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The difference of SSAW steel pipe end flaring and LSAW steel pipe expanding
The main purpose of SSAW steel pipe end flaring is to improve the dimensional accuracy of the circumference of the pipe end, so only flaring the ends of the steel pipe. As the dimensional accuracy of SSAW steel pipe is also OK before flaring, it can choose a smaller expansion ratio when expanding, typically 0.3% is OK. To avoid significant step between the expanding segment and not expanding segment boundaries, set the transition period in the tail section of expanding to achieve a smooth transition. In order to avoid contacting between the mold and the inner weld, use the sanding device to remove the inner weld of the expanding zone.
While LSAW steel pipe uses a whole expanding, with the mechanical expanding machine to achieve the step-by cooling expanding of the full length for the pipe, in addition to improving the accuracy of the geometry of the outer pipe, and LSAW steel pipe cold-expanding adopts a larger diameter expansion rate, general about 11%. In order to avoid contacting between the mold and the inner weld using a grooved mold surface method.
Compared with the SSAW steel pipe, LSAW steel pipe material properties anisotropy is small, easy to implement hierarchical testing of base metal pipe; in the premise of ensuring accurate material width, LSAW steel pipe can guarantee an equal circumference after forming; welding track is easy to implement, inner weld polishing easy to implement automatically with high production efficiency; the pipe end dimensional accuracy is high, and good consistency with the ends of the tubes diameter and can produce large wall thickness, high grade steel tubes with a wide range of pipe wall thickness; easy to implement ultrasonic testing, the blind tube end is small, detection reliability is high, and the pipe quality is reliable.
LSAW steel pipe material utilization is high. What's more important is the high qualified rate of straight seam pipe, and easy to use automatic welding to repair, the passing rate can be up to 99.5%, and its cost performance is superior to SSAW steel pipe.
As the SSAW steel pipe is welded with steel strip as raw materials, with a limited wall thickness, steel grade improvement is also limited by the material heat treatment, combined with the weakness of a long weld, large residual stress and poor reliability which is difficult to overcome, with the continuously increasing requirements for the steel pipe for oil and gas transportation, it has failed to meet project requirements. Large diameter LSAW steel pipe is gradually replacing the SSAW steel pipe. In recent years, long distance oil and gas pipelines and the construction of subsea pipelines, coal pipes and transnational oil and gas pipelines, etc., are all or most required to adopt LSAW steel pipe.
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