Classification of large straight seam steel pipeClassification by weld shape Can be divided into straight seam welded pipe and spiral welded pipe Straight seam welded pipe The production process is simple, the production efficiency is high, the cost is low, the development is fast. Spiral welded pipe The strength is generally higher than that of straight welded pipe, and welded pipes with larger diameters can be produced with narrower billets, and welded pipes with different diameters can also be produced with billets of the same width. However, compared with the straight seam pipe of the same length, the weld length is increased by 30 to 100%, and the production speed is lower. Therefore, the smaller diameter welded pipe is mostly straight seam welding, and the large diameter welded pipe is mostly spiral welding. Classification by use

Welded steel pipe: Also called welded pipe, it is cut from steel strips into narrow steel bars and then cold-processed into a tube shape using a mold. A special welder then welds a pipe seam. The outer welds are polished and bright. The internal burrs of ordinary welded pipes cannot be punched. Only precision welded pipes are internally burred

he surface quenching and tempering heat treatment of straight seam welded pipes is usually carried out by induction heating or flame heating. The main technical parameters are surface hardness, local hardness and effective hardened layer depth. Hardness testing can be done with a Vickers hardness tester, a Rockwell or a surface Rockwell hardness tester. The selection of test force (scale) is related to the depth of the effective hardened layer and the surface hardness of the straight seam welded pipe.

There are many methods for quality inspection of straight seam welded pipes, among which physical methods are also the most commonly used inspection methods. Physical inspection is a method that uses some physical phenomena to measure or inspect. The inspection of internal defects in materials or straight seam welded pipes generally uses non-destructive testing methods. Current non-destructive testing includes magnetic testing, ultrasonic testing, radiographic testing, penetrant testing, etc

Description of the main production processes of large diameter straight seam welded pipes

Straight seam welded pipes, steel pipes made by coil welding of hot-rolled or cold-rolled steel plates or steel strips, and pipes obtained by straight seam welding on welding equipment are called straight seam welded pipes.

Low carbon steel: The carbon content is less than 0.25%. It has good plasticity and toughness and is easy to process. It is often used to make chains, rivets, bolts, etc. Medium carbon steel: The carbon content is between 0.25% and 0.6%, and its strength and hardness are higher than low carbon steel. It is used to manufacture moving parts such as axles, worms, and gears. High carbon steel: with a carbon content of more than 0.6%, high strength and hardness, but poor weldability and plasticity, it is used to make springs, wear-resistant parts and cutting tools.

Hot rolled seamless steel pipe. The outer diameter is usually greater than 38mm, and the wall thickness is between 3~80mm. Cold rolled seamless steel pipe. The outer diameter can be up to 6mm and the wall thickness can be up to 0.25mm. High pressure seamless steel pipe. The outer diameter ranges from 10 to 159mm, and the wall thickness ranges from 2 to 45mm. Precision seamless steel pipe. The outer diameter ranges from 10 to 377mm, and the wall thickness ranges from 1 to 25mm. stainless steel pipe. The outer diameter range is from 6 to 530mm, and the wall thickness is from 0.5 to 15mm.

Steel pipes made of a single piece of metal with no seams on the surface are called seamless steel pipes. Materials include ordinary and high-quality carbon structural steel (Q215-A ~ Q275-A and 10 ~ 50 steel), low alloy steel (09MnV, 16Mn, etc.) Seamless steel pipes are made from steel ingots or solid tube blanks that are perforated into capillary tubes, and then hot rolled, cold rolled or cold drawn.

Elastic stage: The deformation in this stage is completely elastic, and it returns to its original state after being stressed, and no plastic deformation occurs. If all loads are removed, its original length can still be restored.