High-pressure regulating valve repair welding performance analysis and program

Zhanjiang Power Plant on the 2nd of the 1st high-pressure steam turbine control valve to open failure, serious impact on safe and stable operation of generating units. To the disintegration of the check valve and found that high-pressure valve seat sinking speed 10mm, resulting in valve disc from the direction-oriented groove convex shoulder, unable to conduct the normal adjustment process steam. Given the short time than the Pro unit, valve seats, it is very difficult to restore the sinking scene, decided to adopt the surfacing treatment, increase the height of the shoulder convex oriented to the restoration of high-pressure main steam valve of the use of the original function.



1 high-pressure main steam control valve repair program



Convex disc valve 1.1-oriented work of the mechanism of the shoulder for the 2nd unit of the Dongfang Steam Turbine Plant (N300-16.7/537/537-3 type) steam turbine, and its high-pressure main steam control valve is a main steam valve and control valve 2 composed of high-pressure regulating valve for regulating high-pressure steam into the cylinder volume. Run-time unit, the oil motive for mechanical lifting equipment so that valve disc guide groove convex shoulders moved up and down along the direction, control valve opening disc. Unit run-time, high temperature steam valve to 16.7MPa, 537 ℃, the main subject-oriented convex shoulder a certain degree of thermal stress and shear stress to the role of weeks. 1 high-pressure regulating valve and the valve seat disc with a diameter of 170mm, the structure of the valve plate as shown in Figure 1, oriented convex shoulder the size of 55mm × 30mm × 10mm (width × high × thick). 20Cr3MoWVA valve alloy steel plate material used, in order to increase the cavitation resistance valve disc performance, its surface has been dealing with high-temperature nitriding.



1.2 surfacing materials and the choice of welding equipment in accordance with the working conditions of valve, valve guide disc convex shoulder to make sure that there is sufficient high temperature strength, but also a certain degree of wear resistance to meet. Given the repair crew can not be the best match to the material procurement, in the light of the principle of selection of welding materials and welding on the mechanical properties of materials analysis, materials selection and materials similar to TIG-R34 (12Cr2MoWVTIB, Φ2.5mm) wire. The use of welding equipment LincolnV300-1 and argon welding matching tools; temperature monitoring the use of the United States MX2 infrared thermometer.



2 Performance Analysis of Welding



Carbon equivalent calculated in accordance with, the main characteristics of the material 20Cr3MoWVA is more carbon and alloying elements, welding and heat treatment weld area prone to hardening body weldment joint stiffness and greater stress, it is easy to have a cold crack. After nitriding the valve plate to deal with, the surface hardness up to HV900, welding cracks easily.



3 Welding Technology



3.1 polished before welding process line cleaning - Preheating - surfacing - PWHT - turning after welding.



3.2 First of all pre-welded to the wheel with angle polished thoroughly to remove clean-up 20mm surfacing within the scope of the site nitriding layer, grinding depth should be larger than 0.4mm, measuring the hardness of the value of grinding parts and welding facilities to ensure that the regional reach of the HB185 ~ 321 requirements. According to JB4730-94 testing standards, inspection after grinding surface quality-oriented convex shoulder may not have cracks, defects such as slag, reaching the standard for qualified class Ⅰ. Valve and then use acetone to clean the site and the surrounding plate welding range of 50mm to ensure that water, oil, etc.; welding wire with sandpaper to remove surface dirt, such as oil and锈斑.



3.3 Welding procedure and parameters used oxyacetylene flame heating method of preheating before welding, preheating temperature of 350 ~ 400 ℃, preheating temperature measurement with thermometer. Exposed parts of valve plate welding, other parts of the cotton fabric coated with stone to avoid arc burn. Process parameters I = 80 ~ 90A, argon gas flow of 8 ~ 10L/min, DC was next, voltage range 10 ~ 15V, welding speed 30 ~ 45mm/min, each swing width ≤ 10mm, the thickness of each surfacing ≤ 4mm. After pre-heating temperature welding, temperature control between layers in the 300 ~ 400 ℃, the welding process does not allow any defects, the focus of inspection cited close arc, the defects found in the immediate removal with angle grinder. To ensure the allowance, according to Figure surfacing size, increase in outside diameter 5mm, diameter reduction of 5mm, piled high 13mm. After the completion of surfacing surfacing side the other side. Welding is completed, with aluminum-coated fire-resistant cotton relieve cold, cold welding position to 100 ~ 150 ℃, an immediate partial heat treatment after welding. Heat treatment using flame heated to 640 ~ 660 ℃, thermal insulation 30min, with thermometer monitoring, heating rate and cooling rate were <300 ℃ / h, cooling to below 300 ℃ not control, cooling blanket coated with aluminum silicate fibers ease cold.



4 weld inspection



Completed in accordance with the process line valve disc after welding and machining, with penetration testing and ultrasonic testing inspection, there is no weld cracks, slag, porosity and other defects in the quality of welding quality standard JB4730-94 the requirements of Grade Ⅰ; in the processing surface hardness test, the average hardness value of HB241, the original parent material of similar hardness values, the use of performance to meet the workpiece.



5 Conclusion



2 units on the 1st high-pressure main steam valve repair welding and running nearly 1 years later, when the disintegration of the unit overhaul inspection, welding of the valve disc convex shoulder operation after 5616h not found any problems. TIG-R34 can be seen with wire TIG welding using preheating 20Cr3MoWVA material 350 ~ 400 ℃, after welding 640 ~ 650 ℃, heat welding technology 30min handled it is reasonable and feasible. It has not only solved the high-pressure main steam to the steam control valve to regulate the normal, but also saves money on the yuan.

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