TECHNOLOGIES
Long Range Guided Ultrasonics
How does it work?
In recent years much research and development work has gone into the development of techniques for the rapid screening of pipework for corrosion/erosion. This work has resulted in systems such as TeletestTM and WavemakerTM. These systems make use of low frequency guided waves to detect corrosion/erosion in pipework. A unit comprising three rings of piezoelectric transducers is clamped around the pipe and ultrasound is sent simultaneously in both directions along the pipe. Data from one particular direction is interpreted in a single test. The signal obtained is similar to a conventional ultrasonic A-scan, where the horizontal axis represents distance along the pipe and the vertical axis represents signal amplitude, which is indicative of the severity of the corrosion. Unlike conventional A-scans, the signals are displayed from three different wave modes, namely symmetrical, horizontal flexural and vertical flexural. The relative intensities and characteristics of these three signals are important in identifying different distributions of corrosion. Recent advances in the Teletest system allow focussed guided waves to be used. These allow circumferential corrosion locating and improved signal to noise ratio. Although propagation distances vary according to pipe geometry, contents, coating/insulation and general condition, it is not unusual that a range of up to 30m (100') in either direction from the transducer can be inspected. The technique is equally sensitive to internal and external corrosion, but cannot distinguish between them.
The principal advantage of this technique is that it provides 100% initial screening coverage, and only requires local access to the pipe surface (i.e. removal of a small amount of insulation) at those positions where the transducer array is to be attached. It is suitable for use on pipe diameters above 50mm (2.0") and on wall thicknesses up to 40mm (1.6").
What will it find?
Detection of both internal and external corrosion/erosion in thermally insulated, coated and buried pipework, corrosion under pipe supports and hidden welded joints, irregularities in girth weld shape.
Where is it used?
Petrochemical process pipework, oil and gas transmission lines, jetty lines and power station boiler tubes.
In recent years much research and development work has gone into the development of techniques for the rapid screening of pipework for corrosion/erosion. This work has resulted in systems such as TeletestTM and WavemakerTM. These systems make use of low frequency guided waves to detect corrosion/erosion in pipework. A unit comprising three rings of piezoelectric transducers is clamped around the pipe and ultrasound is sent simultaneously in both directions along the pipe. Data from one particular direction is interpreted in a single test. The signal obtained is similar to a conventional ultrasonic A-scan, where the horizontal axis represents distance along the pipe and the vertical axis represents signal amplitude, which is indicative of the severity of the corrosion. Unlike conventional A-scans, the signals are displayed from three different wave modes, namely symmetrical, horizontal flexural and vertical flexural. The relative intensities and characteristics of these three signals are important in identifying different distributions of corrosion. Recent advances in the Teletest system allow focussed guided waves to be used. These allow circumferential corrosion locating and improved signal to noise ratio. Although propagation distances vary according to pipe geometry, contents, coating/insulation and general condition, it is not unusual that a range of up to 30m (100') in either direction from the transducer can be inspected. The technique is equally sensitive to internal and external corrosion, but cannot distinguish between them.
The principal advantage of this technique is that it provides 100% initial screening coverage, and only requires local access to the pipe surface (i.e. removal of a small amount of insulation) at those positions where the transducer array is to be attached. It is suitable for use on pipe diameters above 50mm (2.0") and on wall thicknesses up to 40mm (1.6").
What will it find?
Detection of both internal and external corrosion/erosion in thermally insulated, coated and buried pipework, corrosion under pipe supports and hidden welded joints, irregularities in girth weld shape.
Where is it used?
Petrochemical process pipework, oil and gas transmission lines, jetty lines and power station boiler tubes.
Copyright © 2007, TWI Ltd
Information and advice are provided in good faith. No warranty expressed or implied is given regarding the results or effects of applying information or advice from the website, nor is any responsibility accepted for any consequential loss or damage.
Information and advice are provided in good faith. No warranty expressed or implied is given regarding the results or effects of applying information or advice from the website, nor is any responsibility accepted for any consequential loss or damage.
