The increasing demand for natural gas as an alternative energy source implies continued growth of gas pipeline installations. This trend compels the natural gas transmission industry to consider the construction of larger-diameter, higher-pressure pipelines. The application of high-strength steels in severe conditions will require reliable pipeline designs, as well as inspection and maintenance procedures that will prevent in-service failures. A difficult problem to be solved for the economic and safe operation of high pressure gas lines is the control of ductile fracture propagation. In this case, a safety factor has to be developed for fracture arrest. So, accurate prediction of the resistance to fracture for high-pressurized pipelines is one of the issues to be solved for the new pipeline designs. The application of high-strength steels in severe conditions will require reliable pipeline designs in order to control the ductile fracture propagation. Crack tip opening angle (CTOA) is becoming one of the more widely accepted properties for characterizing fully plastic fracture. In fact, it has been recognized as a measure of the resistance of a material to fracture, in cases where there is a large degree of stable-tearing crack extension during the fracture process. Our current research has applied the CTOA concept in pipeline characterization. A test technique for direct measurement of CTOA was developed, using a modified double cantilever beam (MDCB) specimen. A digital camera and image analysis software are used to record the progression of the crack tip and to estimate CTOA. We present CTOA data on crack growth orientations perpendicular to girth welds, and describe the change in CTOA when a running crack reaches a circumferential butt weld. This study will help the gas pipeline industry to better understand the effect of a running crack propagating through a weld.
Issue: Special Issue July 2007
Conference Dates: July 5-6, 2007
Conference Location: Dubrovnik, YU
Conference Title: Welding & Materials - Technical, Economic and Ecological Aspects
Pub Type: Conferences
crack tip opening angle, high strength pipeline steel, girth weld