1. The priority principle of arc welding with electrodes
For the installation and welding of pipelines whose diameter is not too large (such as below 610mm) and the length of the pipeline is not very long (such as below 100km), electrode arc welding should be considered as the first choice. In this case, electrode arc welding is the most economical Welding method.
Compared with automatic welding, it requires less equipment and labor, lower maintenance costs, and a more mature construction team.
Electrode arc welding has been used for installation and welding for more than 50 years. Various electrodes and various operation methods are relatively mature in technology. A large amount of data, quality assessment is simple.
Of course, for the welding of high-strength grade steel pipes, attention should also be paid to the selection and control of welding rods and process measures. When welding follows the standard pipeline specification AP1STD1104-2005 “Welding of pipelines and related equipment), use qualified welders who have been trained and tested. When 100% radiographic inspection is performed, it is possible to control the repair rate of all welds below 3%.
Due to lower cost and maintenance. Coupled with the guaranteed quality, electrode arc welding has been the first choice of most project contractors in the past.
2. Submerged arc automatic welding priority principle
As mentioned earlier, the submerged arc automatic welding of pipes is carried out in pipe welding stations specially designed for pipes. If the two pipes are welded close to the site (double pipe welding), the number of welds on the main line can be reduced by 40% to 50%, which greatly shortens the laying cycle.
The high efficiency and high quality of submerged arc automatic welding for installation welding are obvious, especially for pipelines with large diameter (above 406mm) and wall thickness exceeding 9.5mm, when the laying distance is long, for economic reasons, Usually, the method of automatic submerged arc welding is considered first.
However, the one-vote veto is whether the road for transporting double pipes is feasible, whether the road conditions allow it, and whether there are conditions for transporting double pipes longer than 25m. Otherwise, the use of automatic arc welding will be meaningless.
Therefore, for long-distance pipelines with a diameter of more than 406mm and large wall thickness, when there are no problems in transportation and road conditions, the method of welding double or triple pipes with automatic submerged arc welding is the best choice for project contractors
3. Flux cored wire semi-automatic welding priority principle
Combined with electrode arc welding, flux cored wire semi-automatic welding is a good welding process for filling welding and cover welding of large-diameter and thick-walled steel pipes.
The main purpose is to change the intermittent welding process into a continuous production mode, and the welding current density is higher than that of electrode arc welding, the welding wire melts faster, and the production efficiency can be 3 to 5 times that of electrode arc welding, so the production efficiency is high.
At present, self-shielded flux-cored wire semi-automatic welding is widely used in field pipeline welding due to its strong wind resistance, low hydrogen content in the weld, and high efficiency. It is the preferred method for pipeline construction in my country.
4. Priority principle of MIG automatic welding
For long-distance pipelines with a diameter greater than 710mm and a large wall thickness, in order to obtain high construction efficiency and high quality, MIGA automatic welding is often considered first.
This method has been used for 25 years, and it has been widely recognized for large-diameter pipelines in the world, including onshore and underwater pipe groups, and is generally valued in Canada, Europe, the Middle East and other countries and regions.
The important reason why this method is widely used is that the quality of installation and welding can be guaranteed, especially when welding high-strength pipelines.
Due to the low hydrogen content of this welding method, and the relatively strict requirements on the composition and manufacture of the welding wire, if the toughness requirement is high or the pipeline is used to transport acidic media, welding high-grade steel pipes with this method can obtain stable welding quality.
It is worth noting that compared with electrode arc welding, the investment in the metal arc welding system is large, and the requirements for equipment and personnel are high. The required advanced maintenance must be considered, and the accessories and the mixed gas that meet the hygienic requirements must be considered. supply.
Post time: Jun-20-2023