1. Metallurgical performance of materials
The straight seam buried arc welded pipe is produced with steel plates, and the spiral welded pipe is produced with hot -rolled coils. The rolling process of hot -rolled steel units has a series of advantages and has the ability to obtain metallurgical technology for production high -quality pipeline steel. For example, a water cooling system is installed on the output table to accelerate cooling, which allows the use of low alloy components to achieve special strength levels and low temperature toughness, thereby improving the weldability of steel.
The alloy content (carbon proper amount) of the rolling plate is often lower than the steel plate of similar levels, which also improves the weldability of the spiral welded pipe. Because the rolling direction of the rolling rolling of the spiral tube is not the direction of the vertical steel pipe axis (its solution depends on the spiral angle of the steel pipe), and the steel plate rolling direction of the straight steel pipe is perpendicular to the steel pipe axis. Occasionally better than straight steel pipes.
2. Welding process
In terms of welding process, the welding method of the spiral welding pipe and the straight seam steel pipe is consistent, but the straight seam welded pipes inevitably have a lot of b -welding seams. Therefore The stress is large, and the weld metal is often in a three -way stress state, increasing the possibility of cracking.
In addition, according to the process of buried arc welding, each welding seam should be attached to the arc and extinguished arc. More welding defects.
3. strength characteristics
When internal pressure, the tube usually produces two main stress on the tube wall, namely the radial stress Δy and axial stress Δx. The synthetic stress Δ = Δy (L/4SIN2α+COS2α) is synthetic at the weld.
The spiral angle of the spiral welded weld is generally 50-75 degrees, so the synthetic stress at the spiral weld is 60-85%of the main stress of the straight seam welded pipe. Under the same working pressure, the spiral tube of the same diameter can be reduced compared to the wall thickness of the straight welded pipe.
