A case study for assessment of consistency between ASME Section III and XI rules

A case study was conducted to evaluate how the current ASME Boiler and Pressure Vessel (B and PV) Code Section XI nuclear piping flaw evaluation rules are affected by the design stress changes in increasing the allowable stress with the B and PV Code Section III piping design rules. A piping model was developed for this purpose from a realistic nuclear piping referred to as BM3 that has been used widely for developing or evaluating the nuclear piping design rules. The piping system was modified so that all the conditions required by the 1995 Section III rules are met. Seismic excitations and internal pressure were increased to reach the maximum allowable stresses under the Section III rules including the effects of pressure, deadweight, seismic inertia, seismic anchor motion, and thermal expansion. The stresses thus calculated elastically using a finite element analysis were then combined using the Section XI rules to evaluate whether the maximum stress ratios for flaw acceptance are exceeded that are allowed by Section XI IWB-3514 for the workmanship standard flaw sizes corresponding to current nondestructive examination capability at butt weld areas. Quantitative results were provided for discussions