ARRESTING PROPAGATING SHEAR IN PIPELINES (Part 2. See no. 1, 2015 for part 1)

Abstract

The consequences of what has been termed running ductile fracture require that pipelines be designed to arrest propagation, and so avoid major incidents due to this type of failure. Approaches to characterize pipeline response and their resistance to such failure to ensure arrest rely on semi-empirical models developed in the mid-1970s. Continuing reliance on such semi-empirical models, which were calibrated using fullscale tests done on segments of pipelines, persists because this failure process involves three interacting nonlinearities, and so is complex. These nonlinearities include: 1) plastic fl ow and tearing instability, 2) soil-structure interaction, and 3) expansion wave response and decompression in the pressurizing media. This paper fi rst reviews the history and related evelopments that represent almost 40 years invested in fracture-based approaches to quantify propagating shear in pipelines. Graphical evidence of the full-scale failure process and related phenomenology lead to an alternative hypothesis to quantify this failure process that is based on plastic collapse rather than fracture. It is shown that the phenomenology does not support a fracture-controlled process, and that instead the metrics of arrest should refl ect the fl ow properties of the steel. Finally, aspects of fracture-based approaches are related to the collapse-based concept as the basis to understand the success that at times has been achieved using fracture-based approaches. Surrogates for CVN energy that has been used in the BTCM as a measure of fracture resistance are reevaluated as functions of the fl ow response, which provides the basis to rationalize the historic successes on the fracture-based formulation. Finally, remaining gaps and issues are addressed.