We know the common defects of steel pipes contain external surface defects,internal surface defects,over and under size also can defect the steel pipes.
1.Uneven wall thickness
Features: The thickness of the steel pipe is uneven on the same section, and the difference between the maximum and minimum wall thickness is large.
cause:
1) Uneven heating of the tube blank.
2) The rolling line of the piercer is not adjusted, and the centering roller is unstable.
3) The plug is worn or the back hole of the plug is eccentric.
4) Correction of centering hole of tube blank.
5) The bending degree and cutting slope of the tube blank are too large.
Judgment: Measure on a branch-by-branch basis. The uneven wall thickness should be removed.
2.Over or under thickness
Features: One-way tolerance of the wall thickness of the steel pipe, the ultra-positive deviation is called the ultra-thick wall thickness; the ultra-negative deviation is called the ultra-thin wall thickness.
cause:
1) Uneven heating of the tube blank.
2) Improper adjustment of the punching machine.
Judgment: Measure one by one, the over-tolerance at the end should be removed, and the over-tolerance of the full-length should be changed or rejected.
24inch weld Corten steel pipes
3.Tolerance of outer diameter
Features: The outer diameter of the steel pipe exceeds the standard. Those with a positive deviation are called a large outer diameter, and those with a negative deviation are called a small outer diameter.
cause:
1) The hole pattern of the sizing machine is too worn, or the design of the new hole pattern is unreasonable.
2) The final rolling temperature is unstable.
Judgment: Measure one by one. If the standard is exceeded, the judgment shall be changed or invalidated.
4.Bending
Features: The steel pipe is not straight along the length or the goose head is bent at the end of the steel pipe is called “goose head bend”.
cause:
1) Local water cooling during manual thermal inspection.
2) Improper adjustment during straightening and serious wear of the straightening roller.
3) Improper sizing machine processing, assembly and adjustment.
4) Bending during lifting and transportation.
Inspection: When the bend exceeds the standard, it can be re-straightened twice, otherwise it will be rejected. Unable to straighten the “goose head bend” should be removed.
Stainless steel pipe fittings
5.The length is out of tolerance
Features: The length of the steel pipe exceeds the requirements, the ultra-positive difference is called the long ruler, and the ultra-negative difference is called the short ruler.
cause:
1) The length of the tube blank exceeds the standard.
2) Rolling is unstable.
3) There is no control when cutting.
Judgment: Long-length tube is recut or revised, short-length tube is revised or rejected.
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