The main differences between SSAW and LSAW steel pipes are in their length and pattern of welding seam. SSAW pipes have longer welding seams than LSAW pieps and so have a higher risk of seam defects. Meanwhile, for SSAW steel pipes, the welding seam is at a certain angle with the orientation of the priciple stress. This shortens the faulty welding joints of an SSAW steel pipe when compared with an LSAW steel pipe of an equivalent lenght. (This reduces the danger of a single defect). The disadvantage and advantage mentioned above cancel out each other. The difference between the orientation of the welded seam and the special directivity ofthe major raw material of a SSAW steel pipe enhance its resistance against fracture.
In 1998, the Tubular Goods Research Centre of CNPC, together with China Petroleum Planning and Engineering Institute conducted a comparative experiment systemically on domestically produced SSAW steel pipes and imported LSAW (UOE) steel pipes.
The following conclusions were drawn:
1. The strength, tensility and fatigue resistance of the major raw material, seam and heat-affected zones of domestically produced SSAW steel pipes were the sam as those of imported UOE pipes.
2. The SSAW steel pipes domestically produced under strict quality control can be used in the trunk pipelines for oil and gas distribution.
3. If measures are adopted to reduce the residual stress in the domestically produced SSAW pipes and enhance the dimensional accuracy in them, their quality and safety can be on the same level of the imported UOE
