Does Heat Treating Metal Change Published ASME Allowable Stress?

[rman487]

I'm running across a code issue that I can't seem to work out. I can look up temperature deratings for allowable stress easily per ASME B31.3 Table A-2. However, if I buy a bolt material (say A354 Grade 8 for example) and I heat treat it by tempering or quenching, would the temperature derating data still apply? If it doesn't apply, how do I find code compliant values to reflect the increase in allowable stress from the results of heat treatment? Thanks.

 

[metengr]

You don't find code compliant values for materials subject to fabrication heat treatment - intentional or otherwise. If you intentionally expose the bolt to heat that alters the original mechanical properties prior to service you must account for this in your design. The allowable stresses are minimum values based on specified heat treatment condition and product form per the original material specification.

 

[rman487]

Ok, so just to make sure that I'm understanding everything correctly; If I heat treat a grade 8 bolt after I buy it, the ASME published values no longer apply? So, in that case, I'd have to calculate bolt strength at temperature? If I'm trying to publish this data somehow for sound engineering practice, will I be allowed to still say the bolt meets ASME code, but has these XXX PSI ratings at temperature higher than the published ASME values?

 

[metengr]

If I heat treat a grade 8 bolt after I buy it, the ASME published values no longer apply?

Correct, if the heat treatment was not part of fabrication. For Section I there is an interpretation on performance of mechanical testing after fabrication to verify original material properties. The reply is no.

In your case if you are subjecting a bolt to heat treatment, which is not part of fabrication, to intentionally alter the mechanical properties, you would not be permitted to use the material.

 

[rman487]

What do you mean permitted to use the material? Use as in stating it meets a certain grade? If I heat treat SS316 to stress relieve a part, will I be able to claim SS316 material properties published in ASME B31.3?

 

[metengr]

What did you do - weld and post weld heat treat or what? 316 stainless steel is not a heat treatable alloy, it hardens by cold working. If you welded or heated the cold worked material you would need to use the lower stress value published for 316 stainless steel.