A method for measuring the creep deformation of high-temperature and high-pressure steam pipelines

Abstract

The application discloses a kind of measurement methods suitable for high temperature high pressure steam pipeline creep deformation, not only can measure the circumferential relative creep deformation ε 周 Of pipeline 轴 , then according to the plastic deformation volume invariable condition formula, the radial relative creep deformation ε 径 Of pipeline is obtained, and further equivalent creep strain formula is obtained equivalent creep strain ε e , that is further, equivalent creep strain velocity is obtained, and the application is equivalent creep strain ε e And equivalent creep strain velocity respectively replace circumferential relative creep deformation ε 周 And circumferential creep deformation velocity can truly reflect the creep law of pipeline under three-dimensional stress state, and be favorable to the creep supervision and evaluation work of high temperature high pressure steam pipeline.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of creep supervision of high-temperature and high-pressure steam pipelines in thermal power plants, and particularly relates to a measurement method suitable for creep deformation of high-temperature and high-pressure steam pipelines, which is mainly used for accurate measurement of creep deformation of high-temperature and high-pressure steam pipelines, and further used for creep supervision. BACKGROUND

[0002] High-temperature and high-pressure steam pipelines in thermal power plants mainly include main steam pipelines and high-temperature reheated steam pipelines, and are prone to creep deformation under long-time high-temperature and high-pressure operating conditions. According to the provisions of DL / T 441-2004 "Creep Supervision Regulation for High-Temperature and High-Pressure Steam Pipelines in Thermal Power Plants", the pipelines should be periodically measured for creep to master the creep law of the pipelines and provide reliable technical basis for creep supervision and evaluation of the pipelines. Creep deformation measurement of the pipelines is an important method for metal supervision.

[0003] At present, the creep deformation measurement method specified in the existing creep supervision regulation has been applied for more than 30 years. Through a large number of actual measurements in the past decades, it is found that the creep expansion measurement results of the same pipeline have great variability, sometimes negative creep occurs, i.e. the creep measurement data is negative (ε < 0), sometimes the creep rate is abnormally high, close to or exceeding the creep rate (1 x 10 -5 % / h) specified in DL / T 441, and sometimes the relative creep deformation is always fluctuating around zero, which brings great trouble to technical personnel.

[0004] The analysis of the causes shows that the above-mentioned negative creep or excessively large creep rate in a short period of time is mainly caused by abnormal working state of the support hanger. When the pipeline is running, the cross section of the pipeline wall is subjected to three-way stress, i.e. circumferential stress σ 周 , axial stress σ 轴 and radial stress σ 径 . The calculation formulae of the three-way stress are as follows:

[0005]

[0006] In the formulae, D w —outer diameter, D n —inner diameter, D—outer diameter of the creep measurement point, P—working pressure, σ ZHW —continuous external load axial stress, σ W —continuous external load equivalent stress.

[0007] The relationship among stress, creep strain and creep strain rate of the pipeline under the three-way stress state can be obtained according to Von. Mises yield condition (fourth strength theory). The Von. Mises equivalent stress is represented by σ e , and the formula is as follows:

[0008]

[0009] Correspondingly, the equivalent creep strain ε e is:

[0010]

[0011] where ε 周 — circumferential relative creep deformation, ε 轴 — axial relative creep deformation, ε 径 — radial relative creep deformation.

[0012] Correspondingly, the equivalent creep strain rate is:

[0013]

[0014] where, — circumferential creep velocity component, — axial creep velocity component, — radial creep velocity component.

[0015] Correspondingly, the plastic constitutive equation of creep deformation under three-dimensional stress state can be obtained from the equivalent stress and Levy-Mises flow rule as:

[0016]

[0017] According to equation (1) and equation (5), when some of the support and hanger conditions are abnormal, the sustained external load axial stress σ ZHW and the sustained external load equivalent stress σ W increase, resulting in an increase in the axial stress σ 轴 suffered by the pipeline. When the axial stress σ 轴 is large, the circumferential creep velocity component will be small, when the axial stress σ 轴 is too large, and negative creep occurs, and when the axial stress σ 轴 is compressive stress, the circumferential creep velocity component will increase significantly.

[0018] Therefore, according to the current creep supervision regulations, there is only one section for creep measurement, and the measured creep data is the circumferential relative creep deformation, i.e. ε 周 . Under normal circumstances, σ 周 > σ 轴 > σ 径 , the circumferential relative creep deformation ε 周 of the pipeline accounts for the main part, and the creep velocity can reflect the creep law of the pipeline in operation. However, when the axial stress σ轴 When the effect is large, only measuring the circumferential relative creep deformation cannot reflect the creep condition of the pipeline, and further correct supervision and evaluation cannot be performed. SUMMARY

[0019] The present application aims to overcome the above-mentioned deficiencies in the prior art, and provides a measurement method suitable for high-temperature and high-pressure steam pipeline creep deformation.

[0020] The technical scheme adopted by the present application to solve the above-mentioned problems is: a measurement method suitable for high-temperature and high-pressure steam pipeline creep deformation, characterized by comprising the following steps:

[0021] Step 1: At a temperature environment of about 20℃, use a standard rod to correct the micrometer for measurement, and calculate the zero correction value of the micrometer according to the following formula.

[0022]

[0023] In the formula:

[0024] B: zero correction value of the micrometer;

[0025] b1: zero value of the micrometer before measurement, mm;

[0026] b2: zero value of the micrometer after measurement, mm.

[0027] Step 2: Measure the outer diameter size of the first measurement section of the high-temperature and high-pressure steam pipeline, slowly rotate the micrometer ratchet, and make the micrometer measurement surface contact with the outer diameter measurement surface of the first pair of creep measurement points; measure three times, and the measurement results are respectively recorded as D 11 , D 12 , D 13 , and take the arithmetic mean value Then Similarly, measure the second pair of creep measurement points, measure three times, and the measurement results are respectively recorded as D 21 , D 22 , D 23 , and take the arithmetic mean value Then In succession, the outer diameter sizes of the third pair and the fourth pair of creep measurement points are respectively measured as and Then the average outer diameter of the creep measurement points of the first measurement section of the high-temperature and high-pressure steam pipeline is recorded as D1, and then (measurement section has two pairs of creep measurement points) or (measurement section has four pairs of creep measurement points).

[0028] Step 3: Measure the outer diameter of the high-temperature and high-pressure steam pipeline at the second measurement section, and the average outer diameter of the creep measurement points at the second measurement section of the high-temperature and high-pressure steam pipeline is recorded as D2. (when the measurement section has two pairs of creep measurement points) or (when the measurement section has four pairs of creep measurement points); then the average outer diameter of the two measurement sections of the high-temperature and high-pressure steam pipeline is recorded as

[0029] Step 4: Measure the axial length of the high-temperature and high-pressure steam pipeline between the two measurement sections, slowly rotate the micrometer ratchet, and make the micrometer measurement surface contact the length measurement surface of the first group of creep measurement points; measure three times, and the measurement results are recorded as L 11 , L 12 , and L 13 , and take the arithmetic mean By analogy,

[0030] The average axial length of the second to eighth groups of creep measurement points is measured and recorded as (when the measurement section has two pairs of creep measurement points) or (when the measurement section has four pairs of creep measurement points).

[0031] Step 5: Convert the outer diameter and length of the high-temperature and high-pressure steam pipeline in the initial state at 0°C to D 初 and L 初 , respectively, and calculate according to the following formula.

[0032]

[0033] In the formula:

[0034] α p : linear expansion coefficient of the high-temperature and high-pressure steam pipeline, mm / (mm·℃);

[0035] α ck : linear expansion coefficient of the micrometer bow, mm / (mm·℃);

[0036] t p : surface temperature near the creep measurement point, ℃;

[0037] t ck : temperature of the micrometer bow, ℃.

[0038] ​​​​Step 6: Measure the outer diameter of the high-temperature and high-pressure steam pipeline after running for a period of time h, and measure the average outer diameter of the two measurement sections of the high-temperature and high-pressure steam pipeline according to steps 1, 2 and 3, denoted as D

[0039] Step 7: Measure the axial length of the high-temperature and high-pressure steam pipeline after running for a period of time h, and measure the average length between the two measurement sections of the high-temperature and high-pressure steam pipeline according to step 4, denoted as L

[0040] Step 8: Convert the outer diameter and length of the high-temperature and high-pressure steam pipeline after running for a period of time h to 0℃, denoted as D 运 and L 运 , and calculate according to the following formula.

[0041]

[0042] Step 9: Calculate the absolute circumferential creep deformation and absolute axial creep deformation of the high-temperature and high-pressure steam pipeline, denoted as ΔD and ΔL respectively, and calculate according to the following formula.

[0043]

[0044] Step 10: Calculate the circumferential relative creep strain and axial relative creep strain of the high-temperature and high-pressure steam pipeline, denoted as ε 周 and ε 轴 respectively, and calculate according to the following formula.

[0045]

[0046] Step 11: According to the condition of constant plastic deformation volume, the radial relative creep strain ε 径 of the high-temperature and high-pressure steam pipeline is calculated according to the following formula.

[0047] ε 周 + ε 轴 + ε 径 = 0 (11)

[0048] Step 12: According to formula (3) and formula (11), the equivalent creep strain ε e of the high-temperature and high-pressure steam pipeline during the running time h is calculated as follows.

[0049]

[0050] Step 13: The equivalent creep strain rate v of the high-temperature and high-pressure steam pipeline during the running time h is calculated according to the following formula.

[0051]

[0052] Further, the reading of the micrometer should be accurate to 0.005 mm, less than 0.0025 mm can be omitted, equal to or greater than 0.0025 mm should be increased to 0.005 mm, less than 0.0075 mm should be reduced to 0.005 mm, equal to or greater than 0.0075 mm should be increased to 0.010 mm.

[0053] Further, if the variation between three readings of each set of creep measurement points exceeds 0.010 mm, the measurement should be re-measured; after measuring each set of creep measurement points, the temperature of the bow of the micrometer and the surface temperature near the creep measurement points should be measured immediately.

[0054] Compared with the prior art, the present application has the following advantages and effects: the present application can realize accurate measurement of the circumferential relative creep deformation and the axial relative creep deformation of the high-temperature and high-pressure steam pipeline, and can calculate the equivalent creep strain and the equivalent creep strain rate of the pipeline according to the plastic deformation volume invariable condition; the equivalent creep strain and the equivalent creep strain rate can respectively replace the circumferential relative creep deformation and the circumferential creep deformation rate, so as to truly reflect the creep law of the pipeline under the three-dimensional stress state, and is beneficial to the creep supervision of the high-temperature and high-pressure steam pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0055] Fig. 1 is a schematic diagram of the arrangement type of the creep measurement points of the main steam pipeline in the embodiment of the present application.

[0056] Fig. 2 and Fig. 3 is a schematic diagram of the cross section of the creep measurement points of the main steam pipeline in the embodiment of the present application.

[0057] Fig. 4 is a flow chart of the measurement method of the creep deformation of the main steam pipeline in the embodiment of the present application.

[0058] In the figure: 1, 2, 3, 4-creep measurement points of the left measurement section, 5, 6, 7, 8-creep measurement points of the right measurement section, 9-left measurement section, 10-right measurement section, 11-main steam pipeline. DETAILED DESCRIPTION

[0059] The present application will be further described in detail below in combination with the drawings and through embodiments, and the following embodiments are an explanation of the present application and the present application is not limited to the following embodiments.

[0060] EMBODIMENT

[0061] Referring to Figs. 1 to 4 In the embodiment, a measurement method suitable for the creep deformation of a high-temperature and high-pressure steam pipeline comprises the following steps:

[0062] Step 1: At a temperature environment of about 20°C, correct the measuring micrometer with a standard bar, and calculate the zero correction value of the micrometer according to the following formula.

[0063]

[0064] In the formula:

[0065] B: the zero correction value of the micrometer;

[0066] b1: the zero value of the micrometer before measurement, mm;

[0067] b2: the zero value of the micrometer after measurement, mm.

[0068] Step 2: Measure the outer diameter of the left measuring section of the main steam pipe, slowly rotate the micrometer ratchet, and make the measuring surface of the micrometer contact the outer diameter measuring surface of the first pair of left measuring section creep measuring points 1 and 3; measure three times, and the measurement results are recorded as D 11 , D 12 , and D 13 , respectively, and take the arithmetic mean as Then Similarly, measure the second pair of left measuring section creep measuring points 2 and 4, measure three times, and the measurement results are recorded as D 21 , D 22 , and D 23 , respectively, and take the arithmetic mean as Then Then the average outer diameter of the left measuring section creep measuring points of the main steam pipe is recorded as D1, and then

[0069] Step 3: Synchronously with Step 2, measure the outer diameter of the right measuring section of the main steam pipe, and the average outer diameter of the right measuring section creep measuring points of the main steam pipe is recorded as D2, and then Then the average outer diameter of the left measuring section 9 and the right measuring section 10 creep measuring points of the main steam pipe is recorded as Then

[0070] Step 4: Measure the axial length between the left measuring section 9 and the right measuring section 10 of the main steam pipe, slowly rotate the micrometer ratchet, and make the length measuring surface of the first group of creep measuring points (left measuring section creep measuring point 1 and right measuring section creep measuring point 5) contact; measure three times, and the measurement results are recorded as L 11 , L 12 , and L 13 , respectively, and take the arithmetic mean Then Similarly, the average axial length of the 2nd group of creep measurement points (left measurement section creep measurement point 2, right measurement section creep measurement point 6) to the 4th group of creep measurement points (left measurement section creep measurement point 4, right measurement section creep measurement point 8) is measured in sequence and recorded as Then the average length between the two measurement sections (left measurement section 9, right measurement section 10) of the main steam pipeline is recorded as Then

[0071] Step 5: Convert the outer diameter and length of the initial state of the main steam pipeline at 0℃ to D 初 and L 初 , and calculate according to the following formula.

[0072]

[0073] In the formula:

[0074] α p : linear expansion coefficient of high-temperature high-pressure steam pipeline, mm / (mm·℃);

[0075] α ck : linear expansion coefficient of the bow of the micrometer, mm / (mm·℃);

[0076] t p : surface temperature near the creep measurement point, ℃;

[0077] t ck : temperature of the bow of the micrometer, ℃.

[0078] Step 6: Measure the outer diameter of the main steam pipeline after running for a period of time h, measure the average outer diameter of the creep measurement points of the two measurement sections (left measurement section 9, right measurement section 10) of the main steam pipeline according to steps 1, 2 and 3, and record it as D h .

[0079] Step 7: Measure the axial length of the main steam pipeline after running for a period of time h, measure the average length between the two measurement sections (left measurement section 9, right measurement section 10) of the main steam pipeline according to step 4, and record it as

[0080] Step 8: Convert the outer diameter and length of the main steam pipeline after running for a period of time h to 0℃, and record them as D 运 and L 运 , and calculate according to the following formula.

[0081]

[0082] Step 9: Calculate the absolute circumferential creep deformation and the absolute axial creep deformation of the main steam pipe, denoted as ΔD and ΔL respectively, and calculate according to the following formula.

[0083]

[0084] Step 10: Calculate the circumferential relative creep strain and the axial relative creep strain of the main steam pipe, denoted as ε 周 and ε 轴 respectively, and calculate according to the following formula.

[0085]

[0086] Step 11: According to the condition of constant plastic deformation volume, the radial relative creep strain ε 径 of the main steam pipe is obtained as ε 周 - ε 轴 , and calculated according to the following formula.

[0087] ε 周 + ε 轴 + ε 径 = 0

[0088] Step 12: According to the equivalent creep strain calculation formula, the equivalent creep strain ε e of the main steam pipe in the operation time h is obtained, and the equivalent creep strain calculation formula is as follows.

[0089]

[0090] Step 13: The equivalent creep strain velocity of the main steam pipe in the operation time h is calculated according to the following formula.

[0091]

[0092] In this way, the measurement and calculation of the creep deformation of the main steam pipe 11 are completed.

[0093] It should be noted that in this embodiment, the measurement section of the main steam pipe has two, which are the left measurement section and the right measurement section, and the left measurement section and the right measurement section are parallel to each other, and the initial interval is set to 1m.

[0094] In this embodiment, the four left measurement section creep measurement points 1, 2, 3, 4 and the four right measurement section creep measurement points 5, 6, 7, 8 are respectively distributed on the diameter endpoints perpendicular to each other of the left measurement section and the right measurement section, and the left measurement section creep measurement points and the right measurement section creep measurement points, the left measurement section creep measurement points and the right measurement section creep measurement points, the left measurement section creep measurement points and the right measurement section creep measurement points, the left measurement section creep measurement points and the right measurement section creep measurement points are two-axially symmetrically distributed.

[0095] In this embodiment, the two pairs of creep measuring points on the left measuring section are used to measure the circumferential relative creep deformation ε of the left measuring section of the main steam pipe 周左 , the two pairs of creep measuring points on the right measuring section are used to measure the circumferential relative creep deformation ε of the right measuring section of the main steam pipe 周右 , the left measuring section creep measuring point and the right measuring section creep measuring point, the left measuring section creep measuring point and the right measuring section creep measuring point, the left measuring section creep measuring point and the right measuring section creep measuring point, the left measuring section creep measuring point and the right measuring section creep measuring point are used to measure the axial creep deformation ε of the main steam pipe 轴 .

[0096] The contents not described in detail in the specification all belong to the prior art known by the person skilled in the art.

[0097] Although the present application has been disclosed in the above embodiments, it is not intended to limit the scope of protection of the present application, and any modification and improvement made by the person skilled in the art without departing from the concept and scope of the present application shall belong to the scope of protection of the present application.

Claims

1. A method for measuring creep deformation in high-temperature and high-pressure steam pipelines, characterized in that, Includes the following steps: Step 1: At a temperature of 20℃, use a standard bar to calibrate the measuring micrometer and calculate the zero-point calibration value of the micrometer according to the following formula. In the formula: B: Micrometer zero-point calibration value; b1: Zero position value of the micrometer before measurement, in mm; b2: Zero value of the micrometer after measurement, in mm; Step 2: Measure the outer diameter of the first measuring section of the high-temperature, high-pressure steam pipeline. Slowly rotate the micrometer ratchet until the micrometer measuring face contacts the outer diameter measuring face of the first pair of creep measuring points; measure three times, and record the results as D. 11 D 12 D 13 Take the arithmetic mean as but Similarly, the second pair of creep measuring points were measured three times, and the results were recorded as D. 21 D 22 D 23 Take the arithmetic mean as but Similarly, the outer diameters of the 3rd and 4th pairs of creep measuring points were measured to be as follows: and Let D1 be the average outer diameter of the creep measuring point at the first measuring section of the high-temperature and high-pressure steam pipeline. or Step 3: Same as Step 2, measure the outer diameter of the second measuring section of the high-temperature and high-pressure steam pipeline. The average outer diameter of the creep measuring points at the second measuring section of the high-temperature and high-pressure steam pipeline is denoted as D2. or The average outer diameter of the two creep measuring points on the high-temperature, high-pressure steam pipeline is denoted as... but Step 4: Measure the axial length between two measurement sections of the high-temperature, high-pressure steam pipeline. Slowly rotate the micrometer ratchet until the micrometer measuring face contacts the length measuring face of the first group of creep measuring points; measure three times, and record the results as L. 11 L 12 L 13 Take the arithmetic mean but Similarly, the average axial length of the creep measuring points from group 2 to group 8 was measured and denoted as follows: The average length between the two measuring sections of the high-temperature, high-pressure steam pipeline is denoted as . but or Step 5: Convert the outer diameter and length of the high-temperature and high-pressure steam pipe to the initial state at 0℃, and denote them as D. 初 and L 初 , and calculate according to the following formula; In the formula: α p : Coefficient of linear expansion of high-temperature and high-pressure steam pipeline, mm / (mm·℃); α ck : Coefficient of linear expansion of the micrometer bow, mm / (mm·℃); t p Surface temperature near the creep measurement point, in °C; t ck Temperature of the micrometer bow, °C; Step 6: Measure the outer diameter of the high-temperature, high-pressure steam pipeline after it has been running for a period of time (h). Measure the average outer diameter of the two creep measurement points on the high-temperature, high-pressure steam pipeline according to steps 1, 2, and 3, and record it as... Step 7: Measure the axial length of the high-temperature, high-pressure steam pipeline after it has been running for a period of time (h). Measure the average length between the two measurement sections of the high-temperature, high-pressure steam pipeline as described in Step 4, and record it as... Step 8: Convert the outer diameter and length of the high-temperature, high-pressure steam pipeline to the value after running at 0℃ for a period of time (h), and denot it as D. 运 and L 运 , and calculate according to the following formula; Step 9: Calculate the absolute circumferential creep deformation and absolute axial creep deformation of the high-temperature and high-pressure steam pipeline, denoted as ΔD and ΔL respectively, and calculate them according to the following formula; Step 10: Calculate the circumferential relative creep strain and axial relative creep strain of the high-temperature and high-pressure steam pipeline, denoted as ε. 周 and ε 轴 , and calculate according to the following formula; Step 11: Calculate the radial relative creep strain ε of the high-temperature, high-pressure steam pipeline based on the condition of constant volume during plastic deformation. 径 =-ε 周 -ε 轴 Calculate using the following formula; e 周 +e 轴 +e 径 =0 Step 12: Calculate the equivalent creep strain ε during the operating time h of the high-temperature and high-pressure steam pipeline using the equivalent creep strain calculation formula. e The formula for calculating equivalent creep strain is as follows; Step 13: Calculate the equivalent creep strain rate during the operating time h of the high-temperature and high-pressure steam pipeline. Calculate using the following formula; 2. The method for measuring creep deformation of high-temperature and high-pressure steam pipelines according to claim 1, characterized in that, Micrometer readings are accurate to 0.005mm. Readings less than 0.0025mm are omitted. Readings equal to or greater than 0.0025mm are rounded up to 0.005mm. Readings less than 0.0075mm are rounded down to 0.005mm. Readings equal to or greater than 0.0075mm are rounded up to 0.010mm.

3. The method for measuring creep deformation of high-temperature and high-pressure steam pipelines according to claim 1, characterized in that, If the variation between three readings at each creep measurement point exceeds 0.010 mm, the measurement should be repeated.

4. The method for measuring creep deformation of high-temperature and high-pressure steam pipelines according to claim 1, characterized in that, After each creep measurement point is measured, the bow temperature of the micrometer and the surface temperature near the creep measurement point are immediately measured.

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