Experimental Characterization Of API-5L X65 Steel And An Improved,Reliable Method For Assessing Hot Cracking Susceptibility Of Materials

Fusion welding is a complex process that requires a lot of control in order to achieve the desired results. Due to its complexity a number of defects may occur during the process. Weld solidification cracking is one of them and it is a critical defect. The presence of this defect will always lead to failure. This failure can occur during the production process where, if detected, the defect will cause significant setbacks and increased cost of production. If undetected it will lead to failure during service where the impact will be more severe. Overall, failures due to solidification cracking can lead to significant environmental, economic and social damage. This thesis examines the capabilities of experimental procedures with the ultimate goal to assess the hot cracking susceptibility of materials. In the first chapters the material used for this work is presented along with its production process for manufacturing pipelines for gas and oil transport. Adding to that, literature on the subject of hot cracking is presented. Tests that have been created for assessing the hot cracking susceptibility of materials (weldability tests) are presented and discussed and the two tests that are the focus of this study are analysed in depth. This thesis is focused on the characterization of the material, weldability tests and post processing of the weldability test samples. During the experimental design of the weldability tests, improvements that allow for increased repeatability and reliability of the tests are presented. These improvements allow for the better control of the application of strain during the tests which is an important parameter for solidification cracking. The results of these tests show that there are significant improvements compared to previous work. This is deemed important since these tests are not standardized and increased control of the tests could lead to standardization of the tests. Furthermore, the post processing by X-ray computed tomography and fractography of the samples provided indications that it is possible to predict the position where a solidification crack will be generated during welding.