Indentation of
hot-rolled seamless steel pipes
1. Defect characteristics: Irregular or regular local indentation and meat loss on the longitudinal surface of seamless steel pipes. The shapes are core-shaped, strip-shaped, transversely pressed, peeling, broken, iron filings, etc.
2. Causes:
① Metal objects are attached to the surface of the finished product stand roller of the tension and reduction machine.
② Scars or other foreign objects are pressed on the surface of the steel pipe and fall off.
③ Hot steel pipes are bruised or scratched.
④ Bumped and embossed by transverse devices or sawing devices.
3. Judgment:
General steel pipes: The indentation depth for wall thickness ≤8mm does not exceed 90% of the negative deviation, and the indentation depth for wall thickness＞ 8 mm does not exceed 80% of the negative deviation. The maximum depth shall not exceed 1.0mm.
Boiler steel pipes: shall not exceed half of the negative deviation of the wall thickness, and the maximum value is 0.6mm.
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.
Straight track of hot-rolled seamless steel pipe
1. Defect characteristics: Grooves distributed along the longitudinal direction of the steel pipe.
2. Causes: 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.
3. Judgment:
General steel 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.
Boiler steel 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.
The shape of the hot-rolled seamless steel pipe is not round
1. Defect characteristics: The cross-section of the seamless steel pipe is not round.
2. Causes: Improper adjustment of clamping force during sawing, incorrect installation of finished product rack and working rack of tension and reduction machine, excessive clamping force of finishing eddy current flaw detection outlet clamping device, improper adjustment of straightening roller pressure or angle.
The uneven wall thickness of hot-rolled seamless steel pipe
1. Defect characteristics: The maximum and minimum wall thickness of the same section of seamless steel pipe exceeds the positive deviation and negative deviation respectively or exceeds ±8-10% of the nominal wall thickness respectively (thick-walled steel pipe takes the upper limit and thin-walled pipe takes the lower limit)
2. Causes: The perforated incoming material does not meet the requirements, the end face of the steel pipe billet is cut obliquely, the hot centering of the steel pipe billet is biased, the heating of the steel pipe billet is uneven, the perforation equipment is improperly adjusted, and the continuous rolling mill equipment is improperly adjusted.
Bending of hot-rolled seamless steel pipe
1. Defect characteristics: The seamless steel pipe is not straight along the length direction, and the end of the steel pipe is goose-head bent.
2. 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 expanded pipe is unreasonable or the temperature is too high during sawing, transportation, and other reasons.
Threeway Steel is known as a professional supplier engaged in manufacturing and distributing a wide range of steel pipe, and our headquarter located the central part of China – Hunan and six associated factories throughout China.
Threeway Steel is known as a professional supplier engaged in designing, manufacturing and distribution of a wide range of steel products with the headquarter located the central part of China – Hunan and six associated factories throughout China.
Threeway Steel is known as a professional supplier engaged in designing, manufacturing and distribution of a wide range of steel products with the headquarter located the central part of China – Hunan and six associated factories throughout China.
Threeway Steel is known as a professional supplier engaged in designing, manufacturing and distribution of a wide range of steel products with the headquarter located the central part of China – Hunan and six associated factories throughout China.
Threeway Steel is known as a professional supplier engaged in designing, manufacturing and distribution of a wide range of steel products with the headquarter located the central part of China – Hunan and six associated factories throughout China.
