Page 136 - Compression Machinery for Oil and Gas

Centrifugal Compressors Chapter 3 123

Condition Monitoring
Compressors and their associated auxiliary systems are instrumented to ensure
safety and reliability. Standard alarms, shutdowns, and control systems are dis-
cussed in detail within API 614 and API 670 standards. Typical parameters that
are monitored online are listed below. Many of these measurements are fed into
a machinery protection system. Trips related to overspeed and bearing oil pres-
sure are generally required. Trips related to vibration level and axial position are
often specified as well.
Typical Instrumentation

l Speed
l Rotor vibration and position (radial and axial)
l Bearing metal temperatures (journal bearings and thrust bearings)
l Lube oil console
Lube oil pressure, inlet temperature, and drain temperature
Lube oil differential pressure across the filter
Lube oil level
Lube oil cooling water temperature
l Dry gas seal
Seal-gas supply
Vent-gas pressure(s) or flow(s)
Separation-gas pressure of flow
Differential pressure at each filter set
l Lube oil cooling water temperature
l Compressor performance
Suction and discharge pressure
Suction and discharge temperature
Flow rates
Manual inspections are also of importance. The compressor and the auxiliary
equipment should be inspected for leaks at piping connections. Lubricating
oil should be periodically checked for the presence of water and for degradation.

Predictive Maintenance
Data collection and measurements can be used for predictive maintenance. The
concept is to base maintenance decisions, and in some cases, operating deci-
sions, on the measured condition of the machine. Trending information over-
time can provide advanced warning of a deteriorating compressor thereby
enabling preparation for maintenance and a shortened turnaround cycle. Better,
more accurate, production planning can also be achieved.
Rotor vibration is measured using noncontacting eddy-current displacement
probes that sense the motion of the rotor relative to the casing and bearings. The
probes are typically located immediately adjacent to each radial bearing
arranged 45 degrees from top dead center and sensing the burnished probe