Approximate creep rupture lifetimes for butt welded ferritic steel pressurised pipes

The creep rupture of butt welded ferritic steel pipes composed of a range o f weld and heat affected zone materials has been previously analysed in det ail (Leckie and Hayhurst, 1994). These analyses required substantial comput ational resources which cannot be justified during the preliminary phases o f the design process. To reduce cost and improve speed an approximate metho d for the analysis of kinematically determinate structures, known as the mo dal method (Leckie and Hayhurst, 1974), has been developed to compute creep rupture lifetimes. This paper reports an extension of the method for the a nalysis of multi-material structures, such as weldments, and its implementa tion as a post processor to a stationary state finite element creep analysi s. Histories of stress and damage have been determined using the modal meth od for weldments with a range of heat affected zone and weld material combi nations. The lifetimes determined in this way are compared with those deter mined using complete continuum damage mechanics analyses, and are shown to be conservative; in addition the regions of intense damage have been shown to be accurately predicted. The modal method is also shown to be superior t o more approximate reference stress methods. (C) 2000 Editions scientifique s et medicales Elsevier SAS.