What are the quality requirements for seamless steel pipes?

1. Chemical composition

Requirements for the contents of harmful chemical elements As, Sn, Sb, Bi, Pb and gases such as N, H and O are put forward. In order to improve the uniformity of the chemical composition in the steel and the purity of the steel, reduce the non-metallic inclusions of the tube blank and improve its distribution, the molten steel is often refined by the refining equipment outside the furnace, and even the electroslag furnace is used to reshape the tube blank.

2. Dimensional accuracy and shape

The geometric dimensions of seamless steel pipes mainly include the outer diameter, wall thickness, ellipticity, length, curvature, pipe end face cut, bevel angle and blunt edges, and cross-sectional dimensions of heterogeneous steel pipes.

3. Surface quality

The standard stipulates the requirements of "smooth and clean surface" of seamless steel pipes. Common defects include: cracks, hair lines, internal folds, external folds, punctures, internal straights, external straights, separation, scars, pits, convex hulls, pits , scratches , inner spiral, outer spiral, blue line, concave correction, roll printing, etc. Among them, cracks, internal folds, external folds, rolling, delamination, scars, pits, convex hulls, etc. are dangerous defects; the pitted surface, blue lines, scratches, slight internal and external straight lines, slight internal and external spirals, correction Concave and roll marks are general defects.

4. Physical and chemical properties

Under normal circumstances, it depends on the chemical composition, structure and performance of the steel, the purity of the steel, and the heat treatment method of the steel. In some cases, the rolling temperature and degree of deformation of the steel pipe will also affect the performance of the steel pipe.

5. Process performance, including pipe flaring, flattening, crimping, bending, ring drawing and welding performance.

6. Metallographic structure, including the low-magnification and high-magnification structures of steel pipes.

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