Crack Arrestors: Closing the Design Basis Gaps

Abstract The demand for pipelines to transport increased volumes of hydrogen and CO2 in the future is widely anticipated. The specific potential sources and nature of the fluids that are anticipated have led to concerns regarding potential gaps related to fracture control plans and operational integrity efforts. One of the specific gaps that has been identified is that of the design basis for the external devices (non-integral) which we generally refer to as “crack arrestors”. Specific concerns focus on anthropogenic CO2 with a more challenging decompression and hydrogen blends which could affect the pipe steel ductility. Crack arrestor devices are generally intended to arrest running ductile fractures or propagating shear. This paper reviews the technical history of this topic. Technical paper publications and intellectual property sources are reviewed. It will document the 1970’s understanding that the deformation in front of the fracture was considerable with specific characteristics. A review of effective and ineffective efforts over a 5-decade period is reviewed, as well as the design basis for these efforts. A review of the commonality of characteristics of effective and non-effective efforts is reviewed with a focus on identifying design basis flaws and the reasons for success. This paper will suggest that the mechanism of the phenomena of propagating shear is a plastic collapse of the pipe structure, with the propagating fracture an artifact. The means to stop the running ductile fracture is to add capacity to the structure or Resistivity to plastic collapse. In this context, the BTCM (or alternatives) with a focus on the speed of the gas decompression and the speed of the crack, are not necessarily the precise or sole path for a complete understanding of how to stop or arrest the event. A change in perspective is suggested from a focus on the speed of the propagation to adding capacity to the pipe structure. This paper will provide the basic details of an updated design basis for these crack arrestors devices.