March 29, 2017
Pipeline defects such as cracks, dents and corrosion often require permanent pressure retaining repairs. Full encirclement metallic repair sleeves with fillet-welded end connections to the pipe-line are often used for this purpose. 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. At present, accurate quantitative fitness for service assessments for circumferential defects in sleeve fillet welds are difficult to carry out due to a lack of detailed stress intensity factor solutions for finite length cracks.
The primary objective of this project was to improve the assessment of circumferential defects in sleeve fillet welds through the development of more accurate stress intensity factors and plastic collapse solutions for finite length sleeve-end fillet weld toe and root cracks. The stress intensity factors were estimated using detailed finite element analysis. These factors were then used to develop simplified parametric equations which are suitable for carrying out defect assessments on a wide range of pipe and sleeve geometries. These equations can be used in the assessment of fatigue crack growth and/or fracture using failure assessment diagram methods at sleeve end fillets alongside the results developed for other structural geometries in national standards. The final report is now available at no charge to members and for sale to non-members. (PRCI Project SIA-1-2)