Comparison of technical characteristics of spiral welded pipe and straight-seam welded pipe:
·Metallurgical properties of materials
LSAW pipes are produced from steel plates, while spiral welded pipes are produced from hot-rolled coils. The rolling process of the hot strip steel mill has a series of advantages, and it has the metallurgical process capability to produce high-quality pipeline steel.
·Welding process
In terms of the welding process, the welding method of spiral welded pipe is the same as that of straight seam steel pipe, but the straight seam welded pipe will inevitably have many T-shaped welds, so the probability of welding defects is greatly increased, and the welding residue at the T-shaped weld The stress is large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks. Moreover, according to the submerged arc welding process regulations, each weld should have an arc ignition point and an arc extinction point, but each longitudinal welded pipe cannot meet this condition when welding the circumferential seam, so there may be an arc extinction point. More welding defects.
·Static pressures blasting strength
Related comparative tests have verified that the yield pressure on the spiral welded pipe and the longitudinally welded pipe is consistent with the actual and theoretical values of burst pressure, and the deviation is close. But whether it is yielding pressure or burst pressure, the spiral welded pipe is lower than that of straight seam welded pipe. The blasting test also showed that the circumferential deformation rate of the spiral welded pipe blasting port was significantly greater than that of the straight welded pipe. This proves that the plastic deformation ability of spiral welded pipe is better than that of straight seam welded pipe, and the blast opening is generally limited to one pitch, which is caused by the strong restraint effect of spiral weld on the expansion of the crack.
·Toughness and fatigue strength
The trend of pipeline development is large diameter and high strength. As the diameter of the steel pipe increases and the grade in steel used increases, the tendency towards the ductile fracture tip to grow steadily becomes greater. According to the test conducted by relevant research institutions in the United States, although spiral welded pipe and longitudinal welded pipe are of the same level, the spiral welded pipe has a higher impact toughness. Due to changes in the transportation volume, the steel pipes are subjected to random alternating loads during actual operation. Understanding the low cycle fatigue strength of steel pipes is of the great significance of judging the service life of pipelines. According to the measurement results, the fatigue strength of spiral welded pipes is the same as that of seamless pipes and resistance welded pipes, and the test data are distributed over the same area as seamless pipes and resistance pipes, and are higher than general submerged arc longitudinal welded pipes.
·Field solderability
The weldability on site is mainly determined by the material of the steel pipe and the tolerance of the port size. Taking into account the requirements of steel pipe installation and construction, the continuity of steel pipes processing and production and the consistency of shape and geometric dimensions are particularly important. The production of a spiral welded pipe is a stable continuous process of the same working conditions: while the production process of straight seam welded pipe is segmented, including the whole plate/indenter/pre-rolling/spot welding/welding/finishing/grouping, etc. Multi-process process. This is an important feature that distinguishes spiral welded pipe production of straight seam welded pipe production. Stable production conditions are very convenient for the control of welding quality and the guarantee of geometric dimensions. Because the spiral welded pipe has a regular pipe shape and evenly distributed weld seams, the spiral steel pipe has very good nozzle ovality and end surface perpendicularity compared with straight seam welded pipes, which ensures the accuracy of the on-site pipe welding assembly.
Post time: Dec-04-2023