Stainless Steel Pipe Fittings

Common defects of steel pipe

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First, the inner surface defects
1 internal fold
Features: in the inner surface of the steel pipe is a straight line or a spiral, a half – Helical zigzag defect.
Cause of production:
1) tube bloom: Center loose, segregation; shrinkage residual serious; non-metallic inclusions.
2) tube billet heating uneven, the temperature is too high or too low, the heating time is too long.
3) perforation area: plug wear; punch hole roller wear improper parameter adjustment; aging.
Examining and judging: steel pipe surfaces are not allowed to exist in the fold and tube in the end of the fold should be grinding or cutting, grinding at the wall of the actual thickness value shall not be less than the standard minimum required; full-length fold sentenced to waste.
2 Inner Scar
Features: the inner surface of the steel tube is spotted, it is generally not easy to peel off.
Cause of production:
1) with impurities in the graphite lubricant.
2) the back end of the waste pipe is pressed into the inner wall of the steel pipe.
Inspection found: steel pipe inner surface is not allowed, the tube end should be grinding and cutting, grinding depth should not exceed the standard requirements of negative deviation;
The actual wall thickness shall not be less than the minimum standards; usually discarded inner scar.
3 raise skin
Features: a linear or intermittent nail like tilt of the skin surface of the pipe. In capillary head, and easy peeling.
Cause of production:
1) punch improper adjustment of parameters.
2) head steel.
3) the accumulation of iron oxide in the waste pipe, etc..
Inspection: the surface of the steel pipe allows the existence of non root easily peeling off (or in the heat treatment can be burned). For the root of the skin should be repaired or removed.
4 inside straight road
Features: the surface of the steel pipe with a certain width and depth of the straight line shape.
Cause of production:
1) the rolling temperature is low, the mandrel is stuck with a metal hard material.
2) graphite containing impurities, etc..
Inspection and judgment:
1) the inner straight channel of the bushing and the general pipe allows the depth of no more than 5% (maximum depth of pressure vessel 0.4mm).
The super Chadenei straight should be grinding, resection.
2) edge sharp internal straight road to be smooth.
5 inner edge
Features: a straight line shape with a certain width and depth in the inner surface of the steel pipe.
Cause: mandrel wear, grinding is not smooth or too deep.
Inspection and judgment:
1) casing, pipe tube allows the existence of height is less than honest wall 8%, the maximum height of no more than 0.8mm diameter of the inner edge does not affect the exist. The ultra poor should repair grinding and cut.
2) the existence of the inner edge of the general pipe and the pipe line pipe which allows the height not exceeding 8% (maximum height of 0.8mm). Super difference should be grinding and cut.
3) on the L2 level (ie N5) testing requirements of the steel pipe, the height of the height shall not exceed 5% (maximum height of 0.5mm). Super difference should be grinding and cut.
4) edge sharp inner edge grinding should be smooth.
6 inner drum kit
Features: the inner surface of the steel tube is characterized by a regular convex super and no damage to the outer surface.
Cause: the grinding amount is too large or the meat and so on.
Inspection: according to the requirements of the inspection and sentenced.
7 pull concave
Features: the inner surface of the steel pipe is presented with regular or irregular pits and no damage on the outer surface.
Cause of production:
1) improper adjustment of continuous rolling, the roll speed does not match.
2) the tube blank is heated evenly or the temperature is too low.
3) rolling is offset from the center line, steel and rolling roller collision generation (Note: this reason 2003.1 proposed, principle is still under discussion.
Check: no more than the wall thickness of the negative deviation, the actual wall thickness is greater than the wall thickness of the required minimum value of the pull concave. Excessive pulling concave should be removed. (Note: pull the concave serious development was ripping, such injury shall be strictly inspected).
8 internal threads (the defects produced only in arthel unit)
Features: steel pipe inner surface spiral traces appear in the thin-walled pipe inner surface, obviously feel uneven. Cause of production:
1) the inherent defects of cross rolling process. The machine parameters adjustment at Assel, this defect is more prominent.
2) deformation distribution, arthel wall reduction quantity too large.
3) Assel roller type improper configuration.
Inspection and judgment: the depth of the depth of internal thread defects of steel pipe is not more than 0.3mm, and within a certain tolerance range.
Two, the external surface defects
1 external fold
Features: the outer surface of the steel tube is a spiral shaped folding.
Cause of production:
1) the surface of the tube blank is folded or cracks.
2) the subcutaneous pores of the tube blank, and the subcutaneous inclusions are more serious.
3) tube surface to clean up bad or wrong side handle, etc..
4) during the rolling process, the surface of the steel pipe is cut off, and the steel tube is pressed into the base of the steel pipe through rolling, and the outer folding and the like are formed.
Inspection: does not allow the existence of: minor can be repaired, the wall thickness and outside diameter of the actual value shall not be less than the minimum standard requirements.
2 separation
Features: the surface of the steel pipe is a spiral or block of delamination and fracture.
Cause: the non – metallic inclusions in the tube are serious, the residual shrinkage holes or serious loose.
Prosecution: does not allow the existence of.
3 scar
Features: the outer surface of the steel tube is presented with spot scar.
Cause of production:
1) roll sticking steel, aging, wear or break roller.
2) a foreign body or wear rollgang stick.
Inspection and judgment:
1) foreign film distribution should be grinding or scar resection.
2) in the pipe outside the scar, outside the scar area of more than 10% should be removed or grinding.
3) more than 5% of the thickness of scar depth should be grinding.
4. The thickness of the wall and the actual value of the outside diameter shall not be less than the minimum value of the standard.
Features: steel pipe surface showing uneven Ma hang.
Cause of production:
1) the length of the steel pipe in the furnace or the heating time is too high, so that the surface of the oxide scale is too thick, clear, rolled into the surface of the steel tube.
2) high pressure water and phosphorus removal equipment is not working, phosphorus removal is not clean, etc..
Inspection and judgment:
1) local does not exceed the negative deviation of the wall thickness of the pits are allowed.
2) surface area not exceeding pitted pipe area 20%.
3) the ultra poor grinding pits or removed, the grinding wall thickness, the outer diameter of the actual value of not less than the standard minimum requirements. 4) serious waste pits found.
5 green line
Features: the outer surface of the steel tube is symmetrical or asymmetrical.
Cause of production:
1) the hole type dislocation or serious wear.
2) the roll pass design is not reasonable.
3) cold rolled steel.
4) roller processing is not good, roll edge chamfer is too small.
5) roll assembly is not good, clearance is too large, etc..
Inspection and judgment:
1) the outer surface of the bushing allows for the presence of a height of not more than 0.2mm of the green line.
2) high pressure vessel type tube does not allow the existence of the touch green line. Feel the blue line must be cleared. Grinding should be smooth without edges and corners.
3) (structure, fluid, hydraulic support, etc.) of the ordinary pipe type steel pipe (structure, fluid, hydraulic support, etc.), the height of the 0.4mm green line is not allowed to exist.
4) edge sharp green line should be smooth.
5. The actual value of the wall thickness and the outside diameter of the grinding mill shall not exceed the minimum standard requirements.
6 hair pattern
Features: in the outer surface of the steel pipe, a continuous or discontinuous hair like fine lines.
Cause of production:
1) the tube blank has the skin pores or inclusions.
2) the surface cleaning is not complete, there is a small crack.
3 roll excessive wear, aging.
4 roll processing accuracy is not good, etc..
Inspection: the outer surface of the steel tube does not allow the existence of visible hair lines, such as the existence of a complete clearance, after removal of the wall thickness, outside diameter of the actual value shall not be less than the minimum standard requirements.
7 mesh crack
Features: the outer surface of the steel pipe has ichthyosifo small crack banded and large pitch.
Cause of production:
Harmful elements (such as arsenic element) in the tube blank of 1.
2) wear hole roller aging, stick steel.
3) steel plate.
Check: should be completely removed. The actual value of the wall thickness and outside diameter is not less than the standard requirements.
8 scratch
Features: the outer surface of the steel pipe is spiral or linear shape groove defects, most of which can be seen at the bottom of the ditch.
Cause of production:
1) mechanical damage mainly occurred in the roller and cooling, straightening and transport.
2) roll processing is not good or wear serious or roll seam clip have foreign body, etc..
Inspection and judgment:
1) on the outer surface of the steel pipe to allow the existence of no more than 0.5mm of the scratch, super 0.5mm scratch should be repaired. Grinding
The actual value of the wall thickness and external diameter shall not be less than the minimum standard requirements.
2) edge sharp scratch should be smooth.
9 touch flat
Features: the outer surface of the steel tube is a convex phenomenon, while the wall thickness of the steel tube is not damaged.
Cause of production:
1) on the trolley to hit flat.
2) the straightening bite into a flat.
3) sizing mill roller touch flat.
Inspection: the local non – Ultra – diameter negative deviation and the surface smooth can exist. Super time difference.
10 bumps
Features: the outer surface of the steel pipe due to the impact of the law of the scars.
Cause: can be produced in the cold region and various collision zone.
Inspection and judgment:
1) the outer surface allows local depth of not more than 0.4mm bumps.
2) more than 0.4mm should be smooth and polished to repair damaged grinding at the outer diameter and wall thickness of the actual value of not less than the standard minimum requirements.
11.
Features: the outer surface of the steel pipe is a spiral.
Cause of production:
1) the angle of the straightening machine is not adjusted properly, the amount of pressure is too large.
2) straightening roller wear and so on.
Inspection: the outer surface of the steel tube is allowed to have no obvious edges and corners, and the inner surface is not prominent, and the outer diameter is in accordance with the tolerance requirements. Removal of excessive correction.
12 roll off
Features: steel pipe wall along the longitudinal fold showed local or long convex outer concave surface into strips, depression.
Cause of production:
1) pass spread coefficient is too small.
2) mill adjustment caused by dislocation or rolling center line is not consistent.
3) the distribution of the weight distribution of each frame of the continuous rolling mill.
Due to the above reasons the pipe in the rolling process of metal into the roll gap or tubes lose stability caused by pipe wall wrinkle.
Prosecution: does not allow the existence of. Should be removed or sentenced to waste.
13.
Features: the surface of the steel pipe has a broken phenomenon, which is produced on the thin wall tube.
Cause of production:
1) due to tube billet heating temperature, so handsome deformation, low temperature part of the tension rolling, when the force is larger, the tube cracking.
2) the rolling mill frame speed and roll gap adjustment caused by improper pulling and tearing.
3) influence of the thickness of the capillary, when supply of the piercer mill, the shell wall thickness is small, in the rolling metal deformation ratio design of deformation decreases, resulting in rolling mill tension, tension and sometimes big tear.
4) the part of the tube billet itself is more serious.
Prosecution: does not allow the existence of. Should be removed or sentenced to waste
Three, the size of super poor
1 wall thickness is uneven
Features: the wall thickness of the steel tube in the same section is not uniform, the maximum wall thickness and the minimum wall thickness difference is large.
Cause of production:
1) tube blank heating uneven.
2) piercer rolling line is not adjustable is unstable, centering roller.
3) after eccentric wear or plug hole plug.
4) billet centering Kong Buzheng.
5) tube bending degree, cut too large.
Detection: one by one measurement, the wall thickness of the uneven end should be removed.
2 wall thickness
Features: steel pipe wall thickness of one direction ultra – poor, the ultra – positive deviation is called the wall thickness of ultra – negative deviation of the wall thickness of the thin.
Cause of production:
1) tube blank heating uneven.
2) punch improper adjustment.
Sentenced by a measurement, the end of the ultra poor should be removed, the full-length super difference should be commuted or discarded.
3 outside diameter
Features: outside diameter of the steel pipe, the super positive difference is called the outside diameter, and the super negative difference is called the outside diameter.
Cause of production:
1. The diameter of the sizing machine is too large, or the new pass design is not reasonable.
2) final rolling temperature is not stable.
Sentenced by a measurement, exceed the standard should be given commuted or discarded.
4 bending
Features: steel pipe along the length of the direction is not straight or in the end of the steel pipe with a goose head shaped bending called “the head of the goose””.
Cause of production:
1) the local water cooling caused by artificial heat.
2) the adjustment is improper, the straightening roller wear is serious.
3) sizing machine processing, assembly and adjustment.
4) the lifting and transportation of bending.
Inspection: when the bending degree exceeds the standard, it can be two times to re straighten, or sentenced to waste. Unable to straighten the “goose head bend” should be given to remove.
5 length super difference
Features: the length of the steel pipe is beyond the requirement, and it is called the long rule.
Cause of production:
1) the length of the tube blank exceeds the standard.
2) rolling instability.
3) when the cutting is not controlled well, etc..
Sentenced: long tube or short tube to cut, commuted or discarded
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)

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