How does seamless carbon steel pipe undergo thermal expansion?

Posted by zora li on February 10th, 2023

How does seamless carbon steel pipe undergo thermal expansion?

Thermal expansion is a processing method of carbon steel pipe, which is to process small-diameter carbon steel pipe into large-diameter carbon steel pipe. The mechanical properties of hot-expanded carbon steel pipes are slightly worse than those of hot-rolled carbon steel pipes.

The two-step push-type pipe expander for thermal expansion steel pipe integrates cone die pipe expansion technology, digital intermediate frequency induction heating technology and hydraulic technology in one machine. It has the characteristics of reasonable technology, low energy consumption, low construction investment, good product quality, wide application range of raw materials and product specifications, and flexible adaptability of low-input production batches. In some respects, it replaces the traditional pull expanding technique in the steel pipe industry.

Advantages of heat expandable carbon steel pipe
It can destroy the forging mechanism of the steel pipe, refine the grains of the heat-expanded steel pipe, eliminate structural defects, make the structure of the heat-expanded steel pipe dense, and improve the mechanical properties. This improvement is mainly manifested in the rolling direction, so that the thermally expanded steel pipe is no longer isotropic to a certain extent. Bubbles, cracks, looseness, etc. generated during pouring can also be welded under high temperature and high pressure.

Disadvantages of thermally expandable carbon steel pipe
1. After thermal expansion, the non-metallic inclusions (mainly sulfides, oxides, and silicates) in the thermal expansion steel pipe are compressed into thin sheets and appear in a layered (interlayer) state. Delamination greatly deteriorates the tensile properties of thermally expanded steel pipes along the thickness direction, and may cause interlayer tearing when the weld shrinks. The local strain caused by the shrinkage of the weld often reaches many times the strain at the yield point, which is much larger than the strain caused by the load.
2. Residual stress caused by uneven cooling. Residual stress is the internal self-balancing stress without external force. This residual stress exists in thermally expanded steel pipes of various cross-sections. In general, the larger the section size of the steel section, the greater the residual stress. Although the residual stress is self-balancing, it still interferes with the performance of steel components under the action of external forces. For example, it will cause adverse effects in terms of deformation and impact resistance.