Surface quality of seamless steel pipes

Surface quality of seamless steel pipes
The standard specifies the requirements for "smooth surface" of steel pipes. However, there are as many as 10 surface defects of steel pipes due to various reasons in the production process. Including: surface cracks (cracks), hair lines, inner folds, outer folds, punctures, inner straights, outer straights, separation, scarring, pits, convex hulls, pits (pits), scratches ( scratches), inner spiral, outer spiral, blue line, concave correction, roll printing, etc. The reasons for these defects are mainly due to the surface defects or internal defects of the tube blank. On the other hand, it occurs in the production process, that is, if the rolling process parameters are unreasonably designed, the surface of the tool (die) is not smooth, the lubrication conditions are not good, and the pass design and adjustment are unreasonable, etc., which may lead to the appearance of steel pipes. Surface quality problems; or in the process of heating, rolling, heat treatment and straightening of the billet (steel pipe), 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. Excessive residual stress may also cause surface cracks in the steel pipe.

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 tube rolling and the process parameters of heat treatment of steel tubes. In the seamless steel pipe standard, according to the different uses of the steel pipe, corresponding requirements are put forward for the smelting of the steel and the manufacturing method of the pipe blank, 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.). In order to improve the uniformity of the chemical composition in the steel and the purity of the steel, reduce the non-metallic inclusions in the billet and improve their distribution, the molten steel is often refined by the refining equipment outside the furnace, and even the electroslag furnace is used to regenerate the billet. Melt refining.


Steel pipe geometric accuracy and outer diameter
Steel tube outer diameter accuracy, wall thickness, ovality, length, steel tube curvature, steel tube end face cut slope, steel tube end face bevel angle and blunt edge, cross-sectional size of special-shaped steel tube


Steel tube outer diameter accuracy
The outer diameter accuracy of seamless steel pipes depends on the method of determining (reducing) diameter (including tension reduction), the operation of equipment, and the process system. And the accuracy of the outer diameter is also related to the machining accuracy of the hole shape of the fixed (reduced) diameter machine and the distribution and adjustment of the deformation amount of each frame. The accuracy of the outer diameter of the cold-rolled (抜) formed seamless steel pipe is related to the accuracy of the die or rolling pass.


Wall thickness
The wall thickness accuracy of the seamless steel pipe 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 the wall thickness of the steel pipe is the uneven wall thickness in the transverse direction and the uneven wall thickness in the longitudinal direction.


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 performance or low temperature performance) and corrosion resistance (oxidation resistance, water corrosion resistance, acid and alkali resistance, etc.). Generally speaking, the physical and chemical properties of steel pipes mainly depend on the chemical composition of the steel, the structure of the steel, the purity of the steel, and the heat treatment method of the steel pipe. Of course, in some cases, the rolling temperature and deformation system of the steel pipe also affect the performance of the steel pipe.


Steel pipe metallographic structure
The metallographic structure of the steel pipe includes the low magnification structure and the high magnification structure of the steel pipe.


Special requirements for steel pipes
Special conditions requested by the customer.