Validation of Sleeve Weld Integrity and Workmanship Level Development

Abstract

Full encirclement repair sleeves with fillet-welded ends are often used as permanent repairs on pipelines to reinforce areas with defects, such as cracks or corrosion. In-service failures have occurred at reinforcing sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks and undercut at the fillet welds, inadequate weld size, and sleeve longitudinal seam ruptures. This work was undertaken to support the development of tools for sleeve design and for conducting an engineering assessment to determine the tolerable dimensions of flaw indications at full encirclement repair sleeves. In particular, the project was intended to validate the stresses estimated using finite element analysis (FEA) models against actual in-service loading conditions experienced at reinforcing sleeves. The experimental work focused on the collection of full-scale experimental data describing pipe and sleeve strains for the following field and laboratory conditions: • Strains induced by sleeve welding, • Strains induced by pressurization of the sleeved pipe, • Strains induced by pressurization of the sleeved pipe and the annulus between the pipe and sleeve. Finite element models of the field and laboratory sleeved pipe segments were developed and subjected to the same applied loading conditions as the full-scale sleeved pipe segments. Comparisons of the measured strains against those estimated using FEA were completed to determine the ability of the models to predict the behaviour of the sleeved pipe segments. Comparisons were made to illustrate the relative strain levels and deformation trends, the accuracies of the strain predictions and trends in changes with pressure, the differences in behaviours between tight and loose fitting sleeves, and the effects of pressurizing the annulus between the pipe wall and sleeve. The analysis of the field data and FEA modeling predictions led to several conclusions regarding to use of numerical models for predicting sleeved pipe behaviour and weld flaw acceptance: • FEA results demonstrated behaviours that were consistent with full scale data, • Trends in the FEA predicted strains agreed with the full-scale data, • FEA models describing the effects of gaps between the pipe and sleeve and annulus pressurization agreed with field experience and engineering judgment, • Evaluation of the significance of root and toe flaws can be completed by extending the models validated in this work.