Magnetic NDT Research Articles

USE OF MAGNETIC NON-DESTRUCTIVE TESTING TO EVALUATE THICKNESS OF CONCRETE PROTECTIVE LAYER FOR ENCLOSING AND BEARING STRUCTURES AT NPP

Introduction. This article discusses methods and means of controlling the diameter and position of reinforcement and the thickness of the concrete protective layer, along with the contemporary techniques and devices for diagnostic and non-destructive testing of concrete. A comparative analysis of the applicability of contemporary devices was carried out.Aim. In this work, magnetic non-destructive testing was used to assess the thickness of the concrete protective layer, along with establishing the location of the upper row of rod reinforcement and embedded parts. Based on analyzing the interaction between the electromagnetic field of the sensor and the electromagnetic field of eddy currents induced by the source coil of the sensor in rebar, this method allows the diameter of the latter to be approximately estimated at an unknown protective layer.Materials and methods. As an example, the thickness of the concrete protective layer of enclosing structures (walls, floors) at power unit № 1 at the Kalinin Nuclear Power Plant (NPP) was measured using the POISK-2.6 device.Results. The analysis of design and as-built drawings for buildings and structures of the main facility of power unit № 1 at the Kalinin NPP was carried out. The state of passive fire protection equipment at the power unit (fire doors, cable penetration seals, and ventilation fire dampers) was evaluated. The actual thickness of the concrete protective layer and the location of the reinforcement of concrete elements at the facilities of the Kalinin NPP power unit were measured as per GOST 22904-93 using electromagnetic NDT. The applicability of the magnetic NDT for determining the thickness of the concrete protective layer was shown during the inspection of building structures.Conclusions. During the inspection of the facilities, it was established that the average thicknesses of the concrete protective layer, including the thickness of the reinforcement, range from 38 to 85 mm, with the diameter of the reinforcement of 12–20 mm. During the measurements, the applicability of the method was shown; it was also confirmed that the examined structures exhibit fire endurance of at least 90 minutes, which meets the requirements of regulatory documents.

On the use of differential permeability and magnetic Barkhausen Noise Measurements for Magnetic NDT Applications

Mapping microstructural to macroscopic magnetic properties is challenging yet necessary for the development of novel non-destructive testing techniques based on magnetic measurements. The macroscopic properties of a material reflect the underlying magnetization processes and the microstructural configuration as a result of the history of the material. Magnetic nondestructive evaluation techniques are needed for the health monitoring in critical structures and the quality monitoring of materials used in components, such as transformers and motors. In this work, we assess the usability of metrics related to AC magnetometry and magnetic Barkhausen Noise through measurements on several series of samples of various grain sizes and levels of plastic deformation. AC magnetometry is preferred to magnetic Barkhausen Noise as it provides more repeatable and reliable metrics than mBN which suffers from higher uncertainty. Also, differential permeability curves are preferred to hysteresis loops because they can be obtained directly through ac magnetometry and provide several types of information, such as the peak value, the coercivity, the overall shape, the emergence and location of multiple peaks which are related to stresses. In the case of stress-dependent magnetization processes, both differential permeability and mBN results are consistent, regardless of the way strain is applied, and corroborate results previously reported. However, permeability measurements are inconclusive on the effect of grain size on magnetization processes while the mBN voltage increases monotonically with decreasing grain size, in both types of samples. The mBN energy associated with each applied field step is proposed as a complementary measure for the assessment of the contribution of the irreversible processes in a material where the permeability measurements are inconclusive. Finally, the experimental observations have been used to set up micromagnetic calculations by modeling a plastically deformed material as a soft matrix with grains enclosed by boundaries with high transverse anisotropy which act as pinning centres and prevent further rotation of the magnetization and its alignment with the applied field thus reproducing the typical phenomenological features of plastically strained materials.

Key Factors for Implementing Magnetic NDT Method on Thin UHPFRC Bridge Elements.

This paper provides an overview of the use of the magnetic NDT method for estimating the fibre content, and fibre orientation and efficiency factors in thin UHPFRC elements/layers, along any two orthogonal directions. These parameters are of utmost importance for predicting the post-cracking tensile strength in the directions of interest. After establishing meaningful correlations at the lab-specimen scale, this NDT method can be effectively implemented into quality control protocols at the industrial production scale. The current study critically addresses the influence of key factors associated with using this NDT method in practice and provides recommendations for its efficient implementation.

Steel Rope Diagnostics by Magnetic NDT: From Defect Detection to Automated Condition Monitoring

Today it is hard to imagine an industry or an application that uses steel wire ropes in which the application of a magnetic flaw detector would be unsuitable. The ropes of loading cranes, mine hoists, ropeways, cable-stayed bridges, flare stacks, antenna masts, overhead power transmission lines, and other installations are not only subject to regular inspections (Sukhorukov and Mironenko 2003; Kotelnikov and Sukhorukov 2006; Sukhorukov et al. 2014), but the appropriate guidelines for these rope types are now described in industrial standards such as the International Organization for Standardization (ISO) standard for crane ropes, ISO 4309 (ISO 2017); the European Standards (EN) standard for ropeways, EN 12927 (BSI 2019); and the International Marine Contractors Association (IMCA) standards for offshore ropes, IMCA LR 004, IMCA HSSE 023, and IMCA M 197 Rev.1 (IMCA 2018). This paper examines how magnetic flux leakage testing (MFL) is used as the basis for an automated wire rope condition monitoring system, in which the human factor is completely removed.

Effect of sample initial magnetic field on the metal magnetic memory NDT result

One of the major concerns regarding the use of Metal Magnetic Memory (MMM) technique is the complexity of residual magnetization effect on output signals. The present study investigates the influence of residual magnetic field on stress induced magnetization. To this end, various initial magnetic fields were induced on a low carbon steel sample, and for each level of residual magnetic field, the sample was subjected to a set of 4-point bending tests and, their corresponding MMM signals were collected from the surface of the bended sample using a tailored metal magnetic memory scanning device. Results showed a strong correlation between sample residual magnetic field and its corresponding level of stress induced magnetic field. It was observed that the sample magnetic field increases with applying the bending stress as long as the initial residual magnet field is low (i.e. <117 mG), but starts decreasing with higher levels of initial residual magnetic fields. Besides, effect of bending stress on the MMM output of a notched sample was investigated. The result, again, showed that MMM signals exhibit a drop at stress concentration zone when sample has high level of initial residual magnetic field.

Hydrogen Embrittlement and Fatigue Fracture of a Crankshaft of an Internal Combustion Engine

A trainer military aircraft, equipped with alternative internal combustion engine, experienced an overspeed during preflight operations. In the aftermath, maintenance personnel performed magnetic particles NDT and found two cracks on the crankshaft. These were located at the front support of the part and were both about 46 ÷ 48mm long. The crankshaft is a critical item for the engine and in order to prevent other similar incidents a technical investigation took place. Therefore, this report shows the results obtained by fractography, metallographic, chemical analysis and numerical simulation: the root cause of the cracks was the embrittlement of material due to an excessive hydrogen content. This made possible a fatigue fracture mechanism under normal operative cyclic loads.

Design of an expert system based on neuro-fuzzy inference analyzer for on-line microstructural characterization using magnetic NDT method

Abstract Tracing microstructural evolution has a significant importance and priority in manufacturing lines of dual-phase steels. In this paper, an artificial intelligence method is presented for on-line microstructural characterization of dual-phase steels. A new method for microstructure characterization based on the theory of magnetic Barkhausen noise nondestructive testing method is introduced using adaptive neuro-fuzzy inference system (ANFIS). In order to predict the accurate martensite volume fraction of dual-phase steels while eliminating the effect and interference of frequency on the magnetic Barkhausen noise outputs, the magnetic responses were fed into the ANFIS structure in terms of position, height and width of the Barkhausen profiles. The results showed that ANFIS approach has the potential to detect and characterize microstructural evolution while the considerable effect of the frequency on magnetic outputs is overlooked. In fact implementing multiple outputs simultaneously enables ANFIS to approach to the accurate results using only height, position and width of the magnetic Barkhausen noise peaks without knowing the value of the used frequency.

Magnetic NDT and Computer Modeling of Steel Rope Deterioration in Suspended Bridges

A combined approach to strength assessment of stay ropes in suspension bridges is considered. The rope working condition is being analyzed by following steps: in-situ magnetic testing of rope structure, computational assessment of ultimate breaking load and evaluation of residual margin of safety. The diagnostic parameters distributed and/or local faults in wires are used as input data for mechanical model of rope structure. The model enables to calculate the stresses in each wire and to simulate the step-wise degradation process thus estimating the rope residual breaking tensile load. The safety factor of deteriorated rope is considered as a generalized parameter that specifies the rope safe operation as an element of bridge stay arrangement. Examples of integrity analysis of stranded stay ropes and locked coil stay ropes are presented.

Outlook of Preisach Modeling and Magnetic Non Destructive Testing

The Preisach formalism is used as a basis for a vector model of magnetic hysteresis in soft magnetic materials subject to tensile stress. The model uses as vector elementary hysteresis operator the Stoner-Wohlfarth mechanism of coherent rotation while the Preisach density is constructed as the weighed sum of probability density functions corresponding to the high and low induction regions. The model reproduces the basic phenomenology of stress-dependent hysteresis: the double peak in differential permeability modeled as the effect of internal demagnetizing fields emerging from residual stresses; the increase in coercivity due to increased pinning; the decrease in magnetic induction as the result of non-180o domain rotation. The role of the negative differential permeability near remanence and its derivative is discussed with respect to residual stresses and magnetic NDT.

Combined approach to damaged wire ropes life-time assessment based on NDT results and rope mechanics

Principles of strength assessment and life-time prediction of deteriorated wire ropes based on magnetic NDT technique are presented. The measured loss of metallic cross-section area due to abrasion, corrosion etc. and local wire breaks are treated as input data for mechanical model of rope structure. The rope is interpreted as a system with two degrees of freedom that enables to calculate the strains and stresses in each wire when the rope is subjected to tension, torsion and bending. Stress safety factor is considered as a generalized parameter that specifies the rope degradation and may be used for predicting the instant lifetimes during the rope operating history. The rope discard criterion refers to residual life-time calculated with respect to minimal allowable strength factor. Examples of integrity analysis of mine hoisting rope and jib crane rope under tension-bending fatigue loading are demonstrated. The residual strength estimates give the rope inspector further information that helps to make a valid decision on testing policy.

Magnetic NDT Technology for characterization of decarburizing depth

From practical point of view, determining the decarburizing depth is important in quality control of steel parts as it has undesirable effects on the mechanical properties such as hardness, wear and fatigue resistance. Traditional destructive methods of determining the depth of decarburized layer include metallographic and hardness test which are time-consuming and costly. Since response to eddy current is sensitive to chemical composition as well as microstructure of the material under consideration, the non-destructive method can be used in determining the depth of the decarburized layer in steel parts. It is mainly due to the difference in the microstructures, and as a result, in the magnetic properties of the decarburized layer with other parts of the specimen. In the present study at the first step, the magnetic properties of decarburized carbon steel bars (0.45 wt.% C) were evaluated using an electromagnetic sensor and correlated with the microstructure changes from surface to the core of the sample. At the second step the steel bars were held in 900 °C for different period of times and the depth of decarburizing layers were measured using hardness testing. Finally, the non-destructive eddy current technique was used and the response of test samples to the induction current including primary and secondary voltages, normalized impedance, phase angle and harmonic analysis parameters were investigated. Results show an acceptable accuracy in comparison to the destructive method.

Quantitative NDT structuroscopy of cast iron castings for vehicles

Cast irons look like 'composites' made of a steel matrix and graphite filler. The standard description of matrix and graphite structure properties, e.g., after EN 945 is not satisfactory. Physical description of its structure can be better carried out using rigidity and hardness of matrix. The expression of this description in a plane using bidimensional vector of tension strength or yield strength offers new useful relations to manufacturing metallurgy. Mathematical models among physical and mechanical properties were derived by statistical analysis. The MAT method is developed for thin-wall castings. Magnetic adaptive testing (MAT) is shortly said magnetic hysteresis NDT method exploiting large datafile created by voltage impulse induced in detection coil winded onto specimen, in dependence on immediate value of magnetic field of specimen. It is combined with another way of testing by a device for remanent magnetism measurement and an ultrasound impulse device with probes placed onto surface of the measured object, together with wall-thickness tester for thick-wall castings.

The influence of rope tension on the LMA sensor output of magnetic NDT equipment for wire ropes

There are many different wire rope constructions in service which are used in a diverse range of applications. Ropes will be discarded, not only because of faults (typically broken wires) and/or owing to other damage such as wear, corrosion and structural deformations. Almost every rope must be and is inspected in service. As a support to visual inspection, magnetic testing is accepted on a world wide basis, and is probably the most effective way for locating degradation. However, debate is ongoing about the quantitative interpretation of the measurements so obtained. The authors have previously published work assessing the reliability of a range of sets of NDT equipment on different ropes and forms of rope degradation. This paper is based on further research work which was sponsored by the British Council and the Polish State Committee for Scientific Research (KBN). It focuses on the problems associated with the accuracy of non-destructive testing of wire ropes by equipment which incorporates a loss of metallic area (LMA) sensor. (The LMA sensor is probably the most popular for quantifying the level of metallic area loss). The new issue discussed in this paper is the practical study of the effect of tension in the wire rope under test on the LMA signal output. The analysis considers the influence of wire rope tension on: equipment calibration; the position of the null base line of the Hall effect (LMA) sensor; and, readings from the LMA trace. The MD120 was used during these tests. The results provide practical information for the user about the accuracy of NDT inspection using NDT equipment with Hall effect LMA sensors.

Magnetic NDT methods for microstructural characterisation in steels : 57730 Bhattacharya, D.K.; Jayakumar, T.; Raj, B. Non-destructive evaluation and quality assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 110–127. Interline publishing (1993) ISBN 81-7296-010-7

Magnetic NDT methods for microstructural characterisation in steels : 57730 Bhattacharya, D.K.; Jayakumar, T.; Raj, B. Non-destructive evaluation and quality assurance. Edited by C.R.L. Murthy, B. Raj, O. Prabhakar and A. Sreenivasulu. pp. 110–127. Interline publishing (1993) ISBN 81-7296-010-7

Near crack in ferromagnetic materials for magnetic NDT

Near crack in ferromagnetic materials for magnetic NDT

Near crack in ferromagnetic materials for magnetic NDT: 37163 Qi, Z.; Lunyuan, Y. 11th World Conference on Nondestructive Testing, Las Vegas, Nevada (United States), 3–8 Nov. 1985. Vol. 1, pp. 216–225. Taylor Publishing Co., Dallas (1985)

Near crack in ferromagnetic materials for magnetic NDT: 37163 Qi, Z.; Lunyuan, Y. 11th World Conference on Nondestructive Testing, Las Vegas, Nevada (United States), 3–8 Nov. 1985. Vol. 1, pp. 216–225. Taylor Publishing Co., Dallas (1985)

Magnetic NDT technique to evaluate fatigue damage

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