A closer look at the interior
Both ultrasound and x-raying are approaches suitable for gaining a non-destructive insight into the component. At Lufthansa Technik Engine Services, both of these procedures, and also eddy-current testing, are employed to supplement fluorescent penetrant inspection and magnetic particle inspection. Mostly they are used to clarify a suspicion which might exist, prompted by the wealth of experience of the specialist technicians with the components and their "weak spots". Which procedure will produce the best information in a given case depends on the location, nature and form of the suspected defect.
Ultrasound measurement entails taking remote measurements above the familiar speed of sound. In the course of this, a sound pulse is emitted by an ultrasound probe, known as a modulator, which penetrates the component through a contact liquid and is reflected by the opposite surface. The signal received is displayed on the measuring device. When calibrated with the speed of sound, it shows the distance directly. If the sound pulse should now hit a pore in the material, it is immediately reflected by this. These signals get back to the receiver faster than the return pulses, as the distance which has to be covered is shorter. They are then visible on the monitor before the deflection which represents the return echo.
Any abnormalities in the material which run parallel to the sound waves are not recognized by them. To ensure that they are still found, the pulse is also transmitted at 45º and 60º angles to the left and right of the vertical as well. This enables the location of an already detected abnormality to be defined in greater detail. Ultrasound measurement offers the possibility of determining the thickness of a component or the strength of a remaining thick wall. It is also used to check welding seams.
X-Raying: The negative shows weak spots
Like ultrasound, x-raying is one of the older test methods. This technology is used to detect cracks, pores and foreign matter which has been left behind in the material during work.
X-raying has the advantage that the x-ray film constitutes a durable form of documentation. The gamma or x-ray radiation penetrates the material and is deflected by different characteristics in different ways. If a component made of titanium, aluminum or steel alloys contains a defect, the rays are absorbed less at those places, causing the negative of the film to be darkened there. If the rays are only bent, this allows analysis of the material structure. The radiation time depends on the thickness and density of the material and is normally between 30 and 120 seconds. The primary features that one is looking for are welding defects, pores and inclusions of heavy metals following repairs.
In the Lufthansa Technik engine shop the radiation is generated using a tube which takes x-ray pictures in a chamber with the legally prescribed, extensive protection. The film is taken to a developing machine and the results can be detected on a classic photographic negative. Evaluation of the negative is performed by a specialist technician with the highest level of qualification.