Wall thickness checking calculation method suitable for low-hardness thick-wall pipe fitting

Abstract

The invention relates to the technical field of strength checking of thick-wall pipe fittings in the power industry, in particular to a wall thickness checking calculation method suitable for low-hardness thick-wall pipe fittings. Comprising the following steps: performing hardness detection on the surface of the thick-wall pipe to judge whether a low-hardness area exists; confirming a low-hardness area range; the minimum actually measured wall thickness of the low-hardness area is measured; the sampling depth of the low-hardness area and the wall thickness of the normal-hardness area are obtained; acquiring allowable stress values of materials in the low-hardness area and the normal-hardness area; calculating the equivalent wall thickness of the low-hardness area; calculating the effective wall thickness of the thick-wall pipe fitting; calculating the minimum required wall thickness of the thick-wall pipe fitting; and comparing the effective wall thickness with the minimum required wall thickness of the thick-wall pipe fitting. The problem that the wall thickness of the low-hardness thick-wall pipe fitting cannot be checked and calculated is solved, so that the pipe does not need to be replaced in a short time, the service time of the thick-wall pipe fitting is prolonged as much as possible, the service life of the thick-wall pipe fitting is prolonged, and meanwhile, the safety and reliability of the thick-wall pipe fitting can be ensured.

Description

Technical Field

[0001] This application relates to the technical field of strength verification of thick-walled pipe fittings in the power industry, and particularly to a wall thickness verification calculation method applicable to thick-walled pipe fittings with low hardness. Background Art

[0002] Thick-walled pipe fittings are the main pressure-bearing components of equipment such as steam-water pipelines, headers, and pressure vessels in power plants. During the design and manufacturing stages, wall thickness verification calculations are required to meet their service conditions and service life. During the maintenance process, when wall thickness thinning is detected, wall thickness verification calculations also need to be carried out to ensure that they meet the operating condition requirements.

[0003] Different equipment corresponds to different design standard specifications. For example, the standard GB / T32270-2024 "Code for Pressure Piping - Power Piping" is applicable to pipelines with steam and water as media within the boundary of thermal power plants, and verification design is carried out through the calculation of the minimum wall thickness and the calculated wall thickness; DL / T 5054-2016 "Code for Design of Steam-Water Pipelines in Thermal Power Plants" is applicable to the design of steam-water metal pipelines within the scope of thermal power plants, and verification design is carried out through the calculation of the minimum wall thickness; GB / T 16507.4-2022 "Water-Tube Boilers - Part 4: Strength Verification" is mainly applicable to the boiler body and pipelines within the scope of the boiler, and verification design is carried out through the calculation of the designed wall thickness, calculated wall thickness, and minimum required thickness, etc. Other domestic and foreign design and verification standards such as GB 50764-2012 "Code for Design of Power Pipelines in Power Plants" and ASME B31.1 "Power Piping" have all elaborated in detail on the wall thickness verification calculation. Although there are many standard specifications, the principle of wall thickness verification is based on strength theory, and the calculation formulas are basically the same in form.

[0004] For normal thick-walled pipe fittings, wall thickness verification calculations can be carried out in accordance with the above standard specifications. However, in inspection and testing, it is often found that many thick-walled pipe fittings have abnormal hardness, and the phenomenon of low hardness is more common. Low hardness will lead to a decline in the mechanical properties and allowable stress of the material, shorten the service life, and pose a hidden danger to the safe and stable operation of the unit.

[0005] However, in the case of abnormal hardness, the wall thickness verification cannot be carried out according to the standard specifications, and it is difficult to confirm the strength condition of thick-walled pipe fittings. This leads to the situation that when many power plants find low hardness in thick-walled pipe fittings during the maintenance process, they either directly replace them or carry out safety assessment or life assessment. If they directly replace them, the power plants generally lack sufficient spare parts, and the cycle of reordering and manufacturing is relatively long, which will seriously affect the power generation of the unit, with poor economy. Moreover, the direct replacement method is a bit blind and will also cause unnecessary waste; while carrying out assessment or evaluation work on thick-walled pipe fittings generally still requires cutting pipes for sampling. Due to the relatively long test cycle, it will also affect the power generation time of the unit, and the economy is not high either. Summary of the Invention

[0006] The purpose of this application is to provide a wall thickness verification calculation method applicable to low-hardness thick-walled pipe fittings, so as to solve the problem that the wall thickness of low-hardness thick-walled pipe fittings with abnormal hardness cannot be verified and calculated, thereby realizing that the pipe can be not replaced in the short term, extending the service time of thick-walled pipe fittings as much as possible, prolonging their service life, and at the same time ensuring their safety and reliability.

[0007] A wall thickness verification calculation method applicable to low-hardness thick-walled pipe fittings provided by this application includes:

[0008] Step 100: Perform hardness detection on the surface of the thick-walled pipe fitting to determine whether there is a low-hardness area;

[0009] Step 200: Confirm the range of the low-hardness area;

[0010] Step 300: Measure the minimum measured wall thickness δ0 of the low-hardness area;

[0011] Step 400: Obtain the sampling depth δ of the low-hardness area l and the wall thickness δ of the normal-hardness area n , δ n =δ0 - δ l ;

[0012] Step 500: Obtain the allowable stress value [σ] of the material in the low-hardness area l t , and the allowable stress value [σ] of the material in the normal-hardness area n t ;

[0013] Step 600: Calculate the equivalent wall thickness δ of the low-hardness area eql , according to the allowable stress value [σ] of the material in the low-hardness area l t , the allowable stress value [σ] of the material in the normal-hardness area n t , the sampling depth δ of the low-hardness areal and calculated from the calculated pressure P;

[0014] Step 700, calculate the effective wall thickness δ of the thick-walled pipe fitting eq , δ eq = δ n + δ eql ;

[0015] Step 800, calculate the minimum required wall thickness δ of the thick-walled pipe fitting min ;

[0016] Step 900, compare the effective wall thickness δ of the thick-walled pipe fitting eq with the minimum required wall thickness δ min to determine whether it can continue to be in service.

[0017] Furthermore, in step 100, use a Leeb hardness tester to perform hardness testing on the surface of the thick-walled pipe fitting. When the hardness value is lower than the standard requirement, conduct hardness verification through a portable Brinell hardness tester, and record the hardness verification deviation, denoted as ΔHB.

[0018] Furthermore, in step 200, increase the hardness testing measurement points. The hardness measurement points are arranged in a grid pattern, and the measurement point spacing is evenly set and adjusted according to the specification dimensions of the thick-walled pipe fitting to ensure the accurate division of the low-hardness area. Then, perform hardness testing and verification in the manner of step 100 to obtain the specific positions of the low-hardness measurement points, and connect the outermost low-hardness measurement points to confirm the range of the low-hardness area of the thick-walled pipe fitting.

[0019] Even further, in step 400, perform multiple small punch sampling along the radial direction of the pipe wall at the center of the low-hardness area. The samples taken are sheet samples. After each small punch sampling, perform hardness testing and verification on the bottom of the sampling area in the manner of step 100. When the hardness value after verification meets the standard requirement, stop sampling and measure the sampling depth, denoted as depth δ l .

[0020] Even further, in step 500, it includes step 510, obtain the allowable stress value [σ] of the material in the low-hardness area l t , and step 520, obtain the allowable stress value [σ] of the material in the normal-hardness area n t ;

[0021] Among them, in step 510, first obtain the tensile test yield strength R of the material in the low-hardness area at the specified temperature through a small punch high-temperature tensile test eLl t , and then according to [σ] l t = R eLlt / 1.5 to obtain the allowable stress value [σ] of the material in the low-hardness region l t .

[0022] Furthermore, in step 520, by continuously sampling downward at the small punch sampling position in the low-hardness region, a small punch specimen with normal hardness is obtained, and the yield strength R of the material in the normal hardness region at the specified temperature is obtained through a high-temperature tensile test of the small punch eLn t , and then according to [σ] n t = R eLn t / 1.5 to obtain the allowable stress value [σ] of the material in the normal hardness region at the specified temperature n t .

[0023] Furthermore, after the verification calculation is completed, the small punch sampling position is repaired by welding, and re-evaluation or assessment is carried out after welding

[0024] Further, in step 300, a multi-point wall thickness measurement is carried out on the low-hardness region of the thick-walled pipe fitting using an ultrasonic thickness gauge to obtain the minimum measured wall thickness δ0 of the low-hardness region

[0025] Further, in step 600, according to the allowable stress value [σ] of the material in the low-hardness region l t , the allowable stress value [σ] of the material in the normal hardness region n t , the sampling depth δ of the low-hardness region l and the calculated pressure P, the equivalent wall thickness δ of the low-hardness region is obtained according to the following calculation formula eql ;

[0026]

[0027] In the formula, is the minimum weakening coefficient

[0028] Further, in step 800, the minimum required wall thickness δ of the thick-walled pipe fitting is calculated according to the following calculation formula min ,

[0029]

[0030] In the formula, Di is the inner diameter of the pipe wall

[0031] Compared with the prior art, the wall thickness checking and calculation method for low-hardness thick-walled pipe fittings provided by the present application determines whether there is a low-hardness area through hardness checking and detection, confirms the range of the low-hardness area, and also obtains the allowable stress of the material in the low-hardness area and the allowable stress of the material in the normal-hardness area. Moreover, the present application defines the concepts and derivation calculation methods of the equivalent wall thickness of the low-hardness area and the effective wall thickness of the thick-walled pipe fitting, and then compares them with the minimum required wall thickness of the thick-walled pipe fitting, so as to determine whether the effective wall thickness of the thick-walled pipe fitting still meets the strength requirements and whether it can continue to be in service.

[0032] The present application does not require pipe replacement or cutting, has simple on-site operations, a short test period, and can quickly realize the wall thickness checking and calculation of low-hardness thick-walled pipe fittings. After checking, if the conditions for continued service are met, the pipe replacement period can be extended, the service life of the thick-walled pipe fitting can be prolonged, and at the same time, the safety performance of the thick-walled pipe fitting can be ensured, which can greatly reduce the economic losses caused by pipe replacement or long-term evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 It is a flowchart of the wall thickness checking and calculation method for low-hardness thick-walled pipe fittings provided by the embodiments of the present application;

[0035] Figure 2 It is a distribution schematic diagram of the low-hardness area and the small punch sampling positions of the P91 thick-walled pipe fitting provided by the embodiments of the present application;

[0036] Figure 3 It is a schematic diagram of the wall thickness measurement of the low-hardness area of the P91 thick-walled pipe fitting provided by the embodiments of the present application;

[0037] Figure 4 It is a schematic diagram of the effect after welding repair of the small punch sampling positions of the P91 thick-walled pipe fitting provided by the embodiments of the present application.

[0038] Reference Signs:

[0039] 10 - Thick-walled pipe fitting;

[0040] 21 - Normal-hardness area;

[0041] 22 - Low-hardness area;

[0042] 30 - Small punch sampling position. Detailed implementation manners

[0043] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are some but not all of the embodiments of the present application. Components of the embodiments of the present application usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0045] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0046] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this application is usually placed when in use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance.

[0047] In addition, terms such as "horizontal", "vertical", "overhanging", etc. do not mean that the components are required to be absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0048] In the description of the present application, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0049] The following will describe in detail some embodiments of the present application in conjunction with the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0050] As Figures 1 to 4 shown, the embodiment of the present application provides a wall thickness checking and calculating method applicable to low-hardness thick-walled pipe fittings, which mainly includes the following steps:

[0051] Step 100: Perform hardness detection on the surface of the thick-walled pipe fitting to determine whether there is a low-hardness area;

[0052] Specifically, a Leeb hardness tester can be used to perform hardness detection on the surface of the thick-walled pipe fitting. When the hardness value is lower than the standard requirement, a portable Brinell hardness tester can be used for hardness verification, and the hardness verification deviation is recorded as ΔHB. This hardness detection and verification method is accurate and reliable.

[0053] Step 200: Confirm the range of the low-hardness area;

[0054] Specifically, the number of hardness detection points can be increased first. The hardness detection points can be arranged in a grid pattern with appropriate spacing, and are appropriately set and adjusted according to the specifications of the thick-walled pipe fitting to ensure the accurate division of the low-hardness area. Then, hardness detection and verification are performed in the same way as in Step 100 to obtain the specific positions of the low-hardness detection points, and the outermost low-hardness detection points are connected to confirm the range of the low-hardness area of the thick-walled pipe fitting.

[0055] Step 300: Measure the minimum measured wall thickness δ0 of the low-hardness area;

[0056] Specifically, an ultrasonic thickness gauge can be used to measure the wall thickness at multiple points in the low-hardness area of the thick-walled pipe fitting, so as to obtain the minimum measured wall thickness δ0 of the low-hardness area.

[0057] Step 400: Obtain the sampling depth δ l of the low-hardness area and the wall thickness δ n of the normal-hardness area. Then, the wall thickness δ n of the normal-hardness area is equal to the difference between the minimum measured wall thickness δ0 of the low-hardness area and the sampling depth δ l of the low-hardness area, that is, δ n = δ0 - δ l ;

[0058] Specifically, the sampling depth δ l, This method is precise and has a short test cycle. Meanwhile, there is no need to change or cut the pipe, and the on-site operation is simple. Specifically, multiple small punch samples can be taken radially along the pipe wall at the center of the low-hardness area. The obtained sample is a flake sample. The diameter d of the sample is preferably about 10 mm, and the thickness δ of the sample is preferably about 0.5 mm. After each small punch sampling, the hardness of the bottom of the sampling area is detected and verified in the manner of step 100. When the hardness value after verification meets the standard requirements, stop sampling and measure the sampling depth, denoted as depth δ l 。

[0059] Step 500, obtain the allowable stress value [σ] of the material in the low-hardness area l t , and the allowable stress value [σ] of the material in the normal-hardness area n t ;

[0060] Among them, it includes step 510, obtain the allowable stress value [σ] of the material in the low-hardness area l t ;

[0061] Specifically, first obtain the tensile test yield strength R of the material in the low-hardness area at the specified temperature through a small punch high-temperature tensile test eLl t , and then according to [σ] l t =R eLl t , obtain the allowable stress value [σ] of the material in the low-hardness area l t 。

[0062] Step 520, obtain the allowable stress value [σ] of the material in the normal-hardness area n t ;

[0063] There are two ways to obtain the allowable stress value of the material in the normal-hardness area. One feasible way is to continue sampling downward at the small punch sampling position in the low-hardness area to obtain a small punch sample with normal hardness, and obtain the tensile test yield strength R of the material in the normal-hardness area at the specified temperature through a small punch high-temperature tensile test eLn t , and then according to [σ] n t =R eLn t / 1.5, obtain the allowable stress value [σ] of the material in the normal-hardness area at the specified temperature n t 。

[0064] Another feasible way is to obtain the allowable stress value [σ] of the material in the normal hardness region at the specified temperature by referring to relevant materials. n t .

[0065] Step 600, calculate the equivalent wall thickness δ of the low hardness region eql , and calculate it according to the allowable stress value [σ] of the material in the low hardness region l t , the allowable stress value [σ] of the material in the normal hardness region n t , the sampling depth δ of the low hardness region l and the calculated pressure P, and calculate it through the following calculation formula (1);

[0066]

[0067] wherein, is the minimum weakening coefficient.

[0068] Step 700, calculate the effective wall thickness δ of the thick-walled pipe fitting eq , the effective wall thickness δ of the thick-walled pipe fitting eq is equal to the sum of the wall thickness δ of the normal hardness region n and the equivalent wall thickness δ of the low hardness region eql , that is, δ eq =δ n +δ eql ;

[0069] Step 800, calculate the minimum required wall thickness δ of the thick-walled pipe fitting min , which can be specifically calculated through the following calculation formula (2),

[0070]

[0071] wherein, Di is the inner diameter of the pipe wall.

[0072] Step 900, compare the size of the effective wall thickness δ eq of the thick-walled pipe fitting with the minimum required wall thickness δ min to determine whether it can continue to be in service;

[0073] Specifically, if δ eq >δ min , it means that the effective wall thickness of the thick-walled pipe fitting meets the strength requirements and can continue to be in service. If δ eq ≤δ min , it means that the effective wall thickness of the thick-walled pipe fitting no longer meets the strength requirements and cannot continue to be in service.

[0074] In addition, after the calibration calculation is completed, the sampling position of the small punch can be repaired by welding, and re-evaluation or assessment can be carried out after welding.

[0075] Compared with the prior art, the wall thickness checking and calculating method for low-hardness thick-walled pipe fittings provided by the embodiments of the present application determines whether there is a low-hardness area and confirms the range of the low-hardness area through multiple small punch sampling and hardness checking detections, and can also accurately obtain the depth of the low-hardness area of the thick-walled pipe fittings. At the same time, through the small punch tensile test, the mechanical properties and allowable stress of the low-hardness area at a specified temperature can be accurately obtained. Moreover, the embodiments of the present application define the concepts and derivation calculation methods of the equivalent wall thickness of the low-hardness area and the effective wall thickness of the thick-walled pipe fittings, and then can be compared with the minimum required wall thickness of the thick-walled pipe fittings, so as to determine whether the effective wall thickness of the thick-walled pipe fittings still meets the strength requirements and whether it can continue to be in service.

[0076] The embodiments of the present application do not require pipe replacement or pipe cutting, the on-site operation is simple, the test period is short, and the wall thickness checking and calculation of low-hardness thick-walled pipe fittings can be quickly realized. After checking, if the conditions for continued service are met, the pipe replacement period can be extended, the service life of the thick-walled pipe fittings can be extended, and at the same time, the safety performance of the thick-walled pipe fittings can be guaranteed, and the economic losses caused by pipe replacement or long-term evaluation can be greatly reduced.

[0077] The present application also provides a specific embodiment, as Figures 1 to 4 shown.

[0078] In this specific embodiment, a P91 thick-walled pipe fitting is taken as an example for illustration. The P91 thick-walled pipe fitting is a main steam pipeline with a specification of ID229×41mm, the main steam pressure in the pipeline is 25.50MPa, and the temperature is 570°C. Hardness inspection found that there is a low-hardness phenomenon in the base metal area of the straight pipe section of the main steam pipeline.

[0079] Next, according to the wall thickness checking and calculating method for low-hardness thick-walled pipe fittings provided by the present application, the wall thickness checking work is carried out on it, and the main steps are as follows:

[0080] Step 100, perform hardness detection on the surface of the thick-walled pipe fitting 10. Use a portable Leeb hardness tester to perform surface hardness detection on the thick-walled pipe fitting 10. It is found that the measured hardness value in some areas is about 140 HBHLD. Through a portable Brinell hardness tester for hardness checking, the hardness value in this area is about 155 HBW after checking, and the hardness checking deviation ΔHB = 15 HB. Therefore, it can be considered that there is a low-hardness phenomenon in the thick-walled pipe fitting 10.

[0081] Step 200: Confirm the range of the low-hardness area 22, increase the hardness detection measuring points, which are arranged in a grid pattern with a moderate distance between the measuring points. According to the specification dimensions of the thick-walled pipe fitting 10, the distance between each grid measuring point is kept at about 50 mm. Conduct hardness detection and verification in the manner of Step 100 to obtain the specific positions of the low-hardness measuring points, and connect the outermost low-hardness measuring points, then the normal hardness area 21 and the low-hardness area 22 of the thick-walled pipe fitting 10 can be confirmed. In this specific embodiment, the outer surface of the low-hardness area 22 of the thick-walled pipe fitting 10 is relatively regular and rectangular, as Figure 2 shown, Figure 2 where Di is the inner diameter of the thick-walled pipe fitting 10 and D is the outer diameter of the thick-walled pipe fitting 10.

[0082] Step 300: Measure the minimum measured wall thickness δ0 of the low-hardness area 22. Use an ultrasonic thickness gauge to measure the wall thickness of the low-hardness area 22 of the thick-walled pipe fitting 10. The number of wall thickness measuring points should cover the low-hardness area 22 as much as possible. Take the minimum measured value as the minimum measured wall thickness δ0 of the low-hardness area 22 = 43.34 mm, as Figure 3 shown.

[0083] Step 400: Obtain the depth δ of the low-hardness area 22 l and the wall thickness δ of the normal hardness area n . Conduct multiple small punch sampling along the radial direction of the pipe wall at the center position of the low-hardness area 22. The center position of the low-hardness area 22 is the small punch sampling position 30. The sample taken is a flake sample, the diameter d of the sample is about 10 mm, and the thickness δ of the sample is about 0.5 mm. After each small punch sampling, conduct hardness detection and verification on the bottom of the small punch sampling position 30 in the manner of Step 100. In this specific embodiment, when a total of 10 small punch samplings are conducted, use a portable Leeb hardness tester to conduct hardness detection on the bottom of the small punch sampling position 30. The detection result is 165 HBHLD. Since the hardness verification deviation ΔHB = 15 HB, it can be confirmed that the hardness value after verification is 180 HBW. The total depth of the measurement sampling is the depth δ of the low-hardness area 22 l = 11.23 mm, then the wall thickness δ of the normal hardness area 21 n = δ0 - δ l = 32.11 mm.

[0084] It should be noted here that using the depth of the small punch sampling position 30 to reflect the depth of the entire low-hardness area 22 is mainly considered from the following two aspects. First, since the reason for the low hardness in this specific embodiment is improper heat treatment, the degree of influence of the entire low-hardness area 22 by this improper heat treatment process is basically the same, so the generated low-hardness depth is also basically the same; second, the small punch sampling position 30 is located at the center position of the low-hardness area 22, which can better represent the influence degree of the entire area.

[0085] Step 510, obtain the allowable stress value [σ] of the material in the low hardness region 22 l t , conduct small punch high temperature tensile tests on a total of 10 specimens respectively, and obtain the minimum high temperature tensile test yield strength R of the material in the low hardness region 22 at 570 °C eLl 570℃ = 98.23 MPa; referring to the regulations on the allowable stress value in GB / T 16507.1, the allowable stress value [σ] of the material in the low hardness region of the thick-walled pipe fitting in this specific embodiment l 570℃ = R eLl 570℃ / 1.5 = 65.49 MPa.

[0086] Step 520, obtain the allowable stress value [σ] of the material in the normal hardness region 21 n t , there are two ways to obtain the allowable stress value of the material in the normal hardness region 21. One way is to continue sampling downward at the small punch sampling position 30 in the low hardness region 22 to obtain the small punch specimen in the normal hardness region 21, conduct small punch high temperature tensile tests, and obtain the tensile test yield strength R of the material in the normal hardness region 21 at 570 °C eLn t ; referring to the regulations on the allowable stress value in GB / T 16507.1, the allowable stress value [σ] of the material in the normal hardness region 21 at 570 °C n 570℃ = R eLn 570℃ / 1.5; in this specific embodiment, another feasible way is adopted, that is, by referring to data, according to the allowable stress values of P91 steel pipes at different temperatures in ASME B31.1-2012 "Power Piping", the allowable stress value of P91 material at 570 °C can be obtained by interpolation calculation as 85.64 MPa, then the allowable stress value [σ] of the material in the normal hardness region at the specified temperature n 570℃ = 85.64 MPa.

[0087] Step 600, calculate the equivalent wall thickness δ of the low hardness region 22 eql , from the allowable stress value [σ] of the material in the low hardness region l 570℃ , the allowable stress value [σ] of the material in the normal hardness region n 570℃ , the sampling depth δ of the low hardness region l and the calculated pressure P, and calculate according to the following calculation formula

[0088]

[0089] Wherein, is the minimum weakening coefficient. According to the regulations on the weakening coefficient in GB / T16507.4, in this specific embodiment the value is taken as 1. From the above formula, the equivalent wall thickness δ of the low-hardness region 22 can be obtained eql = 8.13 mm.

[0090] Step 700, calculate the effective wall thickness δ of the thick-walled pipe fitting 10 eq , the effective wall thickness δ of the thick-walled pipe fitting 10 eq is equal to the sum of the wall thickness δ of the normal-hardness region 21 n and the equivalent wall thickness δ of the low-hardness region 22 eql , that is, δ eq = δ n + δ eql = 40.24 mm.

[0091] Step 800, calculate the minimum required wall thickness δ of the thick-walled pipe fitting 10 min , which can be specifically calculated through the following calculation formula

[0092]

[0093] the minimum required wall thickness δ of the thick-walled pipe fitting 10 can be obtained min = 40.06 mm.

[0094] Step 900, compare the size of the effective wall thickness δ of the thick-walled pipe fitting 10 eq with the minimum required wall thickness δ min . In this specific embodiment, δ eq > δ min , indicating that the effective wall thickness of the thick-walled pipe fitting 10 still meets the strength requirements and can continue to be in service.

[0095] Furthermore, in this specific embodiment, the sampling position 30 of the small punch can also be repaired by welding. The effect after welding is as Figure 4 shown, and after welding, the thick-walled pipe fitting 10 still needs to be further evaluated or assessed. In this way, it can be ensured that the thick-walled pipe fitting 10 can exert the maximum efficiency within the safe service life cycle, not only avoiding the loss of power generation and the waste of pipe fittings, but also gaining sufficient preparation time for the next pipe replacement.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A wall thickness checking and calculating method applicable to low-hardness thick-walled pipe fittings, characterized in that, Including: Step 100: Perform hardness detection on the surface of the thick-walled pipe fitting to determine whether there is a low-hardness area; Step 200: Confirm the range of the low-hardness area; Step 300: Measure the minimum actual wall thickness δ0 of the low-hardness area; Step 400, obtain the sampling depth δ of the low hardness region l and the wall thickness δ of the normal hardness region n , δ n = δ0 - δ l ; Step 500, obtain the allowable stress value [σ] of the material in the low hardness region l t , and the allowable stress value [σ] of the material in the normal hardness region n t ; Step 600, calculate the equivalent wall thickness δ of the low-hardness area eql , according to the allowable stress value [σ] of the material in the low-hardness area l t , the allowable stress value [σ] of the material in the normal-hardness area n t , the sampling depth δ of the low-hardness area l and the calculated pressure P Step 700, calculate the effective wall thickness δ of the thick-walled pipe fitting eq , δ eq = δ n + δ eql ; Step 800, calculate the minimum required wall thickness δ of the thick-walled pipe fitting min ; Step 900, compare the effective wall thickness δ of the thick-walled pipe fitting eq with the minimum required wall thickness δ min to determine whether it can continue to be in service.

2. The wall thickness checking and calculating method according to claim 1, characterized in that In step 100, use a Leeb hardness tester to perform hardness detection on the surface of the thick-walled pipe fitting. When the hardness value is lower than the standard requirement, perform hardness verification with a portable Brinell hardness tester, and record the hardness verification deviation, denoted as ΔHB.

3. The wall thickness checking and calculating method according to claim 2, characterized in that In step 200, increase the hardness detection measuring points. The hardness measuring points are arranged in a grid pattern, and the measuring point spacing is evenly set and adjusted according to the specification size of the thick-walled pipe fitting to ensure the accurate division of the low-hardness area. Then, perform hardness detection and verification in the manner of step 100 to obtain the specific positions of the low-hardness measuring points, and connect the outermost low-hardness measuring points to confirm the range of the low-hardness area of the thick-walled pipe fitting.

4. The wall thickness checking and calculating method according to claim 2, characterized in that In step 400, multiple small punch samplings are performed radially along the tube wall at the central position of the low hardness area. The samples taken are sheet samples. After each small punch sampling, the hardness of the bottom of the sampling area is detected and verified in the manner of step 100. When the hardness value after verification meets the standard requirements, stop sampling and measure the sampling depth, denoted as depth δ l .

5. The wall thickness checking and calculating method according to claim 4, characterized in that In step 500, which includes step 510, obtain the allowable stress value [σ] of the material in the low hardness region l t , and step 520, obtain the allowable stress value [σ] of the material in the normal hardness region n t ; Among them, in step 510, first obtain the yield strength R of the material in the low-hardness region at a specified temperature through a small punch high-temperature tensile test eLl t , and then according to [σ] l t = R eLl t / 1.5, obtain the allowable stress value [σ] of the material in the low-hardness region l t .

6. The wall thickness checking and calculating method according to claim 5, characterized in that In step 520, by continuously sampling downward at the small punch sampling position in the low hardness area, a small punch specimen with normal hardness is obtained, and the yield strength R of the material in the normal hardness area at a specified temperature is obtained through a high temperature tensile test of the small punch. eLn t , and then according to [σ] n t = R eLn t / 1.5, the allowable stress value [σ] of the material in the normal hardness area at a specified temperature is obtained. n t .

7. The wall thickness checking calculation method according to any one of claims 4 to 6, characterized in that After the checking and calculation are completed, repair weld the sampling position of the small punch, and perform re-evaluation or assessment after the repair welding.

8. The wall thickness checking and calculating method according to claim 1, characterized in that In step 300, use an ultrasonic thickness gauge to perform multi-point wall thickness measurement on the low-hardness area of the thick-walled pipe fitting to obtain the minimum actual wall thickness δ0 of the low-hardness area.

9. The wall thickness checking and calculating method according to claim 1, characterized in that In step 600, according to the allowable stress value [σ] of the material in the low hardness region l t , the allowable stress value [σ] of the material in the normal hardness region n t , the sampling depth δ of the low hardness region l and the calculated pressure P, the equivalent wall thickness δ of the low hardness region is obtained according to the following calculation formula eql ; In the formula, is the minimum attenuation coefficient.

10. The wall thickness checking and calculating method according to claim 1, characterized in that In step 800, the minimum required wall thickness δ of the thick-walled pipe fitting is calculated according to the following calculation formula min , Wherein, Di is the inner diameter of the pipe wall.

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