Channel consistency calibration of planar eddy-current sensor arrays

Planar eddy-current sensor arrays have several advantages such as good coherence, fast response speed and high sensitivity, which can be used for defect inspection of crucial parts in mechanical equipments, and a key point to improve the detection performance is to ensure the channelconsistency of the planar eddy-current sensor arrays. The principle and characteristics of planar eddy-current sensor arrays are introduced in this paper, andthe channel consistency calibration algorithm is investigated based on least squares principle. An experimental system was established based on a field programmable gate array (FPGA) and ARM processor, which was utilized to inspect the defects in aluminum alloy. Based on this system, the channel data before and after calibration are analyzed, and the detection effect of three artificial defects is compared when the sensor channel calibration is implemented or not. The experimental results show that the sensor has excellent channel consistency and repeatability after calibration. The detection results of the three defects with size of 5 mm (length) x 0.1 mm(width) x 1 mm (depth), 7 mm (length) x 0.1 mm (width) x 1 mm (depth), 9 mm (length) x 0.1 mm (width) x 1 mm (depth) respectively show that the calibration algorithm has greatly improved the performance of the system.

Implementation of a robust methodology to obtain the Probability Of Detection (POD) curves in NDT: integration of human and environmental factors for Eddy Currents (EC)

In aeronautics, the evaluation of the Non-Destructive Testing (NDT) methods is a key step in the aircraft’s maintenance program. Nowadays, this calculation is performed by a statistical study taking into consideration the sources of uncertainty inherent in the applied NDT method. These uncertainties are due to human and environmental factors during In-Service maintenance tasks. The POD curve is carried out by an experimental process, where a wide range of inspector skills, defect types and locations, material types and procedures are included. At this moment, this experimental process evidences high costs and time consuming for the aircraft manufacturer.
The objective of this paper is to define a methodology of building POD from numerical modelling. The POD robustness is ensured by the integration of the uncertainties through statistical distributions issued from experimental data or engineering judgments. Applications are provided on titanium beta using High Frequency Eddy Currents (HFEC) NDT technique.
First, an experimental database will be created from three environments: laboratory, A321 and A400M aircrafts. A representative sample of operators, with different certification levels in NDT technique, will be employed. Multiple inspection scenarios will be carried out to analyse these human and environmental factors.
This database is used, subsequently, to build statistical distributions. These distributions are the input data of the simulation model. A POD module, based on the Monte Carlo method, is integrated to draw a sampling. This module will be applied to address human influences on POD. Additionally, this module will help us to state the device impact in POD curves.
Finally, the simulation POD model will be compared and validated with the experimental results. Numerical results encourage to replace or complete experimental campaigns in future works.

Numerical and experimental investigation of eddy current thermography technique on metallic samples

Current and future industry requirements demand advances in NDT. Fast and efficient methods and techniques for defect detection and characterization would be one of the main focus thus improving inspection results. Eddy current thermography is an emerging advanced NDT technique which combines the well-established eddy current testing with thermography inspection. It uses induced eddy current to heat the sample being inspected and defect detection is based on the changes of the induced eddy current flows revealed by thermal visualization over a relatively large area captured by an infrared camera. This work presents the results from 3D FEM simulation and experimental investigation of eddy current thermography on defects in metallic samples. The underlying phenomena of eddy current thermography testing are explored through the simulation which provides the explanation and reasoning of results. Experimental validation and investigation offers an insight to its potential for industrial application. The work demonstrates the effectiveness of eddy current thermography in providing comprehensive and reliable defect assessment.

Micro and macro microstructure modelling for the influence of grain size on magnetic properties in structural steel and modelled commercial sensor outputs

The mechanical properties of steels are controlled by their microstructural parameters, such as grain size, phase balance and precipitates, which are developed during thermal mechanical processing. It is desirable to be able to monitor microstructural changes during processing, allowing in-situ feedback control, or to characterize microstructure in steel products in a non-contact and non-destructive manner. Electro-magnetic (EM) sensors are now widely employed in the steel industry, for example to monitor phase transformation during strip cooling (EMspec) and strength in cold rolled strip (IMPOC, HACOM, 3MA), where a combination of empirical correlations and fitted models are used. Models have recently been developed to relate the sensor signals to magnetic properties and, separately, to relate magnetic properties to microstructure.
In this work an ultra-low carbon steel sample was used to generate ferrite grain sizes between 2.5 – 80 µm. EBSD data was used to generate 3D voronoi based microstructure models representing the grain structures, which have been used in multi scale magnetic modelling approaches to predict the magnetic properties. Both micro (EMicroM) and macro (COMSOL Multiphysics based) scale models have been developed and applied to determine magnetic hysteresis curves and low field permeability values. These have been compared to experimentally determined hysteresis curves and magnetic parameters. The modelled and, where available, measured magnetic data have then been used in EM sensor (IMPOC, 3MA and EMspec) models to determine sensor sensitivity to grain size measurements.

Characterization of materials by non-destructive methods

Non-destructive testing can detect defects in structures (welding defects, fatigue cracks, etc.). When characterizing or evaluating the structural or mechanical properties of materials, it is often destructive means that are used in industry (Micrographic cutting, hardness measurement, X-ray diffraction with removal of material, etc.).

The development of non-destructive methods to replace destructive methods is a key activity in CETIM’s missions to mechanical companies. Among NDT methods, some are particularly useful in meeting these needs. For metals, two families of methods are of great interest: ultrasonic methods and electromagnetic methods (eddy currents, ferromagnetic noise, combination of several methods).
We present below some of the applications in this area.
The presentation will cover various applications recently developed at CETIM:
• Characterization of the depth of thermal or superficial thermochemical treatment
• Sorting of parts according to microstructure and phases
• Assessment of applied or residual stresses
• Detection of grinding burns
• On-line monitoring of sheet quality before and after stamping

Reference blocks generated by laser treatment for grinding burn inspection

Grinding burn is defined as a result of unintentional heat impact during processing of hardened steel surfaces such as claimed surfaces of gear parts. Depending on heat intensity local tempered zones or re-hardened zones are generated. The occurrence of grinding burn within the production process is a risk for the safety of the components. Different test methods are applied to verify grinding burn. Surface temper etching (STE) is the most commonly used method for detecting grinding burn up to now. It is the only standardized testing method (ISO 14 104:2014). However, industrial automation of this method is limited and the evaluation of etched parts is performed visually by an operator. For this reason, non-destructive methods are of high interest as they allow reproducible detection of grinding burn without influence of human factors. The 3MA-methode, the Barkhausen noise analysis and in recent times, eddy current testing are already applied.
Components with defined defects of different characteristics are required for the evaluating of non-destructive test methods as well as for STE according to ISO 14104. Generation of reproducible grinding burn on components cause problems regarding to size and depth of the influenced area. An alternative is the generation of artificial defects. Artificial defects have to be fabricated reproducibly in size, location and intensity and they have to show similar physical behavior like real defects.
Experiences and results of manufacturing and assessment of reference blocks with artificial defects generated by laser treatment for grinding burn detection are presented. The artificial defects meet the requirements mentioned above and may be used for non-destructive testing methods as well as for STE. The reference blocks are used for calibration of the test equipment, especially the required test sensitivity. In addition, reference blocks are applied in certain intervals within the process in order to guarantee testing reliability.

Off-centering robust calibration of Eddy Current Array Probe used in Power Plants Steam generators

The Eddy Current examination of Nuclear Plants steam generator tubes is a very demanding process. Challenges include: high number of tubes (5000 per steam generator), small flaws and complex signal analysis, data to be reviewed quickly with precision and accuracy… The tubes are made of Inconel alloy 600TT, with outside diameter 19.05mm (3/4’’) and width 1.09mm: the flaws looked upon can be cracking, thinning, corrosion buildup… To keep up a good tradeoff between accuracy and speed inspection, EDF started using an inside tube array probe which consists of 32 pancake coils (16 on the circumferential and 2 rows of coils in the axial direction). The outside diameter of the probe is 15.5mm (0.61”).
In EDF standard, each steam generator tube is inspected in line with a calibration tube containing artificial flaws allowing for standardization of probe signals and checking of its functionality. The array probe being an emitter to receiver type of probe, it is sensitive to off-centering, specially with probe ageing. A typical solution to limit off-centering effect on the calibration phase is to use two different calibration flaws: 30% outside groove for amplitude setup and dimensional variation for phase setup.
In this paper, we present signal processing algorithms improving calibration with a probe affected by off-centering effects. We start by exploring the cyclic noise related to off-centering on a flawless part of the calibration tube to derive a robust estimator of the average electrical mean. Then, we compare two adaptive filters allowing simultaneous amplitude and phase calibration while minimizing the cyclic noise contribution. Both filters are based on assumptions on the noise phenomenon: the first one assume it to be sinusoidal while the second takes a broader physical model. Results of filtering are evaluated on the probe signal over other calibration tube flaws.

Characterization of an Aluminium Alloy Aircraft Component using Eddy Current Testing

Aircrafts are very important mode of transport and as a result they need diligent care when manufacturing them. To maintain optimum quality and reliability, inspections in critical areas and maintenance of aircraft structure is crucial. Any presence of unwanted alloys may result in fatal accidents. Due to the manufacturing processes involved, high possibilities exist that in-service defects may occur.

The constituting elements of this aluminium alloy aircraft component will be determined using the positive material identification (PMI) to establish its aluminium alloy series. The presence of defects is determined by using Eddy Current Testing method which is based on electromagnetism. The eddy current flowing through the material enables the probe to detect the conductivity of the component.

The results obtained clearly show presence of defects in the aluminium aircraft component and the aluminium alloy series has been established. Various elements were found in an aluminium alloy aircraft component. Some undesired element were detected but they were at a very low level which cannot have an effect on the operation of the aircraft.

Analysis of the spectra of a multi-frequency electromagnetic sensor to determine the magnetic permeability of steel strip

Multi-frequency electromagnetic sensors, such as EMspec, are now being used to non-destructively inspect the properties of strip steel on-line during industrial processing. These sensors measure the relative permeability of the strip during process operations such as controlled cooling and the permeability values are analysed in real time to determine important microstructural parameters such as the transformed fraction of the required steel phases. These parameters are critical to achieving the desired mechanical properties in the strip product.
The inductance spectra produced by the sensor are not only dependent on the magnetic permeability of the strip, but is also an unwanted function of the electrical conductivity and thickness of the strip and the distance between the strip steel and the sensor (lift-off). The confounding cross-sensitivities to these other parameters must be rejected by the processing algorithms applied to inductance spectra.
The paper considers cross-sensitivity of the complex EMspec spectra to the four variables, permeability, conductivity, thickness and lift-off. The paper then goes further to consider the solution of the inverse problem of determining unique values for the four variables from the spectra. Both the finite element method and the Dodd and Deeds formulation are used to solve the forward problem during the inversion process. Results from an industrial scale EMspec sensor are presented including the effects of noise. The results are backed up with measurements of selected cases.
The results are significant because they show for the first time that the inductance spectra can be inverted in practice to determine the key values for the thermal processing of steel strip.

Operation analysis of eddy current and ultrasonic methods in defect detection of weld seam of high frequency electric resistance welding gas pipes

Quality control is the main way to reach desired quality in production processes according to service condition that involves destructive and nondestructive tests. Electromagnetic and Ultrasonic nondestructive technologies are important methods in this point of view to achieve material properties, component tests in production line and semi-finished products; also the advanced new tools and appliances are used to flaw assessment of in service parts in practical condition for RBI and FFS evaluations that are argued in API 579, 580 and 581 standards.
In the other hand in all manufacturing and production methods, quality is major principal for lucre gain. Here we use eddy current and ultrasonic tools with high accuracy and high performance speed to assure optimum efficiency with no influence in practical properties of line pipes; hence this article compare both Phenomenon and physical properties of them to evaluate the applicability of new proposed instruments as a nondestructive test for defect detection and flaw assessment of HF ERW weld seam in gas pipes mill.
Acquaintance and description of HF ERW manufacturing procedure specification as the main method in gas and petroleum steel pipe production is followed by two test software and hardware conditions for quality control system. Final part is abbreviation of advantages and restrictions that are mentioned in practical specially usage of this technology in assurance systems for steel pipeline inspection. The results of this essay have been propagated based on quality control system and production lines of five gas and petroleum pipe mills and more than 10 years gas pipe production experiments and related optimum quantities for calibration of equipment have been used.