Straightness is an important indicator of the quality of HFW seamless steel tubes. The higher the straightness, the easier it is to ensure the thread quality of the oil well pipe, and it also facilitates subsequent processing and inspection.
In production, the reasons for the excessive straightness of HFW steel pipes (including high-frequency electric resistance welded pipes) are as follows:
1. Improper adjustment of the straightening frame: The HFW seamless steel pipe bends out from the sizing unit and is bent in one direction.
Solution: In the HFW straightening, the Turkish head is used to adjust the straightness. Correct adjustment of the deflection of the Turkish head reverse bending is the key to controlling the bending of the HFW steel pipe. For the bending caused by improper adjustment of the straightening frame, the operator should keep the Turkish head frame adjacent to the flying saw fixed, and adjust the other Turkish head in the opposite direction according to the bending direction.
2. The unevenness of the coil is not serious: the bending phenomenon of the steel pipe is serious, and the bending direction of the steel pipe is not one direction.
Solution: For bending due to uneven strength of the coil, it must be solved by the coiling mill by increasing its rolling level. The difference in strength between the coils should be controlled within 30 MPa.
3. The temperature of the upper and lower surfaces of the steel pipe is uneven: the seamless steel pipe in production is straight after cutting, but it is bent when cooling on the finishing stand, and the overall bending direction of the steel pipe is the same.
Solution: Renovate the water cooling device so that the amount of cooling water on the upper surface can be controlled to keep the temperature of the upper and lower surfaces of the steel pipe the same. For large diameter steel pipes, when the water cooling cooling water volume is maximized, the upper surface temperature is still higher than the lower surface, which can be appropriately reduced.
The speed of the production line, or the installation of the coolant water tower, accelerates the cooling of the coolant; the reverse adjustment method is adopted, that is, according to the direction and extent of the bending of the steel pipe on the finishing gantry, the reverse adjustment is made during the sizing straightening.
4. Insufficient sizing amount: The steel pipe is straight before the hydrostatic pressure test, but the bending phenomenon occurs after the hydrostatic pressure test, and the bending direction is fixed.
Solution: By appropriately increasing the sizing amount and reducing the excessive residual stress of the HFW steel pipe, the bending phenomenon can be avoided.
If the sizing amount is increased, the bending phenomenon is still not eliminated, and further adjustment of the forming hole shape is required. The sheet has an additional deformation amount to compensate for the rebound after deformation, reduce residual stress, and finally solve the bending problem of the steel tube.