Ferromagnetic Tubes Research Articles

Examination of Thinning Inspection Method for Ferromagnetic Steel Tubes Using Velocity Effect of Static Magnetic Field

The high-speed movement of an electromagnetic sensor comprising static excitation and detection coils in a steel tube generates an eddy current in the tube. The presence of a defect in the steel tube may be detected via changes in the eddy current. In general, the ferromagnetic heat transfer tubes in oil and chemical plants are inspected for defects by moving an internally inserted electromagnetic sensor at a high speed of 1 m/s. Although previous studies have focused on the detection of localized thinning in the steel tube, there are no reports on a wide range of thinning in the steel tube. Therefore, this study investigated a thickness measurement method for a wide range of thinning in the steel tube using only static magnetic field. Consequently, the possibility of measuring the thickness in the steel tube based on the flux density inside the detection coil of the proposed static magnetic inspection sensor moving at 1 m/s was demonstrated. The flux density in the steel tube was evaluated by the three-dimensional nonlinear finite element method considering the velocity effect.

ТРИВИМІРНА МАТЕМАТИЧНА МОДЕЛЬ ТРИФАЗНОГО ТЕПЛОГЕНЕРАТОРА ІНДУКЦІЙНОГО ТИПУ З ВИКОРИСТАННЯМ МЕТОДУ ВТОРИННИХ ДЖЕРЕЛ

A three-dimensional mathematical model of a three-phase induction heat generator with a load in the form of a ferromagnetic conductive tubes beam has been developed on the basis of the secondary method. The magnetic system symmetry of the heat generator is taken into account, which significantly reduced the search area of unknown electromagnetic field secondary sources densities. References 5, figures 3.

Comprehensive study on radial coil influence in designing segmented remote field eddy current probe for defect detection in ferromagnetic tubes

ABSTRACT In the present study, two types of receiver coils, viz axial and radial type receivers, in the Remote field eddy current technique are considered to detect defects in ferromagnetic tubes. The appropriate distance between the exciter and the receiver coils and the excitation frequency are estimated using the finite element model and validated experimentally. Model-assisted probability of detection studies are performed to examine the capability of radial and axial type receiver coils. Experimental studies on various artificial defects reveal the excellent performance of the radial type receiver coil in terms of the higher number of defect detections, sensitivity and imaging. This paper provides a comprehensive study on radial and axial type receiver coils for developing array probes. Radial coil performs better and also preserves localisation of defect, which is more desirable for developing array probe.

A pulsed eddy current testing method for relative thickness of ferromagnetic components considering local hysteresis characteristics

A pulsed eddy current testing method is proposed for the assessment of the relative thickness of ferromagnetic components with uneven external insulation layer and remanence. By establishing a least squares problem of theoretical and measured value of induced voltage based on the time-domain analytical expression to pulsed eddy current testing model of a ferromagnetic plate, unknown parameters including the thickness, conductivity and relative permeability are determined by inversion algorithm. Then, the coupling relationship among parameters in the inverse problem is verified by experiments on a steel plate, and the detection method for relative thickness is proposed. Furthermore, the function relationship between the inversion results of the thickness and the relative permeability under different amplitudes of the pulsed current is obtained through the linear fitting. Finally, the suppression method is discussed for the influence of the variation of permeability. It is suggested that the reference value of the thickness should be dynamically corrected by this function, as to improve the accuracy and reliability. This paper provides a reliable non-destructive testing method for wall-thinning corrosion detection of coated ferromagnetic tubes or tanks in industry.

Examination of Inspection Method for Outer-side Defect on Ferromagnetic Steel Tube by Velocity Effect Using Insertion-type Static Magnetic Field Sensor

Examination of Inspection Method for Outer-side Defect on Ferromagnetic Steel Tube by Velocity Effect Using Insertion-type Static Magnetic Field Sensor

Model Construction for Far Field Eddy Current Examination Simulation on Ferromagnetic Tubes

Ferromagnetic tubes are widely applied in fossil power plants such as waterfall tubes, overheat tubes or reheating tubes. Outer surface corrosion, wearing, depth reduction, cracks are common defects during manufacturing and long term operation. Eddy current detection is a traditional method for the examination of surface and near surface defects. However the efficiency is restricted by lift-off effect and skim effect. Far field eddy current overcomes the above disadvantages with high efficiency and fast examination speed and high sensitivity. In this paper, numerical simulation has been carried out to study the far field eddy current Detection for defects in small diameter ferromagnetic tubes in fossil power plants.

Simulation on the Effect of Frequency and Ferromagnetic Tubes Specifications by Far Field Eddy Current Examination

Tube leakage frequently occurred in on-service fossil power plants. Traditional NDT testing methods, including RT, UT, MT and PT are not applicable for the examination of large amount tubes. Fat eddy current examination is a new technique for testing ferromagnetic tubes defects, such as inner corrosion, thickness reduction and cracks. Far field eddy current simulation and verification for different specification tubes has been carried out. The result shows that the position of far field eddy current moves backwards with the increase of wall thickness and tube ID. To the defects with same size, examination sensitivity is higher in far field eddy current area. When the defect with same size locates in the inner and outer surface of the tube, the change of magnetic intensify differences is approximately the same, which is in accordance with the experimental result and is satisfied with far field eddy current examination theory. It has been concluded that defects in ferromagnetic tubes could be judged and recognized by far field eddy current examination technique, which shows prospective for the on-line examination and safety evaluation for in-service tubes in fossil power plants.

ECT simulation and measurements in ferromagnetic tube using DC homogeneous magnetic field

ABSTRACT The application of Eddy Current Testing (ECT) to ferromagnetic materials is challenging owing to the difficulties stemming to ferromagnetism. Due to the non-linear magnetic permeability, the use of a strong external DC magnetic field is often necessary in order to bring ferromagnetic materials close to magnetic saturation where permeability is minimised; strongly improving eddy current’s penetration in the material volume. In this work, the main application studied is ECT on a ferromagnetic tube with an Inside Diameter (ID) coil. The effect of different levels of the DC magnetic field on the coil impedance changes is investigated both experimentally and by simulation. It is shown that DC field has a systematic influence both to magnitude and phase of the Eddy Current signal. In addition, for the different defect depths, a critical level is observed, where the signals from discontinuities become visible and stand out from the noise of non-linearity. Moreover, for a range of magnetisation field level, the changes of phase angle are distinct for different defects’ depths allowing thus the application of phase analysis for defect characterisation.

DETECTION OF DEFECTS OF STRUCTURES FROM FERROMAGNETIC STEEL THROUGH THE LAYER OF ANTICORROSION COVER WITHOUT REMOVAL

The detection of the cracks in ferromagnetic steel components by the eddy current method is formidable because of the additional noise originated from magnetic and structural heterogeneities of the inspected material. In this paper, several techniques proposed for the detection of the defects in ferromagnetic steel components are analyzed. One of the possible approaches is based on the additional magnetization of the inspected zone to minimize magnetic heterogeneity. Another trend is concerned with new selective EC probe development. This inspection problem is exercisable by the double differential EC probes application. These probes were developed some decades ago and are characterized by a specific quasi-absolute signal with maximum amplitude when the probe is situated directly over a crack. The main features of such probes can be characterized with: high sensitivity to elongated (like crack) and to local (like pitting or pore) defects; high sensitivity to surface and subsurface defects through the protective coating or with large clearance between the probe and inspected surface; high penetration for low-frequency probes; high lift-off noise suppression. In this study the possibility to detect the cracks through the anticorrosive coating was investigated. Special detectability diagrams were created to estimate the ultimate thicknesses of dielectric coating for the detection of the defects with different depths. For inspection of the objects with large overall dimensions (like tubes, forgings, etc.) array type EC probe (named EDDYLINE) was developed. High sensitivity width (near 60 mm) was achieved to obtain high inspection productivity. At the same time, the high locality was provided because all EC probes are operated separately. Developed EC inspection techniques based on the EDDYLINE type EC probe were successfully applied for the detection of cracks in ferromagnetic and stainless steel tube forgings.

Ferromagnetic resonance in a microtube

Ferromagnetic resonance fields in a microtube with various ratios of the inner and outer diameter of the tube β were studied using micromagnetic simulation. For β<0.15, the resonance field agrees with the prediction of the Kittel equation for an infinite ferromagnetic cylinder for both parallel and perpendicular orientation of the applied field to its axis. For β>0.15, the resonance field increases from the resonance field of the infinite cylinder and approaches the level of a film magnetized along the plane. This behavior only qualitatively agrees with the prediction made using the calculated demagnetizing factor in the ferromagnetic tube. For β>0.15 and the applied transverse field, a number of resonance peaks were observed for the microtube with the outer diameter of 500 nm, but for nanotubes with the diameters of 50 and 100 nm, a single peak was observed.

Experimental Evaluation of Defects in Ferromagnetic Steel Tube by Electromagnetic Sensor Using Square Wave AC Magnetic Field with DC Bias

Experimental Evaluation of Defects in Ferromagnetic Steel Tube by Electromagnetic Sensor Using Square Wave AC Magnetic Field with DC Bias

Optimization of Geometrical Parameters of a Magnetostrictive Ultrasonic Guided Wave Probe for Tube Inspection

Non-destructive examination of steam generator (SG) tubes of Fast Breeder Reactors is of paramount importance. The inspection needs to be carried out from the inner side of an SG tube due to the constraint in accessibility. Recently, the magnetostrictive ultrasonic guided wave (MUGW) technique has been proposed as an alternative for the inspection of SG tubes. As a commercial MUGW probe for small-diameter ferromagnetic tubes is not available, it needs to be designed and developed with optimum parameters. This paper proposes a three-step optimization approach for the development of a MUGW probe, namely optimization of the diameter and length of a permanent magnet (for bias) finite element modeling based, optimization of the width of the transmitter and receiver coils of the probe by empirical modeling and the optimization of the number of turns of the transmitter and receiver coils by equivalent circuit models. A MUGW probe is fabricated and tested experimentally to validate the optimized parameters. Experiments show the validity of the approach in terms of generation, long-range propagation (47.6 m) of L(0,2) mode at 300 kHz, and the required sensitivity (multiple 10% wall thickness deep uniform wall loss circumferential grooves) in SG tubes.

Inspection Method of Outer Side Defect in Ferromagnetic Steel Tube by Insertion-Type Electromagnetic Sensor Using Square Wave Alternating Magnetic Field With DC Bias

The ferromagnetic steel tubes are used for heat transfer tubes of heat exchangers in power plants or oil plants. The outside defect in the ferromagnetic steel tube is generated by friction with the supporting steel plate (baffle). In this research, in order to detect the outer side defect in the ferromagnetic steel tubes, the electromagnetic inspection sensor probe of the type inserted in the ferromagnetic steel tubes using square wave alternating magnetic field with dc bias is proposed. The flux density and eddy current in the ferromagnetic steel tubes are estimated by the 3-D nonlinear finite-element method (FEM) taking account of minor loop curve using the play hysterons model method. The usefulness of this proposal inspection method is shown also from comparison with an experimental verification.

Inversion Method in Pulsed Eddy Current Testing for Wall Thickness of Ferromagnetic Pipes

Based on time-domain analytical expression to pulsed eddy current field of a ferromagnetic pipe, a least squares inverse problem, between the calculated and measured values of induced voltage, is established to determine the wall thickness, conductivity, and relative permeability. And then, the coupling relationship among parameters in the inverse problem is investigated. Furthermore, the inverse problem is reestablished and the method for calculating the relative variation of wall thickness is proposed via taking the ratio of the inversion results between two testing points. Finally, the experiment results on a steel tube indicate that inversion results are independent on the initial value, and can effectively suppress the influence of the magnetic permeability variation, thus the reliability of the thickness testing get improved. Based on the above, a noncontact pulsed eddy current testing method is presented for measuring the relative wall thickness of ferromagnetic pipes. It can be used for nondestructive evaluation of wall-thinning corrosion of in-service coated ferromagnetic tube.

3D Modeling of MFL Imaging System to Detect Surface Discontinuities in Ferromagnetic Tubes

3D Modeling of MFL Imaging System to Detect Surface Discontinuities in Ferromagnetic Tubes

Optimal design methods for the uniform heating of tube ends for stress relieving

Purpose An inductor for the uniform heating of the extremity of a ferromagnetic steel tube for stress relieving is considered. The main goal of the study is to investigate the possibility to achieve a reasonable design of the inductor when dealing with many design variables. Design/methodology/approach Genetic optimization algorithms are used for this purpose, demonstrating the applicability of these techniques to the design of induction heating inductors. Genetic algorithms provide to the designer several optimal solutions belonging to Pareto Front, and this way they allow choosing the solution that better fits the technological requirements. In any case, the designer has to adapt the chosen solution to fit in with the real possibilities in industrial application. Findings The study demonstrates that automatic optimization methods may help the designer of the induction heating system to solve complex problems with very conflicting technological requirements. Originality/value In the paper, a problem with a high number of design variables is solved. Moreover, the goals of the optimization process are strongly conflicting, and the proposed problem is a challenging one.

Simulation on Far Field Eddy Current Detection on Condenser Tube Groups in Fossil Power Plants (II)

Condenser tube tubes are widely applied in condenser in thermal power plants. Leakage often occurs in condenser tube groups due to the quality of condenser media or high serving stress. Condenser tube leakage not only brings economic losses to power stations, but even influences the safety operation of the power generation units. This paper simulates and experimentally studies the influence of wall thickness and frequency on the far field current. Experiment on ferromagnetic tube with defects detecting by eddy current has also been carried out. The result verifies the simulation conclusions. Far field current examination technique could judge and recognize the defects in ferromagnetic tube. It is a useful and effective method in defect emanation in fossil power plant

Simulation on Far Field Eddy Current Detection on Condenser Tube Groups in Fossil Power Plants (I)

Condenser tube tubes are widely applied in condenser in thermal power plants. Leakage often occurs in condenser tube groups due to the quality of condenser media or high serving stress. Condenser tube leakage not only brings economic losses to power stations, but even influences the safety operation of the power generation units. This paper simulates and experimentally studies the ferromagnetic heat exchanger tubes based on the detection mechanism of far field eddy current. The results show that the position of the far field is with the increase of the wall thickness and the inner diameter of the tubes, and the detection sensitivity of the far field is high for the same size defect, but the difference of the magnetic flux intensity varies equally when the defects with the same size are located at the inner and outer walls. This is consistent with the experimental results of real tube defect detection and meets the principle of far field eddy current detection. It is concluded that far field eddy current testing technology can better determine and identify ferromagnetic tube defects, and has a good application prospect for online nondestructive testing and safety performance evaluation of service tubes

Electromagnetic inspection for defect of ferromagnetic tube using rectangular wave with DC bias

The ferromagnetic steel tubes are used as heat exchangers in power plants or oil plants. When the usual eddy current testing (ECT) of inner type is used for the defect inspection of these steel tubes, it is difficult to detect defects on the opposite side due to the influence of skin effects. In this research, the non-destructive inspection method using rectangular wave excitation current with DC bias is proposed for detecting of the opposite side defect. It is shown that the detecting of the opposite side defect in the steel tube is possible, and the detection sensitivity using the alternating magnetic field of rectangular wave is higher than that with sine wave. The detailed phenomenon of the inspection method is examined using the 3-D nonlinear FEM (finite element method) taking account of minor loop magnetizing properties using the play model method.

A compact guided-wave EMAT with pulsed electromagnet for ferromagnetic tube inspection

Small-diameter tubes that are widely used in petroleum industries and power plants experience corrosion during long-term services. In this paper, a compact inserted guided-wave EMAT with a pulsed electromagnet is proposed for small-diameter tube inspection. The proposed transducer is noncontact, compact with high signal-to-noise ratio and unattractive to ferromagnetic tubes. The proposed EMAT is designed with coils-only configuration, which consists of a pulsed electromagnet and a meander pulser/receiver coil. Both the numerical simulation and experimental results validate its feasibility on generating and receiving L(0,2) mode guided wave. The parameters for driving the proposed EMAT are optimized by performance testing. Finally, feasibility on quantification evaluation for corrosion defects was verified by experiments.