Acoustek®

Acoustek® is a patented technique that has been developed at the University of Manchester for the detection of leakage and blockage in long lengths of gas-filled pipelines and is now being commercialised by Pipeline Engineering Ltd. A series of trials have been undertaken in the UK and USA on static and live gas pipelines and these tests have shown that the technique is able to accurately survey pipelines with lengths of up to approximately 10km. In summary, the technique is able to:

• Survey pipelines that are:
• in static or flow conditions
• pressurised to between atmospheric and 5000 psi
• up to, and perhaps exceeding 10km in length
• large or small diameter
• composed of plastic or steel
• Detect full and partial blockages
• Detect holes in the pipe wall
• Locate any defect in a pipeline with a high degree of accuracy (depending on conditions in the pipe the accuracy is between approximately 0-5m)

For further information on how Acoustek® was used to survey an offshore gas pipeline and correctly identify and locate a near complete blockage approximately 500m from the host platform see UMIP News.

Background:

The University of Manchester has been investigating the use of an acoustic system, known as Acoustek®, to detect, locate and characterise leakages and blockages in pipelines, since 2000. The work has been supported financially by BP Exploration since 2004, by the University of Manchester’s Innovation Fund (2005 -2006) and, most recently, through a KTP Award with Pipeline Engineering Ltd (from September 2008) and ITF. Pipeline Engineering Ltd is now actively commercialising an ATEX certified Acoustek® system for use in the oil and gas industry.

Theory

The basis for the Acoustek® system is the observation that the propagation of acoustic waves in a fluid medium is very sensitive to any discontinuity in the properties of the fluid. To illustrate this, figure 1 shows an expansion in the diameter of a pipeline containing a stagnant fluid. If an acoustic wave is injected from the left into the pipe then it will be partially reflected at the interface, producing reflected and transmitted acoustic components. For weak plane waves of the type considered here, the waves propagate at the local speed of sound, which will vary depending upon the local conditions of the fluid. Reflective waves will occur wherever there is a change in the cross-sectional area of the pipe. In industrial pipeline systems this will occur wherever there is a valve, ‘T’ piece or blockage, for example. Further to this any leakage within a pipe will act like a change in the cross-sectional area and hence a fraction of the incident acoustic energy would be reflected.

Figure 1: Acoustic transmission at pipe joint

Results from Trials

The Acoustek® system has been trialed on long lengths of pipelines in Scotland and the USA. To assess the capabilities of the technique, Acoustek® was used to survey the pipeline training facilities operated by Petrofac Training in Montrose. A picture of this pipeline, which is approximately 1km long and 10” diameter is displayed in figure 2.

Figure 2: Pipeline layout

The Acoustek® system was able to identify a series of features in the pipeline, which were believed to be deposits of water of varying size. Figure 3 shows the reflections produced by the pipeline and figure 4 shows the locations of features that were identified in the pipeline.

The large peak in figure 3 indicates a full blockage of the pipeline, while the smaller peaks indicate partial blockages. Careful analysis of the reflected signals showed that secondary and tertiary reflections were detectable, suggesting a range of approximately 10 km of this technique.

In a recent trial on an offshore installation, Acoustek® was able to survey a section of gas pipeline and correctly identify and locate a near complete blockage approximately 500m from the host platform (for further details of this see: UMIP News).

For further details of this technology there is a paper available here or you can contact Professor Barry Lennox at the University of Manchester.

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