Circumferential Magnetic Flux Leakage Research Articles

Automated Box Data Matching for Multi-Modal Magnetic Flux Leakage Inspection of Pipelines

Magnetic flux leakage (MFL) is one of the most popular in-line inspection techniques to detect pipeline corrosion defects. However, the measurement limitation and random error associated with the individual MFL could introduce observable variations to the inspection. One potential way to reduce such variation is to fuse the inspection data from axial MFL (aMFL) and circumferential MFL (cMFL) due to their complementary measurement nature. Data from the multi-modal MFL must be matched before the fusion operation. However, there is no literature reporting the multi-modal MFL data matching yet. In this article, we propose an automatic box data matching framework that consists of four major steps, i.e., pre-processing, grouping, alignment, and matching. The pre-processing step accomplishes the 3-D to 2-D data mapping and cleansing. The grouping of the box data from the cMFL based on their location information is given in the following. Then, the coordinate systems of two MFL data sets are aligned. Finally, in the aligned coordinate system, the density-based spatial clustering of applications with noise (DBSCAN) algorithm is revised to perform many-to-many matching. The experimental results demonstrate that the proposed framework can accurately match the multi-modal MFL box data. Thus, this solution will enable the multi-modal MFL data fusion for a more reliable and accurate pipeline corrosion assessment.

Identification and Sizing of Neighboring Pits Using Three-Axis Magnetic Flux Leakage Technique

Neighboring corrosion pits are one of the most frequently found defects in gas pipelines. Because of the interaction with each other, these defects accelerate the corrosion growth rates in the wall of the pipelines. Hence, it is meaningful to discriminate multiple neighboring pits from single isolated pits by analyzing their characteristics. This article presents the results of a study on the use of a three-axis magnetic flux leakage (MFL) technique for the identification and sizing of neighboring corrosion pits. Various patterns of two neighboring pits are considered by modifying the separation distances between them. Finite element modeling as well as experimental measurements is used to investigate the spatial distributions of the three MFL components (axial, radial, and circumferential) generated by the neighboring pits. The results indicate that the axial as well as the radial MFL components of the neighboring pits merge to one signature the closer the two defects are, and thus, no width sizing of the individual pits is possible anymore. In contrast, both pits are still discernible in the circumferential MFL signatures. The described method can help to identify neighboring corrosion pits and thus improve the sizing accuracy of MFL measurements.

Design of a lightweight magnetizer to enable a portable circumferential magnetic flux leakage detection system.

We proposed a lightweight magnetizer toward the realization of a portable circumferential magnetic flux leakage (MFL) inspection tool for the detection of longitudinal defects with a linear motion between pipes and the inspection tool. The proposed magnetizer consists of four permanent magnetic poles constructing a configuration in which the like poles are separated by a θ angle ranging from 30° to 60° and the opposite poles are separated by a supplemental angle of θ. The distribution of the magnetic field generated by this magnetizer and caused by defects was studied by finite element methods as well as by experimental measurements. The results reveal that the new magnetizer has advantages of high amplitude and good uniformity of magnetic field over the state-of-the-art ones with configurations of two facing poles or quadrupole geometries. With the new magnetizer, the theoretical and experimental results show that the magnetization in the pipe increases slightly with the θ angle, but the uniformity of magnetization in the pipe and the magnetic field on the surface of pipe decrease dramatically with this angle. So, the optimum angle θ is proposed at around 30°-40°. The finite element calculation and the measurements of the MFL signal caused by artificial defects evidence the capabilities in detecting shallow longitudinal defects of the MFL inspection tool with our novel magnetizer.

Modeling and Optimization of a Tubular Permanent Magnet Linear Motor Using Transverse-Flux Flux-Reversal Topology

In this paper, a novel tubular transverse-flux flux-reversal linear motor for long stroke applications is proposed. The proposed motor not only has the low-cost advantage of the existing flux-reversal permanent magnet (PM) linear motor (PMLM) by combining both PMs and armature winding in short primary, but also address the problem of complicated structure in conventional tubular PMLM by using the manufacturing process of the rotary motor. First, in order to reduce circumferential magnetic flux leakage and improve the utilization ratio of PM, the motor structure with the alternating distribution of double N poles and double S poles in the circumferential direction is designed, and the operating principle of the motor is presented. Then, the equivalent magnetic circuit model of the unit motor is established to derive the expressions of the back electromotive force (EMF) and the electromagnetic thrust. Third, the equivalent two-dimensional (2-D) finite-element method (FEM) is used to optimize the structural dimensions and analyze the static characteristics including the back EMF, the detent force, and the thrust. Meanwhile, the three-dimensional FEM verify the validity of the equivalent 2-D FEM. Finally, the experimental results verify the validity and the correctness of the topology structure and the design method of the motor.

Defect Estimation of a Crack in Underground Pipelines by CMFL Type NDT System

A crack which is axially oriented with small size is hard to detect in conventional system. CMFL(Circumferential Magnetic Flux Leakage) type PIG(Pipelines Inspection Gauge) in the NDT(Nondestructive Testing), is operated to detect this defect called axially oriented cracks in the pipe. It is necessary to decompose the size and shapes of cracks for the maintenance of underground pipelines. This article is mainly focused on the decomposing method of the size and shape of the axially oriented cracks by using inspection signal data for defect.

축방향 미소결함 검출을 위한 자기누설 비파괴 검사 방법에 관한 연구

비파괴 검사방법 중 자기누설 방법을 이용한 비파괴 검사방법은 높은 자기 투자율을 갖고 있는 배관 검사에 적합하다. 자기누설 방식이 적용된 시스템을 MFL PIG라고 하는데 이전 MFL PIG는 금속 손실이나 부식과 같은 결함을 검출하는 데 높은 성능을 보인다. 하지만 MFL PIG는 배관 내 외부의 압력차에 의해 발생하는 크랙을 검출하는데 어려움이 있다. 크랙은 매우 가늘고 길게 발생하기 때문에 축방향으로 자기장을 형성하는 기존의 MFL PIG에서는 자기장이 통과하는 크랙의 단면적이 변화가 거의 없게 된다. 크랙은 배관에서 빈번히 발생하는 결함으로 사고의 위험은 금속 손실이나 부식에 의한 것보다 훨씬 크다. 그러므로 크랙을 검출하기 위한 새로운 PIG가 연구 개발 될 필요가 있다. CMFL PIG는 자기장을 원주방향으로 형성하여 크랙에서의 자기 누설을 최대화할 수 있다. 본 논문에서는 3차원 비선형 유한요소해석법을 이용하여 CMFL PIG를 설계하고 자기장 분포를 분석하였다. CMFL PIG를 이용하여 NACE의 표준인 크랙을 검출할 수 있고 크랙의 형상을 추정하기 위해 많은 종류의 크랙에 대해 자기장의 누설을 분석하고 신호 처리를 통해 형상 추정을 하였다. From among the NDT (nondestructive testing) methods, the MFL (magnetic flux leakage) method is specially suitable for testing pipelines because pipeline has high magnetic permeability. The system applied to MFL method is called the MFL PIG. The previous MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is highly unlikely to detect the cracks which occur by exterior-interior pressure difference in pipelines and the shape of crack is long and very narrow. In MFL PIG, the magnetic field is performed axially and there is no changes of cross-sectional area at cracks that the magnetic field passes through. Cracks occur frequently in the pipelines and the risk of the accident from the cracks is higher than that from the metal loss and corrosions. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The circumferential MFL (CMFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). In CMFL PIG, cracks, standards of NACE, are detectable. To estimate the shape of crack, the leakage of magnetic fields for many kinds of cracks is analyzed and the method is developed by signal processing.

Finite element modelling of a circumferential magnetiser

Pipeline integrity is vital and should be maintained through regular inspection. A popular inspection technique is magnetic flux leakage (MFL) where an in-line inspection (ILI) tool magnetically saturates the pipeline locally as it traverses the pipe inner bore. Pipe defects cause magnetic flux patterns to change and this change is detected by a set of magnetic sensors mounted on the tool. For the MFL technique to be optimised, magnetic saturation in the pipe material is required. This paper examines finite element (FE) simulations in which a section of line pipe is magnetised along its circumference under both static and moving tool conditions. Early findings are reported that highlight difficulties associated with maintaining a stable magnetic circuit for a moving ILI tool. The results provide insights into the design considerations and challenges of employing circumferential MFL tools and their associated sensors.

강자성 배관 외.내부 벽의 racetrack형 결함깊이와 부피응력이 누설자속에 미치는 영향

Non-linear anisotropic materials were used to simulate the effects of bulk tensile stress in 3D finite element analysis (FEA). FEA was used to calculate the effects of near and far-side racetrack pit depth and simulated bulk tensile stress on magnetic flux leakage (MFL) signals. The axial and radial MFL signals were depended on near and far-side racetrack pit depth and on the bulk stress, but the circumferential MFL signal was not depended on them. The axial and radial MFL signals increased with greater pit depth and applied bulk stress, but the circumferential MFL signal was scarcely changed.

강자성 배관 외.내부 면의 이중 원형 결함의 깊이와 응력이 누설자속에 미치는 영향

Non-linear anisotropic materials were used to simulate the effects of tensile stress in 3D finite element analysis (FEA). FEA was used to calculate the effects of far and near-side pit depth and tensile stress on magnetic flux leakage (MFL) signals. The axial and radial MFL signals were depended on far and near-side double circular pit depth and on the stress, but the circumferential MFL signal was not depended on them. The axial and radial MFL signals increased with greater pit depth and applied stress, but the circumferential MFL signal was scarcely changed.ﾖ⨀᠏?㌶㌮㌷〵㬅K䍄乍퐗ᘍ㔀܀㘱㐮㠴㬅K䍄乍밗ጊ缀Ѐ㘰〻Ԁ䭃䑎䴀