I have a question regarding the setting pressure of a boiler safety valve: what exactly is the operating pressure?
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I have a newly installed gas steam boiler here, with a rated pressure of 1.25 MPa; however, we actually use only 0.4 MPa, and 0.6 MPa is also possible. So, what should be the setting pressure for the safety valve on this boiler? At 0.4 MPa? So what if you want to heat it to a higher temperature?
It should be determined based on your actual usage needs; it should be 1.05–1.15 times higher than the actual working pressure, without exceeding the design pressure.
The function of a safety valve is to provide ultimate protection; in my opinion, it is best to set it at 1.25 MPa. For overpressure protection in boilers, research suggests setting it at 0.6 MPa – once the pressure exceeds this level, the boiler will automatically shut down.
It is recommended to use the system security pressure as the set value for the safety valve. The boiler only represents the pressure-bearing capacity of the vessel itself; it does not represent the pressure of the gas supply and delivery system.
Table 6-3 of the Boiler Regulations provides clear specifications: the setting pressure for the safety valve of your boiler should be 1.04 times the operating pressure, or 1.06 times that pressure. The operating pressure refers to the pressure at the location where the safety valve is installed; in the case of your boiler, this is the pressure inside the boiler drum. You can calculate this by taking 0.6 Mpa as the base value and multiplying it by 1.04 and 1.06.
There are many different opinions; it seems this issue is quite controversial.
It is recommended to follow the certificates and regulations issued by the boiler factory, as well as the information registered with the local boiler inspection agency. Additionally, safety requirements and process requirements are not contradictory; do not mix them up. Safety is a guarantee, and the process is adjustable.
If the adjustment is to be made based on the actual operating pressure used by the user, then a problem arises: if I am a boiler manufacturer, I don’t know what the actual operating pressure is for each user. And since valve and instrument diagrams are required for the approval process of boilers, how then can I determine the set pressure for the safety valves specified in my diagrams? And what should be used as a reference for purchasing safety valves to supply to users? In the drawings submitted by boiler manufacturers for approval, the valves and instruments are selected based on the rated operating pressure. Therefore, even if the user specifies the pressure at which the equipment will be used and the manufacturer installs a safety valve as required by the user, this will result in parameters for the valves that differ from those specified in the original factory drawings. Could this affect the final acceptance process?
According to Table 6-3 of the Boiler Code, when the operating pressure is 0.8 or less, the minimum set pressure for the safety valve of this boiler should be the operating pressure plus 0.03, while the maximum set pressure should be the operating pressure plus 0.05. That is 0.63/0.65.