In the first phase of Qujing Power Plant, two domestic 30CMW coal-fired units were installed. The main steam pipeline was made of American imported steel A335P22 (technical standard ASTMA335) and specification Y534 private 83.1. This steel was first used in the Yunnan power system, with a large pipe diameter and an excessive wall thickness Thick wall. The main steam pipeline is an important monitoring pipeline for thermal power plants. The quality of its welding quality is related to the safe and economic operation of the power plant. Therefore, we must conduct welding process research on the basis of weldability analysis and testing, conduct welding process evaluation, solve relevant technical and process problems in engineering welding, formulate reasonable welding procedures, and determine better processes and parameters. As a technical guideline for engineering welding, to ensure the quality of engineering welding.
2 Welding process research 2.1.1 Chemical composition According to the material certificate provided by the supplier, its chemical composition is shown in Table 1. 2.1.2 Carbon equivalent according to the carbon equivalent formula recommended by the International Welding Society Ceq = C + steel has a larger value when welding Hardening tendency.
21.3 Welding stress The main steam pipe has a large pipe diameter, a thick pipe wall, and a large structural rigidity. It is easy to produce large constrained stress and three-dimensional residual stress during welding, and the stress state is complicated.
21.4 Due to the thick wall of the pipe and the deep groove of the diffused hydrogen, the cooling speed is fast during welding, the diffused hydrogen in the weld is not easy to escape, and the content of diffused hydrogen in the weld is high.
During 5X83.1 welding, under the effect of hardened structure, diffused hydrogen and welding stress, cold cracks are easy to occur.
2.2 Bevel form and size 22.1 The bevel form and size design principles are easy to operate, and it is easy to ensure the quality of the weld root and the remaining layers of the weld bead.
Minimize the amount of filler metal to reduce welding stress and welding deformation.
Must have good adaptability to engineering welding.
22.2 After the simulation operation, the bevel form and size are determined, see.
2.3 Welding process 23.1 Welding process procedures, see 23.2 Weld bead arrangement form Weld bead arrangement Multi-layer multi-pass welding is important for reducing welding line energy, reducing weld stress level, preventing bad metal structure, and controlling welding deformation. Moreover, when welding the subsequent weld bead, it has a tempering effect on the previous weld bead, which can improve the structure and performance of the weld metal. When multi-layer multi-pass welding, the following requirements should also be met: The thickness of the welding layer of 0 argon arc welding is not less than 3mm. The main purpose is to ensure the basic strength of the weld and prevent cracking.
When welding the sub-layer welding pass, the bottom layer will not be burned through. According to the experience of large unit construction, the minimum thickness of the bottom layer of argon arc welding is specified as the thickness of the single layer of the other weld bead is not greater than the diameter of the used electrode 2mm. The swing width of the single bead is not greater than 5 times the diameter of the used electrode.
23.3 Welding materials: Welding electrode selection E6015B3 23.4 welding process parameters, see Table 2, Table 3. 23.5 preheating, tracking preheating can reduce the cooling rate and the temperature difference in the welding zone, thereby reducing the hardening structure and reducing welding stress. At the same time, it also facilitates the escape of diffused hydrogen in the weld. Prevent cold cracks.
The temperature is 250 ~ 350 using far infrared electric heating method. The temperature control uses DWK 23.6 post-heating (ie dehydrogenation treatment) to eliminate the diffusible hydrogen in the weld. Prevent cold cracks.
Electric heating method. DWK-A-180 computer temperature controller for temperature control. The post-heating should be carried out to 15 ~ 20mm after welding is stopped.
23.7 Post-weld heat treatment table 2 Vertical fixed position (2G) Welding process parameters Welding methods Welding materials and specifications Welding current (A) Polar arc voltage (V) Welding speed Argon gas flow forward and reverse connection Table 3 Horizontal fixed position (5G) welding Process parameters Welding method Welding materials and specifications Welding current (A) Polar arc voltage (V) Welding speed Argon gas flow forward and reverse connection can reduce the residual stress of the welded joint, improve the welding seam gold electric heating method, temperature control DWK-A Organization and performance. instrument.
Heating to 720 ~ 750 * C, constant temperature 4h. Use far infrared 23.8 preheating, tracking preheating, postheating, post-weld heat treatment process curve, see.
Preheating, tracking preheating, postheating, post-weld heat treatment process curve preheating, tracking preheating, postheating, post-weld heat treatment process curve () Description: AB: first preheating to 150 * Q heating rate is 75 * C / h manual tungsten argon arc welding (TIG) primer, tracking preheating during welding.
75 * C / h, the first manual arc welding (SMAW) filling welding, tracking preheating during the welding process.
75 * C / h, the second SMAW filling welding, until the complete welding seam is welded, and the preheating is followed during the welding process.
The cooling rate is 75 * C / h. During the cooling process, the temperature below 300 * C does not control the cooling rate.
23.9 Non-destructive inspection adopts a comprehensive inspection method combining intermediate radiographic inspection (RT) and final ultrasonic inspection (CUT).
24 Welding process qualification 241 Welding process qualification was carried out on the vertical fixed position (2G) and horizontal fixed position (5G) of A335P22 and Y534.5X83.1 pipelines according to the groove form, size, process and parameters determined above. The test piece is alternately welded by four welders in two or two turns, and the welding is performed in the preheated state, and the conditions are very difficult.
24.2 After the inspection and test welding of the process qualification test piece, non-destructive inspection, tensile, lateral bending, impact test, macroscopic metallography, microscopic metallography and hardness test are all passed.
3 Conclusion The weldability of 83.1 is analyzed, a method to prevent cold cracks is proposed, the welding process and parameters are determined, the welding process evaluation is carried out, the test piece is inspected and tested, and all the indicators meet the requirements of the standard.
3.2 The process and parameters provided by the welding procedure evaluation have been applied to the welding of the 2X300MW main steam pipeline of the first phase project of Qujing Power Plant. A total of 39 welded joints have been welded. After inspection, the primary pass rate is 100% and the welding quality is excellent.
3.3 The welding procedure of the main steam pipeline is complicated and the process requirements are high. It is required to strictly implement the procedures and processes to ensure the welding quality.
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