 Thick walled x80 pipelines for oil and gas transportation are difficult to relocate due to their large size. In the process of narrow gap overhead welding, welding defects, such as bulges and lack of sidewall fusion, can appear easily. To avoid these defects and to improve the welding quality of thick walled pipelines, the GMAW welding method is adopted in this paper. It was found that, in the NGGMAW overhead welding position, there was a downward trend in the middle of the formed surface of the weld pool. Defects, such as finger shaped penetrations and lack of sidewall fusion, were prone to occur due to gravity. The increased oscillation width was beneficial for reducing the protrusion in the middle of the weld seam, but an excessive oscillation width can easily cause undercut defects. The sidewall dwell time has little effect on the protrusion in the middle of the weld seam, but it can increase sidewall penetration, thereby avoiding the occurrence of incomplete sidewall penetration. This article was authored by Yang Bao, Rui Lei Shui, Jian Pian Zhou, and others. We are article.tv, links in the description below.