Influence of post-weld heat treatment (PWHT) on the tensile behaviour of P91 weldments
type: CreativeWork
description: A key factor for successful installation of Grade 91 steel for high pressure-high temperature applications in power plant is optimised welding and post weld heat treatment (PWHT) which restores homogeneous mechanical properties after welding. Although optimum PWHT is prescribed in standards, deviations in the field practices can potentially lead to accelerated component degradation and failure. Consequently, a full understanding of cross-weld behaviour as a function of deviations in PWHT is required. This study investigates the influence of PWHT on the occurrence of strain localisation in cross-weld tensile specimens tested at temperatures up to typical power plant service temperature. Localised strain maps were obtained during high temperature tensile deformation. These assist in understanding the influence of PWHT on the overall performance of the cross-weld, and the identification of the location most susceptible to failure in the welded specimens. Specimens used in this work were extracted from as-welded new Grade 91 pipe material. Wire cut EDM was used to extract rectangular blocks with the weld in the centre which were machined to required geometry. Specimens for as-welded (AW) tests were not subjected to PWHT. The recommended PWHT for P91 steel is tempering at 760°C for 2 hours. Post weld heat treatments that were performed on specimens included soaking at 720°C, 760°C and 800°C for 2 hours respectively, as well as so-called excursion heat treatments that included extended treatment at 760°C for up to 6 hours. In addition, excursion heat treatments also included over-heating up to 840°C followed by soaking for 2 hours at 760°C. A Gleeble 3800D thermomechanical simulator was used for high temperature tensile testing at a strain rate of 103 s-1 . High temperature tensile tests were performed at 300°C and 535°C. Three-dimensional (3D) digital image correlation (DIC) was used for non-contact strain measurement (i.e., application of virtual strain gauges) to accur…
abstract: A key factor for successful installation of Grade 91 steel for high pressure-high temperature applications in power plant is optimised welding and post weld heat treatment (PWHT) which restores homogeneous mechanical properties after welding. Although optimum PWHT is prescribed in standards, deviations in the field practices can potentially lead to accelerated component degradation and failure. Consequently, a full understanding of cross-weld behaviour as a function of deviations in PWHT is required. This study investigates the influence of PWHT on the occurrence of strain localisation in cross-weld tensile specimens tested at temperatures up to typical power plant service temperature. Localised strain maps were obtained during high temperature tensile deformation. These assist in understanding the influence of PWHT on the overall performance of the cross-weld, and the identification of the location most susceptible to failure in the welded specimens. Specimens used in this work were extracted from as-welded new Grade 91 pipe material. Wire cut EDM was used to extract rectangular blocks with the weld in the centre which were machined to required geometry. Specimens for as-welded (AW) tests were not subjected to PWHT. The recommended PWHT for P91 steel is tempering at 760°C for 2 hours. Post weld heat treatments that were performed on specimens included soaking at 720°C, 760°C and 800°C for 2 hours respectively, as well as so-called excursion heat treatments that included extended treatment at 760°C for up to 6 hours. In addition, excursion heat treatments also included over-heating up to 840°C followed by soaking for 2 hours at 760°C. A Gleeble 3800D thermomechanical simulator was used for high temperature tensile testing at a strain rate of 103 s-1 . High temperature tensile tests were performed at 300°C and 535°C. Three-dimensional (3D) digital image correlation (DIC) was used for non-contact strain measurement (i.e., application of virtual strain gauges) to accur…
author: Jambo, Tinashe
keywords: Engineering
date published: 2023
date modified: 2026-07-22T22:22:44Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Mechanical Engineering

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/39514