September 2010 - Are you metric?

Mid ‘80s, one of us was paying a visit to the plant of a large French metallurgical group.

He was told by the man who welcomed him that, quite recently, an American prime asked the question:

- "Are you metric?" which means: ‘‘Do you use the metric system?”

You bet the man was surprised: such a question by an American friend! Americans have not yet accepted the International System even nowadays!

Have in mind that the metric system has been replaced by the “Système International d’unités” (International System for Units), also known as the SI, a modern format of the metric system(1).

About this topic you may read a paper we  wrote:  considered  as  valuable, it has been published in the May 2010 issue of Materials Evaluation(2), and you find it on our Website, DPCNewsletter 026, July 2010.

In the June 21-25, 2010 PRI-NADCAP meeting, held in Singapore, several topics have been talked about, such as:

1) Marking the use-by dates on non-aqueous wet developer (NAWD) spray cans used in PT. This makes us give you some points to think about in our DPCNewsletter(3) of this month.

2) One point of interest is how the tangential magnetic field meters are called in American documents: ‘‘gaussmeters’’! The Gauss is an obsolete unit of magnetic flux density.

The SI unit of magnetic flux density is the Tesla(T). Therefore, if these meters really measured a magnetic flux density, they should be called “teslameters”.

Furthermore, as one of our readers (4) pointed out: ‘‘Since this parameter (the magnetic flux density) is very difficult to measure, it is easier to measure the magnetic field which is tangential relative to the surface of the part; this field is identical on both sides of the surface (internal Ht = external Ht) and gives us an idea of this magnetic flux density ... but, doing so, we forget a characteristic of the material: the magnetic permeability (B = µ.H). We may guess that the figure of the tangential magnetic field should be different on different parts according to their respective materials. For practical purposes, this is impossible, and we are then not surprised to find that different ranges of tangential magnetic field are given, depending on the industries which use MT (Automotive/Railways/Aerospace); this could be understood as due to differences in materials.’’

Therefore, the so-called "gaussmeters", fitted with a Hall effect probe, must be called "tangential magnetic field meters".

3) The ASTM-1444 -05(5) standard requires a “magnetic field” of 30 gauss minimum and no maximum as long as the part is not saturated. Here again, we have to point out the non-conformance of this ASTM document to the SI System.

The document should ask for 3 mT instead of 30 gauss; even better if a minimum tangential magnetic field figure was required.

Our American friends have yet a long way to come to the daily use of the SI, world wide accepted!!

References

(1) BIPM, The International System of Units (SI), 8th edition, Sèvres, France, Bureau International des Poids et Mesures, 2006.

(2) Patrick DUBOSC et Pierre CHEMIN, MT/PT units: Follow the rules stop the mess!, Dpcnewsletter N° 026 – July 2010, Reproduced on our Website with permission of the’©American Society for Nondestructive Testing.
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info

Paper also published under the title: ‘‘MT/PT units: Follow the rules stop the mess!,’’ the monthly journal Materials Evaluation (Volume 68, Issue 5, May 2010) of the ASNT (American Society for Nondestructive Testing). PO Box 28518, 1711 Arlingate Lane, Columbus, OH 43228-0518, USA.

(3) Pierre CHEMIN and Patrick DUBOSC ‘‘DPCNewsletter N° 028 - September 2010, Use-by dates of PT/MT materials, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info

(4 ) Stéphane GRAVELEAU from SREM TECHNOLOGIES, Mail Inbox – August 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info

(5) ASTM, E 1444 – 05: Standard Practice for Magnetic Particle Testing. American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA, 2005.