March 2018

Powerful new cost saving vibration measurement device added to Xodus’ vibration engineering tool box

Jim McGhee

Jim McGhee

Our vibration engineers have added a powerful new motion visualisation capability to their suite of vibration assessment tools. The IRIS-M Motion Amplification System consists of a highly specified video camera and a PC-based controller and capture device. The software package allows standard recorded video images to be amplified, revealing the detail of vibration which cannot be seen by the naked eye.

In this example, the high magnitude transient behaviour of the line is not visible on the unamplified video (left), while it is obvious on the amplified video (right).

Krk Co 12Mm Wide 1 Filtered 1

Click to view video

Vibration magnitude and frequency can be captured from any point in the image allowing non-contact vibration measurements to be made from significant distances away from the subject. In the above example, the distance between camera and pipework is over 5m but by using a more powerful camera lens, the system can be used at much greater distances. The system can be deployed and data recording can start within minutes of a problem being identified, saving significant time and costs that are associated with constructing scaffold access platforms and/or organising rope access to reach difficult locations.

The transient behaviour (magnitude modulation) of the pipework can clearly be seen in the time history below and the resulting vibration spectrum shows that this vibration is in the ‘concern’ region, just below the ‘problem’ category when referencing the Energy Institute Vibration Guidelines.

Krk Co 12Mm Wide 1 X Thspectrum

As with any vibration measurement that is used to quantify an integrity threat, caution should be used when interpreting the data. The following points should therefore be considered when using this system:

The motion can be amplified to any arbitrary level. While this facility is useful when analysing the relative motion between different parts of the system, high levels of ‘perceived vibration’ can cause alarm. Anyone with experience of interpreting Operational Deflection Shape analysis results will be familiar with this concept.

Obtaining Vibration measurements (magnitude and frequency) from the video image is not a trivial task. Measurement location, frame rate, length of recording and even background lighting all have a major impact on the accuracy of any measurement extracted from the video image. This is not a simple process so if you are unsure, don’t try, as significant errors can be introduced.

Understand the results. Knowledge of pipework vibration response is necessary to correctly interpret any vibration measurement and this is perhaps more important for data captured using this camera system. In the example above, the problem looks severe but due to the low frequency and transient nature of the pipework response, the actual integrity threat is low.

Vibration measurement should only be considered as a screening tool. If the vibration measurement gives rise to concern, a more detailed assessment should always be performed using dynamic stress measurement.

The IRIS-M Motion Amplification System is a fantastic addition to the comprehensive suite of vibration measurement devices available to Xodus’ vibration engineers. For the assessment of a wide range of common machinery problems the system is very powerful and in many ways unparalleled. For the assessment of pipework integrity however, careful consideration must be given to the data capture aspects and to the interpretation of the data. As with so many things in life, the results are only as good as the user!

Contact: Jim McGhee