A large number of Non-Destructive Techniques (NDT) have been developed and successfully used over the past decades for the detection of surface breaking flaws in various materials, such as: cracks, pitting, corrosion, etc. Those are more or less sophisticated, but all provide valuable information on the integrity of the component being inspected, and come with specific advantages and limitations.
Established methods such as penetrant testing (PT) and magnetic particle inspection (MPI) are effective but can lack practicality in some applications. Others, such as conventional eddy current inspection technique (ECT) mainly deploy single element probes resulting in protracted inspection times. Results are also typically greatly affected by operator’s skills, material properties and geometry.
Advances in electronics enabled the development of more modern inspection techniques like Eddy Current Array (ECA), increasing the reliability of surface inspection over traditional methods. Indeed, being able to tailor coil designs and multiplexing patterns allows users to optimize the acquisition chain to their specific application. Moreover, by multiplexing and leveraging advanced data processing capabilities, ECA solutions allow inspections to be carried out quickly, often with less surface preparation. They also provide additional benefits such as state-of-the-art imaging (e.g. 2D and 3D C-Scan displays), improved surface coverage, ease of deployment and data archiving. Finally, on top of defect detection, ECA technology can also provide quantitative sizing.
This paper describes the eddy current array method along with variations on the theme, inclusive of their benefits and limitations. The deployment of ECA on real components, subject to representative field conditions is also discussed. Typical applications are presented, providing valuable insights on the use of ECA in lieu of more conventional techniques.
There are often inspection challenges regarding attenuation, geometry or limitation due to obstacle of testing valve connection welds in nuclear power plants. This can also be the case of other components in certain material not suitable for UT and requirements to inspect the media surface. There are also high doses in these areas that makes a efficient mechanized system necessary. DEKRA has developed a system using qualified mechanized Dye Penetrant technique. The manipulator, named Bläckfisken, uses special arms with rails to apply the DPI tool to the inspection area. The manipulator follows a predefined trajectory that is unique for each valve. New valve trajectories can be generated and tested offline in the control software.
The NDT system is currently in use for periodic in-service inspection at Forsmark 3 BWR. The system is qualified by the Swedish Qualification Body and fulfilling the demands in Sweden and ENIQ. The arms is developed to fit into many different valve types and manage very small valve openings and long distances from the mounting of the manipulator to the weld. There are many challenges regarding DPI technique with small spray nozzles and small camera systems working around obstacles etc. This new generation of manipulators is also prepared for full inner surface DPI inspection of the pipe surface.
The LED-Technology is strongly substituting the conventional bulb based UV source (Mercury-Vapor, Xenon and Metal-Halide) in the fluorescent NDT methods in all industries.
The NDT industry is getting more and more aware that the quality and characteristics of the LED UV lamps is essential to ensure at least the quality and performance of the inspection process as when using a 100W Mercury vapor lamp. There are also made big efforts by the Aerospace industry to explain the need and the technical background to the users in parts manufacturing.
A new and more restrictive Aerospace manufacturer standard has been released in the Aerospace industry that ensures adequate quality of the LED UV sources for mag and pen. It also requires that the user takes care about the proper function during the usage of LED UV sources on a regular basis.
The presentation will give an overview of the requirements and characteristics that came up, will explain the technical need of those to ensure a secure and reliable inspection process and will explain the new parametrization that has been established to describe easy and understandable the characteristics of LED UV sources for easy selection and good practical use of LED UV sources.
Successful implementation of damage tolerant (DT) methodology for aero-engines requires reliability estimation of various NDT techniques. Probability of Detection (POD) being a standard metric for measuring the NDT reliability is usually established with the help of huge number of service expired aero-engine components containing several fatigue cracks. However, morphology of cracks, a factor effecting POD, is also dependent on the in-situ microstructure present in a service expired component. Therefore, considering the POD value generated using a service expired component for estimating safe inspection limit is conservative in nature. For example, eddy current technique is dependent on electrical conductivity of material which is in-turn dependent on microstructural degradation. Hence, it is essential to understand the relation between POD of NDT technique and in-situ microstructure degradation. It is also understood that not all NDT techniques POD are effected by microstructural degradation. Therefore, in the current study, an attempt has been made to understand the effect of service induced microstructure degradation in aero-engine components on POD studies. Accordingly, samples with representative geometric stress concentration factor of a typical bolt hole in a turbine disc were prepared from a mid-life service expired aero-engine turbine disc. These samples were subjected to thermal degradation under laboratory conditions. Further, all the samples were subjected to 3-point bend compressive-compressive fatigue testing at a constant load, stress ratio (R = 0.1) and constant number of fatigue cycles. Natural fatigue cracks generated on these samples under laboratory conditions were inspected using qualitative and/or quantitative NDT techniques. This paper discusses the variability associated in the POD or a90/95 (flaw detection with 90 % probability and 95 % confidence) values with respect to the service induced microstructure degradation. A comparison will be drawn between the POD curves generated using mid-life and further service exposed samples to understand the effect of microstructure degradation.
In a first example a semi-automated highly flexible system is described which can be used for a broad variety of components. Cast workpieces for power generation in varying sizes and geometries were specified in the duty book. It should be possible to use optionally two fluorescent penetrants of different sensitivity. During the whole inspection process the components are placed in baskets and are pushed manually from station to station. The pneumatic lowering and lifting of the baskets at each station is automated. Each step of the process is started via pushbuttons and is then executed automatically. This ensures the reproducibility of the test results. Because of the broad spectrum and the sometimes only low number of workpieces, the process steps for penetrant removal and developer application are designed as manual stations. This enhances the flexibility of the whole system in view of future workpieces.
The second example describes a fully automated system, optimized for maximum throughput with a high level of automation and low testing costs per workpiece. Stainless steel forgings for the automotive industry shall be tested with high sensitivity for surface cracks. At the loading station the components are placed in workpiece holders that are optimized for the components geometry. Once the workpiece holder is inserted manually the system takes over control of the transport for the entire testing line.
A third example shows a large semi-automated testing system where an oval crane runway is used for the workpiece handling.
Supervisors using MT and PT-consumables in their area of responsibility are well advised to consider the use of chemicals with the lowest possible impact to the work safety, the environment and the overall process costs. The REACH-legislation is fully in force and the new labelling regulation CLP has to be applied as well and brings an additional pressure to this situation. Leading manufacturers of NDT consumables have modified their products in order to match these requests without influencing the technical performance. Pfinder is going one step further and started an approach to improve the general NDT process sustainability by the campaign GREEN NDT. For the sake of the work safety more and more products are free of hazardous ingredients and therefore free of any hazard labeling. Completely biodegradable products and a carbon footprint evaluation of widely used NDT consumables help to optimize the environmental impact. Several measures can reduce substantially the NDT process costs. This enables the users of magnetic particle and penetrant testing consumables to make decisions not only based on purchasing costs. The improvement of the work safety and the environment protection can now be taken into consideration better than ever before. For standards-compliant and future-save NDT processes.