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Experimental observations of the kind of ultrasonic pulse that is used in flow-meters to travel around the inside circumference of a pipe.

Oil and Gas

Inspecting risers

A manufacturer and operator of down-hole inspection equipment had used a national centre to design and build a new ultrasonic system to inspect oil-well risers. The prototype was expected to produce images of the interior of risers based upon ultrasonic pulse-echo signals. Unfortunately, the system was unreliable and image signals were only received about 5% of the time. 

Cambridge Ultrasonics was asked to investigate the operation of the transducer and to find out what was wrong. We used our visualization system with the client's transducer in water and a section of riser pipe so that waves could be seen travelling from the transducer to the inside surface of the riser and reflecting back to the transducer. Visualization quickly showed (see video  to right) that there was an unexpected difficulty in locating the transducer at the centre of the riser and that the position had to be very accurately set otherwise the reflected ultrasonic waves would never return to the transducer. This was a design that could never work and Cambridge Ultrasonics recommended an entirely different approach for the location of transducers. In a few months the client modified its system and had a new reliable tool to use.

Another client had a similar problem with a down-hole ultrasonic inspection system that was not working properly. The R&D engineers had spent 6 months unable to fix the problem. The client's system was brought to our premises and linked to Cambridge Ultrasonics' visualization system, again with some riser section to provide a real ultrasonic path through water. The signal out of the receiver transducer went into the client's signal processing computer and the processed signal was shown on an oscilloscope. Our visualization system can be synchronized with an oscilloscope in a variety of modes but the most useful is to watch waves arriving at the transducer - it allows us to cross-reference a physical wave that is arriving at the receiver with a portion of the signal on the oscilloscope. In the client's system there were several peaks in the processed signal, watching waves arriving at the receiver identified the one peak in the output of the signal processing that came from the riser; other peaks were caused by internal reverberations in the transducer assembly. Visualization and wave watching found the problem quickly - the client's software was analyzing the wrong peak in the signal. When the client's engineers switched to analyzing the correct peak their system worked well. Cambridge Ultrasonics resolved the problem in half a day after the client had spent 6 months unable to solve it.

Offshore concrete structures

Concrete is sometimes used to make offshore production structures, where wind and wave forces are high, such as the North Sea. There are two applications of ultrasonic technology that Cambridge Ultrasonics has been asked to investigate: developing an imaging system for concrete and developing a monitoring system for concrete.

Imaging systems are used to check for internal signs of deterioration in the structure at specific, localized positions; it can also be used when making an hole through a concrete wall where there is a need to avoid damaging steel tendons or reinforcement in the concrete. An imaging system is attached to the location of interest on the structure for the period of the test, typically a few minutes, and then removed when the test is completed.

Monitoring systems (CMS) are attached permanently to a structure, with many sensors checking the concrete in the immediate vicinity of each sensor (to a range of about 2 m). Data from all the sensors (between about 10 and possibly 500) is collected at a central archiving computer where it is analysed to find signs of significant structural deterioration. The CMS monitoring system injects known patterns of ultrasound at each sensor and detects instances of the pattern in the return echo. This makes the system very robust against operational noise (wave impact for example) and marks a significant difference from the acoustic emission method. Another significant difference is that CMS detects structural change at any time after it happens whereas acoustic emission can only detect change at the instant it happens. These are substantial advantages.