Development of Novel Crack Arrest Designs for High Pressure Gas Pipelines

Gas transmission pipelines designed to Australian Standard AS 2885.1, “Pipelines – Gas and Liquid Petroleum” are often subjected to higher design pressures than pipelines in the United States. This results in thicker walls to accommodate hoop stress and other design considerations. As part of fracture control, 2885.1 mandates crack arrest properties (Drop Weight Tear Testing (DWTT)). However, meeting DWTT requirements presents challenges due to significantly higher Charpy V-Notch (CVN) energy values exhibited by modern high-strength pipeline steels when compared to older steels. High CVN energy values create difficulties achieving necessary DWTT shear fracture values. Higher CVN values indicating a material’s ability to absorb energy plastically, inhibiting crack initiation, complicates fractographic examinations (percent shear morphology) of fracture surfaces. While this paper does not discuss fracture control method details/fundamentals, it does address the challenge of developing an alternate solution, and details development and testing of a compression sleeve system, which underwent three design iterations: a two-piece compression sleeve, an epoxy mold, and a collet system. Each design aimed to apply compressive stress, locally reducing hoop stress to meet fracture control requirements. Despite facing technical challenges related to pipe out-of-roundness and material properties in the first two designs, the final collet system successfully reduced hoop stress, and achieved the desired fracture control. Findings highlight the necessity for innovative approaches in fracture control, and emphasize the importance of continuous research to adapt to evolving materials and regulatory standards in high-pressure gas transmission pipeline design.