API 5L line pipe is a pipeline that transports the oil, gas or water extracted from the ground to the oil and gas industry enterprises through the line pipe. API 5L line pipe includes two kinds of seamless pipe and welded pipe, and its pipe ends include flat end, threaded end and socket end; its connection methods are end welding, coupling connection, socket connection, etc.
At present, the welding process of API 5L line pipe mainly includes the following:
1. When there is a pipeline with severe hydrogen sulfide corrosion or a pipeline running in a cold environment, use a low-hydrogen type vertical downward electrode for welding. Due to the flexibility of manual welding and the low requirements of welding equipment, the current outdoor pipeline welding, manual arc welding still accounts for 40-50% of the workload.
2. Make bottom welding to the cellulose electrode, and fill the surface with CO2 gas shielded welding. Due to the high productivity and low cost of CO2 welding, this method has been continuously promoted and applied in recent years.However, for oil and gas pipelines, to achieve all-position welding, it must be completed in the form of short-circuit transition within a relatively small current range, and the short-circuit transition method is used for bottom welding, which is prone to defects such as incomplete penetration.Therefore, the bottoming of the cellulose electrode is used to realize single-sided welding, the back is formed, and then the high-efficiency CO2 gas shielded welding is used to fill the surface. This method is widely used.
3. Self-shielded flux-cored wire semi-automatic welding. It is especially suitable for outdoor windy occasions. It does not use CO2 gas protection generated by flux cores. It has good wind resistance and can be used for all-position welding of pipelines with high deposition rate. This method also has the defect that the weld root is easy to be unfused during bottom welding.
4. CO2 gas shielded semi-automatic or fully automatic welding of high-performance welding machine. Based on the improvement of the performance of the welding equipment, the semi-automatic and fully automatic co2 gas shielded welding of the pipeline can be well realized, and the welding efficiency and welding quality are improved. In addition, automatic TIG welding is also used for pipe welding in the factory, which has good quality but low production efficiency.
At present, the welding process of API 5L line pipe mainly includes the following:
1. When there is a pipeline with severe hydrogen sulfide corrosion or a pipeline running in a cold environment, use a low-hydrogen type vertical downward electrode for welding. Due to the flexibility of manual welding and the low requirements of welding equipment, the current outdoor pipeline welding, manual arc welding still accounts for 40-50% of the workload.
2. Make bottom welding to the cellulose electrode, and fill the surface with CO2 gas shielded welding. Due to the high productivity and low cost of CO2 welding, this method has been continuously promoted and applied in recent years.However, for oil and gas pipelines, to achieve all-position welding, it must be completed in the form of short-circuit transition within a relatively small current range, and the short-circuit transition method is used for bottom welding, which is prone to defects such as incomplete penetration.Therefore, the bottoming of the cellulose electrode is used to realize single-sided welding, the back is formed, and then the high-efficiency CO2 gas shielded welding is used to fill the surface. This method is widely used.
3. Self-shielded flux-cored wire semi-automatic welding. It is especially suitable for outdoor windy occasions. It does not use CO2 gas protection generated by flux cores. It has good wind resistance and can be used for all-position welding of pipelines with high deposition rate. This method also has the defect that the weld root is easy to be unfused during bottom welding.
4. CO2 gas shielded semi-automatic or fully automatic welding of high-performance welding machine. Based on the improvement of the performance of the welding equipment, the semi-automatic and fully automatic co2 gas shielded welding of the pipeline can be well realized, and the welding efficiency and welding quality are improved. In addition, automatic TIG welding is also used for pipe welding in the factory, which has good quality but low production efficiency.
