Different between LSAW Steel Pipe and SSAW Steel Pipe

LSAW steel pipe and SSAW steel pipe are important production processes in the national production and construction. They have many differences, such as material properties, production processes, and features. Here's a specific introduction:

1. the metallurgical properties of materials: LSAW pipe is produced with steel plate, and spiral welded pipe is produced with hot rolled coil. The rolling process of the hot strip mill unit has a series of advantages, and has the metallurgical process capability to obtain high quality pipeline steel. For example, a water cooling system is installed on the output stage to accelerate cooling, which allows the use of low-alloy compositions to achieve special strength levels and low temperature toughness, thereby improving the weldability of the steel. However, this system is basically absent from the steel plate production plant. Coil alloy content (carbon equivalent) is often lower than similar grades of steel, which also improves the weldability of spiral welded pipe. It should be noted that since the spiral rolling direction of the spiral welded pipe is not perpendicular to the axial direction of the steel pipe (the solution depends on the helix angle of the steel pipe), the steel plate rolling direction of the straight seam steel pipe is perpendicular to the axial direction of the steel pipe. Thus, the spiral Welded pipe material has better crack resistance than straight seam steel pipe.

2. welding process: from the welding process, spiral welded pipe and straight seam steel pipe welding method is the same, but the straight seam welded pipe inevitably there will be a lot of T-welding, so there is a great increase in the probability of welding defects, and T-welding The welding residual stress at the seam is large, and the weld metal is often in a three-dimensional stress state, increasing the possibility of cracking. Moreover, according to the submerged-arc welding process specification, each weld should have an arc striking point and an arc extinguishing point. However, each straight-seam welding pipe cannot achieve this condition when welding a circumferential ring, and thus may have an arc extinguishing position. More welding defects.

Straight seam welded pipe production process is relatively simple, the main production processes are high-frequency welding straight seam welded pipe and submerged arc welded straight seam welded pipe. Longitudinal seam welded pipe has high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of longitudinal welded pipes. The main production process is submerged arc welding. Spiral welded pipes can produce pipes with different diameters from the same width of blanks, and narrower blanks can also be used to produce larger diameter pipes. However, compared with the longitudinal welded pipe of the same length, the weld length is increased by 30 to 100% and the production speed is low. Therefore, the smaller diameter welded pipe mostly adopts the straight seam welding, and the large diameter welded pipe adopts the spiral welding.

3. Strength characteristics: When the tube is subjected to internal pressure, it usually produces two main stresses on the tube wall, namely radial stress δY and axial stress δX. Weld seam synthetic stress δ = δY (l/4sin2α cos2α) 1/2, where α is the spiral angle of the spiral welded pipe weld. The helix angle of the spiral welded pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral welded joint is 60-85% of the principal stress of the longitudinal welded pipe. At the same working pressure, the spiral welded pipe with the same pipe diameter can be reduced in wall thickness than the straight welded pipe.
Therefore, the designer can use different welding techniques according to the specific conditions in the production process to meet the customer's requirements.