Welding Solutions Advancement of High-Strength Pipeline Steels

During last two decades, continuously increasing energy delivery rates and the expansion of oil and gas exploration to cold and harsh regions have demanded advancements of the assigned materials and employment of higher strength pipeline steels, such as grade X100 and X120. However, there are significant challenges with conventional arc welding of these high-strength steels, such as heat affected zone (HAZ) softening, cold cracking (Hydrogen-assisted cracking (HAC)), and lack of information on their corrosion behavior in harsh arctic environments. The proposed Discovery grant application will focus on developing welding solutions for advanced high-strength steels and understanding their corrosion behavior in harsh environment with a specific emphasis on API X100 and X120 steels to support the large-scale implementation of the materials in offshore and oil and gas projects. The use of advanced Gas Metal Arc Welding (GMAW) transfer modes, such as Surface Tension Transfer (STT) for the root pass followed by Pulsed (P)-GMAW, will be employed to improve the joint strength and achieve a higher level of reliability and integrity. The unique feature of STT transfer mode is that it offers a combined reduced energy and improved energy control through droplet by droplet control of the fusion zone penetration, which can be beneficial to minimize the extent of HAZ softening and HAC. The key objectives of the proposed work are: (i) evaluate the role of STT/P-GMAW process on microstructure and mechanical properties of X100 and X120 pipeline steels joint; (ii) develop an integrated thermal and microstructural model to simulate the transient heat transfer and microstructure evolution in the fusion zone (FZ) as well as HAZ using a commercial finite element analysis package; (iii) investigate the corrosion behavior of the joints in harsh environment by studying the hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) susceptibility of the joints in H2S/CO2 containing environment. These deliverables will act as a platform for the long-term vision of large-scale utilization of high-strength X100 and X120 steel in offshore and oil and gas industry, particularly in arctic environments leading to a significant investment cost saving. The successful fulfillment of this project will not only develop critical fundamental insight into science and technology of welding and corrosion behavior of high-strength steels, but will improve predictability, integrity, and consistency of the pipeline welding operation. The proposed work will significantly impact dissemination of core research to industry and train five highly qualified personnel (10 counting Co-op students), which will provide a competitive advantage to Canadian offshore and oil and gas industries.