Magnetic Flux Leakage Inspection Tools Research Articles

Development of a convolutional neural network model to predict the size and location of corrosion defects on pipelines based on magnetic flux leakage signals

This study employs the convolutional neural network (CNN) to predict the dimensions and locations of corrosion defects on steel pipelines based on magnetic flux leakage (MFL) signals. Extensive three-dimensional parametric finite element analyses are carried out to generate MFL signals corresponding to semi-ellipsoidal-shaped corrosion defects with different sizes and locations on a pipe model. The white noises characterized by different signal-to-noise ratios are considered in the analysis to represent the measurement errors in the real MFL inspection tool. The numerically generated MFL signals are used to train and validate the CNN model to predict the dimensions and locations of the corrosion defects. The results indicate that the developed CNN model achieves a high predictive accuracy. The study demonstrates the application of CNN model to improve the pipeline integrity management practice.

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.

Effects of Magnetic Concentrator on MFL Signals Using FEA

Magnetic flux leakage (MFL) is a non-destructive testing method used to inspect ferrous materials. However, there are a variety of factors that can affect the MFL inspection tool’s ability to detect and characterize anomalies. MFL signals obtained during the inspection of pipes have been simulated using 3D finite element analysis (FEA) and the effects of magnetic concentrator on MFL signals are investigated. Measurements of the leakage flux with various defect depths or widths indicate that the axial component of MFL are improved by magnetic concentrator with the result that significant advantages could be obtained in defect detection schemes, in that the signal to noise ratio (SNR) of MFL signals can be improved by magnetic concentrator.

3D Finite Element Analysis for Magnetic Flux Leakage Testing

Magnetic flux leakage (MFL) is a non-destructive testing method used to inspect ferrous materials. However, apparatus parameters could affect the MFL inspection tool’s ability to characterize anomalies. In this paper, MFL signals obtained during the inspection of pipes have been simulated using three-dimensional finite element analysis and the effects of magnet assembly on MFL signals are investigated. According to numerical simulations, an increase in the leakage flux amplitude is observed with an increase in the permanent magnet size and the inflexion point may indicate the presence of magnetizing pipe wall to near saturation. It clearly illustrates degradation in the MFL with increasing backing iron length. The relationship between MFL apparatus parameters and MFL signals could be utilized in the MFL technique to characterize the defect.

Effects of Apparatus Parameters on MFL Signals Using Orthogonal Experimental Design

Magnetic flux leakage (MFL) is a non-destructive testing method used to inspect ferrous materials. However, there are a variety of factors that can affect the MFL inspection tool’s ability to detect and characterize anomalies. An orthogonal experimental design (OED) method is applied to study the effects of apparatus parameters on MFL signals. Integration of OED method of analysis into a routine sample preparation technique could improve the repeatability and quantization capabilities of MFL tools. Three key apparatus parameters, namely permanent magnet (PM) height, magnetic concentrator (MC) length and backing iron (BI) length are chosen for the present study. The importance of each of these key parameters on MFL signals for different defects is determined by a series of experiments.

The effect of the defect location on the finite element modelling of defect MFL fields

Magnetic flux leakage (MFL) measurement is one of the most widely used non-destructive testing techniques for in-service inspection of oil & gas pipelines. Numerical computation techniques, such as the finite element method (FEM), have been successfully employed for the study of flux leakage fields. FEM has special advantages when predicting the field profiles of simulated corrosion defects because it can model complex boundary geometries and non-linear material characteristics. According to the traditional FEM modelling method, the defect should be placed at different locations along the pipe to simulate the movement of the MFL inspection tool inside the pipe. In this paper, the effect of defect location within the finite element model is discussed and a simplified FEM modelling method is introduced. The simulation results obtained from the new method are compared to those of the traditional method. It is found that the new method can significantly shorten the solution times without compromising the accuracy of the FEM model of MFL inspection.

Defect characterisation using magnetic flux leakage inspection of tailor-welded blanks

With the increasing use of tailor-welded blanks (TWB) in the automotive industry, TWB manufacturers are struggling with the challenge to automate the quality monitoring process. The following paper examines the use of magnetic flux leakage (MFL) as a novel and economical means to evaluate the weld quality of TWBs. The development of a laboratory-based MFL inspection tool is outlined. The ability of the MFL technique to detect weld defects that occur in the production environment from CO 2 and Nd:Yag welds is clearly demonstrated. Defects include porosity, missed weld, pinholes, mismatch, concavity, and convexity. In addition, a discussion of defect signal characteristics is presented. The issues surrounding system implementation in a production environment are addressed and recommendations for future research are made.

A study on the reliability assessment methodology for pipelines with active corrosion defects

A study on the probabilistic methodology for the estimation of the remaining life of pressurized pipelines containing active corrosion defects is presented. This reliability assessment is carried out using several already published failure pressure models. A steady state corrosion rate is assumed to estimate the growth in the dimensions of corrosion defects. The first-order second-moment iterative reliability method, the Monte Carlo integration technique and the first order Taylor series expansion of the limit state function (LSF) are used in order to estimate the probability of failure associated with each corrosion defect over time. The uncertainty of the statistical variables on which the LSF depends are modeled using normal and lognormal distributions and the sensitivity of pipeline reliability to these variables is evaluated. This extended probabilistic analysis framework is applied to a sample operating pipeline which was inspected using a high resolution magnetic flux leakage inspection tool.

Magnetic flux leakage (MFL) technology for natural gas pipeline inspection. Topical Report, November 1992 : Bubenik, TA.; Nesdroth, J.B.; Eiber, RJ.; Saffell, B.F. Battelle Memorial Inst., Columbus, Ohio (United States), PB93181899/GAR, 125 pp. (Nov. 1992)

The report is one of a series of four topical reports published by the Gas Research Institute (GRI) on the methods being used by pipeline operators to assure the integrity and safe operation of the domestic natural gas transmission system. The pipeline system in the United States has been constructed over the past half century. Assuring the integrity of the system will provide long-term serviceability to meet the future demands for natural gas. The topical report summarizes the current state of the most commonly used in-line inspection method, magnetic flux leakage (MFL). Not everything about MFL technology is known. Rather, the report presents current information on MFL techniques for pipeline inspection as they are understood by the authors. MFL is an in-line inspection method used to inspect gas-transmission pipelines. MFL inspection tools are completely self-contained units that move through pipelines at 2 to 6 miles per hour. All MFL tools have systems for magnetizing, sensing, data recording, and power. MFL tool performance is affected by many design and operational parameters. On-going research efforts are aimed at more fully understanding these parameters. MFL can generally detect metal-loss corrosion in pipelines. However, MFL cannot reliably detect all types of anomalies.

Test rigs for magnetic flux leakage inspection tools for pipelines: Mackintosh, D.D.; Atherton, D.L.; Porter, P.C.; Teitsma, A. Materials Evaluation, Vol. 50, No. 1, pp. 13–17 (Jan. 1992)

Test rigs for magnetic flux leakage inspection tools for pipelines: Mackintosh, D.D.; Atherton, D.L.; Porter, P.C.; Teitsma, A. Materials Evaluation, Vol. 50, No. 1, pp. 13–17 (Jan. 1992)

Test rigs for magnetic flux leakage inspection tools for pipelines

Test rigs for magnetic flux leakage inspection tools for pipelines