What is the largest safety valve that may be attached to a steam drum of a high pressure boiler by threading?

The largest safety valve that may be attached to a steam drum of a high-pressure boiler by threading is commonly specified as 3 inches. This limit is established to ensure that safety valves can handle the required flow capacity and pressures effectively while also maintaining structural integrity. Threaded connections, although practical for smaller valves, can introduce issues such as stress concentrations and potential leaks when larger diameters are used.

Using a larger size than 3 inches, such as 4 inches or 5 inches, for threaded attachments could compromise the performance of the safety valve and the overall safety of the system. In high-pressure applications, it is crucial that the connection type provides adequate support and reliability, which is why larger safety valves typically use flanged connections instead of threaded ones. This is to ensure a secure seal and structural stability under high pressure scenarios. Thus, 3 inches is the maximum to maintain a balance of safety, efficiency, and adherence to code requirements.