Class 5 Boiler Practice Exam

According to ASME sec IV part HG400, the safety valve size for a 15lb steam heating boiler with over 15000 btu heat input shall be no smaller than what?

1. 1 inch

2. 2 inches

3. 1 NPS

4. 3 NPS

The correct answer is: 1 NPS

In accordance with ASME Section IV Part HG-400, the requirements for safety valve sizing are established to ensure adequate protection for steam heating boilers. For a 15 lb steam heating boiler with a heat input exceeding 15,000 BTU, the minimum safety valve size must be at least 1 NPS (Nominal Pipe Size). This sizing is critical because the safety valve is designed to release excess pressure to prevent potential boiler failure or explosion. The 1 NPS size establishes a standard for the flow capacity needed to handle the steam generation at that pressure and heating input level efficiently. Using a larger valve than the specified minimum can be permitted, but using a smaller one could compromise safety and lead to unsafe operating conditions. Therefore, the requirement for 1 NPS is a baseline ensuring the valve can adequately relieve pressure per the safety standards outlined in the ASME code.