Seamless pipe size problem

The problem of the size of the seamless pipe is mainly manifested in the bending in the longitudinal direction (axial direction) and the ellipticity and outer diameter of the cross-sectional direction (radial).

1. The reason why the seamless pipe is bent
a. Seamless heating of the seamless pipe produces bending
The seamless steel tubes are unevenly heated, and the temperatures along the axial direction of the seamless steel tubes are different. The microstructure transition time is different during quenching, and the volume of the seamless steel tubes varies with time, resulting in bending.

b. Seamless steel tube quenching produces bending
Quenching is the preferred heat treatment method for the production of high-strength seamless pipe casings and high-grade seamless pipe. The microstructure changes very rapidly during quenching, and the structural transformation of the seamless steel tube brings about a change in volume. Since the cooling speed of each part of the seamless pipe is inconsistent, the speed of the tissue transformation is inconsistent, and bending also occurs.

c. Tube blank causes bending
If the chemical composition of the seamless pipe is segregated, even if the cooling conditions are completely the same, bending will occur during cooling.

d. Uneven cooling causes bending
After the heat treatment of the alloy seamless pipe, the seamless pipe is usually cooled by the side of the rotary side. At this time, the axial and circumferential cooling speeds of the seamless pipe are uneven, and bending occurs. If the bending of the seamless pipe does not meet the requirements, it will affect the subsequent processing (such as transportation, straightening, etc.) and even affect its performance.

f. Bending on the sizing machine
Alloy steel pipes, especially seamless pipe with narrow outer diameter tolerance range (such as line pipe and casing), generally require sizing after tempering. If the centerline of the sizing rack is inconsistent, the seamless pipe will bend.

2. The main reason for the ellipticity and outer diameter of seamless steel tubes
When quenching, the structural transformation of the seamless pipe is inconsistent, the seamless pipe will produce ellipticity; due to the ellipticity, most of the seamless pipe needs to be sized after quenching and tempering, if the sizing control process is not good The outer diameter will be out of tolerance.