The Use of Ultrasonic Testing in Condition Monitoring

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The use of ultrasonic testing in condition monitoring is a relatively new method in the field of condition monitoring. It monitors the high frequencies sound that is generated by plant machines and systems. Ultrasonic sound is not audible by the human ear, and occurs at a frequency above 20 kHz. The different ultrasonic equipment records ultrasonic sound between 20 kHz and 100 kHz. There exist two types of ultrasonic monitoring, airborne and structural. Both methods receive ultrasonic sound, airborne through the air and structural through solid surfaces. The airborne method can further be separated into two modes. The scanning mode primarily used in detection of gas leaks. It uses the fact that the instrument is only sensitive to ultrasound and that it is ultrasonic sound that is transmitted from a gas leak to register the leakage from valves, pipes etc. The contact mode is on the other hand used to locate turbulent or restricted flow in process piping. In this case study we are going to focus on the airborne scanning method of ultrasonic condition monitoring. [1] Failure scenario A vital part of an offshore oilrig is the compressors. The compressors are used for many different tasks such as reservoir management, production enhancement and transmission of gas. If the compressor handles combustible gases, such as hydrocarbon gases, a leak could in worst-case lead to a fire or an explosion. A typical failure scenario is a compression unit offshore used for natural gas transmission to land. A leak in one of the bearings occurs, and because of the outdoor environment the gas does not make contact with the regular gas detectors before it has reached a high concentration. How will this be monitored and detected so that workers are... ... middle of paper ... ...larm is set with a delay time of 30 seconds the diagnosis that there is a gas leak from the compressor package is determined instantaneously when the alarm is triggered. As soon as possible after the alarm the leak has to be located using the portable ultrasonic detector. When the leak is detected it has to be determined if it can be quickly fixed or stopped. If this cannot be done the safety management should be informed and the platform should prepare for evacuation. [5] Conclusion Ultrasonic gas detection is a useful tool to detect a gas leak on an early stadium. It is excellent in open areas where the environment can make it difficult for ordinary gas detectors to make contact with the gas. This combined with the low installation and maintenance cost and low space requirement, we would recommend using it as a supplement to ordinary gas detection systems.

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