Non-intrusive strain monitoring device and method for marine flexible riser

Abstract

The invention discloses a non-intrusive strain monitoring device and method for a marine flexible riser, and belongs to the technical field of pipeline monitoring. The invention discloses a non-intrusive strain monitoring device and method for a marine flexible riser, and the device comprises two supporting frames, the two supporting frames are parallel to each other, the middle part of each supporting frame is provided with a mounting groove, the mounting groove is circular, four cylindrical measuring rods are arranged between the two supporting frames, each measuring rod is internally provided with a fiber bragg grating sensor, and the fiber bragg grating sensors are arranged in the mounting grooves. The four measuring rods are annularly arranged at equal intervals, each measuring rod is parallel to the axis where the circle centers of the two mounting grooves are located, the distances between the measuring rods and the axis where the circle centers of the mounting grooves are located are equal, the two ends of each measuring rod are fixedly connected with connecting parts, the connecting parts are fixedly connected with the supporting frame, and the connecting parts are detachably connected with the supporting frame. A non-intrusive measurement method is adopted, damage to the pipeline caused by the sensor is avoided, and the sensor is convenient to disassemble and can be repeatedly used.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline monitoring, and more particularly to a non-invasive strain monitoring device and method for a marine flexible riser. Background Art

[0002] With the rapid development of national industry, energy demand has become more and more vigorous, which in turn has promoted the rapid development of pipeline engineering. So far, my country has built several trunk oil and gas pipelines. According to the long-term planning of national oil and gas long-distance pipelines, many pipelines will be built and operated in the future. However, due to the particularity of the laying space of oil and gas pipelines, it is inevitable to encounter various adverse geological conditions, which are difficult to completely avoid. Therefore, the disaster risk control of pipelines has become a challenge.

[0003] After searching, the patent document with the existing publication number CN103453844A provides an online monitoring method for flexible pipeline deformation based on fiber grating. This method applies the fiber grating strain measurement technology to the deformation monitoring of the tensile layer of the marine flexible pipeline, and combines the optical fiber laying process with the production process of the flexible pipe. The sensor laying work is completed in the production stage of the flexible pipeline.

[0004] In the above scheme, since the optical fiber is laid in the flexible pipe, the cost of deformation detection is increased, and flexible arrangement and replacement are not possible. In view of this, 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 object of the present invention is to provide a non-intrusive strain monitoring device and method for a marine flexible riser to solve the problems raised in the above background technology.

[0007] 2. Technical solution

[0008] The present invention is achieved through the following technical solutions:

[0009] A non-invasive strain monitoring device and method for an offshore flexible riser, comprising a support frame, wherein two support frames are provided, the two support frames are parallel to each other, a mounting groove is provided in the middle of the support frame, the mounting groove is arranged in a circular shape, four measuring rods are provided between the two support frames, the measuring rods are cylindrical, and fiber optic grating sensors are installed inside, the four measuring rods are arranged in a ring with equal intervals, each measuring rod is parallel to the axis where the centers of the two mounting grooves are located, and the distances between each measuring rod and the axis where the centers of the mounting grooves are located are equal, and both ends of the measuring rods are fixedly connected with connecting parts, the connecting parts are fixedly connected to the support frame, and the connecting parts are detachably connected to the support frame.

[0010] As an optional solution of the technical solution of the present application document, 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 fixed by bolts.

[0011] As an optional solution to the technical solution of the present application document, 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, slots are provided inside the pipe clamps, the connecting part is inserted into the slots, bolt rods are installed at the ends of the pipe clamps, and the bolt rods are used to adjust the clamping force of the pipe clamps on the connecting part.

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

[0013] As an optional solution of the technical solution of the present application document, the measuring rod is made of glass fiber, the length of the measuring rod is 400 mm, the radius is 4 mm, and the radius of the connecting part is 8 mm.

[0014] A non-intrusive strain monitoring method for an offshore flexible riser comprises the following steps:

[0015] S1. Two support frames are fixedly installed on the outside of the flexible riser, and the measuring rod is fixedly installed between the two support frames through the connecting part;

[0016] S2, obtaining the central wavelengths of the fiber grating sensors inside the four measuring rods;

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

[0018]

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

[0020] S4, correcting 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] Among them, ε1 is the maximum value of the positive strain of the measuring rod, ε2 is the minimum value of the positive strain of the measuring rod, α is the angle between the position of the measuring rod corresponding to the maximum positive strain in the cross section of the flexible riser and the maximum positive strain of the cross section of the flexible riser and the center of the cross section of the flexible riser, ε max is the maximum strain of the flexible riser, R C It is the distance between the measuring rod and the center axis of the flexible riser, and R is the radius of the flexible riser.

[0024] As an optional solution of the technical solution of this application document, 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, r m is the radius of the measuring rod and R is the radius of the flexible riser.

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

[0028]

[0029] Among them, ε i is the strain of the ith measuring rod, is the measured strain of the i-th measuring rod.

[0030] 3. Beneficial effects

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[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 dismantle and reuse.

[0033] 2) The measuring rod for measuring strain in the present 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 material of the object being measured and ensure the accuracy of the measurement.

[0034] 3) This application can realize distributed monitoring, and multiple sets of structures can realize multi-point monitoring of flexible risers, which is very consistent with the characteristics of flexible riser layout, can realize long-distance and large-scale monitoring, and is suitable for a variety of actual engineering operation environments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Figure 2It is a schematic diagram of the support frame structure of a non-intrusive strain monitoring device for marine flexible risers;

[0037] Figure 3 It is a schematic diagram of a first structural part of a non-invasive strain monitoring device for a marine flexible riser;

[0038] Figure 4 It is a schematic diagram of the structure of a measuring rod of a non-invasive strain monitoring device for 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 DESCRIPTION

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

[0041] Embodiment 1:

[0042] See also Figure 1 and Figure 2 The present 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, a mounting groove is provided in the middle of the support frame 1, the mounting groove is arranged in a circular shape, four measuring rods 2 are provided between the two support frames 1, the measuring rod 2 is cylindrical, and a fiber optic grating sensor is installed inside, the four measuring rods 2 are arranged in a circular shape with equal spacing, each measuring rod 2 is parallel to the axis where the centers of the two mounting grooves are located, and the distance between each measuring rod 2 and the axis where the centers of the mounting grooves are located are equal, and both ends of the measuring rod 2 are fixedly connected with a connecting portion 201, the connecting portion 201 is fixedly connected to the support frame 1, and the connecting portion 201 is detachably connected to the support frame 1.

[0043] When performing strain detection on the marine flexible riser, the measuring rod 2 can be installed on the outside of the marine flexible riser using the support frame 1. When the flexible riser is deformed, the support frame 1 can be used to transfer the deformation to the measuring rod 2. By measuring the deformation of multiple measuring rods 2, the deformation of the flexible riser can be deduced, thereby 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 fixed by bolts. Four pipe clamps 102 are fixedly connected to the support frame 1. A slot 103 is provided inside the pipe clamp 102. 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, the user can easily install and disassemble the support frame 1; and the bolt rod 104 at the end of the pipe clamp 102 can be used to quickly disassemble and assemble the measuring rod 2, which facilitates the maintenance of the device and reduces the use cost of the device.

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

[0047] The support frame 1 made of rigid metal material 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] Embodiment 2:

[0049] The present invention provides a non-invasive strain monitoring method for a marine flexible riser, using a non-invasive strain monitoring device for a marine flexible riser described in Example 1. When the flexible riser is strained, the neutral axis of its cross section passes through the center of the cross section, and the strains measured by two measuring rods 2 arranged opposite to each other are of the same magnitude but opposite signs. Therefore, the following method can be used for monitoring:

[0050] S1, two support frames 1 are fixedly installed on the outside of the flexible riser, and the measuring rod 2 is fixedly installed between the two support frames 1 through the connecting part 201;

[0051] S2, obtaining the central wavelengths of the fiber grating sensors inside the four measuring rods 2;

[0052] S3. Calculate the strain of each measuring rod 2 according to the central wavelength of the fiber Bragg grating sensor. The calculation formula is as follows:

[0053]

[0054] Among them, ε xw is the measured strain of measuring rod 2, Δλ B is the change in the optical fiber center wavelength, λ B is the central wavelength of the optical fiber, P e is the photoelastic coefficient, K ε is the strain sensitivity coefficient;

[0055] S4, correcting the strain of the measuring rod 2;

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

[0057]

[0058] Among them, ε1 is the maximum value of the positive strain of measuring rod 2, ε2 is the minimum value of the positive strain of measuring rod 2, α is the angle between the position of measuring rod 2 corresponding to the maximum positive strain in the cross section of the flexible riser and the center of the cross section of the flexible riser at the maximum positive strain, ε max is the maximum strain of the flexible riser, R C is the distance between the measuring rod 2 and the center axis of the flexible riser, and R is the radius of the flexible riser.

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

[0060]

[0061] 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.

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

[0063]

[0064] Among them, ε i is the strain of the i-th measuring rod 2, is the measured strain of the i-th measuring rod 2.

[0065] In order to verify the reliability of theoretical calculation and numerical simulation, the experimental system includes a fiber Bragg grating demodulator, a 300N exciter, a flexible riser fixed platform, a measuring rod 2, several bare optical fibers, several strain gauges, etc. The flexible riser used is a nylon mixed glass fiber carbon fiber bonding riser with an inner diameter of 100mm, an outer diameter of 120mm, and a wall thickness of 10mm. The maximum sampling frequency of the fiber Bragg grating demodulator used is 1000HZ, and the wavelength accuracy is 1pm. Since it is impossible to test the flexible riser upright in actual conditions, we simplified it to fixed supports at both ends of the flexible riser, and conducted multiple groups of tests with different excitation frequencies and forces in the overhead position of the flexible riser to simulate the actual working conditions of the flexible riser.

[0066] Table 1: Comparison of strain test results errors of various packaging materials at different excitation frequencies at 4mm radius of sensitive parts (%)

[0067]

[0068] Table 2: Comparison of the error of the radius strain monitoring results of various sensitive parts of the measuring rod under glass fiber material (%)

[0069]

[0070] It has been verified experimentally that the actual monitoring accuracy is highest when the measuring rod 2 is made of glass fiber, has a length of 400 mm, a radius of 4 mm, and a distance of 8 mm between the measuring rod 2 and the outer surface of the flexible riser.

Claims

1. A non-intrusive strain monitoring device for marine flexible riser, characterized in that: The invention comprises a support frame (1), wherein two support frames (1) are provided, the two support frames (1) are parallel to each other, a mounting groove is provided in the middle of the support frame (1), the mounting groove is arranged in a circular shape, four measuring rods (2) are provided between the two support frames (1), the measuring rods (2) are cylindrical, and optical fiber grating sensors are installed inside, the four measuring rods (2) are arranged in a circular shape with equal intervals, each measuring rod (2) is parallel to the axis where the centers of the two mounting grooves are located, and the distance between each measuring rod (2) and the axis where the centers of the mounting grooves are located are equal, and both ends of the measuring rod (2) are fixedly connected with a connecting portion (201), the connecting portion (201) is connected and fixed to the support frame (1), and the connecting portion (201) is detachably connected to the support frame (1).

2. A non-invasive strain monitoring device for a marine flexible riser according to claim 1, characterized in that: The support frame (1) is composed of a first structural part (101) and a second structural part of the same shape, and the first structural part (101) and the second structural part are connected and fixed by bolts.

3. The non-intrusive strain monitoring device for marine flexible riser according to claim 1, characterized in that: The diameter of the connecting portion (201) is greater than the diameter of the measuring rod (2); four pipe clamps (102) are fixedly connected to the support frame (1); a slot (103) is provided inside the pipe clamp (102); the connecting portion (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 portion (201).

4. The non-intrusive strain monitoring device for a marine flexible riser according to claim 1, characterized in that: The support frame (1) is made of a rigid metal material, and the measuring rod (2) is made of a material having mechanical properties similar to those of an offshore flexible riser.

5. The non-intrusive strain monitoring device for 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 400 mm, the radius is 4 mm, and the radius of the connecting portion (201) is 8 mm.

6. A non-invasive strain monitoring method for a marine flexible riser, using a non-invasive strain monitoring device for a marine flexible riser as described in any one of claims 1 to 5, characterized in that: The following steps are involved: S1, two support frames (1) are fixedly installed on the outside of the flexible riser, and a measuring rod (2) is fixedly installed between the two support frames (1) via a connecting portion (201); S2, obtaining the central wavelength of the fiber grating sensors inside the four measuring rods (2); S3. Calculate the strain of each measuring rod (2) according to the central wavelength of the fiber Bragg grating sensor. The calculation formula is as follows: Among them, ε cw is the measured strain of the measuring rod (2), Δλ B is the change in the optical fiber center wavelength, λ B is the central wavelength of the optical fiber, P e is the photoelastic coefficient, K ε is the strain sensitivity coefficient; S4, correcting the strain of the measuring rod (2); S5. Calculate the maximum strain of the flexible riser based on the strain of the measuring rod (2). The calculation formula is as follows: Wherein, ε1 is the maximum value of the positive strain of the measuring rod (2), ε2 is the minimum value of the positive strain of the measuring rod (2), α is the angle between the position of the measuring rod (2) corresponding to the maximum positive strain in the cross section of the flexible riser and the position of the maximum positive strain in the cross section of the flexible riser relative 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 center axis of the flexible riser, and R is the radius of the flexible riser.

7. A non-invasive strain monitoring method for marine flexible riser according to claim 6, characterized in that: The distance 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.

8. A non-invasive strain monitoring method for marine flexible riser according to claim 6, characterized in that: In S4, the strain of the measuring rod (2) is corrected using the following formula: Among them, 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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