Defects and causes of ERW steel pipes

ERW steel pipe inner surface defects

1. Fold inward

Characteristics: linear, spiral, or semi-helical jagged defects appear on the inner surface of the steel pipe.

 

cause:

1) Tube blank: The center is loose and segregated; the shrinkage cavity remains serious; non-metallic inclusions exceed the standard.

2) The tube blank is heated unevenly, the temperature is too high or too low, and the heating time is too long.

3) Perforation area: The head is severely worn; the parameters of the perforator are improperly adjusted; the perforation roller is aging, etc.

 

Inspection and Judgment: Inward folds are not allowed on the inner surface of steel pipes. Inward folds at the end of the pipe should be repaired or re-cut. The actual wall thickness at the ground should not be less than the minimum value required by the standard; full-length inner folds will be deemed scrapped.

2. Internal scarring

Features: The inner surface of the steel pipe shows scars, which generally do not take root and easily peel off.

cause:

1) Graphite lubricant contains impurities.

2) The iron ear at the rear end of the waste pipe is pressed into the inner wall of the steel pipe, etc.

 

Inspection and Judgment: The inner surface of the steel pipe is not allowed to exist. The pipe end should be ground and re-cut. The grinding depth should not exceed the negative deviation required by the standard. The actual wall thickness should not be less than the minimum value required by the standard. If there is scarring within the full length, it will be discarded.

 

3 warped skin

Features: The inner surface of the steel pipe presents straight or intermittent nail-like raised skin. They often appear on the heads of hair tubes and are easy to peel off.

 

cause:

1) Improper adjustment parameters of the punching machine.

2) The head is glued to steel.

3) Accumulation of iron oxide scale in waste pipes, etc.

 

Inspection and Judgment: The inner surface of the steel pipe is allowed to have peeling skin that is rootless and easy to peel off (or can be burned during heat treatment). Rooted warped skin should be trimmed or removed.

 

4 inside straight

Features: There are linear scratches with a certain width and depth on the inner surface of the steel pipe.

 

cause:

1) The rolling temperature is low and the mandrel is stuck with metal hard objects.

2) Graphite contains impurities, etc.

 

Judgment:

1) The casing and general pipe are allowed to have inner straight channels with a depth not exceeding 5% (maximum depth of 0.4mm for pressure vessels).

 

2) Inner straights with sharp edges should be smoothed.

 

5 inner edge

Features: There are linear protrusions with a certain width and depth on the inner surface of the steel pipe.

Cause: The mandrel is severely worn, and the grinding result is not smooth or too deep, etc.

 

Judgment:

1) The allowed height of casing and line pipe does not exceed 8% of the wall thickness, and the maximum height does not exceed 0.8mm and does not affect the diameter of the inner edge. If it is out of tolerance, it should be repaired, ground and cut again.

2) General pipes and line pipes are allowed to have inner edges with a height not exceeding 8% of the wall thickness (maximum height is 0.8mm). If the tolerance is exceeded, it should be ground and re-cut.

3) For steel pipes required for L2 level (i.e. N5) flaw detection, the inner edge height shall not exceed 5% (the maximum height is 0.5mm). If the tolerance is exceeded, it should be ground and re-cut.

4) Sharp inner edges should be smoothed.

 

6. Inner bulge

Features: The inner surface of the steel pipe shows regular convexity and there is no damage on the outer surface.

Cause: excessive grinding amount of continuous roller or meat loss, etc.

Inspection: Inspection according to the requirements of the inner edge.

 

7 pull concave

Features: The inner surface of the steel pipe shows regular or irregular pits and there is no damage to the outer surface.

cause:

1) The continuous rolling adjustment is improper and the rolling speed of each roller does not match.

2) The tube blank is heated unevenly or the temperature is too low.

3) The rolling center line deviates, the steel pipe collides with the roller table after continuous rolling, etc.

 

Inspection and Judgment: The negative deviation of the wall thickness is not exceeded, and the actual wall thickness is greater than the required minimum value of the wall thickness. It is allowed to exist. Exceeding dents should be removed. (Note: Severe denting is considered to be a tear, and such injuries should be strictly inspected).

 

8. Internal thread (this defect only occurs in Asser units)

Features: There are spiral marks on the inner surface of the steel pipe, which mostly appear on the inner surface of thin-walled pipes, and have an obvious uneven feel. cause:

 

1) Inherent defects of cross rolling process. This defect is more prominent when the process parameters of the Asel pipe rolling mill are improperly adjusted.

2) The distribution of deformation is unreasonable and the Asser wall reduction is too large.

3) The Axel profile roll configuration is improper.

 

Inspection and Judgment: The depth of defects in the internal thread of the steel pipe is not greater than 0.3mm and is within a certain tolerance range.

 

External surface defects of ERW steel pipes

1. Fold outward

Features: There are spiral layered folds 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 cracking 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

Features: There are scars 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. Ma Mian

Features: The surface of the steel pipe shows 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

Features: The outer surface of the steel pipe shows 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 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.Hair lines

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.Network cracks

Features: There are small fish scale-like cracks with band-like and large pitch 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: 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

Features: The outer surface of the steel pipe has spiral or linear groove-like defects, and most of the groove bottoms can be seen.

 

cause:

 

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

 

2) The rolls are poorly processed or severely worn, or there are foreign objects caught in the roll 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.Bumped

Features: The outer surface of the steel pipe is concave on the outside and convex on the inside, 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 .bruises

Features: 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.

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