The thermal expansion seamless steel pipe adopts the expansion technology of the original pipe. The expansion is a pressure processing process that uses hydraulic or mechanical means to force the steel pipe to expand outward along the radial direction. The mechanical method is simpler than the hydraulic method, and the equipment is simpler and more efficient. The most advanced large-diameter seamless steel pipe pipeline expansion process in the world is adopted.
The process is: mechanical expansion and expansion using the end of the expansion machine The fan-shaped block of the valve is radially expanded, so that the tube blank is stepwisely formed in a stepwise manner to realize the process of plastic deformation of the entire pipe length, thereby producing a thermally expanded seamless steel pipe. It is divided into 5 phases:
1. Initial rounding stage. The fan-shaped block is opened until all the fan-shaped blocks are in contact with the inner wall of the steel pipe. At this time, the radius of each point in the inner pipe of the steel pipe is almost the same in the step length, and the steel pipe is initially rounded.
2. Nominal inner diameter stage. The segment reduces the speed of movement from the front position until it reaches the desired position, which is the desired inner circumference of the finished tube.
3. The rebound compensation stage. The fan-shaped block begins to move at a lower speed in the 2-stage position until it reaches the required position, which is the inner circumferential position of the steel pipe before the rebound of the process design.
4. The pressure stabilization phase. The fan-shaped block remains in the inner circumferential position of the steel pipe for a certain period of time before the rebound, which is the pressure-stabilizing stage required by the equipment and the expansion process.
5. Unloading return phase. The segment is rapidly retracted from the inner circumferential position of the steel pipe before the rebound until it reaches the position of the initial expansion, which is the minimum contraction diameter of the segment required by the expansion process.
In practical applications, in the process simplification, the steps 2 and 3 can be combined and simplified, which has no effect on the diameter expansion of the steel pipe.
In order to improve the corrosion resistance of seamless steel pipes, general steel pipes are galvanized. Galvanized seamless steel pipe is divided into two types: hot-dip galvanizing and cold-galvanizing (electro-galvanizing). The hot-dip galvanized seamless pipe has a thick galvanized layer and has the advantages of uniform plating, strong adhesion and long service life.
Galvanized steel pipe is a method of electroplating. The amount of galvanizing is very small, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipe. Regular hot-dip galvanized seamless steel pipe manufacturers, in order to ensure quality, most do not use electro-galvanizing (cold plating).
The hot-dip galvanized seamless steel pipe is first pickled with a seamless steel pipe in order to remove iron oxide on the surface of the steel pipe, and after pickling, it is carried out by using an ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride. Wash and then feed into the hot dip bath. Hot-dip galvanized seamless steel pipes have many advantages, so most of them are hot-dip galvanized seamless steel pipes.
Now the gas, heating and air conditioning in the building are all hot-dip galvanized seamless steel pipes. Hot-dip galvanized seamless steel pipes are used as water pipes. After several years of use, a large amount of rust is generated in the pipes. The yellow water flowing out not only pollutes the sanitary ware, but also contains impurities. Bacteria that grow on the inner wall of the slick, the rust causes the heavy metal content in the water to be too high, which seriously endangers the health of the human body.
