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API 6A Secondary Stresses

API 6A Secondary Stresses

API 6A Secondary Stresses

API 6A section for non standard materials limits the hydro membrane, stress intensity at working pressure, and primary + secondary stress limits as follows:

ST = min[(5/6) x Sy, (2/3) x Rm]
Sm = min [(2/3) x Sy, (1/2) x Rm]
Ss = min [2xSy, Rm]

My question is can the primary + secondary stresses for the hydro-test case scenario be taken as St x 3.0 as in ASME VIII, Div 2?

Surely the hydro-test case would not be limited to the above Ss for design working pressure, right?

Thank you in advance for your help.

RE: API 6A Secondary Stresses

Please note that according to VIII-2, there is NO LIMIT on the secondary membrane-plus-bending stresses for the test condition.


Well, the secondary stress limits are to manage a failure mode called Ratcheting. However, ratcheting requires repetition for the loading. A hydrostatic test only occurs once. So, no possibility of ratcheting.

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