【History of Haichuan Pipelines】On 20200615, automatic welding technology for fillet welds in operational oil and gas pipelines was put into use
Thread Content
Automatic welding technology for corner welds of in-service pipelines was put into use. On June 15, 2020, this technology was applied industrially for the first time on the China-Myanmar Pipeline (Guizhou section), marking the successful overcoming of this technical challenge and representing a breakthrough in this field in China. This on-site application represents a strong collaboration between China National Petroleum Pipeline Bureau Engineering Co., Ltd. and Southwest Pipeline Company in the field of research and development, providing important technical support for improving the integrity management system of the pipelines in China’s petroleum energy infrastructure and enhancing the intrinsic safety level of these pipelines. This technology represents a critical bottleneck in the automatic welding of existing oil and gas pipelines. In the automatic welding of existing pipelines, there is usually an uneven gap of 1 to 5 millimeters at the junction between the repair fittings and the existing pipeline. Using traditional manual arc welding methods poses significant risks in terms of quality and safety, while the key technologies for automatic welding are still at a developmental stage. To achieve a breakthrough, the research team conducted six months of metallographic experiments on circumferential fillet welds, testing over 60 specimens. They developed a set of welding process parameters suitable for different welding positions and gap sizes, successfully overcoming the challenges. This approach not only ensured quality and safety but also increased efficiency while significantly reducing labor costs. This field application was carried out on pipelines located in mountainous areas of Guizhou Province, where the climate and geological conditions are quite complex and construction is challenging; as a result, the findings are highly relevant and specific, fully demonstrating that this technology enables full compatibility with various factors such as construction conditions, pipeline materials, construction methods, and properties of the fluid carried.
Welding of existing oil and gas pipelines generally refers to the welding of pipe fittings onto pipelines under specific flow rates, velocities, and pressure conditions, in order to carry out maintenance or modifications to the pipelines. The welding safety of operational oil and gas pipelines is primarily concerned with two issues: one is the burn-through of the pipe wall due to localized heating ； Secondly, the cooling rate during welding is too fast, which leads to an increase in the hardness of the heat-affected zone (HAZ), increasing the likelihood of hydrogen-induced cracking. Welding of existing pipelines usually involves two types: the transverse butt welds for creating tee joints or repair sleeves at the weld seams, and the circumferential fillet welds to connect the ends of the repair fittings to the existing pipeline. Manual arc welding is used for almost all welding of existing pipelines both domestically and internationally.
As the construction of long-distance oil and gas pipelines moves toward higher pressures, larger diameters, and higher steel grades, the sizes of the fittings used in welding operations also increase. Taking a pipeline made of X80-grade steel with a diameter of Φ1,219 and a design pressure of 12 MPa as an example, the thickness of the protective plates on its blocking tees (usually made of Q345R material) can reach 80 mm or even more, which significantly increases the workload associated with repair welding. The currently used manual arc welding method has a slow welding speed and long welding time, which severely limits the efficiency of maintenance and repair work, and makes it difficult to ensure welding quality. The common welding processes for automatic pipeline welding include gas shielded welding with solid wire and gas shielded welding with flux-cored wire. Gas shielded welding with flux-cored wires requires relatively low precision in on-site groove preparation and alignment, and it is more easy to operate ； Given the characteristic of rapid welding cooling rates caused by heat being carried away by the flow of welding media during operation, its process parameters are more easily able to meet the requirements regarding welding heat input ； Moreover, this process can be applied in a wider range of environments; automatic welding is possible even in steep mountainous areas, making it more suitable for use in harsh conditions during maintenance and repair tasks. Therefore, gas shielded welding with flux-cored wires is a relatively promising welding process.
【History of Haichuan Pipes】The summary post is being updated continuously; learn about the development process of various pipes at https://bbs.hcbbs.com/thread-3068575-1-1.html (Source: Haichuan Chemical Industry Forum)