This case study illustrates the advantage of utilizing segmented analysis (8 segment peak to peak) rod position as part of a multi-layer protection strategy together with crosshead acceleration for reciprocating machinery.

Sequence of Events

  • Compressor commissioned in 2011
  • On Aug. 15,2016 at 5:47:04 am the system was tripped on high 1st stage crosshead vibration after 3 month of running on steady state at 100% load
  • Analysis of crosshead vibration data shown no increase
  • Analysis of peak-peak rod position data shows a slight increase in Seg. 2 several minutes prior to failure, but protection limit of 36 mils was not violated
  • Machine was restarted by operations risking further damage

Several Trend Views for Analysis

See how the signal developed during the month, days and hours before the event and machine shutdown occurs.

RMS Vibration Amplitude
3D Crosshead Trend (4 month)
Peak to Peak Vertical Rod Displacement
3D Trend Peak-Peak Rod Position (4 month)
Peak to Peak Vertical Rod Displacement 2D
2D Trend Peak-Peak Rod Position (all segments 4 month)
Peak to Peak Vertical Rod Displacement Violation
Trend Rod Position for Segment 2 (4 days) – 1st Upper Threshold = 18 mils 2nd Upper Threshold = 24 mils Protection Limit = 36 mils
Peak to Peak RP Trend
Peak to Peak Rod Position Trend (4 days)
1 revolution prior to break
Revolution Prior to Break
Rod Break
Next Rev. – Rod Breaks in Tension

Key Learnings

  • The development of this type of rod fracture did not show significant signs of impending failure using x-head vibration
  • Crosshead vibration initiated immediate shutdown of the machine preventing consequential damage
  • Segmented peak to peak piston rod position analysis did show an increase in rod movement leading up to the event, however similar levels had been seen in past trend data
  • Data review confirmed that for the type of failure experienced, the machine protection parameters were properly configured requiring no adjustment