|
Comparison Dimension |
Traditional Valves |
Low Emission Valves |
|
Leakage Rate |
Typically ≥1000 ppm (for gases) |
≤100 ppm (some can reach ≤10 ppm) |
|
Sealing Structure |
Single seal (e.g., packing gland) with poor initial stability, susceptible to temperature changes and impact |
Single seal (e.g., packing gland) with long-term extreme stability, unaffected by temperature changes and impact |
|
Testing Requirements |
Hydrostatic / Pneumatic tests |
Helium leak detection (leakage rate ≤1×10⁻⁷ Pa・m³/s) |
|
Cost |
Lower |
Slightly higher, but less than 1-2% more than traditional valves |
|
Applicable Media |
General industrial fluids |
High-risk, high-value, and high environmental protection requirement media |
Storage Performance Deficiencies of Traditional Valves
Traditional valves using ordinary graphite packing face dual storage risks.
1. Physical Adsorption Leading to Operational Failure
During long-term static storage, graphite molecules adhere to the valve stem surface due to van der Waals forces, forming a rigid adsorption layer. This increases the valve opening torque by 2-3 times compared to the initial value. In extreme cases, it may cause the actuator to overload and fail.
2. Chemical Corrosion Leading to Seal Degradation
Ordinary graphite packing typically has a sulfur content of ≥1200 ppm (by mass). In storage environments with humidity ≥60%, sulfur reacts with the metal valve stem through electrochemical corrosion, forming a FeS corrosion layer. This enlarges the seal interface gap, causing the leakage rate to increase exponentially over time, with an average annual leakage increase of 30%-50%.
Storage Performance Advantages of Low Emission Valves
Low Emission Valves achieve a breakthrough in storage stability through the following means:
1. Upgraded Material System
Sealing Packing: High-purity sulfur-free graphite (sulfur content ≤0.01%) with ≥99.5% purity is used. The interlayer bonding is enhanced through nano-scale flake orientation technology, blocking the migration path of sulfur elements.
Mid-flange Gasket: Modified flexible graphite composite material with 15%-20% nickel-based alloy reinforcement is used to form a corrosion-resistant skeletal structure.
2. Performance Verification Data
Traditional Valves: Opening torque increases from 80 N•m to 220 N•m, and leakage rate rises from 500 ppm to 2800 ppm.
Low Emission Valves: Opening torque fluctuation is ≤±5%, and leakage rate remains below 20 ppm, fully meeting the stringent long-term storage performance requirements of API 624.