Good Vibrations
Eike Drewes, PROGNOST Systems GmbH, Germany, presents a case study that illustrates effective machine protection for vertical reciprocating compressors.
Vibration monitoring systems for machine protection on reciprocating compressors employ a variety of sensor positions, depending on the machine’s design. The case study discussed in this article deals with the actual damage on a vertical reciprocating compressor, and illustrates the vibration behaviour at various measuring points. It also clearly demonstrates what points must be taken into consideration when positioning sensors in order to achieve optimum machine protection.
Damage findings
While the machine was running, the top piston face struck a loosened screw, which fractured the cylinder cover of stage 1.
Application
A chemical production facility in Gelsenkirchen, Germany, uses a double acting, 4 stage, oil free, vertical reciprocating compressor for compression of polypropylene. This machine is protected with vibration sensors (accelerometers), which are mounted on each crosshead slide inside the crankcase, perpendicular to the direction of the piston movement (Figure 1). The space between the individual vibration sensors is 750 mm. In addition, the machine is equipped with dynamic pressure sensors measuring the pressure of both compression spaces from each cylinder to monitor the p-V diagram. A PROGNOST®-NT online monitoring and diagnostic system evaluates the acceleration and pressure signals.
Damage sequence of events
On the morning of 3rd March 2000, gas detectors in the compressor building set off an alarm in order to shutdown the compressor. An inspection of the machine identified a broken cylinder cover of stage 1. The cause of the damage was a loosened piston nut on the top end of the piston face. While the machine was running, this screw repeatedly struck sharply against the cylinder cover in the top dead centre (TDC) position, finally destroying it. This caused the release of gas.
To learn more about PROGNOST Systems visit www.prognost.com.