Inspecting turbine disks - quickly and precisely with ultrasound
Testing of a turbine disk
Testing before initial operation
Turbine disks are inspected using non-destructive testing methods. On the one hand, this is justified by the economic aspect, since components in the aviation industry in particular are very cost-intensive. On the other hand, 100% inspection during production is mandatory for these highly safety-relevant components in order to protect people and the environment. This means that every turbine disk installed in an aircraft is precisely inspected beforehand for material defects using a non-destructive testing method. Typical defects are imperfections in the material such as overlaps, forging cracks, inclusions and pore nests.
Recurring inspection during maintenance
At regular intervals during their life cycle, the turbine disks are subjected to periodic inspections after flight cycles or flight hours in order to detect e.g. stress cracks in the material at an early stage and thus prevent cost-intensive or life-threatening damage. Here, ultrasonic testing is used rather rarely. Visual inspections and surface crack tests are given priority.
VOGT test center
VOGT Ultrasonics is your service provider for turbine disk testing
In our VOGT test center in Burgwedel near Hanover, we provide the production-accompanying single and series testing of your turbine disks in 3-shift operation with our large ultrasonic equipment park. We have years of experience in working for the aerospace industry and have established a fast and reliable automated inspection process for turbine disks.
VOGT Ultrasonics is certified according to EN 9100 for aviation and tests according to manufacturer standards. In addition, VOGT Ultrasonics has various special process approvals from leading engine manufacturers. These include, for example, MTU, GE and Rolls Royce. Customer-specific requirements are also met here, such as multi-zone testing, 1000Gates technology and evaluation of the signal-to-noise ratio in relation to the material structure.
Depending on the material, we can determine component defects from a size of 0.1 mm KSR (circular disc reflector). All tests are 100% reproducible due to complete documentation.
If you would like to carry out the inspection of your turbine disks yourself on site, with your inspection system, we can support you with qualified inspection personnel within the framework of an employee leasing agreement.
VOGT test center
Inspection of turbine disks with ultrasonic immersion technology
Ultrasonic testing is a method of non-destructive material testing and is suitable for detecting and precisely locating the smallest internal defects in the component. So-called ultrasonic testing systems are used for this purpose.
Sound has the property of reflecting completely or partially at interfaces. Such interfaces are transitions from one material to another or state, e.g. from steel to air. Thus, sound is also partially reflected at defects in the material, such as inclusions, pores and cavities. Ultrasonic testing takes advantage of this fact. For this purpose, a probe connected to an ultrasonic inspection system transmits sound into the material and picks up the reflections from the flaws. Simplified, this results in a so-called A-scan, which makes the interior of the material and thus also defects visible to the inspector. The sound is transmitted with the aid of a coupling agent, usually water or gel, which is applied to the component
Ultrasonic testing of turbine disks, which requires extremely high accuracy, is performed using ultrasonic immersion technology. As the name implies, the component is immersed in a water tank during immersion testing. This has the advantage that the turbine disk is now in the coupling medium (water) itself, which means that the coupling is subject to only minor fluctuations. This test setup is therefore ideal for safe and cost-efficient automation.
Fig.: Set-up of a turbine disk inspection using ultrasonic immersion technology
In the immersion tank there is a turntable on which the turbine disk is placed. This rotates the disc around its own axis. A so-called immersion probe transmits the sound through the water into the component. A manipulator is used here, which moves the probe in 5 axes (X, Y and Z axes as well as the probe axes a, b) and can thus be optimally positioned. While the turntable rotates the turbine disk along the inspection probe, the probe can be insonified over different angles. In this way, possible defects are reliably found and precisely located.
For high reproducibility and accuracy, these movements are previously stored in the test system as a fixed test sequence for serial testing and then automated. In this way, each disc is tested identically and a high level of testing reliability and accuracy is achieved.
The automated inspection and the support of the inspector by an automated evaluation proposal saves time and creates inspection reliability.
Preconditions for the inspection of turbine disks with ultrasound
Turbine disks always have a rotationally symmetrical component geometry. The surface must not exceed a certain roughness to ensure sufficient defect detectability. Greater surface roughness scatters the sound and thus ensures poor introduction of the sound into the component and thus poorer detectability of defects. As a guideline, values between 0.8µm and 2.3µm roughness can be quoted. In general, the better the surface, the smaller the defects that can be detected.
Test reports are created according to standard requirements or individually according to customer requirements. Here, there is the possibility of the graphic representation of a display or also the tabular listing with coordinates for the exact determination of the defect position. Due to the possibility of real-time data storage, it is even possible to subsequently re-evaluate, using adapted evaluation parameters, a component that is physically no longer in the test facility and has already been returned to the customer. By recording data on amplitude (return sound energy of the defect) and sound path (location of the indication), a defect can also be displayed as a 3D image. For the analysis of a defect, sectional images from different angles of incidence and positions are common.
Testing turbine disks in the VOGT test center
Is the inspection mandatory?
Certain inspections are prescribed by law by the aviation organizations. They define exactly which component must be tested, how, when and by whom. The inspectors must be officially certified for this task. Thus, VOGT Ultrasonics uses inspectors with EN 4179 Level 2 (UT-2) for the aviation industry to perform the inspection. In addition, VOGT Ultrasonics also has ultrasonic Level III(UT-III) and FPI Level III (PT-III) certified personnel according to EN4179 and is therefore also allowed to create and release inspection instructions.
The type and frequency of testing of components from the aviation industry are component-specific and depend on the loads to which they are exposed. Turbine disks are critical parts and are subject to the most stringent testing requirements.
Why are turbine disk inspections necessary?
If a turbine disk cracks during flight, splintered parts can damage the wing or fuselage, endanger human life and even cause the engine to explode. Tiny hairline cracks that are barely visible to the naked eye, or even invisible to the naked eye, can be enough to cause such damage. This is why turbine disks are subject to particularly stringent inspection requirements. Spot checks are therefore not sufficient here. All manufactured disks must undergo ultrasonic testing before they are installed.
PRO & CONTRA
Advantages of ultrasonic inspection of turbine disks
Due to its properties, ultrasonic testing is the ideal test method for turbine disks. This is prescribed by the manufacturer and standard requirements. With its help, the inspector gains a comprehensive insight into the inside of the turbine disks in a short time without destroying them.
In contrast to other non-destructive testing methods, ultrasonic volume testing, vertically and at different angles of incidence, also offers exact spatial localization of the material defects. This also makes so-called multi-zone testing possible. Here, by focusing on different component areas, the best defect resolutions can be achieved at all depths.
if there are still questions
Turbine disks are subject to the highest quality requirements, as they are subjected to high thermal and mechanical stresses during operation. That is why most turbine disks are subjected to 100% testing. This means that every turbine disk that leaves production is thoroughly tested.
At regular intervals during their life cycle, turbine disks are subjected to repeated testing (visually or using surface crack detection methods) in order to detect stress cracks in the material at an early stage, for example, and thus prevent cost-intensive or life-threatening damage.
Ultrasonic testing of turbine disks detects material defects on the surface as well as in the volume of the turbine disks, such as cracks, stress cracks, pores, blowholes and inclusions.
We stand for quality
Certified quality management for the industry
Certified quality management for the aviation industry
for the inspection of turbine disks (MTU)
for the ultrasonic testing of turbine disks in our testing center in Burgwedel (Hanover, Germany)