Guided waves are mechanical stress waves that propagate contained within the structural boundaries of pipes or plates with wavelengths that are comparable to the thickness dimensions of the pipe or plate. Guided waves are used in rapid testing or Screening tools to detect, locate and classify corrosion defects. Large sections of piping can be quickly screened with 100 percent volumetric coverage to determine precise locations of corrosion damage. More detailed inspections can then be concentrated on the locations that are critical, thus saving money and time. These local inspections can be done using guided wave Scanning equipment or with another complementary non-destructive testing method. This approach of screening and scanning provides a cost‑effective means of ensuring that representative measurements are made over considerable lengths of piping.
The fact that guided waves can propagate over many tens of meters means that you can often inspect areas that are very costly to inspect using other methods; for example, the buried sections of road crossings or insulated pipelines. Moreover, guided wave testing can be either performed as single inspection or repeat inspections from the same location which can be used for Monitoring purposes. Different testing configurations are possible when working with guided wave testing. Typically Pulse‑Echo techniques are employed, where the same transducer system is used to send and receive the signals. Pitch‑Catch techniques use two transducer systems located a known distance apart, each transducer acting independently to capture the data sets required.
Synthetic Focusing is a development of the guided wave technology that utilizes the information from data in different clock locations of the pipe circumference. The results of this method of processing the data allows for a more accurate prediction of the defect characteristics and provides a more intuitive method of looking at the results. When using guided waves for non-destructive testing or evaluation applications, the interpretation of the resulting information must be carried out by suitably qualified and experienced engineers working to validated procedures. As part of the interpretation, calibration of the guided wave test is typically carried out by the inspector through approximation. Absolute Calibration is a patented development of GUL which facilitates precise calibration by automatically calculating the amplitude of the outgoing signal. This allows for accurate, inspector‑independent calibration, and increases the reliability of inspection by avoiding over- or under‑calling of defects. New users of the equipment find this feature particularly valuable.
Guided Wave Methodologies