Difference Between LSAW and HSAW Pipes
Longitudinally Submerged Arc Welding, shorthand for LSAW
Helical submerged arc welding (spiral) steel pipe is the full name of HSAW pipe.
1 welding technology in terms of:
spiral welded pipe and straight seam welded pipe welding method is consistent, straight seam steel pipe, inevitably, there will be a lot of the t-shaped weld, so the probability of weld defects is also greatly improved, and the t-shaped seam welding residual stress is larger, the stress state of the weld metal are often in a three-way increases the possibility of a crack.In addition, according to the technical provisions of submerged arc welding, each welding seam should have an arc ignition place and an arc extinguishing place, but each straight seam welding pipe cannot reach this condition when welding the circular seam, so there may be more welding defects at the arc extinguishing place.
2. When the pipe is under internal pressure, two main stresses are usually generated on the pipe wall, namely, radial stress and axial stress.The synthetic stress at the weld , where, the spiral Angle of the weld.
3. The weld of spiral steel tube is the spiral angle, so the synthetic stress at the spiral weld is the main stress.Under the same working pressure, the wall thickness of spiral pipe with the same diameter can be reduced than that of straight seam welded pipe.According to the above characteristics, when the spiral steel pipe bursts, because the normal stress and synthetic stress on the welding seam are relatively small, the bursting port generally does not originate from the spiral welding seam, and its safety is higher than that of the straight seam welded pipe.When there is a parallel defect near the spiral weld, the expansion risk of the spiral weld is not as high as that of the straight weld due to the low stress of the spiral weld.Because the radial stress is the maximum stress existing on the steel pipe, the welding seam bears the maximum load when it is in the direction of vertical stress.That is, the straight seam bears the largest load, the circumferential weld bears the smallest load, and the spiral seam is between the two.
4. Static pressure blasting strength: through relevant comparative tests, it is verified that the yield pressure of spiral steel pipe and straight-seam welded pipe is basically consistent with the measured and theoretical values of blasting pressure, with the deviation close.But no matter the yield pressure or blasting pressure, the spiral steel pipe is lower than the straight seam welded pipe.The blasting test also showed that the annular deformation rate of the blasting mouth of spiral steel pipe was significantly higher than that of straight seam welded pipe.It is proved that the plastic deformation capacity of spiral steel pipe is better than that of straight welded pipe, and the blasting mouth is generally limited to one pitch, which is caused by the strong restraint effect of spiral weld on the expansion of the crack.
5. Toughness and fatigue strength: the trend of pipeline development is large diameter and high strength.With the increase of the diameter of steel pipe and the increase of the steel grade used, the trend of the cusp stability extension of ductile fracture becomes larger.According to the test of the related research institution in the United States, although the spiral steel pipe and the straight seam welded pipe are the same grade, the spiral steel pipe has higher impact toughness.
6. The pipeline is subject to random alternating loads during the actual operation.It is important to know the low cyclic fatigue strength of steel pipe to judge the service life of pipeline.
7. According to the measurement results, the aromatic strength of spiral steel pipe is the same as that of seamless pipe and resistance welded pipe. The test data are distributed in the same area as that of seamless pipe and resistance welded pipe, but higher than that of general submerged arc welded pipe.