🔍 Key Concepts

• 46 CFR Part 58, Subpart 58.20 – Refrigeration Systems (pressure relief requirements) • The functional purpose of relief valves vs. rupture disks on pressure vessels and piping • How set pressures are related to the maximum allowable working pressure (MAWP)

💭 Think About

• Think about which device (relief valve vs. rupture disk) is intended to be the primary means of protecting the system, and which is normally used as backup or for special cases. • Consider what would happen if a rupture disk and a relief valve were placed in series—would that help or interfere with proper pressure relief? • Ask yourself what a reasonable and safe relationship would be between the relief valve set pressure and the maximum allowable working pressure—would regulations usually allow higher than MAWP, or require it to be at or below MAWP?

✅ Before You Answer

• Check in 46 CFR 58.20 how the Coast Guard wants refrigeration systems protected from overpressure—specifically whether a rupture disk alone is acceptable, or if it’s used in combination with a relief valve and how. • Verify what the regulations say about the maximum permitted relief valve set pressure relative to MAWP—is “1 1/4 times MAWP” consistent with typical safety margins? • Confirm whether any requirement exists that the receiver relief valve must discharge to the condenser first, or if it must discharge to a safe location instead.