After long-term operation, the sealing surface of a pressure reducing valve plug suffers wear from high-velocity media erosion and frequent impact, leading to internal leakage and unstable outlet pressure. Direct replacement is costly and has long lead times. Hardfacing with cemented carbide is an economical and reliable repair method.

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I. Assessing Valve Plug Wear

Common wear patterns include erosion grooves, pitting cavities, and sealing surface deformation. Conditions suitable for hardfacing repair are: no through cracks in the plug base metal, wear depth not exceeding one-third of the wall thickness, and no significant deformation of the overall shape.

II. Hardfacing Material Selection Pressure relief valve Suppliers

Commonly used hardfacing materials include stellite cobalt-based alloys and nickel-based alloys. Stellite No.6 has a hardness of HRC38-42, offers good impact resistance, and is suitable for steam service. Stellite No.12 has a hardness of HRC45-50 and provides better wear resistance. Nickel-based Ni60 has a hardness of HRC55-60, offers good corrosion resistance but is brittle, making it suitable for corrosive media with minimal impact.

III. Hardfacing Repair Procedure About Pressure relief valve

Pre-weld preparation: Clean the sealing surface with acetone, machine away the worn layer to expose fresh base metal, and create a hardfacing groove 2-3 mm deep. Preheat the plug to 300-400℃, holding for one hour per 25 mm of thickness.

Hardfacing process: Use oxy-acetylene flame welding or TIG welding. Flame welding is suitable for stellite powder, melted with a neutral flame. TIG welding requires 80-120 amps, short arc and fast passes, with each weld bead not exceeding 50 mm. Peen lightly after welding to relieve stress. Leave a 1.5 mm machining allowance on the hardfaced layer.

Post-weld treatment: Cool slowly in lime powder or in a furnace to room temperature. Do not quench. Machine to original dimensions, achieving a sealing surface roughness below Ra0.4. Lap with the valve seat and check for uniform contact.

IV. Post-Repair Inspection

Check hardfacing hardness, allowing a tolerance of plus or minus 5 HRC. Perform dye penetrant inspection to confirm no cracks or porosity. After assembly, conduct pressure tests and seat leakage tests according to applicable standards. Ensure proper alignment between plug and seat during installation.

V. Conclusion

Hardfacing a pressure reducing valve plug with stellite cemented carbide, with strict preheating, proper welding procedure, slow cooling, and lapping, yields a repaired plug life exceeding 80% of a new part at only 30-50% of replacement cost. This method is both economical and practical.

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