When specifying alloys it is sometimes thought that simply requesting supply to ASTM standards will be adequate. However, there are potential corrosion problems that can arise due to incorrect manufacturing. One example is copper and copper alloy tubing for heat exchangers, which may contain carbon films from the manufacturing process that cause pitting in service. Only BS2871 Part 3 specifies that tubes must be free of “deleterious films” in the bore, although it does not specify a test.

Nickel aluminium bronze can have undesirable phases in it that can be rapidly attacked in seawater. To combat this, it is common to specify that the nickel content should be 0.5% or more than the iron content. In addition a final heat treatment after all hot working and welding operations is recommended to restore the optimum microstructure. Neither of these recommendations is included in ASTM specifications.

Similarly, the ASTM requirements for duplex stainless steels are very basic and it is common to also require a low temperature impact toughness test, a corrosion test to ASTM G48 and a microsection at X500 to ensure the quality is adequate and there will not be a premature failure.

Posted on: 7th Aug 2016

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Image (top left) by Agnieszka