Straight seam welded steel pipes are divided into high frequency resistance welding and submerged arc welding according to the welding process. Straight seam submerged arc welding is referred to as LSAW, and longitudinal high frequency resistance welding is referred to as ERW.
Compared with submerged arc welding, high frequency electric resistance welded steel pipes (ERW steel pipes) do not add any welding materials during the welding process in the ERW process, and the weld formation does not undergo a thermal melting state, but the weld metal undergoes a recrystallization process. Therefore, the formed weld seam is completely consistent with the chemical composition of the base metal. After the steel pipe is welded, it is annealed to produce the cold working internal stress and welding internal stress. Therefore, the comprehensive mechanical properties of the ERW steel pipe are better.
LSAW steel pipes (UOE) adopt the post-weld cold expansion process to expand the pipes, so the geometric dimensions of LSAW steel pipes are more accurate, and the matching quality when using LSAW steel pipes is good to ensure the quality of welding. Eliminate part of the internal stress. In addition, LSAW steel pipes are welded with multi-wire welding (three-wire, four-wire), and the heat input generated by this welding process is small, the degree of influence on the heat affected zone of the base metal is also small. After multi-wire welding, the welding wire of the first pass can eliminate the stress generated during welding, thereby improving the mechanical properties of the steel pipe. The base material can achieve 100% ultrasonic flaw detection of steel plates one by one to meet the requirements of high-pressure pipelines for base materials. However, although the overall performance of LSAW steel pipe is better than other steel pipes, its high price discourages users with tight funds.
1. The difference between raw materials and production capacity
The raw material of ERW steel pipe is hot rolled steel coil, and the raw material of LSAW steel pipe is hot rolled steel plate. Therefore, ERW steel pipe can realize continuous assembly line operation with high production efficiency and low production cost; while SAW steel pipe is processed by steel plate, continuous assembly line operation cannot be realized, and the production efficiency is low, and the production cost is high. ERW steel pipe is limited by the thickness of the steel coil. Generally, the maximum thickness that can be produced is 25mm, and the maximum diameter that can be produced is 660mm; while the maximum thickness that can be produced for LSAW steel pipe is 40mm, the maximum diameter that can be produced is only limited by the width of the steel plate. The maximum production diameter is 1422mm.
LSAW steel pipes can be divided into different forming methods:
UOE steel pipe: After the single steel plate is pre-bent at the edge, it undergoes U forming, O forming, internal welding, external welding, mechanical cold expansion and other processes.
JCOE steel pipe: according to "J-C-O-E" pre-welding, forming, and cold expanding after welding
HME steel pipe: It is formed by mandrel rolling method according to "C-C-O", welded and then cold-expanded.
2. The difference in welding
ERW steel pipe welding does not need to add welding wire; LSAW steel pipe requires welding wire.
3. The difference in appearance
Both the inner and outer welds of the ERW steel pipe need to be removed, so it is beneficial to anti-corrosion; the extra height of the weld on the inner and outer walls of the LSAW steel pipe is not good for corrosion.
4. The difference between purchase cost and difficulty
The purchase cost of ERW steel pipe is low, and the cost of LSAW steel pipe is very high, and the general price difference is 15%-25%.
There are few domestic LSAW steel pipe manufacturers and it is difficult to purchase. When the diameter