Assessment of API X65 steel pipe puffiness by a strain based design (SBD) approach under bi-axial loading

Puffiness formation can occur during process of pipelines component fabrication and transportation or during construction, operation, maintenance and their repair processes. The present paper addresses issues related to pipeline design and associated with the unintended actions due to external loads or ground movements. These may introduce longitudinal strains in the pipeline owing to combinations of curvatures and axial forces. Such scenarios can be tackled with Strain-Based Design approaches. Elaboration on checking the strain capacity of pipelines was achieved via the material testing in which a full-scale test was performed on a pressurized pipe under bending load. Numerical modeling procedures for predicting the structural behavior using certain assumptions are also described in this study. The result in local buckling hereafter referred to as puffiness. Such local damages are associated with large plastic deformations, substantial changes of the pipeline geometry and mechanical properties of its material.