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(Part 1)

1- INTRODUCTION:

Many test methods, such as ASTM, and manufacturers' specifications (aerospace, railroad industries, among others) top numerous standards and codes dealing with Magnetic Testing.

Documents listed underneath do not come as an exhaustive list. Further, except for the French AFNOR standards, numbers and dates of issue are not necessarily updated. This applies mainly to all the American documents, which are not used as the main source of requirements in France. Nevertheless we think these pieces of information may help readers to find out the right updated documents they need.

 

2- FIRST GENERATION" FRENCH AFNOR STANDARDS

 

2.1- BACKGROUND

In a way it was a privilege for Pierre CHEMIN and Patrick DUBOSC to be members of the first working groups for Magnetic Testing and Penetrant Testing, be it on the French level ( through AFNOR) or on the European level (through the CEN committee). In these days these engineers were given a wide latitude by their respective companies to spare some time for not-for-profit activity beneficial to the entire PT/MT community. This time was thought of as PR (Public Relations), an investment to be better recognised.

Standardisation in France is a not-so-bad consequence of this not-for-profit thinking. Nowadays, economical conditions make it difficult for engineers to proceed the same way.

We have to consider two types of standards: general standards on one hand and standards for specific applications on the other hand.

General standards are for any industrial application and are a kind of "backbone" for specific applications standards.

Specific applications standards detail NDT processes for different manufactured parts: foundries, cast-iron, steel forged parts, railroad parts, pipes, welding, etc.

2.2- OVERVIEW Only general standards are displayed here.

2.2.1 AFNOR NF-A-09-590 ‘‘Non destructive testing- Magnetic particle examination- General principles” Issued in July 1989, it replaced the NF-A-09-125 issued in January 1982.

This standard was mainly for Magnetic Testing users. General points helped users to suitably carry out inspection; it helped in increasing testing reliability. There was no significant change when compared to NF-A-09-125. Two paragraphs, one titled "references" and the second titled "personnel qualification" had been added.

Members of the Working Group at the origin of this standard came from different fields: schools, training centers, Services Companies, manufacturers and/or suppliers of MT products/equipment.

In Annex D of this standard two test parts were shown, respectively AFNOR nbr 1 and AFNOR nbr 2. Nbr 1 was then already obsolete. Nbr 2 is still widely used in the French Railways (SNCF).

 

2.2.2 AFNOR NF-A-09-570 ‘‘Non destructive testing- Magnetic particle testing- Characterization of products” Issued in July 1988.

Once again this standard helped to increase MT reliability by describing some tests to be performed on the magnetic products.

Physicochemical data were given the user by the manufacturer and/or the supplier. The user was then able to check products on arrival or while in use.

In the '70s we saw in France the first water-based magnetic liquids supplied as concentrates. Carmakers were the vanguard of users.

Indeed on a few months span, several magnetic benches used for high-speed inspection of mass-produced parts, such as connecting rods, went on fire.

Oil-based magnetic inks were then based on a low flash-point hydrocarbon (PMCC fp, i.e. flash point in a Pensky-Martens closed cup), lower than 70 °C (158 °F) when now a 93 °C (200 °F) flash-point is mandatory in these units.

MT manufacturers had to speed up to give users the right answer. Being the first one to market a good water-based magnetic ink would be a tremendous advantage. This led to dubious choices; following are some examples.

a) To prevent steel corrosion, the best way would be to use a pH 11 or more waterbased product. The parts would then be in passivation conditions and would not corrode.

But the operators wore no gloves, even if gloves were recommended. So the maximum allowable pH was 9, and the concentrate formula was to include corrosion inhibitors.

The simplest and cheapest way was to use nitrites (sodium nitrite mainly), which were then largely used in hydrosoluble machining fluids.

Some years later, several research teams discovered that nitrites may react with primary amines and produce nitrosamines, which are cancer-inducing. Operators may face this risk just by eating ham (high in amines) without first washing their hands at lunch break.

So as to prevent use of this corrosion inhibitor, this AFNOR standard required that no nitrites be used; check was made after paragraph 4.22 in which the AFNOR T 90-013 method was mandatory. This method is now replaced by AFNOR NF EN 26777 "Quality of water. Nitrites measuring. Molecular absorption spectrometry method."

Nowadays corrosion inhibitors use in high-quality concentrates are non dangerous, but quite expensive.

b) Surfactants were a major problem: they produced impressive foam! This was more evident on high workpace benches or in the units drawing high amperage. This led to heating due to Joule effect. Foam went out of benches trough hoses, recirculating pumps sucked air or foam instead of the liquid. Furthermore, this foam made the particles float on top, decreasing sensitivity down to almost zero.

To prevent foam the simplest way, maybe the most expensive was to use silicon emulsions as in fabrics (textile industry).

One of the silicon drawbacks is that they are consumed quite fast: add-ons were required as soon as foam reappeared; not very convenient in workshops. Another drawback is that, when parts needed some marking, this marking did not stay on. Worse, when parts were to be painted, paint did not stick on the surface.

Nowadays very efficient antifoams, such as those based on polyalkylenglycol for instance, are part of water-based concentrates.

 

2.2.3 AFNOR NF-A-09-599 “Non destructive testing- Surface control methods (penetrant testing, magnetic particle testing..)- Characterization of ultraviolet light sources” Issued in Oct 1988.

This standard described a method for black light (as said then) sources characterisation and had requirements for checks and calibration periodicity. It was intended to increase reliability of inspection with fluorescent products. Previous to this standard no attention was given to:

- Illuminance when using white light inspection.

- Illuminance (visible light) due to the UV-A sources, when using UV-A.

This method was in no way similar to the then ISO 3059-1974.

In this lSO standard a sensor, similar to the obsolete British Standard BS 4489-1984 ‘‘Method for measurement of UV-A radiation (black light) used in non-destructive testing’’, was described.

The meter is graduated in lux, but it is an indirect way of measuring UV-A irradiance. In fact a fluorescent screen "transforms" the UV-A in green light, and some kind of correlation was established between the lux reading and UV-A irradiance.

This will be the topic of a future DPC NEWS.

 

3. AFNOR EN ISO STANDARDS (2001-2002)

 

3.1 FROM AFNOR TO EN STATUS

Almost every European country has its own standards (DIN in Germany, BS in UK, AFNOR in France...) which were different, requiring different test blocks. The European Union, the unified market made it necessary to harmonise standards, habits. In our NDT area, many European Norms (EN) as they are called took precedent on National standards. Some of them have even won the ISO (International Standard) status.

The French Engineers who worked in the European Working Groups, especially Pierre CHEMIN and Patrick DUBOSC, were then in a very favourable situation to stand up for the AFNOR documents. Our German counterparts asked for a very easy way: the DIN standards would become the EN standards, full stop! As our British friends had a very similar idea for their own standards, we, French, know that without the "1st generation standards" issued in 1988-1989, we would have been unable to balance things.

The French AFNOR (the French acronym for "French Association for Standardisation") had had a very clear understanding of the stakes involved; it took in charge and at its own expenses the Secretariat of the Technical Group CEN/TC138, in charge, among other points, of translating the documents in the three official languages: English, German, French.

These EN have now been adopted by: Germany, Austria, Belgium, Denmark, Spain, Finland, France, Greece, Ireland, Iceland, Italy, Luxembourg, Norway, Netherlands, Portugal, Czech Republic, United Kingdom, Sweden and Switzerland.

 

 

(Part 2)

3.2 AND NOW, TO THE EN AND ISO STANDARDS!

 

Once again, only the general standards are explained in this paper.

 

• EN 1330-1 Standard: “Non-destructive testing-Terminology – Part 1: List of general terms.”
• EN 1330-2 Standard: “Non-destructive testing-Terminology – Part 2: Terms common to the non-destructive methods.”
• EN 1330-7 Standard: “Non-destructive testing- Terminology - Part 7: Terms used in magnetic particle testing.”

 

3.2.1- EN ISO 9934-1 Standard “Non-Destructive testing- Magnetic particles testing- Part 1: General principles” dated February 2002. Supersedes AFNOR NF A 09-590 Standard “Non destructive testing- Magnetic particle examination - General principles” dated July 1989.

 

This standard introduces, besides the training of personnel, the certification according to the standard EN 473 “Non-destructive testing. Qualification and certification of NDT personnel. General principles” and the precautions to be taken because of the surrounding high magnetic fields.

 

Any flux indicator may be used to determine the direction of the magnetic field lines and to give some idea of the intensity of this field. Nevertheless this standard recommends the operator uses a tangential magnetic field meter to check the figure is in the specified range.

 

The different magnetising methods are detailed and their respective advantages explained as well as needed precautions.

 

Once again no mention of permanent magnets! See comments given after the examples about the residual method.

 

The residual method is rarely used. Let us give two examples with explanations:

 

• Inspection of drilling pipe ends (drilling pipes used to find oil and gas deposits, or water tables). The tubes are screwed end-to-end to make the drilling-pipe front go down. The column is regularly taken out of the hole and threads and ends are then inspected by the residual method. In fact the tubes are immersed in the Earth magnetic field and continuously rotate in the same direction; due to the steel formula, they are magnetised and become a kind of permanent magnet. The inspector has only to clean the surfaces, to apply a magnetic medium (quite often: a dry powder, as per the American specifications and habits, sometimes an oil-based magnetic medium). This product is very often visible under white light. Then: inspect! Looked-after discontinuities are quite large (refer to acceptance criteria) and as a result these operating conditions show the simplicity, reliability and sensitivity suitable to the problem.
• Crack detection of discontinuities at the bottom of the thread on screws far smaller than in the previous example with tight screw-thread. The thread shape by itself attracts magnetic particles at the bottom of each "turn" if standard products are used along standard processes. If a crack is there, no chance to detect it! To counter that geometric effect, two alternatives: either by using liquid magnetic inks which contain FAR LESS powder than usual (5 to 10 times less), or use the residual method when the steel allows for. In both cases particles build-up at the bottom of a screw-thread only if there a discontinuity. But then the process is out of any specification!

 

Permanent magnets give a true DC field. But they are scarcely used. Indeed the magnetic lines scatter in the whole part: at the surface the magnetic field is weak. An AC or a HWDC magnetic field shakes the particles easing the build-up of indications and making it easier to see them. This favourable effect is completely missing when using a true DC field.

 

Further even if in theory discontinuities deep under the surface are more easily detected using a true DC field, the fact is that this is more of a delusion. First the "energy sent" to the part from permanent magnets is very small. Second deep discontinuities give rise to faint indications on the surface which needs inspectors with a lot of expertise to be correctly interpreted.

 

Nevertheless, once again, it may be worth to process "out of specs": work in flash-prone areas, in metallic tanks, reservoirs, wagons, lorries (no electric current needed for the permanent magnets; but lighting shall be battery-operated), underwater inspection. In any case it is recommended to inspect only small lengths/surfaces at a time, again due to the weak field. Very small discontinuities cannot be detected. Users must understand the limits of the Magnetic Testing techniques involved so as not to wait for impossible results.

 

And yet permanent magnets are used on a large scale by Services Companies for maintenance inspections, where using electromagnetic yokes is impractical or prohibited for safety reasons, and where proof is given of satisfactory results.

 

However specific precautions shall be taken. For instance permanent magnets may lose part or all of their magnetisation under impacts, high temperatures or if stored without the ferrous plate (keeper bar) in place between the two poles. This plate closes the magnetic circuit and prevents a kind of mutual neutralisation of both poles. Periodic lift test is just specified to detect any loss in "magnetic energy". Further measuring the true DC field is not always possible with a Hall effect probe (due to the electronic circuit's design) nor with the Berthold Indicator nor with the ASME pie gauge: only Castrol strips may give some idea of the magnetising conditions.

 

Permanent magnets come in two sorts: the yoke-shaped unit and the unit comprising two straight magnets connected by a wire. This non magnetic cable can be metallic or much better made of aluminium-reinforced nylon: this is the best way as it is highly resistant to corrosion, has an outstanding sturdiness and a nice aspect.

                                                         

Two straight magnets Model                             Yoke-shaped unit    

 

The yoke-shaped magnet is very handy for inspection of simple geometry parts but its magnetic energy is very low. By contrast the "two-magnet-unit" allows for inspection in very remote areas that cannot be checked with an electromagnet (on-spot weld inspection on bogies for instance). These units are made now from very powerful magnets.

 

Due to the above-mentioned reasons permanent magnets must not be used instead of electromagnets when these latter units are specified, as it is sometimes seen!

 

3.2.2- EN ISO 9934-2 Standard: “Non-destructive testing- Magnetic particle testing-Part 2: Detection media” dated July 2003. Supersedes AFNOR NF A 09-570 Non destructive testing- Magnetic particle testing- Characterization of products” dated July 1988.

 

Three tests are specified:

• Q: Type testing.
• B: Batch testing.
• P: On-site testing.

 

Type Testing is to demonstrate that the product meets all the requirements of this standard and its capability for use. Batch Testing assures users that batch after batch the product has the same physicochemical data as the product used for Type Testing. The Declaration of Conformity to this standard states: test methods, results, acceptable tolerance. On-site test is to be carried out by the user to check that the in-use product still meets requirements.

 

Almost all the tests are similar to those in the AFNOR NF A 09-570. Nitrites are no longer checked as they are supposed not to be in any formula.

 

Reference blocks as displayed in the standard are the result of a compromise between the German side and the French side. The French "Témoin C" has been accepted by the German experts as far as the MTU N°3 Test block from MTU (MAN TURBO MÜNCHEN) was agreed by the French experts.

 

So the MTU Test block is now the N°1 Reference Test Block while the French "Témoin C" is now known as the N°2 Reference Test Block.

 

 

 

N°1 Reference Test Block

 

N°2 Reference Test Block

 

This N°2 Test block is similar to the AFNOR A 09-570 Témoin C. This block had been designed by one of the most important French experts of Magnetic Testing: Michel TOITOT, who worked with Louis NEEL, Nobel Prize for Physics in 1970 for his work on magnetic properties of materials. The French NDT Association (COFREND) awarded Michel TOITOT its COFREND Medal, in 1999, as an acknowledgement of his entire work in Magnetic Testing.

 

The manufacturing process as described in Annex 2 paragraph B.2.2 of the AFNOR standard was improved by a common work of Michel TOITOT and a French Company well known for its MT equipment/products. This Test Block is now reliable, and this company is the only manufacturer in the world.

 

This N°2 Test Block shall be verified every 12 months. Sensitivity of the magnetic media, dry powders, oil-based or water-based is measured in millimeters of an artificial discontinuity as seen under the pertinent lighting. So a figure allows for an easy detection of decrease of performance of an in-use product.

 

The N°1 Test Block allows only for a qualitative assessment of the performance of the product. This N°1 block is not often used in France.

 

3.2.3- EN ISO 9934-3 Standard “Non-destructive testing- Magnetic particle testing- Part 3: Equipment” dated December 2002.

 

This standard gives new clues for users for a more thorough choice of the equipment they need. Equipment suppliers shall provide them with technical data dealing with electromagnetic yokes, current generators, magnetic benches, specific units such as automatic benches, UV-A sources, pump/reservoir/spraying items of the magnetic ink circuit, inspection booths, demagnetization systems, magnetic field meters. The standard states the minimum requirements every equipment shall meet.

 

(Part 3)

 

3.2.4- EN ISO 3059 Standard: “Non-destructive testing- Penetrant testing and magnetic particle testing- Viewing conditions” dated December 2001, which supersedes AFNOR NF A 09-599 Standard “Non destructive testing- Surface control methods (penetrant testing, magnetic particle testing..)- Characterization of ultraviolet light sources” dated October 1988.

 

Writing this European standard led to harsh discussions between the European experts. Further disagreements between European and American experts rose when this European Standard entered the way to become an ISO standard. Here some of the main stumbling blocks are summarised:

 

For inspection under "white light" (natural or artificial) the American experts staid stubborn on the 1,000 lux figure. A 1,000 lux illuminance is usually recommended (as per the CIBSE Code, dealing with indoors lighting, issued in 1984, available from CIBSE. United Kingdom) for acute visual work, i.e. those where indications are 2 to 3 minutes of arc wide against a faint background and which may require some colour identification.

 

A 350 lux figure minimum was written in the French AFNOR A 09-599 standard. The European standard stated a minimum of 500 lux, which had been a main reason for France to vote against the draft. Several works carried out by the French Electricity Board (EDF) and one MT products supplier proved no difference in reliability or in capability of detection between 350 and 500 lux. Further, a 1,000 lux illuminance may be counter-productive when examining machined surfaces with a high reflective index: inspector's eyes may be affected by glare on the surface.

 

For inspection under UV-A radiation (note that the "black-light" word SHALL NOT BE USED...but our American friends have some trouble to delete it from their documents!), some of the German experts asked for an irradiance of up to 50,000 µW/cm². This was specifically for the German car industry, where inspectors may inspect parts without being in an inspection booth--a more "comfortable" situation.

 

The AFNOR standard stated a minimum of 800 µW/cm².The ISO standard requires a 1,000 µW/cm² minimum--everyone agreed, some specifications requiring 1,500 µW/cm².

 

The ISO standard asks for a maximum of 5,000 µW/cm² when using fluorescent penetrants, while no upper limit is specified for magnetic testing. This limit is due mainly to the fading of fluorescent dyes, to the "whitening effect" coming from brighteners used in conjunction with fluorescent dyes in fluorescent penetrants; this effect modifies the colour of the indication under high UV-A irradiance. The colour shifts from a shining green to a bluish/whitish colour indication detection is far more difficult. Green comes in line with the highest human eye's sensitivity, and the contrast of green against a very dark surface is far better for the eye than a bluish/whitish indication against this same very dark surface. Further, with very high UV-A irradiance, glare may also occur with machined surfaces, leading again to a decrease in overall eyes performances. And here we don't think of any of the safety concerns about UV-A for skin and eyes!!

 

The most important new requirement in ISO 3059: illuminance (visible light) shall be less than 20 lux on the surface under inspection. It was also suggested that illuminance at the inspector's eyes level be 20 lux maximum. That was deleted in the final version. The idea was to prevent inspection using fluorescent products in full daylight or in well-illuminated workshop. Nevertheless, this requirement is in the SNECMA DMC 0010 specification.

 

In France many large primes in aerospace industry, in car industry and railways industry required an irradiance of 1,500 µW/cm² minimum at the surface under inspection.

 

One of the main points of disagreement between the European experts and our American counterparts is as follows: no distance between the UV-A source and the surface under inspection is required in this standard when measuring UV-A irradiance.

 

- The basic idea is very clear: measurements shall be done in the REAL VIEWING CONDITIONS, i.e. ALL UV-A SOURCES IN THE "ON" POSITION, AND UV-A SOURCES PUT IN THE PLACE THEY HAVE WHEN INSPECTORS CHECK PARTS. Why would users have to make measurements in "artificial conditions", such as:

 

Measure the visible illuminance on the surface to be inspected when all the UV-A sources are switched off. 5, or 10 or 20 lux max, depending on pertaining specifications.

 

Switch on the UV-A source 10 minutes before the following step.

 

The UV-A source shall be at 15" (38 cm) from the meter's sensor. Find THE POINT (quite often, only one cm²!) with the maximum figure.1,000 or 1,500 µW/cm² required there.

 

Then adjust UV-A source/parts' surface so as to get a 1,200 µW/cm² reading. Then measure the visible light illuminance. 5 or 10 or 20 lux max, depending on pertaining specifications.

 

We think it far easier, and far more consistent to check the real viewing conditions: less paper work, less room for a mistake detected by an auditor--and far more useful, reliable results!

 

The ISO 3059 requires a periodic verification or calibration of the radiometers and luxmeters at least every 24 months. In fact, many specifications ask for a 6-month period.

 

4-AMS (Aerospace Material Specifications) SPECIFICATIONS

 

When all the European aircraft manufacturers and subcontractors rely upon the AMS 2644E specification for Penetrant Testing, the situation is a bit more different when looking at Magnetic Testing (MT). Especially in France--once again, the "French difference"! No one asks for any of the AMS dealing with MT. Some refer to ASTM E-1444 (current issue).

 

Here are the main ASME and ASTM documents for MT.

 

4.1 - AMS 2641 “Vehicle, magnetic particle inspection, Petroleum base” which details the physicochemical data that the Type I (flash point over +93 °C/ +200 °F) and Type II (flash point in the range +60 °C/+140 °F--+93 °C/+200 °F) oil bases shall meet.

 

4.2 - AMS 3040C “Magnetic Particles, Non Fluorescent, Dry Method” details the physicochemical data that dry powders to be used under white light shall meet.

 

4.3 - AMS 3041D “Magnetic Particles, Non Fluorescent, Wet Method, Oil Vehicle, Ready-to-Use” details the physicochemical data that oil-based, ready-to-use, visible-under-white-light inks shall meet.

 

4.4 - AMS 3042D “Magnetic Particles, Non Fluorescent, Wet Method, Dry Powder” details the physicochemical data that colour-contrast powders to be used in a liquid shall meet.

 

4.5 - AMS 3043C “Magnetic Particles, Non Fluorescent, Wet Method, Oil Vehicle, Ready-to-Use, Aerosol packaged” is similar to AMS 3041D, except that it specifically deals with aerosol cans.

 

4.6 - AMS 3044E “Magnetic Particles, Fluorescent, Wet Method, Dry Powder” is similar to AMS 3042D except it deals with fluorescent particles.

 

4.7 - AMS 3045D “Magnetic Particles, Fluorescent, Wet Method, Oil vehicle, Ready-to-Use” is similar to AMS 3041D except it deals with fluorescent inks.

 

4.8 - AMS 3046E “Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle, Aerosol packaged” is similar to AMS 3043C except it deals with fluorescent inks.

 

 

5 – ASME Code: ASME Boiler and Pressure Vessel Code Section V, Non- Destructive Examination, Article 25.

 

 

6 – ASTM METHODS.

 

6.1 - ASTM E 1444 Method (current issue) “Standard Practices for Magnetic Particle Examination”.

 

6.2 - ASTM E109 Method “Procedure for magnetic particle inspection with dry powder magnetic particles”.

This document deals with dry magnetic powder inspection. Dry powders are very often used in the US and in Italy, but in France, except for tube inspection, they are almost never used. A noticeable exception is for high-temperature inspection, from +70 °C up to 300 °C, depending on the type of magnetic particle material and on the dye formulation.

 

6.3 - ASTM SE-709 Method: Superseeds ASTM E709-95 ‘‘Standard Guide for Magnetic Particle Examination’’.

ASTM SE-709 appears in ASME, Section V, article 25-‘‘Magnetic particle standards”.

 

7 – Some specifications from French aerospace primes

For information purpose, let us quote, among others:

 

7.1 - DASSAULT AVIATION:

- "Magnetic Particle Inspection Qualification Requirements Card" DGQT 0.8.3.50 document dated 02/2000.

 

- "Magnetic Particle Inspection Instruction" DGQT 1.0.1.73 dated 03/1999

 

 

7.2 - EADS:

- "Inspection Rules, Metallic elements, Magnetic particle inspection". IGC 04.25.105.

 

- "Inspection Rules, Visual Inspection under UV-A radiation". IGC 04.25.102.

 

 

7.3 - SNECMA (SAFRAN Group): "Directive for Magnetic Testing". DMC 0070.

 

7.4 - TURBOMECA (SAFRAN Group): "Magnetic Testing. Technical requirements" LC 616 document. This document refers to ASTM 1444.

 

7.5 - MESSIER BUGATTI (SAFRAN Group): "Magnetic Testing". IFC 40-932-01 document.

 

 

8 – NUCLEAR INDUSTRY

 

The French Nuclear Industry relies mainly upon one general document: the RCC-M "(Design and construction rules for mechanical components of PWR* Nuclear Islands (*Pressurised Water Reactors)) " Code, written and published by AFCEN (French association for design, construction and in-service inspection rules for nuclear island components) which was created in October, 1980 on the initiative of ÉLECTRICITÉ DE FRANCE (EDF) and FRAMATOME (today AREVA NP).

 

In its TOME III, MC 5000 Magnetic Testing part, Magnetic Testing General Requirements are explained.

 

 

9 –French Railways (SNCF) - The TR 1-004 document gives some clues to SNCF requirements for Magnetic Testing.

 

 

THE END

A survey of Standard and Codes

for Magnetic testing

Part 1

 

Part 2

 

Part 3