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

Outer folding

Defect characteristics:

The appearance of the steel pipe shows regular folding in the form of triangular, double-seam straight line, single-seam straight line or irregular sheet folding.

The longitudinal appearance of the pipe shows a usually continuous or intermittent sewing machine stitch or staggered 60 °, 120 °, 180 ° sewing stitch-like folds.

The longitudinal appearance of the pipe shows a spiral fold.

The longitudinal surface of the tube shows a longitudinal fold of a longitudinal point or a short diagonal line, or, in severe cases, two or three staggered at 120°.

Causes:

Longitudinal cracks on the surface of the billet or the presence of serious inclusions, shrinkage holes, etc. to produce spiral folding.

Poor cleaning of the surface of the billet, sharp edges or the presence of warped skin.

Tumor on the guide plate of the piercing machine or the exit nozzle of the piercing machine scrapes the tube.

Cracks or bruises on the rolls of continuous rolling or tension reduction rolls.

Chamfering of the rolls of the tension reducer is not in accordance with the requirements, and the life expectancy is too high, and the new and old racks are not used properly.

Mechanical abrasion or bruise during the transportation of steel pipe.

Tension reducer roller cooling water is small or no cause tension reducer roller sticky steel.

Indentation

Defect characteristics: in the longitudinal surface of the steel pipe presents irregular or regular localized indentation, meat. The shape of the nucleus, strip, transverse indentation, warped skin-like, broken, iron chip-like.

Causes:

The surface of the rolls of the finished stand of the tension reduction machine is adhering to metal objects.

Scarring or other foreign matter pressed on the surface of the steel pipe off and formed.

Bumping or scratching of hot steel pipe.

Bumped or imprinted by traversing device or sawing device.

Judgment: general pipe: wall thickness ≤ 8mm indentation depth does not exceed 90% of the negative deviation , wall thickness > 8mmm 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, the maximum value of 0.6mm.

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