Ultrasonic water level measurement method for preventing water blockage of u-shaped tube on heated surface of power station boiler

Abstract

An ultrasonic water level measurement method for preventing a water blockage of a U-shaped tube on a heated surface of a power station boiler. The method comprises the following steps: (1) determining a measured part of a U-shaped tube, polishing the measured part to make same have metallic luster, and coating the measured part with a coupling agent (2); (2) placing a longitudinal-wave normal probe (3) at the measured part of the tube, so as to cause the central axis of the longitudinal-wave normal probe (3) to be perpendicular to the axis of the measured tube, and starting an ultrasonic flaw detector (4) for measurement; (3) a reflected wave appearing on a display screen of the ultrasonic flaw detector (4), and comparing the position of the reflected wave with the position of a reference reflected wave; and (4) if the reference reflected wave appears, this indicating that the tube is full of water, moving the longitudinal-wave normal probe (3) upwards until the reference reflected wave disappears, wherein the center of the longitudinal-wave normal probe (3) is the current liquid level (5) inside the tube, and making a mark. The measurement method can accurately determine the water level inside a closed vertical steel tube, thereby providing data support for boiler operations.

Description

An ultrasonic water level detection method for preventing water blockage in U-shaped tubes on the heating surface of power station boilers

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the Patent Office of China on October 25, 2023, with application number 202311392612.5 and invention name “An ultrasonic water level detection method for preventing water plugging in U-shaped tubes on the heating surface of a power station boiler”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of engineering nondestructive testing, and specifically relates to an ultrasonic water level detection method for preventing water blockage in U-shaped tubes on the heating surface of a power station boiler. Background Art

[0004] The heating surface of a power plant boiler, referred to as the "four-tube" system, consists of the water-cooled wall, superheater, reheater, and economizer. The superheater and reheater contain numerous vertical U-shaped enclosed pipes.

[0005] To detect potential leaks on the heating surface, a hydraulic pressure test is performed after unit maintenance. Power plant boilers' platen superheaters, high-temperature superheaters, and high-temperature reheaters often utilize a U-shaped tube suspension structure. After the hydraulic pressure test, water trapped within the heating surface tubes cannot be released. Improper parameter control during unit startup can easily cause "water plugging" and bursting of the heating surface tubes.

[0006] Causes of water plug formation: Before the boiler is ignited and started, water accumulates in the U-shaped tubes at the lower part of the serpentine tube bundle of the vertical high-temperature heating surface tube bank. This is mainly because the drain pipe of the vertical high-temperature heating surface is installed on the upper header. After the boiler water pressure test, the water accumulated in the tube bundle cannot be discharged; during the boiler shutdown and cooling process, some steam condenses and accumulates in the lower part of the superheater U-shaped tube; before the boiler is ignited and started, external steam is introduced from the lower header of the boiler water-cooled wall for heating. When steam is generated in the boiler drum, the steam condenses in the convection superheater tube bundle and accumulates in the U-shaped tube at the lower part of the tube bundle.

[0007] Water plugs mostly occur during boiler ignition startup, low-load phase of the unit, and startup after boiler water pressure test. The accumulated water caused by water plugs takes a considerable amount of time to evaporate gradually, which can be judged by the change in wall temperature of the heating surface. The outlet temperature of the heating surface is close to or lower than the saturated steam temperature at the same pressure; most of the wall temperature measurement points are installed on the furnace top or in the large hood. The initial measurement data of the metal wall temperature after the water plug is formed is not representative. The moment the water plug is removed, the steam carries water, causing the metal temperature of the heating surface tube wall to drop instantly, then quickly rise again, and return to normal after a few minutes; the cooling water that is not fully vaporized will flow into the nearby tube bundle, where water plugs are easily formed. The shape, color and metal structure of the burst pipe have the characteristics of short-term overheating.

[0008] Water blockage can cause four pipes to overheat, burst, and fail, shutting down the unit. Promptly inspect the four-pipe U-shaped pipe for water accumulation and eliminate the blockage. However, in production practice, cutting open each closed U-shaped pipe for inspection and then welding it back together is not practical.

[0009] Summary of the Invention

[0010] The purpose of this application is to provide an ultrasonic water level detection method for preventing water blockage in U-shaped tubes on the heating surface of power station boilers. This method uses a type A pulse reflection ultrasonic flaw detector to detect the water level in the vertical steel pipeline. According to the water level conditions, data support is provided for maintenance personnel to perform equipment maintenance and for operating personnel to perform operation operations, thereby avoiding water blockage and pipe burst.

[0011] This application is implemented using the following technical solutions:

[0012] An ultrasonic water level detection method for preventing water blockage in a U-shaped tube on a heating surface of a power station boiler comprises the following steps:

[0013] 1) Determine the tested part of the U-shaped pipe, polish it to a metallic luster, and apply coupling agent;

[0014] 2) Place the probe on the tested part of the pipeline, making sure the probe's central axis is perpendicular to the tested pipeline's axis, and start the ultrasonic flaw detector for testing;

[0015] 3) A reflected wave appears on the display screen of the ultrasonic flaw detector, and the position of the reflected wave is compared with the position of the reference reflected wave;

[0016] 4) If a reference reflection wave appears, it means the pipe is full of water. Move the probe upward until the reference reflection wave disappears. The center of the probe is the current water level and is marked.

[0017] An optional improvement of the present application is that the ultrasonic flaw detector selects a type A pulse reflection ultrasonic flaw detector with an operating frequency range of 0.5 to 10 MHz.

[0018] An optional improvement of the present application is that the probe is a longitudinal wave straight probe.

[0019] An optional improvement of the present application is that the coupling agent is industrial paste.

[0020] An optional improvement of the present application is that it also includes setting an alarm gate on the ultrasonic flaw detector.

[0021] An optional improvement of the present application is that the alarm gate is set at 50% of the full screen scale, the lateral position of the alarm gate is set at 10% of the full scale of the highest wave of the reference reflection wave, and the alarm width is 10% of the full scale of the instrument screen.

[0022] The optional improvement of this application is to further adjust the detection sensitivity of the ultrasonic flaw detector, as follows:

[0023] Water is injected into the comparison test block through the water injection port, and the water level is 1 / 2 of the pipe length;

[0024] Place the probe under the reference block, below the water level, with the probe's central axis perpendicular to the reference block's axis. Apply coupling agent to the contact area between the probe and the reference block.

[0025] Start the ultrasonic flaw detector to scan, adjust the ultrasonic detector, find the reflected wave signal from the outer wall of the pipe on the opposite side of the probe, and adjust the detection range so that the reflected wave signal is within the detection range after filling with water; make the reflected wave signal height at 80% of the full screen scale, and then gain 3dB as the detection sensitivity;

[0026] The probe moves upward along the axis of the pipe. The location where the bottom wave disappears and the center of the probe is the water level in the pipe.

[0027] An optional improvement of the present application is that the comparison test block is a vertical steel pipe of the same specification and material as the tested pipe, and one end of the vertical steel pipe is sealed.

[0028] This application has at least the following beneficial technical effects:

[0029] The ultrasonic water level detection method for preventing water blockage in the U-shaped tube of the heating surface of a power station boiler in the present application is based on the principle that ultrasonic longitudinal waves will produce refraction and reflection of waves at heterogeneous interfaces, and can accurately determine the water level without destroying the pipe.

[0030] Ultrasonic water level testing of waterproof plugs utilizes the pulse reflection method using a Type A ultrasonic straight probe. Longitudinal waves are compression waves that can propagate through solids, liquids, and gases, so this method utilizes longitudinal waves. Ultrasonic waves propagate at different speeds in different media. Furthermore, the different densities of steel, water, and air result in different acoustic impedances for steel. Ultrasonic waves reflect and transmit at varying sound pressures at these interfaces. Total reflection occurs at the air interface. The height of the reflected wave on the oscilloscope screen is proportional to the sound pressure, so the water level in the pipe can be determined by the location where the reflected signal appears and disappears. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic diagram of an ultrasonic water level detection method for preventing water blockage in a U-shaped tube on a heating surface of a power station boiler according to the present application.

[0032] Explanation of reference numerals: 1 – comparison test block; 2 – coupling agent; 3 – longitudinal wave straight probe; 4 – ultrasonic flaw detector; 5 – liquid level in pipe. DETAILED DESCRIPTION

[0033] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments in this application and the features described in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0034] The present application provides an ultrasonic water level detection method for preventing water blockage in a U-shaped tube on the heating surface of a power station boiler, comprising the following steps:

[0035] (1) Ultrasonic flaw detector: Select a type A pulse reflection ultrasonic flaw detector with an operating frequency range of 0.5 to 10 MHz.

[0036] (2) Probe: The diameter of the four pipes of the power station boiler ranges from 32 to 60, and the material is stainless steel such as super304 or ferrite (including P91 martensitic) steel such as 12Cr1MoV. 5PΦ10 longitudinal wave straight probe is selected.

[0037] (3) Select a vertical steel pipe with the same specifications and material as the pipe to be tested as a comparison test block. One end of the vertical steel pipe should be sealed.

[0038] (4) Adjustment of the detection sensitivity of the ultrasonic flaw detector, as shown in Figure 1:

[0039] ① Add water to the comparison test block 1 through the water injection port. The water level 5 in the tube is 1 / 2 of the tube length.

[0040] ② Place the longitudinal wave probe 3 below the water level of the reference block 1. Make sure the central axis of the longitudinal wave probe 3 is perpendicular to the axis of the reference block. Apply coupling agent 2 to the contact area between the longitudinal wave probe 3 and the reference block 1.

[0041] ③ Start the ultrasonic flaw detector 4 to scan, adjust the ultrasonic detector 4, find the reflected wave signal of the outer wall of the opposite pipe of the longitudinal wave straight probe 3, and adjust the detection range so that the reflected wave signal is within the detection range after filling with water; make the reflected wave signal height at 80% of the full screen scale, and then gain 3dB as the detection sensitivity.

[0042] ④ The longitudinal wave straight probe 3 moves upward along the axis of the pipe. The position where the bottom wave disappears and the center of the longitudinal wave straight probe 3 are the water level in the pipe.

[0043] (5) Determine the tested part of the U-shaped pipe, polish it to a metallic luster, and apply coupling agent.

[0044] (6) Place the probe on the tested part of the pipeline, make the central axis of the probe perpendicular to the axis of the tested pipeline, and start the ultrasonic flaw detector for testing.

[0045] (7) A reflected wave appears on the display screen of the ultrasonic flaw detector, and the position of the reflected wave is compared with the reference reflected wave position.

[0046] (8) If a reference reflection wave appears, it means the pipe is full of water. Move the probe upward until the reference reflection wave disappears. The center of the probe is the current water level and mark it.

[0047] The coupling agent is industrial paste. An alarm gate is set on the ultrasonic flaw detector at 50% of the full-screen scale. The horizontal position of the alarm gate is set at 10% of the full-scale of the reference reflection wave's highest wave. The alarm width is 10% of the instrument's full-scale screen. The vertical steel pipe used in the comparison test block is 300 mm long.

[0048] In summary, the present application provides an ultrasonic water level detection method for preventing water blockage in U-shaped tubes on the heating surface of a power station boiler. The ultrasonic water level detection method for preventing water blockage adopts the pulse reflection method of a type A ultrasonic straight probe. Longitudinal waves are compression waves that can propagate in solids, liquids, and gases, so this detection method adopts longitudinal wave detection. The propagation speed of ultrasonic waves in different media is different. At the same time, the densities of steel, water, and air are different, so the acoustic impedance of steel is different, and ultrasonic waves produce different sound pressure reflectivities and transmittances at heterogeneous interfaces. Total reflection occurs at the air interface. The wave height of the reflected wave on the oscilloscope screen is proportional to the sound pressure, so the water level in the pipeline can be detected by the position where the reflected signal appears / disappears.

[0049] Although the present application has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements, which do not depart from the spirit of the present application, are within the scope of protection claimed in the present application.

Claims

1. An ultrasonic water level detection method for preventing water plugging on the U-shaped tube of a power station boiler heating surface, characterized in that: The following steps are involved: 1) Determine the tested part of the U-shaped pipe, polish it to give it a metallic luster, and apply coupling agent; 2) Place the probe on the tested part of the pipeline, make the central axis of the probe perpendicular to the axis of the tested pipeline, and start the ultrasonic flaw detector for testing; 3) A reflected wave appears on the display screen of the ultrasonic flaw detector, and the position of the reflected wave is compared with the reference reflected wave position; 4) If a reference reflection wave appears, it means the pipe is full of water. Move the probe upward until the reference reflection wave disappears. The center of the probe is the current water level and is marked.

2. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 1 is characterized in that: The ultrasonic flaw detector is a type A pulse reflection ultrasonic flaw detector with an operating frequency range of 0.5 to 10 MHz.

3. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 1 is characterized in that: The probe selected is a longitudinal wave straight probe.

4. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 1 is characterized in that: The coupling agent is industrial paste.

5. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 1 is characterized in that: It also includes setting an alarm gate on the ultrasonic flaw detector.

6. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 5 is characterized in that: The alarm gate is set at 50% of the full screen scale, the lateral position of the alarm gate is set at 10% of the full scale of the highest wave of the reference reflection wave, and the alarm width is 10% of the full scale of the instrument screen.

7. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 1 is characterized in that: It also includes the adjustment of the detection sensitivity of the ultrasonic flaw detector, as follows: Water is poured into the comparison test block through the water injection port, and the water level is 1 / 2 of the pipe length; Place the probe at the bottom of the comparison block, below the water level, so that the central axis of the probe is perpendicular to the axis of the comparison block. Apply coupling agent to the contact part between the probe and the comparison block. Start the ultrasonic flaw detector to scan, adjust the ultrasonic detector, find the reflected wave signal on the outer wall of the pipe on the opposite side of the probe, and adjust the detection range so that the reflected wave signal is within the detection range after filling with water; make the reflected signal height at 80% of the full screen scale, and then gain 3dB as the detection sensitivity; The probe moves upward along the axis of the pipe, and the position where the bottom wave disappears and the center of the probe are the water level in the pipe.

8. The ultrasonic water level detection method for preventing water plugging of U-shaped tubes on the heating surface of a power station boiler according to claim 7 is characterized in that: The comparison test block is a vertical steel pipe with the same specification and material as the tested pipe, and one end of the vertical steel pipe is sealed.

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