Quality requirements for carbon steel pipes

1. Chemical Composition

Standards specify limits for harmful chemical elements such as As, Sn, Sb, Bi, Pb, and gases like N, H, and O. To enhance the uniformity of the chemical composition, purity, and distribution of non-metallic inclusions in the steel, molten steel is often refined using external refining equipment. Sometimes, the billet is further refined by remelting in an electroslag furnace.

2. Dimensional Accuracy and Shape

The geometric measurements of carbon steel pipes should include:

Diameter

Wall thickness

Ovality

Length

Curvature

End face inclination

Bevel angle and blunt edge

Cross-sectional dimensions for shaped steel pipes

3. Surface Quality

Standards specify requirements for the "surface finish" of carbon steel seamless pipes. Common defects include:

Cracks

Hairlines

Inner and outer folds

Crushing

Inner and outer straights

Delaminations

Scars

Pits

Convex hulls

Pimples (hemp pits)

Scratches

Internal and external spirals

Green lines

Concave corrections

Roll marks

Dangerous defects include cracks, folds, crushing, delaminations, scarring, and pits, while pitted surfaces, blue lines, scratches, slight internal and external straights, spirals, concave corrections, and roll marks are considered general defects.

4. Physical and Chemical Properties

These include mechanical properties at room temperature and specific temperatures (such as thermal strength and low-temperature properties) and corrosion resistance (e.g., oxidation, water corrosion, acid, and alkali resistance). These properties generally depend on the chemical composition, microstructure, purity, and heat treatment method of the steel. Additionally, the rolling temperature and degree of deformation can also affect the steel pipe's performance.

5. Process Performance

This includes the flaring, flattening, hemming, bending, ring drawing, and welding properties of steel pipes.

6. Metallographic Structure

This encompasses the low-magnification and high-magnification structures of steel pipes.

7. Special Requirements

These are user-specified requirements that go beyond the standard specifications when using steel pipes.