RFEC Corrosion Inspection Using 3-Axis Fluxgate Magnetometer
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Solution Overview
Problem
Current electromagnetic (EM) methods for corrosion inspection in oil and gas industry pipes fail to accurately determine the location, shape, and depth of defects, leading to misleading interpretations due to averaging metal loss information over the entire circumference, which can result in false assessments of well integrity.
Innovation Solution
A remote field eddy current (RFEC) system utilizing a three-axis fluxgate magnetometer to generate and measure magnetic fields, allowing for the determination of the azimuth location and extent of defects in pipes by interpreting radial components of the measured magnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional EM methods (time-domain or frequency-domain) are used for corrosion inspection, then the inspection can be performed with straightforward tool design and lower power usage, but the measurement precision is insufficient because metal loss information is averaged over the entire circumference, leading to inability to determine azimuth location of defects
Solution Approach 1:
The patent segments the magnetic field measurement into three orthogonal components (radial, tangential, and axial) using a 3-axis fluxgate magnetometer. This segmentation allows the system to measure different aspects of the magnetic field separately, enabling determination of both the presence and azimuth location of corrosion defects by analyzing the pattern of perturbations in each component.
Solution Approach 2:
The patent transitions from traditional single-component or two-component magnetic field measurements to three-dimensional vector measurements using a 3-axis fluxgate magnetometer. By measuring the magnetic field in three orthogonal dimensions, the system can determine the azimuth location of defects through the spatial pattern of field perturbations, adding the dimension of angular resolution to the inspection capability.
2Measurement precision
If traditional coil-based receivers are used in RFEC methods, then the tool design is straightforward, but the sensitivity to magnetic field is insufficient, resulting in low signal-to-noise ratio for outer barriers
Solution Approach 1:
The patent replaces traditional coil-based magnetic field receivers with a fluxgate magnetometer, which uses a fundamentally different measurement principle based on magnetic saturation and harmonic detection rather than electromagnetic induction. This substitution provides significantly higher sensitivity to magnetic field variations, enabling detection of corrosion in outer casings where the magnetic field signal is very weak.
3Productivity
If the receiver coil is placed close to the transmitter coil, then the signal strength is higher, but the logging speed is reduced due to separate stimulation and reception stages required in time-domain methods
Solution Approach 1:
The patent employs frequency-domain measurement with continuous sinusoidal excitation at frequencies typically between 1-100 Hz. This periodic action allows the system to maintain continuous measurement while using signal processing techniques to separate the response signal from noise, achieving both high logging speed and reliable detection through frequency-based signal separation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate and detailed characterization of corrosion defects, including azimuthal information, overcoming the limitations of existing EM tools by enhancing sensitivity and resolving the challenge of localized defect detection in multi-casing systems.
Implementation Method 1
a magnetic field generator located within the holder and configured to generate a first magnetic field B0
Implementation Method 2
a 3-axis fluxgate magnetometer located within the holder, at a given distance away from the transmitter, along the longitudinal axis X, wherein the fluxgate magnetometer is configured to measure a second magnetic field B
Implementation Method 3
The Time domain method, also known as the 'Pulsed Eddy Current' method (PEC), generates pulsating EM fields within the well, using transmitter coils. At fixed time intervals, the transmitters are switched off and the decaying EM fields, resulting from the eddy currents induced in the pipes, are measured and recorded.
Data Source
AI summary
A remote field eddy current, RFEC, system for detecting an azimuth location of a defect in a pipe includes a holder extending along a longitudinal axis X and shaped to flow through the pipe, a magnetic field generator located within the holder and configured to generate a first magnetic field B0, a 3-axis fluxgate magnetometer located within the holder, at a given distance away from the transmitter, along the longitudinal axis X, wherein the fluxgate magnetometer is configured to measure a second magnetic field B, which is a result of the first magnetic field B0 interacting with the defect in the pipe, and a controller located within the holder and configured to receive a value of the second magnetic field B and to determine an azimuth of the defect in the pipe by interpreting radial components of the measured field, and an extent of the defect based on the second magnetic field B.