# Research Status and Progress of All-Position Narrow-Gap GMAW for Pipelines
## 4 All-Position Narrow-Gap GMAW Development Direction  
In all-position pipeline GMAW, the molten pool is significantly affected by gravity, leading to issues such as side-wall lack of fusion and interlayer lack of fusion. Despite numerous studies indicating that the GMAW technique offers significant advantages in narrow-gap all-position welding, such as ease of automation and high productivity [72; 73; 74], there are some difficulties in ensuring the correctness of multiple welding parameters due to their relatively large number and strong interrelations [75]. In practical industrial applications, GMAW faces challenges like poor adaptability to complex geometries and difficulty in controlling heat input. Compared with other welding techniques, such as hybrid laser-arc welding and magnetic field-assisted welding, it is found that hybrid laser-arc welding offers several advantages, including reduced heat input, enhanced weld penetration, and improved process stability [61; 76]. Additionally, by integrating solid-state phase transformation theories from materials science, a better understanding can be achieved regarding the impact of different cooling rates on weld quality. However, there remain some technical challenges that need to be overcome, including the complexity of welding equipment and the low level of intelligence in weld seam detection. Future technological development directions should focus on the following aspects:  
1. Optimization methods for process parameters have overlooked the impact of interactions among multiple parameters on the overall weld bead formation. Future research should focus more on establishing comprehensive mathematical models or employing machine learning algorithms to predict and optimize the effects of multi-parametercombinations. Developing intelligent all-position welding technology for pipelines can reduce reliance on the skill level of welders, ensuring consistency in welding quality. This includes technologies for online monitoring and quality assessment of the welding process, such as real-time detecting of sidewall lack of fusion, interlayer lack of fusion, and weld bead formation. It also involves dynamically adjusting process parameters based on real-time feedback, assessing potential defect locations, and providing guidance for post-weld inspection. By doing so, not only can welding quality be improved, but it also facilitates a more systematic approach to achieving high standards of weld integrity and performance. 2. In laboratory settings, ideal magnetic field control can be achieved; however, in actual industrial production, the stability of equipment and the convenience of operation are often limited. To overcome these challenges, future research should focus on developing intelligent control systems, optimizing the design of magnetic field generators, and integrating advanced sensing technologies with real-time monitoring systems. Ensuring consistent, high-quality weld seams across different welding positions requires robust solutions that can adapt to varying conditions. 3. Hybrid laser-arc welding offers advantages such as high welding efficiency and a small heat-affected zone, achieving notable research outcomes and seeing engineering applications. However, the introduction of a laser makes the equipment more complex, which limits its application in the field construction of pipelines. Developing compact, integrated hybrid laser-arc welding equipment is essential to promote the widespread use of this technology in all-position pipeline welding. Conceptualization, W.L. and Q.L. ; methodology, W.L. and Q.L. ; validation, W.L. and J.Y. ; formal analysis, J.Y. ; resources, P.Z. ; data curation, B.L. ; writing--original draft preparation, W.L. and Q.L. ; writing--review and editing, W.L. and Q.L. ; visualization, P.Z. ; supervision, B.L. ; funding acquisition, W.L. All authors have read and agreed to the published version of the manuscript. This research was supported by the National Natural Science Foundation of China (Grant No. 51975410). Not applicable.