Papers and Case Studies

Diagnosing Repeating Machinery Failure

Red Wolf Reliability was contracted to perform a vibration condition monitoring program at an oil refinery. In the Alky unit at this refinery, a mixer driven by a motor and single-stage gearbox was having a high failure rate of the gearbox and coupling between the mixer and the gearbox.

The vibration data at the gearbox as shown in Figure 1 below showed large increases at 1x, 2x, and 3x of the output shaft speed. This signature would proceed coupling and gearbox failures and can be indicative of a problem with alignment.

Figure 1: Output Shaft Axial Location Showing a Large Increase in 1X, 2x, and 3x Output Shaft Speed Amplitudes.

The refinery maintenance personnel confirmed the alignment between the gearbox and mixer was no longer within specifications and had to be adjusted. This solved the problem for a few months before the same vibration signature returned and the alignment was found to be out again. The vibration overall trend below in Figure 2 shows clearly when the elevated amplitudes occurred due to the shifts in alignment.

Figure 2: Vibration Overall Trend Showing Amplitude Spikes When Alignment Shifted.

Red Wolf Reliability recommended inspecting the foundation beneath the mixer for any issues and it was confirmed the foundation was settling. This was leading to continued problems with alignment, high vibration, and early component failures of the machine train.

Red Wolf Reliability recommended putting in a new foundation beneath the mixer to keep the machine train alignment and reduce early failure of the machine train. Since this is an expensive and time-consuming process continuous vibration monitoring has been installed at the gearbox and mixer so that any change in alignment can be seen quickly and can be adjusted before any major damage occurs to the machine train.