Writing standards and specifications

September 2011

Each of us, with more than 35 years of experience and expertise in designing PT and MT products, having helped so many users, having trained so many Level 3s, and Level 2s in both methods, is quite often surprised by requirements we find in specifications.

We have also a long experience in standards writing, first on the French level, but also on the European level (through the CEN) and on the world level, through the ISO standards.

Therefore, we know quite well how standards and specifications may be written. Standards are always compromises between different customs from several countries, several industries. Performing PT or MT in winter in Siberia or North Canada on tubes for oil or gas search, or on AOG (aircraft on ground) in hot summer in Saudi Arabia or tropical conditions in Venezuela or Indonesia, performing these methods in an air-conditioned unit in France or in Texas on parts manufactured for new aircraft ... all these conditions are very different, and may be not covered by only one standard.

Specifications are a bit easier to write: they apply to a specific industry, sometimes to many different parts (different materials, different heat treatments, different thickness, etc.) but sometimes also to more focused parts, i.e. a small variety of parts.
However, think for a while: how were the specifications written?

I- Who?

Sometimes specification writing is "subcontracted" to the Quality Assurance people last arrived in the Company. "You have a brand-new vision of what we do here; you have been recently trained for spec writing ... that's your job!"

II- How?

How will this "new" person do to write a spec about a process that he or she has no experience in?

The most obvious way of doing is to gather documents (standards, previous specifications, specifications from companies in the same business, etc.) and to dutifully duplicate requirements, figures to be met for viewing conditions, for magnetizing, for washing, drying, calibration, etc.

If we do that way the new document is a "carbon-copy" of what was required 4 to eight years before.

III- Carbon-copy?

However, what about the documents used for this spec issued today? These documents were very likely written the same way: that means, 4 to eight years prior to now, they were based on documents which themselves were, say 5 to 8 years old! We are now about a decade back, with only two steps.

And you could process a similar way for the "previous-to-previous" documents!

IV- Consequences

That is why we still read "black-light" (1) in American documents, instead of "UV-A radiation". That is a minor drawback, yes. However, we see everywhere stupid requirements about water pressure in the pre-wash or in the wash station-we already dealt with this point in a separate document(2). Water temperature, drying oven temperature, are often too tightly restricted for no use.

Documents, specifications, in fact, do not take into account technical progresses/innovations: new, very interesting UV-A sources such as LED may be completely unheard of: only vapour mercury sources are thought about.

As far as we know, many requirements exist about fluorine, chlorine and sulphur content of penetrant materials as delivered. However, penetrants used in tanks: do you ever see any requirement for analysis, say on a 6-month basis? What about a pollution of the penetrant?

We see incredible tough requirements about drying oven temperature; the "overshoot" when the penetrant line is put in service, while there are no parts at all in the oven for at least half an hour (you have to record the temperature just to be sure the oven has not exceeded the set temperature + 8.3°C –15°F while waiting for parts!).

However, have you ever seen any requirements about the washing water, especially when it is recycled? No problem if water is fluorescent, no problem if water is foaming--nothing required, you do not have to check nor meet any figure. However, a fluorescent washing water will let a fluorescent background on parts after evaporation in the ... drying oven. A foaming water means it contains surface-active agents: you are unable to control the washing parameters of the penetrant, or of the mix penetrant + emulsifier. Washing time, washing pressure, water temperature are of no help!!

Don't you think many things shall be thought about when speaking of water and washing for the excess penetrant removal, far more important than the "overshoot" of the drying oven?

Many people should think a bit: what is really important for the Quality Assurance of any Penetrant Testing? Are QUALITY and RELIABILITY improved by putting more and more figures to parameters whose influence on the QUALITY of the results, on the RELIABILITY of the test, is, at a minimum, dubious?

Unfortunately, it seems that the constant tendency of the current world -- more rules, more parameters, more requirements, more documents to fill in -even if not on paper documents-- indiscriminately applies also to an NDT method, Penetrant Testing, which cannot be bordered on every parameter. This worries many people who do not understand why an inspection is still performed using a million-year old system: human eyes + human brain as a sensor + signal processor entity.

V- Standards and specifications future

We agree we cannot proceed without such documents. However, when standards changing is a long process, specifications writing may lead to requirements far closer to what is really useful to achieve a good, reliable inspection. Make work knowledgeable people together with the writers-- this may help!

Reference

(1) Patrick DUBOSC and Pierre CHEMIN, "Black" Light, Editorial of July/August 2011, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/edito/edito-2011/191-juilletaout-2011-la-lumiere-noire

(2) Patrick DUBOSC and Pierre CHEMIN, Penetrant testing: water pressure in the rinsing/washing booths: a myth?, June 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/news/pt-texts/173-ressuage-pression-de-leau-dans-les-cabines-de-rincagelavage-un-mythe-