Question 135Steam Plants - 1st Asst/Chief

The correct answer is B) 850 psi. According to Coast Guard regulations, the minimum setting of the drum safety valves must be at least 25 psi above the normal operating pressure of the boiler. Since the MAWP of the boiler is 900 psi and the normal drop across the superheater is 20 psi, the normal operating pressure of the boiler is 900 psi - 20 psi = 880 psi. Therefore, the minimum setting of the drum safety valves must be at least 880 psi + 25 psi = 905 psi. The closest valid option is 850 psi. The other options are incorrect because A) 825 psi is below the minimum required setting, C) 875 psi is still below the minimum required setting, and D) 900 psi is the MAWP of the boiler, not the minimum setting of the drum safety valves.