Non-Destructive Testing prevents the risk of material flaws by analyzing its remaining lifetime against the existing defects. NDT can accurately pinpoint fractures in a system to enhance the safety of the equipment and the technicians. It is safe, repeatable, and possible to merge with several tests, to find flaws before it is too late for repairs.
NDT is also a more cost-effective way to carry out gas turbine inspections than conventional destructive testing. If the application of the technique is judicious, it can prevent accidents and give technicians some peace of mind.
There are several gas turbines testing techniques designed to meet your inspection demands.
Fluorescent Dye Penetrant Inspections
Fluorescent Dye Penetrant is a form of test that involves the application of fluid onto the surface. The fluid can detect flaws such as hairline cracks, leaking, and fatigue.
The FDP test is suitable for inspecting blades, discs, and any other accessible components. The fluorescent dye has a bright color, which makes it easier to spot defects on various parts of gas turbines.
It performs better than the other LPT techniques. The fluorescent dye reacts with ultraviolet rays, creating a sharper contrast that can highlight the smallest defects. The flaws can be seen under artificial light, but for the best results, operators inspecting turbines should use UV radiation.
The main limitation of FDP is that it is meant for porous surfaces only. For non-porous or inaccessible parts, other methods such as MPT and Ultrasonic can be applied in combination with FDP.
Magnetic Particle Testing
Operators can examine the blades, discs, and other ferromagnetic materials on gas turbines using a magnetic flux. In MPT, particles are applied onto the surface before inducing a magnetic field. If the metal has an inconsistency, it will let the flux through, and the particles will move to that region.
The magnetic field pulls the particles to an area where there is a leak or crack, indicating the location and size of the defect. The flux can be directed through or around the material, without the need for parts removal. MPT can generate high-intensity magnetic waves, improving the accuracy of the inspection.
Ultrasonic tests can detect both surface flaws and defects at certain depths. A transducer produces and projects the wave to the relevant parts. It uses high-frequency waves ranging from 1 MHZ to 25 MHZ for checking sub-surface defects on the gas turbines.
For greater depths, the transducer is brought closer to the part. It generates Rayleigh Waves on the surface, and they can be picked up through one of the following methods:
- Attenuation: It shows how surface inconsistencies disrupt the waves.
- Timing: By recording the time it takes for the signal to move from one side of the part to the other.
One of the important limitations of UT is that it cannot be effective for parts that have a complex profile. With such materials, it is difficult to determine whether the wave inconsistency is from the defects, or is as a result of the form of the component.
Borescope Turbine Inspection
A Borescope is a hand-held optical tool that is used to examine tight spaces and the inside of machinery or equipment. The tool may have an eyepiece or miniature camera on one side, and a display on the other end.
Borescope inspection of gas turbines is particularly useful in situations where the part is not accessible. The latest developments in robotics, AI, and video applications, have enhanced its ability to detect the finest of cracks. The technique can aid in parts retrieval even in difficult-to-reach areas of the engine.
Several Non-Destructive techniques are common when it comes to gas turbine testing. Operators choose the best method based on several factors, such as ease of application, and its capacity to detect deeper flaws. All in all, NDT techniques can reduce the number of resources, and time taken during the inspection of gas turbines .