In high temperature environments, specially designed valves need to be selected according to the specific temperature range. The following are the key points and adaptation solutions for high temperature valve selection:
1. Material selection according to temperature range
- Below 425℃
Carbon steel valves (WCB/WCC materials): suitable for steam, oil and gas pipelines, with a maximum temperature resistance of 425℃.
Seal optimization: PTFE seals are limited to ≤200℃ and need to be upgraded to PPL seals (such as Q41PPL ball valves) to support ≤350℃ working conditions.
- 425℃～600℃
Low alloy steel valves: Chromium-molybdenum steel materials (such as 1.25Cr-0.5Mo, 2.25Cr-1Mo) are preferred, with strong creep resistance and a temperature resistance upper limit of 600℃.
Typical models: WC6 (up to 550℃), WC9 (up to 570℃) gate valves/stop valves.
- 600℃～980℃
High temperature alloy valves:
Nickel-based alloys (such as Inconel series): resistant to 980℃, strong oxidation resistance, suitable for cracking furnaces and aerospace exhaust systems;
Cobalt-based alloys: excellent resistance to thermal fatigue, suitable for high-temperature flue gas containing particle erosion (such as metallurgical kilns).
2. Valve type and structural design
- Preferred type:
Stop valve: best thermal expansion compensation capability, reducing the risk of high temperature stagnation;
Gate valve: elastic gate structure (anti-thermal expansion and jamming) is required.
- Special sealing structure:
Metal hard seal: chromium carbide sprayed on the sealing surface (hardness ≥HRC60), resistant to 980℃ high temperature;
Elastic compensation design: valve stem extension + disc spring structure, absorbing thermal deformation stress.
- Prohibited type:
When the creep temperature of the bolt material is exceeded (usually ≥425℃), the wafer-type butterfly valve is prohibited.
3. Solutions for extreme working conditions
- Ultra-high temperature above 1000℃:
Ceramic valve: Double-disc ceramic valve is resistant to high temperature and high pressure + particle erosion, suitable for coal-fired power plants and chemical reactors;
Composite structure: Carbon steel shell + lining refractory concrete (such as high-temperature flue gas butterfly valve).
- Corrosive high-temperature medium:
Austenitic stainless steel (316L): acid resistant, suitable for sulfur-containing oil and gas below 600℃;
Lined valve: Non-metallic heat-resistant layer (such as ceramic lining) isolates corrosive media.
4. Selection considerations
- Welding connection is preferred: When the temperature is greater than 425℃ and the pressure is ≥PN100, the flange connection is prone to failure, and welding of the valve body is recommended.
- Bypass setting: High-temperature steam pipeline valves need to be equipped with bypass pipelines to avoid thermal shock damage.
- Testing requirements: High-temperature valves must pass the thermal cycle test (maximum operating temperature ±10%) and the 2,000 opening and closing life test.