Please use this identifier to cite or link to this item: http://bura.brunel.ac.uk/handle/2438/16658
Title: Investigation of residual stresses in X65 narrow-gap pipe girth welds
Authors: Ren, Yao
Advisors: Wang, B
Wrobel, L
Janin, Y
Keywords: Neutron diffraction;Post weld heat treatment;Finite element analysis;Strain-free reference sample;Engineering critical assessment
Issue Date: 2018
Publisher: Brunel University London
Abstract: This research investigated the residual stresses in narrow-gap API 5L X65 pipe girth welds in as-welded and after post weld heat treatment (PWHT) conditions. The PWHT included global furnace and local practices. Non-destructive neutron diffraction (ND) strain scanning was carried out on selected pipe spools and strainfree reference samples for the determination of the lattice spacing before and after PWHT. The as-welded and post-heat treatment residual stresses measured in the pipe spools were examined and compared. Experimental work also included full residual stress mapping in the weldment and through-thickness measurement at weld centre and close to the external and internal pipe surfaces. The measured profiles were compared with the recommendations given in British flaw assessment procedure BS 7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the UK nuclear industry’s R6 procedure. The design, preparation and experimental neutron diffraction measurement procedures for the determination of the strain-free lattice parameter in various configurations of reference samples and in the required directions were discussed. The variability of the lattice spacing in the reference samples was found depended on the specimen manufacture methods and thermal process. Welding residual stresses were also simulated using finite element analysis (FEA) modelling approach. The simulated thermal cycles and transient strains at specific locations were compared with the experimental readings. The residual stress profiles derived from finite element model were compared with the measurements from neutron diffraction. It was found, the measured and simulated, as-welded - residual stress profiles showed good consistency in terms of stress distribution and magnitude to reasonable extent. Measurement results also indicated that local PWHT was effective in reducing the residual stresses in the pipes to a level similar to that achieved by a global approach.
Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London
URI: http://bura.brunel.ac.uk/handle/2438/16658
Appears in Collections:Mechanical and Aerospace Engineering
Dept of Mechanical Aerospace and Civil Engineering Theses

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