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Quality requirements for large diameter thick wall seamless steel pipes

①Chemical composition of steel: The chemical composition of steel is one of the most important factors affecting the performance of seamless steel pipes. 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 purpose
b. Residual elements: brought in from steelmaking, properly controlled
c. Harmful elements: strictly controlled (As, Sn, Sb, Bi, Pb), gases (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 non-metallic inclusions in the tube blank and improve its distribution pattern.

②Geometric dimensional accuracy and shape of steel pipes.
a. Steel pipe outer diameter accuracy: depends on the diameter determination (reduction) method, equipment operation conditions, 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 tool quality and its lubrication quality, etc.
Allowable deviation of wall thickness: ρ=(S-Si)/Si×100% S: maximum or minimum wall thickness on cross section. Si: nominal wall thickness mm. C. Steel pipe ovality: indicates the degree of out-of-roundness of the steel pipe.
d. Steel pipe length: normal length, fixed (multiple) ruler length, length tolerance
e. Steel pipe curvature: Indicates the curvature of the steel pipe: curvature per meter of steel pipe length, curvature of the entire length of the steel pipe
f. Steel pipe end face slope: Indicates the degree of inclination between the steel pipe end face and the steel pipe cross section
g. Steel pipe end bevel angle and blunt edge

Surface quality of large-diameter thick-walled seamless steel pipes: surface smoothness requirements
a. Dangerous defects: cracks, inward folds, outward folds, rolling breaks, delamination, scarring, dents, convex bulges, etc.
b. General defects: pockmarks, green lines, scratches, bruises, slight inside and outside straights, roller marks, etc.
① Caused by surface defects or internal defects of the tube blank.
② Caused during the production process, such as incorrect design of rolling process parameters, uneven mold surface, poor lubrication conditions, and unreasonable pass design and adjustment.
③ During the heating, rolling, heat treatment and straightening process of the tube blank (steel pipe), if excessive residual stress is generated due to improper heating temperature control, uneven deformation, unreasonable heating and cooling speed or excessive straightening deformation, then It may also cause surface cracks in steel pipes.

Post time: Feb-01-2024