Welding Heat Treatment Process for Alloy Steel Pipe
The welding of 15CrMo pipeline adopts argon arc welding and multi-layer multi-pass welding method. The argon itu welding is to use argon arc welding to weld the bottom of the weld, and then use arc welding to cover the weld. It has the characteristics of high welding quality, fast welding speed, high qualified rate of radiographic inspection, and easy for welders to master. In order to verify the correctness of pipeline welding process, welding process qualification tests are required, including welding method, welding process parameters, assembly sequence, preheating, post heating, post welding heat treatment, etc. After passing the test, prepare a welding process guide book or welding process card, with an accuracy of 426 mm × 22 mm, accurate to 377 mm × Welding process card for 19 mm pipeline
Immediately after welding, heat treatment is carried out to reduce the tendency of cold cracks and eliminate stress cracks, improve the internal structure of the weld seam, and improve the comprehensive mechanical properties of the welded joint. The heat treatment temperature is 700~750 ℃, and the rope or track type heater is controlled by the heat treatment equipment. The principle of the track type heater is shown in Figure 2. After heating to 300 ℃, it is heated at a speed of 3.5 ℃/min; Heat to 710 ℃ and maintain a constant temperature for 30 minutes; Cool at a rate of 4 ℃/min and cool freely to 300 ℃. The construction drawing of the tracked heater is shown in Figure 3. Thermocouples are uniformly distributed around the welding seam for temperature measurement, and an automatic recorder is used to record the heat treatment curve. The heat treatment control equipment is shown in Figure 4. On both sides of the weld seam, it should be no less than 6 times the width of the weld seam and no less than 25 mm. Outside the heating zone, it should be insulated with asbestos insulation felt, and the pipe ends should be closed. After the heat treatment of the weld bead, the Leeb hardness tester shall be used to test the hardness of the weld bead. Each weld bead shall be tested for 3 points, and each point shall be tested for 3 points. The positions are respectively the base metal, the Heat-affected zone and the weld bead. The hardness test shall be conducted according to the requirements of SY/T 0599 (NACE standard MR0175), and the hardness shall be ≤ HV250.
conclusion
According to the welding process and heat treatment in this article, on-site welding of 15CrMo pipeline was carried out, with beautiful weld formation and high weld quality. After appearance inspection, there are no surface defects such as pores, cracks, and bumps, and the qualification rate is 100%; X-ray non-destructive testing, its identification and classification are carried out according to Class II qualification, and the testing result is a one-time qualification rate of 98%. 15CrMo pipeline successfully welded on site