Q&A | Stop Valves on Relief Valves

Question: Can a stop valve be installed before or after a relief valve?

Answer: If your initial reaction to this question is “NO“, then you are in good company. Most refrigeration experts (and people with common sense) can see the danger in installing stop valves before/after pressure relief valves….However, as is the case with many issues, there are exceptions where installing stop valves may be helpful or necessary. IIAR 2 makes special allowance for stop valves if “procedures specified in the governing edition of the ASME Boiler and Pressure Vessel Code Section VIII Appendix M are followed” (ANSI/IIAR 2-2008 Addendum B §11.3.1) and the valves are “locked open whenever any relief device upstream is in service” (ANSI/IIAR 2-2008 Addendum B §11.1.2)

Let’s breakdown the important requirements of ASME Boiler and Pressure Vessel Code Section VIII Appendix M.

1. Appendix M does not recommend stop valves in the relief path, rather it allows it.
   2013 B&PV Code Section VIII Appendix M-5.1 General
   (a) Stop valve(s) located within the relief path is not allowed except as provided for in M-5.5, M-5.6, M-5.7, and M-5.8, and only when specified by the user. The responsibilities of the user are summarized in M-5.3. The specific requirements in M-5.5, M-5.6, M-5.7, and M-5.8 are not intended to allow for normal operation above the maximum allowable working pressure.
2. When a facility elects to install stop valves in the relief path, the facility “has the responsibility to establish and maintain a management system that ensures a vessel is not operated without overpressure protection” (See 2013 B&PV Code Section VIII Appendix M-5.3). These responsibilities include:
   (a) Deciding and specifying if the overpressure protection system will allow the use of stop valve(s) located in the relief path.
   (b) Establishing the pressure relief philosophy and the administrative controls requirements.
   (c) Establishing the required level of reliability, redundancy, and maintenance of instrumented interlocks, if used.
3. The management system must include written procedures (M-5.4a), documented training (M-5.4b), and be periodically audited by management (M-5.4b).

2013 B&PV Code Section VIII Appendix M-5.6 specifies requirements when stop valves are used upstream or downstream of relief devices exclusively for the purpose of maintenance. If that is your situation, you must adhere to the following:

1. Administrative controls must be present to prevent unauthorized valve operation.
2. Valves must be provided with mechanical locking elements.
3. Valve failure controls must be provided to prevent accidental valve closure due to mechanical failure.
4. Procedures must be in place to provide pressure relief protection during the time when the system is isolated from its pressure relief path. These procedures must ensure that when the system is isolated from its pressure relief path, an authorized person will continuously monitor the pressure conditions of the vessel and must be capable of responding promptly with documented, pre-defined actions, either stopping the source of overpressure or opening alternative means of pressure relief. This authorized person must be dedicated to this task and must have no other duties when performing this task.
5. The system must be isolated from its pressure relief path only for the time required to test, repair, and or replace the pressure relief device.