Measurement and evaluation of residual stresses within aged and overlay repair welded piping components

Abstract

When steel components are fabricated through welding, the component is exposed to intense thermal inputs with regions of high temperature located directly adjacent to relatively cool material. This non-homogeneous temperature distribution leads to significant, localised strain mismatch in the region of the weld; these strains cause residual stresses found in components. Residual stresses are known to impact the structural integrity of components as higher magnitude stresses, increasing the probability of effects such as stress corrosion cracking and, therefore, an increased chance of premature failure during service.
The current assessment methods of structural integrity consider the impact of residual stresses. Still, they can be better improved by an enhanced understanding of the changes made during service, such as ageing and repair welding. A better understanding of the change in residual stress levels through the time in service will allow the improvement in evaluating the structural integrity of these components.
This thesis will present the experimental data on residual stresses for welded steel pipes representing different forms of post-manufacture stress change. Firstly, the effect of ageing on the residual stresses of a stainless-steel girth welded pipe is investigated. This demonstrated that a welded pipe’s long-term heating could relax the peak stresses through the wall thickness. Secondly, the residual stresses input into low ally steel piping through the application of external overlay repair welds is investigated with the confirmation of significant input stresses and their distribution evaluated.
The work shown in this thesis will contribute to the improved knowledge of the stresses present in components when in service and allow components to be kept in service for longer using assessment methods more representative of the operational components.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mahmoud Mostafavi (Supervisor) & Christopher E Truman (Supervisor)