Turbine engine components are put under a great deal of stress at varying temperatures and pressures. During operation, engine components can experience wear and tear that is not visible under normal circumstances, such as very small surface or subsurface discontinuities that may lead to catastrophic failures over time. Discontinuities are also sometimes created during repair processes and maintenance activities. It is important to find these potential defects without damaging components. The industry term for these inspections is “non-destructive testing,” or NDT. CRT performs various types of NDT processes including Fluorescent Penetrant Inspection (FPI), Magnetic Particle Inspection (MPI), Pressure Test, Ultrasonic Inspection, Eddy Current Inspection, and X-Ray.
Fluorescent Penetrant Inspection (FPI) is a type of dye penetrant inspection where fluorescent dye is applied to the surface of a non-porous material in order to enhance detection of small surface discontinuities. Noted for its low cost and simple application process, the FPI process is commonly used to find defects in turbine engine components, and is used on most components repaired by CRT.
Magnetic Particle Inspection (MPI) detects surface and subsurface discontinuities in ferrous materials. After applying an electrical current, a magnetic field is created in the component. Discontinuities disrupt the magnetic pattern and attract fluorescent magnetic particles that are applied to the part while suspended in fluid, making them visible under a black-light.
X-Ray is a “volumetric” inspection designed to give the inspector access to subsurface areas of the component, similar to medical radiography. X-Ray is excellent at finding discontinuities generated during welding processes. While X-Ray can find subsurface defects that other NDT methods cannot find, X-Ray is not as effective for small surface defects and is usually required along with surface inspections such as FPI, MPI, and visual inspection.