Commonly used NDT methods include:
- Ultrasonic Testing (UT): Used to detect delamination, inclusions, and other internal discontinuities. UT uses a piezoelectric probe connected to a flaw detector, which in its most basic form is a pulser receiver and oscilloscope display. The transducer is passed through the object being tested, to which it is usually coupled by a gel, oil, or water. This couplant is required to effectively transmit the acoustic energy from the transducer into the part, but is not required when testing with non-contact techniques such as electromagnetic acoustic transducers (EMAT) or laser excitation.
- Radiographic Testing (RT): Used to identify weld defects, porosity, and other defects within the pipe wall. In radiographic testing, the test part is placed between a radiation source and film (or detector). Differences in material density and thickness of the test part will attenuate (i.e., reduce) the penetrating radiation through an interaction process involving scattering and/or absorption. The absorption differences are then recorded on film or electronically.
- Magnetic Particle Inspection (MPI): Effective for detecting surface and near-surface defects such as cracks and seams. The technology works by inducing a magnetic field in the component being tested. If a surface or near-surface defect is present, the magnetic flux becomes distorted and "leaks" around the defect. By dusting with fine magnetic particles such as ferrous shavings (either dry or suspended in a liquid), the particles will be attracted to the area of flux leakage, creating visible signs of the defect.
