What are the quality requirements for seamless steel pipe

Seamless steel pipe is a long, seamless steel strip with a hollow cross-section. Steel pipes with a hollow cross-section are widely used to transport fluids, such as oil, natural gas, coal gas, water, and certain solid materials. Compared to solid steel materials like round bar, steel pipes are lighter while maintaining the same bending and torsional strength. They are economical cross-section steels and are widely used in the manufacture of structural and mechanical parts, such as oil drill pipes, automobile drive shafts, bicycle frames, and steel scaffolding used in construction.

Seamless Steel Pipe Quality Requirements

1. Chemical Composition of Steel: The chemical composition of steel is one of the most important factors affecting the performance of seamless steel pipes and is the primary basis for determining the pipe rolling and heat treatment process parameters. a. Alloying Elements: Intentionally added, depending on the intended use.

b. Residual Elements: Carried over during steelmaking, appropriately controlled.

c. Harmful Elements: Strictly controlled (As, Sn, Sb, Bi, Pb). Gas (N, H, O) refining or electroslag remelting improves the chemical composition uniformity and purity of the steel, reduces non-metallic inclusions in the tube, and improves their distribution.

2. Geometric Dimensional Accuracy and Appearance of Seamless Steel Pipes

(a) Tube Outside Diameter Accuracy: Depends on the sizing (reducing) method, equipment operation, and process specifications. Outside Diameter Permissible Deviation δ = (D - Di) / Di × 100% D: Maximum or minimum outside diameter (mm), Di: Nominal outside diameter (mm)

(B) Tube Wall Thickness Accuracy: Depends on the quality of tube heating, process design, and adjustment parameters for each deformation step, tool quality, and lubrication quality. Wall Thickness Permissible Deviation: ρ = (S-Si) / Si × 100% S: Maximum or minimum wall thickness across the cross section. Si: Nominal wall thickness (mm)

(c): Pipe ovality: Indicates the degree of out-of-roundness of the pipe.

(d) Pipe length: Normal length, fixed (multiple) length, and allowable length deviation.

(e) Pipe curvature: Indicates the curvature of the pipe: curvature per meter of pipe length, curvature over the entire pipe length.

(f) Pipe end face bevel: Indicates the degree of inclination between the pipe end face and the pipe cross section.

(g) Pipe end face bevel angle and blunt edge.

3. Surface quality of seamless steel pipe: Surface finish requirements.

(a) Dangerous defects: Cracks, internal folds, external folds, roll cracks, delamination, scars, dents, and bulges.

(b) General defects: Pits, blue lines, scratches, bruises, minor internal and external straight lines, and roller marks.

Causes:

① Surface or internal defects of the pipe blank.

② Caused during the production process, such as incorrect rolling process parameter design, uneven die surface, poor lubrication conditions, and improper pass design and adjustment.

③ During the hot rolling, heat treatment, and straightening processes of the tube (steel pipe), if excessive residual stress is generated due to improper heating temperature control, uneven deformation, unreasonable heating and cooling rates, or excessive straightening deformation, this can also cause surface cracks in the steel pipe.

4. Chemical Properties of Seamless Steel Pipes: Room-Temperature Mechanical Properties, High-Temperature Mechanical Properties, Low-Temperature Mechanical Properties, and Corrosion Resistance. The physical and chemical properties of steel pipes are primarily determined by the chemical composition, microstructure, purity of the steel, and the heat treatment method used.

5. Processing Properties of Seamless Steel Pipes: Flattening, flaring, curling, bending, welding, etc.

6. Metallographic Structure of Seamless Steel Pipes: Macrostructure (macroscopic), Macrostructure (microscopic) M, B, P, F, A, S

7. Special Requirements for Seamless Steel Pipes: Contract Annexes and Technical Agreement.