Yushi Sun

Magnetic flux leakage modeling for mechanical damage in transmission pipelines

This paper presents a two stage FE model for prediction of magnetic flux leakage, resulting from mechanical damage. In the first stage the stress distribution associated with mechanical damage is obtained from a structural model. In the second stage the stress distribution is incorporated into a magnetic FE model, by mapping stress levels to permeability. MFL signals are calculated and compared with experimental gouge MFL signatures.

Solution of inverse problems in electromagnetic NDE using finite element methods

This paper presents a technique for solving inverse problems in magnetostatic nondestructive evaluation (NDE), using finite element models. In-line inspection of ferromagnetic gas pipelines containing pipe-wall defects, is chosen as the candidate NDE process. The signal inversion technique consists of iteratively solving the forward problem by updating the finite element mesh, rather than the material properties of the finite elements. Preliminary simulation results obtained using a 2D finite element model are presented.

3D simulation of velocity induced fields for nondestructive evaluation application

The challenges associated with finite element modeling of a tight crack in an otherwise large geometry encountered in a typical nondestructive evaluation application are considered. A novel approach for decomposing the modeling of velocity induced fields in a conducting ferro- or nonferromagnetic material is presented.

Alternative magnetic flux leakage modalities for pipeline inspection

Increasing quality consciousness is placing higher demands on the accuracy and reliability of inspection systems used in defect detection and characterization. Non-destructive testing techniques often rely on using multi-transducer approaches to obtain greater defect sensitivity. This paper investigates the possibility of taking advantage of alternative modalities associated with the standard magnetic flux leakage tool to obtain additional defect information, while still using a single excitation source.

Motion induced remote field eddy current effect in a magnetostatic non-destructive testing tool: a finite element prediction

A hitherto unobserved phenomenon motion induced remote field eddy current effect, is presented in this paper. A numerical study of the non-destructive inspection of tubing with conducting walls, using a DC electromagnetic probe led to the detection of this interesting effect. This paper describes a bi-directional transmission of the electromagnetic field energy through the tube walls, similar to the phenomenon responsible for the Remote Field Eddy Current (RFEC) effect in eddy current (an AC electromagnetic nondestructive testing tool) inspection of tubing. Thus far it was considered that the RFEC effect by the nature of its physics was possible only in the presence of AC excitation in tubular geometries. However, it is shown in this paper that currents induced by magnetic flux moving over conducting material produce a RFEC effect even when a DC probe is used. This phenomenon may enable extraction of valuable information regarding the entire thickness of the tube wall from measurements made on the same side as the excitation source. >

An equivalent linear model for magnetostatic nondestructive evaluation

Numerical models capable of modeling magnetic flux leakage (MFL) methods of nondestructive testing are of significant interest to industry. The nonlinear nature of the MFL problem necessitates the use of an iterative model, thereby resulting in excessive computational effort. This paper describes an approach for developing an equivalent linear model (ELM) where the ferromagnetic region is appropriately partitioned into different domains with each domain being assigned a constant permeability value depending on the magnetization level and the flaw size. The nonlinear behavior of the multi-layered object is then modeled using a linear MFL model. The strategy results in significant computational savings without a substantial loss in accuracy. Results supporting the validity of the approach have been obtained using a 3D magnetostatic finite element (FE) model.

Inspection of Metallic Plates Using a Novel Remote Field Eddy Current NDT Probe

The remote field eddy current (RFEC) technique was invented in 1951 [1], [2] and is widely used as a nondestructive evaluation tool for inspecting metallic pipes and tubing. Essentially, the RFEC phenomenon can be observed when an AC coil is excited inside a conducting tube (see Fig. 1). The RFEC signal can be sensed by a pick-up coil located 2–3 diameters away from the excitation coil. The signal is closely related to the tube wall condition, thickness, permeability, and conductivity. The signal phase, especially, has approximately linear relationship with the tube wall thickness.

Efforts towards gaining a better understanding of the remote field eddy current phenomenon and expanding its applications

The paper begins with a brief summary of previous work done by the authors on gaining a better understanding of the remote field eddy current (RFEC) phenomenon and expanding the range of applications. It then introduces three new findings: (1) Modeling and experimental study of the RFEC phenomenon as observed from one side of both ferromagnetic and non-ferromagnetic plates. (2) Numerical prediction of possible existence of the RFEC phenomenon external to conducting tubes. (3) Numerical study of its possible application in underwater target detection problems.

Pulsed RFEC probe response

A finite element/finite difference algorithm is described for modeling the pulsed excitation of a remote field eddy current (RFEC) probe used in steel pipeline inspection. Previous work has largely been concerned with the steady-state AC operation of the probe and physical explanations, based on finite element studies, of the probes sensitivity to outer wall defects. In the present work, the authors discuss the probe response to a sinusoidal pulse and show that such an excitation mode can also be used for outer wall defect detection. >

Application of perturbation methods in finite element analysis of stress corrosion cracking

Finite elements analysis of magnetic nondestructive evaluation phenomena often involves modeling of complex interactions between the magnetostatic fields and tight, zero volume cracks in large structures. The modeling effort therefore faces significant challenges in terms of large memory storage and computation time requirements. This paper presents an approach based on perturbation methods for finite element modeling of a colony of stress corrosion cracks in a gas transmission pipeline.