(a) Overpressure protection devices shall be tested in place once each calendar year at intervals not exceeding 15 months to determine if they are in proper working condition. They are to be subjected to such maintenance and overhaul as may be indicated by said tests. Overpressure protection devices used solely for the protection of "fuel piping" as, for example, to compressors at the compressor stations, shall be tested and inspected in like manner.
(b) Nonworking monitoring regulator equipment shall be subject to a performance test once each calendar year at intervals not exceeding 15 months and shall be internally inspected and overhauled if so required by the results of the test.
(c) Once each calendar year at intervals not exceeding 15 months, a review of the required capacity of the relieving equipment at each station shall be made and these required capacities compared with the calculated or experimentally determined recorded relieving capacity of the installed equipment for the operating conditions under which it works.
(d) If the relieving equipment is of insufficient capacity, a new or additional device shall be installed to provide the additional capacity required or the station regulator capacity reduced commensurate with the existing relief capacity.