Welded carbon steel pipe includes LSAW (longitudinal submerged arc welded) steel pipe and spiral welded pipe. Some people those do not very understand this industry may not know differences between the former and the latter very clearly. Don’t worry, today we will talk about this topic.
Spiral welded pipe is made by using low carbon construction steel strip or low alloy structural steel strip to roll into a tube according to a certain helix angle (called the forming angle), and then welding the seam together. It can use the narrow band steel to produce steel pipe with large diameter. Spiral welded pipe is mainly used for oil and natural gas pipeline, its specifications are expressed by outer diameter * wall thickness. Spiral welded pipe with also includes single-sided welding and double-sided welding.
LSAW steel pipe is made by using strip steel as raw materials and doing longitudinal welded in the high-frequency welding equipment(hence the name due to the weld forms a straight line). In accordance with the use of different, there are different following production process (can be divided into scaffolding tube, fluid tube, wire casing, bracket tube, fence tube, etc.).
From the production process, the production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and it develops rapidly. But the strength of the spiral welded pipe is generally higher than that of the LSAW steel pipe. Spiral welded pipe with larger diameter can be produced with the narrow billet, and the pipe with different diameter can also be produced with the same width. However, compared with the same length of the LSAW steel pipe, the weld length of spiral welded pipe increased by 30 to 100%, and the production rate of it is low.
From the welding process, the welding method of spiral welded pipe and straight seam welded pipe is consistent. But the straight seam welded pipe will inevitably have a lot of T-shaped welds, so the probability of appearing welding defects are greatly improved. And the welding residual stress at TIG welding is large, the weld metal is often in three-dimensional stress condition, which increases the possibility of producing crack. Moreover, according to the submerged arc welding process, each weld should have starting arc place and arc blowout place, but each LSAW steel pipe can not achieve the conditions in the welding ring, which may cause there are more welding defects in the arc blowout place.