Difference between SSAW steel pipe and LSAW steel pipe

Difference between LSAW steel pipe and SSAW steel pipe are followings below:

Metallurgical properties of raw materials
Straight seam submerged arc welding tube is made of steel, but spiral submerged arc welding steel pipe production is usd hot rolled steel coil strip. The hot strip rolling process with a series of advantages, has a metallurgical process for production of high-quality line pipe capacity.

LSAW (Longitudinally Submerged Arc Welded Steel pipes) in leaflets plate as raw material, the steel plate in the mold or molding machine pressure (volume) into using double-sided submerged arc welding and flaring from production.

Spiral submerged arc welding(SSAW) is its forward direction and forming tube centerline hose reel molding angle (adjustable), side molding edge welding and weld them into a spiral.

Welding process

From the welding process, spiral steel pipe welding method is the same as lsaw steel pipe, but the straight seam submerged arc welding tube inevitably will be a lot of T-weld, so the probability of presence of welding defects also greatly improved, and T-welds welding residual stress weld metal are often in a three dimensional stress state, increasing the possibility of cracks.

According to the submerged arc welding process requirements, each weld should have the arc at the extinction,but each steel pipe is unable to meet the conditions in welding girth,which may be at the extinction more welding defects.

1. The welding process is concerned: a consistent spiral welded pipe and Longitudinal welding, straight seam steel pipe will inevitably have a lot of T-weld, and therefore the probability of the existence of welding defects has greatly improved, and welding residual T welds stress is large, the weld metal are often in three-dimensional stress state, increases the likelihood of cracks. Furthermore, according to the provisions of submerged arc process, each weld shall have the arc at the place and extinction, but in each Longitudinal seam welding ring, unable to meet the conditions, which may have a place in the extinction more weld defects.

2. When the pressure in the pipe to withstand, typically produces two main stress on the wall, that the radial and axial stress stress δ . Weld resultant stress δ, wherein the helix angle of the weld.

3. Spiral Weld Pipe degree helix angle is generally, therefore synthetic spiral weld stresses are the principal stresses. Under the same operating pressure, spiral pipe of the same diameter than the Longitudinal wall thickness can be reduced.

4. The hydrostatic burst strength: by the relevant comparison test, to verify the yield pressure and burst pressure measured and theoretical values spiral pipe and Longitudinal basic agreement, deviation close. But neither the yield stress or burst pressure, spiral pipe were lower than Longitudinal. Blasting test also shows spiral steel hoop blasting mouth deformation rate significantly greater than the Longitudinal. It was thus confirmed, spiral pipe plastic deformation than Longitudinal, blasting the mouth is generally confined to within a pitch, which is spiral weld for expansion gap played a powerful role in binding due.

5. Toughness and fatigue strength: pipeline development trend of large diameter, high strength. With the increase of the diameter of the pipe, the steel grade increase, resulting in greater the ductile fracture tip steady expansion trend. Spiral pipe and Longitudinal although the same as a level, but the spiral steel pipe has a high impact toughness.

6. Because of the transfer line output volume changes: in actual operation, the pipe is subjected to random alternating loads of action. Learn low cycle fatigue strength of steel, judging life of the pipeline is of great significance.

7. Press the measuring result: fatigue strength spiral steel seamless and ERW pipe with the same test data and seamless pipe distribution and resistance in the same area, while Longitudinal submerged arc than the average higher.

Weled steel pipe specification, Standard and identification

Welded steel pipe (steel pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp, that are formed, bent and prepared for welding.