The relief device calendar
Under 49 CFR 192.731, each pressure relieving device in a compressor station, except for rupture discs, must be inspected and tested in accordance with the pressure limiting station rules, and must be operated periodically to determine that it opens at the correct set pressure. Any defective or inadequate equipment found must be promptly repaired or replaced. The rule is specific because the relief device is the station's pressure safety valve: it sits silent for months, and the only way to know it still opens at set pressure is to test it. A relief valve that has never been lifted is a gamble on the station's worst day.
The shutdown device gets an annual check
The same section requires each remote control shutdown device to be inspected and tested at intervals not exceeding 15 months, but at least once each calendar year, to determine that it functions properly. The shutdown device is the station's emergency brake, and the annual test is the evidence that it will stop the station when the gas detector trips or the operator hits the button. The calendar matters twice: the interval cannot exceed 15 months, and the test cannot skip a calendar year, so the date is tracked and the record is kept.
Gas detection and combustible storage
Section 192.736 requires each compressor building to have a fixed gas detection and alarm system, unless the building has at least 50 percent of its upright side area permanently open, or it is an unattended field station of 1,000 horsepower or less. The system must continuously monitor for a concentration of gas in air of not more than 25 percent of the lower explosive limit, warn persons about to enter and inside the building, and be maintained with performance tests. Section 192.735 adds the storage rule: flammable or combustible materials beyond everyday use are stored a safe distance from the compressor building, and aboveground oil or gasoline tanks are protected in accordance with NFPA 30.
Compressor station maintenance sits inside the same record system as MRO inventory, remote monitoring, and lockout/tagout. If test dates and gas detector performance checks live in a logbook that gets filled in at renewal time, an operations audit will show which stations are inside their intervals and which are past due.