L51409 Fracture Toughness of Pipeline Girth Welds

Abstract

Over the past few years, greater and greater emphasis has been placed on the reliability of transmission pipelines resulting in more frequent engineering critical assessments. One of the areas of high interest in such critical assessments is the behavior of the field girth weld. However, before any fracture assessment can be carried out on the weld, the fracture toughness of the girth weld must be known. The design requirements of a transmission pipeline usually means that an elastic-plastic analysis is appropriate, and hence a test is needed to assess the general yielding fracture behavior of the girth weld. One of the most appropriate is the British Crack Tip Opening Displacement (CTOD) method. The use of the CTOD approach to evaluate weld defect significance has been widely used throughout the world, and these applications have highlighted potential problems with the test. The object of this present program was to study the effect of this test technique and specimen location on the CTOD toughness of pipeline girth welds. This report covers the testing of three manual and one automatic girth weld under a variety of conditions and considers the significance of the various techniques. The experimental program was divided into two distinct phases. The first phase was designed to study experimental techniques, including the effects of constraint, fatigue pre-cracking, specimen design and crack-tip location. The second phase was a systematic study of the weld, concentrating on the effects of specimen location on toughness around the circumference.