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Comparison Of Spiral Steel Pipe, Straight Seam Steel Pipe And Seamless Steel Pipe

Dec. 04, 2019
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The production process of straight seam welded pipe is relatively simple. The main production processes are high-frequency welded straight seam steel pipe and submerged arc welding straight seam steel pipe. The production efficiency of straight seam pipe is high, the cost is low and the development is fast.The strength of spiral welded pipe is generally higher than that of straight welded pipe, and the main production process is submerged arc welding. Spiral steel pipe can be used to produce different pipe diameters with blank of the same width, and can also be used to produce larger pipe diameters with narrow blank.However, compared with the straight seam pipe of the same length, the weld length increases by 30~100%, and the production speed is lower.Therefore, the smaller diameter welded pipe mostly used straight seam welding, large diameter welded pipe is mostly used spiral welding.They have been used in the industry production of straight steel tube located at a t-shaped welding technology, the short sections of straight seam steel pipe for docking, the length of the connect accords with the need of engineering, t the probability straight seam welded steel defect is greatly improved, and the t-shaped seam welding residual stress is larger, the stress state of the weld metal are often in a three to increase the possibility of a crack.

Straight Seam Steel Pipe

Straight Seam Steel Pipe

Welding process: from the welding process, the spiral welded pipe and straight seam steel pipe welding method is consistent, but the straight seam welded pipe will inevitably have a lot of 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 regulations of submerged arc welding, every welding seam should have arc initiation and arc quenching, but each straight welded pipe cannot achieve this condition when welding circular seam, so there may be more welding defects at the arc quenching.

Strength characteristics: when the pipe is under internal pressure, there are usually two main stresses on the pipe wall, namely radial stress and axial stress.The resultant stress at the weld is, wherein, is the spiral Angle of the weld of the spiral welded pipe.The helical Angle of spiral welded pipe is usually degree, so the synthetic stress of spiral welded seam is the main stress of straight welded pipe.Under the same working pressure, the wall thickness of spiral welded pipe with the same diameter can be reduced compared with that of straight welded pipe.According to the above characteristics, it can be seen that when the spiral welded pipe is blasted, because the normal stress and synthetic stress of the weld are relatively small, the blasting mouth will not generally originate from the spiral weld, and its safety is higher than that of the straight welded pipe.When there is a defect parallel to the spiral weld, the spiral weld has less stress, so its expansion risk is not as great as that of the straight weld.Since the radial stress is the maximum stress existing on the steel tube, the weld will bear the maximum load when it is in the direction of vertical stress.That is, the straight seam bears the maximum load, the circumferential weld bears the minimum load, and the spiral seam is between the two.Static pressure blasting strength: through relevant comparative tests, it is verified that the yield pressure of spiral welded pipe and straight welded pipe is basically consistent with the measured value and theoretical value of blasting pressure, and the deviation is close.But the spiral welded pipe is lower than the straight welded pipe no matter the yield pressure or the bursting pressure.The test also shows that the annular deformation rate of spiral welded pipe is obviously higher than that of straight welded pipe.It is proved that the plastic deformation capacity of spiral welded pipe is better than that of straight welded pipe, and the blasting hole is generally limited to a screw pitch, which is caused by the strong constraint effect of spiral weld on the expansion of the crack. Toughness and fatigue strength: pipeline development trend is large diameter, high strength.With the increase of the diameter of the steel tube and the grade of steel used, the trend of the ductile fracture tip steady expansion is larger.According to the test of American research institute, spiral welded pipe and straight welded pipe are the same level, but spiral welded pipe has higher impact toughness.Due to the change of the conveying volume, the steel pipe is subjected to random alternating load in the actual operation.Understanding the low cyclic fatigue strength of steel pipe is of great significance to judge the service life of pipeline.

According to the measured results, the fatigue strength of the spiral welded pipe is the same as that of the seamless pipe and the resistance welded pipe.

Quality Customized Construction Pipe

Quality Customized Construction Pipe

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