Steel pipes are divided into two types of seamless steel pipes and welded steel pipes according to their manufacturing methods. Seamless steel pipe is made of high-quality carbon steel or alloy steel, hot-rolled, cold-rolled (drawn). Welded steel pipe is rolled into a tube-shaped steel plate to butt seam or spiral seam welding, in the manufacturing method, and is divided into low-pressure fluid transmission with welded steel pipe, spiral seam electric welding steel pipe, direct coil welding steel pipe, electric welding pipe, etc.. Seamless steel pipe can be used for various liquid and gas pipelines, etc. Welded pipes can be used for water pipelines, gas pipelines, heating pipes, etc.

1, welded steel pipe
1.1 Low-pressure fluid transmission with welded steel pipe and galvanized welded steel pipe
Welded steel pipe for low-pressure fluid transmission is made of soft carbon steel, a small diameter pipe most commonly used in pipeline engineering, suitable for transporting water, gas, steam and other media, according to its surface quality, divided into galvanized pipe (commonly known as white iron pipe) and non-galvanized pipe (commonly known as black iron pipe). Those with a protective layer of zinc plated on the inner and outer walls are about 3%-6% heavier than the non-galvanized ones. According to its pipe wall thickness, it is divided into three kinds: thin-walled pipe, ordinary pipe and thickened pipe. Thin-walled tubes are not suitable for transporting media, but can be used as casing.
1.2 Longitudinal rolled electric welded steel pipe
Longitudinal rolled electric welded steel pipe, can be divided into electric welded steel pipe and the site with steel plates in pieces rolled and welded into a longitudinal rolled welded steel pipe. Can be made of several wall thickness.
1.3 Spiral welded steel pipe
Spiral welded steel pipe is divided into automatic submerged arc welded steel pipe and high-frequency welded steel pipe two.
a. Spiral automatic submerged arc welded steel pipe according to the pressure of the transport medium is divided into two categories: Class A pipe and Class B pipe. Class A pipes are generally made of ordinary carbon steel q235, q235f and ordinary low-alloy structural steel 16mn welded, Class B pipes are made of q235, q235f, q195 and other steel welding, used as low pressure fluid transfer pipe
b. Spiral high-frequency welded steel pipe spiral high-frequency welded steel pipe, there is no uniform product standards, generally using ordinary carbon steel q235, q235f and other steel manufacturing.

2, seamless steel pipe
Seamless steel pipe according to the manufacturing method is divided into hot-rolled pipe and cold-drawn (rolled) pipe. The maximum nominal diameter of cold-drawn (rolled) pipe is 200 mm, and the maximum nominal diameter of hot-rolled pipe is 600 mm. In pipeline engineering, the pipe diameter exceeds 57 mm, often choose hot-rolled pipe, the pipe diameter is less than 57 mm when commonly used cold-drawn (rolled) pipe. The following three types of seamless steel pipes are commonly used in pipeline projects.

2.1 General seamless steel pipe
General seamless steel pipe is referred to as seamless steel pipe, made of ordinary carbon steel, high-quality carbon steel, ordinary low-alloy steel and alloy structural steel, used for the production of liquid pipelines or the production of structures, parts. Seamless steel pipes are supplied by outer diameter and wall thickness, with a wide range of wall thicknesses at the same outer diameter, and withstand a wide range of pressures. Usually the length of steel pipe, hot-rolled pipe for 3-12.5m, cold-drawn (rolled) pipe for 1.5-9m.

2.2 Seamless steel pipe for low and medium pressure boilers
Seamless steel pipe for low and medium pressure boilers is made of No. 10, No. 20 high-quality carbon steel, working temperature.