Guided Wave Pipe Screening
The Wavemaker G3 Pipe Screening System uses guided waves to screen long lengths of pipes for corrosion or cracks. Conventional ultrasonic testing such as thickness gauging uses bulk waves and only tests the region of structure immediately below the transducer. Therefore, it is an extremely slow process to scan a large structure and it is frequently necessary to resort to testing at a grid of points and hoping that they are representative of the whole structure.
However, even this strategy breaks down when part of the structure is inaccessible because it is either buried or covered in insulation. It is much more attractive to be able to screen a large area of structure from a single transducer location, and this is possible using guided waves which propagate along the structure.
The Wavemaker G3 Pipe Screening System uses special arrays of transducer elements, referred to as rings, which fit around the pipe under test. After a ring has been fitted around a pipe, the operator uses the Wavemaker system to perform a single test that screens a number of meters of pipe on either side of the test location. The length of pipe that can be effectively screened on either side of the test location in a single test depends on numerous factors and typically ranges from several tens of meters for pipes in good condition down to a few meters for pipes in poor condition or with certain types of coatings.
In order to understand how the Wavemaker system works, the whole ring of transducer elements may be regarded as behaving like a conventional ultrasonic transducer operating in pulse-echo mode. The ring sends out a burst of ultrasonic guided waves and then listens to signals that are reflected back. Figure 1.1(a) shows a schematic diagram of the ring of the Wavemaker system operating on a typical pipe that contains an assortment of features around the test location.
A schematic of the corresponding results are shown in figure 1.1(b). The Wavemaker system is composed of three primary components, labelled in 1.1(a) as the transducer ring, the Wavemaker instrument, and the controlling computer. The transducer rings are specific to a certain pipe size. They use either springs or air pressure to dry couple piezoelectric transducer elements to the pipe being inspected. Internal circuitry allows each transducer ring (and therefore the diameter of the pipe being tested) to be automatically detected by the electronics. All of the signal generation and detection is housed in the Wavemaker G3 instrument, which operates from an internal rechargeable battery and is connected to a standard laptop PC via a USB connection.
The control of the instrument as well as the signal processing and report sheet generation is done via the Wavemaker WaveProG3 software (although when access is limited, the Wavemaker G3 instrument can collect data independently).
Figure 1.1: Schematic diagram showing the major components of the Wavemaker G3 system in atypical test configuration.
Figure 1.2: Schematic diagram showing the clearance that is normally required around a pipe.