A Study On Welding Procedure Of X70 Pipeline Steel

With the development of the oil industry, pipeline was choose to carry petroleum and natural gas, because this kind of method has many advantages, such as safe, economic, efficient and energy-saving. In the recent years, the construction of the internal and external oil and natural gas pipeline develops rapidly. So long-distance, big-diameter and high-pressure have been becoming into the development trends of land oil and natural gas pipeline. The West-East Pipeline Project is the key fundamental construction project in our country's"ten five-year plans". It is the longest, biggest-diameter ,most-spots and high-pressure natural gas pipeline in our country. By the internal research, Acicular Ferrite X70 steel, with high intensity and good toughness, it meets the requirements of petroleum and natural gas transportation. There is still no systemic welding research for X70 steel, and the formal welding method can't meet the requirements of the West-East construction. According to the above problems, this paper introduced development condition and trends of the pipeline steels. The good quality welding construction method was found.The mechanical property, microstructures and hardness distribution pattern of the girth welding joints under different welding process conditions were tested and analyzed.In the research, one process is using the cellulose electrode for root pass and self-shielded flux-cored wire for filler passes and cap pass. Another process is STT for root pass and NOREAST for filler passes and cap pass. The result of this study indicates the two processes put forward in this paper can meet the working conditions and application requirements, and they have been used in the West-East construction; also they have made great contributions to the West-East construction, received big economic and social profits, and produced great significance both in theory and project practice. The result of this study has important theoretic, academic and practical construction application guiding significance and reference value for the construction projects adopting more advanced pipeline steel.