The surface quality of steel pipe: requirements for smooth surface a. Dangerous defects: cracks, inward folds, outward folds, crushing, delamination, scarring, concaves, convex hulls, etc. b. General defects: pockmarks, green lines, scratches, bruises, slight inner and outer straights, roller marks, etc. Causes: ① Due to the surface defects or internal defects of the tube blank. ② Produced during the production process, such as incorrect rolling process parameter design, rough mold surface, poor lubrication conditions, unreasonable pass design, and adjustment. ③ During the heating and rolling, heat treatment, and straightening process of the tube blank (steel pipe), if excessive residual stress is generated due to improper heating temperature control, uneven deformation, unreasonable heating and cooling speed, or too large straightening deformation, then It may also cause surface cracks in the steel pipe.
Steel pipe surface quality inspection: 100% ①Manual visual inspection: lighting conditions, standards, experience, marks, steel pipe rotation. ②Non-destructive testing inspection: a. Ultrasonic testing UT: It is sensitive to the surface and internal crack defects of various materials with uniform materials. Standard: GB/T 5777-1996 Level: C5 level b. Eddy current flaw detection ET: (Electromagnetic induction) It is mainly sensitive to point (hole-shaped) defects. Standard: GB/T 7735-2004 Class: Class B c. Magnetic Particle MT and Flux Leakage Inspection: Magnetic inspection, is suitable for the detection of surface and near-surface defects of ferromagnetic materials. Standard: GB/T 12606-1999 Grade: C4 d. Electromagnetic ultrasonic flaw detection: No coupling medium is required, and it can be applied to high temperature, high speed, and rough steel pipe surface flaw detection. e. Penetrant flaw detection: Fluorescence, coloring, detection of steel pipe surface defects. 4. Steel management performance inspection: ① Tensile test: measure stress and deformation, determine the strength (YS, TS) and plasticity index (A, Z) of the material, longitudinal and transverse sample pipe sections, arc and circular samples (￠10,￠12.5)
Seamless steel pipes are widely used, but there are also many defects in seamless steel pipes, as follows
First, does the diameter of the seamless steel pipe bend meet the standard? The bending radius must be at least 4 times the diameter. If it is too small, it will cause plastic deformation.
Second, what materials are used for seamless steel pipes? If it is carbon steel, the heating temperature should be 750-1050, if it is stainless steel, the heating temperature should be 900-1200. Is the heating temperature not suitable?
Third, it may be the defects of the steel pipe itself, such as cracks in the material, slag inclusions, etc.
Heat treatment defects of seamless steel pipes:
1. If the temperature in the furnace is uneven and the atmosphere is not good, it will lead to the uneven performance of the steel pipe, decarburization phenomenon, burning pitting, and serious oxide skin.
2. When the normalizing and tempering temperature is not well controlled, there may be coarse grains (or wrong metallographic structure), unqualified mechanical properties, and over-burning.
3. The cooling effect is not good, and the above-unqualified phenomena appear. Appeared Wei's organization and so on.
4. The cutting of the equipment is not good, and the steel pipe is thrown out of the pit.
