Under what condition is a fusible plug not required to be installed on a boiler?

A fusible plug is a safety device in boilers designed to melt and relieve pressure when the water level in the boiler drops too low, thereby preventing overheating and potential explosions. The requirement for the installation of a fusible plug is primarily dictated by the operating pressure of the boiler.

For boilers operating at pressures under 200 psig, the installation of a fusible plug is typically mandated. This is because at lower pressures, the risks associated with overheating and water level deficiencies necessitate an additional layer of safety that the fusible plug provides.

When the operating pressure exceeds 200 psig, the need for a fusible plug diminishes significantly. At higher pressures, other safety mechanisms and operational controls are put into place, reducing reliance on the fusible plug for safety management. Hence, if a boiler operates over 200 psig, it is not required to have a fusible plug installed, aligning with industry practices and safety regulations.

This understanding of pressure levels and safety device requirements is a crucial aspect of boiler operation and maintenance within the regulatory framework established for high-pressure systems.