Manual welding mainly includes cellulose covered electrode downward welding and low hydrogen covered electrode downward welding.
In the automatic welding of pipelines, there is a pipeline flash butt welding machine developed by the former Soviet Union, which accumulated tens of thousands of kilometers of large-diameter pipelines during the former Soviet Union.
Its remarkable characteristics are high efficiency and strong adaptability to the environment.
The automatic welding system of CRC multi-head gas shielded pipeline developed by CRC Company in the United States consists of three parts: pipe end beveling machine, internal butt welding machine and internal welding machine combination system, and external welding machine.
Up to now, the cumulative length of welded pipelines in the world has exceeded 34,000 kilometers.
France, the former Soviet Union and other countries have also studied and applied similar automatic welding technology inside and outside pipelines, which has become the mainstream of automatic welding technology for large-diameter pipelines in the world today.
China steel pipe girth welding technology has undergone several major changes. In 1970s, traditional welding method was adopted, and low hydrogen covered electrode manual arc welding overhead welding technology was adopted. In 1980s, manual arc welding downward welding technology was popularized, and cellulose covered electrode and low hydrogen covered electrode downward welding technology were adopted. Self-shielded flux-cored wire semi-automatic welding technology was applied in 1990s, and today all-position automatic welding technology has been fully promoted.
Manual arc welding includes the application of cellulose covered electrode and low hydrogen covered electrode.
Manual arc welding overhead welding technology is the main welding method in pipeline construction in China in the past, which is characterized by large gap between nozzle groups, arc stopping method, large thickness of each welding layer and low welding efficiency.
Manual arc welding downward welding is a welding technology introduced from abroad in 1980s, which has the characteristics of small nozzle gap, high current, multi-layer and fast welding, and is suitable for assembly line operation with high welding efficiency.
Due to the thin thickness of each welding layer, the toughness of the ring welding joint can be improved by heat treatment of the front welding layer by the rear welding layer.
Manual arc welding method is flexible, simple and adaptable. The organic combination of downward welding and upward welding and the good adaptability of cellulose covered electrode to root welding are still irreplaceable by automatic welding method in many occasions.
Self-shielded flux-cored wire semi-automatic welding technology was applied to pipeline construction in 1990s, mainly for filling and covering.
It is characterized by high deposition efficiency, good all-position forming, strong environmental adaptability and easy mastery by welders. It is an important welding process method for pipeline construction.
With the increase of strength grade, pipe diameter and wall thickness of steel pipes for pipeline construction, automatic welding technology is gradually applied to pipeline construction.
Pipeline automatic welding technology has the advantages of high welding efficiency, low labor intensity and little influence from human factors in the welding process, and has great application potential in the construction of large-diameter thick-walled pipelines.
However, China's pipeline automatic welding technology is in its infancy, the problem of automatic root welding has not been solved, and the supporting facilities such as pipe end groove forming machine are not yet mature, which leads to the large-scale application of automatic welding technology.