Effects of Detector Dynamics on Magnetic Flux Leakage Signals From Dents and Gouges

2012 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Magnetic Flux Leakage ◽  
Signal Loss ◽  
Magnet System ◽  
High Speeds ◽  
Study Results ◽  
Dynamic Case ◽  
Corrosion Defects ◽  
Flux Leakage

The current study was designed to model the dynamic effects of detector ride and magnet liftoff on Magnetic Flux Leakage (MFL) signals from dents as well as gouges that have significant denting. The MFL tools have long been used for the detection and sizing of corrosion defects. This is comparatively straightforward for a number of reasons, one of which is that the MFL detector assembly can ride relatively smoothly along the inner pipe wall surface. This is not the case when significant denting is present, since the dent presents a perturbation in the pipe wall that can cause liftoff of the detector or magnet system. Since the tool travels at relatively high speeds down the pipe, the dent itself can cause the detector to lose contact with the trailing half of the dent. In addition, the magnet pole piece may experience partial liftoff as it traverses the dent, thus causing a change in the local flux density. In this study results from ‘static’ measurements are compared with a dynamic case in which detector liftoff is simulated through modeling and experiment. Results are discussed regarding the severity of MFL signal loss at the trailing edge of the defect as a result of detector liftoff. The effect of partial liftoff of the magnet as it passes over the dent is also examined. Magnet liftoff is found to increase the local magnetic flux near the liftoff region, causing the MFL signal from the dent wall to increase rather than decrease in the vicinity of magnet liftoff region.

The Design of a Mechanical Damage Inspection Tool Using Dual Field Magnetic Flux Leakage Technology

2005 ◽  
Vol 127 (3) ◽  
pp. 274-283 ◽  
Author(s):  
J. Bruce Nestleroth ◽  
Richard J. Davis
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
High Magnetic Field ◽  
Mechanical Damage ◽  
Magnetic Flux Leakage ◽  
Metal Loss ◽  
Unexpected Result ◽  
Lower Field ◽  
Study Results ◽  
Flux Leakage

This paper describes the design of a new magnetic flux leakage (MFL) inspection tool that performs an inline inspection to detect and characterize both metal loss and mechanical damage defects. An inspection tool that couples mechanical damage assessment as part of a routine corrosion inspection is expected to have considerably better prospects for application in the pipeline industry than a tool that complicates existing procedures. The design is based on study results that show it is feasible to detect and assess mechanical damage by applying a low magnetic field level in addition to the high magnetic field employed by most inspection tools. Nearly all commercially available MFL tools use high magnetic fields to detect and size metal loss such as corrosion. A lower field than is commonly applied for detecting metal loss is appropriate for detecting mechanical damage, such as the metallurgical changes caused by impacts from excavation equipment. The lower field is needed to counter the saturation effect of the high magnetic field, which masks and diminishes important components of the signal associated with mechanical damage. Finite element modeling was used in the design effort and the results have shown that a single magnetizer with three poles is the most effective design. Furthermore, it was found that for the three-pole system the high magnetization pole must be in the center, which was an unexpected result. The three-pole design has mechanical advantages, including a magnetic null in the backing bar, which enables installation of a pivot point for articulation of the tool through bends and restrictions. This design was prototyped and tested at Battelle’s Pipeline Simulation Facility (West Jefferson, OH). The signals were nearly identical to results acquired with a single magnetizer reconfigured between tests to attain the appropriate high and low field levels.

Understanding Magnetic Flux Leakage Signals From Dents

2006 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar ◽  
Alex Rubinshteyn
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Experimental Studies ◽  
Mechanical Damage ◽  
Magnetic Behaviour ◽  
Magnetic Flux Leakage ◽  
Element Analysis ◽  
Aspect Ratios ◽  
Stress Relieving ◽  
Flux Leakage

The Magnetic Flux Leakage (MFL) technique is sensitive both to pipe wall geometry and pipe wall stresses, therefore MFL inspection tools have the potential to locate and characterize mechanical damage in pipelines. However, the combined influence of stress and geometry make MFL signal interpretation difficult for a number of reasons: 1) the MFL signal from mechanical damage is a superposition of geometrical and stress effects, 2) the stress distribution around a mechanically damaged region is very complex, consisting of plastic deformation and residual (elastic) stresses, 3) the effect of stress on magnetic behaviour is not well understood. Accurate magnetic models that can incorporate both stress and geometry effects are essential in order to understand MFL signals from dents. This paper reports on work where FEA magnetic modeling is combined with experimental studies to better understand dents from MFL signals. In experimental studies, mechanical damage was simulated using a tool and die press to produce dents of varying aspect ratios (1:1, 2:1, 4:1), orientations (axial, circumferential) and depths (3–8 mm) in plate samples. MFL measurements were made before and after selective stress-relieving heat treatments. These annealing treatments enabled the stress and geometry components of the MFL signal to be separated. Geometry and stress ‘peaks’ tend in most cases to overlap — however stress features are most prominent in the dent rim region and geometry peaks over central region. In general the geometry signal scales directly with depth. The stress scales less significantly with depth. As a result deep dents will display a ‘geometry’ signature while in shallow dents the stress signature will dominate. In the finite element analysis work, stress was incorporated by modifying the magnetic permeability in the residual stress regions of the modeled dent. Both stress and geometry contributions to the MFL signal were examined separately. Despite using a number of simplifying assumptions, the modeled results matched the experimental results very closely, and were used to aid in interpretation of the MFL signals.

Numerical Simulation and Analysis on Magnetizing Exciter for Magnetic Flux Leakage

2011 ◽  
Vol 474-476 ◽  
pp. 1187-1190
Author(s):  
Qiang Song
Keyword(s):  
Magnetic Flux ◽  
Permanent Magnet ◽  
Flux Density ◽  
Pipe Wall ◽  
Three Dimensional ◽  
Magnetic Flux Leakage ◽  
Magnetic Flux Density ◽  
Outer Diameter ◽  
Element Analysis ◽  
Flux Leakage

Magnetic flux leakage (MFL) is a non-destructive testing method used to inspect the pipe and magnetization of the pipe wall to saturation is essential for anomalies to be reliably and accurately detected and characterized. Axial components of magnetic flux density obtained during the MFL inspection have been simulated using three-dimensional finite element analysis and the effects of magnetizing exciter parameters on magnetic flux density are investigated. The pipe modeled in this paper has an outer diameter of 127mm (5 in.) with a wall thickness of 9 mm (0.354 in.). According to numerical simulations, an increase in the magnetic flux density of pipe wall is observed with an increase in the permanent magnet length and height. It clearly illustrates that Nd-Fe-B permanent magnet assembly with 70 mm length and 40 mm height may magnetize pipe wall to near saturation.

Understanding Magnetic Flux Leakage Signals From Gouges

2010 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar ◽  
Jian Dien Chen ◽  
Chris Alexander
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Mechanical Damage ◽  
Internal Surface ◽  
Magnetic Flux Leakage ◽  
Wall Surface ◽  
Pipe Surface ◽  
Early Results ◽  
Flux Leakage ◽  
Wall Geometry

The Magnetic Flux Leakage (MFL) technique is sensitive both to pipe wall geometry and pipe wall strain, therefore MFL inspection tools have the potential to locate and characterize mechanical damage in pipelines. The present work is the first stage of a study focused on developing an understanding of how MFL signals arise from pipeline gouges. A defect set of 10 gouges were introduced into sections of 12″diameter, 5m long, end capped and pressurized X60 grade pipe sections. The gouging tool displacement ranged (before tool removal) between 2.5 to 12.5mm. Gouges were approximately 50mm in length. The shallowest indentation created only a very slight scratch on the pipe surface, the deepest created a very significant gouge. All gouges were axially oriented. Experimental MFL measurements were made on the external pipe wall surface (pressurized) as well as the internal surface (unpressurized). The early results of the experimental MFL studies, and a hypothesis for the origin of the MFLaxial signal “dipole” are discussed in this paper.

Pipeline corrosion defect parameterisation with magnetic flux leakage inspection: a contextual representation approach

2021 ◽  
Vol 63 (2) ◽  
pp. 95-101
Author(s):  
Xiang Peng ◽  
Huan Liu ◽  
Kevin Siggers ◽  
Zheng Liu
Keyword(s):  
Magnetic Flux ◽  
Population Distribution ◽  
Strength Function ◽  
Gaussian Function ◽  
Interaction Strength ◽  
Magnetic Flux Leakage ◽  
Structural Safety ◽  
Corrosion Defects ◽  
Contextual Representation ◽  
Flux Leakage

Corrosion is one of the significant reasons for oil and gas pipeline failures. In pipeline integrity management programmes, the magnetic flux leakage (MFL) technique is widely used to detect and quantify corrosion defects. The inspection results of MFL list the profiles of individual corrosion defects; however, the structural safety of a pipeline not only depends on the size of individual corrosion defects but also the pattern of closely spaced defects. To achieve a contextual defect representation, the concept of parameterisation, which considers the adjacent defects as additional information of the central defect, is proposed in this study. The process through which to realise this contextual representation is described in this paper. Three parameterisation models are proposed and a two-dimensional Gaussian function is employed to model the interaction strength between adjacent defects. The experimental results demonstrate that the shape context (SC) model associated with the interaction strength function (ISF) shares the highest similarity with human inspectors in comparison with the other two models. Thus, the proposed parameterisation approach can be used to retrieve similar corrosion defects and analyse defect population distribution along a pipeline.

Modelling Magnetic Flux Leakage Signals From Dents

2008 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar ◽  
Kris Marble ◽  
Alex Rubinshteyn ◽  
Mures Zarea
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Mechanical Damage ◽  
Magnetic Behaviour ◽  
Magnetic Flux Leakage ◽  
Element Analysis ◽  
The Past ◽  
Fea Modeling ◽  
Flux Leakage ◽  
Wall Geometry

The Magnetic Flux Leakage (MFL) technique is sensitive both to pipe wall geometry and pipe wall strain, therefore MFL inspection tools have the potential to locate and characterize mechanical damage in pipelines. However, the combined influence of strain and geometry makes MFL signals from dents and gouges difficult to interpret for a number of reasons: 1) the MFL signal from mechanical damage is a superposition of geometrical and strain effects, 2) the strain distribution around a mechanically damaged region can be very complex, often consisting of plastic deformation and residual (elastic) strain, 3) the effect of strain on magnetic behaviour is not well understood. Accurate magnetic models that can incorporate both strain and geometry effects are essential in order to understand MFL signals from mechanical damage. This paper reviews work conducted over the past few years involving magnetic finite element analysis (FEA) modeling of MFL dent signals and comparison with experimental results obtained both from laboratory-dented samples and dented pipe sections.

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