Quality requirements for seamless steel pipes

1. Chemical composition of steel; The chemical composition of steel is the most important factor affecting the performance of seamless steel pipes. It is also the main basis for formulating the process parameters of rolling tubes and heat treatment of steel pipes. In the seamless steel pipe standard, according to the different uses of steel pipes, corresponding requirements are put forward for the smelting of steel and the manufacturing methods of tube blanks, and strict regulations are made on the chemical composition. In particular, requirements are put forward for the content of certain harmful chemical elements (arsenic, tin, antimony, lead, bismuth) and gases (nitrogen, hydrogen, oxygen, etc.). To improve the uniformity of chemical composition and purity of steel, reduce non-metallic inclusions in tube blanks, and improve their distribution morphology, refining equipment outside the furnace is often used to refine molten steel, and even electro-slag furnaces are used to remelt and refine tube blanks.

2. Geometric dimensional accuracy and outer diameter of steel pipes; outer diameter accuracy, wall thickness, ovality, length, curvature of steel pipes, bevel of steel pipe end face, angle of bevel and blunt edge of steel pipe end face, and cross-sectional dimensions of special-shaped steel pipes

2.1. Outer diameter accuracy of steel pipes: The outer diameter accuracy of seamless steel pipes depends on the method of sizing (reducing) diameter (including tension reduction), equipment operation, process system, etc. The outer diameter accuracy is also related to the hole processing accuracy of the sizing (reducing) machine and the deformation distribution and adjustment of each frame. The outer diameter accuracy of cold-rolled (rolled) seamless steel pipes is related to the accuracy of the die or rolling hole.

2.2. Wall thickness: The wall thickness accuracy of seamless steel pipes 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 its lubrication quality. The uneven distribution of steel pipe wall thickness is uneven transverse wall thickness and uneven longitudinal wall thickness.

3. Surface quality of steel pipes; the standard stipulates the "surface finish" requirements of steel pipes. However, there are as many as 10 kinds of surface defects in steel pipes due to various reasons during the production process. Including surface cracks (cracks), hairline, inner fold, outer fold, puncture, inner straight, outer straight, delamination, scar, pit, convex, pitting (pit), abrasion (scratches), inner spiral, outer spiral, blue line, concave correction, roller mark, etc. The main reasons for these defects are due to surface defects or internal defects of the tube blank. On the other hand, they are generated during the production process, that is, if the rolling process parameters are not designed reasonably, the surface of the tool (mold) is not smooth, the lubrication conditions are not good, the hole design and adjustment are unreasonable, etc., which may cause surface quality problems of the steel pipe; or if the tube blank (steel pipe) is heated, rolled, heat treated and straightened if the heating temperature is improperly controlled, the deformation is uneven, the heating and cooling speed is unreasonable, or the straightening deformation is too large, it will cause excessive residual stress, which may also cause surface cracks in the steel pipe.

4. Physical and chemical properties of steel pipes; The physical and chemical properties of steel pipes include mechanical properties at room temperature, mechanical properties at a certain temperature (thermal strength or low-temperature performance), and corrosion resistance (anti-oxidation, anti-water erosion, acid and alkali resistance, etc.). Generally speaking, the physical and chemical properties of steel pipes mainly depend on the chemical composition, organizational structure, and purity of steel, and the heat treatment method of steel pipes. Of course, in some cases, the rolling temperature and deformation system of steel pipes also affect the performance of steel pipes.

5. Process performance of steel pipes; The process performance of steel pipes includes the flattening, flaring, curling, bending, ring pulling, and welding of steel pipes.

6. Metallographic structure of steel pipes; The metallographic structure of steel pipes includes low-magnification and high-magnification structures of steel pipes.

7. Special requirements for steel pipes; Special conditions required by customers.