1. Advantages of LSAW steel pipe:
(1) The tube expansion process used in LSAW steel pipe manufacturing results in residual stress close to zero and eliminates the ‘Bauschinger’ effect.
However, in the case of SSAW steel pipe, the manufacturing process results in molding stress and the occurrence of the ‘Bauschinger’ effect. To counter this, steel with a higher strength level, such as X07 steel, is used to produce X56 welded pipe. It is important to note that welding stress can lead to pipeline stress corrosion. Over the past twenty years, China has used more than 8000 kilometers of SSAW. However, due to stress corrosion and accidents, the pipeline has experienced destruction at a rate of up to 1-2 times per year.
(2) The length of the weld in LSAW steel pipes is shorter than that of SSAW steel pipes, resulting in a lower incidence of weld defects.
(3) Non-destructive testing of LSAW steel pipes is more convenient compared to SSAW steel pipes, and online inspection is easier. Straight-seam submerged arc welding is easier to control than oblique seam submerged arc welding in terms of welding quality.
(4) The quality of LSAW steel pipe molding is high, whereas SSAW steel pipe is prone to hard corners, biting edges, and unequal inside and outside welds due to simultaneous molding and welding.
(5) The heat-affected zone in LSAW steel pipes is smaller than that in SSAW steel pipes, which makes it the weak link in the quality of welded pipes.
(6) SLAW steel pipe can produce thick-walled steel pipes for ultra-high-pressure pipelines. For instance, X07 steel and SSWA can produce steel pipes with a wall thickness of 12-17 mm, while LSAW can produce steel pipes with a wall thickness of 25 mm or even higher under certain conditions.
2. Advantages of SSAW steel pipe：
(1) Welded seams avoid the main stress direction
After the pipe is pressurised internally, the main stress is in the annular direction. The SSAW weld is angled at approximately 45 degrees to the axis, which avoids the main stress direction. The LSAW weld is perpendicular to the ring direction, which is the main stress direction.
(2) The steel plate has the highest impact toughness in the rolling direction, and the lowest impact toughness in the vertical rolling direction. LSAW welding involves vertical rolling of the steel plate, while SSAW welding involves staggered rolling in the vertical direction. The difference between the two is several times. Therefore, the SSAW tube has better impact toughness than the LSAW steel pipe when subjected to internal pressure.
(3) The production of SSAW steel pipes requires low investment and is cost-effective. It is also easy to change the product specifications and source raw materials.
Post time: Dec-13-2023