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Nozzle Loads - Stress Intensity Factor (ASME VIII div. 2, AD-560.7)

Nozzle Loads - Stress Intensity Factor (ASME VIII div. 2, AD-560.7)

Nozzle Loads - Stress Intensity Factor (ASME VIII div. 2, AD-560.7)

(OP)
We are calculating local stresses in shell from nozzle loads according to WRC 107 and WRC 297 using stress indices from ASME VIII div. 2, AD-560.7 for evaluating the effect of internal pressure.  Vessels are designed as per ASME VIII div. 1 and div. 2. (fatigue analysis is not required).

As maximum stress index taken from AD-560.7 is as high as 3.3 (inside corner, longitudinal plane) we encounter the next problem:
In case of self reinforcing nozzles on high pressure vessels the shell thickness adjacent to nozzle is nearly the same as the min. calculated thickness. Calculated stresses S are then very close to allowable stresses Sm. Now 3.3 * S > 3*Sm for combined stresses let alone S >>1.5*Sm for local primary membrane (int. pressure). The result is that nozzle calculation reports failure even if no external load is applied.
This approach is used for instance by PVElite program.

Our nozzles are reinforced acc. to AD-520 for div.2 or UG 37-41 for div.1. In my opinion this should guarantee that stresses due to internal pressure around openings are kept within acceptable limits, presumably 1.5*Sm. Shouldn’t be values of stress indices for "outside corner" used (table AD-560.7)?

Could anyone advise me of the interpretation of par. AD-560.7 or/and some references to this matter?

Thank you in advance.
Antonin

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