I. Common Failure Modes and Root Causes
1. Sealing Leakage
Symptom: The safety valve outlet continuously leaks under normal pressure. Root cause:
Seal surface damage: Impurities (such as rust, welding slag) get embedded in the seal surface, or the valve core and valve seat collide and wear (Figure 1).
Seal surface deformation: High temperature causes uneven thermal expansion of the seal surface (for example, cast iron valve bodies tend to deform at temperatures above 200°C).
Spring relaxation: Long-term force application leads to a decrease in elastic modulus and insufficient pre-tightening force (for every 5% decrease in spring stiffness, the leakage increases by 30%).
2. Failure to open or deviation in opening pressure
Symptoms: The safety valve does not act when the system is overpressurized, or the opening pressure deviates by more than ±3% from the set pressure. Root cause:
Spring failure:
Poor material quality (for example, ordinary carbon steel springs tend to rust in humid environments).
High-temperature creep (the spring works continuously at > 200℃, and its stiffness decreases by approximately 10% each year).
Valve core jamming:
Internal parts rust (such as if condensate water is not regularly drained, the valve stem gets rusty).
Foreign matter blockage (such as sealing glue fragments entering the valve interior).
Adjustment mechanism loosening: The adjusting nut is not tightened, and during operation, the set pressure changes due to vibration.
3. Frequency jumping or tremor
Symptom: The safety valve frequently opens and closes during the discharge process, emitting abnormal sounds. Root cause:
Excessive back pressure in discharge: The resistance of the discharge pipe is too high (such as a too small pipe diameter or too many elbows), and the back pressure exceeds the allowable value (generally ≤ 10% of the opening pressure).
Inappropriate flow channel design: The throat diameter of the valve does not match the inlet and outlet pipe diameters, resulting in unstable flow of the fluid.
Incorrect position of the regulating ring: The upper regulating ring is positioned too low, causing the valve to be unable to be fully opened stably.
4. Spring fracture
Symptom: The safety valve suddenly loses its pressure control capability. Root cause:
Fatigue fracture: Frequent start-stop operations cause the spring to bear alternating stress (for example, if the start-stop operation exceeds 5 times per day, the lifespan is shortened by 50%).
Material defect: The spring material contains impurities (such as excessive sulfur content), resulting in stress concentration.
Corrosion embrittlement: Acidic environment (such as compressed air containing SO₂) makes the spring material brittle.
5. Insufficient discharge capacity
Symptom: When the system is overpressurized, the safety valve is unable to quickly release the pressure, and the pressure continues to rise. Root cause:
Selection error: The throat diameter is too small, and the emission coefficient does not take into account the actual working conditions (for example, the presence of moisture in the gas will reduce the emission coefficient).
Emission pipe blockage: Accumulated carbon or ice formation inside (in cold regions without insulation) leads to a reduction in the flow area.
