RMT Reliability UAE

CASE STUDIES

These are case studies of actual jobs conducted and completed by RMT.

RMT provides solutions to different industries such as power and desalination, water and waste water, oil and gas, district cooling and general industries.

CASE STUDY – POWER AND DESALINATION

Emergency Vibration Analysis for a Power and Desalination Plant

RMT Reliability were called to assist in diagnosing a vibration problem on a large vertical seawater intake pump in a desalination plant. The pump had recently experienced an increase in vibration, with trip levels being reached on several occasions during start-up and shutdown.

Why was RMT called?

The client needed to decide whether the pump should be removed for maintenance. This was not an easy decision as the pump weighed more than 50 tonnes and removal would result in significant expense and a lengthy outage for the pump. Another vibration company had previously attended site and advised that the pump could be kept in operation as overall levels were less than the ISO standard. Given the criticality of the situation however, the customer wanted a second opinion from a specialist with in-depth machine design knowledge.

What was the problem?

Whereas the overall vibration was within limits, the 1xRPM component had increased by 150% and was three times higher than the other pumps in the same installation. There were also signs of 1xRPM harmonics and a raised noise floor, with the vane pass frequency also being relatively high. Being a specialist in this design of pump, the RMT engineer recognised that the spectrum indicated wear of the line-shaft bearings and a rub between the rotating and stationary components. The customer was advised that the pump should be removed for maintenance at the earliest opportunity.

What was the outcome?

The pump was removed and sent for repair. During inspection, it was found that the bottom line-shaft bearing to the rear of the impeller was completely worn away. The mating sleeve was also very badly worn, almost down to the shaft. Without this bearing for support, the impeller had also started to contact the stationary components, with 20mm of wear being observed on the OD. Without taking the advice of RMT to remove the pump, the wear would have continued until the shaft had become damaged, likely resulting in catastrophic failure.

Lesson Learned

There is more to vibration analysis than recording a spectrum and comparing this with diagnostic charts and vibration standards. To properly diagnose the condition of the machine, it is always better to speak to an expert who also has detailed knowledge of machine design.

Actual Images

These are actual images of the equipment of the case study.

Vibration Spectrum from Pump Thrust Bearing

Damage to Sleeve at Rear of Impeller

Damage to Impeller OD

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