Fatigue lifetime assessment procedures for welded pressure vessel components

Abstract

Design against fatigue of welded pressure vessel components is usually based on structural or notch stress approaches. Post weld treatment methods such as grinding or TIG dressing provide significant improvements of the fatigue behaviour by blunting of the weld toe notches and by using materials of higher strength. Although well established on the level of welding technologies, fatigue design rules for improvement methods are not yet available within design codes. The local strain approach can be applied as a method of lifetime assessment in these cases. The methodology is demonstrated for cylinder-to-cylinder intersections and butt welded joints as typical pressure vessel structures. Concept-conforming modelling and numerical stress and strain analysis are relevant modules of the procedure. The derivation of fatigue curves for special weld details is shown under the aspect of practical application. Once determined, these fatigue curves can be used in the same sense as the traditional nominal stress approach.