According to the production method,  seamless steel pipescan be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and top pipes.

① The chemical composition of steel

The chemical composition of steel is one of the most important factors affecting the performance of seamless steel pipes, and it is also the main basis for formulating pipe rolling process parameters and steel pipe heat treatment process parameters.

a. Alloying elements: intentionally added, according to use

b. Residual elements: brought in by steelmaking, properly controlled

c. Harmful elements: strictly control (As, Sn, Sb, Bi, Pb), gas (N, H, O)

Out-of-furnace refining or electroslag remelting: improve the uniformity of the chemical composition of the steel and the purity of the steel, reduce the non-metallic inclusions in the tube billet and improve its distribution shape.

② Geometric dimensional accuracy and shape of steel pipe

a. The accuracy of the outer diameter of the steel pipe: depends on the method of sizing (reducing) the diameter, the operation of the equipment, the process system, etc.

Allowable deviation of outer diameter δ=(D-Di)/Di ×100% D: Maximum or minimum outer diameter mm

Di: Nominal outer diameter mm

b. Steel pipe wall thickness accuracy: It is related to the heating quality of the tube blank, the process design parameters and adjustment parameters of each deformation process, the quality of the tool and the quality of lubrication, etc.

Allowable deviation of wall thickness: ρ=(S-Si)/Si×100% S: the maximum or minimum wall thickness on the cross section

Si: Nominal wall thickness mm

C. Ovality of steel pipe: indicates the degree of out-of-roundness of the steel pipe.

d.steel pipelength: normal length, fixed (double) length, length tolerance

e. Steel pipe curvature: indicates the curvature of the steel pipe: the curvature per meter of the length of the steel pipe, the curvature of the full length of the steel pipe

f. Steel pipe end face cut slope: indicates the degree of inclination between the steel pipe end face and the steel pipe cross section

g. Bevel angle and blunt edge of steel pipe end face

③Surface quality of steel pipe: surface finish requirements

a. Dangerous defects: cracks, internal folds, external folds, crushing, delamination, scarring, dents, convex hulls, etc.

b. General defects: pits, blue lines, scratches, bruises, slight inner and outer straights, roller marks, etc.

Cause:

① Due to surface defects or internal defects of the tube blank.

② Produced in the production process, such as incorrect design of rolling process parameters, unsmooth mold surface, poor lubrication conditions, unreasonable pass design and adjustment.

③ In the process of heating, rolling, heat treatment and straightening of the tube billet (steel tube), if the heating temperature is not properly controlled, the deformation is uneven, the heating and cooling rate is unreasonable, or the straightening deformation is too large to produce excessive residual stress, then It may also cause surface cracks in the steel pipe.

Steel management performance: normal temperature mechanical performance, high temperature mechanical performance, low temperature performance, corrosion resistance. The physical and chemical properties of steel pipes mainly depend on the chemical composition of the steel, the structure and purity of the steel, and the heat treatment method of the steel pipe.

Steel pipe process performance: flattening, flaring, crimping, bending, welding, etc.

Steel tube metallographic structure: low magnification structure (macro), high magnification structure (micro) M, B, P, F, A, S

Special requirements for steel pipes: contract attachments, technical agreements.