The thermal expansion seamless pipe is a steel pipe produced by the thermal expansion process, which is a waste pipe finishing process of diameter expansion. The thermally expanded steel pipes usually mentioned are seamless steel pipes. There are many classification methods for thermal expansion steel pipes. According to the purpose, it can be divided into heat-expanded steel pipes for high-temperature equipment, heat-expanded steel pipes for low-temperature, heat-expanded steel pipes for pressure facilities, heat-expanded steel pipes for pipelines, heat-expanded steel pipes for gas cylinders, heat-expanded steel pipes for structures, and fluid transportation. Thermally expanded steel pipes and mechanical roller thermally expanded steel pipes, etc. According to the steel pipe material, it can be divided into carbon steel thermal expansion tube, low alloy thermal expansion tube, high alloy thermal expansion tube, stainless steel thermal expansion tube and titanium alloy steel thermal expansion tube. Divided into cross-rolled heat-expanded steel pipes, drawn heat-expanded steel pipes, push-type heat-expanded steel pipes, etc.
Thermally expanded steel pipes are widely used and adaptable. In addition to being widely used in petroleum, water vapor and medium and low pressure flammable or non-flammable fluid pipelines, it is also widely used in petroleum, natural gas and chemical industries. It is also used in power industry such as high and low temperature pressure vessels. Pipes and pipes for urban construction and other structures.
Since thermal expansion steel pipes are seamless steel pipes obtained by thermally expanding small and medium diameters into large diameters through thermal expansion technology, the general characteristics of thermal expansion steel pipes are large diameters and thin walls. The thermal expansion steel pipe process originated from the secondary piercing. The traditional heat-expanded steel pipe production processes mainly include cross-rolling heat-expanding process, drawing-type heat-expanding process and push-type heat-expanding process.
Cross-rolling thermal expansion process
1. The cross-rolling thermal expansion process is to send the rolled piece heated to an appropriate temperature into the rolling mill in a spiral rotation, and roll the diameter of the thermal expansion process steel pipe between the roll and the plug.
①The torsional deformation and elongation coefficient are small, the energy consumption is small, the angular velocity of the pipe is constant, and the torsional and shear stress are minimal. The cross-sectional area and length of the rolled piece remain basically unchanged before and after diameter expansion, and the elongation is close to 1.
②Propelling speed is slow. Due to the large angle of the skew rolling mill, the large silver rolling angle and the small bite angle, the lateral flow speed of the metal is high, the longitudinal flow speed is small, and the forward speed of the pipe is slowed down. Sometimes it is possible to better ensure the stability of expansion and the accuracy of joint thickness by reducing the forward speed of expansion;
③The pipe expansion quality is stable, and the mandrel is positioned by a hydraulic small cabin, which can compensate the length and dimension changes of the rolling mill caused by the displacement of the head during the rolling process. In addition, the cross-rolling thermal expansion process can also improve the dimensional accuracy of the main pipe, especially the uneven thickness of the main pipe joint, which will not adversely affect the surface quality;
④The production investment is large, and the production equipment of the cross-rolling thermal expansion process is huge, the investment is high, and the production cost is also high. The most suitable pipe diameter range for cross rolling thermal expansion process is 425-762mm.
The cross-rolling and thermal expansion process is considered to be one of the best processes for thermally producing large-diameter and medium-thin-wall seamless steel pipes
Stretch thermal expansion process
The cable-stayed thermal expansion process first expands a bell mouth at the end of the waste pipe, and the diameter of the expanded surface is about 100mm larger than the diameter after thermal expansion. This is beneficial for the internal and external snap rings to clamp the pipe end during thermal expansion and carry out water cooling, and then pull the mandrel with a chain to drive the plug to pass through the waste pipe to realize the deformation process of expanding diameter, shrinking wall and reducing diameter. Shorten the length.