Common defects in steel pipes
An inner surface defect
Features: In the steel pipe on the inner surface of a straight or spiral, semi-spiral jagged defects.
1) tube: the center of loose, segregation; shrinkage of serious residual; non-metallic inclusions exceeded.
2) tube heating uneven, the temperature is too high or too low, the heating time is too long.
3) perforation area: the head wear serious; improper adjustment of perforator parameters; perforation roll aging.
Judgment: the inner surface of the pipe is not allowed to be folded, the end of the tube should be repaired or re-cut, grinding the wall thickness of the actual value of the minimum value shall not be less than the standard;
2 within the scar
Features: steel pipe surface scars, generally not easy to peel off the root.
1) graphite lubricant with impurities.
2) the back of the iron tube, was pressed into the steel pipe wall.
Inspection: the inner surface of the pipe is not allowed to exist, the pipe end should be grinding and re-cutting, grinding depth should not exceed the standard requirements of negative deviation, the actual wall thickness shall not be less than the minimum standard requirements;
3 Alice skin
Features: the inner surface of the steel pipe appears straight or intermittent nail-like tilt of the small skin. Mostly appear in the head of the capillary, and easy to peel off.
1) improper adjustment of the punching machine.
2) head sticky steel.
3) the accumulation of iron oxide skin in the pipe.
Judgment: The inner surface of the pipe allows the presence of rootless peeling (or burnable during heat treatment). The root of the Alice should be grinding or removal.
4 inner straight
Features: There is a linear scratches with a certain width and depth on the inner surface of the pipe.
1) the rolling temperature is low, the mandrel sticks with metal hard objects.
2) graphite contains impurities and so on.
1) Casing and plain pipe allow the depth of not more than 5% (pressure vessel class maximum depth of 0.4mm) within the straight channel exists.
Cautious ultra-Chad's straight should be grinding, removal.
2) the edge of the sharp straight should be smooth grinding.
5 inner edge
Features: There is a linear protrusion with a certain width and depth on the inner surface of the pipe.
Cause: the core rod wear serious, grinding is not smooth or too deep.
1) casing, pipe pipe allows the existence of a height of not more than 8% of the wall, the maximum height of not more than 0.8mm does not affect the diameter of the inner edge. Oversight should be repaired and cut again.
2) Pipes, pipelines allow the presence of an inner edge that does not exceed a wall thickness of 8% (maximum height of 0.8 mm). Supernatural grinding and re-cutting.
3) for the L2 level (ie N5) testing requirements of steel, the height of the edge shall not exceed 5% (maximum height of 0.5mm). Supernatural grinding and re-cutting.
4) sharp edges of the edge should be smooth grinding.
6 inside the drum package
Features: The inner surface of the steel pipe has a regular convex and the outer surface is not damaged.
Cause: roll roll grinding is too large or lost meat and so on.
Judgment: according to the requirements of the inner edge of the judge.
7 pull concave
Features: The inner surface of the steel pipe has a regular or irregular pits and no damage to the outer surface.
1) improper adjustment of rolling, roller rolling speed does not match.
2) The tube is heated unevenly or the temperature is too low.
3) Rolling centerline deviation, steel pipe and rolling after rolling collision occurred (Note: this reason 2003.1 proposed, the principle is still being discussed).
Check: no more than the wall thickness of the negative deviation, the actual wall thickness is greater than the minimum wall thickness required to allow the existence of pull. Excessive pull concave should be removed. (Note: pull serious development is pulling, this injury should be strictly tested).
8 internal thread (this defect is only generated in the Arcelor unit)
Features: The inner surface of the steel pipe with spiral traces, mostly in the thin-walled tube on the surface, there are rugged obvious feel. cause:
1) inherent defects in the skew rolling process. This defect is more pronounced when the process parameters of the Asher rolling mill are not properly adjusted.
2) the allocation of deformation is unreasonable, Asher reduced the amount of too large.
3) Arcelor roll type improperly arranged.
Check: the depth of the steel pipe thread defect is not more than 0.3mm, and within a certain tolerance range.
Two outer surface defects
1 outside the fold
Features: in the outer surface of the steel pipe appears in a spiral-like folding.
1) The surface of the tube has a fold or crack.
2) subcutaneous stomata of the tube, subcutaneous inclusion is more serious.
3) tube surface clean-up or ear, wrong surface and so on.
4) During the rolling process, the surface of the steel pipe was lifted and scratched by rolling and pressed into the base of the steel pipe to form an outer fold.
Check: not allowed to exist: a slight grinding can be done after grinding the wall thickness and diameter of the actual value shall not be less than the minimum required by the standard.
Features: In the steel pipe surface appears spiral or massive layered and broken.
Reason: non-metallic inclusions in the tube serious, residual shrinkage or serious loose and so on.
Judgment: not allowed to exist.
3 outside the scar
Features: The outer surface of the steel pipe appears scarred.
1) Roller sticky steel, aged, wear serious or roll.
2) Conveyor roller glued with foreign matter or serious wear.
1) The distribution of external scarring should be done by grinding or resection.
2) in the outside of the scar on the tube, the outer scar area of more than 10% should be removed or grinding.
3) depth of more than 5% of the wall outside the scar should be grinding.
4) grinding the wall thickness, diameter actual value shall not be less than the minimum standard requirements.
Features: steel pipe surface appears uneven ridge.
1) pipe stay in the furnace for too long or too long heating time, so that the surface of the oxide scale is too thick, not clean, rolled into the steel pipe surface.
2) high-pressure water and phosphorus removal equipment is not working properly, phosphorus is not clean and so on.
1) The local area does not exceed the wall thickness negative deviation of the hemp allowed to exist.
2) The area of the noodles shall not exceed 20% of the area of the hemp section.
3) the amount of incense can be repaired or removed, grinding wall thickness, diameter actual value shall not be less than the minimum standard requirements. 4) Serious hemp.
5 green line
Features: The outer surface of the pipe is symmetrical or asymmetrical.
1) sizing hole misalignment or wear serious.
2) sizing machine roll hole design is unreasonable.
3) rolling low temperature steel.
4) Roll processing is not good, roll side chamfer is too small.
5) roll assembly is not good, the gap is too large and so on.
1) the outer surface of the casing to allow the height of not more than 0.2mm green line exists, tolerance should be grinding.
2) high-pressure container tube is not allowed to feel the presence of green lines. There is a feeling that the green line must be cleared. Grinding should be smooth without edges and corners.
3) general type of steel pipe (structure, fluid, hydraulic support, etc.) to allow the height of not more than 0.4mm green line exists, tolerance should be grinding.
4) sharp edges of the green line should be smooth grinding.
5) grinding the wall thickness, diameter value of the actual value shall not exceed the minimum standard requirements.
Features: On the outer surface of the pipe, there are continuous or discontinuous hair fine lines.
1) Tubes have subcutaneous stomata or inclusions.
2) tube surface cleaning is not complete, there are small cracks exist.
3) Roller over-wear and aging.
4) roll processing accuracy is not good and so on.
Check: the outer surface of the pipe does not allow the presence of visible hair, such as the existence should be completely removed, remove the wall thickness, diameter actual value shall not be less than the minimum standard requirements.
7 mesh crack
Features: The outer surface of the steel pipe with a large pitch and small scales of small cracks.
1) The content of harmful elements in the tube is too high (eg arsenic).
2) piercing roll aging, sticky steel.
3) guide plate sticky steel and so on.
Check: should be completely cleared. After the removal of the wall thickness, the actual value of the outer diameter shall not be less than the minimum standard requirements.
Features: The outer surface of the steel pipe is spiral or linear groove-like defects, most can see the ditch at the end.
1) mechanical scratches are mainly produced in the roller, cooling bed, straightening, transport.
2) Roll processing is not good or wear serious or roll gap with foreign body and so on.
1) the outer surface of the pipe allows the presence of no more than 0.5mm scratches, over 0.5mm scratches should be grinding. Grinding the wall thickness, diameter actual value shall not be less than the minimum standard requirements.
2) sharp edges of the scratches should be smooth grinding.
9 touch deflated
Features: The outer surface of the steel pipe appears convex concave phenomenon, and steel pipe wall thickness without damage.
1) in the lifting of the collision to deflated.
2) Straighten bite when bruised.
3) after the sizing machine roller and so on.
Judgment: Partial non-outer diameter negative deviation and smooth surface of the collision can be present. Overdose.
Features: The outer surface of the steel pipe due to collision produce irregular scars.
Cause: can be generated in the cold zone and the hot zone of the various collisions.
1) the outer surface allows the existence of local depth of not more than 0.4mm bruise.
2) more than 0.4mm bruises should be smooth grinding and grinding outside diameter, wall thickness of the actual value shall not be less than the minimum standard requirements.
Features: The outer surface of the steel pipe is spiral concave.
1) Straightening roller angle adjustment improper, the amount of pressure is too large.
2) straightening roller wear and so on.
Judgment: The outer surface of the pipe is allowed to have no obvious edges and corners and the inner surface is not protruding, and the outer diameter dimension conforms to the tolerance requirements. On the excessive correction should be removed.
12 rolling off
Features: pipe wall along the longitudinal part of the longitudinal or long showing the concave convex convex fold, the outer surface into a strip depression.
1) The hole width coefficient is chosen to be too small.
2) Improper adjustment of the rolling mill causes the misalignment of the holes or the inconsistency of the rolling centerline.
3) continuous rolling mill rolling down the amount of improper distribution.
For the above reasons, the steel pipe in the rolling process of metal into the roll gap or the loss of stability caused by pipe wall wrinkles.
Judgment: not allowed to exist. Should be removed or rejected.
Features: steel pipe surface has opened the phenomenon of rupture, and more produce in the thin-walled tube.
1) due to the uneven heating temperature of the tube, making the deformation of the Ministry of high temperature and low tensile strength rolling, when the tension is large, the pipe cracking.
2) continuous rolling mill speed and roll gap adjustment properly, resulting in pulling steel and tear.
3) the impact of capillary wall thickness, when the punching machine supply rolling mill capillary wall thickness is small, in the continuous rolling mill metal deformation than the design of the amount of deformation, resulting in rolling mill rolling, tensile strength and tear.
4) The tube itself has more serious inclusions.
Judgment: not allowed to exist. Should be removed or rejected
Three size tolerance
1 uneven wall thickness
Features: steel pipe in the same section of the wall thickness is not uniform, the maximum wall thickness and the difference between the minimum wall thickness.
1) Uneven heating of the tube.
2) punching machine rolling line is not adjusted, centering roller instability.
3) head wear or head hole eccentric.
4) tube blank center hole correction.
5) tube curvature, cutting slope is too large.
Judgment: by branch measurement, uneven wall thickness should be removed.
2 wall thickness tolerance
Features: steel pipe wall thickness of one-way ultra-poor, ultra-positive deviation, said the wall thickness is thick; ultra-negative deviation, said the wall thickness is thin.
1) Uneven heating of the tube.
2) improper adjustment of the punching machine.
Judgment: by branch measurement, the end of the tolerance should be removed, the full length of the difference should be commuted or sentenced.
3 Outside diameter
Features: steel pipe diameter exceeding the standard, the difference is called the difference between the large diameter, super negative difference is called the small diameter.
1) sizing machine hole wear is too large, or new hole design is not reasonable.
2) The finish rolling temperature is unstable.
Judgment: by branch measurement, should be given overdue or sentenced.
Features: steel pipe along the length of the direction is not straight or in the steel pipe at the end of the goose-like bend called "goose head bend."
1) Local hot water test caused by local water cooling.
2) improper adjustment when straightening, straightening roller wear serious.
3) sizing machine processing, assembly and improper adjustment.
4) Bending caused by bending.
Judgment: bending degree exceeded, can be re-straightening, or waste. Can not straighten the "goose head bend" should be given to the excision.
5 length difference
Features: steel pipe length exceeds the requirements, super-difference is called length, super negative difference called short foot.
1) The length of the tube is excessive.
2) Rolling instability.
3) no control when cutting and so on.
Judgment: long tube re-cut or commutation, short pipe correction or conviction