Bearing Condition

Monitoring bearing condition is essential for maintaining machinery health, and various techniques can be employed for this purpose. One effective method is the “bearing envelope,” which helps in detecting early symptoms of component wear. Recently, during an analysis of a Fresh Water ejector pump electric motor, a significant increase in amplitude was observed. The locations of the measurement points are illustrated below:

Fig. 1. Measurement points in FW ejector pumps.

In September, the measurements showed normal amplitude levels:

Fig.2 Measurements results: Velocity in RMS (mm/s) and bearing Envelope in Peak (m/s2) – September

The first column indicates the measurement point locations as described in Figure 1.

The second column shows velocity in RMS (mm/s) according to ISO 10816, with yellow indicating class “C” and gray indicating class “A” or “B.”

The third column presents the bearing envelope in Peak (m/s²), providing early insights into the bearing condition.

In January, a dramatic rise in the bearing envelope on the Drive End bearing was detected, nearly 10 times higher than the previous measurement:

Fig.3 Measurements results: Velocity in RMS (mm/s) and Envelope bearing in Peak (m/s2) – January

The FFT spectrum of the bearing envelope revealed multiple nonsynchronous peaks, with one peak identified as the ball spin frequency.

According to the fact that such a high envelope signal appeared so fast, we decided to ask the Crew to make additional measurements to confirm the trend of the signal.The next measurement was done in April and the maximum envelope increased during those 3 months.

Fig.4 Measurements results: Velocity in RMS (mm/s) and Envelope bearing in Peak (m/s2) – April

Fig.5 Trend of maximum overall value from bearing envelope signal.

As a result, we recommended replacing the Drive End bearing. The crew followed our recommendation and provided photographic evidence confirming the diagnosis.

Fig.6 Damaged rolling element in bearing

Fig.7 Damaged rolling element in bearing

The initial signs of wear were detected three months prior, allowing the crew to plan for a bearing replacement in advance. Monitoring bearing condition solely through basic vibration signals like Velocity provides insufficient time for maintenance planning, offering only a brief window to shut down the machine. Hence, understanding and applying the bearing envelope technique is crucial in the marine industry for effective maintenance and longevity of machinery.

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