Articles  

CM on Rotating Machines

Harald Reiners
Harald Reiners | Manager Condition Monitoring Services, FAG Industrial Services

FAG’s parent company, Schaeffler, has 80,000 employees around the world in two divisions: 

automotive and industrial. FAG is part of the industrial division and deals with mechanical maintenance, lubrication, reconditioning, and condition monitoring.

It is a challenge to perform condition monitoring on rotating

machines that do not have electrical connections. For example, how do you perform vibration analysis on this thruster, located under an oil rig?

FAG was assigned to measure some of these thrusters. This presented several challenges: First, this is a device that is difficult to access. The bearings are located underneath, and the gearbox is completely full of oil and sealed so that no water can enter, so there is no access to the sensors. Everything that you build in has to stay inside the thruster for ten years.

The normal service interval for an offshore thruster was five years, and after five years it had to be taken out since there was no other way to tell whether or not there was damage. The repair time resulted in lost days of production and, therefore, loss of money.

The owners wanted to extend the service interval of the thruster. This would allow them to keep oil prices low and still make money. If a condition monitoring product could be left on the machine, that five-year interval could be increased, and the machine would only have to be taken out when a problem was detected.

This project would be done in partnership with an OEM, who wanted to use this opportunity to improve their product and get an edge on the competition. Monitoring the condition of the bearings would also ensure the safety of anyone working on the oil rig, and it would allow the OEM to improve the performance of their thrusters. At that time, the company could not see a solution to the above challenges, and reliability was required for at least ten years.

Most of the time, these machines run at 50–70 rpm, unless they are transporting the rig, in which case they may be running at full speed, around 200 rpm. Another condition monitoring company had sensors on the machine, but there was a distance of 8–10 meters between them and the bearing, so the readings were not accurate.

Before, there were sensors monitoring oil particle count and water content mounted at the top of the device, where the two red lines are in the diagram above. They also measured additional signals, such as speed and load.

They conducted some measurements on the thruster and found three different measurement positions for the bearing and, after measuring (in demodulation) at the nearest location to the bearing, found a bearing defect.

Even one meter away, the bearing defect could not be accurately measured.

The original measurement point, at the top of the thruster, registered nothing.

As for the normal progression of a bearing defect, the OEM often had warning of a bearing defect, only to open up the bearing and find nothing wrong. The original position of the sensors gave false data. A goal of this project was to take more accurate measurements so that the pre-warning time would likewise be precise, and this was achieved by moving the sensors closer to the bearing. 

A slip ring unit in the thruster would help them keep a sensor near the bearing, but no one was willing to make it for them, so they had to design it themselves. Most slip ring units do not work when they are immersed in oil for long periods of time. They designed one with sealed sensors.

They also used water content analyzers, oil particle counters, acceleration sensors, and a CMS device. There is a standard condition monitoring system with sensors outside as well and on the gearbox. The data is sent to the OEM and to FAG by email, and workers on the oil rig have access to it.

The slip ring and sensors were running for nine years and still appeared new. There was no wear, and they worked perfectly. They now have over 200 of these devices in the field. It is a plus that they can be monitored remotely.

FAG was recently contracted to monitor smaller thrusters in a similar way. They accepted, but they cannot use the slip ring. Slip rings are expensive, and they are too big for these thrusters. Existing slip rings cannot be made smaller. When designing a new slip ring, the first unit costs €150,000. They have to be specially designed for each thruster type, so it is only worth it if many slip rings of the same size are needed. There is limited interchangeability between thruster types, so a different solution was necessary.

They decided on wireless CMS.

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About the Author

Harald Reiners
Harald Reiners Manager Condition Monitoring Services, FAG Industrial Services

Harald Reiners, born 1966 in Germany, got his training as an electronic engineer. After that he worked in a computer company for 14 years as the head of the hardware department. 2002 he joined the condition monitoring group of FAG Industrial services as a field service engineer which he is now leading for 9 years. As a level III certified specialist he did condition monitoring in several industries as wind power, marine, oil and gas, paper and steel. Additionally, he worked as a trainer and developed several special condition monitoring hardware and solutions.