The Outer Surface of The Cold-rolled Steel Pipe Is Uneven After Rolling, And The Eddy Current Alarms The Entire Length.

1. External folding characteristics: spiral layered folding on the outer surface of the steel pipe.

cause:

1) There are folds or cracks on the surface of the tube blank.

2) The subcutaneous pores of the tube blank have serious subcutaneous inclusions.

3) The surface of the tube blank is poorly cleaned or has ears or wrong surfaces, etc.

4) During the rolling process, the surface of the steel pipe is lifted and scratched and is pressed onto the base of the steel pipe through rolling, forming outward folds, etc.

Inspection and Judgment: Not allowed: slight grinding can be carried out, and the actual value of wall thickness and outer diameter after grinding shall not be less than the minimum value required by the standard.

2. Separation layer characteristics: spiral or massive delamination and rupture on the surface of the steel pipe.

Causes: Serious non-metallic inclusions, residual shrinkage cavities, or serious looseness in the tube blank.

Judgment: Not allowed to exist.

3. External scarring characteristics: Scars appear on the outer surface of the steel pipe.

cause:

1) The roller is stuck to steel, aged, severely worn, or chipped.

2) The conveying roller is stuck with foreign matter or is seriously worn.

Judgment:

1) External scars distributed in patches should be repaired or removed.

2) On pipe sections with external scarring, if the area of the external scar exceeds 10%, it should be removed or ground.

3) External scabs whose depth exceeds 5% of the wall thickness should be repaired.

4) The actual wall thickness and outer diameter of the grinding area shall not be less than the minimum value required by the standard.

4. Pockmark characteristics: The surface of the steel pipe presents uneven pits.

cause:

1) The steel pipe stays in the furnace for too long or the heating time is too high, causing the iron oxide scale on the surface to be too thick, not clean, and rolled into the surface of the steel pipe.

2) The high-pressure water phosphorus removal equipment is not working properly and the phosphorus removal is not clean, etc.

Judgment:

1) Local pitting that does not exceed the negative deviation of the wall thickness is allowed to exist.

2) The pockmarked area shall not exceed 20% of the area of the pockmarked pipe section.

3) The out-of-tolerance pitted surface can be ground or removed. The actual wall thickness and outer diameter of the ground should not be less than the minimum value required by the standard.

4) Severe pockmarks will result in disqualification.

5. Green line characteristics: The outer surface of the steel pipe presents symmetrical or asymmetric linear rolling marks.

cause:

1) The hole pattern of the sizing machine is misaligned or severely worn.

2) The roll pass design of the sizing machine is unreasonable.

3) Rolling low-temperature steel.

4) The roll processing is not good, and the chamfering of the edge of the roll is too small.

5) The roller assembly is not good, the gap is too large, etc.

Judgment:

1) The outer surface of the casing is allowed to have a green line with a height not exceeding 0.2mm. If it exceeds the tolerance, it should be ground.

2) High-pressure vessel pipes are not allowed to have green lines. There are blue lines that feel like they must be removed. The grinding area should be smooth and without edges.

3) Common steel pipes (structure, fluid, hydraulic supports, etc.) are allowed to have a green line with a height of no more than 0.4mm. If it exceeds the tolerance, it should be ground.

4) The sharp edges of the green lines should be smoothed.

5) The actual wall thickness and outer diameter of the grinding area shall not exceed the minimum values required by the standard.

6. Hairline characteristics: On the outer surface of the steel pipe, there are continuous or discontinuous hair-like fine lines.

cause:

1) The tube blank has subcutaneous pores or inclusions.

2) The surface of the tube blank is not completely cleaned and there are small cracks.

3) Excessive wear and aging of the rollers.

4) The roller processing accuracy is not good.

Inspection and Judgment: Hair lines visible to the naked eye are not allowed to exist on the outer surface of the steel pipe. If they exist, they should be completely removed. After removal, the actual wall thickness and outer diameter must not be less than the minimum value required by the standard.

7. Characteristics of reticular cracks: Small fish scale-like cracks with large pitch and strips appear on the outer surface of the steel pipe.

cause:

1) The content of harmful elements in the tube blank is too high (such as arsenic).

2) The perforated roller is aging and sticking to steel.

3) Guide plate glued to steel, etc.

Judgment: This should be completely cleared. The actual values of wall thickness and outer diameter after cleaning shall not be less than the minimum values required by the standard.

8. Scratch characteristics: The outer surface of the steel pipe has spiral or linear groove-like defects, and the bottom of the groove can be seen in most cases.

cause:

1) Mechanical scratches mainly occur on roller tables, cooling beds, straightening, and transportation.

2) The rollers are poorly processed or severely worn, or there are foreign objects caught in the roller gaps.

Judgment:

1) The outer surface of the steel pipe is allowed to have local scratches not exceeding 0.5mm. Scratches exceeding 0.5mm should be repaired. The actual wall thickness and outer diameter of the grinding area shall not be less than the minimum value required by the standard.

2) Sharp edge scratches should be smoothed.

9. Collision characteristics: The outer surface of the steel pipe is concave and convex, but the wall thickness of the steel pipe is not damaged.

cause:

1) It was crushed due to impact during lifting.

2) Flatten when biting into straightened parts.

3) The rear roller table of the sizing machine is damaged, etc.

Inspection and Judgment: Local bumps that do not exceed the negative deviation of the outer diameter and have a smooth surface may exist. Removal when out of tolerance.

10. Bump characteristics: Irregular scars on the outer surface of the steel pipe due to collision.

Cause: It can occur from various collisions between cold areas and hot areas.

Judgment:

1) Local bruises with a depth not exceeding 0.4mm are allowed on the outer surface.

2) Bumps exceeding 0.4mm should be smoothed and the actual values of the outer diameter and wall thickness of the ground should not be less than the minimum values required by the standard.

11. Concave correction features: The outer surface of the steel pipe is spirally concave. cause:

1) The angle of the straightening machine roller is improperly adjusted and the reduction amount is too large.

2) The straightening roller is severely worn, etc.

Inspection and Judgment: The outer surface of the steel pipe is allowed to have no obvious edges and corners, the inner surface is not protruding, and the outer diameter size meets the tolerance requirements. Excessive correction of dents should be removed.

12. Rolling and folding characteristics: The steel pipe wall presents concave and convex wrinkles along the longitudinal part or the entire length, and the outer surface forms a strip-shaped depression.

cause:

1) The hole width coefficient is selected too small.

2) Improper adjustment of the rolling mill results in pass misalignment or inconsistent rolling center line.

3) Improper distribution of reduction in each frame of the continuous rolling mill, etc. Due to the above reasons, metal enters the gap between the rolls during the rolling process of the steel pipe or the pipe loses its stability, causing the pipe wall to wrinkle.

Judgment: Not allowed to exist. It should be removed or discarded.

13. Crack characteristics: The surface of the steel pipe has a cracking phenomenon, which mostly occurs on thin-walled pipes.

cause:

1) Due to the uneven heating temperature of the tube blank, the deformed part is rough and the parts with low temperature are tensile rolled. When the tensile force is large, the tube will be cracked.

2) The speed and roll gap of each frame of the continuous rolling mill is improperly adjusted, causing the steel to be pulled and torn.

3) The influence of capillary wall thickness. When the capillary wall thickness of the capillary tube supplied by the piercing machine to the continuous rolling mill is small, the metal deformation amount in the continuous rolling mill is smaller than the designed deformation amount, causing the continuous rolling mill to roll under tension, and sometimes tear when the tension is high.

4) There are serious inclusions in the tube blank itself.

Judgment: Not allowed to exist. Should be removed or condemned