Relief Valve Replacement (Dual Assembly)

This is an update to a blog that was originally posted on 3/10/15. You can read the original blog here.

Question: Do both relief valves on a dual assembly have to be replaced every five (5) years, or just the relief valve that has been subject to system pressure?

Answer: Most pressure vessels in an ammonia refrigeration system exceed 10 cubic feet in volume (normal exceptions are oil pots and small oil separators), and therefore are required to be equipped with a dual pressure relief valve assembly (ANSI/IIAR 2-2021 §15.3.6). Correct installation of a dual pressure relief valve assembly will allow only one of the two relief valves to be subject to system pressure, with the other valve available for backup should the position of the 3-way relief isolation valve require adjustment. Regardless of whether the valve is subject to continuous system pressure, both of the relief valves on the dual assembly must be replaced or bench tested every five (5) years. The key is that each of the valves has been installed for five (5) years and therefore exposed to the surrounding elements, corrosion, weather, etc. If you are still struggling to agree, just consider a situation where a relief valve is installed downstream of a rupture disk (picture on the right). Following the logic that a valve must be subject to system pressure to require 5-year replacement would mean neither valve would be replaced until after a rupture disk bursts.

The required frequency of relief valve replacement is addressed by ANSI/IIAR 6-2019 §13.1.1. The standard states the following on this topic:

• All pressure relief valves (PRVs) that relieve to atmosphere shall be recertified or replaced on the 5-year time-based frequency. [§13.1.1]
• The service life of the PRV shall not exceed 5 years of service after it is installed on the system. [§13.1.1.1]
• Where the PRV Date Tag was not punched during installation, and PRV records do not indicate the installation date, then the worst-case installation date on the PRV Date Tag is assumed and shall be punched upon inspection. [§13.1.1.1.1]
• The PRV shall be recertified or replaced once determined to have been exposed to an overpressure event. [§13.1.1.2]

It is beyond the scope of this blog to dive into the requirements of recertifying relief valves. For more information, refer to ANSI/IIAR 6-2019 §13.1.2.