Uneven wall thickness
Features: The wall thickness of the steel pipe is uneven on the same section, and the difference between the maximum wall thickness and the 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 rear hole of the plug is eccentric.
4) Correction of the centering hole of the tube blank.
5) The bending degree and cutting slope of the tube blank are too large.
Judgment: measure one by one, and the ends with uneven wall thickness should be removed.
Wall thickness out of tolerance
Features: The wall thickness of the steel pipe is out of tolerance in one direction. Those with a positive deviation are called super-thick wall thickness; those with a super-negative deviation are called super-thin wall thickness.
Cause:
1) Uneven heating of the tube blank.
2) Improper adjustment of the punching machine.
Judgment: measure one by one, the ends should be removed if the tolerance is exceeded, and the judgment should be changed or discarded if the total length is out of tolerance.
Outer diameter out of tolerance
Features: The outer diameter of the steel pipe exceeds the standard. Those who exceed the positive difference are called large outer diameters, and those who exceed negative differences are called small outer diameters.
Cause:
1) The hole pattern of the sizing machine is worn too much, or the new hole pattern design is unreasonable.
2) The final rolling temperature is unstable.
Judgment: Measure one by one, if the exceeding standard is exceeded, the judgment should be changed or rejected.
Bending
Features: The steel pipe is not straight along the length direction or the goose-head-like bend at the end of the steel pipe is called “goose-head bend”.
Cause:
1) It is caused by local water cooling during manual thermal inspection.
2) Improper adjustment during straightening and serious wear of the straightening roller.
3) Improper sizing machining, assembly and adjustment.
4) Bending during hoisting and transportation.
Judgment: When the bending degree exceeds the standard, it can be re-straightened for a second time, otherwise it will be rejected. A “goose head bend” that cannot be straightened should be excised.
Length out of tolerance
Features: The length of the steel pipe exceeds the requirements, the excess positive difference is called a long ruler, and the excess negative difference is called a short ruler.
Cause:
1) The length of the tube blank exceeds the standard.
2) Rolling is unstable.
3) The slitting is not well controlled and so on.
Judgment: The long tube is re-cut or the sentence is revised, and the short tube is revised or invalidated.