Dual (multiple) certification of stainless steel products
Although dual or multiple certification can mean the issue of two separate EN 10204 certificate types for the same inspected / tested or delivered batch of steel, the term normally infers the mention of more than one standard or grade (or both) on the same test certificate.
Where more than one standard is ordered, the chemical (cast) composition and mechanical properties are checked against each of the standard's ranges, for each grade. Often this involves both standard and low carbon variants of the grade being certified together
This form of multiple certification is not recognised by the individual standards organizations. The practice is the result of commercial pressure from stockholders to minimise stock levels for each size range, so that the same piece of steel can be sold to as many standards and grade designations as is possible for the same basic steel composition. These requirements became widespread in the 1980's and is now considered in the stainless steel supply industry as acceptable.
Multiple grade and standard certification
The principle of multiple certification can be illustrated by considering a product that can conform to either 1.4301 or 1.4307.
If the actual carbon content of the steel product is 0.020% it is likely to meet both the full chemical analysis and mechanical property requirements of both steel grade numbers ie 1.4301 and 1.4307 (1.4306 may not be met as the nickel ranges for 1.4301 and 1.4306 only overlap at the top end of the 1.4301 range).
The steel designation (number) should conform to the standard, so where BSEN 10088 is involved the European steel number has to be used ie 1.4307 and 1.4301 in this case and not 304L and 304. These steel designations can only be used if the second certified standard uses these designations, as they for example in American ASTM standards. So '304/304L to BSEN 10088-2' for a batch of plates is incorrect
An illustration of this approach to multiple certification is to mention both standards and grade designations, in an appropriate format : -
BSEN 10088-2 1.4301/1.4307, ASTM A240 304/ 304L
It is important that the steel products multi-certified in this way are not assumed to fully comply with all requirements of each standard mentioned, taken individually. For example it may not be possible for a product to comply with all dimensional tolerance requirements of all the cited (and related) standards. The format of the declared standards should however make this clear. The steel should comply with ALL the requirements of the first (primary) standard mentioned. For standards and grades mentioned after the primary standard only the cast chemical composition and mechanical properties of the products certified can be expected to meet these 'secondary' standards.
There are no universally agreed rules for secondary standard conformance however so it is advisable to check with the manufacturing mill that issued the certificate to confirm the scope of the certified steel properties. This is especially important in a case where separate certificates might have been issued to different standards for the same batch of steel products. Taken individually both these certificates imply FULL compliance of the products with the standards certified.