CRACK-OPENING-AREA ANALYSES FOR CIRCUMFERENTIAL THROUGH-WALL CRACKS IN PIPES - PART III - OFF-CENTER CRACKS, RESTRAINT OF BENDING, THICKNESS TRANSITION AND WELD RESIDUAL-STRESSES

This is the third of three papers generated from a recent study on cra ck-opening-area analysis of circumferentially cracked pipes for leak-b efore-break applications. The first two papers [1,2] [Rahman, S., Brus t, F. W., Ghadiali, N. and Wilkowski, G., Crack-opening-area analyses for circumferential through-wall cracks in pipes. Part I-Analytical mo dels. International Journal of Pressure Vessels and Piping, (this issu e). Rahman, S., Brust, F. W., Ghadiali, N. and Willrowski, G., Crack-o pening-area analyses for circumferential through-wall cracks in pipes. Part II-Model validations. International Journal of Pressure Vessels and Piping, (this issue).] dealt with crack-opening-area analysis of p ipes assuming simple loading, pipe and crack geometries, and boundary conditions. This paper (Part III-Off-center cracks, restraint of bendi ng, thickness transition, and weld residual stresses) examines several practical aspects of crack-opening-area analysis involving off-center cracks, restraint of pressure-induced bending, girth-weld nozzle crac ks at thickness transition, and weld-induced residual stresses. Curren tly, there are no engineering methods or guidelines available to analy ze pipes under these conditions. Both linear-elastic and elastic-plast ic finite element analyses were conducted to determine quantitatively their effects on various crack-opening characteristics. From the resul ts of these analyses, recommendations are made on how an off-center cr ack can be analyzed based on fracture-mechanics equations for a center ed crack. It was found when the restraint of bending effects become im portant and how they should be taken into account. Cracks located in t he thickness transition with thickness gradients on both sides of a no zzle girth weld were analyzed. Finally, simplified finite element simu lations were performed to determine if the residual stresses should be considered and when they become important for crack-opening evaluatio ns. (C) 1998 Elsevier Science Ltd. All rights reserved.