Seamless pipe is manufactured by extruding the metal to the desired length; therefore ERW pipe have a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length. etc.
1. The process is different. The seamless pipe is made by piercing a billet or a solid tube blank, and then processing it by hot rolling or cold rolling. Welded pipes are made by bending and welding steel plates or strips.
2. The appearance is different. There is no seam on the surface of the seamless steel pipe. There are generally welded seams on the surface of the welded pipe.
3. Different wall thickness The precision of seamless steel pipe is low, and the wall thickness is relatively thick. The steel pipe of the welded pipe has high precision and the wall thickness is usually relatively thin
Seamless steel pipes are widely used. General-purpose seamless steel pipes are rolled from ordinary carbon steels, low-alloy tool steels or alloy tool steels, and the production volume is large, mainly used as pipelines or structural parts for transporting liquids.
According to different purposes, there are three types of supply:
a. Supply according to composition and physical properties;
b. Supply according to physical performance;
c. Supply according to pressure test. Seamless steel pipes supplied by Types a and b, if used to withstand liquid pressure, also need to be subjected to a pressure test.
The main purpose of seamless steel pipes are seamless steel pipes for heating furnaces, seamless steel pipes for geological environment and seamless steel pipes for crude oil.
Welded steel pipes, also known as welded pipes, are seamless steel pipes made of steel or chains that are rolled and shaped and then welded by electric welding. Welded steel pipes have simple processing technology, high production efficiency, many varieties and specifications, and less equipment investment, but their general strength is lower than that of seamless steel pipes.
From the 20th century to the 30th era, with the rapid development of high-quality hot-rolled strip mill production and the development of electric welding and testing technology, the welding quality has continued to improve, and the types and specifications of welded steel pipes have increased day by day, and have been replaced in many industries. seamless steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes according to the welding method.
The production process of straight seam welded pipe is simple, the production is fast, the cost is low, and the development trend is relatively fast. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. It can be used to produce welded pipes with relatively large diameters from narrow blanks, and it is also possible to produce welded pipes with different diameters from blanks with the same width.
However, compared with the straight seam pipe of the same size, the welding length is increased by 30~100%, and the production rate is lower.
Therefore, most of the welded pipes with smaller diameters use straight seam welding, and most of the large-diameter welded pipes use spiral welding.
