Creep and Creep-Fatigue Behavior of Grade 92 Base Metal and Welded Joints

摘要

Grade 92 steel (ASME SA-213, T92 / ASME SA-335, P92) is one of the Creep Strength-Enhanced Ferritic (CSEF) steels developed for use in boilers and piping systems of supercritical steam fossil power plants. Although creep strength is a primary concern and many efforts have been made for evaluating it, consideration of the interaction of creep and fatigue damage is also important in evaluating the integrity of components that will experience a range of cyclic loading. Although some efforts have already been made to understand creep-fatigue behavior of this steel, test data under the conditions of creep damage dominance more relevant to plant evaluation, need to be supplemented. Girth welds often constitute critical locations dominating the integrity of piping systems and their creep-fatigue behavior is also of significant importance.Such a situation prompted EPRI and CRIEPI to initiate a project aimed at development of an extensive database on creep-fatigue behavior of base metal and welded joints of Grade 92 steel and establishment of an appropriate life estimation procedure. This paper presents the results obtained so far which can be summarized as follows:(i) A thick pipe with Submerged Arc Welding (SAW) has been manufactured as a test material.(ii) Base metal and cross-weld specimens taken from the pipe were shown to exhibit similar behavior under short-term creep conditions as well as under cyclic loading. (iii) The creep strengths of these specimens were lower than the average properties reported in the literature for the class of steel, in short time regime, but the difference seems to shrink as the stress decreases.(iv) Fatigue and creep-fatigue behavior of the base metal and welded joint specimens were similar to counterparts of Grade 91 and 122 steels and creep-fatigue failure prediction models exhibited common characteristics for the three CSEF steels.