Welding Different Grades of Steel in API 650

[Clamont]

What are the rules and/or guidelines in API 650 of the shell plate of a storage tank having different grades of steel? Is there anywhere where it explicitly allows or does not allow this? We want to use a slightly higher grade on the lower courses and then a higher grade steel towards the top of the tank and cannot find any guidelines in the standard.

Thanks in advance

 

[fegenbush]

5.6.1.3 of API 650 specifically allows different shell courses to have different allowable stresses (i.e. different material grades).

 

[IFRs]

It is very common to use higher strength material for the lower courses. If by grades you mean the API groups then it would be somewhat unusual to have a higher group number steel above a lower group number steel but there is no provision against it.

 

[Clamont]

Thank you very much, I have now seen it.