Evaluation of a Welded Joint Using the Structural Stress Method

The Structural Stress Method of determining the fatigue strength of welded joints was formally incorporated into the ASME Boiler and Pressure Vessel Code in the 2007 edition of ASME Section VIII Division 2 and is also included in API 579-1/ASME FFS-1 2007, “Fitness-For-Service”. This method presents a number of advantages over the commonly applied approach of determining a peak stress, various fatigue and stress factors, and polished bar S-N fatigue curves to determine the fatigue strength. In this paper, the author illustrates the use of the Structural Stress Method as a means of assessing the fatigue strength of a welded joint through evaluation of a weldment attaching a carbon steel stiffening ring to a stainless steel vessel undergoing thermal cycles. Some advantages of this method and particular points of interest are discussed.