The production and testing of S355 plates is quite different to SA516 Grade 70. Some main differences:
1) SA 516 requires a fine grain steel. Most of the S355 grades are not necessarily fine grain treated, e.g. the most common S355J2.
2) The limitations for the chemical composition between SA 516 and S355 are quite different. E.g. SA 516 limits the Nb(Cb)-content to 0.02%. Or most S355 grades are Nb-alloyed to meet the carbon-equivalent limitations of EN 10025.
3) SA 516 requires a reduction ratio (slab thickness to plate thickness) of 3.0:1 for strand cast (or other metallurgical and testing measures). This is not required for S355. In material certificates, the reduction ratio is usually not indicated, so not available to the client.
4) SA516 requires other dimensional tolerances, e.g. an under tolerance in thickness of max. 0.3 mm. S355 is generally delivered with dimensional tolerances according EN 10029 class A, which allows under thicknesses between 0.3 and 1.3 mm depending on the nominal plate thickness.
5) For surface condition of S355 grades EN 10163 applies. This standard is less severe than SA 20. E.g. Surface imperfections need not to be grinded up to a depth depending on nominal thickness (0.2 to 1.5 mm). Grinded areas may have a thickness under the minimum thickness (0.3 up to 2.2 mm depending on nominal thickness), not allowed for SA 516.
6) SA 516 requires a furnace normalising for thicknesses over 1.5 inch, or for all thicknesses if impact tested. S355 is produced either as-rolled (e.g. S355J2+AR), thermomechanical rolled (S355M) or normalised (S355J2+N, S355N). Normalising can be done either by normalising rolling or furnace normalizing. If normalised, only the letter N is indicated in the certificate. Usually the client is not able to identify if furnace normalised or normalising rolled. Normalising rolling is considered by ASME not to be equivalent to furnace normalising, in contrary to EN.
7) For normalised plates, ASME requires the indication of temperature and holding time in the certificate. This is not required by EN 10025 and usually not done.
8) SA 516 requires testing per plate-as-rolled, S355 requires testing per lot (heat and 60 t). Depending on plate thickness a plate-as-rolled often weights less than 10 t.
9) The form of test specimen is different in both Standards. E.g. flat tensile specimen need to have full thickness in ASME whereas EN allows a machining down to a thickness of 30 mm.
10) S355 requires the determination of the upper yield point (ReH), SA 516 requires the determination of yield strength either by the 0.2% offset or by the 0.5% extension under load method.
11) S355 requires the determination of the proportional elongation A5, SA516 requires the determination of non-proportional elongation A2" or A8"-
12) If impact tests are required, the hammer radii are different (2mm vs 8 mm).
Another 10 differences can easily be found.
Sure, it is possible to produce a multiple grade SA516-70/S355J2+N. In this case, the manufacture has to produce to the most stringent requirements of both standards. The production and testing costs are always higher than the costs of the most expensive of the different grades (SA 516-70). Nevertheless multiple grades can be profitable for a stockholder as he may save to stock the individual grades.
