A pipeline compressor station is the equipment that keeps gas moving down a long transmission line. Gas loses pressure to friction as it travels, so stations sit at intervals of roughly 60 to 160 km to boost it back up, usually with centrifugal compressors driven by gas turbines or electric motors, sometimes with reciprocating units on smaller lines. From a functional safety point of view a compressor station is a rotating equipment problem wrapped in a gas inventory problem.
The machine needs overspeed protection, vibration and axial displacement trips, and lube oil protection. It also needs anti-surge control to keep it out of the operating region where flow reverses and the compressor damages itself. The station around it needs gas detection, emergency shutdown, and a blowdown that can isolate and depressurize the yard.
Functional safety relevance: Yes. Overspeed, surge, and gas detection shutdowns on a compressor station are routinely assigned SIL targets and verified under IEC 61511, even though the station is not a process plant in the usual sense.
Key Points
- Restores transmission line pressure at intervals along a gas pipeline, using turbine or motor driven centrifugal compressors.
- Machine protection covers overspeed, vibration, axial displacement, and lube oil, and these are frequently implemented as instrumented functions with their own integrity targets.
- Anti-surge is a control function rather than a protective one, usually backed by a separate surge trip. Keeping those two apart is a recurring design argument.
Example
A 36-inch transmission line runs 700 km with compressor stations along the route. At one station a turbine-driven compressor trips on high vibration. The unit shuts down, the recycle valve opens to protect the machine from surge as it coasts to a stop, and the station bypasses so gas keeps moving down the line while the unit is investigated.
See Also: pipeline pump station, onshore gas processing plant, HIPPS
Cited Sources
- ASME B31.8, Gas Transmission and Distribution Piping Systems
- API Standard 670, Machinery Protection Systems