Oil and gas pipeline welding construction technology

1.1 Manual welding with cellulose downward electrode

When there is a pipeline with severe hydrogen sulfide corrosion or a pipeline operating in a cold environment, use a low-hydrogen type vertical downward welding electrode. 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. For example, in recent years, the pipeline project from Shaanxi to Beijing in my country has been purchased from Bo Le There are more than 1,000 tons of various cellulose electrodes. It is predicted that the annual demand for welding electrodes for my country's oil and gas pipelines in the next few years will be 3 to 5,000 tons, and there will be an increasing trend.

1.2 Bottom welding to the cellulose electrode standing down, and filling 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 pipeline welding, all-position welding must be completed in a smaller current range and completed in the form of short-circuit transfer. In the bottom welding, defects such as incomplete penetration are easy to occur. Therefore, the single-sided welding is realized by using the vertical cellulose electrode to bottom, and the back is formed, and then the surface is filled with CO2 gas shielded welding with high efficiency. This process is widely used.

1.3 Semi-automatic welding with self-shielded flux-cored wire

The self-shielded flux-cored wire semi-automatic welding is especially suitable for outdoor windy occasions. It does not use CO2 gas protection generated by the flux core. It has good wind resistance and can be used for all-position welding with a high deposition rate of pipelines. At present, Lincoln Corporation The self-shielded flux-cored welding wire produced is recognized by various countries, and its brands are NR-207, NR-204-H, NR-208-H, etc., which can be used for vertical downward welding of X70, X80, and other pipelines. However, this method also has the defect that the weld root is prone to not fusion during bottom welding.

1.4 CO2 gas shielded semi-automatic or fully automatic welding of high-performance welding machines.

As a result of in-depth research on the short-circuit transition process control technology of CO2 gas shielded welding, high-performance power supplies for timely control of welding current and voltage waveforms or power control of output characteristics have been produced abroad. The aforementioned STT surface of Lincoln Corporation of the United States The tension transition welding technology belongs to the category of waveform control. Based on the improvement of the performance of welding equipment, semi-automatic and fully automatic CO2 gas shielded welding of pipelines can be well realized, which greatly improves welding efficiency and welding quality. Besides, automatic TIG welding is also used for pipe welding in the factory. This method has good quality but low production efficiency.