How to control the ovality of austenitic stainless steel pipes

Austenitic stainless steel pipes are widely used in industries such as chemical, petrochemical, pharmaceutical, and food processing. Their dimensional accuracy directly impacts the sealing, installation accuracy, and long-term performance of piping systems. Ovality is a key indicator of pipe cross-sectional roundness deviation. Improper ovality control can lead to welding difficulties, leaks in pipe connections, and premature equipment failure. Therefore, scientific and systematic control of the ovality of austenitic stainless steel pipes is a critical step in production and application.

The Impact of Raw Material Selection on Ovality

The production of high-quality austenitic stainless steel pipes begins with the raw materials. The chemical composition uniformity and microstructural stability of the billet directly impact the pipe's formability. Selecting low-carbon, homogeneous austenitic stainless steel billets can reduce cross-sectional deformation caused by grain inhomogeneity during hot working. Strictly controlling the tolerance range of billet dimensions ensures uniform stress distribution during drawing or rolling, thereby reducing ovality deviation at the source.

Hot Working Process Control of Ovality

Hot working is the core stage of austenitic stainless steel pipe forming. Hot rolling temperature and rolling speed directly affect the pipe's elastic recovery and cross-sectional roundness. High-temperature, uniform heating reduces internal stress concentration in the material and prevents elliptical deformation caused by uneven cooling. During multi-pass rolling, the reduction in each pass must be precisely controlled to avoid localized excessive deformation. Using online dimensional measurement equipment to monitor pipe diameter changes in real time allows for timely adjustment of rolling parameters and dynamic control of ellipticity.

Cold Working and Sizing Technology

Cold working is crucial for improving the surface quality and dimensional accuracy of austenitic stainless steel pipes. The sizing mill is the core equipment for controlling pipe ellipticity. The sizing roll set should be designed to ensure uniform force distribution, with precise calculation of the roll gap spacing and pressure distribution. During the sizing process, the pipe passes through multiple sets of precision rollers, gradually correcting its cross-sectional shape and minimizing ellipticity deviation. After cold working, a straightening mill can further eliminate internal stresses and improve roundness stability.

Precautions for Welding and Joining Processes

Welding can induce localized thermal stresses in austenitic stainless steel pipes, which can affect ellipticity. When using TIG or MIG welding, the heat input and welding speed should be strictly controlled. Segmented welding and uniform heating can minimize localized expansion in the weld area and prevent pipe cross-sectional deformation. For high-precision piping systems, mechanical correction can be performed after welding to ensure that the weld area meets the required roundness.

Online Inspection and Quality Control

In modern production, online inspection technology is a key means of controlling ovality. Laser diameter gauges and optical scanners can measure pipe cross-sectional deviations in real time and automatically generate ovality curves. Feedback control systems allow for real-time adjustment of production parameters, reducing manual intervention and improving production consistency. Quality control not only includes production process monitoring but also incorporates factory inspections, such as ultrasonic or three-dimensional coordinate measurement, to ensure that pipe ovality meets standard requirements.

Stress Relief and Post-Processing Technologies

Stress relief is essential for stabilizing the ovality of austenitic stainless steel pipes. Residual stresses in pipes after cold working or welding can easily cause deformation if directly used. Annealing or vibration stress relief treatments can effectively reduce internal stresses and ensure the pipe's roundness stability during use. These treatments are particularly suitable for high-precision piping systems, such as pharmaceutical equipment and high-pressure pipelines.