Abstract
This paper presents the findings of a study to investigate the phenomena of girth weld strength undermatching and strain concentration in SMAW girth welds of API 5L X70 pipe, and to identify the significance of some key factors that may affect these phenomena including filler metal strength, heat input, and carbon equivalency of pipe base material. Test welds were subjected to a novel small-scale instrumented cross-weld tensile testing (ICWT) method employing multiple extensometers in different regions of the gage section. Hardness mapping of each weld cross-section was also performed.
This study highlights the importance of considering filler metal strength relative to base material strength when designing welded joints, as well as the importance of controlling welding heat input. It also points out potential issues with relying on failure location as an acceptance criterion in cross-weld tensile testing (CWTT) samples. The observations from this study may be useful in the development of strategies and practices for mitigating the risk of excessive weld strain concentration and premature girth weld failure under moderate tensile or bending loads typical of stress-based pipeline designs.
