Troubleshooting Axial Shuttling through Field Testing & Analysis

A nuclear utility had been observing axial shuttling on their three single stage, double suction Condensate Booster pumps. To better understand the circumstances driving this phenomenon, they asked Hydro Reliability Services to provide in-depth field testing of the equipment at different operating loads.

Evaluation of the vibration performance took place over the course of six days, in which data was recorded from the startup of the plant through to full unit load. To properly identify and understand the axial shuttling described by site personnel, the broad range of data was studied and fifteen individual data points more closely examined.

Axial shuttling is observed in proximity probe data to be a sub-synchronous event with non-periodic perturbations (spikes) occurring at low frequency. These perturbations are not present in radial channels and spectra of radial channels do not show sub-synchronous excitation.

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The field data taken shows that axial shuttling occurs in cases where the flow rate is below 70% of the rated flow and occurs most frequently and with a higher incipient flow rate in Pump A. For pumps B and C, the axial shuttling was not as widely observed and only occurred in the lowest flow rate scenarios, where the flow was less than 55% of the rated flow.



It was determined that the axial shutting could not be detected in the bearing housing vibration, only the rotor vibration, and does not appear to negatively impact hydraulic performance. However, it is very likely that prolonged operation with axial shuttling will reduce the life of the pumps, motors, and mechanical seals.

Understanding which pumps are more susceptible to axial shuttling and under what operating conditions helps the plant to assess the combination of pumps working in parallel for different operating modes. Knowing that Pump A is more prone to axial shuttling and will exhibit thrust reversals at a higher flow rate gives an important insight into how to operate the system more reliably.

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Centaur Condition Monitoring Early Detection Saves Over $200,000

As part of Hydro’s support of a Midwest steel mill’s descaling pumps, the Centaur condition monitoring service has been installed on five of their pumps machine trains. Using wireless sensors, Hydro has been continuously collecting real-time vibration and surface temperature levels on the pump, gearbox, and motor. The goal of this monitoring service is to work directly with the end-user to improve rotating equipment maintenance strategies through better, more frequent data collection and Hydro’s subject matter expertise in rotating equipment.

graphical user interface, text, applicationThe value of having continuous monitoring was proven during a vibration even that occurred shortly after the installation of a newly refurbished rotor on one of the pumps. After noticing a concerning upward trend in vibration, Centaur’s engineering team suspected that the pump was suffering from structural looseness in the outboard bearing housing.  Learn more about how the discovery and remediation of this vibration transpired in the timeline below.

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What Happens When Things Go Bump in the Night?

What happens when an alarm is signaled from our Condition Monitoring System? Is the software customizable to customers’ needs? Glad you asked.

It all starts in the home of our Centaur engineers – the Monitoring and Diagnostic Center, where dedicated personnel are checking the status of monitored equipment 24/7. These vibration and pump subject matter experts keep an eye on concerning trends and use the digital twin interface to identify areas of concern.

At the same time that our engineers are alerted to the alarm condition and begin investigating, the Centaur system automatically begins taking more frequent vibration sampling to increase the amount of data available for analysis and capture as much information on the event as possible.

The alarm that is triggered is based on limits set by the end-user and the Centaur team at the beginning of the installation. Centaur software allows users to have configurable alarm notification settings based on their preferred diagnostics and notification methods. Such diagnostics include vibration amplitudes, temperature, and gateway connectivity status. These automated alarms can be sent using SMS and email messaging.

diagramSome individuals may prefer to configure the system to only notify them after a high-level alarm event has occurred. The Centaur software provides the flexibility to be notified after Alarm 1, Alarm 2, Alarm 3, or Alarm 4 events. Although the client may wish to only be notified of higher alarm level incidents, Hydro’s Condition Monitoring team is made aware of all alarm levels incidents and investigates the source. If further action is deemed necessary, the team may reach out to plant personnel and notify them of a possible fault so the appropriate measures can be taken. They may also suggest actions that can be completed on-site to validate probable causes of the alarm.

Here’s an example of the process at work. In this case, a machine train’s vibration amplitudes trigger an alarm:

  • Hydro’s Condition Monitoring team will be notified of the alarm incident, as will any personnel if the alarm level falls in their notification settings
  • Hydro engineers will conduct vibration analysis of the data sample
  • Hydro engineers will respond to alarm notification, with all pertinent personnel included, and elaborate on the possible source of the alarm and detail the recommended next steps
  • In the case of rapid increase of vibration levels, Hydro engineers may reach out to plant personnel directly for more immediate necessary actions
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State of the Art Parts: Nozzle Head Casting

Hydro Parts Solutions recently provided a cast nozzle head to a Canadian oil and gas end-user. As is standard with Hydro’s cast parts, this complex component was:

  • Scanned
  • Reverse engineered
  • Reviewed by Hydro’s engineering team
  • Cast
  • Final machined
  • Compared to original model

The nozzle was modeled, cast, machined, and verified for a delivery time that beat the original customer request.

IIoT Trial Provides Hands-On Experience

Hydro’s Condition Monitoring system, Centaur, has aided many end-users in catching real-time faults in rotating machinery. In many instances, end users see the value of the system through a no-cost, on-site trial. This includes the hardware, installation support, commissioning, and monitoring starting from the date that the sensors are commissioned on-site. The purpose of the free trial is to allow a “proof-of-concept” evaluation period before a further commitment is made.

After an initial period of data acquisition, typically a few weeks to one month, Centaur’s Condition Monitoring Engineers hold a virtual meeting to walk the end-users through the data collected and the extensive software capabilities. A monthly report is provided with an overall equipment health assessment and alarm event analysis. The analysis often includes trend data, waveform analysis, spectrum analysis, and cross-phase analysis between multiple sensors on a given machine train. The report also includes predictive failure analysis and proactive steps to mitigate component failure in the future. Continue reading