Non-intrusive strain monitoring apparatus and method for a marine flexible riser

Abstract

The application discloses a non-invasive strain monitoring device and method for a marine flexible riser and belongs to the technical field of pipeline monitoring. The non-invasive strain monitoring device and method for the marine flexible riser comprise two support frames, the two support frames are parallel to each other, a mounting groove is formed in the middle of each support frame, the mounting groove is circularly arranged, four measuring rods are arranged between the two support frames, the measuring rods are cylindrical, an optical fiber grating sensor is arranged in the inside of each measuring rod, the four measuring rods are arranged in a ring shape at equal intervals, each measuring rod is parallel to an axis of the center of the mounting groove, the distance between each measuring rod and the axis of the center of the mounting groove is equal, a connecting part is fixedly connected to the two ends of each measuring rod, the connecting part is connected and fixed with the support frame, and the connecting part is detachably connected with the support frame. The non-invasive measurement method is adopted, damage of the sensor itself to the pipeline is avoided, and the device is convenient to disassemble and reusable.

Description

Technical Field

[0001] This invention relates to the field of pipeline monitoring technology, and more specifically, to a non-invasive strain monitoring device and method for marine flexible risers. Background Technology

[0002] With the rapid development of national industry, energy demand has become increasingly strong, which in turn has driven the rapid development of pipeline engineering. To date, my country has built several main oil and gas pipelines, and according to the national long-term plan for oil and gas long-distance pipelines, many more pipelines will be built and put into operation in the future. However, due to the special nature of the spaces where oil and gas pipelines are laid, they inevitably encounter various adverse geological conditions, which are difficult to completely avoid. Therefore, pipeline disaster risk control has become a challenge.

[0003] A search revealed a patent document with publication number CN103453844A that provides an online monitoring method for the deformation of flexible pipelines based on fiber optic gratings. This method applies fiber optic grating strain measurement technology to the monitoring of tensile layer deformation in marine flexible pipelines and combines the fiber optic deployment process with the flexible pipe manufacturing process, completing the sensor deployment during the flexible pipeline manufacturing stage.

[0004] In the above-mentioned solutions, the deployment of optical fibers within the flexible pipe increases the cost of deformation detection and restricts flexible arrangement and replacement. Therefore, we propose a non-invasive strain monitoring device and method for marine flexible risers. Summary of the Invention

[0005] 1. Technical problems to be solved

[0006] The purpose of this invention is to provide a non-invasive strain monitoring device and method for marine flexible risers, so as to solve the problems mentioned in the background art.

[0007] 2. Technical Solution

[0008] This invention is achieved through the following technical solution:

[0009] A non-invasive strain monitoring device and method for marine flexible risers includes two parallel support frames. Each support frame has a circular mounting groove in its center. Four cylindrical measuring rods, each housing a fiber optic grating sensor, are arranged in a ring with equal spacing. Each measuring rod is parallel to the axis of the center of the two mounting grooves, and the distance between each measuring rod and the axis of the mounting groove is equal. Each measuring rod has a connecting portion fixedly connected to both ends, and the connecting portion is detachably connected to the support frame.

[0010] As an optional solution to the technical solution in this application, the support frame is composed of a first structural part and a second structural part of the same shape, and the first structural part and the second structural part are fixedly connected by bolts.

[0011] As an optional solution to the technical solution of this application, the diameter of the connecting part is larger than the diameter of the measuring rod, four pipe clamps are fixedly connected to the support frame, the pipe clamps are provided with slots inside, the connecting part is inserted into the slots, and a bolt rod is installed at the end of the pipe clamp, the bolt rod is used to adjust the clamping force of the pipe clamp on the connecting part.

[0012] As an optional solution to the technical solution in this application, the support frame is made of rigid metal, and the measuring rod is made of a material with mechanical properties similar to those of a marine flexible riser.

[0013] As an optional solution to the technical solution of this application, the measuring rod is made of glass fiber, the measuring rod is 400mm long and 4mm in radius, and the radius of the connecting part is 8mm.

[0014] A non-invasive strain monitoring method for marine flexible risers includes the following steps:

[0015] S1. Fix two support frames to the outside of the flexible riser, and fix the measuring rod between the two support frames through the connecting part;

[0016] S2. Obtain the center wavelength of the fiber optic grating sensor inside the four measuring rods;

[0017] S3. Calculate the strain of each measuring rod based on the center wavelength of the fiber Bragg grating sensor. The calculation formula is as follows:

[0018]

[0019] Where, ε xw The measured strain of the measuring rod is Δλ. B λ is the change in the center wavelength of the optical fiber. B P is the center wavelength of the optical fiber. e K is the photoelastic coefficient. ε This is the strain sensitivity coefficient;

[0020] S4. Correct the strain of the measuring rod;

[0021] S5. Calculate the maximum strain of the flexible riser based on the strain of the measuring rod. The calculation formula is as follows:

[0022]

[0023] Where ε1 is the maximum value of the normal strain of the measuring rod, ε2 is the minimum value of the normal strain of the measuring rod, α is the angle between the location of the measuring rod corresponding to the maximum normal strain in the cross-section of the flexible riser and the center of the flexible riser cross-section, and ε max R is the maximum strain of the flexible riser. C R is the distance between the measuring rod and the central axis of the flexible riser, and R is the radius of the flexible riser.

[0024] As an optional solution to the technical solution of this application, the distance between the measuring rod and the outer surface of the flexible riser is determined by the following formula:

[0025]

[0026] Where d is the distance between the measuring rod and the outer surface of the flexible riser, and r m R is the radius of the measuring rod, and R is the radius of the flexible riser.

[0027] As an optional solution to the technical solution in this application, in S4, the strain of the measuring rod is corrected using the following formula:

[0028]

[0029] Where, ε i Let the strain of the i-th measuring rod be... Let be the measured strain of the i-th measuring rod.

[0030] 3. Beneficial effects

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1) This application adopts a non-invasive measurement method, which avoids damage to the pipeline caused by the sensor itself, and is easy to remove and reuse.

[0033] 2) The measuring rod for measuring strain in this application is made of a material with properties similar to those of the measuring pipe material, which can reduce the difference in mechanical properties between the measuring device and the object being measured, thus ensuring the accuracy of the measurement.

[0034] 3) This application enables distributed monitoring, and multiple sets of structures can monitor flexible risers at multiple points, which is very much in line with the flexible layout of flexible risers and can achieve long-distance and large-scale monitoring, making it suitable for various practical engineering operation environments. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall structure of a non-invasive strain monitoring device for marine flexible risers;

[0036] Figure 2This is a schematic diagram of a support frame structure for a non-invasive strain monitoring device used in marine flexible risers;

[0037] Figure 3 A schematic diagram of the first structural component of a non-invasive strain monitoring device for marine flexible risers;

[0038] Figure 4 This is a schematic diagram of a measuring rod structure for a non-invasive strain monitoring device used in marine flexible risers;

[0039] In the figure: 1. Support frame; 101. First structural part; 102. Pipe clamp; 103. Slot; 104. Bolt rod; 2. Measuring rod; 201. Connecting part. Detailed Implementation

[0040] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0041] Example 1:

[0042] Please see Figure 1 and Figure 2 This invention provides a non-invasive strain monitoring device for marine flexible risers, comprising: a support frame 1, wherein two support frames 1 are provided, the two support frames 1 are parallel to each other, and an installation groove is provided in the middle of the support frame 1. The installation groove is circular. Four measuring rods 2 are provided between the two support frames 1. The measuring rods 2 are cylindrical and have fiber optic grating sensors installed inside. The four measuring rods 2 are arranged in a ring with equal spacing. Each measuring rod 2 is parallel to the axis of the center of the two installation grooves. The distance between each measuring rod 2 and the axis of the center of the installation groove is equal. Each end of the measuring rod 2 is fixedly connected to a connecting part 201. The connecting part 201 is fixedly connected to the support frame 1 and is detachably connected to the support frame 1.

[0043] When performing strain testing on a marine flexible riser, a measuring rod 2 can be installed on the outside of the marine flexible riser using a support frame 1. When the flexible riser deforms, the deformation can be transferred to the measuring rod 2 using the support frame 1. By measuring the deformation of multiple measuring rods 2, the deformation of the flexible riser can be deduced, thus realizing the detection of the deformation of the flexible riser.

[0044] like Figure 3 As shown, the support frame 1 is composed of a first structural part 101 and a second structural part of the same shape. The first structural part 101 and the second structural part are fixedly connected by bolts. Four pipe clamps 102 are fixedly connected to the support frame 1. The pipe clamps 102 are provided with slots 103 inside. The connecting part 201 is inserted into the slot 103. A bolt rod 104 is installed at the end of the pipe clamp 102. The bolt rod 104 is used to adjust the clamping force of the pipe clamp 102 on the connecting part 201.

[0045] By dividing the support frame 1 into a first structural part 101 and a second structural part, it is convenient for users to install and disassemble the support frame 1; and the measuring rod 2 can be quickly installed and removed through the bolt rod 104 at the end of the pipe clamp 102, which facilitates the maintenance of the device and reduces the cost of using the device.

[0046] like Figure 4 As shown, the diameter of the connecting part 201 is larger than the diameter of the measuring rod 2. The support frame 1 is made of rigid metal, and the measuring rod 2 is made of a material with mechanical properties similar to those of a marine flexible riser. Preferably, the measuring rod 2 is made of glass fiber, and the length of the measuring rod 2 is 400 mm and the radius is 4 mm. The radius of the connecting part 201 is 8 mm.

[0047] The support frame 1, made of rigid metal, can effectively transfer the strain generated by the flexible riser to the measuring rod 2. By designing the length and radius of the measuring rod 2, the influence of the measuring rod 2 on the local mechanical properties of the flexible riser can be reduced.

[0048] Example 2:

[0049] This invention provides a non-invasive strain monitoring method for marine flexible risers, employing a non-invasive strain monitoring device for marine flexible risers described in Example 1. Since the neutral axis of the cross-section of the flexible riser passes through the center of the cross-section when strain occurs, the strain measured by the two oppositely positioned measuring rods 2 is the same in magnitude but opposite in sign. Therefore, the following method can be used for monitoring:

[0050] S1. Fix two support frames 1 on the outside of the flexible riser, and fix the measuring rod 2 between the two support frames 1 through the connecting part 201;

[0051] S2. Obtain the center wavelength of the fiber optic grating sensor inside the four measuring rods 2;

[0052] S3. Calculate the strain of each measuring rod 2 based on the center wavelength of the fiber optic grating sensor. The calculation formula is as follows:

[0053]

[0054] Where, ε xw For the measured strain of rod 2, Δλ B λ is the change in the center wavelength of the optical fiber. B P is the center wavelength of the optical fiber. e K is the photoelastic coefficient. ε This is the strain sensitivity coefficient;

[0055] S4. Correct the strain of measuring rod 2;

[0056] S5. Based on the strain of measuring rod 2, calculate the maximum strain of the flexible riser. The calculation formula is as follows:

[0057]

[0058] Where ε1 is the maximum value of the normal strain of measuring rod 2, ε2 is the minimum value of the normal strain of measuring rod 2, α is the angle between the location of measuring rod 2 corresponding to the maximum normal strain in the cross-section of the flexible riser and the center of the flexible riser cross-section, and ε max R is the maximum strain of the flexible riser. C R is the distance between measuring rod 2 and the central axis of the flexible riser, and R is the radius of the flexible riser.

[0059] To increase the accuracy of strain detection, the distance between measuring rod 2 and the outer surface of the flexible riser is determined using the following formula:

[0060]

[0061] Where d is the distance between the measuring rod 2 and the outer surface of the flexible riser, and r m R is the radius of measuring rod 2, and R is the radius of the flexible riser.

[0062] In S4, to reduce the impact of temperature strain on the detection accuracy of the flexible pipe, the strain of measuring rod 2 is corrected using the following formula:

[0063]

[0064] Where, ε i Let be the strain of the i-th measuring rod 2. Let be the measured strain of the i-th measuring rod 2.

[0065] To verify the reliability of theoretical calculations and numerical simulations, the experimental system included a fiber Bragg grating demodulator, a 300N exciter, a flexible riser fixing platform, measuring rod 2, several bare optical fibers, and several strain gauges. The flexible riser was a nylon-glass fiber-carbon fiber bonded riser with an inner diameter of 100mm, an outer diameter of 120mm, and a wall thickness of 10mm. The fiber Bragg grating demodulator used had a maximum sampling frequency of 1000Hz and a wavelength accuracy of 1pm. Since it was impossible to conduct the experiment with the flexible riser upright in practice, we simplified it by fixing both ends of the riser and performing multiple sets of experiments with different excitation frequencies and forces in an elevated position to simulate the actual working conditions of the flexible riser.

[0066] Table 1: Comparison of Errors in Strain Measurement Results of Various Packaging Materials with Different Excitation Frequencies at a Sensitive Part Radius of 4mm (%)

[0067]

[0068] Table 2: Comparison of Errors in Radius Strain Monitoring Results of Various Measuring Rods Made of Glass Fiber (%)

[0069]

[0070] Experiments have shown that the highest monitoring accuracy is achieved when the measuring rod 2 is made of fiberglass, is 400mm long, has a radius of 4mm, and the distance between the measuring rod 2 and the outer surface of the flexible riser is 8mm.

Claims

1. A non-invasive strain monitoring method for a marine flexible riser, adopting a non-invasive strain monitoring device for a marine flexible riser, comprising two support frames (1), the two support frames (1) are parallel to each other, a mounting groove is arranged in the middle of the support frame (1), the mounting groove is circularly arranged, four measuring rods (2) are arranged between the two support frames (1), the measuring rod (2) is cylindrical, and an optical fiber grating sensor is arranged inside, the four measuring rods (2) are arranged in a ring shape at equal intervals, each measuring rod (2) is parallel to the axis of the two mounting groove centers, the distance between each measuring rod (2) and the axis of the mounting groove center is equal, and the two ends of the measuring rod (2) are fixedly connected with a connecting part (201), the connecting part (201) is connected and fixed with the support frame (1), and the connecting part (201) is detachably connected with the support frame (1); characterized in that: The method comprises the following steps: S1, two support frames (1) are fixedly installed outside the flexible riser, and a measuring rod (2) is fixedly installed between the two support frames (1) through a connecting part (201); S2, the center wavelengths of the four measuring rods (2) are obtained; S3, according to the center wavelengths of the fiber grating sensors, the strain of each measuring rod (2) is calculated, and the calculation formula is as follows: where ε cw is the measured strain of the measuring rod (2), Δλ B is the change in the center wavelength of the optical fiber, λ B is the center wavelength of the optical fiber, P e is the photoelastic coefficient, and K ε is the strain sensitivity coefficient. S4, the strain of the measuring rod (2) is corrected; S5, according to the strain of the measuring rod (2), the maximum strain of the flexible riser is calculated, and the calculation formula is as follows: wherein ε1 is the maximum value of the normal strain in the measuring rod (2), ε2 is the minimum value of the normal strain in the measuring rod (2), a is the angle of the measuring rod (2) at which the maximum normal strain in the cross section of the flexible riser and the relative position of the maximum normal strain in the cross section of the flexible riser to the center of the cross section of the flexible riser, ε max is the maximum strain of the flexible riser, R C is the distance between the measuring rod (2) and the central axis of the flexible riser, and R is the radius of the flexible riser. The support frame (1) is made of rigid metal material, the measuring rod (2) is made of a material similar to the mechanical properties of the marine flexible riser, and the spacing between the measuring rod (2) and the outer surface of the flexible riser is determined by the following formula: where d is the distance between the measuring rod (2) and the outer surface of the flexible riser, r m is the radius of the measuring rod (2) and R is the radius of the flexible riser.

2. A method of non-intrusive strain monitoring of a marine flexible riser according to claim 1, characterised in that: The support frame (1) is composed of a first structure part (101) and a second structure part, and the first structure part (101) and the second structure part are fixedly connected by bolts.

3. A method of non-intrusive strain monitoring of a marine flexible riser according to claim 1, characterized in that: The diameter of the connecting part (201) is greater than the diameter of the measuring rod (2), the support frame (1) is fixedly connected with four pipe clamps (102), the pipe clamp (102) is provided with a slot (103) inside, the connecting part (201) is inserted into the slot (103), and the pipe clamp (102) is provided with a bolt rod (104) at the end.

4. A method of non-intrusive strain monitoring of a marine flexible riser according to claim 1, characterized in that: The measuring rod (2) is made of glass fiber, the length of the measuring rod (2) is 400mm, the radius is 4mm, and the radius of the connecting part (201) is 8mm.

5. A method of non-intrusive strain monitoring of a marine flexible riser according to claim 1, characterized in that: In S4, the strain of the measuring rod (2) is corrected by the following formula: where ε i is the strain of the i-th measuring rod (2), is the measured strain of the i-th measuring rod (2).

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