"316 and 316L interchangeability"

Question:

"The ASME III code allows the use of AISI316 in aqueous applications where welding will take place (not necessarily with a PWHT). Theory indicates that for carbon concentrations above 0.03% sensitisation can occur resulting in IGA. The 316L grades would be suitable for applications where the component will be welded. The use of the 316 (welded and no PWHT) in pressure retaining applications seems to be inconsistent with the requirements of the ASME code. Have you got any opinion on the justification for this inconsistency? Or is IGA in welded 316 at 300 deg C and at 16 bar not an issue?"

Answer:

I am more familiar with ASME Section VIII, compared with Section III. I am not certain that I understand your question; however, based on my understanding of ASME Section VIII, div. 1, the corrosion resistance of a material in a specific environment is not addressed by the code in new construction. Material/environment compatability issues are the responsibility of the end user. The code addresses mechanical property considerations. As such, ASME does distinguish between 316SS and 316LSS at elevated temperatures as it relates to allowable stresses, based on the reduced strength of 316LSS at temperature vs. 316SS.

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