April 4, 2018
From David Chislea
Manager, Gas Operations Section
Michigan Public Service Commission

1. Are compressor station relief valves that protect downstream facilities, when a pressure control failure causes an exceedance of MAOP (maximum allowable operating pressure), the only relief valves required to be inspected under 49 CFR 192.731(a)?

2. If the answer to question #1 is "no," what relief valves must be inspected at a minimum, such as thermal relief or redundant relief valves that were not explicitly installed to comply with the inspection and testing requirements of 49 CFR 192.731(a)?

3. If the answer to question #1 is "no," what inspection intervals are required on non-MAOP protecting relief valves (such as thermal relief or redundant relief valves), specifically in regards to:

a. 49 CFR 192.739?

b. 49 CFR 192.743?

c. 49 CFR 192.201?

4. If the answer to question #1 is "no," how are non-MAOP protecting relief valves expected to comply with the requirement of 49 CFR 192.739 in regards to being "set to control or relieve at the correct pressure consistent with the pressure limits of § 192.201(a)" if they are not installed to limit MAOP but for a different purpose, such as redundant relief valves or thermal relief valves in the case of ASME pressure vessels?