Reasons for external folding and indentation of hot rolled seamless steel pipe

External folding defect characteristics:

① Hot-rolled seamless steel pipe appearance shows regular folding, triangular, double-seam linear, single-seam linear, or irregular flake folding, and so on.

② The longitudinal appearance of the steel pipe presents a usually continuous or intermittent sewing machine stitch-like or staggered 60 °, 120 °, 180 ° sewing stitch-like folding.

③ The longitudinal appearance of the steel pipe shows a spiral fold.

(iv) The longitudinal surface of the steel pipe shows a longitudinal folding of a longitudinal point or a short diagonal line, and in serious cases, two or three staggered 120°.

 

 

Produce the cause:

① longitudinal cracks on the surface of the billet or the presence of serious inclusions, shrinkage holes, and other spiral folding.
② poorly cleaned surface of the billet, there are sharp edges or the presence of warped skin.
③ perforator guide plate, tumor, or perforator exit nozzle abrasion of the tube.
④Cracks or bruises on the continuous rolling rolls or tensioning rolls.
⑤ The chamfering of the rolls of the tensioning and reducing machine is not in accordance with the requirements, the life expectancy is too high, and the new and old racks are not used properly.
(6) Mechanical abrasions or bruises during the transportation of the steel pipe of the tension reducer.
(7) The cooling water of the tension reducer roller is small or none, which causes the tension reducer roller to stick to the steel.

 

Indentation defect characteristics:

The longitudinal surface of the hot rolled seamless steel pipe presents irregular or regular localized indentation, meat. The shape of the nuclear strip, transverse indentation, warped, skin-like, broken, and iron chip-like.

 

Causes:

① tension reduction machine finished rack roll surface stuck with metal objects.
② scars or other foreign objects pressed on the surface of the steel pipe, and the formation of shedding.
③ Hot steel pipe bruises or scratches.
④ Being touched and embossed by the traversing device or sawing device.

 

Judgment:

General pipe: wall thickness ≤ 8mm, indentation depth does not exceed 90% of the negative deviation, wall thickness > 8 mm, indentation depth does not exceed 80% of the negative deviation, maximum degree shall not exceed 1.0mm.

Boiler tube: shall not exceed half of the negative deviation of the wall thickness, with a maximum value of 0.6mm.

Oil casing: the depth of indentation shall not exceed half of the negative deviation of wall thickness, the maximum value of the depth shall not exceed 0.6mm when S ≥ 10mm, and the maximum depth shall not exceed 0.5mm when S < 10mm.

 

The above is about the hot rolled seamless steel pipe's external folding and indentation, of the reasons I hope to be useful to you.