A method for visual real-time monitoring of corrosion of a steel pipe in a marine environment

Abstract

The application discloses a kind of steel pipe structure in marine environment corrosion visual real-time monitoring method, data acquisition module can gather the Brillouin frequency shift amount signal of all distribution type optical fiber sensor measuring point of current steel pipe structure at any time;Real-time call the Brillouin frequency shift data of steel pipe structure before and after corrosion collected in data acquisition module in calculation and analysis module, according to the Brillouin frequency shift amount of measuring optical fiber and temperature compensation optical fiber, the strain of each measuring point caused by corrosion can be obtained, and then according to the conversion relationship between the corrosion strain of different regions of steel pipe structure and corrosion mass loss, the real-time non-uniform corrosion monitoring of steel pipe structure is realized.The application realizes the monitoring, quantification and visual real-time monitoring of steel pipe structure corrosion in complex marine environment using distributed optical fiber sensor, and the method is suitable for real-time non-uniform corrosion monitoring of various steel pipe structures.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of structure monitoring in marine environment, and particularly relates to a real-time monitoring method for visualizing corrosion of a steel pipe structure in a marine environment, and more particularly to a real-time monitoring method for monitoring, quantifying and visualizing corrosion of a steel pipe structure in a complex marine environment by using a distributed optical fiber sensor. BACKGROUND

[0002] Steel pipe piles are commonly used components in offshore engineering foundation construction and are widely used in marine infrastructure. However, steel pipe piles in harsh marine environments are prone to corrosion damage, which seriously threatens the stability and safety of the structure. At the same time, different regions of the steel pipe pile are in different environments, which can be divided into four regions: atmospheric zone, water level fluctuation zone, immersion zone and mud zone, which are subjected to atmospheric corrosion, splash corrosion caused by seawater salt spray-seawater scouring coupling, direct seawater immersion corrosion and marine mud-microorganism corrosion, respectively, and different regions exhibit significantly different corrosion characteristics. Therefore, it is necessary to monitor the real-time health of different regions of the steel pipe during service to understand the non-uniform corrosion of the steel pipe. The widely used steel structure corrosion monitoring technologies include direct current method, resistance probe method, acoustic emission method, linear polarization method, electrochemical biosensor and galvanic current monitoring technology. These detection methods have problems such as large detection result error or limited application range.

[0003] In previous corrosion monitoring experimental research based on distributed optical fiber sensors, it is known that distributed optical fibers are feasible for corrosion monitoring of steel bars in reinforced concrete structures, but there are few application researches on steel pipe structures, and the corrosion characteristics of steel pipe piles are significantly different from those of reinforced concrete structures: (1) The size of the steel pipe pile structure is larger, and the non-uniform corrosion characteristics are more obvious. In existing researches, the relationship between corrosion strain and corrosion mass damage is established by assuming uniform corrosion of the steel bar cross section, and there is still a lack of conversion relationship between corrosion strain and corrosion mass damage under the condition of non-uniform corrosion of the steel pipe cross section; (2) There is no constraint effect of concrete on the periphery of the steel pipe pile, and the corrosion products are more likely to be lost, and the corrosion characteristics of different regions of the steel pipe in the marine environment are different, making it more difficult to establish the relationship between the corrosion strain and the corrosion mass of the steel pipe in the marine environment. For example, in the atmospheric environment, the steel pipe corrodes and expands, and the corrosion products accumulate on the surface of the structure, resulting in an increase in pipe diameter, while in the area with water flow scouring, the corrosion products are detached from the surface of the structure under the action of water flow, showing a phenomenon of pipe diameter reduction. SUMMARY

[0004] Based on this, in order to efficiently and accurately measure the non-uniform corrosion of the steel pipe pile in the ocean, the primary object of the present application is to provide a visual real-time monitoring method for the corrosion of the steel pipe in the marine environment, which uses a single-mode single-core optical fiber as a distributed sensor to monitor the corrosion of the steel pipe in the complex marine environment, and can monitor the real-time non-uniform corrosion of various steel pipe structures.

[0005] In order to achieve the above object, the technical scheme of the present application is:

[0006] A visual real-time monitoring method for the corrosion of the steel pipe in the marine environment, the system of the monitoring method mainly comprises an optical fiber sensor arranged on the monitored steel pipe, a data acquisition module, a calculation and analysis module, and a non-uniform corrosion result real-time display module; wherein the data acquisition module acquires and stores the Brillouin frequency shift amount sent by the distributed optical fiber sensor arranged under the pre-corrosion and to-be-measured state of the steel pipe; the calculation and analysis module calls the Brillouin frequency shift amount sent by the optical fiber sensor under the pre-corrosion and current state of the steel pipe, and performs calculation; the corrosion degree result real-time display module displays the calculation result in the form of a cloud chart, and gives the overall non-uniform corrosion result of the entire steel pipe; the data acquisition module can acquire the Brillouin frequency shift amount signal transmitted by all the measurement points of the steel pipe where the optical fiber sensor is arranged at any time; the calculation and analysis module calls the Brillouin frequency shift amount data acquired before and after the corrosion of the steel pipe stored in the data acquisition module in real time, and can obtain the strain of each measurement point caused by corrosion according to the Brillouin frequency shift amount of the corrosion measurement optical fiber and the temperature compensation optical fiber, and then realize the real-time non-uniform corrosion monitoring of the entire steel pipe according to the conversion relationship between the corrosion strain and the corrosion mass loss of different regions of the steel pipe structure.

[0007] The characteristics of the steel pipe after corrosion in different environments are different, and the corrosion loss calculation methods are also different. The corrosion calculation model of the steel pipe structure in the marine environment can be mainly divided into two types: one is the model that the diameter of the steel pipe increases due to the accumulation of corrosion products on the surface of the steel pipe, and the other is the model that the diameter of the steel pipe decreases due to the corrosion products being washed away by the water flow. The specific steps are as follows:

[0008] Step one: optical fiber arrangement, a certain pre-stress is applied to the optical fiber on each section corresponding to the measurement point of the steel pipe, and the optical fiber is spirally wound on the outer surface at equal intervals;

[0009] In order to realize temperature compensation, the optical fiber is pasted on the inner surface of the steel pipe in the form of waves, the optical fiber remains in a natural relaxed state, and the inner surface is uniformly coated with anticorrosive paste to prevent the temperature compensation optical fiber from deforming due to corrosion of the inner surface.

[0010] Step two: under the action of the environment, the data acquisition module first acquires and stores the Brillouin frequency shift amount signal of each measurement point before the corrosion of the steel pipe, for calling during long-term real-time monitoring;

[0011] Step three: the data acquisition module collects and stores the Brillouin frequency shift signal of the corrosion measurement fiber and the temperature compensation fiber of all measuring points of the steel pipe in real time under the to-be-tested state;

[0012] Step four: the calculation and analysis module calls the Brillouin frequency shift signal of the fiber at all measuring points of the steel pipe before and after corrosion stored in the data acquisition module in real time, and performs calculation and analysis based on the following steps and outputs the monitoring results:

[0013] (1) The fiber will change the frequency of the Brillouin scattering light under the action of temperature and strain, and the Brillouin frequency shift change ΔV B is linearly related to the temperature change and strain change of the fiber:

[0014] ΔV B = K1ΔT + K2Δε (1)

[0015] Where K1 and K2 represent the temperature influence coefficient and the strain influence coefficient respectively; ΔT and Δε represent the temperature change and the strain change respectively;

[0016] The Brillouin frequency shift change ΔV B measured by the corrosion measurement fiber, and the Brillouin frequency shift change K1ΔT caused only by the temperature change obtained by the temperature compensation fiber, the strain change Δε of the distributed optical fiber sensor at each measuring point is obtained by the above formula, that is, the strain change ε ij caused by corrosion at each measuring point of the steel pipe along the sensor direction;

[0017] (2) According to the different corrosion characteristics of the steel pipe structure in the marine environment, it is divided into four regions: atmospheric zone, water level fluctuation zone, immersion zone and mud zone. According to the established conversion relationship between corrosion strain and corrosion mass loss in different regions of the steel pipe structure, the corrosion mass loss of each measuring point, that is, the mass loss Δm ij of each measuring point is calculated.

[0018] Where, in the atmospheric zone, the expansion corrosion product will always accumulate on the surface, causing the diameter of the steel pipe containing the rust layer to increase compared with the diameter of the uncorroded steel pipe, causing the fiber strain to increase, so the mass loss of each measuring point of the steel pipe in the atmospheric zone can be calculated by the following formula:

[0019]

[0020] In the water level fluctuation zone, the immersion zone and the mud zone, the corrosion products on the surface of the steel pipe are continuously lost with the flow of water, causing the diameter of the steel pipe containing the rust layer to decrease compared with the diameter of the uncorroded steel pipe, causing the fiber strain, so the mass loss of each measuring point of the steel pipe in the water level fluctuation zone, the immersion zone and the mud zone can be calculated by the following formula:

[0021]

[0022] where p is the density of the steel pipe; h is the distance between two adjacent fibers in the longitudinal direction; L0 is the arc length between two measuring points on the outer surface of the steel pipe, which is related to the sampling resolution of the system; R0 is the outer radius of the steel pipe before corrosion; λ is the volume expansion coefficient of the steel pipe in the atmospheric zone; β k is the corrosion volume reduction coefficient of the steel pipe in the water level fluctuation zone, the submerged zone and the zone below the sediment.

[0023] The first formula is derived from the following process:

[0024] The angle size a of the steel pipe can be determined by the radius R0 of the steel pipe and the arc length L0 between two measuring points on the outer surface of the steel pipe,

[0025]

[0026] Therefore, the volume V p1 of the part of the steel pipe that has occurred corrosion and the volume V r1 of the corrosion product can be expressed as:

[0027]

[0028]

[0029] where R0 is the outer radius of the steel pipe before corrosion, R W is the outer radius of the steel pipe after corrosion and removal of the rust layer, and R c is the outer radius of the steel pipe containing the rust layer measured by the fiber.

[0030] Therefore, the mass loss Δm ij of each measuring point due to corrosion can be expressed as:

[0031]

[0032] Due to the accumulation of corrosion products in the atmospheric zone, the volume of the steel pipe after corrosion expands. The volume expansion coefficient λ of the steel pipe in the atmospheric zone is defined as:

[0033]

[0034] According to the definition of strain, the radius R c of the steel pipe containing the rust layer after corrosion can be expressed as:

[0035] R c = R0(1+ε ij ) (9)

[0036] Substituting formula (9) into formula (8) and then into formula (7), the mass loss Δm ijThe size of:

[0037]

[0038] The strain ε caused by corrosion in the above formula ij is much smaller than 1, so the high-order small quantity ε ij 2 can be ignored, and the formula is arranged as:

[0039]

[0040] The second formula is derived from the following process:

[0041] The volume V of the part of the steel pipe where corrosion occurs p2 and the volume V of the corrosion product r2 are expressed as:

[0042]

[0043]

[0044] Therefore, the mass loss Δm of each measuring point caused by corrosion ij can be expressed as:

[0045]

[0046] Due to the loss of corrosion products in the water level fluctuation zone, the submerged zone and the zone below the mud, resulting in the volume of the steel pipe after corrosion shrinkage, the steel pipe corrosion volume expansion coefficient β of the water level fluctuation zone, the submerged zone and the zone below the mud k is defined as:

[0047]

[0048] According to the definition of strain, it is known that the radius R of the steel pipe containing the rust layer after corrosion shrinkage c can be expressed as:

[0049] R c = R0(1-ε ij ) (16)

[0050] and formula (16) is substituted into formula (15), and then into formula (14), to obtain the mass loss Δm of each measuring point ij The size of:

[0051]

[0052] The strain ε caused by corrosion in the above formula ij is much smaller than 1, so the high-order small quantity ε ij 2 can be ignored, and the formula is arranged as:

[0053]

[0054] The total corrosion mass loss of the whole steel pipe can be obtained by the following formula:

[0055] Since there are m optical fibers in each area of the steel pipe loss measurement and n measuring points on each optical fiber, when the corrosion loss of each corrosion area of the steel pipe is calculated, the following calculation can be used,

[0056] The total mass loss Δm of the atmospheric zone corrosion is:

[0057]

[0058] The total mass loss Δm of each corrosion area of the water level fluctuation zone, the submerged zone and the mud zone is:

[0059]

[0060] (3) The mass loss of each measuring point due to corrosion in different areas of the steel pipe can be calculated using the formula, and the mass loss of each measuring point is converted into a cloud chart by matrix using analysis software, so that the non-uniform corrosion of the steel pipe can be intuitively reflected in the form of a cloud chart.

[0061] The present application has the advantages of distributed measurement, high sensitivity, good precision, strong anti-electromagnetic interference ability and the like compared with the traditional direct current method, resistance probe method, acoustic emission method, linear polarization method, electrochemical biosensor and galvanic current monitoring technology, and has certain application value in practical engineering.

[0062] The present application realizes the real-time monitoring method for monitoring, quantifying and visualizing the corrosion of the steel pipe in a complex marine environment by using a distributed optical fiber sensor, and the method is suitable for real-time non-uniform corrosion monitoring of various steel pipe structures. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 The present application is a specific flowchart.

[0064] Figure 2 The present application is a four-area division diagram of a steel pipe structure in a marine environment.

[0065] Figure 3 The present application is a distributed optical fiber layout diagram of a steel pipe.

[0066] Figure 4 The present application is a calculation model diagram of the surface corrosion mass loss of the atmospheric zone of a steel pipe.

[0067] Figure 5 The present application is a calculation model diagram of the surface corrosion mass loss of the water level fluctuation zone, the submerged zone and the mud zone of a steel pipe.

[0068] Figure 6 The experimental setup for the specific embodiment;

[0069] Figure 7 The strain distribution map along the measurement length of the distributed optical fiber arranged in the submerged zone of the present application.

[0070] Figure 8 The strain distribution map along the measurement length of the distributed optical fiber arranged in the submerged zone of the present application.

[0071] Figure 9 The strain distribution map along the measurement length of the distributed optical fiber arranged in the water level fluctuation zone of the present application.

[0072] Figure 10 The strain distribution map along the measurement length of the distributed optical fiber arranged in the atmospheric zone of the present application.

[0073] Figure 11 The quality loss cloud chart caused by non-uniform corrosion of the steel pipe of the present application. Specific embodiment

[0074] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0075] As shown in Figure 1 , the method realized by the present application has the following specific steps:

[0076] Step one: fiber arrangement, in the section corresponding to each measurement point of the steel pipe, a certain pre-stress is applied to the optical fiber and it is spirally wound on the outer surface at equal intervals, as shown in Figure 3 , in order to realize temperature compensation, the optical fiber is pasted on the inner surface in the form of waves, the optical fiber remains in a natural relaxed state, and the inner surface is uniformly coated with anticorrosive paste to prevent the inner surface from causing deformation of the temperature compensation optical fiber due to corrosion;

[0077] Step two: under the action of the environment, the data acquisition module first acquires and stores the Brillouin frequency shift signal of each measurement point of the steel pipe before corrosion, which is called for long-term real-time monitoring;

[0078] Step three: the data acquisition module real-time acquires and stores the Brillouin frequency shift signal of the corrosion measurement optical fiber and the temperature compensation optical fiber of all measurement points of the steel pipe in the to-be-measured state;

[0079] Step four: the calculation and analysis module real-time calls the Brillouin frequency shift signal of the optical fiber at all measurement points before and after corrosion of the steel pipe stored in the data acquisition module, and the calculation and analysis module performs calculation and analysis based on the following steps and outputs the monitoring results:

[0080] (1) The frequency of Brillouin scattering light will change under the action of temperature and strain, and the change of Brillouin frequency shift ΔV B is linearly related to the change of temperature and strain of the optical fiber:

[0081] ΔV B = K1ΔT + K2Δε (1)

[0082] wherein K1 and K2 represent the temperature influence coefficient and the strain influence coefficient respectively; ΔT and Δε represent the change of temperature and the change of strain respectively;

[0083] The change of Brillouin frequency shift ΔV B is measured by the corrosion measurement optical fiber, and the change of Brillouin frequency shift K1ΔT caused only by the change of temperature is obtained by the temperature compensation optical fiber, and then the change of strain Δε of each measuring point of the distributed optical fiber sensor, i.e. the change of strain ε caused by corrosion of the steel pipe along the sensor direction at each measuring point, is calculated according to the above formula. ij ;

[0084] (2) As shown in Figure 2 , according to the different corrosion characteristics of the steel pipe structure in the marine environment, it is divided into four regions of atmospheric zone, water level fluctuation zone, immersion zone and mud zone, and the corrosion mass loss of each measuring point, i.e. the mass loss Δm of each measuring point, is calculated according to the established conversion relationship between the corrosion strain and the corrosion mass loss of the steel pipe structure in different regions. ij ,

[0085] Wherein, in the atmospheric zone, the expansive corrosion product will always accumulate on the surface, resulting in the increase of the diameter of the steel pipe containing rust layer compared with the diameter of the steel pipe before corrosion, causing the increase of the strain of the optical fiber, so the mass loss of each measuring point of the steel pipe in the atmospheric zone can be calculated by the following formula:

[0086]

[0087] In the water level fluctuation zone, the immersion zone and the mud zone, the corrosion product on the surface of the steel pipe is continuously lost with the flow of water, resulting in the decrease of the diameter of the steel pipe containing rust layer compared with the diameter of the steel pipe before corrosion, causing the strain of the optical fiber, so the mass loss of each measuring point of the steel pipe in the water level fluctuation zone, the immersion zone and the mud zone can be calculated by the following formula:

[0088]

[0089] Wherein, ρ is the density of the steel pipe; h is the distance between the adjacent two optical fibers in the longitudinal length; L0 is the arc length between the two measuring points on the outer surface of the steel pipe, which is related to the sampling resolution of the system; R0 is the outer radius of the steel pipe before corrosion; λ is the volume expansion coefficient of the corrosion in the atmospheric zone of the steel pipe; β k is the volume reduction coefficient of the corrosion in the water level fluctuation zone, the immersion zone and the mud zone of the steel pipe.

[0090] The first formula (2) is applied to situations where expansive corrosion products continuously accumulate on the surface, the diameter of the steel pipe containing the rust layer is larger than the diameter of the steel pipe before corrosion, and the strain of the optical fiber increases, such as... Figure 4 As shown; the second formula (3) is applied to the case where some corrosion products on the surface of the steel pipe are continuously washed away by the water flow, and the diameter of the steel pipe containing the rust layer is smaller than that of the steel pipe before corrosion, and the fiber strain is reduced, such as Figure 5 As shown.

[0091] The first formula (2) is derived by the following process:

[0092] The angle α of the steel pipe can be determined by the steel pipe radius R0 and the arc length L1 between two measuring points on the outer surface of the steel pipe.

[0093]

[0094] Therefore, the volume V of the corroded part in the steel pipe p1 and the volume V of corrosion products r1 Represented as:

[0095]

[0096]

[0097] The outer radius of the steel pipe before corrosion is R0, and the outer radius after corrosion and removal of the rust layer is R. W And the outer radius including the rust layer measured by the optical fiber is R. c ,

[0098] Therefore, the mass loss Δm at each measuring point due to corrosion ij It can be represented as:

[0099]

[0100] Due to the accumulation of corrosion products in the atmospheric region, the steel pipe expands in volume after corrosion. The coefficient of volume expansion λ for steel pipe corrosion in the atmospheric region is defined as:

[0101]

[0102] According to the definition of strain, the radius R of the steel pipe containing the rust layer after corrosion expansion is known. c It can be represented as:

[0103] R c =R0(1+ε ij (9)

[0104] Substituting formula (9) into formula (8), and then into formula (7), we can obtain the mass loss Δm at each measuring point.ij Size:

[0105]

[0106] Due to the strain ε caused by corrosion in the above formula ij Since it is much smaller than 1, the higher-order small quantity ε can be ignored. ij 2 And by rearranging the formula, we get:

[0107]

[0108] The second formula (3) is derived by the following process:

[0109] The volume V of the rusted part in the steel pipe p2 and the volume V of corrosion products r2 Represented as:

[0110]

[0111]

[0112] Therefore, the mass loss Δm at each measuring point due to corrosion ij It can be represented as:

[0113]

[0114] Due to the loss of corrosion products in the water level fluctuation zone, submerged zone, and mud-covered zone, the steel pipe shrinks in volume after corrosion. This leads to an increase in the coefficient of volume expansion β of the steel pipe corroded in the water level fluctuation zone, submerged zone, and mud-covered zone. k Defined as:

[0115]

[0116] According to the definition of strain, the radius R of the steel pipe including the rust layer after corrosion shrinkage is known. c It can be represented as:

[0117] R c =R0(1-ε ij (16)

[0118] Substituting the above formula into the formula for calculating mass loss, we can obtain the mass loss Δm at each measuring point. ij Size:

[0119]

[0120] Due to the strain ε caused by corrosion in the above formula ij Since it is much smaller than 1, the higher-order small quantity ε can be ignored. ij 2 And by rearranging the formula, we get:

[0121]

[0122] The total corrosion mass loss of the whole steel pipe can be obtained by the following formula:

[0123] Since there are m optical fibers in each area of the steel pipe loss measurement and n measuring points on each optical fiber, the corrosion loss of each corrosion area of the steel pipe can be calculated by the following formula:

[0124] The total mass loss Δm of the corrosion area with diameter increase (atmosphere area) is:

[0125]

[0126] The total mass loss Δm of the corrosion area with diameter decrease (water level fluctuation area, immersion area and mud area) is:

[0127]

[0128] (3) The mass loss of each measuring point due to corrosion in different areas of the steel pipe can be calculated by the formula, and the mass loss of each measuring point is converted into a cloud chart by matrix through the analysis software, so that the non-uniform corrosion of the steel pipe can be intuitively reflected in the form of the cloud chart.

[0129] The non-uniform corrosion monitoring is studied by taking an accelerated corrosion experiment of a steel pipe in a simulated marine environment as an example, and the technical solutions of the present application are described in detail in combination with the accompanying drawings as follows:

[0130] As shown in Figure 2 , in the marine environment, there are usually four areas, i.e. atmosphere area, water level fluctuation area, immersion area and mud area. As shown in Figure 3As shown, a steel pipe (Q235) with a height of 30 cm, an outer diameter of 16.5 cm, and a wall thickness of 0.3 cm is used to simulate a steel pipe pile in a marine environment. A sodium chloride solution with a concentration of 3.5% is used to simulate seawater. Sand and gravel are laid at the bottom of the water tank to simulate the subaqueous zone in the marine environment by embedding the lower part of the steel pipe in the sand and gravel. The top surface of the sand and gravel layer to the lowest water level line simulates the submerged zone in the marine environment. The water level is periodically changed by pumping the simulated seawater in the water tank and preventing water, and the water level variation is divided into two stages of high tide and low tide. The water level variation zone is simulated by the lowest water level to the highest water level. The atmospheric zone is above the highest water level. The steel pipe is periodically heated by an infrared radiation heater. In the same experimental period, the temperature is divided into four different stages: normal temperature stage, heating stage, high temperature stable stage, and cooling stage. The specimen is exposed to sunlight, with one side facing the heater and the other side facing the shade. The room temperature is controlled by an air conditioner, and the indoor temperature can be considered constant during the experiment. The Brillouin frequency shift data is collected by an RP1020 type Brillouin optical time domain analyzer with a spatial resolution of 20 cm, a sampling resolution of 5 cm, a strain accuracy of less than or equal to ±20με, a temperature accuracy of less than or equal to ±1℃, a temperature influence coefficient K1 of 1.12 MHz / ℃, and a strain influence coefficient K2 of 0.0482 MHz / με.

[0131] The experimental steps are as follows:

[0132] (1) Connect the cleaned FC / APC fiber jumper connector to the Brillouin optical time domain analyzer to ensure good contact between the fiber and the instrument during measurement. Figure 3 Figure 6 as shown.

[0133] (2) Place the steel pipe sample in the water tank, and lay the sand and gravel soaked in a 3.5% sodium chloride solution for 1 day on the bottom of the water tank. The thickness is just enough to bury the subaqueous zone by 7.5 cm. Then pour the salt solution, and the water level reaches the junction of the submerged zone and the water level variation zone at 15 cm.

[0134] (3) Adjust the sensor parameters. The sensor parameters mainly adjust the pump light intensity to ensure that the fiber arranged on the surface of the steel pipe pile can be measured completely.

[0135] (4) Sunlight simulation. As shown in Figure 6 , a heater is arranged on one side of the steel pipe to simulate the real environment of the steel pipe being irradiated by sunlight. The specimen is exposed to sunlight with one side facing the heater and the other side facing the shade.

[0136] (5) Steel pipe accelerated corrosion simulation. Connect the positive electrode of the adjustable DC stabilized power supply to the steel pipe and the negative electrode to the carbon rod, and apply a current of 2A.

[0137] ​(6) Before corrosion, the Brillouin frequency shift data of 12 groups of different temperature environments are measured respectively each day.

[0138] (7) When the accelerated corrosion is started, the influence of temperature change on the measured Brillouin frequency shift is eliminated by changing the corrosion environment so that the corrosion temperature environment of the corresponding group each day is the same (i.e. the temperature size of the 5th group measured each day before corrosion is consistent with the temperature size of the 5th group measured each day during the accelerated corrosion process). Then the strain size caused by corrosion can be calculated by the difference of the Brillouin frequency shift of the corresponding groups before and after corrosion.

[0139] (8) The collected data is post-processed by a calculation and analysis software.

[0140] By using the method, firstly, the Brillouin frequency shift amount ΔV B is collected by measuring the optical fiber sensor, the temperature change amount ΔT is collected by the temperature compensation optical fiber, and the strain change amount Δε of each measuring point of the distributed optical fiber sensor is calculated by formula (1), i.e. the corrosion strain value ε ij of each measuring point of the steel pipe along the sensor direction. Figures 7-10 are respectively the strain distribution diagrams of the distributed optical fiber in the mud area, the immersion area, the water level fluctuation area and the atmospheric area along the measuring length direction at different times in the experiment. Then, the mass loss amount m ij of each measuring point of the atmospheric area is calculated by formula (2) and the calibrated atmospheric area corrosion volume expansion coefficient λ, the mass loss amount m k of each measuring point of the water level fluctuation area, the immersion area and the mud area is calculated by formula (3) and the calibrated corrosion volume reduction coefficient β ij respectively, and finally the mass loss cloud diagram is drawn by using the drawing software. Figure 11 is the mass loss cloud diagram caused by the non-uniform corrosion of the steel pipe of the present application, and the diagram shown includes the atmospheric area, the water level fluctuation area, the immersion area and the mud area (36h, 72h, 90h, 108h).

[0141] From the cloud analysis results of Figure 11 , it can be seen that by using the method of the present application, the monitoring, quantification and visualization of the steel pipe corrosion under the marine environment can be realized, and the following conclusions can be drawn: the corrosion of the steel pipe can cause the strain change of the distributed optical fiber sensor arranged on the surface of the steel pipe; under the electrochemical accelerated corrosion of the steel pipe, the immersion area is the most serious (as shown in Figure 8 ), the mud area is the second (as shown in Figure 7 ), the atmospheric area is the lightest (as shown in Figure 10 ), and the water level fluctuation area is the second (as shown in Figure 9 ).

[0142] The above experiment can show that the real-time monitoring method for monitoring, quantifying and visualizing the corrosion of the steel pipe under the complex marine environment by the distributed optical fiber sensor can be well applied to the non-uniform corrosion monitoring of the steel pipe under the complex marine environment in terms of data collection integrity, accuracy, real-time performance, calculation convenience and result visualization degree.

[0143] The above merely describes preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for visualizing real-time monitoring of corrosion of a steel pipe structure in a marine environment, characterized by The system of the monitoring method comprises optical fiber sensors arranged on the steel pipe structure to be monitored, a data acquisition module, a calculation analysis module, and a non-uniform corrosion result real-time display module; the data acquisition module acquires and stores the Brillouin frequency shift amount sent by the distributed optical fiber sensors arranged before corrosion and in the state to be measured; the calculation analysis module calls the Brillouin frequency shift amount sent by the optical fiber sensors before corrosion and in the current state, and performs calculation; the corrosion degree result real-time display module displays the calculation result in the form of a cloud chart, and gives the entire non-uniform corrosion result of the steel pipe structure. The data acquisition module can acquire the Brillouin frequency shift amount signal sent by all the optical fiber sensors arranged at the measuring points of the steel pipe structure at any time; the calculation analysis module calls the Brillouin frequency shift amount data acquired before and after corrosion of the steel pipe structure stored in the data acquisition module, and can obtain the strain of each measuring point caused by corrosion according to the Brillouin frequency shift amount of the corrosion measuring optical fiber and the temperature compensation optical fiber, and then realizes real-time non-uniform corrosion monitoring of the entire steel pipe structure according to the conversion relationship between the corrosion strain and the corrosion mass loss of different regions of the steel pipe structure. The method comprises the following steps: Step 1: optical fiber arrangement, a certain pre-stress is applied to the optical fiber arranged on the section corresponding to each measuring point of the steel pipe structure, and the optical fiber is spirally wound on the outer surface at equal intervals, Step 2: under the action of the environment, the data acquisition module first acquires and stores the initial Brillouin frequency shift amount signal of each measuring point before corrosion of the steel pipe structure; Step 3: the data acquisition module acquires and stores the Brillouin frequency shift amount signal of the corrosion measuring optical fiber and the temperature compensation optical fiber of all the measuring points of the steel pipe in the state to be measured in real time; Step 4: the calculation analysis module calls the Brillouin frequency shift amount signal of the optical fiber at all the measuring points of the steel pipe before and after corrosion stored in the data acquisition module in real time, and performs calculation and analysis by the calculation analysis module and outputs the monitoring result; Specifically, the mass loss amount of each measuring point of the steel pipe in the atmospheric zone is calculated by the formula: (1) The frequency of the Brillouin scattered light will change under the action of temperature and strain on the optical fiber, and the change amount of the Brillouin frequency shift is linearly related to the temperature change and the strain change of the optical fiber: wherein and respectively represent a temperature influence coefficient and a strain influence coefficient; and respectively represent a temperature change amount and a strain change amount; The amount of change in the Brillouin frequency shift is measured by a fiber for corrosion The amount of change in the Brillouin frequency shift due to temperature change only is obtained from a temperature-compensated fiber The amount of change in the strain at each measuring point of the distributed fiber sensor is calculated from the above formula The amount of change in the strain at each measuring point of the steel pipe in the direction of the sensor due to corrosion ; (2) According to the different corrosion characteristics of steel pipe structure in marine environment, it is divided into four regions of atmospheric zone, water level fluctuation zone, submerged zone and mud zone. According to the conversion relationship between the corrosion strain change of each measuring point in different regions of steel pipe structure and the mass loss of each measuring point , the mass loss of each measuring point is calculated . The mass loss amount of each measuring point of the steel pipe in the water level fluctuation zone, the submerged zone and the mud zone is calculated by the formula: In step 1, the temperature compensation optical fiber is pasted on the inner surface of the steel pipe in the form of waves, the optical fiber is kept in a natural relaxed state, the inner surface is uniformly coated with anticorrosive paste to prevent the temperature compensation optical fiber from deforming due to corrosion of the inner surface. wherein is the density of the steel pipe; is the pitch of two adjacent longitudinal length of the optical fiber; is the arc length between two measuring points on the outer surface of the steel pipe, which is related to the sampling resolution of the system; is the outer radius of the steel pipe before corrosion; is the volume expansion coefficient of the steel pipe in the atmospheric zone; is the volume reduction coefficient of the steel pipe in the water level fluctuation zone, the submerged zone and the mud zone.

2. The method of visualizing real-time monitoring of corrosion of the steel pipe in a marine environment according to claim 1, characterized in that In step 4, after the mass loss amount of each measuring point due to corrosion in different regions of the steel pipe is calculated, the mass loss amount of each measuring point is converted into a cloud chart by matrix conversion by using the analysis software, and the non-uniform corrosion of the steel pipe is intuitively reflected in the form of the cloud chart.

3. The method of visualizing real-time monitoring of corrosion of the steel pipe in a marine environment according to claim 1, characterized in that Mass loss at each measuring point of the steel pipe in the atmospheric zone It is derived from the following process, Steel pipe angle size Can be determined by the steel pipe radius And the arc length between the two measuring points of the outer surface of the steel pipe Determined, Volume of the part of the steel pipe in which corrosion has occurred and the volume of the corrosion product is expressed as: wherein the outer radius of the steel pipe before corrosion is , the outer radius of the steel pipe after corrosion and removal of the rust layer is , and the outer radius of the steel pipe including the rust layer as measured by the optical fiber is , Thus, the amount of mass loss at each measurement point due to corrosion may be expressed as: The volume expansion coefficient of the steel pipe in the atmospheric zone after corrosion caused by the accumulation of corrosion products in the atmospheric zone is defined as: According to the definition of strain, the radius of the steel pipe containing rust layer after corrosion expansion can be known may be expressed as: And the above formula into the mass loss amount calculation formula can be obtained each measuring point mass loss amount Size: The amount of strain due to corrosion in the above equation is much less than 1, so the higher order small quantities can be ignored and the equation is rearranged to 。 4. The method of visualizing real-time monitoring of corrosion of the steel pipe in a marine environment according to claim 1, characterized in that The mass loss amount of each measuring point of the steel pipe in the water level fluctuation area, the submerged area and the mud area is derived from the following process, Volume of the part of the steel pipe in which corrosion has occurred and the volume of the corrosion product is expressed as: Thus, the amount of mass loss at each measurement point due to corrosion may be expressed as: Due to the loss of corrosion products in the fluctuating water level zone, submerged zone and mud zone, the volume of the steel pipe is reduced after corrosion. The expansion coefficient of the steel pipe in the fluctuating water level zone, submerged zone and mud zone is defined as: is defined as: According to the definition of strain, the radius of the steel pipe containing the rust layer after corrosion shrinkage may be expressed as: And the above formula into the mass loss amount calculation formula can be obtained each measuring point mass loss amount Size: The amount of strain due to corrosion in the above equation is much less than 1, so the higher order small quantities can be ignored and the equation is rearranged to 。 5. The method of visualizing real-time monitoring of corrosion of a steel pipe in a marine environment according to claim 3 or 4, characterized in that Each area of steel pipe quality loss measurement has one measuring point, and the corrosion loss of each corrosion area of the steel pipe is calculated by one measuring point, and the corrosion loss of each corrosion area of the steel pipe is calculated by The total mass loss in the atmospheric zone Is: The total mass loss in each corrosion zone of the water level fluctuation zone, the submerged zone and the submersion zone Is: 。 6. The method of visualizing real-time monitoring of corrosion of the steel pipe in a marine environment according to claim 1, characterized in that ​

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