Quick answer: in power service the working temperature usually decides the material. Carbon steel covers steam and condensate up to its limit; above that, alloy steels with better elevated temperature strength take over. Trim hardness is the second decision, because steam erodes seats and discs.
Recommended valve matrix
| System | Valve type | Notes |
|---|---|---|
| Main steam and hot reheat | Gate valve, globe valve | Material and trim must suit continuous high temperature |
| Feedwater and boiler | Gate valve, globe valve, check valve | Check closure behaviour matters for pump protection |
| Condensate | Gate valve, globe valve | Carbon steel is usually sufficient |
| Cooling water | Butterfly valve, gate valve | Corrosion and coating decide the material |
| Auxiliary and drain lines | Globe valve, ball valve | Small sizes, frequent operation |
Temperature is the first decision
- Carbon steel has an upper working limit, above which alloy steel grades are required
- Below the low temperature limit, carbon steel becomes brittle and austenitic stainless steel is used instead
- Thermal cycling affects gasket and packing life as much as the body material
- Welded bonnets are chosen where leakage paths must be minimised
Testing and documentation
- Shell and seat leakage tests before shipment
- Material certificates traceable to heat number
- Non-destructive examination where specified by the project
- Third-party inspection on request
待补内容位：待补：可做的合金钢材质等级（WC6 / WC9 / C12A 等以实际为准）、主蒸汽参数上限、电站项目案例。