Fiber Bragg grating for measuring internal metal loss

Abstract

A system and method for monitoring internal corrosion in a damaged pipeline are provided. One example includes: applying a reinforcing layer to the outer surface of the pipeline above a defect detected in the inner surface of the pipeline. A test fiber Bragg grating (FBG) detector is mounted on the outer surface of the pipeline above the defect. A reference FBG detector is mounted on the outer surface of the pipeline. The difference in circumferential strain between the test FBG detector and the reference FBG detector is monitored to identify the amount of change in wall thickness above the defect.

Description

Priority requirements

[0001] This application claims priority to U.S. Patent Application No. 18 / 406,845, filed January 8, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to a method for quantifying metal loss occurring on the inner surface of a repaired pipe section having an overlying reinforcement layer, using a fiber Bragg grating (FBG) sensor. Background Technology

[0003] Pipelines are a vital part of the oil and gas industry because they provide a safe and efficient way to transport oil and gas over long distances. Pipelines help maintain a stable energy supply, support economic growth, and ensure the smooth operation of modern society. Therefore, pipeline integrity is crucial for ensuring the safe and reliable transportation and distribution of oil and gas, while preventing leaks, ruptures, and potential failures.

[0004] Metal pipes are subject to various forms of corrosion, both external and internal. When the base wall thickness is less than the minimum required thickness (T... min When this happens, action is needed to cut and replace, or repair the defective asset. In many cases, repair is considered necessary because asset replacement is preferred during normal downtime.

[0005] Compared to other forms of corrosion, internal corrosion affecting the inner wall thickness of pipelines is particularly important for pipeline integrity. Internal metal loss is typically caused by mixtures of transported gases or liquids, such as water, acidic gases, and other factors including flow conditions, the metallurgical composition of the pipeline, microbial corrosion, and operational factors.

[0006] Many repair solutions exist, such as metal sleeves, clamps, and composite / non-metallic sleeves. Composite sleeves / wraps are becoming a common repair method for restoring pipeline integrity due to their ease of installation, immediate repair, minimal production interruption, no hot work (safety), no shoveling / drainage, lightweight design, no added structural stress, and durability (non-corrosive). Regardless of these benefits, composite sleeves are used as a temporary solution, especially for internal corrosion, as they do not prevent corrosion progression, and once the sleeve is in place, the area beneath the repair cannot be inspected using conventional techniques.

[0007] In principle, pipeline operators typically rely on non-destructive testing methods to monitor pipeline integrity, such as routine visual inspection, ultrasonic testing, and other methods. In-line inspection (ILI) tools are also used. However, applying ILI tools is impractical for most pipelines. Furthermore, ILI tools may be unable to detect smaller defects due to their limited resolution. Additionally, ILI tools may be difficult to use in pipelines with sharp bends.

[0008] Therefore, common methods used to monitor pipeline integrity are often time-consuming and expensive, and may be ineffective in detecting early corrosion or metal loss. Furthermore, the reliance on only periodic inspections leaves pipeline operators without real-time information about the pipeline's condition. Summary of the Invention

[0009] The embodiments described herein provide a method for monitoring internal corrosion in a damaged pipeline. The method includes: applying a reinforcing layer to an outer surface of the pipeline above a defect detected in the inner surface of the pipeline; mounting a test fiber Bragg grating (FBG) detector on the outer surface of the pipeline above the defect; and mounting a reference FBG detector on the outer surface of the pipeline. The difference in circumferential strain between the test FBG detector and the reference FBG detector is monitored to identify the amount of change in wall thickness above the defect.

[0010] Another embodiment discloses a system for monitoring internal corrosion in a damaged pipe. The system includes a reinforcement layer located on an outer surface of the pipe above a defect detected on the inner surface of the pipe. A test fiber Bragg grating (FBG) detector is mounted on the pipe above the defect on the inner surface of the pipe; a reference FBG detector is mounted on the outer surface of the pipe. An interrogator is coupled to the test FBG detector, wherein the interrogator measures a first wavelength offset of the reflected signal from the test FBG detector. The interrogator is coupled to the reference FBG detector, wherein the interrogator measures a second wavelength offset of the reflected signal from the reference FBG detector. An analysis system is coupled to the interrogator, wherein the analysis system includes a processor and instructions. The instructions are operable to instruct the processor to acquire the first wavelength offset from the interrogator, acquire the second wavelength offset from the interrogator, calculate circumferential strain below the test FBG detector, and calculate metal loss on the inner surface of the pipe below the reinforcement layer. Attached Figure Description

[0011] Figure 1This is a schematic diagram of a fiber Bragg grating (FBG) system used to monitor metal loss beneath a reinforcing layer or composite sleeve.

[0012] Figure 2 This is a process flow diagram of a method 200 for monitoring metal loss in defects on the inner surface of a pipe.

[0013] Figure 3A and Figure 3B It is a view of the simulated structure design.

[0014] Figure 4A This is a graph showing the change in the center wavelength of the FBG under different strains, corresponding to different metal loss thicknesses.

[0015] Figure 4B This is a graph showing the correlation between the change in the center wavelength of the FBG and the strain, illustrating the metal loss thickness in millimeters.

[0016] Figure 5A and Figure 5B This is a graph showing the simulation results of differential circumferential strain versus internal uniform metal loss thickness (in millimeters) for two configurations of GFRP structures (on the pipe and on the sleeve).

[0017] Figure 6A and Figure 6B This is a graph showing the simulation results of differential circumferential strain versus internal uniform metal loss thickness (in millimeters) for two configurations of CFRP structures (on the pipe and on the sleeve).

[0018] Figure 7A and Figure 7B The results are simulations of the differential circumferential strain of the GFRP structure at two different locations (on the pipe and on the sleeve) relative to the thickness (in millimeters) of the internal local metal loss.

[0019] Figure 8A and Figure 8B This is a graph showing the simulation results of the differential circumferential strain of the CFRP structure versus the thickness (in millimeters) of the internal local metal loss at two different locations (on the pipe and on the sleeve).

[0020] Figure 9A and Figure 9B This is a simulated graph showing the change in circumferential strain relative to the thickness of the metal loss at two different locations (on the pipe and on the sleeve), with different values ​​of the defect size (local metal loss).

[0021] Figure 10A and Figure 10BThis is a simulated graph showing the change in circumferential strain relative to the thickness of the metal loss at two different locations (on the pipe and on the sleeve), with different values ​​of the defect size (local metal loss). Detailed Implementation

[0022] In recent years, advanced sensing technologies, such as fiber Bragg grating (FBG) sensors, have become valuable tools for pipeline monitoring. FBG sensors reflect and filter light of specific wavelengths, making them ideal for measuring physical quantities such as temperature, strain, and pressure. FBG sensors are compact and offer high sensitivity and reliability, thus providing economic viability in harsh environments.

[0023] Pipe segments used to form pipelines are typically selected from standard-grade pipes used for oil and gas pipeline transmission. For example, the steel alloy used for pipe segments can include carbon steel such as API 5L, ASTM, API-5CT, including grades such as API 5L B, APIX60, A106 B, and A333 6. Pipe thickness can range from 5.5 to 40 inches, and pipe diameter can range from 2 inches to 50 inches.

[0024] When defects or metal loss are detected in a pipe segment (or pipe), temporary repairs are performed until the pipe segment is replaced. Two types of metal loss are observed in operation: uniform metal loss and non-uniform (localized) metal loss. In uniform metal loss, a uniform reduction in pipe wall thickness occurs along many or all pipe segments. This is the case for general metal loss or corrosion. Non-uniform or localized metal loss occurs when this reduction only affects a small area within the inner side of the pipe (such as due to pitting corrosion). The size of localized metal loss can vary from 1 mm to a diameter of 100 mm or larger. Accumulation of localized metal loss can occur in an area, such as a lower point in the pipe, a side feed point from a high-water-content well, etc.

[0025] Reinforcing layers, such as sleeves made of composite materials for wrapping, have become a standard method for restoring the structural integrity of pipe segments. Composite materials are easy to apply, require no welding or thermal work, do not significantly add stress or load to the structure, and are relatively durable, lasting, for example, up to 20 years. Reinforcing layers or composite sleeves can be made of glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP), aramid fiber reinforced plastic, etc. The thickness of the reinforcing layer or sleeve is calculated based on the design pressure of the steel pipe, the pipe diameter, the allowable circumferential strain, the circumferential modulus of the sleeve, and the expected time range for the pipe wall to end its life. For example, according to the aforementioned standards, the thickness of composite sleeves can range from 1 mm to 50 mm or greater. The reinforcing layer includes fibers embedded in a matrix resin, which acts as a binder to reinforce the fibers and form a solid structure. The matrix resin is typically a thermosetting resin, such as epoxy resin, vinyl ester, polyurethane, etc. In some embodiments, the matrix material may also be made of a thermoplastic resin. Generally, a filler material is applied under the reinforcing layer to transfer the load between the steel surface of the pipe and the reinforcing layer.

[0026] In most applications where corrosion occurs on the inner surface of pipelines, and in subsea environments, reinforcement layers are considered a temporary solution. These layers are held in place until the next planned shutdown, during which time the defective section of the pipeline is removed and replaced. Reinforcement layers pose a challenge to monitoring internal corrosion growth using conventional inspection methods, as the layer itself creates an obstacle to optically or by the applied tools used to monitor corrosion. The inability to monitor corrosion presents significant operational problems because the timing of repairing any faults in the section cannot be anticipated.

[0027] Pipeline failures can have severe environmental and economic consequences, often resulting in prolonged downtime that disrupts production. Therefore, even when the composite enclosure remains intact and corrosion on the inner surface is under control, maintenance departments typically adopt a conservative approach, mitigating the risk of sudden failures by replacing repair sections during scheduled downtime. However, this method is costly because replacing segmented pipelines requires shutdown, isolation, and cleaning.

[0028] Therefore, there is a need for technologies that enable corrosion monitoring beneath the reinforcement layer to avoid unnecessary replacements and thus extend the service life of pipeline assets. The embodiments described herein provide a method that uses FBG sensors to quantify metal loss on the inner surface of a repaired pipe section covered with a composite sleeve or reinforcement layer. Internal metal loss affects the stiffness of the pipe, resulting in changes in circumferential or annular strain on the outer surface of the pipe. This strain change can then be transmitted to the reinforcement layer or composite sleeve wrapped around the pipe.

[0029] In some embodiments, FBG sensors placed outside the composite sleeve are configured to monitor these changes in circumferential strain and use the collected data to monitor the metal loss condition of the pipeline. Therefore, using the methods described herein, pipeline operators can accurately and reliably monitor internal metal loss, thereby allowing for proactive maintenance and prevention of pipeline failures. These methods allow for the detection of, for example, uniform metal loss from general corrosion and erosion, as well as localized metal loss or pitting.

[0030] Figure 1 This is a schematic diagram of a fiber Bragg grating (FBG) system 100 used to monitor metal loss beneath a reinforcing layer or composite sleeve 102. A first FBG (referred to as test FBG sensor 104) is mounted on the composite sleeve above an internal defect 106 (such as localized metal loss in the wall of pipe 108). A second FBG sensor (referred to as reference FBG sensor 110) is mounted to the composite sleeve 102, away from the internal defect 106, and serves as a reference to compensate for temperature effects. In some embodiments, adhesive 112 is used to mount each of the FBG sensors 104 and 110 to the composite sleeve 102. In some embodiments, the FBG sensors 104 and 110 are mounted inside the composite sleeve 102 (e.g., placed on layers of the composite sleeve 102) and then covered by other layers of the composite sleeve 102 as the composite sleeve 102 is wound around the pipe 108. In other embodiments, FBG sensors 104 and 110 are mounted directly on pipe 108, and composite sleeve 102 is wound around FBG sensors 104 and 110.

[0031] Two FBG sensors 104 and 110 are connected to an interrogation unit or interrogator 114, which is configured to send optical signals to the FBG sensors 104 and 110 via fiber optic cable 116 or single-mode fiber to measure the wavelength shift of the reflected signals. The wavelength shift is directly related to the strain experienced by the FBG sensors 104 and 110 and can be used to measure the extent of internal defects 106 beneath the composite sleeve 102. A computer 118 is used to analyze the data on the wavelength shift collected by the FBG sensors 104 and 110. The use of a reference FBG sensor 110 for temperature compensation improves the accuracy of measurements under varying temperature conditions.

[0032] Computer 118 includes a sensor interface 120 that connects computer 118 to interrogator 114, thereby allowing computer 118 to acquire wavelength offset data from each of FBG sensors 104 and 110. Computer 118 includes processor 122 and data memory 124, wherein the data memory 124 includes instructions instructing processor 122 to collect wavelength offset data from each of FBG sensors 104 and 110 and convert the wavelength offset into strain data, which allows for accurate measurement of metal loss.

[0033] As described herein, in some embodiments, filler 126 is applied over conduit 108 before being applied to composite sleeve 102. Filler 126 transfers stress from conduit 108 to composite sleeve 102. The adhesive 112 used to encapsulate FBG sensors 104 and 110 and adhere the sensors to composite sleeve 102 can be selected based on the location of the conduit. For example, a hydrophilic adhesive is used for subsea applications.

[0034] Figure 1 The configuration shown is used in pipes where localized corrosion or pitting corrosion has been detected on the inner surface. In embodiments where the pipe is experiencing general corrosion or "corrosion lakes" are observed, several FBGs covering the entire circumference of the pipe can be utilized. A "corrosion lake" is a region of material loss that is neither as narrow as pitting corrosion nor as wide as general corrosion. A "corrosion lake" has depth and area and may have pitting corrosion within the region of metal loss. In these embodiments, a fiber grating array can be integrated along the length of the composite sleeve 102.

[0035] As described herein, metal loss can be calculated based on the circumferential strain of pipe 108. In these calculations, it can be assumed that the pipe has a radius R, a wall thickness δ, and a Young's modulus E, and is subjected to an internal pressure P 128. The expression for the strain along the circumferential direction (called circumferential strain) can be expressed as ε = P·R / E·δ. Under normal conditions where the pipeline pressure is generally stable, the circumferential strain ε is inversely proportional to the pipe wall thickness. Therefore, the change in any measured value of the circumferential strain can be used to estimate the reduction in wall thickness caused by internal corrosion, where R and E are assumed to remain constant even in the case of metal loss.

[0036] The circumferential strain on the conduit 108 is transferred to a composite sleeve 102 mounted on the conduit 108. A test FBG sensor 104 mounted on the composite sleeve 102 captures this strain. FBG sensors 104 and 110 are composed of shorter length optical fibers comprising, for example, an array of periodic defects created by laser etching, which produces an interference pattern that reflects light of a specific wavelength. When strain occurs in the test FBG sensor 104, the spacing between these periodic defects changes, and the wavelength of the light reflected by this spacing shifts proportionally to the strain value. An interrogation unit 114 is used to detect and analyze the change in the wavelength of the light. As described herein, the interrogation unit 114 is connected to the FBG sensors 104 and 110 via an optical fiber cable 116, for example, comprising a single-mode optical fiber for each of the FBG sensors 104 or 110. Therefore, by utilizing the change in the wavelength of reflected light, the test FBG sensor 104 can accurately measure the strain experienced by the composite sleeve, and this strain is related to the amount of metal loss affecting the pipe wall. Furthermore, since the FBG sensor is sensitive to both strain and temperature changes, a reference FBG sensor 110 placed near the test FBG sensor 104 on the composite sleeve 102 is used to compensate for the temperature. The reference FBG sensor 110 does not directly measure temperature, but rather measures the change in circumferential strain due to pipe expansion and contraction during temperature variations.

[0037] Therefore, the strain measurements from the test FBG sensor 104 are correlated with the corrosion status of the pipeline. If multiple corrosion defects exist on the same pipeline, multiple FBG sensors can be deployed in a distributed manner along the pipeline or along the repair section to collectively provide information about the corrosion status of each section. A single interrogation unit can be used to receive signals, locate positions, and track the wavelength offset of all FBG sensors.

[0038] This method and system are non-invasive, thus eliminating the need for invasive procedures that could damage pipeline structures. It provides accurate and reliable measurements of internal metal loss, making it an effective tool for long-term monitoring. The FBG sensors 104 and 110 are durable and can withstand harsh environmental conditions, making them suitable for challenging environments. Monitoring metal loss is a cost-effective method compared to traditional inspection methods, making it an attractive option for pipeline operators seeking to improve their maintenance and inspection capabilities.

[0039] Figure 2 This is a process flow diagram of a method 200 for monitoring metal loss in a defect on the inner surface of a pipe. Method 200 begins at block 202 when the defect is located on the inner surface of the pipe. Method 200 can be performed by ultrasonic testing, imaging, or other testing techniques. In some embodiments, at block 204, a surface is prepared for repair, for example, by applying a filler to the outer surface of the pipe above the defect. At block 206, a sleeve is mounted over the filler. As described herein, the sleeve can be a plastic reinforcement layer, such as glass fiber reinforced plastic or carbon fiber reinforced plastic. At block 208, a test FBG sensor is mounted on the sleeve above the defect on the inner surface of the pipe. At block 210, a reference FBG sensor is mounted on the sleeve away from the defect. At block 212, the test FBG sensor and the reference FBG sensor are connected to an interrogator via fiber optic cables (such as single-mode fiber). In some embodiments, the single-mode fiber is coupled to each FBG sensor. In other embodiments, a single fiber is used in series to each FBG sensor, wherein each sensor responds to a different wavelength. At box 214, the interrogator is connected to a computer via, for example, a serial interface, parallel interface, Wi-Fi interface, or network interface. At box 216, corrosion on the inner surface of the pipe is monitored. At box 218, if premature corrosion is detected, the pipe is replaced. Example

[0040] The utility and efficiency of the FBG sensor in monitoring internal metal loss in carbon steel pipes with glass fiber reinforced plastic (GFRP) and carbon reinforced plastic (CFRP) sleeves were tested through simulation. The amount of circumferential strain change was tested in two configurations. In the first configuration, the FBG sensor was placed on top of the composite sleeve. In the other configuration, the FBG sensor was embedded at the interface between the steel surface and the composite sleeve. Two design structures were simulated for each defect type (uniform defect and localized defect). As shown in the examples below, the sensitivity of the technology increases with the size of the defect. For example, the response increases with changes in thickness or metal loss.

[0041] Figure 3A and Figure 3B This is a view of the simulated structural design. Different pipe wall thicknesses are used to simulate uniform metal loss, while an internal defect section 106 (e.g., 10×10mm in size) is also considered. Figure 3B Simulations were performed for localized metal loss (as shown in the illustrations). The material and design characteristics of the different layers are summarized in Tables 1 and 2, which were used as inputs to the simulation jobs of the proposed example.

[0042] Table 1: Material properties of different layers for the simulation example

[0043] Table 2: Exemplary piping designs for simulated operations

[0044] Figure 4A This is a curve showing the change in the center wavelength of the FBG under different strains, corresponding to different metal loss thicknesses. Figure 4B This is a graph showing the correlation between the change in the center wavelength of the FBG and strain, illustrating the metal loss thickness in millimeters.

[0045] An FBG (Fast-Fiber Gap) sensor is a passive optical component that queries data by periodically recording wavelength modulation along the length of the fiber core. The measured data is encoded in the wavelength of the light reflected by the FBG. The FBG reflects a narrow band of light at a specific wavelength, commonly referred to as the Bragg wavelength: λ. b Any change in temperature or strain results in a shift in the reflected wavelength, Δλ. By combining this with a reference FBG used for temperature effect compensation, the amount of strain change caused by metal loss can be distinguished. Figure 4A The figure shows the offset of the center reflection wavelength of the FBG due to strain changes.

[0046] Figure 4B This is a schematic diagram illustrating the variation of the Bragg wavelength with respect to strain and equivalent metal loss thickness. The minimum detectable metal loss thickness is limited by the sensitivity of the FBG sensor, the sensor's placement on the sleeve, background noise (e.g., temperature), interrogator resolution, and pipe diameter, internal pressure, thickness, and dimensions. The minimum detectable metal loss is also affected regardless of whether the pipe is located on land, underground, or underwater. The benefits of FBG sensors make them suitable and effective for monitoring the integrity and performance of onshore and offshore pipelines. Therefore, depending on the desired sensitivity and applicability, the method described herein can use an FBG sensor (placed on the sleeve or at the interface between the composite sleeve and the pipe) to monitor internal metal loss beneath the composite sleeve.

[0047] Figure 5A and Figure 5B This is a graph showing the simulation results of differential circumferential strain versus internal uniform metal loss thickness (in millimeters) for two configurations of GFRP structures (on the pipe and on the sleeve). Figure 5A and Figure 5B The graphs in the figure represent various internal pressures between 200 psi and 1000 psi. Strain increases with increasing metal loss thickness, which is equivalent to a decrease in pipe wall thickness. Because the commercial interrogator has a resolution of approximately 1 pm (which corresponds to a strain resolution of 1 με), the FBG sensor is able to detect slight changes in circumferential strain. The sensitivity of the FBG sensor allows it to detect small changes in circumferential strain with an accuracy of Δε = 1 με. For both configurations, this change can indicate a small, uniform metal loss of less than 0.5 mm.

[0048] Figure 6A and Figure 6B This is a graph showing the simulation results of differential circumferential strain versus internal uniform metal loss thickness (in millimeters) for two configurations of CFRP structures (on the pipe and on the sleeve). Figure 6A and Figure 6B The graphs shown represent various internal pressures between 500 psi and 5000 psi. Strain increases with increasing metal loss thickness, which is equivalent to a decrease in pipe wall thickness. Because the commercial interrogator has a resolution of approximately 1 pm (which corresponds to a strain resolution of 1 με), the FBG sensor is able to detect slight changes in circumferential strain. The sensitivity of the FBG sensors allows them to detect small changes in circumferential strain with an accuracy of Δε = 1 με. For both configurations, this change can indicate a small, uniform metal loss of less than 0.5 mm.

[0049] Figure 7A and Figure 7B The results are simulations of the differential circumferential strain of the GFRP structure at two different locations (on the pipe and the sleeve) relative to the thickness (in millimeters) of the internal local metal loss. Figure 7A and Figure 7BThe graphs in the figure represent various internal pressures between 200 psi, 400 psi, 600 psi, 800 psi, and 1000 psi. In this case, the size of the metal loss is simulated as 10 mm × 10 mm (width × length). Similarly, the strain increases with the thickness of the metal loss, which is equivalent to a decrease in pipe wall thickness. The minimum detectable metal loss is highly dependent on the applied internal pressure. For an FBG strain resolution of 1 με, the minimum detectable metal loss thickness ranges from approximately 3.5 mm to 7 mm for the "on pipe" configuration and from approximately 8 mm to 11 mm for the "on sleeve" configuration.

[0050] Figure 8A and Figure 8B This is a graph showing the simulation results of differential circumferential strain of the CFRP structure versus the thickness (in millimeters) of the internal local metal loss at two different locations (on the pipe and on the sleeve). It is noteworthy that for various internal pressures between 500 psi and 5000 psi, the size of the metal loss is simulated as 10 mm × 10 mm (width × length). Similarly, the strain increases with increasing metal loss thickness, which is equivalent to a decrease in pipe wall thickness. Here, the minimum detectable metal loss is highly dependent on the applied internal pressure. For an FBG strain resolution of 1 με, the minimum detectable metal loss thickness ranges from approximately 2.5 mm to 5 mm for the "on the pipe" configuration and from approximately 5.5 mm to 10 mm for the "on the sleeve" configuration.

[0051] Figure 9A and Figure 9B This is a simulated graph showing the change in circumferential strain relative to the metal loss thickness for different sizes of defects (localized metal loss) at two different locations (on the pipe and on the sleeve). The defect is simulated as a square hole with side length l, where l ranges from 1 mm to 15 mm. The depth of the simulated hole is shown as the "metal loss thickness". Figure 9A and Figure 9B In the simulation, the sleeve was modeled as 7mm GFRP. The pipe thickness was 13mm, and the applied internal pressure was 600psi.

[0052] Figure 10A and Figure 10BThis is a simulated graph showing the change in circumferential strain relative to the metal loss thickness for different sizes of defects (localized metal loss) at two different locations (on the pipe and on the sleeve). The defect is simulated as a hole with radius r, where r ranges from 1 mm to 15 mm. A uniform metal loss scenario is also shown. The depth of the simulated hole is shown as the "metal loss thickness". Figure 10A and Figure 10B In the simulation, the sleeve was modeled as 6 mm thick CFRP. The pipe thickness was 13 mm, and the applied internal pressure was 1200 psi.

[0053] Simulations were performed for two configurations: one with 7 mm GFRP and the other with 6 mm CFRP. The pipe thickness was 13 mm, and the applied internal pressure was 600 psi for the first configuration and 1250 psi for the second configuration. The results for both cases are highlighted: the FBG is mounted on the pipe and placed on the outside of the sleeve.

[0054] Figure 9A , Figure 9B , Figure 10A and Figure 10B The simulation results are summarized in Table 3. The minimum detectable metal loss increases with the size of the defect. This is attributed to the fact that the internal pressure applied at the location of the defect (i.e., the region) is also applied to the wall of the defect. This will increase the area and value of the strain trapped on the outside of the pipe or on the sleeve. Considering the strain resolution of FBG is 1 με, Table 3 shows the minimum detectable metal loss calculated for each case and scenario (i.e., defect size and FBG placement).

[0055] Table 3: Minimum detectable metal loss for different values ​​of simulated configuration and defect size. Example

[0056] The embodiments described herein provide a method for monitoring internal corrosion in a damaged pipeline. The method includes: applying a reinforcing layer to the outer surface of the pipeline above a defect detected on the inner surface of the pipeline. A test fiber Bragg grating (FBG) detector is mounted on the outer surface of the pipeline above the defect. A reference FBG detector is mounted on the outer surface of the pipeline. The difference in circumferential strain between the test FBG detector and the reference FBG detector is monitored to identify the amount of change in wall thickness above the defect.

[0057] In an aspect that can be combined with any other aspect, installing the reinforcing layer includes: applying a filler to the outer surface of the pipe above the defect, and then mounting the reinforcing layer over the filler.

[0058] Among aspects that can be combined with any other aspect, installing a reinforcement layer includes using the reinforcement layer to wrap the pipe.

[0059] In aspects that can be combined with any other aspect, installing the reinforcement layer includes installing a sleeve of the reinforcement layer over the pipe.

[0060] In aspects that can be combined with any other aspect, the reinforcing layer comprises a glass fiber reinforced plastic (GFRP) composite material.

[0061] In aspects that can be combined with any other aspect, the reinforcing layer comprises a carbon fiber reinforced plastic (CFRP) composite material.

[0062] In an aspect that can be combined with any other aspect, mounting the test FBG detector above the defect includes: mounting the test FBG detector on the outer surface of the pipe above the defect, and then applying the reinforcement layer.

[0063] In aspects that can be combined with any other aspect, mounting the test FBG detector above the defect includes: incorporating the test FBG detector into the reinforcement layer.

[0064] In an aspect that can be combined with any other aspect, mounting the test FBG detector above the defect includes: adhering the test FBG detector to the surface of the reinforcement layer.

[0065] In aspects that can be combined with any other aspect, the method of determining local metal loss includes using the amount of variation in wall thickness on the defect. In one aspect, the size of the defect is between about 1 mm and about 100 mm. In another aspect, the local metal loss is between about 0.5 mm and about 10 mm. In another aspect, the local metal loss is between about 3.5 mm and about 7 mm. In another aspect, the local metal loss is between about 8 mm and about 11 mm. In one aspect, the detectable amount of local metal loss is inversely proportional to the size of the defect.

[0066] Another embodiment discloses a system for monitoring internal corrosion in a damaged pipe. The system includes a reinforcement layer located on an outer surface of the pipe above a detected defect on the inner surface of the pipe. A test fiber Bragg grating (FBG) detector is mounted on the outer surface of the pipe above the defect on the inner surface of the pipe; a reference FBG detector is mounted on the outer surface of the pipe. An interrogator is coupled to the test FBG detector, wherein the interrogator measures a first wavelength offset of a reflected signal from the test FBG detector. The interrogator is coupled to the reference FBG detector, wherein the interrogator measures a second wavelength offset of a reflected signal from the reference FBG detector. An analysis system is coupled to the interrogator, wherein the analysis system includes a processor and instructions. The instructions are operable to instruct the processor to acquire the first wavelength offset from the interrogator, acquire the second wavelength offset from the interrogator, calculate circumferential strain below the test FBG detector, and calculate metal loss on the inner surface of the pipe below the reinforcement layer.

[0067] In aspects that can be combined with any other aspect, the test FBG detector is mounted to the surface of the reinforcement layer.

[0068] In aspects that can be combined with any other aspect, the reference FBG detector is mounted to the surface of the enhancement layer.

[0069] In aspects that can be combined with any other aspect, the reinforcing layer comprises a glass fiber reinforced plastic composite material.

[0070] In aspects that can be combined with any other aspect, the reinforcing layer comprises a carbon fiber reinforced plastic composite material.

[0071] In aspects that can be combined with any other aspect, the reinforcing layer includes epoxy resin, polyurethane, or vinyl ester, or any combination thereof.

[0072] Other embodiments are also within the scope of the appended claims.

Claims

1. A method for monitoring internal corrosion in a damaged pipeline, comprising: The reinforcing layer is applied to the outer surface of the pipe above the defect detected in the inner surface of the pipe; A test fiber Bragg grating (FBG) detector is mounted on the outer surface of the pipe above the defect. A reference FBG detector is installed on the outer surface of the pipe; as well as The difference in circumferential strain between the test FBG detector and the reference FBG detector is monitored to identify the amount of change in wall thickness above the defect.

2. The method as described in claim 1, wherein, Installing the reinforcement layer involves applying a filler to the outer surface of the pipe above the defect, and then installing the reinforcement layer over the filler.

3. The method as described in claim 1, wherein, Installing the reinforcement layer includes: using the reinforcement layer to wrap the pipe.

4. The method of claim 1, wherein, Installing the reinforcement layer includes installing a sleeve formed by the reinforcement layer onto the pipe.

5. The method of claim 1, wherein, The reinforcing layer comprises a glass fiber reinforced plastic (GFRP) composite material.

6. The method of claim 1, wherein, The reinforcing layer comprises carbon fiber reinforced plastic (CFRP) composite material.

7. The method of claim 1, wherein, Mounting the test FBG detector above the defect includes: mounting the test FBG detector on the outer surface of the pipe above the defect, and then applying the reinforcement layer.

8. The method of claim 1, wherein, Mounting the test FBG detector above the defect includes: integrating the test FBG detector into the reinforcement layer.

9. The method of claim 1, wherein, Mounting the test FBG detector above the defect includes: attaching the test FBG detector to the surface of the reinforcement layer.

10. The method of claim 1, wherein the method comprises: The amount of change in wall thickness above the defect is used to determine local metal loss.

11. The method of claim 10, wherein, The size of the defect is between approximately 1 mm and approximately 100 mm.

12. The method of claim 10, wherein, The local metal loss is between approximately 0.5 mm and approximately 10 mm.

13. The method of claim 10, wherein, The local metal loss is between approximately 3.5 mm and approximately 7 mm.

14. The method of claim 10, wherein, The local metal loss is between approximately 8 mm and approximately 11 mm.

15. The method of claim 10, wherein the detectable amount of local metal loss is inversely proportional to the size of the defect.

16. A system for monitoring internal corrosion in damaged pipes, comprising: A reinforcing layer located on the outer surface of the pipe above a defect detected on the inner surface of the pipe. A fiber Bragg grating (FBG) detector is installed on the outer surface of the pipe, above the defect on the inner surface of the pipe. A reference FBG detector is mounted on the outer surface of the pipe; An interrogator is connected to the test FBG detector, wherein the interrogator measures a first wavelength offset of the reflected signal from the test FBG detector; The interrogator is coupled to the reference FBG detector, wherein the interrogator measures a second wavelength offset of the reflected signal from the reference FBG detector; and An analysis system, connected to the interrogator, wherein the analysis system includes: Processor; and Instructions, operable to direct the processor to perform the following operations: Obtain the first wavelength offset from the interrogator; Obtain the second wavelength offset from the interrogator; Calculate the circumferential strain below the test FBG detector; and Calculate the metal loss on the inner surface of the pipe below the reinforcement layer.

17. The system of claim 16, wherein, The test FBG detector is mounted on the surface of the enhancement layer.

18. The system of claim 16, wherein, The reference FBG detector is mounted on the surface of the enhancement layer.

19. The system of claim 16, wherein, The reinforcing layer comprises a glass fiber reinforced plastic composite material.

20. The system of claim 16, wherein, The reinforcing layer comprises a carbon fiber reinforced plastic composite material.

21. The system of claim 16, wherein, The reinforcing layer comprises epoxy resin, polyurethane, or vinyl ester, or any combination thereof.

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