Considerations when sizing of relief valves for boiler system
- 2 or more safety relief valves should be provided on boiler/s with heating surface greater than 50 m2 (500 ft2); otherwise comply with local regulation or adhered to international guideline/standard whichever more stringent.
- Safety relief valves should be sized to operate up to >6% of the maximum allowable working pressure for high pressure boiler.
- Isolation valve should not be installed on the relief valves.
Example: Maximum working pressure of the boiler system with heating surface of 60 m2 is 120 barg.
Safety relief valve to operate would be 120 barg + (6% x 120) barg = 127barg.
The second safety relief valve to operate should be set at the maximum working pressure of 120 barg.
Boiler system integrated super heaters
- Safety relief valves for the boiler should be designed to provide relieving capacity of up to 75% of the relieving capacity (in kg/hr) of the boiler system.
- Safety relief valves for the super heaters should be designed to provide relieving capacity of up to 25% of the relieving capacity (in kg/hr) of the boiler system.
Independently fired super heaters
The relieving capacity for the safety valves should be based on 2.7 Kg/0.1m2 of heating surface.
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