Why Conduct SEN(T) Tests and Considerations in Conducting/Analyzing SEN(T) Testing

This paper outlines a methodology used to conduct a SEN(T) fracture test and discusses the analysis procedure used to obtain J-R and CTOD-R resistance curves from the experimental data. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. Significant crack growth can arise from the start of ductile tearing to maximum load in the case of surface-cracked pipes with heavier-wall piping used in recent designs of natural gas pipelines that are required to handle greater pressures and much lower temperatures. CTOD-R curves provide toughness values that are a factor of 2 to 3 times higher at maximum load when compared to the toughness at crack initiation. The impacts of this on stress and strain-based design of pipelines are highlighted. Further, the differences between the traditional approach that uses the crack-tip-opening-displacement at the initial crack tip (CTOD^′) versus the more recent developments that employ the crack-tip-opening-displacement at the growing crack tip (CTOD) are examined. The CTOD-R curve for the growing crack tip is more consistent with J-R curve analyses. Single-edge-notched bend [SEN(B)] or popularly called bend-bar specimens are used for crack-tip-opening-displacement (CTOD) as well as J-integral toughness testing. This paper discusses the advantages of using the fracture toughness data determined from a single-edge-notched tension [SEN(T)] specimen from considerations of the constraints faced by surface cracks in pipelines and the differences in fracture toughness values seen between the SEN(T) and SEN(B) specimens in the transition temperature region.