Develop and validate a strain-based failure assessment diagram (SB-FAD) procedure for girth welds.
Understand how material variability in the girth weld influences use of stress and strain-based methods.
Develop and validate material models for accurate residual stress prediction in pipeline girth welds.
Develop a procedure for including of the effects of residual stresses on crack-tip constraint for assessing girth weld fracture resistance.
The project will be divided into four tasks to achieve each of the objectives. The underlying theme of all of them will be the development of advanced/improved assessment procedures for girth welds in either pipelines of pipe-work. The task will cover the following subjects:
Definition of reference strain which allows for flaw/pipe geometry.
Definition of maximum allowable reference strain.
Validation through numerical analysis and analysis of full-scale tests data.
Effect of material variability
Determination of how strength and fracture toughness vary around the pipe and through the wall thickness in both parent pipe and girth welds in modern steels.
Development of a testing and analysis procedure which best takes these variations into account for stress, but in particular, strain-based assessment methods.
Residual stress prediction
Determination of true cyclic stress history of material. Uniaxial testing under a thermal cycle simulating welding will be done in conjunction with the Dalton Institute.
Use of this information in an Abaqus numerical analysis model to predict residual stresses in girth welds.
Effect of residual stresses on fracture resistance
Experimental and numerical analysis to develop residual stresses (initially starting with uniform residual stresses) and how these redistribute during a fracture test.
Quantify how crack-tip constraint develops during loading.
Extend the simple model to a girth weld.
Relevant Industry Sectors
Oil and Gas, Pipelines, Power Generation (especially Nuclear).
Technical and Economic Benefits
The work will provide a technique that can be used to optimise the structural integrity of girth welds in pipelines and pipework with reductions in whole life costs.