Submarine pipeline anticorrosion agent effectiveness digital intelligence comprehensive evaluation method and system

Abstract

The invention relates to the technical field of data processing, and provides a submarine pipeline anticorrosion agent effectiveness digital intelligence comprehensive evaluation method and system.The method comprises the steps that the deposition influence degree is obtained according to the difference situation of the corrosion thickness of a middle sample and the corrosion thickness of a bottom sample; according to the negative correlation condition of the deposition influence degree and the corrosion thickness, a flow velocity deposition reference index is obtained, and then the analysis reference degree of the bottom sample is obtained; obtaining a flow velocity correlation degree by combining a flow velocity deposition reference index; obtaining a flow velocity-sediment correlation function according to the flow velocity correlation degree; combining the overall flow velocity level and the corrosion thickness of the middle sample and the deposition influence degree and the corrosion thickness of the bottom sample to obtain a deposition flow velocity corrosion ratio; and obtaining an anti-corrosion effectiveness detection result of the corrosion inhibitor according to the deposition velocity corrosion proportion. The influence of the sediment on the pipeline corrosion is analyzed through the deposition velocity corrosion proportion, the accuracy of corrosion rate measurement is improved, and the credibility of corrosion inhibitor effectiveness detection is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of data processing, and particularly relates to a digital comprehensive evaluation method and system for the effectiveness of anti-corrosion agents for subsea pipelines. Background Art

[0002] Subsea oil transportation pipelines are key infrastructure for transporting crude oil in a marine environment. These pipelines are usually laid on the seabed or buried in the seabed sediment layer to reduce the impact of ocean currents and external corrosion. They are usually made of high-strength steel and use special anti-corrosion coatings and cathodic protection technologies to extend their service life and ensure transportation safety. Subsea pipelines can transport oil efficiently and continuously. Compared with tanker transportation, they reduce the risk of leakage and environmental pollution, and at the same time improve the stability of energy supply.

[0003] Crude oil contains corrosive components such as hydrogen sulfide, carbon dioxide, and chlorides. When these components combine with moisture, they will form an acidic environment, causing acidic corrosion or pitting corrosion of the pipeline, affecting its service life. In order to prevent corrosion of the inner wall of the pipeline, anti-corrosion agents are required for internal anti-corrosion of subsea pipelines for transporting oil. By injecting anti-corrosion agents such as corrosion inhibitors, deoxidizers, or bactericides, the impact of corrosive media on the pipe wall can be reduced, the pipeline life can be extended, the transportation efficiency can be improved, and the maintenance and replacement costs can be reduced.

[0004] Since subsea pipelines are in long-term contact with corrosive media in crude oil, corrosion inhibitors must have good chemical stability, durability, and compatibility with pipeline materials. Factory inspections can verify the corrosion inhibition effect of the agent, the ability to resist microbial corrosion, and its performance under high temperature and high pressure conditions, ensuring that it will not decompose and fail or produce side effects during long-term use.

[0005] Currently, mainly through the high-temperature and high-pressure dynamic method in a laboratory scenario, the blank corrosion rate and the corrosion rate with added agent are obtained, and then the effectiveness of the corrosion inhibitor is judged based on the measurement results of the blank corrosion rate and the corrosion rate with added agent. However, the anti-corrosion film of subsea pipelines will be damaged due to oil scouring and sediment coverage, and it is difficult to simulate the corrosion effect of sediments during the high-temperature and high-pressure dynamic method in the laboratory, resulting in inaccurate measurement results of the corrosion rate in the laboratory. Summary of the Invention

[0006] The present invention provides a digital comprehensive evaluation method and system for the effectiveness of anti-corrosion agents for subsea pipelines to solve the problem of inaccurate measurement results of the corrosion rate in existing laboratories. The specific technical solutions adopted are as follows: The present invention proposes a digital comprehensive evaluation method for the effectiveness of anti-corrosion agents for subsea pipelines, and the method includes the following steps: Obtain the overall flow velocity level and corrosion thickness of each middle specimen and each bottom specimen at each thickness sampling moment; Based on the difference in the corrosion thickness of the middle specimen and the bottom specimen at a similar overall flow velocity level, the deposition influence degree of each bottom specimen at each thickness sampling moment is obtained; Based on the negative correlation between the deposition influence degree and the corrosion thickness of the bottom specimen at each thickness sampling moment, the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment is obtained; based on the flow velocity deposition reference index of the bottom specimen at all thickness sampling moments, the analysis reference degree of each bottom specimen is obtained; in combination with the flow velocity deposition reference index, the flow velocity correlation degree of each bottom specimen at each thickness sampling moment is obtained; Based on the flow velocity correlation degree of the bottom specimen at the thickness sampling moment, the flow velocity - sediment correlation function is obtained; in combination with the overall flow velocity level and corrosion thickness of the middle specimen at each thickness sampling moment, and the deposition influence degree and corrosion thickness of the bottom specimen at each thickness sampling moment, the deposition flow velocity corrosion ratio of each flow velocity is obtained; Based on the deposition flow velocity corrosion ratio of each flow velocity, the anti - corrosion effectiveness detection result of the corrosion inhibitor is obtained.

[0007] Further, the specific method for obtaining the deposition influence degree of each bottom specimen at each thickness sampling moment according to the difference in the corrosion thickness of the middle specimen and the bottom specimen at a similar overall flow velocity level includes: Based on the similarity of the overall flow velocity level of the bottom specimen and the middle specimen at the thickness sampling moment, the flow velocity proximity degree of each bottom specimen and each middle specimen at each thickness sampling moment is obtained; The th bottom specimen at the th thickness sampling moment has the deposition influence degree calculated as: ; In the formula, is the deposition influence degree of the th bottom specimen at the th thickness sampling moment; is the flow velocity proximity degree of the th bottom specimen and the th middle specimen at the th thickness sampling moment; is the corrosion thickness of the th bottom specimen at the th thickness sampling moment; is the corrosion thickness of the th middle specimen at the th thickness sampling moment; is the number of middle specimens; is the absolute value function.

[0008] Further, obtaining the flow velocity proximity degree of each bottom sample and each middle sample at each thickness sampling moment according to the similarity of the overall flow velocity levels of the bottom sample and the middle sample at the thickness sampling moment, the specific method included is as follows: For any bottom sample and any middle sample, the inverse proportional normalization result of the absolute value of the difference in the overall flow velocity levels of the bottom sample and the middle sample at any thickness sampling moment is recorded as the flow velocity proximity degree of the bottom sample and the middle sample at the thickness sampling moment.

[0009] Further, obtaining the flow velocity deposition reference index of each bottom sample at each thickness sampling moment according to the negative correlation between the deposition influence degree of the bottom sample at each thickness sampling moment and the corrosion thickness, the specific method included is as follows: The th bottom sample at the th thickness sampling moment and the th bottom sample at the th thickness sampling moment, the calculation method of the deposition flow velocity correlation index is as follows: ; In the formula, is the deposition flow velocity correlation index of the th bottom sample at the th thickness sampling moment and the th bottom sample at the th thickness sampling moment; is the deposition influence degree of the th bottom sample at the th thickness sampling moment; is the deposition influence degree of the th bottom sample at the th thickness sampling moment; is the maximum value of the deposition influence degrees of all bottom samples at all thickness sampling moments; is the maximum value of the overall flow velocity levels of all bottom samples at all thickness sampling moments; is the overall flow velocity level of the th bottom sample at the th thickness sampling moment; is the overall flow velocity level of the th bottom sample at the th thickness sampling moment; is the ceiling function; is the absolute value function; For any bottom specimen at any thickness sampling moment, the sum value of the deposition flow velocity correlation indices of this bottom specimen at this thickness sampling moment and all bottom specimens at all thickness sampling moments is denoted as the flow velocity deposition reference index of this bottom specimen at this thickness sampling moment.

[0010] Furthermore, the specific method for obtaining the analysis reference degree of each bottom specimen according to the flow velocity deposition reference index of the bottom specimen at all thickness sampling moments includes: For any bottom specimen, the linear normalization result of the product of the mean and variance of the flow velocity deposition reference index of this bottom specimen at all thickness sampling moments is denoted as the analysis reference degree of this bottom specimen.

[0011] Furthermore, the specific method for obtaining the flow velocity correlation degree of each bottom specimen at each thickness sampling moment includes: The linear normalization result of the product of the flow velocity deposition reference index of any bottom specimen at any thickness sampling moment and the analysis reference degree of this bottom specimen is denoted as the flow velocity correlation degree of this bottom specimen at this thickness sampling moment.

[0012] Furthermore, the specific method for obtaining the flow velocity - sediment correlation function according to the flow velocity correlation degree of the bottom specimen at the thickness sampling moment includes: Taking the overall flow velocity level as the abscissa and the deposition influence degree as the ordinate to establish a two - dimensional rectangular coordinate system, mapping the data of all bottom specimens at each thickness sampling moment into this two - dimensional rectangular coordinate system to obtain several data points in this two - dimensional rectangular coordinate system, using the flow velocity correlation degree of each bottom specimen at each thickness sampling moment as the fitting weight of the corresponding data points, and using the least - squares method to perform curve fitting on all data points to obtain the flow velocity - sediment correlation function.

[0013] Furthermore, the specific method for obtaining the deposition flow velocity corrosion ratio of each flow velocity includes: According to the overall flow velocity level and corrosion thickness of the middle specimen at each thickness sampling moment, obtain the flow velocity - corrosion correlation function; According to the deposition influence degree and corrosion thickness of the bottom specimen at each thickness sampling moment, obtain the deposition - corrosion correlation function; Substitute the function value of the flow velocity - sediment correlation function into the independent variable of the deposition - corrosion correlation function to obtain the flow velocity - deposition corrosion correlation function; For any flow velocity, the ratio of the corresponding corrosion thickness of this flow velocity in the flow velocity - deposition corrosion correlation function to the corresponding corrosion thickness of this flow velocity in the deposition - corrosion correlation function is denoted as the deposition flow velocity corrosion ratio of this flow velocity.

[0014] Further, obtaining the anti-corrosion effectiveness detection result of the corrosion inhibitor according to the deposition flow rate corrosion ratio at each flow rate includes the following specific methods: Obtain the blank corrosion rate at several flow rates; For any one flow rate, the product of the blank corrosion rate at this flow rate and the deposition flow rate corrosion ratio at this flow rate is denoted as the blank deposition corrosion rate at this flow rate; the maximum value between the blank corrosion rate and the blank deposition corrosion rate at this flow rate is denoted as the actual blank corrosion rate at this flow rate; Obtain the dosing corrosion ratio at each flow rate; obtain the dosing corrosion rate at several flow rates; For any one flow rate, the product of the dosing corrosion rate at this flow rate and the dosing corrosion ratio at this flow rate is denoted as the dosing deposition corrosion rate at this flow rate; the maximum value between the dosing corrosion rate and the dosing deposition corrosion rate at this flow rate is denoted as the actual dosing corrosion rate at this flow rate; According to the actual blank corrosion rate and the actual dosing corrosion rate, obtain the evaluation result of the effectiveness of the subsea pipeline corrosion inhibitor.

[0015] The present invention also proposes a digital comprehensive evaluation system for the effectiveness of subsea pipeline anti-corrosion agents. The system includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the above method are implemented.

[0016] The beneficial effects of the present invention are as follows: During the process of transporting oil through subsea pipelines, when the flow rate of the oil is slow, due to the action of gravity, there will be sediments at the bottom of the pipeline, and the sediments will cause corrosion to the subsea pipeline. The present invention obtains the deposition influence degree of each bottom sample at each thickness sampling moment through the difference in corrosion thickness between the middle sample and the bottom sample at a similar overall flow rate level, and analyzes the degree to which each bottom sample is affected by sediments; when analyzing the variation relationship between the flow rate and sediments, it is necessary to exclude the deviation that may occur in individual samples caused by minor differences in local geometry or installation position. The present invention obtains the flow rate deposition reference index and analyzes the reference degree, and then obtains the flow rate correlation degree to judge the data correlation between the flow rate and sediments at each thickness sampling moment of each bottom sample; during the process of oil transportation, since the high-speed flow of oil will accelerate the corrosion reaction on the metal surface, and the sediments during the slow flow of oil will accelerate the corrosion reaction of the subsea pipeline, the present invention obtains the deposition flow rate corrosion ratio at each flow rate to judge the corrosion influence of sediments and flow rate on the subsea pipeline at each flow rate. Thus, the present invention obtains the anti-corrosion effectiveness detection result of the corrosion inhibitor through the deposition flow rate corrosion ratio, improves the accuracy of corrosion rate measurement, and increases the credibility of the corrosion inhibitor effectiveness detection. Description of the Drawings

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0018] Figure 1 It is a schematic flow chart of a digital and intelligent comprehensive evaluation method for the effectiveness of a submarine pipeline anti-corrosion agent provided by an embodiment of the present invention. Specific embodiments

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0020] Please refer to Figure 1 , which shows a flow chart of a digital and intelligent comprehensive evaluation method for the effectiveness of a submarine pipeline anti-corrosion agent provided by an embodiment of the present invention. The method includes the following steps: Step S001: Obtain the overall flow velocity level and corrosion thickness of each middle specimen and each bottom specimen at each thickness sampling moment.

[0021] It should be noted that the effectiveness of the submarine pipeline corrosion inhibitor is mainly manifested in the change of the corrosion rate of the submarine pipeline before and after adding the drug. The corrosion rate of the submarine pipeline is mainly affected by the oil flow velocity and sediments. Therefore, metal specimens are arranged in the test pipeline to obtain the flow velocity data and corrosion data, and to judge the influence of the oil flow velocity and sediments on the corrosion rate.

[0022] Specifically, a closed pipeline system is built in the laboratory, and the fluid flow velocity of the pipeline system can be controlled; the inner wall of the pipeline of the pipeline system is divided into the top, middle and bottom. A number of metal specimens are respectively set in the middle and bottom of the inner wall of the pipeline. The specific setting method of the metal specimens is to set an installation point every meters, and install a metal specimen made of the same material as the actual pipeline at each installation point. The specimen size and surface treatment need to be unified with the actual pipeline; among them, is the preset installation spacing, and this embodiment takes as an example for description; The metal specimens located in the middle of the inner wall of the pipeline are denoted as middle specimens; the metal specimens located at the bottom of the inner wall of the pipeline are denoted as bottom specimens; An ultrasonic sensor is installed on each metal specimen to measure the thickness of the metal specimen; a flowmeter is installed near each metal specimen to obtain the flow rate of the fluid. Petroleum is added into the pipeline system. Before the start of the test process, the thickness of each metal specimen is detected first. At the start of the test process, the petroleum transportation is controlled at a flow rate of 0.1 m / s, and after that, the flow rate is increased by 0.6 m / s per day until the test is stopped after the petroleum flow rate is greater than 6 m / s. After the start of the test, for any metal specimen, the flowmeter near the metal specimen is used to collect the petroleum flow rate of the metal specimen once every 10 s as a flow rate sampling moment, and the petroleum flow rate of the metal specimen at each flow rate sampling moment is obtained. The ultrasonic sensor on the metal specimen is used to collect the specimen thickness of the metal specimen once every day as a thickness sampling moment, and the specimen thickness of the metal specimen at each thickness sampling moment is obtained. For any metal specimen and any thickness sampling moment, the mean value of the petroleum flow rates at all flow rate sampling moments between the thickness sampling moment of the metal specimen and the previous thickness sampling moment is denoted as the overall flow rate level of the metal specimen at the thickness sampling moment. For any metal specimen and any thickness sampling moment, the difference obtained by subtracting the specimen thickness of the metal specimen at the previous thickness sampling moment from the specimen thickness of the metal specimen at the thickness sampling moment is denoted as the corrosion thickness of the metal specimen at the thickness sampling moment.

[0023] Step S002: According to the difference in corrosion thickness of the middle specimens and the bottom specimens under similar overall flow rate levels, the deposition influence degree of each bottom specimen at each thickness sampling moment is obtained.

[0024] It should be noted that during the process of petroleum transportation, the middle part of the pipeline is usually the area with the largest fluid flow rate, and the scouring effect of the flow rate on the metal surface is more significant. Under turbulent conditions, a high flow rate will lead to an increase in the corrosion rate. The main mechanisms include increasing the mass transfer rate of oxygen or corrosive ions and intensifying the cathodic or anodic reaction. However, due to the high flow rate in the middle, it is not easy to form sediments, so the corrosion is mainly caused by the flow rate. Due to the action of gravity, the bottom of the pipeline is the place where sediments are most likely to accumulate. The low-flow rate area often leads to local flow stagnation, making the sediments unable to be carried away by the fluid, forming an environment conducive to microbial corrosion and local corrosion. The middle specimens reflect the direct influence of the flow rate on corrosion, and the bottom specimens reflect the combined action of the flow rate and sediments. Therefore, combining the middle specimens and the bottom specimens can analyze the corrosion mechanism more comprehensively.

[0025] It should be further noted that generally, the pipeline positions covered by sediments will show a faster corrosion rate. This is because the sediments will form local microenvironments on the metal surface, such as local hypoxia and concentration cell effects, which will induce or exacerbate pitting corrosion and crevice corrosion. While the areas only affected by the flow rate generally mainly exhibit uniform corrosion, and its rate is usually lower than the locally accelerated corrosion phenomenon. At the same flow rate and the same exposure time, if the corrosion degree of the bottom specimen is greater than that of the middle specimen, it indicates that the bottom specimen is affected by sediments, and the greater the difference in corrosion degree, the greater the influence of sediments on the bottom specimen. During the test, the corrosion degree of the metal specimen is reflected in the change of the thickness of the metal specimen. The more the thickness of the metal specimen decreases, the higher the corrosion degree of the metal specimen. When the overall flow rate levels of the bottom specimen and the middle specimen are closer at a certain thickness sampling moment, it indicates that the petroleum flow rate environments where these two metal specimens are located are similar. At this time, the difference in the specimen thickness changes of the two metal specimens can more reflect the influence of sediments on the corrosion rate.

[0026] Specifically, the calculation method for the flow rate proximity degree of the th bottom specimen and the th middle specimen at the th thickness sampling moment is as follows: ; In the formula, is the flow rate proximity degree of the th bottom specimen and the th middle specimen at the th thickness sampling moment; is the overall flow rate level of the th middle specimen at the th thickness sampling moment; is the overall flow rate level of the th bottom specimen at the th thickness sampling moment; is the absolute value function; is the exponential function with the natural constant as the base.

[0027] It should be noted that for any middle specimen and any bottom specimen, if the flow rate proximity degrees of these two metal specimens are similar at a certain thickness sampling moment, but the corrosion thickness of the bottom specimen is greater than that of the middle specimen, it indicates that the bottom specimen is more affected by sediments.

[0028] Specifically, the calculation method for the sediment influence degree of the th bottom specimen at the th thickness sampling moment is as follows: ; In the formula, is the deposition influence degree of the th bottom specimen at the th thickness sampling moment; is the flow velocity proximity degree of the th bottom specimen and the th middle specimen at the th thickness sampling moment; is the corrosion thickness of the th bottom specimen at the th thickness sampling moment; is the corrosion thickness of the th middle specimen at the th thickness sampling moment; is the number of middle specimens; is the absolute value function.

[0029] It should be noted that the larger it is, the more similar the degree of influence of the flow velocity on the th bottom specimen and the th middle specimen during the time interval from the th thickness sampling moment to the th thickness sampling moment. If is larger and at the same time is larger, it indicates that under the condition of similar flow velocity influence, the th bottom specimen is more strongly corroded, and the th bottom specimen is more likely to be affected by sediments.

[0030]

[0031] Step S003: Obtain the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment according to the negative correlation between the deposition influence degree and the corrosion thickness of the bottom specimen at each thickness sampling moment; obtain the analysis reference degree of each bottom specimen according to the flow velocity deposition reference index of the bottom specimen at all thickness sampling moments; and combine the flow velocity deposition reference index to obtain the flow velocity correlation degree of each bottom specimen at each thickness sampling moment.

[0031] It should be noted that under high-speed flow conditions, the scouring effect of the fluid is significantly enhanced, which will accelerate the corrosion reaction on the metal surface. For example, by increasing the mass transfer rate of corrosive substances (such as moisture, CO2, H2S), the metal will be corroded faster. However, high flow velocity also has a "cleaning" effect, which can effectively wash away the deposits and corrosion products formed on the metal surface, thereby reducing the concentration cell effect and pitting risk caused by local deposition. This dual effect indicates that high flow velocity may accelerate corrosion due to enhanced mass transfer, or may slow down local corrosion due to inhibiting sediment aggregation, so that the corrosion rate does not simply increase continuously with the increase of flow velocity, but is regulated by the overall dynamic balance of the flow field.

[0032] It should be further noted that in order to judge the influence of flow velocity on corrosion efficiency and the influence of sediment on corrosion efficiency at different flow velocities, and the flow velocity will also affect the amount of sediment due to the "cleaning" effect while affecting corrosion efficiency. Therefore, it is necessary to make the deposition influence degree of the analyzed metal specimen relatively high due to too slow flow velocity, and the deposition influence degree is negatively correlated with the flow velocity.

[0033] Specifically, the calculation method of the deposition flow velocity correlation index of the th bottom specimen at the th thickness sampling moment and the th bottom specimen at the th thickness sampling moment is as follows: ; In the formula, is the deposition flow velocity correlation index of the th bottom specimen at the th thickness sampling moment and the th bottom specimen at the th thickness sampling moment; is the deposition influence degree of the th bottom specimen at the th thickness sampling moment; is the deposition influence degree of the th bottom specimen at the th thickness sampling moment; is the maximum value of the deposition influence degree of all bottom specimens at all thickness sampling moments; is the maximum value of the overall flow velocity level of all bottom specimens at all thickness sampling moments; is the overall flow velocity level of the th bottom specimen at the th thickness sampling moment; is the overall flow velocity level of the th bottom specimen at the th thickness sampling moment; is the ceiling symbol; is the absolute value function.

[0034] Where is 1, it indicates that the th bottom specimen has a greater deposition influence at the th thickness sampling moment than the th bottom specimen at the th thickness sampling moment. is 0, it indicates that the th bottom specimen has a smaller deposition influence at the th thickness sampling moment than the th bottom specimen at the th thickness sampling moment. If and have the same sign, it indicates that the th bottom specimen at the th thickness sampling moment and the th bottom specimen at the th thickness sampling moment show a negative correlation between the influence degree of the sediment and the flow velocity. It means that by comparing with the influence degree of the sediment of the th bottom specimen at the th thickness sampling moment, the deposition influence degree of the th bottom specimen at the th thickness sampling moment may be affected by the flow velocity.

[0035] It should be noted that the influence degree of the sediment at most metal specimens shows a negative correlation with the flow velocity. The main reason is that the flow field environment where most specimens are located is relatively uniform. That is, in the area with a higher flow velocity, the shear force and scouring effect of the fluid are strong, which can effectively remove or prevent the accumulation of sediment and corrosion products on the metal surface; while in the area with a lower flow velocity, the fluid kinetic energy is insufficient, and the sediment is more likely to settle and accumulate. Therefore, most specimens will show this negative correlation under similar fluid conditions, and the slight differences in local geometry or installation position may cause deviations in individual specimens. So, it is necessary to judge the flow velocity deposition reference degree of each bottom specimen.

[0036] It should be further noted that for any metal specimen at any thickness sampling moment, if the deposition flow velocity correlation index is relatively large compared with that of most metal specimens at each thickness sampling moment, it indicates that the deposition influence degree of this bottom specimen at this thickness sampling moment is more likely to be affected by the flow velocity. Based on this, the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment is calculated.

[0037] Specifically, the th bottom specimen at the The calculation method of the flow velocity deposition reference index at a thickness sampling moment is as follows: ; In the formula, is the flow velocity deposition reference index of the th bottom specimen at the th thickness sampling moment; is the deposition flow velocity correlation index of the th bottom specimen at the th thickness sampling moment and the th bottom specimen at the th thickness sampling moment; is the number of thickness sampling moments; is the number of bottom specimens.

[0038] It should be noted that for any bottom specimen, the position of the bottom specimen in the pipeline remains fixed. Due to the small differences in local geometry or installation position of some individual metal specimens, the correlation between the flow velocity and the sediment is relatively low. Therefore, when the flow velocity deposition reference index of a certain bottom specimen fluctuates greatly in time series or is always in a low state, it indicates that the reference degree of this bottom specimen in analyzing the correlation between the flow velocity and the sediment is relatively low.

[0039] Specifically, the calculation method of the analysis reference degree of the th bottom specimen is as follows: ; In the formula, is the analysis reference degree of the th bottom specimen; is the mean value of the flow velocity deposition reference indexes of the th bottom specimen at all thickness sampling moments; is the variance of the flow velocity deposition reference indexes of the th bottom specimen at all thickness sampling moments; is a linear normalization function, and the normalization object is the of all bottom specimens.

[0040] It should be noted that for any bottom specimen at any thickness sampling moment, if the analysis reference degree of the bottom specimen is relatively high, it indicates that the correlation between the flow velocity and the sediment of this bottom specimen is relatively high due to its location and can be used to analyze the correlation between the flow velocity and the sediment. When the flow velocity deposition reference index of this bottom specimen at this thickness sampling moment is relatively high, it indicates that the correlation between the flow velocity and the sediment at this thickness sampling moment is relatively high. Therefore, the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment is obtained accordingly.

[0041] The The calculation method of the flow velocity correlation degree of the th bottom specimen at the th thickness sampling moment is as follows: In the formula, is the flow velocity correlation degree of the th bottom specimen at the th thickness sampling moment; is the flow velocity deposition reference index of the th bottom specimen at the th thickness sampling moment; is the analysis reference degree of the th bottom specimen; is a linear normalization function, and the normalization object is the of all bottom specimens at each thickness sampling moment.

[0042] Step S004: Obtain the flow velocity-sediment correlation function according to the flow velocity correlation degree of the bottom specimen at the thickness sampling moment; combine the overall flow velocity level and corrosion thickness of the middle specimen at each thickness sampling moment, and the deposition influence degree and corrosion thickness of the bottom specimen at each thickness sampling moment to obtain the deposition flow velocity corrosion ratio of each flow velocity.

[0043] It should be noted that when establishing the corresponding relationship between the flow velocity and deposition influence degree of the bottom specimen, the analysis is mainly based on the data with higher flow velocity correlation degree.

[0044] Specifically, taking the overall flow velocity level as the abscissa and the deposition influence degree as the ordinate, establish a two-dimensional rectangular coordinate system, map the data of all bottom specimens at each thickness sampling moment to this two-dimensional rectangular coordinate system, obtain several data points in this two-dimensional rectangular coordinate system, use the flow velocity correlation degree of each bottom specimen at each thickness sampling moment as the fitting weight of the corresponding data point, and use the least squares method to perform curve fitting on all data points to obtain the flow velocity-sediment correlation function; among them, the least squares method is a well-known technology, and the specific method will not be introduced here.

[0045] It should be noted that after analyzing the correlation between the flow velocity and deposition influence degree, since in the bottom specimen, the flow velocity and sediment will act on corrosion through different mechanisms respectively, the level of the flow velocity directly affects the mass transfer rate of corrosive media (such as water-containing, CO2, H2S, etc.) and the scouring effect on the metal surface protective film. High flow velocity accelerates the contact between the medium and the metal, making the corrosion reaction more intense; at the same time, due to the action of gravity at the bottom, solid particles and corrosion products are easily deposited, and the sediment will form local closed areas on the metal surface, resulting in local concentration cell effects and insufficient oxygen supply, thereby inducing or exacerbating local corrosion. Therefore, both the flow velocity and sediment will have a corrosion effect on the bottom specimen.

[0046] It should be further noted that when analyzing the relationship between flow velocity and corrosion, since the middle specimens are only affected by the flow velocity and not by the sediment, the relationship between flow velocity and corrosion can be constructed therefrom.

[0047] Specifically, taking the overall flow velocity level as the abscissa and the corrosion thickness as the ordinate, a two-dimensional rectangular coordinate system is established. The data of all middle specimens at each thickness sampling moment are mapped into this two-dimensional rectangular coordinate system to obtain several data points in this two-dimensional rectangular coordinate system. The least squares method is used to perform curve fitting on all data points to obtain the flow velocity-corrosion correlation function; among them, the least squares method is a well-known technology.

[0048] It should be noted that when analyzing the correlation between sediment influence degree and corrosion, after being covered by sediment, the degree of direct contact between the metal surface and the fluid will decrease because the sediment forms a barrier, making the direct effects of flow velocity on mass transfer, shear force, etc. on the metal surface relatively weakened, thereby reducing the influence of flow velocity changes on the corrosion process. Therefore, the correlation between sediment and corrosion is mainly analyzed based on the bottom specimens.

[0049] Specifically, taking the sediment influence degree as the abscissa and the corrosion thickness as the ordinate, a two-dimensional rectangular coordinate system is established. The data of all bottom specimens at each thickness sampling moment are mapped into this two-dimensional rectangular coordinate system to obtain several data points in this two-dimensional rectangular coordinate system. The least squares method is used to perform curve fitting on all data points to obtain the sediment-corrosion correlation function; among them, the least squares method is a well-known technology.

[0050] It should be noted that the flow velocity-sediment correlation function represents the corresponding functional relationship of sediment influence degree with respect to flow velocity, and the sediment-corrosion correlation function is the corresponding functional relationship of corrosion thickness with respect to sediment influence degree.

[0051] Specifically, the function values of the flow velocity-sediment correlation function are substituted into the independent variables of the sediment-corrosion correlation function to obtain the flow velocity-sediment-corrosion correlation function.

[0052] It should be noted that the flow velocity-sediment-corrosion correlation function represents the corresponding functional relationship of corrosion thickness caused by sediment with respect to flow velocity. Since the corrosion thickness is mainly affected by sediment at low flow velocities and mainly affected by flow velocity at high flow velocities, the proportional relationship between the influence of sediment and flow velocity on corrosion thickness is judged at different flow velocities.

[0053] Specifically, for any given flow velocity, the ratio of the corresponding corrosion thickness of this flow velocity in the flow velocity-sediment-corrosion correlation function to the corresponding corrosion thickness of this flow velocity in the sediment-corrosion correlation function is denoted as the sediment-flow velocity corrosion ratio of this flow velocity.

[0054] Step S005: Obtain the corrosion inhibition effectiveness test result of the corrosion inhibitor according to the deposition flow rate corrosion ratio at each flow rate.

[0055] It should be noted that in the laboratory scenario, the blank corrosion rate at different flow rates is generally obtained by using the high-temperature and high-pressure dynamic method. After adding the submarine pipeline corrosion inhibitor, the corrosion rate after adding the drug is obtained. The effectiveness of the corrosion inhibitor is judged by comparing the blank corrosion rate and the corrosion rate after adding the drug. However, since the pipeline position covered with sediment will show a faster corrosion rate, the influence of sediment needs to be considered when obtaining the blank corrosion rate. Since the anti-corrosion agent includes corrosion inhibitor, scale inhibitor and bactericide, the effectiveness of corrosion inhibitor, scale inhibitor and bactericide is evaluated.

[0056] Specifically, in the test scenario, using the high-temperature and high-pressure dynamic method, according to Formula A.2 in Section A.8 of Appendix A of the standard "GB T 35509-2017 Application and Evaluation of Corrosion Inhibitors in Oil and Gas Fields", the blank corrosion rate at several flow rates is obtained; among them, the high-temperature and high-pressure dynamic method is a well-known technology, and the specific method will not be introduced here; For any one flow rate, the product of the blank corrosion rate at this flow rate and the deposition flow rate corrosion ratio at this flow rate is denoted as the blank deposition corrosion rate at this flow rate; the maximum value among the blank corrosion rate and the blank deposition corrosion rate at this flow rate is denoted as the actual blank corrosion rate at this flow rate. Add the corrosion inhibitor to the pipeline system. According to the methods in steps S001 to SOO4, the obtained deposition flow rate corrosion ratio is recorded as the corrosion ratio after adding the drug; In the test scenario, for the oil after adding the corrosion inhibitor, using the high-temperature and high-pressure dynamic method according to Formula A.2 in Section A.8 of Appendix A of the standard "GB T35509-2017 Application and Evaluation of Corrosion Inhibitors in Oil and Gas Fields", the corrosion rate after adding the drug at several flow rates is obtained; among them, the high-temperature and high-pressure dynamic method is a well-known technology; For any one flow rate, the product of the corrosion rate after adding the drug at this flow rate and the corrosion ratio after adding the drug at this flow rate is denoted as the deposition corrosion rate after adding the drug at this flow rate; the maximum value among the corrosion rate after adding the drug and the deposition corrosion rate after adding the drug at this flow rate is denoted as the actual corrosion rate after adding the drug at this flow rate.

[0057] Furthermore, in the test scenario, using the high-temperature and high-pressure dynamic method according to Formulas A.3, A.4 and A.5 in Section A.8 of Appendix A of the standard "GB T 35509-2017 Application and Evaluation of Corrosion Inhibitors in Oil and Gas Fields", the pitting rate, uniform corrosion inhibition rate and pitting corrosion inhibition rate are obtained; Evaluate the actual blank corrosion rate, actual corrosion rate after adding chemicals, pitting corrosion rate, uniform corrosion rate, and pitting corrosion inhibition rate according to items 7.1.3.2 and 7.1.3.3 of the enterprise standard "QH / S 2064 Requirements for Internal Corrosion Control and Effect Evaluation in Offshore Oil and Gas Field Production Process Systems". Obtain analysis conclusions and maintenance measures based on the evaluation results. The specific analysis conclusions and maintenance measures are as follows: The analysis conclusions are specifically divided into two types: "qualified" and "unqualified". The situations that can be judged as "qualified" are as follows: 1. Regardless of the size of the actual blank corrosion rate, if the final actual corrosion rate after adding the corrosion inhibitor is not greater than 0.03 mm / a, there is no pitting corrosion, and the compatibility is good, then the corrosion inhibitor meets the requirements; 2. If the final actual corrosion rate after adding the corrosion inhibitor is greater than 0.03 mm / a, but the actual blank corrosion rate is 0.25 mm / a, the corrosion inhibition rate ≥ 70%, and there is no pitting corrosion; 3. If the final actual corrosion rate after adding the corrosion inhibitor is greater than 0.03 mm / a, 0.25 mm / a < actual blank corrosion rate ≤ 0.75 mm / a, the pitting corrosion rate ≤ 0.13 mm / a, and the compatibility: 1) meets the requirements of the corrosion inhibition rate and pitting corrosion rate in this table; 2) the influence of the scale inhibitor rate ≤ 5%; 3) does not reduce the performance of other chemicals; 4) the corrosion inhibition effect still meets the requirements after adding other chemicals; 4. If the final actual corrosion rate after adding the corrosion inhibitor is greater than 0.03 mm / a, the actual blank corrosion rate > 0.75 mm / a, the corrosion inhibition rate ≥ 90%, and the pitting corrosion rate ≤ 0.21 mm / a; When the corrosion inhibitor is judged as "qualified", the maintenance measure is to maintain the current situation; The situations that can be judged as "unqualified" are as follows: 1. The actual blank corrosion rate < 0.25 mm / a, and pitting corrosion occurs after adding chemicals. The corresponding maintenance measure for this situation is: If there is pitting corrosion in the blank and pitting corrosion after adding chemicals, the chemical compatibility needs to be considered, and a chemical compatibility evaluation should be carried out; If there is no pitting corrosion in the blank but pitting corrosion after adding chemicals, the chemical is unqualified, and a chemical type change is required; 2. The actual blank corrosion rate < 0.25 mm / a, there is no pitting corrosion, and the corrosion inhibition rate < 70%. The corresponding maintenance measure for this situation is: Optimize the chemical concentration. If the corrosion inhibition rate does not increase significantly after increasing the chemical concentration, it is recommended to change the chemical type; 3. 0.25 mm / a < actual blank corrosion rate ≤ 0.75 mm / a, and the pitting corrosion rate > 0.13 mm / a after adding chemicals. The corresponding maintenance measure for this situation is: Change the chemical type 4. 0.25mm / a < actual blank corrosion rate ≤ 0.75mm / a, no pitting, actual corrosion rate after adding medicine > 0.076mm / a; the corresponding maintenance measures for this situation need specific analysis: if the actual blank corrosion rate of the on-site water is large, combined with the on-site hanging piece data, if the on-site hanging piece data is stable and not high, it is necessary to consider whether there is a problem in the test process and retest is required; if the actual blank corrosion rate of the on-site water is large, the on-site hanging piece corrosion rate is also high, and the reagent concentration needs to be adjusted. If the concentration is adjusted, it still cannot meet the requirements, then the reagent needs to be replaced; if the actual blank corrosion rate of the simulated water is large, combined with the on-site hanging piece data analysis, if the on-site hanging piece data is stable and all are low-grade corrosion, it is recommended to take the on-site data as the standard; if the actual blank corrosion rate of the simulated water is large, the on-site hanging piece corrosion rate is also high, the reagent concentration needs to be adjusted. If the concentration is adjusted, it still cannot meet the requirements, then the reagent needs to be replaced; 5. The actual blank corrosion rate is greater than 0.75 mm / a, there is no pitting, and the corrosion inhibition rate is less than 90%. The corresponding maintenance measures for this situation are: changing the reagent type; 6. The actual blank corrosion rate is >0.75mm / a, and the pitting rate after adding the agent is >0.21mm / a; the corresponding maintenance measures in this case are: changing the agent.

[0058] Furthermore, the comprehensive anti-scaling rate and pressure change rate of the anti-scaling agent are obtained by titration according to Appendix B7.1 and B7.2 of the enterprise standard "QHS 2057-2021". The titration method is a well-known technology and the specific method is not introduced here. Then, the effectiveness of the anti-scaling agent is evaluated according to 5.3.4 of the enterprise standard "QHS 2057-2021". The analysis conclusions and maintenance measures are obtained according to the evaluation results. The specific analysis conclusions and maintenance measures are as follows: If the anti-scaling rate in the analysis conclusion is greater than 60%, the anti-scaling agent is judged to be "qualified"; If the anti-scaling rate in the analysis conclusion is less than 60%, the anti-scaling agent is judged to be "unqualified" and the corresponding maintenance measures are: consider the compatibility of the agent. If there is no problem with the compatibility of the agent, the agent needs to be replaced.

[0059] Furthermore, the effectiveness of the fungicide was evaluated using the QPCR method according to the standard "SY T 5329-2012 Water Quality Indicators and Analysis Methods for Water Injection in Clastic Reservoirs". The QPCR method is a well-known technology and the specific method is not introduced here. The analysis conclusions and maintenance measures were obtained based on the evaluation results. The specific analysis conclusions and maintenance measures are as follows: If the SRB content in the injected water is less than 25 / ml or the SRB content in the mixed pipeline is less than 110 / ml, the fungicide is judged as "qualified"; If the content of injected SRB ≥ 25 per ml or the content of SRB in the mixed - transportation subsea pipeline ≥ 110 per ml in the analysis conclusion, the bactericide is judged as "unqualified", and the maintenance measure needs to change the type of chemical agent, and select a targeted chemical agent for sterilization.

[0060] Thus, the evaluation and maintenance of the effectiveness of anti - corrosion chemical agents including corrosion inhibitors, scale inhibitors, and bactericides are realized.

[0061] This embodiment adopts a model to present the inverse - proportional relationship and normalization processing, which is the input of the model. The implementer can set the inverse - proportional function and normalization function according to the actual situation.

[0062] Another embodiment of the present invention provides a digital comprehensive evaluation system for the effectiveness of subsea pipeline anti - corrosion chemical agents. The system includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the above - mentioned method steps S001 to step S005 are realized.

[0063] The above are only the preferred embodiments of the present invention, and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents, characterized in that, The method includes the following steps: Obtain the overall flow velocity level and corrosion thickness of each middle specimen and each bottom specimen at each thickness sampling moment; Based on the difference in corrosion thickness between the middle specimens and the bottom specimens under a similar overall flow velocity level, obtain the deposition influence degree of each bottom specimen at each thickness sampling moment; Based on the negative correlation between the deposition influence degree and the corrosion thickness of the bottom specimens at each thickness sampling moment, obtain the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment; based on the flow velocity deposition reference indexes of the bottom specimens at all thickness sampling moments, obtain the analysis reference degree of each bottom specimen; combine the flow velocity deposition reference indexes to obtain the flow velocity correlation degree of each bottom specimen at each thickness sampling moment; Based on the flow velocity correlation degree of the bottom specimens at the thickness sampling moment, obtain the flow velocity - sediment correlation function; combine the overall flow velocity level and corrosion thickness of the middle specimens at each thickness sampling moment, and the deposition influence degree and corrosion thickness of the bottom specimens at each thickness sampling moment to obtain the deposition flow velocity corrosion ratio of each flow velocity; Based on the deposition flow velocity corrosion ratio of each flow velocity, obtain the detection result of the anti - corrosion effectiveness of the corrosion inhibitor.

2. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the deposition influence degree of each bottom specimen at each thickness sampling moment based on the difference in corrosion thickness between the middle specimens and the bottom specimens under a similar overall flow velocity level includes: Based on the similarity of the overall flow velocity levels of the bottom specimens and the middle specimens at the thickness sampling moment, obtain the flow velocity proximity degree of each bottom specimen and each middle specimen at each thickness sampling moment; The deposition influence degree of the bottom specimen at the th thickness sampling moment is calculated as follows: ； In the formula, is the deposition influence degree of the th bottom specimen at the th thickness sampling moment; is the flow velocity proximity degree of the th bottom specimen and the th middle specimen at the th thickness sampling moment; is the corrosion thickness of the th bottom specimen at the th thickness sampling moment; is the corrosion thickness of the th middle specimen at the th thickness sampling moment; is the number of middle specimens; is the absolute value function.

3. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 2, characterized in that, The specific method for obtaining the flow velocity proximity degree of each bottom specimen and each middle specimen at each thickness sampling moment based on the similarity of the overall flow velocity levels of the bottom specimens and the middle specimens at the thickness sampling moment includes: For any bottom specimen and any middle specimen, record the inverse proportional normalization result of the absolute value of the difference in the overall flow velocity level of the bottom specimen and the middle specimen at any thickness sampling moment as the flow velocity proximity degree of the bottom specimen and the middle specimen at the thickness sampling moment.

4. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the flow velocity deposition reference index of each bottom specimen at each thickness sampling moment based on the negative correlation between the deposition influence degree and the corrosion thickness of the bottom specimens at each thickness sampling moment includes: The bottom specimen at the thickness sampling moment and the bottom specimen at the thickness sampling moment are calculated as follows for the deposition flow rate correlation index: ； Wherein, is the deposition flow velocity correlation index of the th bottom sample at the th thickness sampling moment and the th bottom sample at the th thickness sampling moment; is the deposition influence degree of the th bottom sample at the th thickness sampling moment; is the deposition influence degree of the th bottom sample at the th thickness sampling moment; is the maximum value of the deposition influence degrees of all bottom samples at all thickness sampling moments; is the maximum value of the overall flow velocity levels of all bottom samples at all thickness sampling moments; is the overall flow velocity level of the th bottom sample at the th thickness sampling moment; is the overall flow velocity level of the th bottom sample at the th thickness sampling moment; is the ceiling symbol; is the absolute value function; For any bottom specimen at any thickness sampling moment, record the sum value of the deposition flow velocity correlation indexes of the bottom specimen at the thickness sampling moment and all bottom specimens at all thickness sampling moments as the flow velocity deposition reference index of the bottom specimen at the thickness sampling moment.

5. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the analysis reference degree of each bottom specimen based on the flow velocity deposition reference indexes of the bottom specimens at all thickness sampling moments includes: For any bottom specimen, record the linear normalization result of the product of the mean and variance of the flow velocity deposition reference indexes of the bottom specimen at all thickness sampling moments as the analysis reference degree of the bottom specimen.

6. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the flow velocity correlation degree of each bottom specimen at each thickness sampling moment includes: The linear normalization result of the product of the flow velocity deposition reference index of any bottom sample at any thickness sampling moment and the analysis reference degree of the bottom sample is denoted as the flow velocity correlation degree of the bottom sample at the thickness sampling moment.

7. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the flow velocity-sediment correlation function according to the flow velocity correlation degree of the bottom sample at the thickness sampling moment includes: Taking the overall flow velocity level as the abscissa and the deposition influence degree as the ordinate to establish a two-dimensional rectangular coordinate system, mapping the data of all bottom samples at each thickness sampling moment into the two-dimensional rectangular coordinate system, obtaining several data points in the two-dimensional rectangular coordinate system, using the flow velocity correlation degree of each bottom sample at each thickness sampling moment as the fitting weight of the corresponding data point, and using the least squares method to perform curve fitting on all data points to obtain the flow velocity-sediment correlation function.

8. The digital and intelligent comprehensive evaluation method for the effectiveness of submarine pipeline anti-corrosion agents according to claim 1, characterized in that, The specific method for obtaining the deposition flow velocity corrosion ratio of each flow velocity includes: Obtaining the flow velocity-corrosion correlation function according to the overall flow velocity level and the corrosion thickness of the middle sample at each thickness sampling moment; Obtaining the deposition-corrosion correlation function according to the deposition influence degree and the corrosion thickness of the bottom sample at each thickness sampling moment; Substituting the function value of the flow velocity-sediment correlation function into the independent variable of the deposition-corrosion correlation function to obtain the flow velocity-deposition corrosion correlation function; For any flow velocity, the ratio of the corresponding corrosion thickness of the flow velocity in the flow velocity-deposition corrosion correlation function to the corresponding corrosion thickness of the flow velocity in the deposition-corrosion correlation function is denoted as the deposition flow velocity corrosion ratio of the flow velocity.

9. The digital comprehensive evaluation method for the effectiveness of a submarine pipeline anti-corrosion agent according to claim 1, characterized in that, The specific method for obtaining the anti-corrosion effectiveness detection result of the corrosion inhibitor according to the deposition flow velocity corrosion ratio of each flow velocity includes: Obtaining the blank corrosion rate at several flow velocities; For any flow velocity, the product of the blank corrosion rate at the flow velocity and the deposition flow velocity corrosion ratio of the flow velocity is denoted as the blank deposition corrosion rate at the flow velocity; the maximum value of the blank corrosion rate and the blank deposition corrosion rate at the flow velocity is denoted as the actual blank corrosion rate at the flow velocity; Obtaining the dosing corrosion ratio of each flow velocity; obtaining the dosing corrosion rate at several flow velocities; For any flow velocity, the product of the dosing corrosion rate at the flow velocity and the dosing corrosion ratio of the flow velocity is denoted as the dosing deposition corrosion rate at the flow velocity; the maximum value of the dosing corrosion rate and the dosing deposition corrosion rate at the flow velocity is denoted as the actual dosing corrosion rate at the flow velocity; Obtaining the evaluation result of the effectiveness of the submarine pipeline corrosion inhibitor according to the actual blank corrosion rate and the actual dosing corrosion rate.

10. A digital comprehensive evaluation system for the effectiveness of a submarine pipeline anti-corrosion agent, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of a digital comprehensive evaluation method for the effectiveness of a submarine pipeline anti-corrosion agent as described in any one of claims 1-9.

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