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


1. Causes of Seamless Tube Bending
One. Seamless heating of seamless tubes produces bending
Seamless steel tube is not uniformly heated, and the temperature along the axis of seamless steel tube is different. The volume of seamless steel tube changes with time, which results in bending.


Bending of Bay Seamless Steel Tube after Quenching
Quenching is the preferred heat treatment method for producing high strength seamless pipe casing and high-grade seamless pipe. The microstructure changes rapidly during quenching, and the volume of seamless steel tube changes due to the structural transformation. Because the cooling rate of each part of the seamless tube is not uniform, the transformation speed of the structure is not uniform, and bending occurs.


C. Tube blank will cause bending
If the chemical composition of the seamless tube is isolated, even if the cooling conditions are exactly the same, bending will occur during the cooling process.


D. Non-uniform cooling results in bending
After heat treatment of alloy seamless tubes, seamless tubes are usually cooled on the rotating side. At this time, the axial and circumferential cooling rates of seamless tubes are not uniform, and bending occurs. If the bending of seamless pipe does not meet the requirements, it will affect the subsequent processing (such as transportation, straightening, etc.) and even affect its performance.


F. Bend on sizing machine
Alloy steel pipes, especially seamless pipes with narrow tolerances (such as pipelines and sleeves), usually require sizing after tempering. If the center line of the dimension adjusting frame is inconsistent, the seamless pipe will bend.


2. Main Causes of Ellipticity and Outer Diameter of Seamless Steel Tubes
During quenching, the structural transformation of seamless tubes is inconsistent, and the ellipticity of seamless tubes will occur. Because of ellipticity, if the size control process is not good, most seamless tubes need to be adjusted after quenching and tempering. The outer diameter will exceed the tolerance range.