Jürgen Rudolph

Concept-conforming Modeling and Analysis of Welded Pressure Vessel Components in the Context of Structural, Notch Stress and Local Strain Approaches to Design against Fatigue

The general applicability of local stress and strain approaches for engineering components under cyclic loading conditions is one result of intensive international research activities during the past years and decades. The implementation of these methods within specific design codes is currently in progress and will be a primary requirement of the years to come. One common feature of structural, notch stress and local strain approaches is the necessity of using concept-conforming modeling strategies as one basis of numerical stress and strain analysis. A general strategy emanating from an adaptive nominal weld seam contour is presented and examples for lifetime assessment procedures of welded pressure vessel components are given. Special attention is paid to the consequences of post weld fatigue improvement methods, such as grinding and TIG dressing on the damage process, the modeling strategy and the design approach. Direct comparison of structural details with joints in the as welded condition and submitted to post weld treatment is possible making use of the notch stress approach according to Olivier, Kottgen, and Seeger for the former and the local strain approach for the latter.

Failure modes of pressure vessel components and their consideration in analyses

Abstract Metallic pressure vessel components such as dished ends show different modes of failure depending upon the geometrical and loading conditions. These are mainly gross plastic deformation under static load, loss of stability (buckling), fatigue crack initiation at highly stressed locations under cyclic loading (especially in the low cycle regime), progressive plastic deformation (ratcheting) and creep at high temperatures. Existing codes are mostly used to determine necessary wall thickness (design by rule) based on the static load-carrying capacity. Guidelines for other failure modes are given in a more or less general way for complex structures. In this article it is shown that all the failure modes mentioned can be estimated by carrying out linear and non-linear finite elements analyses. The possibility of using the finite elements method as a basis for design by rule and design by analysis is discussed.