Loss analysis method and residual life evaluation method of high-temperature header and computer

Abstract

The invention discloses a loss analysis method, a residual life evaluation method and a computer for a high-temperature header, and the method comprises the steps: determining a reference temperature, and carrying out the fatigue loss analysis of an examination point, so as to obtain a first fatigue loss value; judging the type of the assessment point according to the fatigue loss value; determining creep reference stress for the assessment points with insignificant fatigue influence, and performing creep loss analysis on the assessment points to obtain a first creep loss value, and taking the first creep loss value as a total loss value; and for the assessment points with obvious fatigue influence, obtaining a temperature field and a stress field of the high-temperature header changing with time, respectively carrying out fatigue loss analysis and creep loss analysis on the assessment points to obtain a second fatigue loss value and a second creep loss value, and taking the sum of the two values as a total loss value. By implementing the technical scheme of the invention, quantitative calculation of loss analysis of the high-temperature header of the overdue service and high-frequency deep adjustment generator set can be realized, so that a basis is provided for residual life evaluation of the high-temperature header.

Description

Technical Field

[0001] The present invention relates to the field of power generation, and in particular to a loss analysis method, a remaining life assessment method and a computer for a high-temperature header. Background Art

[0002] The high temperature header is a key component related to the safety of the high temperature pressure boundary of the thermal power unit boiler. Creep and fatigue loads are the main reasons for the loss of life of the high temperature header of the power station boiler. At present, there is no clear creep and fatigue loss analysis method for the high temperature header of the over-service and high-frequency deep-tuning generator set, and it is impossible to evaluate its remaining life. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a loss analysis method, a remaining life assessment method and a computer for a high-temperature header in view of the above-mentioned technical defects in the prior art.

[0004] The technical solution adopted by the present invention to solve the technical problem is: constructing a loss analysis method of a high-temperature header, which is used to perform loss analysis on the assessment points of the high-temperature header, including:

[0005] Step S11, determining a reference temperature, and performing fatigue loss analysis on the assessment point according to the reference temperature and structural parameters of the high-temperature header to obtain a first fatigue loss value;

[0006] Step S12, judging the type of the assessment point according to the fatigue loss value, the type including: insignificant fatigue impact and significant fatigue impact;

[0007] Step S13, for the assessment point where fatigue influence is not significant, determine the creep reference stress, and perform creep loss analysis on the assessment point according to the creep reference stress to obtain a first creep loss value, and use the first creep loss value as the total loss value of the assessment point;

[0008] Step S14, for the assessment points with significant fatigue influence, obtain the temperature field and stress field of the high-temperature header that change with time, and based on the temperature field and stress field, perform fatigue loss analysis and creep loss analysis on the assessment points respectively to obtain a second fatigue loss value and a second creep loss value, and take the sum of the second fatigue loss value and the second creep loss value as the total loss value of the assessment point.

[0009] Optionally, the step S11 includes:

[0010] Step S111, respectively determining a reference temperature for each fatigue condition, and determining a material characteristic parameter for each fatigue condition according to the reference temperature;

[0011] Step S112, respectively calculating the fatigue stress range of the assessment point under various fatigue conditions according to the material characteristic parameters and the structural parameters of the high temperature header;

[0012] Step S113, determining the allowable number of cycles for each fatigue condition according to the fatigue stress range of each fatigue condition and a preset material fatigue performance curve;

[0013] Step S114, obtaining the actual number of operations of each fatigue condition, and calculating the first fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

[0014] Optionally, in step S114, the first fatigue loss value of the assessment point is calculated according to the following formula:

[0015]

[0016] Among them, D f is the first fatigue loss value, k is the number of fatigue conditions, n i is the actual number of operations of the i-th fatigue condition, N fi is the allowable number of cycles for the i-th fatigue condition.

[0017] Optionally, in step S13, the first creep loss value is obtained according to the following steps:

[0018] Step S131, determining the creep reference stress of each creep condition according to the material of the high temperature header, and calculating the allowable creep rupture life of the assessment point in each creep condition according to the creep reference stress of each creep condition;

[0019] Step S132, calculating the first creep loss value of the assessment point according to the allowable creep rupture life and the actual service time of each creep condition.

[0020] Optionally, the first creep loss value of the assessment point is calculated according to the following formula:

[0021]

[0022] Among them, D c is the first creep loss value, m is the number of creep conditions, t i is the service time of the i-th creep condition, is the creep reference stress corresponding to the i-th creep condition And the allowable creep rupture life at service temperature T.

[0023] Optionally, in step S14, the second fatigue loss value is calculated according to the following steps:

[0024] Step S141, according to various fatigue conditions, creep conditions and preset temperature-pressure relationship curves of the high-temperature header, the temperature field and stress field of the high-temperature header that change with time are obtained by modeling and finite element analysis of the high-temperature header, and the total stress range of the assessment point in each fatigue condition is calculated respectively according to the temperature field and stress field;

[0025] Step S142, determining the allowable number of cycles for each fatigue condition according to the total stress range and a preset material fatigue performance curve;

[0026] Step S143, calculating the second fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

[0027] Optionally, in step S14, the second creep loss value is calculated according to the following steps:

[0028] Step S144, determining the creep stress of each creep condition according to the temperature field and the stress field;

[0029] Step S145, calculating the allowable creep rupture time of the assessment point in each creep condition according to the creep stress in each creep condition;

[0030] Step S146, calculating the second creep loss value of the assessment point according to the allowable creep rupture life and service time of each creep condition.

[0031] Optionally, the second creep loss value of the assessment point is calculated according to the following formula:

[0032]

[0033] Among them, D c ' is the second creep loss value, m is the number of creep conditions, T dj is the allowable creep rupture time corresponding to the service temperature and structural stress during the jth creep condition, and t is the service time of the material under the corresponding temperature and structural stress during the jth creep condition.

[0034] The present invention also constructs a method for evaluating the remaining life of a high-temperature header, comprising:

[0035] Step S10, determining a plurality of assessment points to be analyzed on the high temperature header;

[0036] Step S20, for each assessment point, determine the total loss value of the assessment point according to the loss analysis method of the high temperature header described above;

[0037] Step S30, selecting a maximum total loss value from the total loss values ​​of multiple assessment points and using it as the life assessment loss value;

[0038] Step S40: determining the remaining life of the high temperature header according to the life assessment loss value.

[0039] The present invention also constructs a computer, including a processor and a memory storing a computer program, wherein the processor implements the above-mentioned high-temperature header loss analysis method and / or the above-mentioned high-temperature header remaining life assessment method when executing the computer program.

[0040] Through the technical solution of the present invention, first, under the influence of a single fatigue load, the reference temperature is determined, and the first fatigue loss value is determined according to the reference temperature and the structural parameters of the high-temperature header. Then, the type of the assessment point is determined based on the determined first fatigue loss value. For assessment points where fatigue influence is not significant, the first creep loss value is determined according to the determined creep reference stress, and the first creep loss value is used as the total loss value of the assessment point; for assessment points where fatigue influence is significant, the temperature field and stress field that change with time are first obtained, and then the second fatigue loss value and the second creep loss value are obtained according to the temperature field and the stress field, respectively, and the sum of the two is used as the total loss value of the assessment point. Therefore, the quantitative calculation of the loss analysis of the high-temperature header of the over-service and high-frequency deep-tuning generator set can be realized, thereby providing a basis for the remaining life assessment of the high-temperature header. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0042] Figure 1 It is a flow chart of Embodiment 1 of the loss analysis method of the high temperature header of the present invention;

[0043] Figure 2 is a graph of the fatigue performance curve of the material of the present invention;

[0044] Figure 3 is a graph of the creep-fatigue envelope curve of the present invention;

[0045] Figure 4 It is a flow chart of Embodiment 1 of the method for assessing the remaining life of a high-temperature header according to the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The high temperature header will produce certain losses due to the influence of creep and fatigue loads, thus affecting its life. This application analyzes the creep and fatigue losses of the high temperature header in combination with the structural characteristics of the high temperature header and the actual service environment, and evaluates the remaining life of the high temperature header.

[0048] Figure 1 1 is a flow chart of a first embodiment of a loss analysis method for a high temperature header of the present invention. The loss analysis method of this embodiment is used to perform loss analysis on the assessment points of the high temperature header, and specifically includes the following steps:

[0049] Step S11, determining a reference temperature, and performing fatigue loss analysis on the assessment point according to the reference temperature and structural parameters of the high-temperature header to obtain a first fatigue loss value;

[0050] Step S12, judging the type of the assessment point according to the fatigue loss value, the type including: insignificant fatigue impact and significant fatigue impact;

[0051] In a specific embodiment, the type of the assessment point can be determined according to the following method: if the first fatigue loss value is greater than 5%, the assessment point is determined to be an assessment point with significant fatigue influence; if the first fatigue loss value is not greater than 5%, the assessment point is determined to be an assessment point with insignificant fatigue influence.

[0052] Step S13, for the assessment point where fatigue influence is not significant, determine the creep reference stress, and perform creep loss analysis on the assessment point according to the creep reference stress to obtain a first creep loss value, and use the first creep loss value as the total loss value of the assessment point;

[0053] In this step, for assessment points where fatigue effects are not significant, the effect of fatigue damage on the equipment can be ignored, and only the effect of creep loss on the equipment can be considered.

[0054] Step S14, for the assessment points with significant fatigue influence, obtain the temperature field and stress field of the high-temperature header that change with time, and based on the temperature field and stress field, perform fatigue loss analysis and creep loss analysis on the assessment points respectively to obtain a second fatigue loss value and a second creep loss value, and take the sum of the second fatigue loss value and the second creep loss value as the total loss value of the assessment point.

[0055] In this step, for the assessment points with significant fatigue effects, the effect of the coupling effect of creep load and fatigue load on material fatigue failure should be considered.

[0056] In the technical solution of this embodiment, first, under the influence of a single fatigue load, a reference temperature is determined, and a first fatigue loss value is determined based on the reference temperature and the structural parameters of the high-temperature header. Then, the type of the assessment point is determined based on the determined first fatigue loss value. For assessment points where fatigue influence is not significant, the first creep loss value is determined based on the determined creep reference stress, and the first creep loss value is used as the total loss value of the assessment point; for assessment points where fatigue influence is significant, the temperature field and stress field that change with time are first obtained, and then the second fatigue loss value and the second creep loss value are obtained respectively based on the temperature field and the stress field, and the sum of the two is used as the total loss value of the assessment point. Therefore, the quantitative calculation of the loss analysis of the high-temperature header of the over-service and high-frequency deep-tuning generator set can be realized, thereby providing a basis for the remaining life assessment of the high-temperature header.

[0057] Furthermore, step S11 includes:

[0058] Step S111, respectively determining a reference temperature for each fatigue condition, and determining a material characteristic parameter for each fatigue condition according to the reference temperature;

[0059] Step S112, respectively calculating the fatigue stress range of the assessment point under various fatigue conditions according to the material characteristic parameters and the structural parameters of the high temperature header;

[0060] Step S113, determining the allowable number of cycles for each fatigue condition according to the fatigue stress range of each fatigue condition and a preset material fatigue performance curve;

[0061] Step S114, obtaining the actual number of operations of each fatigue condition, and calculating the first fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

[0062] Furthermore, in step S114, the first fatigue loss value of the assessment point is calculated according to the following formula:

[0063]

[0064] Among them, D f is the first fatigue loss value, k is the number of fatigue conditions, n i is the actual number of operations of the i-th fatigue condition, N fi is the allowable number of cycles for the i-th fatigue condition.

[0065] Further, in step S13, the first creep loss value is obtained according to the following steps:

[0066] Step S131, determining the creep reference stress of each creep condition according to the material of the high temperature header, and calculating the allowable creep rupture life of the assessment point in each creep condition according to the creep reference stress of each creep condition;

[0067] Step S132, calculating the first creep loss value of the assessment point according to the allowable creep rupture life and the actual service time of each creep condition.

[0068] Further, in step S132, the first creep loss value of the assessment point is calculated according to the following formula:

[0069]

[0070] Among them, D c is the first creep loss value, m is the number of creep conditions, t i is the service time of the i-th creep condition, is the creep reference stress corresponding to the i-th creep condition And the allowable creep rupture life at service temperature T.

[0071] Further, in an optional embodiment, in step S14, the second fatigue loss value is calculated according to the following steps:

[0072] Step S141, according to various fatigue conditions, creep conditions and preset temperature-pressure relationship curves of the high-temperature header, the temperature field and stress field of the high-temperature header that change with time are obtained by modeling and finite element analysis of the high-temperature header, and the total stress range of the assessment point in each fatigue condition is calculated respectively according to the temperature field and stress field;

[0073] Step S142, determining the allowable number of cycles for each fatigue condition according to the total stress range and a preset material fatigue performance curve;

[0074] Step S143, calculating the second fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

[0075] Further, in an optional embodiment, in step S14, the second creep loss value is calculated according to the following steps:

[0076] Step S144, determining the creep stress of each creep condition according to the temperature field and the stress field;

[0077] Step S145, calculating the allowable creep rupture time of the assessment point in each creep condition according to the creep stress in each creep condition;

[0078] Step S146, calculating the second creep loss value of the assessment point according to the allowable creep rupture life and service time of each creep condition.

[0079] Further, in step S146, the second creep loss value of the test point is calculated according to the following formula:

[0080]

[0081] Among them, D c ' is the second creep loss value, m is the number of creep conditions, T dj is the allowable creep rupture time corresponding to the service temperature and structural stress during the jth creep condition, and t is the service time of the material under the corresponding temperature and structural stress during the jth creep condition.

[0082] The following is a detailed description of the process of loss analysis of the assessment points of the high temperature header:

[0083] 1. Analysis of fatigue loss

[0084] (1) Determine fatigue conditions

[0085] The fatigue conditions (fatigue loss calculation conditions) of the high temperature header should cover all the types of conditions experienced during the operation of the high temperature header, including: cold start and stop of the boiler, warm start and stop, hot start and stop, variable load operation, water pressure test and safety door verification, etc. If there are several of the above conditions during the start and stop of the boiler, only a few of them will be calculated.

[0086] (2) Determine the reference temperature

[0087] The material properties of the component during the cycle are a function of temperature, and the material properties change continuously throughout the loading cycle. During the material fatigue loss stress calculation process, the physical properties of the material can be determined based on the reference temperature. The reference temperature during the fatigue condition can be calculated using Formula 1:

[0088] t * =0.75×t max +0.25×t min Formula 1

[0089] Among them, t * is the reference temperature; tmax is the metal temperature corresponding to the peak stress during cyclic loading; tmin is the metal temperature corresponding to the valley stress during cyclic loading.

[0090] (3) Calculation of fatigue stress range

[0091] During the operation of the unit, the alternating load of the high-temperature header body is generated by the fluctuation of temperature and pressure. The fatigue stress calculation of the high-temperature header is mainly based on the alternating thermal stress caused by temperature and the alternating internal pressure stress caused by internal pressure in fatigue conditions. Under the action of temperature load, it is assumed that the highest stress area also appears on the inner wall of the branch pipe connection and coincides with the maximum pressure stress point.

[0092] The principal stress at the test point can be calculated by formula 2 to formula 4:

[0093] σ 1 =σ cir =σ cir,P +σ cir,T Formula 2

[0094] σ 2 =σ rad =-p Formula 3

[0095] σ 3 =σ axi =-p Formula 4

[0096] Among them, σ cir , σ rad and σ axi are the annular, radial and axial stresses of the test point, σ cir,P is the hoop stress at the test point caused by internal pressure, σ cir,T is the hoop stress at the test point caused by temperature rise, and p is the internal pressure calculated during fatigue loss analysis.

[0097] Hoop stress due to internal pressureσ cir,p It can be calculated by formula 5 to formula 9:

[0098]

[0099] A=-1.14(e b / e h ) 2 -0.89(e b / e h )+1.43 Formula 8

[0100] B = 0.326 (e b / e h ) 2 -0.59(e b / e h )+1.08 Formula 9

[0101] Among them, α p is the internal pressure stress concentration factor, D his the cylinder diameter of the high temperature header, e h is the thickness of the high temperature header, d b is the branch pipe diameter, e b is the branch thickness, A and B are the stress concentration structure size coefficients.

[0102] Hoop stress σ at the test point due to temperature rise cir,T It can be calculated by formula 10 to formula 11:

[0103]

[0104] Among them, α t is the temperature rise stress concentration factor, is the reference temperature t * Thermal expansion coefficient of materials under the conditions, Under the reference temperature condition, t * The elastic modulus of the material, v is the Poisson's ratio of the material, and h is the heat transfer coefficient between the high-temperature header and the internal medium. For steam medium, it can be 1000W / m 2 K; z is the size coefficient, z = d b / d h ; Vt is the temperature difference of the header cylinder along the wall thickness direction. When the header steam temperature rises, Vt>0, and when the header steam temperature decreases, Vt<0, thus generating a cyclic thermal stress range. Vt can be obtained by referring to the unit operating procedures and the unit DSC system header operation record curve.

[0105] The peak principal stress difference components of the high temperature header alternating load caused by the fluctuation of temperature and pressure are shown in formulas 12 to 14, and the valley principal stress difference components of the header alternating load caused by the fluctuation of temperature and pressure are shown in formulas 15 to 17:

[0106] σ f12 =σ f1 -σ f2 Formula 12

[0107] σ f23 =σ f2 -σ f3 Formula 13

[0108] σ f31 =σ f3 -σ f1 Formula 14

[0109] σ g12 =σ g1 -σ g2 Formula 15

[0110] σ g23 =σ g2 -σg3 Formula 16

[0111] σ g31 = σ g3 - σ g1 Formula 17

[0112] where, Vσ fi (i = 1, 2, 3) are the peak principal stresses, and Vσ gi (i = 1, 2, 3) are the valley principal stresses, and the peak / trough principal stress values can be obtained by calculating with Formulas 2 to 4.

[0113] Assuming that the main direction of the assessment point of the pressure-bearing component remains unchanged, then when the assessment point is at the peak (trough), the principal stress difference components Vσ 12 , Vσ 23 and Vσ 13 can be calculated by Formulas 18 to 20:

[0114] Vσ 12 = |σ f12 - σ g12 | Formula 18

[0115] Vσ 23 = |σ f23 - σ g23 | Formula 19

[0116] Vσ 31 = |σ f31 - σ g31 | Formula 20

[0117] The calculation formula for the fatigue stress range Vσ under this fatigue condition is:

[0118] Vσ = max{Vσ 12 , Vσ 23 , Vσ 31} Formula 21

[0119] (4) Correct the fatigue stress range

[0120] To achieve the conversion between the fatigue alternating stress range and the cyclic stress range 2f in the material fatigue performance curve a , the influence of the cyclic mean stress and the service temperature of the component on the fatigue strength of the component should be considered, so the fatigue stress range needs to be corrected. Specifically:

[0121] For the fatigue stress range within the elastic range, that is, is the conditional yield strength at the reference temperature, and the fatigue stress range Vσ can be corrected by Formulas 22 and 23:

[0122]

[0123]

[0124] Among them, Vσ * is the corrected cyclic stress range, is the average stress.

[0125] For the modified cyclic stress range in the partial elastic-plastic interval, that is, The fatigue stress range Vσ can be corrected by Formula 24 and Formula 25:

[0126]

[0127] For the modified cyclic stress range in the plastic range, that is, The fatigue stress range Vσ can be corrected by formula 26:

[0128]

[0129] In addition, the temperature correction factor Correction is made for the decrease in fatigue strength caused by temperature. For ferritic steel, the temperature correction factor is Fatigue stress range at corrected reference temperature Calculated by formula 27:

[0130]

[0131] In summary, after considering the influence of average stress and service temperature on the fatigue strength of components, the corrected fatigue stress range can be obtained by correcting the fatigue stress range:

[0132] (5) Calculate the number of allowable cycles

[0133] For unnotched round bar specimens of ferritic rolled or forged steel, when the mean stress is 0, the Figure 2 , crack initiation load cycle number N A With cyclic stress range 2f a The relationship between the tensile strength R of the material at the reference temperature can be obtained by formula 28 m In addition, since the data obtained by formula 29 comes from experimental data, in order to ensure a certain safety margin, the stress safety factor S is taken s =2 or cycle safety factor S c =20.

[0134]

[0135] The calculation formula for the permissible number of cycles N is:

[0136] N=min(N A,s ,N A,c / S c ) Formula 29

[0137] Among them, N A,s 、N A,c They are respectively the material fatigue performance curve (Formula 28) with 2f a,s and 2f a,c is the allowable number of cycles corresponding to the cyclic stress range, and:

[0138]

[0139] In the formula, is the corrected fatigue stress range.

[0140] (6) Calculate the first fatigue loss value

[0141] For high-temperature header components subjected to fatigue loads, the linear cumulative damage method can be used. When the fatigue cumulative damage reaches the allowable value of 1, the component life loss reaches the critical value:

[0142]

[0143] Among them, D f is the low cycle fatigue life loss (first fatigue loss value), (N f ) i is the allowable number of cycles of the ith fatigue condition, k is the number of fatigue conditions, n i is the actual running number of the i-th fatigue condition.

[0144] 2. Determining the Significance of Fatigue Effects

[0145] For high-temperature header components with insignificant fatigue effects, when calculating equipment creep and fatigue life loss, the effect of fatigue loss on the equipment can be ignored, and only the effect of creep loss on the equipment can be considered. The significance of fatigue effect analysis can be determined by the following two conditions:

[0146] (1) The assessment path does not experience ratchet failure, that is, Where: K is the equivalent stress corresponding to any point x on the assessment path at any time t in any cycle time, s is the ratchet failure coefficient of the material, S y It is the lower limit of 0.2% yield strength of the material corresponding to the temperature at that moment. It can be calculated by the following formula:

[0147]

[0148] (2) Cyclic loads do not have a significant impact on components, i.e., components accumulate fatigue D f The loss is less than 0.05, and the equivalent stress variation range corresponding to each cycle condition They are all within the elastic range of the material, and the cyclic loading has no effect on the creep behavior of the components.

[0149]

[0150] Among them, (K s S y ) c is the material property corresponding to the highest creep temperature during the cycle; (K s S y ) nc is the material property corresponding to the highest non-creep temperature during the cycle; They are the equivalent stress of the test points corresponding to the peak / valley values ​​respectively; Reference stress for creep-rupture analysis.

[0151] Note: For the five commonly used heat-resistant steel materials for headers, P12, P22, 12Cr1MoVG, P91, and P92, the ratchet failure coefficient K s Take 0.9.

[0152] 3. Analysis of creep loss

[0153] (1) Determine creep conditions

[0154] The creep condition (creep loss calculation condition) of the high-temperature header should be determined by the unit load power and the unit operating time in each power range during the operation of the high-temperature header. The unit operating power can be divided into types such as less than 30% load power, 30% to 50% load power, 50% to 75% load power, and 75% to 100% load power. When calculating the creep life loss of the high-temperature header in each power range, the calculated temperature and calculated pressure of the header shall take the upper limit average value of the high-temperature header operating parameters of the corresponding load power. The high-temperature header operating parameters can be obtained through the boiler strength calculation book, boiler manual, unit operating procedures, boiler performance test report, and DCS centralized control operation record data.

[0155] (2) Calculation of allowable creep rupture life

[0156] The creep rupture life can be calculated by the LM parameter method. The Larson-Miller parameter is a parameter that combines time, temperature, and stress. It is expressed as P(σ) in the form shown below:

[0157] P(σ)=(T+273.15)(C+lgt r ) Formula 36

[0158] P(σ)=C 0+C 1 lgσ+C 2 lg 2 σ+C 3 lg 3 σ+C 4 lg 4 σ+... Formula 37

[0159] Where T is the service temperature of the equipment under the corresponding working conditions (Celsius, ℃); t r is the creep rupture life (h); σ is the creep reference stress (MPa) and is material-dependent; C is the Larson-Miller constant; C 0 , C 1 , C 2 , C 3 , C 4 ,...are material constants. For details, please refer to the Larson-Miller constants and P(σ)~σ coefficients of commonly used boiler high-temperature header heat-resistant steels shown in Table 1.

[0160]

[0161] Table 1

[0162] In addition, the creep reference stress can also be corrected in the following ways when calculating the creep life loss: when calculating the creep life loss of the header components directly exposed to fire, the creep reference stress should be multiplied by a safety factor of 1.5; when calculating the creep life loss of the high-temperature header components not directly exposed to fire without an online monitoring system, the creep reference stress should be multiplied by a safety factor of 1.5; when calculating the creep life loss of the high-temperature header components not directly exposed to fire with an online temperature / pressure monitoring system, material structure aging level 4 or below, and material hardness values ​​that meet the requirements of DL / T 438, the creep reference stress should be multiplied by a safety factor of 1.25. Material structure aging rating shall be implemented in accordance with DL / T 884.

[0163] When the creep rupture life t is calculated according to formulas 36 and 37, r After that, the creep loss of the high temperature header is evaluated by the linear accumulation method to determine its damage degree (the first creep loss value) D c :

[0164]

[0165] Where m is the number of creep conditions, t i is the service time of the i-th creep condition, is the creep reference stress corresponding to the i-th creep condition and the allowable creep rupture life at service temperature T, and it is t calculated by the LM parameter method r .

[0166] In addition, the creep rupture analysis reference stress can be calculated using formula 39:

[0167]

[0168] in, is the reference stress for creep rupture analysis (MPa); χ is the stress concentration factor, which should be ≤4.0; P B , P L is the primary bending stress and the primary local membrane stress; It is the maximum equivalent stress along the test section path in elastic analysis.

[0169] The boiler high-temperature header body and branch results are mostly connected in the form of fillet welds, and the header pipe test point is a rectangular section along the axial direction. For a rectangular section, under the action of mechanical load, the reference stress σ along the wall thickness section ref The following formula can be used for calculation:

[0170]

[0171] Among them, P B , P L They are primary bending stress and primary local membrane stress respectively.

[0172] 4. Analysis of fatigue-creep losses

[0173] (1) Creep-fatigue failure criterion

[0174] For high-temperature pressure-bearing components that are subjected to creep-fatigue interaction, the linear cumulative damage method can be used. When the cumulative damage of creep and fatigue reaches the allowable value, the component life loss reaches the critical value:

[0175]

[0176] Among them, D f ' is the low cycle fatigue life loss (second fatigue loss value); (N f ) i is the allowable fatigue life of the ith fatigue condition; D c ' is the creep life loss (second creep loss value); (T c ) j is the allowable creep rupture time of the material corresponding to temperature T and stress σ in the jth creep condition cycle; D is the allowable critical value of creep-fatigue coupling damage, which is given by the creep-fatigue envelope curve (such as Figure 3 As shown in the figure, the area within the creep-fatigue envelope is the safe area, the area outside the envelope is the unsafe area, and the envelope is the creep-fatigue critical damage of the material.

[0177] (2) Calculation of the second fatigue loss value

[0178] First, a three-dimensional model of the high-temperature header is established. When modeling, the corners of the branch pipes of the header body should be chamfered, and the chamfer radius should be greater than 10 mm or one-fourth of the thickness of the thicker part. The three-dimensional model is divided into finite element grids to obtain a finite element model. Combined with the various operating conditions of the high-temperature header and the preset temperature-pressure relationship curve, the stress distribution information and temperature distribution information along the test path can be obtained through finite element analysis.

[0179] After obtaining the stress field and temperature field, the total creep-fatigue strain range Vε during the i-th cycle is calculated according to formulas 43 and 44. t,i :

[0180]

[0181] Vε t,i =Vε max,i =max(Vε e,i ) Formula 44

[0182] Among them, Vε e,i is the equivalent strain range at the corresponding time point; Vε xy 、Vε yz 、Vε xz , Vγ xy , Vγ yz , Vγ xz are the differences in strain components corresponding to the strain peak and valley values ​​in the i-th cycle, respectively, where the strain peak and valley values ​​are extracted from the stress field information; υ is the Poisson's ratio, for example, 0.5.

[0183] In addition, combined with the known elastic modulus of the material, the total strain range Vε can be t,i Calculate the corresponding total stress range.

[0184] According to the total stress range and material fatigue life curve during the i-th fatigue condition, the allowable number of cycles N of the fatigue condition is calculated. fi , combined with the actual number of operations n of the i-th fatigue condition i , calculate the fatigue damage of the i-th fatigue condition: Finally based on Calculate the fatigue life loss (second fatigue loss value).

[0185] (3) Calculation of the second creep loss value

[0186] First, the Mises equivalent stress σ can be calculated according to formula 45 Mises :

[0187]

[0188] Among them, σ xx , σ yy , σ zz , τ xy , τ yz , τ xz is the structural stress component corresponding to the assessment point.

[0189] Then, the structural stress (σ e ) j :

[0190]

[0191] J 1 =σ 1 +σ 2 +σ 3

[0192]

[0193] Finally, the creep damage (second creep loss value) is calculated according to Formula 47:

[0194]

[0195] Among them, D c ' is the second creep loss value, T dj is the temperature T and structural stress (σ e ) j The material allows creep rupture time, creep rupture time T dj It can be calculated by the LM parameter method (see the previous article for details), where t is the material at temperature T and structural stress (σ e ) j Length of service.

[0196] (4) Calculate the total loss value

[0197] The second fatigue loss value D f ′ and the second creep loss value D c ′ and sum them up to get the total loss value of the test point.

[0198] Figure 4 1 is a flow chart of a method for evaluating the remaining life of a high temperature header according to a first embodiment of the present invention. The method for evaluating the remaining life of the high temperature header according to the first embodiment includes:

[0199] Step S10, determining a plurality of assessment points to be analyzed on the high temperature header;

[0200] In this step, the creep and fatigue life calculation of the boiler high temperature header should first determine the assessment points, which should include the pipes, hole bridges and other structural discontinuities and stress concentration locations. Usually, the boiler header is a header with a main body opening and external T-shaped branch pipes. Under the action of temperature and pressure, the inner wall of the connection between the header and the branch pipe is the local highest stress area, so the assessment point is located at the inner corner of the larger opening pipe.

[0201] Step S20, for each assessment point, determine the total loss value of the assessment point according to the loss analysis method of the high temperature header described above;

[0202] Step S30, selecting a maximum total loss value from the total loss values ​​of multiple assessment points and using it as the life assessment loss value;

[0203] Step S40, determining the remaining life of the high temperature header according to the life assessment loss value, specifically, taking the difference between 1 and the life assessment loss value as the remaining life.

[0204] The present invention also constructs a computer, which includes a processor and a memory storing a computer program. When executing the computer program, the processor implements the above-mentioned loss analysis method of the high-temperature header and / or the remaining life assessment method of the high-temperature header described in the claims.

[0205] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A loss analysis method for a high temperature header, used for performing loss analysis on a test point of a high temperature header, characterized in that: include: Step S11, determining a reference temperature, and performing fatigue loss analysis on the assessment point according to the reference temperature and structural parameters of the high-temperature header to obtain a first fatigue loss value; Step S12, judging the type of the assessment point according to the fatigue loss value, the type including: insignificant fatigue impact and significant fatigue impact; Step S13, for the assessment point where fatigue influence is not significant, determine the creep reference stress, and perform creep loss analysis on the assessment point according to the creep reference stress to obtain a first creep loss value, and use the first creep loss value as the total loss value of the assessment point; Step S14, for the assessment points with significant fatigue influence, obtain the temperature field and stress field of the high-temperature header that change with time, and based on the temperature field and stress field, perform fatigue loss analysis and creep loss analysis on the assessment points respectively to obtain a second fatigue loss value and a second creep loss value, and take the sum of the second fatigue loss value and the second creep loss value as the total loss value of the assessment point.

2. The loss analysis method of the high temperature header according to claim 1, characterized in that: The step S11 comprises: Step S111, respectively determining a reference temperature for each fatigue condition, and determining a material characteristic parameter for each fatigue condition according to the reference temperature; Step S112, respectively calculating the fatigue stress range of the assessment point under various fatigue conditions according to the material characteristic parameters and the structural parameters of the high temperature header; Step S113, determining the allowable number of cycles for each fatigue condition according to the fatigue stress range of each fatigue condition and a preset material fatigue performance curve; Step S114, obtaining the actual number of operations of each fatigue condition, and calculating the first fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

3. The loss analysis method of high temperature header according to claim 1, characterized in that: In step S114, the first fatigue loss value of the assessment point is calculated according to the following formula: Among them, D f is the first fatigue loss value, k is the number of fatigue conditions, n i is the actual number of operations of the i-th fatigue condition, N fi is the allowable number of cycles for the i-th fatigue condition.

4. The loss analysis method of high temperature header according to claim 1, characterized in that: In step S13, the first creep loss value is obtained according to the following steps: Step S131, determining the creep reference stress of each creep condition according to the material of the high temperature header, and calculating the allowable creep rupture life of the assessment point in each creep condition according to the creep reference stress of each creep condition; Step S132, calculating the first creep loss value of the assessment point according to the allowable creep rupture life and the actual service time of each creep condition.

5. The loss analysis method of high temperature header according to claim 4, characterized in that: The first creep loss value of the test point is calculated according to the following formula: Among them, D c is the first creep loss value, m is the number of creep conditions, t i is the service time of the i-th creep condition, is the creep reference stress corresponding to the i-th creep condition And the allowable creep rupture life at service temperature T.

6. The loss analysis method of high temperature header according to claim 1, characterized in that: In step S14, the second fatigue loss value is calculated according to the following steps: Step S141, according to various fatigue conditions, creep conditions and preset temperature-pressure relationship curves of the high-temperature header, the temperature field and stress field of the high-temperature header that change with time are obtained by modeling and finite element analysis of the high-temperature header, and the total stress range of the assessment point in each fatigue condition is calculated respectively according to the temperature field and stress field; Step S142, determining the allowable number of cycles for each fatigue condition according to the total stress range and a preset material fatigue performance curve; Step S143, calculating the second fatigue loss value of the assessment point according to the allowable number of cycles and the actual number of operations of each fatigue condition.

7. The loss analysis method of high temperature header according to claim 6, characterized in that: In step S14, the second creep loss value is calculated according to the following steps: Step S144, determining the creep stress of each creep condition according to the temperature field and the stress field; Step S145, calculating the allowable creep rupture time of the assessment point in each creep condition according to the creep stress in each creep condition; Step S146, calculating the second creep loss value of the assessment point according to the allowable creep rupture life and service time of each creep condition.

8. The loss analysis method of high temperature header according to claim 7, characterized in that: The second creep loss value of the test point is calculated according to the following formula: Among them, D′ c is the second creep loss value, m is the number of creep conditions, T dj is the allowable creep rupture time corresponding to the service temperature and structural stress during the jth creep condition, and t is the service time of the material under the corresponding temperature and structural stress during the jth creep condition.

9. A method for assessing the remaining life of a high temperature header, characterized in that: include: Step S10, determining a plurality of assessment points to be analyzed on the high temperature header; Step S20, for each assessment point, determining the total loss value of the assessment point according to the loss analysis method of the high temperature header according to any one of claims 1 to 8; Step S30, selecting a maximum total loss value from the total loss values ​​of multiple assessment points and using it as the life assessment loss value; Step S40: determining the remaining life of the high temperature header according to the life assessment loss value.

10. A computer comprising a processor and a memory storing a computer program, characterized in that: When executing the computer program, the processor implements the loss analysis method of the high-temperature header according to any one of claims 1 to 8, and / or the remaining life assessment method of the high-temperature header according to claim 9.

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