At what pressure is an ASME Section VIII expansion tank required on a hot water boiler?

An expansion tank is a critical component in a hot water boiler system, as it accommodates the expansion of water when it is heated. According to ASME standards, an expansion tank becomes necessary when the pressure in the system exceeds 30 psig. This is because at this pressure level, the risk of water expanding beyond the capacity of the boiler and its components increases, potentially leading to unsafe conditions or equipment failure.

The requirement for an expansion tank at this pressure is in place to ensure that excess pressure can be effectively managed without compromising the integrity of the system. This tank provides a safe space for the expanded water to go, helping to maintain system pressure within safe limits and ensuring reliable operation of the boiler. Thus, the specification that requires an expansion tank at 30 psig is based on safety and performance considerations in managing the dynamics of hot water systems.