After the bent pipe is heat treated by a high-frequency induction heating machine, what are the mechanical properties of each part of it?

Bend pipes are an important part of paint delivery pipelines. In order to meet the needs of the work, we often use high-frequency annealing machines for quenching and tempering heat treatment. Today, the editor will not tell you about the induction heating quenching and tempering heat treatment process of elbows. I will tell you about the mechanical properties of each part of the elbows after induction heating quenching and tempering heat treatment.

(1) Strength properties of different parts of the induction heating elbow after heat treatment. The performance of the yield strength and tensile strength of different parts of the induction heating elbow fully meets the requirements specified by API spec 5L, and meets the requirements of Q/SY GJX 111-2009 "General Technical Conditions for Induction Heating Bends in Oil and Gas Transmission Pipelines". Among them, the strength level of the pipe body on the inner arc side is the lowest, while the strength level of the pipe body in the neutral zone and right transition zone is higher. The reason for this phenomenon is that the quenching and cooling rate of the tube body on the inner arc side is slower, and the metallographic structure contains more ferrite, so the strength is low and the plasticity is high. The quenching and cooling speed of the tube body in the neutral zone and the right transition zone is faster, the ferrite content is less, and the grains are fine, so it has higher strength.

(2) Toughness of different parts of the induction heating elbow after heat treatment. The impact toughness values of different parts are shown in Figure 10-9 above. Although the toughness value fluctuates widely, it fully complies with the standard requirements. Among them, the lowest transverse 4 impact toughness of the outer arc side pipe body is 130J, the highest transverse 3 impact toughness of the inner arc side pipe body is 425J, and the longitudinal 6 impact toughness of the right transition zone pipe body is 160J. The impact toughness value of the elbow is related to the size of the metal grains. The finer the grain structure, the higher the impact toughness value. The coarser the grains, the lower the impact toughness value. The grains in the weld zone are coarse and the grains in the heat affected zone are finer, so the impact toughness of the weld zone is lower than that of the heat affected zone. In addition, since the heating temperature of the outer arc side pipe body is higher than that of the inner arc side pipe body during bending, the austenite grains grow faster in the former, and the grain size obtained after quenching is relatively coarse, so its impact toughness value is higher than that of the inner arc side pipe. Side tube body is low.

To sum up, the strength and low-temperature toughness of the X80 grade, 1219mm diameter, 22mm wall thickness induction heated elbow pipe after induction heating quenching at 950-1000℃, water spray cooling, and 580-630℃ insulation for 60 minutes and tempering treatment have fully reached The relevant provisions of the Q/SY GJX 111-2009 standard have been clarified. The mechanical properties of different parts of the pipe body are basically stable. By further controlling the quenching heating temperature and cooling rate to maintain the stability of the structure and grain size, the metallurgical quality of the bent pipe will be further improved.