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Common defects of titanium tubes

One   Internal surface defect

   1. in the fold

Features: zigzag defects with straight or helical or semi-helical shapes on the inner surface of the titanium tube.

Causes:

     1) titanium billet: center is loose and segregation;Serious shrinkage cavity residual;Non-metallic inclusions exceed the standard.

     2) uneven heating, too high or too low temperature, too long heating time.

     3) perforated area: serious wear on the top;Improper adjustment of punch parameters;Perforated roll aging, etc.

Inspection: no internal folding is allowed on the surface of the titanium tube. The internal folding at the end of the tube should be repaired or re-cut. The actual wall thickness at the grinding point should not be less than the minimum value required by the standard.Pass length inside fold judge invalid.

   2. the scar

Characteristics: the surface of titanium tube shows scar, generally does not root easy to flake.

Causes:

     1) there are impurities in the graphite lubricant.

     2) the iron ear at the back end of the pipe is pressed into the inner wall of the titanium pipe, etc.

Inspection: the surface of the titanium tube shall not be allowed to exist, the pipe end shall be repaired and re-cut, the grinding depth shall not exceed the negative deviation required by the standard, and the actual wall thickness shall not be less than the minimum required by the standard;The inner scar of tong chang is judged as invalid.

   3. become warped skin

Characteristics: the surface of the titanium tube presents a straight line or intermittent nail - shaped upturned skin.It often appears in the head of the capillary and is easy to peel off.

Causes:

     1) improper adjustment parameters of punch machine.

     2) titanium on the top.

     3) oxide coating accumulation in waste tube, etc.

Inspection: the surface of titanium tube is allowed to have peel skin without root and easy to peel off (or burn off during heat treatment).The root of the skin should be trimmed or removed.

   4.The straight

Features: linear scratches with a certain width and depth exist on the surface of titanium tube.

Causes:

     1) low rolling temperature, mandrel stick metal hard object.

     2) graphite contains impurities, etc.

Check to:

     1) the inner straight of the casing and general pipe is allowed to be no more than 5% deep (the maximum depth of pressure vessel class is 0.4mm).

Caution chadney straight should be grinding, excision.

     2) the sharp inner straight should be polished smoothly.

   5.The edge

Characteristics: there are linear protrusions with certain width and depth on the surface of titanium tube.

Causes: mandrel wear serious, repair and grinding not smooth or too deep, etc.

Check to:

     1) it is allowed that the height of the casing pipe and pipeline pipe shall not exceed 8% of the wall thickness, and the maximum height shall not exceed 0.8mm, and the inner edge shall not affect the diameter.Out of tolerance should be repaired and recut.

     2) the inner edge of general pipe and pipeline pipe is allowed to be no more than 8% of wall thickness (the maximum height is 0.8mm).The excess should be milled and recut.

     3) for L2 level (i.e. N5) flaw detection, the inner edge height of the titanium tube shall not exceed 5% (the maximum height shall be 0.5mm).The excess should be milled and recut.

     4) the sharp inner edge of the edge should be polished smoothly.

   6.The bulge

Characteristics: the surface of the titanium tube is regularly convex with no damage on the outer surface.

Causes: even roll grinding too much or off the flesh.

Judgement: according to the requirement of inner edge.

   7.Pull a concave

Characteristics: the surface of the titanium tube is pitted regularly or irregularly and the outer surface is not damaged.

Causes:

     1) improper adjustment of continuous rolling, each frame roller rolling speed does not match.

     2) the heating of tube billet is uneven or the temperature is too low.

     3) deviation of rolling centerline, collision between titanium tube and roller way after continuous rolling, etc. (note: this reason was put forward in 2003.1, the principle is still under discussion).

Inspection: no more than the negative deviation of wall thickness, the actual wall thickness is greater than the minimum wall thickness.Excessive pull concave should be cut.(note: the serious development of depression is known as fracture, and this kind of injury should be strictly tested).

   8.Internal thread (this defect is only produced in assel unit)

Characteristics: the surface of the titanium tube has helical trace, which mostly appears on the surface of the thin-walled tube.Causes:

     1) inherent defects of the skew rolling process.This defect is more prominent when the process parameters of assel tube rolling machine are not adjusted properly.

     2) unreasonable distribution of deformation amount and excessive assel wall reduction.

     3) improper configuration of assel roll.

Inspection: the defect depth of titanium internal thread is no more than 0.3mm and within a certain tolerance range.

Two   Surface defect

   1. Fold the outside

Features: spiral lamellar folding on the outer surface of the titanium tube.

Causes:

     1) there are folds or cracks on the surface of the tube billet.

     2) subcutaneous pores of the tube billet, with serious subcutaneous inclusion.

     3) the surface of the billet is cleaned badly or has ears, wrong surface, etc.

     4) during rolling, the surface of the titanium tube is lifted and scratched. After rolling, it is pressed to the matrix of the titanium tube, forming an outer fold.

Inspection: it is not allowed to exist: slight grinding can be done, the actual value of the wall thickness and outer diameter after grinding shall not be less than the minimum value required by the standard.

   2. Abscission layer

Features: helical or blocky lamination and fracture on the surface of the titanium tube.

Causes: serious non-metallic inclusion, residual shrinkage cavity or serious loose in the tube billet.

Judgement: not allowed.

   3. The scar

Features: the outer surface of the titanium tube shows scar.

Causes:

     1) roll adhesion titanium, aging, serious wear or roll crushing.

     2) there is a foreign body or serious wear on the conveying roller.

Check to:

     1) external scar distribution should be repaired or removed.

     2) on the segment with external scar, the area of external scar over 10% should be cut or polished.

     3) external scarring with a depth of more than 5% of the wall thickness should be milled.

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

   4. piping

Characteristics: the surface of titanium tube is uneven pit.

Causes:

     1) the titanium tube stays in the furnace for too long or the heating time is too long, so that the scale on the surface is too thick, which can be cleaned and rolled into the surface of the titanium tube.

     2) high pressure water phosphorus removal equipment does not work properly, phosphorus removal is not clean, etc.

Check to:

     1) local pockmarks with negative wall thickness deviation are allowed.

     2) the area of the pitted surface shall not exceed 20% of the area of the section with pitted surface.

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

     4) severe pockmarks shall be discarded.

   5. The green line

Features: the outer surface of titanium tube shows symmetric or asymmetric linear rolling mark.

Causes:

     1) hole dislocation or serious wear of sizing machine.

     2) unreasonable roll pass design of sizing machine.

     3) low temperature titanium rolling.

     4) roll processing is not good, roll edge chamfer is too small.

     5) roll assembly is not good, clearance is too large, etc.

Check to:

     1) the outer surface of the casing shall be allowed to be no higher than 0.2mm blue line, and the deviation shall be repaired and polished.

     2) high pressure container tubes are not allowed to have hand blue thread.The green thread must be removed.Grinding should be smooth without edges and corners.

     3) general titanium pipe (structure, fluid, hydraulic support, etc.) is allowed to be no more than 0.4mm blue line, and the deviation should be repaired and ground.

     4) the sharp blue line should be polished smoothly.

     5) the actual value of wall thickness and outer diameter at the grinding place shall not exceed the minimum value required by the standard.

   6.hairline

Features: continuous or discontinuous hairline on the outer surface of the titanium tube.

Causes:

     1) the tube blank has subcutaneous pores or inclusions.

     2) the surface of the billet is not cleaned thoroughly, and there are small cracks.

     3) excessive wear and aging of rollers.

     4) roll processing accuracy is not good.

Inspection: visible hairline is not allowed on the outer surface of titanium tube. If there is any hairline, it should be completely removed. The actual value of wall thickness and outer diameter after removal should not be less than the minimum value required by the standard.

   7. The reticular crack

Features: the outer surface of the titanium tube shows a band of small fissure with large pitch.

Causes:

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

     2) aging of perforation roller and titanium adhesion.

     3) titanium adhesion of guide plate, etc.

Prosecution: shall be completely removed.The actual values of the cleaned wall thickness and outer diameter shall not be less than the minimum value required by the standard.

   8. scratch

Features: the outer surface of titanium tube shows spiral shape or linear groove shape defect, most of which can see the bottom of the groove.

Causes:

     1) mechanical scratches mainly occur in roller beds, cold beds, straightening and transportation.

     2) the roll is badly processed or severely worn, or there is a foreign body in the gap between the rolls, etc.

Check to:

     1) scratch of the outer surface of titanium tube is allowed to exist locally not exceeding 0.5mm. Scratch of over 0.5mm should be repaired and polished.The actual value of wall thickness and outer diameter at the grinding place shall not be less than the minimum value required by the standard.

     2) scratches with sharp edges should be polished and smooth.

   9. Touch flat

Characteristics: the outer surface of titanium tube is concave and convex, while the wall thickness of titanium tube is not damaged.

Causes:

     1) crash and dent during lifting.

     2) flattening when biting.

     3) roller table is dented after sizing machine.

Inspection: local negative deviation of outer diameter and smooth surface can exist.Excision when out of tolerance.

   10. bruised

Characteristics: the outer surface of titanium tube is irregularly scarred by collision.

Causes: can be produced in the cold and hot areas of various collision.

Check to:

     1) the external surface is allowed to have local bruises with a depth of less than 0.4mm.

     2) if the collision exceeds 0.4mm, the grinding shall be smooth and the actual value of outer diameter and wall thickness shall not be less than the minimum value required by the standard.

   11. JiaoAo

Features: the titanium tube has a spiral concave surface.

Causes:

     1) improper adjustment of roller Angle of straightening machine and excessive pressure.

     2) serious wear of straightening roller, etc.

Inspection: the outer surface of titanium pipe is allowed to be concave without obvious edges and corners, and the inner surface is not prominent, and the outer diameter meets the tolerance requirements.Excessive correction should be cut.

   12.Rolling off

Features: the titanium tube wall along the longitudinal part or the full length presents the outer concave convex wrinkles, the outer surface into a strip depression.

Causes:

     1) the selection of pass width coefficient is too small.

     2) improper adjustment of the rolling mill leads to misalignment of pass shape or inconsistent rolling centerline.

     3) each frame of continuous rolling mill pressure distribution is improper, etc.

Due to the above reasons, the metal enters into the gap of the roll or the tube loses its stability during the rolling process and causes the wall crease of the titanium tube.

Judgement: not allowed.Should be excised or condemned.

   13. Rip to

Characteristics: the surface of titanium tube has the phenomenon of pulling and breaking, which is mainly produced on the thin-walled tube.

Causes:

     1) due to the uneven heating temperature of the tube billet, the deformation part is fine and the part with low temperature is rolled. When the tension is large, the tube will be cracked.

     2) influence of wool tube wall thickness: when the thickness of wool tube supplied by the perforator to the tandem mill is relatively small, the metal deformation of the tandem mill is less than the designed deformation, resulting in the tension rolling of the tandem mill, which is torn when the tension is large.

     3) there are serious inclusions in the billet itself.

Judgement: not allowed.Should be excised or condemned

Three   Size out-of-tolerance

   1. Uneven wall thickness

Features: the wall thickness of titanium tube is uneven in the same section, and there is a big difference between the maximum wall thickness and the minimum wall thickness.

Causes:

     1) uneven heating of tube billet.

     2) the rolling line of the perforator is not adjusted, and the centering roller is unstable.

     3) the head is worn or the hole behind the head is eccentric.

     4) tube blank centering hole correction.

     5) the bending degree and cutting inclination of the tube billet are too large.

Judgement: the uneven end of the wall should be cut off.

   2. Wall thickness error

Characteristics: one-way out-of-tolerance of titanium pipe wall thickness, which is referred to as over-thickness in case of over-positive deviation.The supernegative deviation is called superthin wall thickness.

Causes:

     1) uneven heating of tube billet.

     2) improper adjustment of punch machine.

Judgment: measure one by one, the end of the deviation should be removed, the whole length of the deviation should be changed or rejected.

   3. Outside diameter out-of-tolerance

Features: the outer diameter of titanium pipe exceeds the standard, which is called large outer diameter for those with more positive difference, and small outer diameter for those with more negative difference.

Causes:

     1) hole wear of sizing machine is too large, or the new hole design is not reasonable.

     2) the final rolling temperature is unstable.

Judgement: measure one by one, if exceed the standard, the judgement should be changed or rejected

   4. bending

Characteristics: the titanium tube is not straight along the direction of the length or the end of the titanium tube shows a goose-shaped bend called "goose-head".

Causes:

     1) local water cooling during manual heat test.

     2) improper adjustment during straightening and serious wear of straightening roller.

     3) improper sizing machining, assembly and adjustment.

     4) bending is caused during hoisting and transportation.

Inspection and judgment: if the bending degree exceeds the standard, it can be straightened twice; otherwise, it will be judged as invalid.The "goose-head bend" that cannot be straightened should be excised.

   5. The length of the super poor

Features: the length of titanium tube exceeds the requirements, super positive difference is called long ruler, super negative difference is called short ruler.

Causes:

     1) the length of pipe blank exceeds the standard.

     2) rolling instability.

     3) did not control the cutting, etc.

Judgment: re-cut or re-cut long length pipe, re-cut or re-cut short length pipe


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