Seamless steel pipe is a steel pipe made of whole round steel perforated with no welded seam on the surface called seamless steel pipe. Seamless steel pipe can be divided into hot-rolled seamless steel pipe, cold-rolled seamless steel pipe, cold-drawn seamless steel pipe, extruded seamless steel pipe, top pipe, etc. according to the production method. According to the cross-sectional shape, seamless steel pipe is divided into two types: round and shaped. Shaped tubes are square, oval, triangular, hexagonal, melon, star, finned tubes, etc. The maximum diameter is 900mm, and the minimum diameter is 4mm. depending on the use, there are thick-walled seamless steel pipe and thin-walled seamless steel pipe. Seamless steel pipes are mainly used as petroleum geological drilling pipes,
Steel billets and coils are sent to pipe mills to be prepared for making carbon steel pipes. Depending on the capacity of the pipe mill and the end use of the final product, the castings are made into pipe through four different manufacturing processes. Seamless carbon steel pipe, as the name implies, has no longitudinal welds. Essentially, it is a solid piece of homogeneous steel. A solid billet is simply heated and then stretched over a series of mandrels until the pipe reaches the desired diameter and wall thickness.
Seamless steel pipe has a better pressure-bearing capacity and is stronger than ERW welded steel pipe. Therefore it is widely used in high pressure equipment, heat and boiler industry. The weld seam of general welded steel pipe is the weak point and the quality affects the overall performance.

There are two main production processes for seamless steel pipes (cold-rolled and hot-rolled).

① Hot-rolled seamless steel pipe main production process (△ main inspection process)
billet preparation and inspection △ → pipe billet heating → perforation → pipe rolling → pipe reheating → fixed (shrinkage) diameter → heat treatment △ → finished pipe straightening → finishing → inspection △ (non-destructive, physical and chemical, bench inspection) → storage
②The main production process of cold rolled seamless steel pipe.
Prepared billet → pickling lubrication → cold rolling (drawing) → heat treatment → straightening → finishing → inspection → storage

Seamless steel pipe is manufactured from round billets by hot-rolled, cold-rolled or cold-drawn processes, with no seams on the pipe body.
Welded steel pipe is manufactured from flat steel plate with welded seams on the pipe body. It includes ERW pipe, LSAW pipe and SSAW pipe.