High pressure regulating valve open failure, seriously affecting the safe and stable operation of unit. To the collapse of the inspection of the valve, found that high pressure regulating valve seat sinking 10 mm, lead to valve disc guide convex shoulder out of the groove, unable to steam which can adjust the normal. Temporary repair time is short, given the unit seat sinking site difficult to restore, decided to adopt welding processing, increase the height of the guide convex shoulder, the use of high voltage main steam adjusting valves to restore the original function. High pressure main steam valve repair method 1, the working mechanism of the valve disc guide convex shoulder unit 2 built for dongfang ( N300 - 16. 7/537/537 - 3) Steam turbine, its high pressure main steam control valve is made up of a main steam valve and of two regulator, high voltage regulator is used to adjust the volume of the admission of high pressure cylinder. Oil unit operation, motivation as a mechanical lifting device, the valve disc guide convex shoulder move up and down along the guide groove, control the opening of valve disc. Unit is running, the regulator of the high temperature steam is 16. 7 mpa, 537 ℃, guide convex shoulder major under thermal stress and circumferential shear stress function. 1 high pressure regulator valve disc and seat with a diameter of 170 mm, the valve disc structure as shown in figure 1, guide convex shoulder size is 55 mm x 30 mm x 10 mm ( High * width * thickness) 。 Using 20 cr3mowva alloy steel valve plate material, in order to improve the performance of the valve disc cavitation resistance, the surface of high temperature nitriding treatment. 2, the choice of welding material and welding equipment according to the regulator's working conditions, the valve disc guide convex shoulder to ensure the enough high temperature strength, and must meet certain abrasion resistance. In view of the unit repair, unable to purchase the best matching material, welding principle and material selection of references to the analysis of welding material mechanics performance, use TIG - similar to the base material R34( 12 cr2mowvtib,Φ2。 5毫米) Welding wire. Welding equipment using LincolnV300 - 1 and argon arc welding auxiliary tools; Use the MX2 infrared thermometer temperature monitoring. Welding performance analysis according to the carbon equivalent formula, 20 cr3mowva materials are the main characteristics of carbon and alloying elements is more, the weld during welding and heat treatment area prone to hardening organization, when welding pieces of rigid and joint stress is larger, easy to produce cold crack. After nitriding treatment of valve disc, its surface hardness up to HV900, easy to crack during welding.