Welded steel pipe refers to the steel pipe with joint surface after bending and deformation of steel strip or steel plate into round, square and other shapes. The billet used for welding steel pipes is steel plate or strip steel.The quality of welds continues to improve, and the variety specifications of welded steel pipes are increasing, and they have replaced seamless steel pipes in more and more fields. Welded steel pipe has lower cost and higher production efficiency than seamless steel pipe

Straight seam welded pipe, steel pipe made of hot or cold rolled steel plate or steel strip coil welding, straight seam welded pipe on the welding equipment are called straight seam welded pipe. (Because the welding of the steel pipe is a straight line, so named). Among them, according to different uses, and different post-production processes, (can be roughly divided into scaffolding pipe, fluid pipe, wire sleeve, bracket pipe, guardrail pipe, etc.).

Thick wall steel pipe is mainly used in tap water engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction. For liquid transport: water supply, drainage. For gas transport: gas, steam, liquefied petroleum gas.

JIS is the most important and authoritative of Japan's national standards. According to the provisions of the Japanese Industrial Standardization Law, JIS standard objects in addition to the formulation of special standards or technical specifications for drugs, pesticides, chemical fertilizers, silk, food and other agricultural and forestry products, but also involve various industrial fields.

S235JR is a European standard non-alloy structural steel, that is, carbon structural steel with low carbon content, which is used for welding, bolted and riveted structures.
S355NL is a normalizing steel (fine grain steel) in EN10025-3:2004 standard. Its yield strength and tensile strength correspond to the Q345 low alloy steel in China.

Thick wall square pipe is a hollow square cross-section of light thick wall steel pipe, also known as steel cooling curved profile. In addition to the thickening of the wall, the corner size and the flatness of the edge of the hot rolled special thick wall square pipe reach or even exceed the level of the resistance welding cold formed square pipe.