A method and apparatus for detecting corrosion inside water pipes

Abstract

This invention discloses a method and apparatus for detecting internal corrosion in water pipelines. By calculating the pressure drop in the water pipeline, the method predicts the sensitive points for internal corrosion. Based on the direct excavation and detection results of these sensitive points, the internal corrosion status of the entire pipeline is evaluated. This method avoids the limitations imposed by intelligent internal corrosion detection on pipeline diameter, bend radius, and cleaning equipment conditions. Through a scientific prediction method, the method selects the pipe section most prone to internal corrosion for direct excavation and detection, improving excavation and detection efficiency and the detection rate of internal corrosion defects. It avoids the high costs and low efficiency associated with random or full-line excavation methods.

Description

Technical Field

[0001] This invention relates to the field of pipeline corrosion technology, and in particular to a method and apparatus for detecting corrosion inside water pipelines. Background Technology

[0002] Water pipelines are frequently started and stopped, with drastic changes in flow rate. Due to pumping and changes in operating conditions, gas can easily be introduced. When the pipeline is stopped, bubbles tend to accumulate at the top of the pipeline, and the coexistence of gas and liquid creates conditions conducive to internal corrosion.

[0003] If disinfectant is dissolved in the water supply pipes, ClO2 is produced. When ClO2 comes into contact with water, the following reaction occurs:

[0004] 8ClO2 + H2O → 2Cl2 + 7O2 + 4HClO

[0005] The oxygen and hypochlorous acid produced are both strong oxidizing agents. Therefore, the following electrochemical reaction occurs inside the pipeline:

[0006] Anode: Fe → Fe 2+ +2e, Fe 2+ +OH - →FeOH+e

[0007] Cathode: HClO + 2e - +H₂O→Cl - +OH - O2 + H2O + e - →OH -

[0008] At the same time, the scale and corrosion products adhering to the pipes mix to form a hard crust, creating an under-scale corrosion environment, which is then formed by Cl. - Accelerate pitting corrosion.

[0009] Since corrosion inside water pipes can cause defects and failures, it is necessary to conduct detection and evaluation of corrosion inside water pipes in order to take corresponding control measures.

[0010] Currently, there are two main methods for detecting internal corrosion in water pipelines: one is to conduct intelligent internal inspection, which is expensive and has certain requirements on pipe diameter, bend radius, and cleaning equipment conditions, making it impossible to conduct internal inspection on a large number of water pipelines; the other is to excavate the pipeline for non-destructive testing, which currently can only be done by full-line excavation or random excavation. Full-line excavation is inefficient, time-consuming, and expensive, while random excavation has a low probability of detecting internal corrosion defects. Summary of the Invention

[0011] The purpose of this invention is to provide a method and apparatus for detecting corrosion inside water pipes, in order to solve the above-mentioned technical problems.

[0012] To achieve the above objectives, the present invention provides a method for detecting corrosion inside water pipes, the method comprising:

[0013] To identify multiple low-pressure points in the water pipeline;

[0014] Non-destructive testing was performed on the multiple low-pressure points to obtain the minimum wall thickness data at the target low-pressure point;

[0015] Based on the minimum wall thickness data at the target low-pressure point, the corrosion parameters at the target low-pressure point are obtained, and these corrosion parameters are used as the corrosion parameters for corrosion inside the water pipe.

[0016] The technical effects and advantages of this invention are as follows:

[0017] This invention calculates the pressure drop in water pipelines to predict sensitive points for internal corrosion. Based on the direct excavation and inspection results of these sensitive points, the internal corrosion status of the entire pipeline is evaluated. This avoids the limitations imposed by intelligent internal corrosion inspection methods on pipeline diameter, bend radius, and cleaning equipment. Through a scientific prediction method, the most corrosion-prone sections are selected for direct excavation and inspection, improving excavation and inspection efficiency and the detection rate of internal corrosion defects. This avoids the high costs and low efficiency associated with random or full-line excavation methods.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0019] Figure 1 A flowchart of a method for detecting corrosion inside water pipes;

[0020] Figure 2 Elevation data map;

[0021] Figure 3 This is a diagram showing the pressure distribution along the entire line.

[0022] Figure 4A This is a diagram showing the X-ray detection results for X-ray No. 6.

[0023] Figure 4B This is a diagram showing the X-ray detection results for image number 7.

[0024] Figure 4C This is a diagram showing the X-ray detection results for image number 8. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Furthermore, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0027] In the detection and evaluation of internal corrosion in oil and gas pipelines, there are direct evaluation methods for internal corrosion that can solve the above problems. The technical route is as follows: select the low-lying points of the pipeline through multiphase flow analysis, that is, the points most prone to water accumulation and internal corrosion, and excavate them. Then, select one or more methods such as X-ray, ultrasonic testing, and ultrasonic C-scan for non-destructive testing. Based on the internal corrosion status of the pipe section most prone to corrosion, infer and evaluate the internal corrosion status of the entire oil and gas pipeline. The logical basis is the bucket effect.

[0028] Internal corrosion detection in water pipelines can be conducted using methods analogous to those used for direct evaluation of internal corrosion in oil and gas pipelines. However, the corrosion patterns in water pipelines differ from those in oil and gas pipelines. Management practice has revealed that the most susceptible locations for internal corrosion in water pipelines are at elevations such as pipeline bends. Through research on the internal corrosion mechanism of water pipelines, it has been found that the pipe sections most prone to internal corrosion are those with low pressure, leading to this invention. The principle behind this method is that water pipelines easily form a gas-liquid coexistence space at low pressure points, which is calculated using multiphase flow calculations and corrosion rate calculations.

[0029] To better explain the present invention, the following is combined with... Figure 1 A detailed explanation of a method for detecting corrosion inside water pipes is provided, the method comprising:

[0030] 1. Obtain multiple low-pressure points in the water pipeline.

[0031] Specifically, obtaining multiple low-pressure points of the water pipeline includes: obtaining basic data of the water pipeline; and obtaining multiple low-pressure points of the water pipeline based on the basic data.

[0032] The basic data includes: elevation data, starting pressure, flow rate, temperature, pipe wall roughness, and downtime.

[0033] 2. Perform non-destructive testing on the multiple low-pressure points to obtain the minimum wall thickness data at the target low-pressure point.

[0034] The pressure calculation is as follows: The pressure along the pipeline is calculated using both Bernoulli's equation and the pressure drop equation. Low-pressure points are selected as the internal corrosion-sensitive points of the pipeline, with a density of 1-3 points per 1km, and any point less than 1km is counted as 1km. If a selected internal corrosion-sensitive point is located in a river, concrete road, or other location where excavation is not feasible for direct testing, it is determined whether this point is the lowest pressure point along the entire pipeline. If so, a point with a similar pressure value is selected nearby for excavation and testing; otherwise, this 1km section can be tested directly without excavation.

[0035] In addition, pressure calculation along pipelines is common in this field, and various types of simulation software have been developed for this pressure distribution, such as OLGA software (available from Schlumberger, USA) and Pipephase software (available from SimSci, USA). By inputting parameters such as the flow rate, pipe diameter, and elevation data of the target pipeline into the above software, the multiphase fluid movement in the pipeline can be simulated, thereby obtaining relevant parameters (such as temperature and pressure) at a certain location in the pipeline.

[0036] Excavation is performed on selected corrosion-sensitive points, and non-destructive testing (NDT) is conducted using methods such as X-ray + ultrasonic thickness measurement, X-ray + ultrasonic C-scan, or X-ray + ultrasonic thickness measurement + ultrasonic C-scan to obtain the minimum wall thickness data at the excavation point (i.e., the target low-pressure point). X-rays are used for qualitative analysis, ultrasonic thickness measurement for quantitative analysis, and ultrasonic C-scan provides continuous wall thickness variation data, resulting in a contour map; ultrasonic thickness measurement measures the wall thickness at a single point, which is discontinuous. Therefore, after excavation, technicians can choose the appropriate NDT method based on testing needs and cost.

[0037] 3. Based on the minimum wall thickness data at the target low-pressure point, obtain the corrosion parameters at the target low-pressure point, and use the corrosion parameters at the target low-pressure point as the corrosion parameters for corrosion inside the water pipeline.

[0038] The corrosion parameters at the target low-pressure point include: degree of internal corrosion, remaining lifespan, and maintenance and usage recommendations.

[0039] Specifically, the minimum wall thickness data of the excavation inspection points is obtained through non-destructive testing, and the maximum wall thickness reduction ratio of each excavation inspection point is calculated using the following formula:

[0040]

[0041] In the formula, η is the maximum wall thickness reduction ratio, δ is the original / design wall thickness of the pipe at the excavation and inspection point, in mm. s —The minimum wall thickness detected at this excavation detection point, in mm.

[0042] The degree of internal corrosion is obtained according to the evaluation criteria table for wall thickness corrosion thinning in Table 1.

[0043] Table 1 Evaluation Criteria for Wall Thickness Corrosion Thinning

[0044] rating level light middle Heavy serious Maximum wall thickness reduction ratio ≤20％ 20％＜～≤40％ 40＜～≤60 >60％

[0045] Specifically, calculate the remaining lifespan of the detected area.

[0046]

[0047] In the formula, S represents the remaining lifespan of the detection site, a; δ min —Minimum wall thickness requirement, mm;

[0048] v corr —Corrosion rate, mm / a;

[0049] The corrosion rate is calculated as follows:

[0050]

[0051] In the formula, t represents the number of years the pipeline has been in operation, and a represents the number of years it has been in operation.

[0052] The calculation method for the minimum required wall thickness is as follows:

[0053]

[0054] Where, δ min —Minimum wall thickness requirement, mm; P s —Design pressure, MPa; D —Pipe outer diameter, mm; θ —Strength design coefficient of steel pipe; σ s — Yield strength, MPa.

[0055] Specific recommendations for pipeline maintenance and use.

[0056] Based on the degree of corrosion and remaining lifespan at the excavation inspection points, recommendations are given regarding pipe replacement, continued use, and the next evaluation time. Preferably, the next evaluation time is half of the calculated remaining lifespan, but not exceeding 8 years.

[0057] To better explain the present invention, embodiments are also provided below.

[0058] Taking a water pipeline A in a gas field as an example, the specifications are Φ323.9mm×5.6mm, the material is L245N, the design pressure is 4.0MPa, the starting pressure during normal operation is 3.5MPa, and the daily water transmission capacity is 900~2500m³. 3 The water supply is conducted for 3-5 hours per day, with supply stopped at the rest of the time. The methods for detecting corrosion inside the water pipeline are as follows:

[0059] 1. Basic data collection for water pipelines.

[0060] The collected data shows that steel water pipe A has a diameter of 323.9 mm, a wall thickness of 5.6 mm, a design pressure of 4 MPa, and is made of L245N steel, therefore its minimum yield strength is 245 MPa. The inner wall roughness of the steel pipe is 0.2 mm, the transport temperature is approximately 20℃, the pipeline strength design coefficient is 0.72, and the water viscosity is 1.01 × 10^(-3) Pa·s. The normal operating starting pressure of pipeline A is 2950 kPa, and the water transport volume is 900–2500 m³ / s. 3 The water supply time is 3-5 hours per day, with supply stopped at other times. Pipeline A has a service life of 5 years. Elevation-mileage data for pipeline A has been collected; the elevation map is available here. Figure 2 .

[0061] 2. Calculate the pressure distribution and analyze the points susceptible to internal corrosion.

[0062] In this evaluation, the pressure along the line was calculated using the pressure calculation formula:

[0063]

[0064] In the formula, z1 is the starting elevation (m); p1 is the starting pressure (kPa); ρ is the density of the transported water (kg / m³); and g is the acceleration due to gravity (9.8 m / s²). 2 v1—Initial flow velocity, m / s; z2—Elevation of this point, m; p2—Pressure at this point, kPa; v2—Flow velocity at this point, m / s; —Flow velocity along the path (m / s); λ —Friction coefficient along the path (can be found in hydraulic handbooks); d —Pipe inner diameter (mm); L —Distance from the starting point (m).

[0065] 3. The calculated pressure distribution map for the entire line is shown below. Figure 3 .

[0066] Based on the calculation results, following the method of selecting 1-3 points of lowest pressure per kilometer, 8 internal corrosion-sensitive points were selected for pipeline A, as shown in Table 2.

[0067] Table 2 Results of Selection of Internal Corrosion Sensitive Points

[0068]

[0069]

[0070] Of the eight internal corrosion-sensitive points, points 1, 2, 3, 4, and 5 are not suitable for excavation and are not the points with the lowest pressure along the entire line, so there is no need to select points near them for excavation. Therefore, points 6, 7, and 8, a total of three points, should be excavated for direct testing.

[0071] 4. For the selected corrosion-sensitive points inside the water pipe, direct detection is carried out using non-destructive testing methods such as X-ray and ultrasonic thickness measurement.

[0072] ① X-ray detection results, such as Figure 4A , Figure 4B , Figure 4C As shown.

[0073] according to Figure 4A , Figure 4B , Figure 4C It can be seen that corrosion and thinning of the pipe wall are present near the 12 o'clock position in the three excavated and inspected pipe sections.

[0074] ② Ultrasonic thickness measurement results.

[0075] At each excavation point, an ultrasonic thickness gauge was used to measure the wall thickness in 12 clockwise directions around the pipe for 6 circles. A total of 72 wall thickness values ​​were measured at each excavation point. The wall thickness measurement results at excavation point No. 6 are shown in Table 3.

[0076] Table 3. Wall thickness measurement results at excavation location No. 6

[0077]

[0078]

[0079] Finally, the minimum wall thickness and maximum wall thickness reduction of each excavated pipe section were obtained, as shown in Table 4.

[0080] Table 4. Minimum wall thickness measured at excavation monitoring points.

[0081]

[0082] 5. Post-evaluation.

[0083] ①The degree of internal corrosion is determined based on the maximum wall thickness reduction ratio, as shown in Table 5.

[0084] Table 5. Results of Corrosion Assessment at Excavation Detection Points

[0085]

[0086] It can be seen that the maximum wall thickness reduction ratio at excavation locations 6, 7, and 8 is within the range of 21% ≤ to 40%, therefore the degree of internal corrosion is moderate.

[0087] ②Calculate the corrosion life of the tested area based on the data obtained from the test.

[0088]

[0089] In the formula, S represents the remaining lifespan of the detection site, a; δ min —Minimum wall thickness requirement, mm; v corr —Corrosion rate, mm / a.

[0090] The minimum required wall thickness for pipeline A is as follows: calculate:

[0091]

[0092] The remaining lifespan at point 6 is calculated based on the test results:

[0093] The remaining lifespan at point 7 is calculated based on the test results:

[0094] The remaining lifespan at point 8 is calculated based on the test results:

[0095] ③ Therefore, the following maintenance and usage recommendations can be obtained for the pipeline: When pipeline A was inspected, the most severely corroded section was classified as having moderate internal corrosion; based on the current state of internal corrosion, the minimum remaining service life is 1.43 years; the next evaluation will be conducted in 8 months (0.715 years).

[0096] The present invention also provides a corrosion detection device for water pipes, the device comprising: a low-pressure point acquisition unit for acquiring multiple low-pressure points of the water pipe; a data acquisition unit for performing non-destructive testing on the multiple low-pressure points to obtain minimum wall thickness data at a target low-pressure point; and a parameter acquisition unit for obtaining corrosion parameters at the target low-pressure point based on the minimum wall thickness data at the target low-pressure point, and using the corrosion parameters at the target low-pressure point as corrosion parameters for corrosion inside the water pipe.

[0097] Since the protection provided by this device is similar to that provided by the method described above, it will not be described in detail here. Please refer to the discussion section of the method described above for more information.

[0098] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting corrosion inside water pipes, characterized in that, The method includes: To identify multiple low-pressure points in the water pipeline; Non-destructive testing was performed on the multiple low-pressure points to obtain the minimum wall thickness data at the target low-pressure point; Based on the minimum wall thickness data at the target low-pressure point, the corrosion parameters at the target low-pressure point are obtained, and the corrosion parameters at the target low-pressure point are used as the corrosion parameters for corrosion inside the water pipe. Obtaining multiple low-pressure points of a water pipeline includes: obtaining basic data of the water pipeline; and obtaining multiple low-pressure points of the water pipeline based on the basic data; wherein the basic data includes: elevation data, starting pressure, flow rate, temperature, pipe wall roughness, and downtime. Based on the aforementioned basic data, multiple low-pressure points of the water pipeline are obtained, including by processing the basic data using Bernoulli's equation and pressure drop equation to obtain multiple low-pressure points of the water pipeline.

2. The method according to claim 1, characterized in that, The multiple low-pressure points were subjected to non-destructive testing using X-ray and ultrasonic thickness measurement.

3. The method according to claim 1, characterized in that, The corrosion parameters at the target low-pressure point include: the degree of internal corrosion and the remaining life.

4. The method according to claim 3, characterized in that, Based on the minimum wall thickness data at the target low-pressure point, the degree of internal corrosion at the target low-pressure point is obtained, including: Based on the minimum wall thickness data at the target low-pressure point, the wall thickness reduction ratio at the target low-pressure point is obtained by the following formula; The degree of internal corrosion at the target low-pressure point is obtained based on the wall thickness reduction ratio at the target low-pressure point. In the formula, This represents the maximum wall thickness reduction ratio; The original / designed wall thickness of the pipeline at the target low-pressure point; The minimum wall thickness detected at the target low-pressure point.

5. The method according to claim 3, characterized in that, Based on the minimum wall thickness data at the target low-pressure point, the remaining lifetime at the target low-pressure point is obtained, including: obtaining the remaining lifetime at the target low-pressure point using the following formula; In the formula, S represents the remaining lifespan at the target low-pressure point; The minimum wall thickness detected at the target low-pressure point; Minimum required wall thickness; The corrosion rate is represented by the value of .

6. The method according to claim 5, characterized in that, The corrosion rate and minimum required wall thickness are obtained using the following formulas; In the formula, For corrosion rate; The original / designed wall thickness of the pipeline at the target low-pressure point; The minimum wall thickness detected at the target low-pressure point; t is the pipeline's operational lifespan; Minimum required wall thickness; Design pressure; The outer diameter of the water pipe; This is the strength design factor for the water pipeline; It represents the yield strength.

7. The method according to claim 3, characterized in that, The method further includes: obtaining maintenance and usage recommendations for the target low-pressure point based on the degree of internal corrosion and the remaining lifespan at the target low-pressure point; The maintenance and usage recommendations include: replacing the tube, continuing to use, and the next evaluation time.

8. A corrosion detection device for water pipes, characterized in that, The device includes: Low-pressure point acquisition unit, used to acquire multiple low-pressure points in the water pipeline; The data acquisition unit is used to perform non-destructive testing on the multiple low-pressure points to obtain the minimum wall thickness data at the target low-pressure point. The parameter acquisition unit is used to obtain the corrosion parameters at the target low-pressure point based on the minimum wall thickness data at the target low-pressure point, and to use the corrosion parameters at the target low-pressure point as the corrosion parameters for corrosion inside the water pipe. Obtaining multiple low-pressure points of a water pipeline includes: obtaining basic data of the water pipeline; and obtaining multiple low-pressure points of the water pipeline based on the basic data; wherein the basic data includes: elevation data, starting pressure, flow rate, temperature, pipe wall roughness, and downtime. Based on the aforementioned basic data, multiple low-pressure points of the water pipeline are obtained, including by processing the basic data using Bernoulli's equation and pressure drop equation to obtain multiple low-pressure points of the water pipeline.

Images