Oil and gas steel pipeline welding

With the development of the petroleum industry, pipeline transportation of oil and gas has developed rapidly due to its safety, economy, professionalism, and high efficiency. Long-distance, large-diameter, and high-pressure pipelines are becoming the development direction of onshore oil and gas transmission pipelines. X56—X70 series high-strength steels for pipelines have been widely used in pipeline construction, and X80 high-strength pipelines are also in the development and application stage, such as the German 1993 In 1994, an X80 pipeline with a diameter of 1200mm and a length of 126km was built. In 1994, a Φ1200mm\33km X80 pipeline was trial-built in Canada. Due to the rapid construction of oil and gas pipelines, steel pipeline welding technology, welding equipment, and welding materials have also developed greatly. Many manufacturers have participated in market competition. There are many mature welding equipment and welding materials for pipeline construction at home and abroad. The following is the investigation of the equipment and materials for pipeline welding produced by famous foreign manufacturers for reference.
1 Overview of common welding processes for oil and gas pipelines at home and abroad
In the 1970s and 1980s, the welding of pipelines was mainly manual welding of downward cellulose electrodes and semi-automatic CO2 welding. Since these methods were manually operated, the efficiency was low, and the welding quality was also restricted by the level of manual skills. In the mid-1980s, Due to the continuous development of power electronics technology and computer technology, the control technology of welding equipment entered the era of intelligence, thus creating conditions for the successful implementation of new equipment and new processes for pipeline welding automation, which greatly improves the welding efficiency and welding quality of pipelines. Great improvement, such as the STT (Surface Tension Transfer) CO2 gas-shielded welding power supply technology and equipment developed by an American company, has attracted the attention of the world with their soft arc, minimal spatter, and excellent bottom welding quality, and has become a pipeline Welding, especially root welding is one of the preferred methods. Another example is the all-position automatic welding equipment for pipelines produced by other companies. The adaptive control technology is applied, which not only overcomes the level constraints of manual operation but also greatly improves welding efficiency and quality.

In summary, the current pipeline welding construction technology mainly includes the following types:
1.1 Use cellulose downward electrode for manual welding. When there are pipelines with severe hydrogen sulfide corrosion or pipelines operating in cold environments, use low-hydrogen type vertical electrode welding. Due to the flexibility of manual welding and the low requirements for welding equipment, the workload of manual arc welding still accounts for 40-50% of outdoor pipeline welding. It is predicted that the annual demand for welding rods for my country's oil and gas pipelines will be 3-5 in the next few years. thousand tons, and there is an increasing trend.
1.2 Stand down to the cellulose electrode for bottom welding, and CO2 gas-shielded welding to fill the surface. 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, to realize all-position welding, it must be completed in a small current range and in the form of short-circuit transition, while the short-circuit transition method uses Because bottoming welding is prone to defects such as incomplete penetration, it is common to use vertical cellulose electrode bottoming to realize single-sided welding, the back is formed, and then the surface is filled with high-efficiency CO2 gas shielded welding.
1.3 Self-shielded flux cored wire semi-automatic welding
Self-shielded flux-cored wire semi-automatic welding is especially suitable for outdoor windy occasions. It does not use CO2 and relies on the gas protection generated by the flux core. It has good wind resistance and can be used for all-position welding with high deposition rates for pipelines. It is currently produced in the United States. The self-shielded flux-cored welding wire is recognized by all countries, and it can be applied to the vertical down welding of X70, X80, and other pipelines. However, this method also has the defect that the weld root is prone to infusion during back welding.
1.4 CO2 gas shielded semi-automatic or fully automatic welding of high-performance welding machine.
Due to the results of in-depth research on the control technology of the CO2 gas-shielded welding short-circuit transition process, foreign countries have successively produced high-performance power supplies that control the welding current and voltage waveforms promptly or that control the output characteristics. The aforementioned STT surface of the American Lincoln company The tension transition welding technology belongs to the category of waveform control. 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, which greatly improves the welding efficiency and welding quality. In addition, automatic TIG welding is also used for pipe welding in the factory. This method has good quality but low production efficiency.
2 Welding consumables for pipe welding
2.1 Cellulose vertical electrode
2.2 Solid and flux-cored wire