specifications and standards will be written without sufficiently considering the practical exigencies of manufacturing and using penetrants throughout the world. Similarly, there is the possibility that global expertise concerning penetrant manufacture and usage will not materialize as quickly as it otherwise would, because a far flung network of manufacturers and users will be less able to influence centralized deliberations.

 

Conclusion
The picture concerning the convergence and divergence of penetrant specifications and standards is one of confusion. And, insofar as the - now global - penetrant industry has an interest in maintaining the integrity of, and faith in, inspection penetrants as a reliable methodology, it is important that the industry work to alleviate the confusion.

In the short run, the move of the US Department of Defense to hand responsibility for MIL-I-25135 and MIL-STD-6866 to civilian agencies appears to be the most significant factor affecting the evolution of penetrant regulations. Under the new regime, there will not be a strong authority to resolve issues concerning penetrant performance and usage. Developing and maintaining penetrant regulations will become the work of committees, inevitably leading to inefficiencies. Disseminating information is likely to become more haphazard.

In the face of decentralization in the United States, and in a discussion of progress in centralizing penetrant regulations under the aegis of the CEN, it was noted that the Europeans have suggested establishing a neutral "examining board" to test penetrant products. In an era when penetrant usage is becoming increasingly widespread, it would be important for users throughout the world to know that a disinterested, and respected, third party had approved a particular penetrant product.

Unfortunately, and assuming one could even be established, having an international penetrant examining board would only be one aspect of resolving the regulatory confusion facing the penetrant industry. With the Department of Defense stepping out of the picture, there will be an international leadership vacuum in maintaining standards. For this reason, it is worth urging that the penetrant industry take steps to alleviate the regulatory confusion which it faces, and which threatens to worsen.

It is easy to urge action, but it is difficult to prescribe what action to take. One useful action would be establishing an international custodian of penetrant regulations, which would also test new products, resolve usage questions, and disseminate information.

Certainly, there are many reasons to recommend establishing such an agency. However, given the current disarray, obtaining from penetrant manufacturers and users throughout the world the cooperation and agreement required to ensure the agency’s success would be a monumental, if not impossible, task.

For now, the most that can be done is sound the alarm that the international penetrant industry faces serious circumstances to which it must adapt. At risk is the reputation for penetrant inspection as a reliable NDT methodology.

 

Acknowledgment
Material for this article was first presented as a conference paper, "The Convergence and Divergence of Penetrant Specifications and Standards: Beyond 2000," by Ronald G. Sherwin and Patrick DuBosc, presented at the 14th World Conference on NDT, December 8-13, 1996, New Delhi, India.

 

References
"Instruction Qualité : Choix des produits de ressuage," Dassault Aviation, Direction de la Qualité Totale, Doc. 1.0.1.20 (Apr. 1993).

"Instruction Générale de Contrôle: Ressuage fluorescent produits qualifiés," Aérospatiale, Normalisation Générale, Doc. IGC 04.25.101 (Jun. 15, 1995).

"Directives Pour Contrôle Ressuage," SNECMA (Société Nationale d’Étude et de Construction de Moteurs d’Aviation), Doc. DMC 0010 (Mar. 15, 1995).

"Essais non destructifs: Ressuage; Sensibilité et mise en oeuvre des produits," AFNOR, NF A 09-521 (Oct. 1988).

 

* Sherwin Incorporated, 5530 Borwick Ave., South Gate, CA 90280; (310) 861-6324; fax (310) 923-8370; e-mail ronsherwing@aol.com.

⁺ Babb Co., 3 Avenue Nagelmackers, Zac du Val Joyeux, 78450 Villepreux, France; [33] (01) 30-80-81-82; fax [33] (01) 30-80-81-99.

 

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