Full encirclement repair sleeves with fillet-welded ends are often used as permanent repairs on pipelines to reinforce and develop pressure retaining repairs on areas with defects, such as cracks, dents, or corrosion. In-service failures have occurred at pressure retaining sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks, undercut at the fillet welds and inadequate weld size.
Currently, there are no reliable methods to carry out a quantitative fitness for service assessment for a sleeve fillet weld with a weld fault because: the stresses at the sleeve end fillet weld roots and toes are not easily determined; stress intensity factor solutions are not available for the sleeve fillet weld geometry; and current inspection procedures cannot effectively define the size of weld defects.
Following completion of a sleeve fillet weld it is currently common practice to carry out a visual inspection and magnetic particle inspection (MPI) to determine whether weld toe defects exist. With continuing advances in nondestructive examination (NDE) technologies, the ability not only to inspect for toe and root flaws but also to size these cracks is becoming a reality.
This project aims to develop flaw acceptance criteria which will fill gaps in the available engineering critical assessment procedures for sleeve repairs on all grades of pipelines.
Phase I of this research has recently been completed with the acceptance of the Final Report which includes the results of preliminary investigations, development of modeling parameters, ranges and the matrix for the finite element analyses that will form the basis of the assessment tools developed as part of this project. Because of the thousands of finite element analysis models involved, an automated approach for creating, analyzing, and post processing was also developed. Phase II is beginning now. The Phase I report is available to PRCI Members.