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REPLACING “DUAL” PRESSURE RELIEF VALVES

PART B:

See Plant Safe Practices binder for Line Break procedures, Confined Space Entry and Hot Work Permits. Use the lock-out/tag-out log to document which valves or switches have been opened or closed. STEP NUMBER DESCRIPTION SAFETY AND HEALTH HAZARDS/ STEPS TO AVOID DEVIATION 1 Close three-way valve port connected to the relief valve that will be replaced. Note: See appropriate diagram.

2

Slowly disconnect pipe unions using primary and back-up pipe wrenches on outlet line from both relief valves to slowly vent any trapped pressure.

Note: Monitor local environment for presence of NH 3 using portable detector.

3

Remove pipe nipple and half of union from outlet of old/defective relief valve.

Note: Once replacement has begun, do not stop until new valve has been completely installed. Warning: Do not completely remove valve until sure that all pressure has been relieved through pipe threads.

4

Break loose threaded inlet connection to old relief valve while using back-up wrench on inlet pipe nipple. Unscrew old relief valve Slowly , while wiggling valve to allow trapped pressure to leak through threads. Clean threads of inlet pipe nipple and apply new Teflon tape and a light coating of Teflon paste to pipe threads. Verify that replacement relief valve is rated for the same pressure as the vessel it is protecting and then install new relief valve and tighten using back-up wrench on inlet pipe nipple. Clean threads of outlet pipe nipple and apply new Teflon tape and a light coating of Teflon paste. Re-install pipe nipple and half of union in outlet of the new relief valve and tighten. Then reconnect union halves and tighten. After repairs or service is completed return the stem on three-way valve to the normal operating position (fully counter-clockwise) and leak check new relief valve connections using sulfur sticks.

5

Note: Always use ammonia grade fittings, Sch. 80, seamless pipe.

6

Note: The relief valve rating must NOT be higher than the vessel rating.

7

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9

Note: Light sulfur stick and slowly wave burning stick around all pipe joints. A white smoke plume will indicate an ammonia leak reacting with the sulfur. Note: Record all information from new valve on the master list of relief valves.

Procedure: Operation, Isolation and Replacement of Pressure Relief Valves Reviewed: 11/01/2023

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