Revision of Material Requirements of the EPRG Tier 2 Guidelines for Weld Defect Acceptance

Abstract The 2014 modification of the EPRG Tier 2 guidelines for the assessment of girth weld defects includes a modified criterion for weld strength overmatching. First experiences have shown it to be highly restrictive and to potentially limit the use of manual girth welding techniques. Recognizing this, EPRG launched a project to develop a sound justification to a potential new modification of the EPRG weld strength criteria, supported by a database of mechanical weld characteristics provided by EPRG members and a probabilistic analysis. This paper summarizes the findings of the project. The weld strength undermatch probability is strongly influenced by the ratio between overmatch criterion and standard deviation of pipe yield strength. The current guidelines correctly reflect the importance of this ratio, which is prescribed to be five. However, the requirements table of the guidelines mentions a fixed overmatch criterion of 100 MPa. The inherent assumption of 20 MPa for standard deviation of pipe yield strength is not mentioned and therefore easy to overlook. In the next issue the table will be modified such that it reflects the “five standard deviations” idea. The modified requirements stimulate the use of pipeline steels with a lower variability yield strength, as illustrated by the Dutch code NEN 3650-2. This code involves pipe yield strength and overmatch criteria in line with the suggested modification.