Yield strength vs tensile strength for grade number

[salmon2]

Hi, hope all is well.

I am interested to know why the grade number sometime refers to yield strength; but sometime tensile strength.

Such as ASTM A516 Gr70, its TS is 70ksi and YS is only min 38ksi. On the other hand, ASTM A572 Gr65 means the min YS is 65ksi. I have to say, from where I have worked, oil and gas, GR numbers means YS for 99% of time because most time design is per YS and no plastic deformation is allowed. GR = TS is really rare. I would like to hear your comments on this and also curious on the fundamental reason on why it is one way or another. Thanks.

 

[phamENG]

For that particular example, you're looking at steel intended specifically for pressure vessels. I've never designed one and don't plan on it, but as I understand it the yield point is important but not generally the limiting factor. You want high ductility and plastic properties to allow for equal stress distribution through the shell, high fracture toughness, and the primary design strength comes from the tensile strength.

 

[Geoff13]

SA516-70 is primarily used for pressure vessels. In the case of ASME Section VIII Division 1 the ambient allowable for carbon steels is typically limited by TS/3.5, so for SA516-70 the ambient allowable is 70/3.5 = 20 ksi. There is also a limit of 2/3 YS, but this would be 25.3 ksi in this case.

I guess I use so many steels where the grade means nothing I just consider them to be arbitrary names. SA204 Grade A, SA240 Grade 304L, SA387 Grade 11 Class 1, SA537 Class 2, etc.

A572 is a structural grade of steel, and I have no familiarity with those steels.

 

[dik]

As alluded to above, I suspect the value depends on those using the material and what properties are being used.

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-Dik