Method and device for estimating water inlet frost heaving radial stress of casing cement binding layer

Abstract

The invention discloses a method and a device for estimating water inlet frost heaving radial stress of a casing cement binding layer, and the method comprises the following steps: carrying out a frost heaving experiment on a cement sample to obtain the densities of the cement sample before and after freezing under different water absorption rates; determining the cement frost heaving radial stress under different water absorption rates according to the density of the cement sample before and after freezing under different water absorption rates; according to the cement frost heaving radial stress under different water absorption rates, fitting a corresponding relation between the water absorption rates of the cement and the frost heaving radial stress; and based on the corresponding relationship, estimating the water inlet frost heaving radial stress of the to-be-detected cement binding layer according to the water absorption rate of the to-be-detected cement binding layer. According to the method, the actual condition of the cement binding layer after water inflow frost heaving can be truly reflected, so that the distribution state of water in cement can be better estimated, and the water inflow frost heaving radial stress estimation result of the cement binding layer is more accurate.

Description

Technical Field

[0001] The present invention belongs to the technical field of power equipment state perception and fault diagnosis, and in particular relates to a method and device for estimating radial stress of water ingress frost heave of a casing cement adhesive layer. Background Art

[0002] Bushing is a device with a relatively large usage in power equipment. For power equipment with voltage levels of 500kV and below, porcelain bushing is usually used. Porcelain bushings are mainly composed of porcelain bushings, metal flanges, glued cement, etc. Their structural connection method is: the ends of the porcelain bushings are connected to the metal flanges through cement at both ends of the porcelain bushings, so that the bushings can be installed on the power equipment as an inlet and outlet channel. Due to the different thermal expansion coefficients of the porcelain bushings and metal flanges, their thermal expansion and contraction degrees are different when the temperature rises or falls, which will cause forces to act between them. In order to alleviate the strength of the force between them, a certain amount of asphalt is filled between the porcelain bushings and cement, and between the cement and the metal flange as a buffer. At the same time, in order to make the porcelain bushings and cement bond more firmly, a layer of sand should be brushed on the porcelain bushings, and the sand should be exposed 1-2 cm from the flange. At present, the production and manufacturing process of bushings has made great progress, and the firing strength of ceramics has fully met the needs of the site. However, for the bushings used in old equipment, especially those used in equipment over 15 years old, the product quality was uneven under the production environment at that time, and the porcelain bushings often broke during operation. The main reasons for the fracture are that the porcelain sleeve is made of ordinary porcelain and is not strong enough; the porcelain sleeve is of poor quality, with sand holes and impurities inside, or green edges and black centers caused by unqualified firing; the porcelain sleeve and flange are seriously eccentric during casting, resulting in uneven thickness of the cement glue layer and uneven force.

[0003] Casing rupture can cause serious short-circuit accidents, which will have a great impact and loss on equipment and power grids. During operation, if moisture enters the cement glue joint, when the temperature drops in winter, the internal moisture will freeze, causing the cement volume to expand and generating extrusion stress on the porcelain casing flange. Normally, according to operation and maintenance requirements, a layer of waterproof glue will be applied to the cement and exposed sand parts to prevent the entry of moisture. However, if the waterproof glue fails and ages, moisture may enter the cement glue layer. For areas with large temperature differences between day and night in winter or in extremely harsh conditions, the winter temperature can drop rapidly to -25°C or even lower. At such extremely low temperatures, the casing flange glue joint will be subjected to great extrusion stress. If the stress exceeds the allowable stress of the casing, the casing will break, which seriously threatens the safety of the equipment.

[0004] At present, the quantitative calculation of the expansion stress of the casing flange cement layer after water ingress and freezing can only be done through software simulation. However, since the simulation software cannot truly reflect the actual situation of the cement adhesive layer and cannot simulate the distribution of water in the cement, the estimated results have large errors. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method and device for estimating the radial stress of water frost heave in the cement bonding layer of the bushing, so as to more accurately estimate the distribution state of water in the cement bonding layer, thereby better providing early warning of bushing rupture and improving the reliable operation of the high-voltage switchgear where the bushing is located.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0007] According to a first aspect of the present invention, a method for estimating radial stress of frost heave of a casing cement adhesive layer due to water ingress is provided. The method comprises the following steps:

[0008] The frost heave test was carried out on cement samples to obtain the density of cement samples before and after freezing at different water absorption rates.

[0009] According to the density of cement samples before and after freezing at different water absorption rates, the radial stress of cement frost heave at different water absorption rates is determined.

[0010] According to the radial stress of cement frost heave under different water absorption rates, the corresponding relationship between cement water absorption rate and frost heave radial stress is fitted;

[0011] Based on the corresponding relationship, the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave is estimated according to the water absorption rate of the cement adhesive layer to be tested.

[0012] Furthermore, frost heave experiments were conducted on cement samples to obtain the density of cement samples before and after freezing at different water absorption rates, including:

[0013] Prepare multiple identical cement samples, place them in an oven and dry them to a constant weight m0, and then process them after weighing;

[0014] Place multiple cement samples after drying in containers filled with constant temperature distilled water for different predetermined time periods, and record the initial volume change V0 of each container when each cement sample is just placed in the container;

[0015] Take out multiple cement samples after immersion and wipe off the surface moisture, record the weight m1 of each cement sample after wiping off, put the multiple cement samples after immersion and wiping off into a freezer and freeze them, take them out after freezing and put them into a pure water container and record the volume change V1 after freezing;

[0016] The water absorption rate λ of the corresponding cement sample after immersion for the corresponding predetermined time is determined according to m1 and m0, and the water-free cement density ρ3 of the corresponding cement sample is determined according to m0 and V0.

[0017] Further, the water absorption rate λ of the corresponding cement sample is determined according to m1 and m0, including determining the water absorption rate λ by the following formula:

[0018] λ=(m1-m0) / m0.

[0019] Furthermore, according to the density of cement samples before and after freezing at different water absorption rates, the radial stress of cement frost heave at different water absorption rates is determined, including determining the radial stress of cement frost heave at different water absorption rates by the following formula:

[0020]

[0021] Among them, F is the radial stress of cement after freezing, K is the elastic coefficient of cement, ρ1 is the density of water, ρ2 is the density of ice, ε is the equivalent strain coefficient of cement after expansion; α is the thermal expansion coefficient of cement, which is the temperature difference before and after freezing.

[0022] Furthermore, the method further comprises the following steps:

[0023] Determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing;

[0024] Compare the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave with the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

[0025] Further, the maximum radial allowable stress of the porcelain bushing is determined according to the size and shape of the porcelain bushing, including determining the maximum radial allowable stress F by the following formula: max :

[0026]

[0027] Among them, M is the bending moment of the porcelain sleeve, D is the diameter of the outer ring of cement, and d is the diameter of the inner ring of cement.

[0028] According to a second aspect of the present invention, a device for estimating radial stress of frost heave of a casing cement adhesive layer due to water ingress is provided. The device comprises:

[0029] An acquisition module is used to obtain the density of cement samples before and after freezing at different water absorption rates, and to obtain the water absorption rate of the cement adhesive layer to be tested;

[0030] A processing module is used to determine the radial stress of cement frost heave under different water absorption rates according to the density of cement samples before and after freezing under different water absorption rates;

[0031] A fitting module is used to fit the corresponding relationship between the water absorption rate of cement and the radial stress of frost heave according to the radial stress of cement frost heave under different water absorption rates;

[0032] The estimation module is used to estimate the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave according to the water absorption rate of the cement adhesive layer to be tested based on the corresponding relationship.

[0033] Furthermore, the processing module is also used to determine the radial stress of cement frost heave under different water absorption rates by the following formula:

[0034]

[0035] Among them, F is the radial stress of cement after frost heave, K is the elastic coefficient of cement, λ is the water absorption rate of cement, ρ1 is the density of water, ρ2 is the density of ice, ρ3 is the density of cement without water, ε is the equivalent strain coefficient after cement expansion, α is the thermal expansion coefficient of cement, and is the temperature difference before and after freezing.

[0036] Furthermore, the device also includes:

[0037] A threshold determination module, used to determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing;

[0038] The early warning module is used to compare the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave with the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

[0039] Furthermore, the threshold determination module is also used to determine the maximum radial allowable stress F by the following formula: max :

[0040]

[0041] Among them, M is the bending moment of the porcelain sleeve, D is the diameter of the outer ring of cement, and d is the diameter of the inner ring of cement.

[0042] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0043] By conducting frost heave experiments on cement samples, the density of cement samples before and after freezing at different water absorption rates is obtained, and the radial stress of cement frost heave at different water absorption rates is determined; then, according to the radial stress of cement frost heave at different water absorption rates, the corresponding relationship between the water absorption rate of cement and the radial stress of frost heave is fitted; finally, based on the corresponding relationship, the radial stress of water frost heave of the cement adhesive layer to be tested is estimated according to the water absorption rate of the cement adhesive layer to be tested. The present invention can more accurately estimate the distribution state of water in the cement adhesive layer by estimating the radial stress of water frost heave of the cement adhesive layer to be tested, thereby better pre-warning of bushing rupture and improving the reliable operation of the high-voltage switchgear where the bushing is located. In addition, the method of the present invention has strong operability, high credibility, and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1(a) , 1(b) and 1(c) are the cross-sectional view, sectional view and stereoscopic view of the cement adhesive layer structure, respectively.

[0045] Where R1 and R2 represent the inner radius and outer radius of the cement adhesive layer respectively, and h represents the height of the cement adhesive layer;

[0046] Figure 2 It is a flow chart of the method for estimating radial stress of water frost heave of cement adhesive layer of porcelain casing according to the present invention;

[0047] Figure 3 It is a schematic diagram of a cement adhesive layer test block used in the present invention;

[0048] Figure 4 A high-precision container used in the present invention;

[0049] Figure 5 The electronic scale used in the present invention;

[0050] Figure 6 The curve showing the relationship between water absorption and stress obtained by the method for estimating radial stress of the casing cement adhesive layer due to water ingress and frost heave of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0052] The present invention relates to a method and device for estimating the radial force of frost heave on the cement glue layer of the porcelain bushing of a high-voltage switch when rainwater or moisture in the air enters the cement glue layer of the porcelain bushing and expands in winter. The method and device are applicable to the cement glue layer of porcelain bushings used in all high-voltage power equipment, and are also applicable to the estimation of the radial stress of frost heave on the cement glue layer of high-voltage post insulators.

[0053] Example 1

[0054] This embodiment provides a method for estimating radial stress of frost heave caused by water ingress into cement bonding layer of casing.

[0055] When the temperature drops, the water in the cement adhesive layer gradually freezes at a certain temperature, expands in volume, and produces extrusion stress on the porcelain sleeve. If the stress on the porcelain sleeve exceeds the allowable stress of the casing, the casing will break. At this time, the root of the porcelain sleeve of the casing is subjected to radial inward force, which is perpendicular to the circumference of the casing; the flange is subjected to radial outward force, which is perpendicular to the circumference of the flange. This force will cause slight deformation of the porcelain sleeve and flange, thereby generating force acting on the inside of the porcelain sleeve.

[0056] From the above analysis, we can know that this stress is caused by the expansion of cement after absorbing water and freezing during the temperature drop, which produces extrusion stress on the root of the porcelain bushing. The magnitude of the stress is related to the water absorption rate of cement. The greater the water absorption rate, the greater the expansion volume after freezing, and the greater the stress generated. Therefore, there is a critical stress, that is, the allowable stress, which corresponds to a moisture content, which is the moisture content actually controlled in operation and maintenance.

[0057] The fracture of the porcelain sleeve can be analyzed by the double shear unified strength theory. The material begins to fail because the two larger shear stresses and the normal stress function acting on the unit body exceed a certain limit value. When the material component is under the action of external stress, stress distribution will also be generated inside the material itself. When the point with a larger stress value reaches the critical maximum tensile stress, the material will undergo brittle fracture along the section where the maximum tensile stress is located.

[0058] In order to make the conclusion universal, it is assumed that water is evenly distributed in the cement, and that the expansion degree of water in all directions is the same after freezing at low temperature, and that the expansion coefficient of the material is linear when the material shrinks or expands. As shown in Figure 1, when the temperature is constant, the volume of cement per unit angle in the flange is

[0059] V1=(πR1 2 -πR2 2 )θh / 360 (1)

[0060] In the formula, R1 is the inner radius of the cement adhesive layer, R2 is the outer radius of the cement adhesive layer, θ is the angle, and h is the height of the water. Due to the uneven distribution of water in the cement, when the temperature drops, the water in the cement within the angle θ freezes, and the ice causes the cement volume to expand. The volume after expansion is

[0061] V2=π(R1+ΔR) 2 ×θ×π(R1 2 -R2 2 )×(h+Δh) / (360πR1 2 ) (2)

[0062] According to formula (1) and formula (2), the relative expansion rate of cement is

[0063]

[0064] in,

[0065]

[0066] In the formula, ρ1 is the density of water, ρ2 is the density of ice, ρ3 is the density of cement without water, and λ is the water absorption rate of cement. It can be seen from formula (3) to formula (5) that the expansion rate of cement is related to its water content. The greater the water content, the greater the expansion rate of cement.

[0067] Formula (3) shows that cement expansion has nothing to do with the angular position of the internal water, but is related to the vertical height of the water.

[0068] In winter, as the temperature drops, the water in the cement freezes and expands. The expanded cement will produce axial and radial stresses. Since radial stress is the main factor that causes the casing flange to fail, the radial force can be obtained from formula (4) and Hooke's law:

[0069]

[0070] Where F is the radial stress of cement after frost heave, K is the elastic coefficient of cement, λ is the water absorption rate of cement, ε is the equivalent strain coefficient of cement after expansion, preferably 0.3; α is the thermal expansion coefficient of cement, and ΔT is the temperature difference before and after freezing.

[0071] Ignore the umbrella outside the porcelain sleeve, assume that the cross section of the porcelain sleeve is a right circular ring, and the normal stress on its cross section is

[0072]

[0073] Where M is the bending moment of the porcelain sleeve, D is the diameter of the outer cement ring, and d is the diameter of the inner cement ring. If F ≥ Fmax, the force generated by the cement expansion at the flange due to freezing will cause the sleeve to break.

[0074] Based on the above analysis and reasoning, if Figure 2 The method for estimating radial stress of water frost heave of cement adhesive layer of porcelain casing in this embodiment comprises the following steps:

[0075] Step S101: Perform a frost heave test on a cement sample to obtain the density of the cement sample before and after freezing at different water absorption rates.

[0076] Specifically, step S101 may include the following sub-steps:

[0077] Step S1011, prepare a plurality of identical cement samples, and place them in an oven and dry them to a constant weight m0.

[0078] Among them, electronic scales can be used for weighing, such as Figure 4 shown.

[0079] Step S1012, placing the plurality of cement samples after drying into containers filled with constant temperature distilled water and soaking them for different predetermined time periods, and recording the initial volume change V0 of each cement sample in each container when it is just placed therein.

[0080] Wherein, the container is preferably used as Figure 3 The high-precision container shown has an accuracy of mL.

[0081] Step S1013, take out the multiple cement samples after immersion and wipe off the surface moisture, record the weight m1 of each cement sample after wiping dry, put the multiple cement samples after immersion and wiping dry into a freezer and freeze them. After freezing, take them out and put them into pure water containers and record the volume change V1 after freezing.

[0082] In this step, the duration of freezing the soaked and dried cement samples in a freezer is preferably 60 hours to 84 hours, more preferably 72 hours.

[0083] Step S1014: determine the water absorption rate λ of the corresponding cement sample after being immersed for a corresponding predetermined time according to m1 and m0.

[0084] The water absorption rate λ can be calculated according to the following formula:

[0085] λ=(m1-m0) / m0.

[0086] Step S1015: Determine the water absorption rate λ of the corresponding cement sample after immersion for a corresponding predetermined time according to m1 and m0, and determine the water-free cement density ρ3 of the corresponding cement sample according to m0 and V0. Specifically, the water-free cement density ρ3 can be obtained by the following formula:

[0087] ρ3=m0 / V0.

[0088] Step 102: Determine the radial stress of cement frost heave at different water absorption rates according to the density of cement samples before and after freezing at different water absorption rates.

[0089] The radial stress of cement frost heave under different water absorption rates can be determined by substituting the water absorption rate λ, the density of water ρ1, the density of ice ρ2, and the density of water-free cement ρ3 into formula (6).

[0090] Step 103: fitting the corresponding relationship between the water absorption rate of cement and the frost heave radial stress according to the frost heave radial stress of cement under different water absorption rates.

[0091] The fitting can be achieved, for example, by the least squares method.

[0092] Step 104: Based on the corresponding relationship, estimate the radial stress of the cement adhesive layer to be tested due to water intrusion and frost heave according to the water absorption rate of the cement adhesive layer to be tested.

[0093] The method of this embodiment is further described below using a specific example. The test equipment required for this example includes: 525# cement, pure water, a container, an electronic scale, and a freezer.

[0094] 525# Cement: Since the porcelain sleeve and flange are bonded by cement, the density and strength of the cement bonding layer will vary due to differences in the formulation process.

[0095] Purified water: In order to reduce the impact of impurities or minerals in the water on the cement binder layer, purified water is used and the amount is determined according to the needs of the test.

[0096] Container: Wide-caliber high-precision container, accuracy 0.01ml, such as Figure 5 shown.

[0097] Electronic scale: accuracy 0.01g, such as Figure 4 shown.

[0098] Freezer: The lowest temperature can reach -18℃.

[0099] The cement is obtained by mixing 525# cement and pure water, and the cement adhesive layer specimen is made by using the shear-broken residual block outside the fixture during the compressive strength test or specially made, such as Figure 2 Among them, the cross section of the broken piece or the largest plane of the specially made sample should be ground by a grinding wheel to make a sample with a size of 40mm×40mm×15mm, with a total of 7 samples.

[0100] The acquisition of the water absorption rate λ1 and the stress F1 of the sample 1 may include the following steps:

[0101] Step A1: Dry sample 1 in an oven at 60°C to 65°C until constant weight

[0102] Step A2: Place sample 1 in a container of constant temperature distilled water at (20±2)℃ and record the volume change as Soak for 1 day and record the volume change as

[0103] Step A3: After taking out, wipe off the surface moisture and weigh it, record it as The water absorption rate is Then put it in a -18℃ freezer for 1 day, keeping it well sealed. After taking it out, put it in a container of pure water and record the volume change as

[0104] Step A4: Calculate the density of sample 1 without water The density of water ρ1, the density of ice ρ2, and λ1 are substituted into the following formula to calculate a set of relationships between water absorption and stress (λ1, F1):

[0105]

[0106] The water absorption rate λ2 and stress F2 of sample 2 are obtained as follows:

[0107] Step B1: Dry sample 2 in an oven at 60°C to 65°C until constant weight

[0108] Step B2: Place sample 2 in a container of constant temperature distilled water at (20±2)℃ and record the volume change as Soak for 2 days, keep the seal well, and record the volume change:

[0109] Step B3: After taking out, wipe off the surface moisture and weigh it, record it as The water absorption rate is Then put it in a -18℃ freezer for 1 day, take it out and put it in a container of pure water, and record the volume change as

[0110] Step B4: Calculate the density of sample 2 without water cement The density of water ρ1, the density of ice ρ2, and λ2 are substituted into the following formula to calculate a set of relationships between water absorption and stress (λ2, F2):

[0111]

[0112] The test methods of samples 3, 4, 5, 6, and 7 are similar, and the relationships between water absorption and stress are (λ3, F3), (λ4, F4), (λ5, F5), (λ6, F6), and (λ7, F7). Thus, the following can be drawn: Figure 5 The relationship curve between water absorption and stress is shown in FIG. 1 . By fitting the curve, the relationship equation between water absorption and stress can be obtained.

[0113] Preferably, in order to better perform bushing operation and maintenance of the high-voltage switch by measuring the radial stress of water frost heave of the cement adhesive layer to be measured, the above method may further include the following steps:

[0114] Step 5: Determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing.

[0115] Among them, the maximum radial allowable stress can be calculated by equations (7) and (8).

[0116] Step 6: Compare the radial stress of the cement adhesive layer to be tested due to water ingress and the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

[0117] Example 2

[0118] This embodiment provides a device for estimating radial stress of frost heave caused by water ingress into cement adhesive layer of casing. The device comprises:

[0119] An acquisition module is used to obtain the density of cement samples before and after freezing at different water absorption rates, and to obtain the water absorption rate of the cement adhesive layer to be tested;

[0120] A processing module is used to determine the radial stress of cement frost heave under different water absorption rates according to the density of cement samples before and after freezing under different water absorption rates;

[0121] A fitting module is used to fit the corresponding relationship between the water absorption rate of cement and the radial stress of frost heave according to the radial stress of cement frost heave under different water absorption rates;

[0122] The estimation module is used to estimate the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave according to the water absorption rate of the cement adhesive layer to be tested based on the corresponding relationship.

[0123] Furthermore, the processing module is also used to determine the radial stress of cement frost heave under different water absorption rates by the following formula:

[0124]

[0125] Among them, F is the radial stress of cement after frost heave, K is the elastic coefficient of cement, ρ1 is the density of water, ρ2 is the density of ice, ρ3 is the density of cement without water, λ is the water absorption rate of cement, ε is the equivalent strain coefficient after cement expansion, α is the thermal expansion coefficient of cement, and is the temperature difference before and after freezing.

[0126] Preferably, the device further comprises:

[0127] A threshold determination module, used to determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing;

[0128] The early warning module is used to compare the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave with the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

[0129] Furthermore, the threshold determination module is also used to determine the maximum radial allowable stress F by the following formula: max :

[0130]

[0131]

[0132] Among them, M is the bending moment of the porcelain sleeve, D is the diameter of the outer ring of cement, and d is the diameter of the inner ring of cement.

[0133] The beneficial effect of the present invention is that, compared with the prior art, by conducting frost heave experiments on cement samples, the density of cement samples before and after freezing at different water absorption rates is obtained, and the radial stress of cement frost heave at different water absorption rates is determined; then, according to the radial stress of cement frost heave at different water absorption rates, the corresponding relationship between the water absorption rate of cement and the radial stress of frost heave is fitted; finally, based on the corresponding relationship, the radial stress of water frost heave of the cement adhesive layer to be tested is estimated according to the water absorption rate of the cement adhesive layer to be tested. The present invention can more accurately estimate the distribution state of water in the cement adhesive layer by estimating the radial stress of water frost heave of the cement adhesive layer to be tested, thereby better pre-warning of bushing rupture and improving the reliable operation of the high-voltage switchgear where the bushing is located. In addition, the method of the present invention has strong operability, high credibility, and strong practicality.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for estimating radial stress of casing cement adhesive layer due to water ingress, characterized in that: include: The frost heave test was carried out on cement samples to obtain the density of cement samples before and after freezing at different water absorption rates. According to the density of cement samples before and after freezing at different water absorption rates, the radial stress of cement frost heave at different water absorption rates is determined. According to the radial stress of cement frost heave under different water absorption rates, the corresponding relationship between cement water absorption rate and frost heave radial stress is fitted; Based on the corresponding relationship, the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave is estimated according to the water absorption rate of the cement adhesive layer to be tested.

2. The method according to claim 1, characterized in that The frost heave test was carried out on the cement samples to obtain the density of the cement samples before and after freezing at different water absorption rates, including: Prepare multiple identical cement samples, place them in an oven and dry them to a constant weight m0, and then process them after weighing; Place multiple cement samples after drying in containers filled with constant temperature distilled water for different predetermined time periods, and record the initial volume change V0 of each container when each cement sample is just placed in the container; Take out multiple cement samples after immersion and wipe off the surface moisture, record the weight m1 of each cement sample after wiping off, put the multiple cement samples after immersion and wiping off into a freezer and freeze them, take them out after freezing and put them into a pure water container and record the volume change V1 after freezing; The water absorption rate λ of the corresponding cement sample after immersion for the corresponding predetermined time is determined according to m1 and m0, and the water-free cement density ρ3 of the corresponding cement sample is determined according to m0 and V0.

3. The method according to claim 2, characterized in that Determine the water absorption λ of the corresponding cement sample according to m1 and m0, including determining the water absorption λ by the following formula: λ=(m1-m0) / m0.

4. The method according to claim 2, characterized in that: According to the density of cement samples before and after freezing at different water absorption rates, the radial stress of cement frost heave at different water absorption rates is determined, including determining the radial stress of cement frost heave at different water absorption rates by the following formula: Among them, F is the radial stress of cement after freezing, K is the elastic coefficient of cement, ρ1 is the density of water, ρ2 is the density of ice, ε is the equivalent strain coefficient of cement after expansion; α is the thermal expansion coefficient of cement, and ΔT is the temperature difference before and after freezing.

5. The method according to claim 1, characterized in that The following steps are also included: Determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing; Compare the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave with the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

6. The method according to claim 5, characterized in that The maximum radial allowable stress of the porcelain bushing is determined according to the size and shape of the porcelain bushing, including determining the maximum radial allowable stress F by the following formula: max : Among them, M is the bending moment of the porcelain sleeve, D is the diameter of the outer ring of cement, and d is the diameter of the inner ring of cement.

7. A device for estimating radial stress of casing cement adhesive layer due to water ingress, characterized in that: include: An acquisition module is used to obtain the density of cement samples before and after freezing at different water absorption rates, and to obtain the water absorption rate of the cement adhesive layer to be tested; A processing module is used to determine the radial stress of cement frost heave under different water absorption rates according to the density of cement samples before and after freezing under different water absorption rates; A fitting module is used to fit the corresponding relationship between the water absorption rate of cement and the radial stress of frost heave according to the radial stress of cement frost heave under different water absorption rates; The estimation module is used to estimate the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave according to the water absorption rate of the cement adhesive layer to be tested based on the corresponding relationship.

8. The device according to claim 7, characterized in that The processing module is also used to determine the radial stress of cement frost heave under different water absorption rates by the following formula: Among them, F is the radial stress of cement after frost heave, K is the elastic coefficient of cement, λ is the water absorption rate of cement, ρ1 is the density of water, ρ2 is the density of ice, ρ3 is the density of cement without water, ε is the equivalent strain coefficient after cement expansion, α is the thermal expansion coefficient of cement, and ΔT is the temperature difference before and after freezing.

9. The device according to claim 7, characterized in that Also includes: A threshold determination module, used to determine the maximum radial allowable stress of the porcelain bushing according to the size and shape of the porcelain bushing; The early warning module is used to compare the radial stress of the cement adhesive layer to be tested due to water ingress and frost heave with the maximum radial allowable stress. If it is greater than or equal to the maximum radial stress, it indicates that the risk of porcelain bushing fracture is high; if it is less than the maximum radial stress, it indicates that the risk of porcelain bushing fracture is low.

10. The device according to claim 9, characterized in that The threshold determination module is also used to determine the maximum radial allowable stress F by the following formula: max : Among them, M is the bending moment of the porcelain sleeve, D is the diameter of the outer ring of cement, and d is the diameter of the inner ring of cement.

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