Nuclear power plant cantilever small branch pipe vibration risk assessment method and system

Abstract

The invention provides a vibration risk assessment method and system for a small cantilever branch pipe of a nuclear power plant, and the method comprises the steps: obtaining the parameters of the branch pipe, and calculating the first-order inherent frequency of the branch pipe according to the parameters of the branch pipe; calculating the ratio of the concentrated mass of the valve to the uniform distribution mass of the branch pipes, and determining a speed coefficient and a stress coefficient; and pump information and main pipeline information are obtained, and pump-induced vibration analysis and flow-induced vibration analysis are sequentially carried out to determine whether the branch pipe has a vibration fatigue failure risk or not. By adopting the evaluation method, pump-induced vibration and flow-induced vibration analysis can be carried out on the small branch pipe in sequence, so that the vibration fatigue risk can be detected before the vibration fatigue fault occurs, the vibration fatigue fault of the small branch pipe is reduced, and the safety and economical efficiency of nuclear power plant operation are improved.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline vibration risk prediction, and in particular to a method and system for assessing vibration risk of a cantilever small branch pipe in a nuclear power plant. Background Art

[0002] The operating experience of nuclear power plants shows that small branch pipe connections are easily affected by vibration fatigue. A series of problems such as fatigue failure, leakage and fracture induced by vibration of small branch pipes have greatly affected the normal operation of nuclear power plants, causing great safety risks and economic losses.

[0003] It should be noted that small branches specifically refer to pipes with a nominal pipe diameter less than or equal to DN50.

[0004] Small branch vibration fatigue is characterized by cyclic stresses in the branch pipes caused by the fluctuations of the fluid inside the main pipe or by mechanical vibrations of the equipment connected to the pipe. Such conditions may be exacerbated by the added mass of the valve, resulting in high stress amplitudes, or may cause branch resonances due to the proximity of the structural natural frequency to the excitation.

[0005] At present, in order to deal with the vibration problem of small branches in nuclear power plants, the usual method is to discover the vibration problem during the power plant inspection and then evaluate and solve it. Faced with a large number of small branches in nuclear power plants, the power plant inspection is not targeted, and there is no systematic branch vibration risk assessment to actively predict vibration fatigue failure before it occurs to reduce the probability of failure.

[0006] Based on this, the inventor of the present application has designed a vibration risk assessment method and system for a cantilever small branch pipe in a nuclear power plant to overcome the above-mentioned technical problems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of the prior art that the vibration of small branch pipes is based on passive inspection of vibration measurement, the vibration risk assessment based on design analysis and the lack of active prediction capabilities, and to provide a method and system for vibration risk assessment of small branch pipes of cantilever in nuclear power plants.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] The present invention provides a vibration risk assessment method for a cantilever small branch pipe of a nuclear power plant, which is characterized by comprising:

[0010] Step 1: Obtain branch pipe parameters, and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters;

[0011] Step 2: Calculate the ratio of the concentrated mass of the valve to the uniformly distributed mass of the branch pipe, and determine the velocity coefficient and stress coefficient;

[0012] Step 3: Obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has a risk of vibration fatigue failure.

[0013] According to one embodiment of the present invention, in step 1,

[0014] The branch pipe parameters include: pipe material, pipe diameter, wall thickness, length and valve quality.

[0015] According to one embodiment of the present invention, the pump-induced vibration analysis process of step 3 includes:

[0016] Step 31, obtaining the pump speed, the number of blades, and the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump;

[0017] Step 32, calculating the excitation frequency of the pump;

[0018] Step 33, determining whether the excitation frequency is within 20% of the first-order natural frequency of the branch pipe;

[0019] Step 34, calculating the dynamic amplification factor of the excitation frequency ratio and calculating the vibration velocity and stress of the branch pipe;

[0020] Step 35: Compare the maximum calculated stress of the branch pipe under pump-induced vibration with the infinite life fatigue limit of the material to determine the failure risk.

[0021] According to one embodiment of the present invention, in step 32,

[0022] The excitation frequency of the pump is calculated as follows:

[0023]

[0024] Wherein, N is the number of blades, RPM is the pump speed, and m is the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump.

[0025] According to one embodiment of the present invention, in step 33,

[0026] If the excitation frequency of the pump is not within 20% of the first-order natural frequency of the branch pipe, the branch pipe has no risk of pump-induced vibration and the flow-induced vibration analysis is performed; if the excitation frequency of the pump is within 20% of the first-order natural frequency of the branch pipe, the step 34 is performed.

[0027] According to one embodiment of the present invention, in step 34,

[0028] The dynamic amplification factor Dr is as follows:

[0029]

[0030] Among them, ξ=0.02, β=f / f1; f1 is the first-order natural frequency of the branch pipe.

[0031] The formulas for the maximum vibration velocity and maximum stress of the branch pipe are as follows:

[0032] Vp=3.96*Vr*Dr;

[0033] Sp = 1.68 * Sr * Dr;

[0034] Wherein, Vp is the maximum velocity; Sp is the maximum stress considering the socket stress index; Vr is the velocity coefficient; Sr is the stress coefficient.

[0035] According to one embodiment of the present invention, in step 35,

[0036] If the maximum calculated stress is greater than the fatigue limit, the branch pipe has a risk of pump-induced vibration fatigue failure; if the maximum calculated stress is less than the fatigue limit, the branch pipe has no risk of pump-induced vibration fatigue failure and enters flow-induced vibration analysis.

[0037] According to one embodiment of the present invention, the flow-induced vibration analysis process in step 3 includes:

[0038] Step 36, obtaining the main pipeline information, and calculating the frequency ratio between the branch pipe and the main pipeline, and calculating the dynamic amplification coefficient under fluid excitation of the main pipe frequency and the branch pipe frequency;

[0039] Step 37, determining the turbulent kinetic energy and dynamic pressure and calculating the vibration velocity at the branch pipe seat under turbulent excitation;

[0040] Step 38, calculating the maximum vibration velocity and maximum stress of the branch pipe under turbulent excitation;

[0041] Step 39: superimpose the maximum calculated stress of the branch pipe under the pump-induced vibration and turbulence excitation, and compare it with the infinite life fatigue limit of the material to determine the failure risk.

[0042] According to one embodiment of the present invention, in step 36,

[0043] The main pipeline information includes: main pipe material, outer diameter, wall thickness, span, distance between branch pipe and nearest support and span ratio, operating condition pressure, temperature, flow rate and medium;

[0044] The dynamic amplification factor Dr under the fluid excitation of the main pipe frequency and the branch pipe frequency is as follows:

[0045]

[0046] in,

[0047] E is the elastic modulus of the material, I r is the moment of inertia of the main pipe section, A r is the cross-sectional area of ​​the main pipe, ρ r is the main pipe equivalent density of the medium; L r The main pipeline span.

[0048] According to one embodiment of the present invention, in step 37,

[0049] The turbulent kinetic energy and pressure are:

[0050]

[0051] Where Δp is the turbulent kinetic energy and pressure, in Pa, f t is the turbulent kinetic energy frequency;

[0052] The vibration speed at the branch pipe seat is:

[0053]

[0054] Among them, A ri is the flow area of ​​the main pipeline; α is the distance of the small branch pipe from the nearest support to the span ratio; ρ f is the density of the medium in operating conditions; v is the flow velocity of the main pipeline.

[0055] According to one embodiment of the present invention, in step 38,

[0056] The maximum vibration velocity and maximum stress of the branch pipe under turbulent excitation are:

[0057] Vf=135.8*Vs*Vr;

[0058] Sf=57.6*Vs*Sr;

[0059] Wherein, Vf is the maximum vibration velocity of the branch pipe; Sf is the maximum vibration stress of the branch pipe considering the pipe seat stress index.

[0060] According to one embodiment of the present invention, after step 39, the method further includes:

[0061] Step 40, determine whether there is a pressure reducing device around the branch pipe; if there is a pressure reducing device, calculate whether there is a risk of cavitation and high-frequency acoustic vibration in the main pipe; if there is no pressure reducing device, determine whether there is a risk of flow-induced acoustic vibration.

[0062] According to one embodiment of the present invention, the cavitation is determined by calculating the choked flow pressure drop; if the pressure loss of the pressure reducing device is greater than the choked flow pressure drop, cavitation will occur; otherwise, cavitation will not occur; wherein,

[0063] The choked flow pressure drop calculation formula is as follows:

[0064]

[0065] Among them, Δp m is the choked flow pressure drop, p1 is the upstream pressure, p 1c is the saturated vapor pressure corresponding to the upstream liquid temperature, p c is the thermodynamic critical pressure of water.

[0066] According to one embodiment of the present invention, the high-frequency acoustic vibration risk is calculated by the sound power level generated by the pressure reducing device. If the sound power level is greater than or equal to 155 dB, there is a high-frequency acoustic vibration risk; otherwise, there is no high-frequency acoustic vibration risk.

[0067] The sound power level is calculated as follows:

[0068]

[0069] Where p1 is the upstream pressure; p2 is the downstream pressure; W is the mass flow rate; T e is the upstream temperature; M w is the molecular molar mass.

[0070] According to one embodiment of the present invention, when there is no high-frequency acoustic vibration risk in the branch pipe, it is further determined whether there is a flow-induced acoustic vibration risk;

[0071] Among them, for the retention branch, if the vortex shedding frequency and the acoustic frequency are both within 20% of the first-order natural frequency of the cantilever small branch, there is a risk of flow-induced acoustic vibration, otherwise there is no risk of flow-induced acoustic vibration;

[0072] The formulas for vortex shedding frequency and acoustic frequency are as follows:

[0073]

[0074] Where v is the flow velocity of the main pipe, D is the inner diameter of the branch pipe, S is the Strouhal number, c is the sound velocity of the medium under operating conditions, and L is the length from the branch pipe to the closed end.

[0075] The present invention also provides a nuclear power plant cantilever small branch pipe vibration risk assessment system, which is characterized in that the nuclear power plant cantilever small branch pipe vibration risk assessment system adopts the nuclear power plant cantilever small branch pipe vibration risk assessment method according to any one of claims 1 to 15, and the assessment system comprises:

[0076] A dynamic characteristic acquisition module, used to acquire branch pipe parameters and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters;

[0077] Key parameter determination module, used to calculate the ratio of valve concentrated mass to branch pipe uniform mass, and determine the velocity coefficient and stress coefficient;

[0078] The vibration risk analysis module is used to obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has a risk of vibration fatigue failure.

[0079] The positive and progressive effects of the present invention are:

[0080] The vibration risk assessment method for a cantilever small branch pipe of a nuclear power plant of the present invention can analyze the pump-induced vibration and flow-induced vibration of the small branch pipe in turn, thereby detecting the vibration fatigue risk before the vibration fatigue failure occurs, reducing the vibration fatigue failure of the small branch pipe, and improving the safety and economy of the operation of the nuclear power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0082] Figure 1 It is a flow chart of the vibration risk assessment method of a cantilever small branch pipe of a nuclear power plant according to the present invention;

[0083] Figure 2 is the velocity coefficient of the cantilever small branch pipe of the present invention;

[0084] Figure 3 is the stress coefficient of the cantilever small branch pipe of the present invention;

[0085] Figure 4 It is a logical structure diagram of the cantilever small branch pipe vibration risk assessment method of the present invention;

[0086] Figure 5 It is a schematic structural diagram of the electronic device of the present invention. DETAILED DESCRIPTION

[0087] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0088] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Reference will now be made in detail to preferred embodiments of the present invention, examples of which are shown in the accompanying drawings. Wherever possible, the same reference numerals will be used in all drawings to represent the same or similar parts. In addition, although the terms used in the present invention are selected from well-known and commonly used terms, some of the terms mentioned in the specification of the present invention may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this article. In addition, it is required to understand the present invention not only by the actual terms used, but also by the meaning implied by each term.

[0089] Please refer to Figures 1 to 4 The present invention proposes a vibration risk assessment method for a cantilever small branch pipe of a nuclear power plant, comprising:

[0090] Step 1: Obtain branch pipe parameters, and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters.

[0091] Among them, branch pipe parameters include: pipeline material, pipe diameter, wall thickness, length and valve quality.

[0092] Step 2: Calculate the ratio of the concentrated mass of the valve to the uniformly distributed mass of the branch pipe, and determine the velocity coefficient and stress coefficient.

[0093] Specifically, the first-order natural frequency f1 of the cantilever small branch pipe is calculated according to the branch pipe parameters through theoretical or finite element modeling methods.

[0094] Among them, the ratio of the concentrated mass of the valve to the uniform mass of the branch pipe is μ, which can be specifically referred to Figure 2 and Figure 3 , Figure 2 and Figure 3 The coefficients in are obtained by analyzing the dynamic response of cantilever small branches with different branch sizes, different valve concentrated mass ratios, and different frequencies under the same excitation. Figure 2 The velocity coefficient Vr can be determined by Figure 3 The stress coefficient Sr can be determined. It can be seen that, Figure 2 and Figure 3 The coefficient has nothing to do with the cantilever branch size and frequency, but is only related to the valve concentrated mass ratio μ.

[0095] Step 3: Obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has a risk of vibration fatigue failure.

[0096] Specifically, the pump-induced vibration analysis process is as follows:

[0097] Step 31, obtaining the pump rotation speed, the number of blades, and the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump.

[0098] Step 32: Calculate the excitation frequency of the pump.

[0099] If the number of restraining supports of the main pipeline along the branch pipe transversely from the pump is less than two, the pump's rotational frequency and twice the rotational frequency mechanical vibration are considered to be transmitted to the branch pipe through the main pipeline, and the pump's excitation load frequency considers the rotational frequency, twice the rotational frequency, and N times the blade passing frequency.

[0100] If the number of supports is greater than or equal to two, the pump's rotational frequency and twice the rotational frequency mechanical vibration are basically absorbed by the main pipe support, and the vibration transmitted to the small branch pipe can be ignored. The pump's excitation load frequency only needs to consider the blade passing frequency N times the rotational frequency. Calculation formula 1 is as follows:

[0101]

[0102] Among them, the pump speed is RPM, the number of blades is N, and the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump is m.

[0103] Step 33: Determine whether the excitation frequency is within 20% of the first-order natural frequency of the branch pipe.

[0104] That is, it is determined whether the excitation frequency f is within 20% of the first-order natural frequency of the branch pipe: 0.8f1≤f≤1.2f1. f is the excitation frequency, and f1 is the first-order natural frequency of the branch pipe.

[0105] If the pump excitation frequency is not within 20% of the first-order natural frequency of the branch pipe, there is no risk of pump-induced vibration in the branch pipe, and flow-induced vibration analysis is performed; if the pump excitation frequency is within 20% of the first-order natural frequency of the branch pipe, a detailed pump-induced vibration analysis is performed, which can be specifically referred to the following steps:

[0106] Step 34, calculating the dynamic amplification factor of the excitation frequency ratio and calculating the branch pipe vibration velocity and stress.

[0107] The calculation formula 2 of the dynamic amplification factor is as follows:

[0108]

[0109] Among them, the damping ratio is generally taken as ξ=0.02, β=f / f1.

[0110] The vibration limit of the pump is generally taken as an effective value of 2.8mm / s, including the pump's rotational frequency, twice the rotational frequency and its blade frequency. The effective speed limit is fully converted into a maximum speed of 3.96mm / s at each main frequency. Then, under pump excitation, the calculation formula 3 for the maximum vibration speed Vp of the cantilever branch pipe is:

[0111] Vp=3.96*Vr*Dr; unit is mm / s; (3)

[0112] The stress index at the pipe seat is 4.0, and the calculation formula 4 of the maximum stress Sp is:

[0113] Sp=1.68*Sr*Dr; unit is MPa. (4)

[0114] Step 35: Compare the maximum calculated stress of the branch pipe under pump-induced vibration with the infinite life fatigue limit of the material to determine the failure risk.

[0115] Specifically, the maximum calculated stress of the cantilever small branch under pump-induced vibration is compared with the infinite life fatigue limit of the material to determine the failure risk, where the carbon steel limit is 48MPa and the stainless steel limit is 93.7MPa.

[0116] If the calculated stress is greater than the fatigue limit, the branch pipe is at risk of pump-induced vibration fatigue failure; if the calculated stress is less than the fatigue limit, the branch pipe is not at risk of pump-induced vibration fatigue failure and enters flow-induced vibration analysis.

[0117] The flow-induced vibration analysis process is as follows:

[0118] Step 36: Obtain the main pipeline information, calculate the frequency ratio between the branch pipe and the main pipeline, and calculate the dynamic amplification factor.

[0119] The main pipeline information includes: main pipe material, outer diameter, wall thickness, span L r , the distance between the branch pipe and the nearest support and the span ratio α, operating conditions pressure, temperature, flow and medium.

[0120] Use the following formula 5 to calculate the branch pipe to main pipe frequency ratio β1, and substitute β1 and 1 / β1 into the above formula respectively.

[0121] The β calculation dynamic amplification factor in formula 2 takes the maximum value of Dr, and the formula is as follows:

[0122]

[0123] in:

[0124] E is the elastic modulus of the material, I r is the moment of inertia of the main pipe section, A r is the cross-sectional area of ​​the main pipe, ρ r is the main pipe equivalent density of the medium under consideration.

[0125] Step 37, determine the turbulent kinetic energy and dynamic pressure and calculate the vibration velocity at the branch pipe seat under turbulent excitation.

[0126] It can be seen that when the fluid flows through a discontinuous position, turbulent excitation will be formed.

[0127] Although turbulence excitation is broadband, the main excitation is within 100 Hz. The lower the frequency, the higher the turbulence excitation. Therefore, attention should be paid to branches with lower frequencies.

[0128] Where, turbulent kinetic energy is ρv 2 / 2=10000kg / (m*s 2 ), the relationship between turbulent pressure and frequency can be expressed as the following formula 6:

[0129]

[0130] Where Δp is the turbulent kinetic energy and pressure, in Pa, f t is the turbulent kinetic energy frequency.

[0131] Then the vibration velocity Vs at the branch pipe seat under turbulent excitation can be calculated using the following formula 7:

[0132]

[0133] Among them, A ri is the main pipeline flow area, ct = ρ f v 2 / 20000,ρ f is the medium operating density, and v is the main pipeline flow velocity.

[0134] Step 38: Calculate the maximum vibration velocity and maximum stress of the branch pipe under turbulent excitation.

[0135] Since turbulent excitation is a broadband excitation, the total response of the branch pipe near the natural frequency needs to be considered. Combining the analysis and vibration measurement experience data, the ratio of the total response to the natural frequency response is 5.43. The maximum vibration velocity Vf of the cantilever branch pipe under turbulent excitation is shown in the following formula 8, in mm / s, and the formula is:

[0136] Vf=135.8*Vs*Vr; (8)

[0137] The stress index at the pipe seat is 4.0, and the maximum stress Sf is shown in the following formula 9, in MPa, and the formula is:

[0138] Sf=57.6*Vs*Sr. (9)

[0139] Step 39: Superimpose the maximum calculated stress of the branch pipe under pump-induced vibration and turbulence excitation, and compare it with the infinite life fatigue limit of the material to determine the failure risk.

[0140] Among them, the limit for carbon steel is 48MPa and the limit for stainless steel is 93.7MPa.

[0141] It should be noted that if the calculated stress is greater than the fatigue limit, the branch pipe is at risk of vibration fatigue failure; if the calculated stress is less than the fatigue limit, the branch pipe has no risk of vibration fatigue failure under pump-induced vibration and turbulence excitation, and the failure risks of other flow-induced vibration mechanisms need to be further evaluated.

[0142] Specifically, after step 39, the method further includes:

[0143] Step 40, determine whether there is a pressure reducing device around the branch pipe; if there is a pressure reducing device, calculate whether there is a risk of cavitation and high-frequency acoustic vibration in the main pipe; if there is no pressure reducing device, determine whether there is a risk of flow-induced acoustic vibration.

[0144] It is known that in piping systems, pressure relief devices, such as pressure relief valves, control valves or orifice plates, can cause cavitation flash under excessive pressure reduction. When the fluid changes from liquid to gas, flashing can cause potentially high levels of unstable vibration due to sudden changes in volume.

[0145] However, due to the formation and instantaneous collapse of countless tiny gaps or cavities in the liquid, cavitation will lead to high levels of vibration, and the risk of vibration fatigue failure of branch pipes near cavitation flash is relatively high.

[0146] Check whether there is a throttling element near the branch pipe. If so, calculate the blocked flow pressure drop according to the following formula. Formula 10 is as follows:

[0147]

[0148] Where p1 is the upstream pressure, p 1c is the saturated vapor pressure corresponding to the upstream liquid temperature, p c is the thermodynamic critical pressure of water.

[0149] If the pressure loss of the throttling element is greater than the choked flow pressure drop, the branch pipe is at risk of vibration fatigue failure. If the pressure loss of the throttling element is less than the choked flow pressure drop, the branch pipe is not at risk of vibration fatigue failure caused by cavitation flash.

[0150] Additionally, in piping systems, pressure relief devices can generate high levels of high-frequency acoustic energy, which can create acoustically induced vibrations that can lead to higher stresses in cantilevered branch pipes on the pipe wall.

[0151] The sound power level PWL generated by the pressure reducing device can be calculated by the following formula 11:

[0152]

[0153] Where p1 is the upstream pressure; p2 is the downstream pressure; W is the mass flow rate; T e is the upstream temperature; M w If the sound power level is greater than or equal to 155dB, the branch pipe has the risk of vibration fatigue failure; if the sound power level is less than 155dB, the branch pipe has no risk of high-frequency acoustic vibration fatigue failure.

[0154] Furthermore, the high-speed fluid in the main pipeline will form boundary layer separation and generate vortices at the stagnant branch pipe mouth. The vortices will continuously and evenly fall off periodically, generating pressure pulsations with a certain frequency range. When the fluid excitation frequency, acoustic frequency and structural frequency coincide, a relatively obvious pipeline flow-induced acoustic vibration problem will occur.

[0155] For the stranded cantilever branch pipe, the vortex shedding frequency is calculated according to the following formula 12:

[0156]

[0157] Where v is the main pipe velocity, D is the inner diameter of the small branch pipe, and S is the Strouhal number, which can be taken as 0.44 based on experience.

[0158] Then the acoustic frequency can be calculated according to the following formula 13:

[0159]

[0160] Where c is the medium sound velocity under the operating condition, and L is the length from the small branch to the closed end. v 、f a If both are within 20% of the first-order natural frequency f1 of the cantilever branch pipe, there is a risk of flow-induced acoustic vibration; otherwise, there is no risk of flow-induced acoustic vibration.

[0161] Example 1

[0162] A cantilevered small branch pipe with a steam trap is designed on the main pipeline before the inlet of an electric auxiliary pump. The small branch pipe is made of carbon steel, with an outer diameter of 26.7mm, a wall thickness of 2.87mm, a length of 238mm, and a valve weight of 6.482kg. A vibration risk assessment is conducted on the cantilevered small branch pipe.

[0163] Calculate the first-order natural frequency of the cantilever small branch f1 = 50.76Hz. Calculate the concentrated mass ratio and use Figure 2 Determine the velocity coefficient Vr using Figure 3 Determine the stress coefficient Sr.

[0164] The RPM of the electric auxiliary pump is 2975rpm, the number of blades N = 5, and the minimum number of pump supports along the lateral distance of the branch pipe is m = 0. The slidable supports that only bear their own weight have no vibration reduction effect and are not considered effective supports. The pump excitation frequencies are calculated according to the above formula 1 as 49.6Hz, 99.2Hz, and 248Hz. The rotation frequency of 49.6Hz in the pump excitation is within 20% of the first-order natural frequency of the cantilever branch pipe, and further detailed pump-induced vibration analysis is required.

[0165] The dynamic coefficient Dr is calculated according to the ratio of the pump excitation frequency to the first-order natural frequency of the cantilever small branch pipe and the above formula 2. According to the above formula 3, the vibration velocity of the cantilever small branch pipe under pump-induced vibration is 66.4 mm / s. According to the above formula 4, the stress of the cantilever small branch pipe under pump-induced vibration is 114.9 MPa, which is greater than the fatigue limit of carbon steel 48 MPa. Therefore, the cantilever small branch pipe of this embodiment has the risk of pump-induced vibration fatigue failure and needs to be redesigned, vibration monitored or modified.

[0166] Example 2

[0167] A cantilevered small branch pipe with a steam trap is designed on the outlet main pipe of an electric auxiliary pump. The branch pipe is made of carbon steel, with an outer diameter of 13.7 mm, a wall thickness of 2.24 mm, a length of 250 mm, and a valve weight of 2.5 kg. A vibration risk assessment is conducted on the cantilevered small branch pipe.

[0168] Calculate the first-order natural frequency of the cantilever branch pipe f1 = 22.64Hz. Calculate the concentrated mass ratio and use Figure 2 Determine the velocity coefficient Vr using Figure 3 Determine the stress coefficient Sr.

[0169] The RPM of the electric auxiliary pump is obtained to be 2975 rpm, the number of blades N=5, and the minimum number of blades m=3 along the lateral distance of the branch pipe from the pump support. The pump excitation frequency is calculated according to the above formula 1 to be the blade pass frequency of 248 Hz.

[0170] The pump excitation frequency of 248 Hz is not within 20% of the first-order natural frequency of the cantilever branch pipe. The cantilever branch pipe has no pump-induced vibration risk and flow-induced vibration analysis is required.

[0171] Get the main pipe outer diameter 273mm, wall thickness 6.35mm, span L r =4614mm, the distance of the small branch pipe from the nearest support to the span ratio α=0.274. The main medium under operating conditions is water at room temperature with a flow rate of 4m / s. According to the above formula 8, the vibration velocity of the cantilever small branch pipe under turbulent excitation is 112.5mm / s. According to the above formula 9, the flow-induced vibration stress of the cantilever branch small pipe under turbulent excitation is 201.2MPa. The calculated stress is greater than the fatigue limit of carbon steel 48MPa. Therefore, the cantilever branch pipe of this embodiment has the risk of flow-induced vibration fatigue failure and needs to be redesigned, vibration monitored or modified.

[0172] The main reason for the high risk of flow-induced vibration in the cantilevered small branch pipe in this embodiment is that the frequency of the cantilevered small branch pipe is low and close to the frequency of the main pipe, resulting in vibration amplification at the natural frequency of the main pipe under turbulent excitation, and further superposition amplification at the natural frequency of the small branch pipe.

[0173] Example 3

[0174] This embodiment is a vibration risk analysis after the design optimization of Example 2, and the design of the small branch is optimized to shorten the length of the small branch to 200mm. The first-order natural frequency of the cantilever small branch after calculation is f1=31.7Hz. The pump excitation frequency is not within 20% of the first-order natural frequency of the cantilever branch, and the cantilever branch has no pump-induced vibration risk. According to the above formula 8, the vibration velocity of the cantilever small branch under turbulent excitation is 11.69mm / s. According to the above formula 9, the flow-induced vibration stress of the cantilever small branch under turbulent excitation is 23.23MPa, and the calculated stress is less than the fatigue limit of carbon steel 48MPa. Therefore, the cantilever branch after design optimization has no risk of vibration fatigue failure under turbulent excitation.

[0175] Example 4

[0176] A throttling orifice plate is designed on the small flow pipeline of a certain injection system. There is a cantilevered small branch pipe downstream of the orifice plate. The small branch pipe is made of stainless steel with an outer diameter of 26.7mm, a wall thickness of 2.11mm, a length of 250mm, and a valve weight of 7kg. A vibration risk assessment is conducted on the cantilevered small branch pipe.

[0177] Calculate the first-order natural frequency of the cantilever small branch f1 = 8.25Hz. Calculate the concentrated mass ratio and use Figure 2 Determine the velocity coefficient Vr using Figure 3 Determine the stress coefficient Sr.

[0178] The RPM of the electric auxiliary pump is obtained to be 2975 rpm, the number of blades N=5, and the minimum number of blades m=3 along the lateral distance of the branch pipe from the pump support. The pump excitation frequency is calculated according to the above formula 1 to be the blade pass frequency of 123.3 Hz.

[0179] The pump excitation frequency of 123.3 Hz is not within 20% of the first-order natural frequency of the cantilever small branch. The cantilever small branch has no pump-induced vibration risk and flow-induced vibration analysis is required.

[0180] Get the main pipe outer diameter 114.3mm, wall thickness 3.05mm, span L r =3315mm, the distance of the branch pipe from the nearest support to the span ratio α=0.371. The main medium under the operating condition is water at room temperature, with a flow rate of 5m / s. According to the above formula 8, the vibration speed of the cantilever small branch pipe under turbulent excitation is 25.1mm / s. According to the above formula 9, the vibration stress of the cantilever small branch pipe under turbulent excitation is 28.9MPa, and the calculated stress is less than the fatigue limit of stainless steel 93.7MPa. Therefore, the cantilever branch pipe of this embodiment has no risk of turbulent excitation vibration fatigue failure, and the failure risk of other flow-induced vibration mechanisms needs to be further evaluated.

[0181] There is a throttling orifice upstream of the small branch pipe, where the pressure before the orifice is 1.65 MPa and the orifice pressure drop is 1.55 MPa. According to the above formula 10, the choked flow pressure drop is 1.31 MPa. If the orifice pressure drop is greater than the choked pressure drop, cavitation will occur in the main pipe and the small branch pipe is at risk of vibration fatigue failure.

[0182] The vibration risk assessment method for cantilever small branch pipes of nuclear power plants proposed in the present invention is based on the laws formed by a large number of small branch pipe vibration case tests and dynamic response analysis, combined with the mechanism characteristics of pump-induced vibration and flow-induced vibration, and quantitatively gives the vibration risk assessment results of cantilever small branch pipes of nuclear power plants. It can detect vibration fatigue risks before vibration fatigue failures occur, reduce branch pipe vibration fatigue failures, and improve the safety and economy of nuclear power plant operation by improving detection methods, vibration monitoring, vibration control and other measures.

[0183] The present invention also proposes a nuclear power plant cantilever small branch pipe vibration risk assessment system, the nuclear power plant cantilever small branch pipe vibration risk assessment system adopts the nuclear power plant cantilever small branch pipe vibration risk assessment method as described above, and the assessment system comprises:

[0184] A dynamic characteristic acquisition module is used to obtain branch pipe parameters and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters;

[0185] Key parameter determination module, used to calculate the ratio of valve concentrated mass to branch pipe uniform mass, and determine the velocity coefficient and stress coefficient;

[0186] The vibration risk analysis module is used to obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has the risk of vibration fatigue failure.

[0187] Reference Figure 5 The present invention also provides an electronic device 900, including: a processor 901 and a memory 902, the memory 902 stores a program or instruction that can be run on the processor 901, and the program or instruction is executed by the processor 901 to implement the above-mentioned nuclear power plant cantilever small branch vibration risk assessment method. When the program or instruction is executed by the processor 901, each process of the implementation method of the above-mentioned nuclear power plant cantilever small branch vibration risk assessment method is implemented, and the same technical effect can be achieved. In order to avoid repetition, it will not be repeated here.

[0188] The present invention also provides a readable storage medium, on which a program or instruction is stored, and when the program or instruction is executed by a processor, the vibration risk assessment method for a small branch pipe of a cantilever of a nuclear power plant as described above is implemented. When the program or instruction is executed by a processor, each process of the implementation method of the vibration risk assessment method for a small branch pipe of a cantilever of a nuclear power plant described above is implemented, and the same technical effect can be achieved, and in order to avoid repetition, it will not be described here.

[0189] For those skilled in the art, the above invention disclosure is only used as an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary implementation of the present application.

[0190] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0191] Some aspects of the present application may be performed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The above hardware or software may be referred to as "data blocks", "modules", "engines", "units", "components" or "systems". The processor may be one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. In addition, various aspects of the present application may be expressed as computer products located in one or more computer-readable media, which include computer-readable program codes. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, tapes ...), optical disks (e.g., compact disks CDs, digital versatile disks DVDs ...), smart cards, and flash memory devices (e.g., cards, sticks, key drives ...).

[0192] A computer-readable medium may include a propagated data signal containing computer program code, such as in baseband or as part of a carrier wave. The propagated signal may have a variety of manifestations, including electromagnetic, optical, etc., or a suitable combination. A computer-readable medium may be any computer-readable medium other than a computer-readable storage medium, which may be connected to an instruction execution system, device or apparatus to communicate, propagate or transmit a program for use. The program code on the computer-readable medium may be propagated via any suitable medium, including radio, cable, fiber optic cable, radio frequency signal, or similar medium, or any combination of the above mediums.

[0193] Similarly, it should be noted that in order to simplify the description disclosed in this application, so as to help understand one or more embodiments of the invention, in the above description of the embodiments of the present application, sometimes multiple features are merged into one embodiment, drawings or descriptions thereof. However, this disclosure method does not mean that the features required by the object of the present application are more than the features mentioned in the claims. In fact, the features of the embodiment are less than all the features of the single embodiment disclosed above. In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "approximately", "approximately" or "substantially" in some examples. Unless otherwise specified, "approximately", "approximately" or "substantially" indicate that the number allows a variation of ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may change according to the characteristics required by individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining the digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of the present application are approximate values, in specific embodiments, such numerical settings are as accurate as possible within the feasible range.

[0194] Although the present invention is disclosed as above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A vibration risk assessment method for a cantilever small branch pipe in a nuclear power plant, characterized in that: include: Step 1: Obtain branch pipe parameters, and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters; Step 2: Calculate the ratio of the concentrated mass of the valve to the uniformly distributed mass of the branch pipe, and determine the velocity coefficient and stress coefficient; Step 3: Obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has a risk of vibration fatigue failure.

2. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 1 is characterized in that: In the step 1, The branch pipe parameters include: pipe material, pipe diameter, wall thickness, length and valve quality.

3. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 1 is characterized in that: The pump-induced vibration analysis process of step 3 includes: Step 31, obtaining the pump speed, the number of blades, and the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump; Step 32, calculating the excitation frequency of the pump; Step 33, determining whether the excitation frequency is within 20% of the first-order natural frequency of the branch pipe; Step 34, calculating the dynamic amplification factor of the excitation frequency ratio and calculating the vibration velocity and stress of the branch pipe; Step 35: Compare the maximum calculated stress of the branch pipe under pump-induced vibration with the infinite life fatigue limit of the material to determine the failure risk.

4. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 3 is characterized in that: In the step 32, The excitation frequency of the pump is calculated as follows: Wherein, N is the number of blades, RPM is the pump speed, and m is the minimum number of lateral supports of the main pipeline along the branch pipe between the branch pipe and the pump.

5. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 3 is characterized in that: In the step 33, If the excitation frequency of the pump is not within 20% of the first-order natural frequency of the branch pipe, the branch pipe has no risk of pump-induced vibration and the flow-induced vibration analysis is performed; if the excitation frequency of the pump is within 20% of the first-order natural frequency of the branch pipe, the step 34 is performed.

6. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 3 is characterized in that: In step 34, The dynamic amplification factor Dr is as follows: Where, ξ=0.02, β=f / f1; f1 is the first-order natural frequency of the branch pipe; The formulas for the maximum vibration velocity and maximum stress of the branch pipe are as follows: Vp=3.96*Vr*Dr; Sp = 1.68 * Sr * Dr; Wherein, Vp is the maximum velocity; Sp is the maximum stress considering the socket stress index; Vr is the velocity coefficient; Sr is the stress coefficient.

7. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 3 is characterized in that: In step 35, If the maximum calculated stress is greater than the fatigue limit, the branch pipe has a risk of pump-induced vibration fatigue failure; if the maximum calculated stress is less than the fatigue limit, the branch pipe has no risk of pump-induced vibration fatigue failure and enters flow-induced vibration analysis.

8. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 1, characterized in that: The flow-induced vibration analysis process in step 3 includes: Step 36, obtaining the main pipeline information, and calculating the frequency ratio between the branch pipe and the main pipeline, and calculating the dynamic amplification coefficient under fluid excitation of the main pipe frequency and the branch pipe frequency; Step 37, determining the turbulent kinetic energy and dynamic pressure and calculating the vibration velocity at the branch pipe seat under turbulent excitation; Step 38, calculating the maximum vibration velocity and maximum stress of the branch pipe under turbulent excitation; Step 39: superimpose the maximum calculated stress of the branch pipe under the pump-induced vibration and turbulence excitation, and compare it with the infinite life fatigue limit of the material to determine the failure risk.

9. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 8, characterized in that: In step 36, The main pipeline information includes: main pipe material, outer diameter, wall thickness, span, distance between branch pipe and nearest support and span ratio, operating condition pressure, temperature, flow rate and medium; The dynamic amplification factor Dr under the fluid excitation of the main pipe frequency and the branch pipe frequency is as follows: in, E is the elastic modulus of the material, I r is the moment of inertia of the main pipe section, A r is the cross-sectional area of ​​the main pipe, ρ r is the main pipe equivalent density of the medium; L r The main pipeline span.

10. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 8, characterized in that: In step 37, The turbulent kinetic energy and pressure are: Where Δp is the turbulent kinetic energy and pressure, in Pa, f t is the turbulent kinetic energy frequency; The vibration speed at the branch pipe seat is: Among them, A ri is the flow area of ​​the main pipeline; α is the distance of the small branch pipe from the nearest support to the span ratio; ρ f is the density of the medium in operating conditions; v is the flow velocity of the main pipeline.

11. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 8, characterized in that: In step 38, The maximum vibration velocity and maximum stress of the branch pipe under turbulent excitation are: Vf=135.8*Vs*Vr; Sf=57.6*Vs*Sr; Wherein, Vf is the maximum vibration velocity of the branch pipe; Sf is the maximum vibration stress of the branch pipe considering the pipe seat stress index.

12. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 8, characterized in that: After step 39, the method further includes: Step 40, determine whether there is a pressure reducing device around the branch pipe; if there is a pressure reducing device, calculate whether there is a risk of cavitation and high-frequency acoustic vibration in the main pipe; if there is no pressure reducing device, determine whether there is a risk of flow-induced acoustic vibration.

13. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 12, characterized in that: The cavitation is determined by calculating the choked flow pressure drop; if the pressure loss of the pressure reducing device is greater than the choked flow pressure drop, cavitation will occur; otherwise, cavitation will not occur; wherein, The choked flow pressure drop calculation formula is as follows: Among them, Δp m is the choked flow pressure drop, p1 is the upstream pressure, p 1c is the saturated vapor pressure corresponding to the upstream liquid temperature, p c is the thermodynamic critical pressure of water.

14. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 12, characterized in that: The high-frequency acoustic vibration risk is calculated by the sound power level generated by the pressure reducing device. If the sound power level is greater than or equal to 155 dB, there is a high-frequency acoustic vibration risk; otherwise, there is no high-frequency acoustic vibration risk; The sound power level is calculated as follows: Where p1 is the upstream pressure; p2 is the downstream pressure; W is the mass flow rate; T e is the upstream temperature; M w is the molecular molar mass.

15. The vibration risk assessment method for cantilever small branch pipes in nuclear power plants according to claim 14, characterized in that: When the branch pipe does not have a high-frequency acoustic vibration risk, further determining whether there is a flow-induced acoustic vibration risk; Among them, for the retention branch, if the vortex shedding frequency and the acoustic frequency are both within 20% of the first-order natural frequency of the cantilever small branch, there is a risk of flow-induced acoustic vibration, otherwise there is no risk of flow-induced acoustic vibration; The formulas for vortex shedding frequency and acoustic frequency are as follows: Where v is the flow velocity of the main pipe, D is the inner diameter of the branch pipe, S is the Strouhal number, c is the sound velocity of the medium under operating conditions, and L is the length from the branch pipe to the closed end.

16. A vibration risk assessment system for cantilever small branch pipes in a nuclear power plant, characterized in that: The nuclear power plant cantilever small branch pipe vibration risk assessment system adopts the nuclear power plant cantilever small branch pipe vibration risk assessment method according to any one of claims 1 to 15, and the assessment system comprises: A dynamic characteristic acquisition module, used to acquire branch pipe parameters and calculate the first-order natural frequency of the branch pipe according to the branch pipe parameters; Key parameter determination module, used to calculate the ratio of valve concentrated mass to branch pipe uniform mass, and determine the velocity coefficient and stress coefficient; The vibration risk analysis module is used to obtain pump information and main pipeline information and perform pump-induced vibration analysis and flow-induced vibration analysis in sequence to determine whether the branch pipe has a risk of vibration fatigue failure.

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