Defects that are easy to occur in hot-rolled seamless steel pipes

Defects that are easy to occur in hot-rolled seamless steel pipes First, the indentation of hot-rolled seamless steel pipes Defect characteristics: irregular or regular local indentations and meat loss on the longitudinal surface of seamless steel pipes. The shapes are core-shaped, strip-shaped, transversely crushed, peeling, broken, iron filings, etc. Causes: ①Metal objects are attached to the surface of the roll of the finished product rack of the tension and reduction machine. ②Scars or other foreign objects are pressed on the surface of the steel pipe and fall off. ③Hot steel pipes are bruised or scratched. ④Bumped and embossed by transverse devices or sawing devices. Defect judgment: ①General pipes: The indentation depth for wall thickness ≤8mm does not exceed 90% of the negative deviation, and the indentation depth for wall thickness＞8mm does not exceed 80% of the negative deviation. The maximum depth shall not exceed 1.0mm. ②Boiler pipes: shall not exceed half of the negative deviation of the wall thickness, and the maximum value is 0.6mm. ③ Oil casing: The indentation depth shall not exceed half of the negative deviation of the wall thickness. When S≥10mm, the maximum depth shall not exceed 0.6mm, and when S＜10mm, the maximum depth shall not exceed 0.5mm. Second, the straight track of hot-rolled seamless steel pipe Defect characteristics: grooves distributed along the longitudinal direction of the steel pipe. Cause: When the rolling temperature is low, the metal sticks to the head and scratches the inner surface of the steel pipe, and the head is severely worn. The mandrel is poorly lubricated or severely worn. Defect judgment: ① General pipe: The depth of the outer straight track shall not exceed 90% of the negative deviation of the wall thickness and the maximum depth shall not exceed 1.0mm. The depth of the inner straight track shall not exceed 70% of the negative deviation of the wall thickness and the maximum depth shall not exceed 0.6mm. ② Boiler pipe, oil casing: The depth of the straight track shall not exceed 5% of the wall thickness, and the maximum shall not exceed 0.4mm. Third, the shape of the hot-rolled seamless steel pipe is not round Defect characteristics: The cross-section of the seamless steel pipe is not round. Causes: Improper adjustment of clamping force during sawing, incorrect installation of finished product rack and working rack of the tension and reduction machine, excessive clamping force of the clamping device at the outlet of the finishing eddy current flaw detection, improper adjustment of the straightening roller pressure or angle. Fourth, uneven wall thickness of hot-rolled seamless steel pipe Defect characteristics: The maximum and minimum wall thickness of the seamless steel pipe on the same section exceed the positive deviation and negative deviation respectively or exceed ±8-10% of the nominal wall thickness respectively (thick-walled pipe takes the upper limit and thin-walled pipe takes the lower limit) Causes: The perforated incoming material does not meet the requirements, the end face of the tube billet is cut obliquely, the hot centering of the tube billet is biased, the heating of the tube billet is uneven, the perforation equipment is improperly adjusted, and the continuous rolling mill equipment is improperly adjusted. Fifth, the bending of hot-rolled seamless steel pipe. Defect characteristics: The seamless steel pipe is not straight along the length direction, and the end of the steel pipe is goose-head bent. Causes: The center line of the last few holes of the tension and reduction machine is misaligned. The diameter reduction amount distribution of the finishing hole of the tension and reduction machine is unreasonable. The cooling method of the expansion pipe is unreasonable or the temperature is too high during sawing, transportation, and other reasons. Post time: Oct-22-2024