Procedure to establish critical threshold strain value for strain-based-design in fracture mechanics assessment for ductile material

In Oil&Gas industry Engineering Criticality Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines welds joints. Methodologies for industrial application are given in BS7910 (2013), API579-1 (2007), R6, DNV-OS-F101 (2013). Failure Assessment Diagram (FAD) is commonly used for ECA of flawed components. However for ductile material, the use of stress-based approach leads to very conservative assessment. In such case the strain based design could be more appropriated. The purpose of this paper is to introduce a method in order to establish the threshold value of plastic failure criterion for ECA Strain-Based design application.