Self-Sealing Rings in High-Temperature, High-Pressure Plug Valves: Function, Installation, and Failure Analysis

Installation and Maintenance Essentials for Plug Valve Self-Sealing Rings

I. Pre-Installation Preparation:

1. Clean Sealing Surfaces: Ensure that the sealing surfaces of the valve seat and valve core are free of scratches, rust, and oil stains. Grinding and polishing should be performed if necessary, and the surface roughness must comply with design requirements (typically Ra≤1.6μm).
2. Inspect Sealing Ring: Verify that the material and dimensions match the plug valve model. Check the sealing ring for defects such as cracks, deformation, or aging. For metal sealing rings, confirm that the surface is free of burrs.

II. Installation Requirements:

3. Avoid Forced Assembly: Gently place the sealing ring during installation to prevent deformation due to misalignment or collision. Metal sealing rings must be concentric with the sealing surface.
4. Control Pre-tightening Force: Based on the sealing ring material and operating conditions, uniformly tighten the bolts according to the design torque. Avoid over-tightening, which can cause plastic deformation and failure of the sealing ring, or under-tightening, which can lead to poor initial sealing.

III. Maintenance and Replacement:

5. Regular Inspection: During plug valve overhauls, inspect the sealing ring for wear, corrosion, and creep. If signs of steam erosion (such as scouring marks, scaling, or discoloration) or leakage are found on the sealing surface, the ring must be replaced immediately.
6. Replacement Cycle: Affected by high temperature and high-pressure conditions, the service life of the sealing ring is usually synchronized with the plug valve overhaul cycle (e.g., 1-3 years). Under extreme conditions, the replacement cycle must be shortened to prevent leakage caused by aging failure.

Common Failure Causes and Countermeasures

Self-sealing ring failure can lead to high-temperature, high-pressure steam leakage, causing equipment damage, energy waste, and even safety incidents. Common failure causes and countermeasures are:

• Material Aging: Material performance degradation (e.g., graphite embrittlement, metal creep) under long-term high temperatures.
  • Countermeasure: Select high-temperature resistant materials that match the operating conditions, and regularly test material performance.
• Sealing Surface Damage: Scratches or deformation on the sealing surface lead to poor fit.
  • Countermeasure: Strictly check the precision of the sealing surface before installation; repair or replace the valve seat/valve core if necessary.
• Improper Pre-tightening Force: Too loose leads to initial sealing failure; too tight causes sealing ring damage.
  • Countermeasure: Control the pre-tightening torque according to specifications, and use a symmetrical tightening method.

The plug valve self-sealing ring is the "last line of defense" for the safe operation of high-temperature and high-pressure steam systems. Its material selection, structural design, and installation and maintenance must strictly match the operating conditions to ensure the reliable sealing of the plug valve.