Background to the use of CTOA for prediction of dynamic ductile fracture arrest in pipelines

The use of crack tip opening angle (CTOA) for the prediction of ductile fracture propagation and arrest phenomena in gas filled pipelines is currently the subject of study by the gas pipeline industry. The newly found interest is driven by the desire to develop a prediction methodology that is fundamentally based on fracture mechanics principles. This has been fuelled by proposed new pipelines using high strength steel (Grade 550 MPa, Grade 690 MPa and possibly greater) combined with higher operating pressures. This combination of steel strength, operating pressure, and possibly richer gas mixtures, has been shown to be beyond the calibration range for current ductile arrest prediction models. Therefore, a means to characterise pipeline steel’s resistance, under these extreme conditions, is required––CTOA looks promising. aper is intended to serve as an introduction to the two pipeline related papers that follow in this Journal. A description of the factors affecting propagation and arrest, and a brief overview of current prediction tools, will serve as preliminary information required to introduce these papers.