Pipeline welding is an integral part of oil and gas exploration industries. Often the welded joint failures were due to lack of weld quality, improper heat treatment and even poor workmanship. Further, the use of new material in pipeline industry puts focus on a better understanding of qualifying requirements of welding for reducing the failures in future. This necessitates the need for development and design of suitable welding fluxes for joining these materials. In this paper an attempt is made to study the effects of submerged arc welding fluxes on weldability as well as structural integrity issues in pipeline steels. Physicochemical and thermophysical properties of submerged arc fluxes widely affects the mechanical behaviour of pipeline steels. This paper presents an overview of the role of welding parameters, flux composition, cooling rate, slag behaviour and physicochemical properties of slag on final welded joint properties such as tensile strength, impact toughness etc. during submerged arc welding.

API X70 steel requires high strength and toughness for safety in extreme environments like high pressure and low temperature. Submerged Arc Welding (SAW ) is effective for manufacturing thick steel pipes. However, the welding heat input during SAW alters the microstructure and mechanical properties of the heat affected zone (HAZ). Therefore, investigating the correlation between microstructure and mechanical properties in welded X70 pipes is important to address potential degradation of HAZ and weld metal (WM). In this study, post weld heat treatment (PWHT) was performed to improve mechanical properties of HAZ and WM and to reduce residual stress caused by the welding process. We performed PWHT at 640°C for 15 hours and followed by air cooling. After heat treatment, we observed the microstructure through OM and SEM analysis, and investigated the mechanical properties through tensile test, hardness test, and Charpy impact test.