Question: For one of my projects, a designer has specified some HSS frames of A500 Grade 50ksi yield strength. The supplier has proposed an A500 Grade B but this type of steel, as per the ASTM A500 standard, has only a 46ksi yield strength. So I asked him to find A500 Grade C and now he’s responding that when steel suppliers purchase HSS tubes from the mill, both material types are retrieved from the same stockpile, essentially saying that they are the same.

Is that true? Can we go with A500 GrB instead of A500 GrC?

Answer: No. If a designer has specified ASTM A500 Grade C HSS then you must use that grade. It is true that all STI manufacturers in North America will dual-certify their HSS, meaning that it meets both ASTM A500 Grades B and C. If the manufacturer’s test certificate states this, then this product is acceptable for use with both Grade B and Grade C designs. If the manufacturer’s test certificate only states that the product meets ASTM A500 Grade B then it can only be used for Grade B designs.