Pressurized Piping Elbows under Simulated Seismic Bending: Design Code Implications

Abstract

A series of 16 pairs of carbon and stainless steel, long and short radius 90° piping elbows, 2 inch NPS, schedule 40 and 80 (60.3 mm outside diameter, 3.91 mm and 5.54 mm thick respectively) have been tested under conditions of steady internal pressure and either in-plane or out-of-plane resonant bending to simulate seismic conditions. Experimental conditions are reviewed before some comments are made about the ASME Code Section III design stress indices. Next the stress limits achieved in the described tests are presented and compared with newly proposed allowable stresses. Ratios of applied dynamic moment to calculated limit moment in excess of unity and up to 2.11 have been consistently obtained. Finally, a summary of the experimentally obtained ratchet strain accumulation is presented and assessed against a recently proposed ‘strain control approach'.