Local Strain Accumulation in Pipeline Girth Welds

The majority of existing pipeline design codes are stress based and provide limited guidance on the design and assessment of pipelines that may experience high local strains in service. High strains can occur in service due to ground movement, bending over an unsupported span and seismic loading. In such cases pipelines should be designed based on strain capacity. The rigors of strain-based analyses pose a number of challenges, particularly related to pipeline girth welds and general material behavior. This paper presents a summary of an ongoing multi-year project co-funded by the US Minerals Management Service (MMS) and US Dept of Transportation (DOT) to develop design and assessment guidelines for pipelines that may experience high strains in service. Specific topics to be addressed by the project include: • Parent Pipe specifications (Y/T limits, stress-strain behavior, material toughness, etc.); • Welding specifications (joint design, joint geometry, weld strength mismatch, etc.); • Engineering Critical Assessment (ECA) Methods for strain based loading; • Validation test methods to verify pipeline performance (criteria for full-scale testing).