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Does the MoD need standards?

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10 January 2014

Martin Trigg-Hogarth of Nu-Pro responds to the article in the last issue of Surface Matters:

I am sad to see the passing of the Def Stans but the growth of Nadcap has pushed the AMS and MIL standards to the fore in the aerospace industry.

I have come down on the side of the US style standards as they have a fundamental difference to the Def Stans which in the end makes them easier to live with.

The AMS and Mil standards do not define the chemistry you have to use but rather the testing you have to do to prove you have the desired properties and no harmful properties. An example here would be cadmium plate where you prove you have the right thickness, adhesion, and corrosion resistance and prove you don’t cause hydrogen embrittlement.

The Def Stans took a different view where the process is defined as in the chemistry to use with only minimal testing, eg adhesion and thickness, this is fine if you want to use exactly what is defined in the Def Stan but there is little latitude to use something different and prove it is OK.

There have also been issues were Def Stans have been replaced by other standards such as ISO specifications and something has been lost in the process such as the requirement to dichromate seal in Def Stan 03-26 but in the first line replacement BS 5599 the seal had to specified by the customer and the general properties talked of grey colour coating which would be unsealed or hot water sealed.

This in some ways has brought us closer to our customers, as we have had to ask what they want and in many cases explain what is best for them!

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