Evaluation of pipeline laser girth weld properties by Charpy (V) toughness and impact tensile tests

摘要

Developments of CO_2 laser sources have promoted new applications, such as on-site pipeline offshore welding. These laser applications offer increased competitiveness and quality as compared to conventional arc welding systems. Due to the weld narrowness and to the high microstructural and mechanical gradient, determination of laser weld fracture properties appears to be sometimes difficult. Scatter may be important in the transition range, partly due to fracture path deviation phenomenon, and thus causes difficulties to optimise steel compositions or welding conditions. Based on a previous work of Grumbach and Sanz [Revue de Metallurgie (1972)145], the possibility of characterising laser welds by impact tensile testing (ITT) has been studied. Specimens, including a smooth part and a notched part, are tested with a device mounted on impact pendulum. According to testing conditions and material toughness, fracture occurs in one of these two zones with a very sharp transition. This test allows to study easily the "matching" effects in laser welds. Some applications of this test concerning weld heat affected zones (HAZ) are also presented. Relations between transition temperature derived through this test, weld or HAZ microstructures, and Chanpy (V-notch) toughness test results are also discussed in this paper.