Built-in ultrasonic detection safety assessment method for U-shaped tube bundle of high-pressure heater of power plant

Abstract

The invention discloses a built-in ultrasonic detection safety assessment method for a U-shaped tube bundle of a high-pressure heater of a power plant. The method comprises the following steps: S1, sampling a core detection area determined based on a flow field and a structure in the U-shaped tube bundle of the high-pressure heater; s2, cleaning the inner wall of the sampling tube bundle and calibrating an ultrasonic detection system; s3, performing spiral scanning on the sampling tube bundle by adopting a built-in rotary ultrasonic detection system to obtain wall thickness distribution data; s4, identifying a defect type based on the scanned image, determining the minimum residual wall thickness, and calculating a safety coefficient in combination with a bursting pressure formula; and S5, making a hierarchical maintenance decision based on the safety coefficient. Compared with the prior art, the built-in ultrasonic detection safety assessment method for the U-shaped tube bundle of the high-pressure heater of the power plant has the advantages of integrating area positioning, accurate detection, defect diagnosis and safety assessment.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing and evaluation technology for power plant equipment, specifically to a method for safety evaluation of built-in ultrasonic testing of U-shaped tube bundles in high-voltage heaters of power plants. Background Technology

[0002] High-pressure heaters are key equipment in the regenerative systems of thermal power plants. They typically contain a large number of U-shaped carbon steel tube bundles for heating feedwater.

[0003] These tube bundles operate for extended periods in high-temperature (approximately 470°C), high-pressure (tube-side pressure can reach 38 MPa) and complex flow field environments, making them susceptible to various failure modes, including steam erosion, fretting wear, and flow-accelerated corrosion (FAC).

[0004] The aforementioned damage often manifests as local or overall thinning of the wall thickness, and in severe cases, it can lead to tube rupture, causing unplanned shutdowns or even safety accidents.

[0005] Traditional detection methods often employ eddy current testing or conventional ultrasound, but these methods are difficult to accurately quantify wall thickness loss and have limited ability to identify the causes of complex thinning defects.

[0006] In recent years, the Internal Rotary Inspection System (IRIS) technology has been gradually applied to the inspection of small-diameter tube bundles due to its advantages such as high precision, quantification, and imaging.

[0007] However, existing IRIS applications mostly remain at the data acquisition level, lacking a systematic approach that combines actual power plant operating conditions, failure mechanisms, and safety margin assessments, making it difficult to directly translate test results into maintenance decision-making basis. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned technical defects and provide a built-in ultrasonic testing safety assessment method for U-shaped tube bundles of high-voltage heaters in power plants that integrates regional positioning, precise detection, defect diagnosis and safety assessment.

[0009] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: a method for safety assessment of built-in ultrasonic testing of U-shaped tube bundles in high-voltage heaters of power plants, comprising the following steps:

[0010] S1: Sampling of the core detection area in the U-shaped tube bundle of the high-pressure heater, determined based on the flow field and structure;

[0011] S2: Perform internal wall cleaning and ultrasonic testing system calibration on the sampling tube bundle;

[0012] S3: The sampling tube bundle is spiral-scanned using a built-in rotating ultrasonic detection system to obtain wall thickness distribution data;

[0013] S4: Based on the defect type identification of the scanned image, determine the minimum remaining wall thickness, and calculate the safety factor in combination with the burst pressure formula;

[0014] S5: Develop graded maintenance decisions based on safety factors.

[0015] Preferably, the U-shaped tube bundle in S1 is a small-diameter thin-walled carbon steel tube with an outer diameter of 15.88 mm and a wall thickness of 2.31 mm. The operating conditions are a tube pressure of 38 MPa and a temperature of 470 °C.

[0016] Preferably, the core detection area in S1 is the upper and middle row of pipe bundles within a range of 1.8 meters to 2.3 meters downstream of the steam inlet pipe, and the sampling adopts stratified sampling method.

[0017] Preferably, in step S2, the inner wall cleaning is performed using a high-pressure water jet with a pressure greater than 20 MPa, in conjunction with a dedicated pipeline cleaning tool.

[0018] Preferably, step S3 further includes calibration of the rotating ultrasonic testing system, wherein:

[0019] The calibration was performed using a standard test block of the same material and specifications as the tube bundle under test, and without defects, to calibrate the sound velocity and ultrasonic beam path.

[0020] Preferably, the parameters of the rotating ultrasonic testing system are set as follows: ultrasonic frequency 15MHz, scanning speed 12mm / s, axial sampling interval 0.3mm, circumferential sampling interval 2°, coupling water pressure 0.3MPa, and water temperature below 50℃.

[0021] Preferably, the defect types in S4 include: large-scale continuous wall thickness reduction caused by steam scouring, axial grooves formed by fretting wear at the baffle support point, and uniform wall thickness loss caused by flow-accelerated corrosion (FAC).

[0022] Distinguishing based on the morphological features of scanned images.

[0023] Preferably, the formula for the burst pressure in S4 is:

[0024] P_b = 2S_ut / (D - 0.8t);

[0025] Where t is the minimum remaining wall thickness, S_u is the tensile strength of the material, and D is the outer diameter of the tube bundle.

[0026] Preferably, the graded maintenance decision is as follows: if the safety factor is less than 2, the pipe is blocked immediately; if the safety factor is between 2 and 3, replacement is planned; and if the safety factor is greater than 3, monitoring is strengthened and operation continues.

[0027] The advantages of this invention compared to the prior art are:

[0028] High detection accuracy: The absolute wall thickness measurement accuracy can reach ±0.05mm, which is far superior to eddy current testing;

[0029] Defect visualization and diagnostics: The C-scan images visually display the shape, size, and precise location of defects, and can distinguish different types of failure modes, supporting accurate root cause analysis;

[0030] Scientific safety assessment: The accurate data provided provides an indispensable scientific basis for safety assessment, remaining life prediction and maintenance decisions, avoiding over-maintenance or under-maintenance, and ensuring the safe and economical operation of equipment;

[0031] Preventive maintenance: By applying this method regularly, a database of wall thickness variations can be established, enabling the prediction of the remaining life of the tube bundle and predictive maintenance of the equipment. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the scan.

[0033] Figure 2 This is a schematic diagram of steam scouring and thinning.

[0034] Figure 3 This is a schematic diagram of fretting wear thinning.

[0035] Figure 4 This is a schematic diagram of corrosion thinning.

[0036] As shown in the figure: Figure 1 In the diagram, B represents the scan (section) and C represents the scan (unfolded) image. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings.

[0038] Combined with appendix Figure 1 As shown, a method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater includes the following steps:

[0039] S1: Sampling of the core detection area in the U-shaped tube bundle of the high-pressure heater, determined based on the flow field and structure;

[0040] S2: Perform internal wall cleaning and ultrasonic testing system calibration on the sampling tube bundle;

[0041] S3: The sampling tube bundle is spiral-scanned using a built-in rotating ultrasonic detection system to obtain wall thickness distribution data;

[0042] S4: Based on the defect type identification of the scanned image, determine the minimum remaining wall thickness, and calculate the safety factor in combination with the burst pressure formula;

[0043] S5: Develop graded maintenance decisions based on safety factors.

[0044] The key point of this invention lies in providing a complete set of customized IRIS detection and diagnosis methods for specific equipment and specific operating conditions, the core protection points of which include:

[0045] 1. Targeted sampling strategy based on flow field analysis: The "upper and middle row tube bundles within 1.8 to 2.3 meters from the tube sheet" were clearly identified as the core sampling area, which solved the problem of how to accurately locate high-risk areas in a large number of tube bundles.

[0046] 2. Dedicated testing parameter system for small-diameter thin-walled pipes: To solve the testing challenges under extreme working conditions, a series of key parameters have been optimized (such as ultrasonic frequency of 15MHz, axial sampling interval of 0.3mm, circumferential sampling interval of 2°, coupling water pressure of 0.3MPa, etc.).

[0047] 3. Image feature recognition and diagnosis method for composite defects: Using C-scan images generated by IRIS technology, a correlation and identification criterion was established between specific image features (such as large-area thinning, axial grooves, and uniform thinning) and three specific failure mechanisms: "steam erosion", "fretting wear", and "flow-accelerated corrosion", thus achieving accurate diagnosis of composite defects.

[0048] 4. Integrated safety assessment and decision-making process: The minimum remaining wall thickness measured by IRIS is directly applied to the calculation of burst pressure and safety factor assessment based on specific formulas (such as BASF specifications), providing a direct and quantitative basis for decision-making on "immediate repair", "preventive maintenance" or "continued operation".

[0049] This invention provides a method for built-in rotating ultrasonic testing and safety assessment of U-shaped tube bundles in high-voltage heaters of power plants, the specific implementation steps of which are as follows:

[0050] Step 1: Preparation and Targeted Sampling Before Testing

[0051] Determine the test object: Clarify the specifications of the high-pressure heater tube bundle to be tested (e.g., Φ15.88×2.31 mm carbon steel tube) and operating conditions (tube side 38MPa, 470℃ high-temperature water; shell side steam).

[0052] Based on flow field analysis, the core area was determined as follows: According to the equipment structure and fluid dynamics simulation and operational failure experience, the upper and middle pipe bundles within a range of about 1.8-2.3 meters downstream of the steam inlet pipe were identified as the core detection area. This area is most affected by high-speed steam scouring and complex vibration, and is a high-incidence area for defects.

[0053] Stratified sampling was used: a statistically significant number of tube bundles (e.g., 1000) were systematically extracted from the key areas mentioned above for testing to ensure the representativeness of the results.

[0054] Step 2: Tube Pretreatment and System Precision Calibration

[0055] High-pressure cleaning: High-pressure water jets (pressure > 20 MPa) and specialized cleaning tools are used to thoroughly clean the inner walls of each sampled tube bundle, ensuring that there is no scale or impurities on the inner walls to meet the stringent cleanliness requirements of IRIS technology. This is fundamentally different from the simple wiping of conventional ultrasonic cleaning.

[0056] System calibration: Using standard test blocks of the same material, specifications, and without defects as the tube bundle under test, the sound velocity and geometric path of the IRIS system are precisely calibrated to ensure the absolute accuracy of the measurement reference.

[0057] Step 3: Customized parameter settings and data acquisition

[0058] Targeting the characteristics of small-diameter, thin-walled tubes in high-pressure heaters, the following optimized detection parameters were set. These parameters differ significantly from conventional, general IRIS detection parameters and are key to achieving high-precision detection:

[0059] Ultrasonic frequency: set to 15 MHz to meet the high-resolution measurement requirements of thin walls (2.31 mm). If the frequency is too low, the resolution will be insufficient, and if it is too high, the attenuation will be severe.

[0060] Scanning speed and sampling interval: The scanning speed is controlled at 12 mm / s, the axial sampling interval is 0.3 mm, and the circumferential sampling interval is 2°. This combination ensures both detection efficiency and high sampling density in both the circumferential and axial directions, achieving 100% helical coverage of the tube bundle with no omissions.

[0061] Coupling water system: The coupling water pressure is stably controlled at 0.3 MPa, and the water temperature is below 50℃. This pressure ensures that the turbine can stably drive the probe to rotate, forms a stable water column to couple the acoustic waves, and protects the probe from high-temperature damage.

[0062] Starting from the tube end, each tube bundle is spirally scanned, and B-scan (section) and C-scan (developed diagram) data are recorded throughout the process.

[0063] Step 4: Defect Identification, Analysis, and Security Assessment

[0064] Image analysis and defect diagnosis: Generate high-resolution C-scan images and perform diagnosis according to the following criteria.

[0065] In C-scan images, if a large, continuous area of ​​wall thinning is found in the direct steam impact zone, it is diagnosed as steam erosion. If the image shows axial, banded, grooved thinning at the location corresponding to the baffle support point, it is diagnosed as fretting wear. If the image shows a relatively uniform, overall wall thickness loss on the inner wall of the tube bundle, it is diagnosed as flow-accelerated corrosion (FAC).

[0066] Quantitative statistics and location: The system automatically counts and outputs the minimum wall thickness and maximum thinning rate of different regions, and accurately marks the location of defects in the tube bundle length and circumferential direction.

[0067] Safety Assessment and Decision-Making: Substitute the measured minimum remaining wall thickness (e.g., 1.09 mm) into the burst pressure formula P_b = 2S_ut / Calculations are performed to obtain the safety factor. Based on the size of the safety factor, a graded maintenance decision is made directly (e.g., if the safety factor is <2, the pipe should be blocked immediately; if the safety factor is 2 < the safety factor < 3, replacement should be planned; if the safety factor is > 3, monitoring should be strengthened).

[0068] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0069] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0070] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for safety assessment of built-in ultrasonic testing of U-shaped tube bundles in high-voltage heaters of power plants, characterized in that: Includes the following steps: S1: Sampling of the core detection area in the U-shaped tube bundle of the high-pressure heater, determined based on the flow field and structure; S2: Clean the inner wall of the sampling tube bundle and calibrate the ultrasonic testing system; S3: The sampling tube bundle is spiral-scanned using a built-in rotating ultrasonic detection system to obtain wall thickness distribution data; S4: Based on the defect type identification of the scanned image, determine the minimum remaining wall thickness, and calculate the safety factor in combination with the burst pressure formula; S5: Develop graded maintenance decisions based on safety factors.

2. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: The U-shaped tube bundle in S1 is a small-diameter thin-walled carbon steel tube with an outer diameter of 15.88 mm and a wall thickness of 2.31 mm. The operating conditions are a tube-side pressure of 38 MPa and a temperature of 470 °C.

3. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: The core detection area in S1 is the upper and middle pipe bundles within a range of 1.8 meters to 2.3 meters downstream of the steam inlet pipe. Stratified sampling is used for sampling.

4. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: The inner wall cleaning in S2 is carried out using a high-pressure water jet with a pressure greater than 20MPa, in conjunction with a special pipeline cleaning tool.

5. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: S3 also includes the calibration of the rotating ultrasonic testing system, wherein: The calibration was performed using a standard test block of the same material and specifications as the tube bundle under test, and without defects, to calibrate the sound velocity and ultrasonic beam path.

6. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 5, characterized in that: The parameters of the rotating ultrasonic testing system are set as follows: ultrasonic frequency 15MHz, scanning speed 12mm / s, axial sampling interval 0.3mm, circumferential sampling interval 2°, coupling water pressure 0.3MPa, and water temperature below 50℃.

7. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: The defect types in S4 include: large-scale continuous wall thickness reduction caused by steam scouring, axial grooves formed by fretting wear at the baffle support point, and uniform wall thickness loss caused by flow-accelerated corrosion (FAC). Distinguishing based on the morphological features of scanned images.

8. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 1, characterized in that: The formula for the burst pressure in S4 is: P_b = 2S_ut / (D - 0.8t); Where t is the minimum remaining wall thickness, S_u is the tensile strength of the material, and D is the outer diameter of the tube bundle.

9. The method for safety assessment of built-in ultrasonic testing of a U-shaped tube bundle in a power plant high-voltage heater according to claim 8, characterized in that: The graded maintenance decision is as follows: if the safety factor is less than 2, the pipe should be blocked immediately; if the safety factor is between 2 and 3, replacement should be planned; if the safety factor is greater than 3, monitoring should be strengthened and operation should continue.

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