This work provides the development of compliance solutions and eta-factors for experimental measurements of resistance curves in structural and pipeline steels using SENT specimens. A summary of the methodology upon which J and crack extension are derived sets the necessary framework to determine crack resistance data from the measured load vs. displacement curves. The extensive plane-strain analyses enable numerical estimates of the nondimensional compliance, μ, and parameters η for a wide range of specimen geometries and material properties characteristic of structural and pipeline steels. The results presented here produce a representative set of solutions which lend further support to develop standard test procedures for constraint-designed SENT specimens applicable in measurements of crack growth resistance for pipelines.
Predictive methodologies aimed at quantifying the impact of defects in oil and gas pipelines play a key role in safety assessment procedures (such as, for example, repair decisions and life-extension programs) of in-service facilities. Conventional failure assessment procedures applicable to piping systems containing defects (e.g., cracks, blunt corrosion, inclusions, weld flaws, etc.) generally employ simplified failure criteria derived from a plastic collapse analysis of the remaining ligament ahead of the crack-like defect or linear elastic fracture mechanics, such as the leak-before-break criterion (see Eiber and Kiefner, 1986, AWS, 1987 and National Energy Boarding, 1996). However, for high strength pipeline steels, the material failure (leakage or sudden rupture) is most often preceded by large amounts of slow, stable crack growth. Under sustained ductile tearing of the (macroscopic) crack-like defect, large increases in the load-carrying capacity of the pipe, as characterized by J-Δa resistance curves (Rcurves), are possible beyond the limits given by the crack driving force at the onset of stable crack extension (JIc). Consequently, advanced procedures for defect assessments in pipelines (API 579, 2000) seek to incorporate the increase in toughness of these materials during ductile crack extension.
