When bending, stop when the bending angle is greater than the required angle l °～ 2 °, return the pipe bending machine to the starting point, and measure the bending radius and angle with a sample plate. It should be noted that the outer diameter of the bent pipe must fit closely with the bending die, otherwise the pipe will be concave. When heating the simmer pipe with gas welding, first draw a straight section on the steel pipe, then draw the heating length L, first preheat the L section, and then start from the bending point, heating while bending, and the bending radius should be as consistent as possible to prevent wrinkles on the surface of the bending section. Since the angle is about 2 °～ 3 ° back after bending and cooling, the bending angle is slightly 2 °～ 3 ° larger than the preset bending angle. The heating length L can be calculated by a simple formula: L=π dR/180=0.0175dR.

Hot simmering method: when the hot simmering method is used for pipes with large diameter, the pipe shall be filled with compacted and fried sand before simmering, and the two ends shall be plugged tightly. After heating on the oven or coke fire, bend it on the mold.

The basic technological process of alloy forming technology is as follows: first, weld a polygonal polygonal ring shell or a polygonal sector shell with two ends blocked. After the internal pressure medium is filled, apply internal pressure. Under the internal pressure, the cross-section gradually changes from polygon to circle, and finally becomes a circular ring shell. The alloy elbow is mainly used as a connecting pipe fitting in pipeline installation, and is used for connection at pipe bends. Connect two pipes with the same nominal diameter to make a 90 degree turn.