PCCP life assessment method considering performance degradation of interface material

Abstract

The application discloses a PCCP life assessment method considering interface material performance degradation, comprising the following steps: (1) determining key quantitative time-varying evaluation indexes of material performance degradation; (2) determining time-varying functions of material performance degradation according to the time-varying evaluation indexes of material performance degradation; (3) determining predicted residual service life of each component material of PCCP according to the time-varying functions of material performance degradation and bearing capacity design requirement values thereof; and (4) according to the residual service life calculation results of each material, a life assessment correction method based on a dominant failure mode is proposed, and the residual service life of the dominant failure material is corrected as the residual service life of PCCP. The application can obtain more reasonable PCCP service life, solves problems existing in the prior art PCCP life prediction and life calculation method, and provides method support and technical guidance for managers in decision-making contents such as PCCP retirement and life extension.

Description

TECHNICAL FIELD

[0001] The application relates to a PCCP life assessment method considering interface material performance degradation, and belongs to the field of water conveyance pipeline systems. BACKGROUND

[0002] Prestressed Concrete Cylinder Pipe (PCCP) is a composite pipe material combining the high tensile strength of steel and the compressive performance of concrete, and has the advantages of high strength and high bearing capacity, high durability, excellent anti-seepage performance, strong economy, strong adaptability to complex environments, green environmental protection and the like. PCCP is widely used in water conveyance engineering in the fields of water conservancy and electric power. In order to reveal and master the operation safety state of the whole PCCP engineering and each pipe section in service, the expected life of the engineering needs to be evaluated in multiple dimensions, which is quite necessary for the operation management, risk elimination and reinforcement and the exertion of benefits of the engineering. Meanwhile, if scientific life prediction is lacked, blind replacement may be caused, huge funds (the replacement cost of a single PCCP may reach hundreds of thousands of yuan) may be wasted, and the accumulated hidden risks caused by the risk elimination and reinforcement not in place may finally lead to catastrophic accidents. Therefore, the PCCP life prediction is not only a technical problem, but also a systematic problem related to public safety, economic benefits and social stability.

[0003] At present, the existing SL 702-2015 "Water Conservancy and Hydropower Engineering PCCP Technical Specification" has clear provisions for the reasonable service life of PCCP, among which the reasonable service life of large-scale water transfer projects is more than 50 years. GB / T 19685-2017 "Prestressed Concrete Cylinder Pipe" does not directly specify the specific service life, but gives the concrete cover thickness ≥ 20 mm as a durability control index. The American standard AWWA C304-2014 uses a two-stage model of concrete cover degradation and steel wire corrosion to calculate the predicted life of PCCP. At present, the existing SL 702-2015 "Water Conservancy and Hydropower Engineering PCCP Technical Specification" has clear provisions for the reasonable service life of PCCP, among which the reasonable service life of large-scale water transfer projects is more than 50 years. GB / T 19685-2017 "Prestressed Concrete Cylinder Pipe" does not directly specify the specific service life, but gives the concrete cover thickness ≥ 20 mm as a durability control index. The American standard AWWA C304-2014 uses a two-stage model of concrete cover degradation and steel wire corrosion to calculate the predicted life of PCCP. In the thesis "Theoretical Research on Structural Performance and Durability of Prestressed Concrete Cylinder Pipe" (Zhang Hongyu. [D]. Wuhan University, 2014), a theoretical model of chloride ion diffusion in each layer of PCCP was established by combining the cross-sectional characteristics of PCCP, and a PCCP residual service life evaluation model considering chloride ion corrosion was further established to estimate the residual service life of PCCP. In the thesis "Theoretical Research on Structural Performance and Durability of Prestressed Concrete Cylinder Pipe" (Zhang Hongyu. [D]. Wuhan University, 2014), a theoretical model of chloride ion diffusion in each layer of PCCP was established by combining the cross-sectional characteristics of PCCP, and a PCCP residual service life evaluation model considering chloride ion corrosion was further established to estimate the residual service life of PCCP.

[0004] The thesis "Theoretical Research on Structural Performance and Durability of Prestressed Concrete Cylinder Pipe" (Zhang Hongyu. [D]. Wuhan University, 2014) published a method for estimating the life of PCCP. The thesis assumes that the beginning of corrosion of prestressed steel wire or steel cylinder as the sign of PCCP structure failure, in the PCCP residual service life evaluation model, the beginning of steel wire corrosion can be used as an approximate but reasonable and effective structure life endpoint. Various factors affecting the durability degradation of PCCP structure were analyzed, and it was determined that chloride ion corrosion has the greatest impact on PCCP durability. The two-dimensional diffusion law of chloride ion corrosion of PCCP was summarized, and a modified Fick's second law diffusion model for chloride ion diffusion in concrete was established. From the development cycle of PCCP structure damage caused by chloride ion corrosion, when the chloride ion concentration on the surface of the prestressed steel wire reaches the critical concentration, the steel wire begins to rust. Further combining the theoretical model of chloride ion diffusion in PCCP, a PCCP residual service life evaluation model was established. Based on the critical concentration of chloride ion for steel wire corrosion and the current detected chloride ion concentration and the chloride ion diffusion coefficient, the residual service life of PCCP was calculated to determine the reasonable and effective life endpoint of PCCP structure.

[0005] Although the above domestic specifications stipulate the service life of PCCP, they do not provide a method for estimating the service life of PCCP, which leads to the fact that engineering managers cannot quantitatively evaluate the remaining service life of each pipe section of PCCP. The AWWAC304-2014 only considers the degradation and corrosion of concrete and steel wires to calculate the service life of PCCP, without comprehensively considering the comprehensive bearing capacity of the interface materials of PCCP. The method for calculating the service life of PCCP in the paper "Theoretical Research on Structural Performance and Durability of Prestressed Concrete Cylinder Pipe" (Zhang Hongyu. [D]. Wuhan University, 2014) only considers the corrosion effect of chloride ions on the prestressed steel wire, and ignores the influence of other factors on the service life of the pipe material. The method assumes that chloride ions mainly migrate to the inside of PCCP in the form of diffusion, and PCCP reaches the end of life when the chloride ion concentration on the surface of the prestressed steel wire reaches the critical concentration. It can be seen that the method does not comprehensively consider the degradation of the interface materials of PCCP, the calculated service life is smaller, and the precision is lower, which has a large deviation from the actual service life, thereby leading to lower engineering applicability of the calculation method, and it is difficult to reflect the actual remaining service life of the project. SUMMARY

[0006] The purpose of the application is to overcome the deficiencies in the prior art, and provide a PCCP service life evaluation method considering the performance degradation of interface materials, which can obtain a more reasonable service life of PCCP, solve the problems existing in the prior art PCCP service life estimation method, and provide method support and technical guidance for managers in making decisions such as PCCP retirement and life extension.

[0007] Technical scheme: To solve the above technical problems, the PCCP service life evaluation method considering the performance degradation of interface materials comprises the following steps:

[0008] (1) Collect and organize the PCCP structural design parameters, field monitoring and detection data, determine that the main bearing force structures of PCCP are concrete material, prestressed steel wire and steel cylinder, according to the characteristics of the main bearing force structures of PCCP, obtain the main influencing factors of the performance degradation of each material, and determine the key quantitative time-varying evaluation indexes of the performance degradation of each material according to the main influencing factors of the performance degradation of each material;

[0009] (2) According to the time-varying evaluation indexes of the performance degradation of each material, determine the time-varying function of the performance degradation of each material;

[0010] (3) According to the time-varying function of the performance degradation of each material and the design requirement value of the bearing capacity, determine the predicted remaining service life t1, t2 and t3 of the concrete material, the prestressed steel wire and the steel cylinder of PCCP according to the most unfavorable principle;

[0011] (4) The material determining the minimum value is the PCCP dominant failure material, and the minimum value is the benchmark value of the PCCP residual service life, i.e. the benchmark value t0 of the residual service life;

[0012] (5) A life assessment correction method based on the dominant failure mode is proposed to determine the influence degree of the other two materials and system factors on the dominant material, and the residual service life of the dominant failure material is corrected to be the residual service life of the PCCP.

[0013] As preferred, the specific steps of step (2) are:

[0014] (21) Establish a concrete performance degradation model;

[0015] (22) Establish a prestressed steel wire degradation model;

[0016] (23) Establish a steel cylinder performance degradation model.

[0017] As preferred, the specific steps of step (21) are:

[0018] (211) The compressive strength attenuation (based on damage mechanics) model is

[0019] f c (t)=fc0• exp(-λt) (1)

[0020] In the formula, f c is the compressive strength; fc0 is the initial compressive strength of the concrete; λ is the degradation rate parameter, which is determined by regression test data; t is the time;

[0021] (212) The chloride ion diffusion time-varying function is

[0022] C(x,t)=C0+(C s -C0)• [1-erf(x / 2(D(t)• t) 0.5 ] (2)

[0023] In the formula, C s is the chloride ion concentration; C0 is the initial concentration; x is the thickness of the protective layer; t is the time; D(t) is the time-varying diffusion coefficient, wherein D(t) =D0• t n , D0 is the initial diffusion coefficient (measured by rapid chloride ion migration test), i.e. through electro-migration to accelerate the penetration of chloride ions, to measure the unsteady migration coefficient D RCM , and then convert it to D0; n is the aging coefficient (usually 0.2~0.6), which can be derived by combining time scaling factor through wet heat cycle or electro-migration accelerated aging;

[0024] (213) The carbonation depth model is

[0025] xc (t)=k(t) 0.5 (3)

[0026] where x c is carbonation depth; k is environmental coefficient (related to humidity, CO2 concentration); t is time. k is obtained by fitting the carbonation depth measured by periodically spraying phenolphthalein reagent on concrete specimens placed in actual environment (e.g. soil or atmosphere environment where PCCP is laid) or accelerated carbonation in laboratory under high CO2 concentration (usually 3%~20%) and constant temperature and humidity, and then converted to k of actual environment by time scaling factor.

[0027] As preferred, the step (22) comprises the following steps:

[0028] (221) the time-varying function of residual tensile strength is

[0029] f p (t) = f p0 • (1-D p (t)) (4)

[0030] where f p is residual tensile strength; f p0 is initial tensile strength of steel wire (design value); D(t) is damage factor (value range 0~1) representing strength degradation over time t, D p (t) can be calculated by 1-e -ωt , where ω is a fitting parameter related to material and environment (calibrated by experiment or field data); t is time;

[0031] the time-varying function of corrosion depth is

[0032] d p (t) = r p • t b (5)

[0033] where d p is corrosion depth; r p is corrosion rate (related to chloride ion concentration and humidity); b is time index (usually 0.5~1.0); t is time. The high-chloride salt environment is simulated by salt spray test, the corrosion current density i corr of steel wire is measured by electrochemical method (such as polarization resistance), and then converted to corrosion rate according to Faraday's law;

[0034] The probability model of wire breakage rate is established by Weibull distribution, and its expression is

[0035] η(t) = 1- exp[-(t / α)β ] (6)

[0036] where η is the cumulative wire breakage rate; α is the shape parameter, which characterizes the control failure mode (early failure, random failure or aging failure); β is the scale parameter, which characterizes the characteristic life. If there are PCCP detection data (such as the number of broken wires and time recorded by electromagnetic detection, acoustic emission monitoring), α and β are fitted based on the historical broken wire data by linear regression. If there is a lack of long-term service data, accelerated corrosion tests can be carried out, and α and β can be fitted according to the Arrhenius model or the corrosion rate ratio.

[0037] As preferred, the specific step of step (23) is

[0038] The steel cylinder performance degradation model adopts a steel cylinder corrosion model and is calculated by a residual thickness time-varying function, and the expression is

[0039] δ(t) = δ0- r s • t b (7)

[0040] where δ is the thickness of the steel cylinder; r s is the corrosion rate (related to soil resistivity, pH value); δ0is the residual thickness at the initial time; t is the time; b is the time index (usually b=1 for linear corrosion, b=0.5 for diffusion-controlled corrosion). The corrosion rate r s and the time index b can be obtained from laboratory accelerated corrosion tests or long-term exposure tests.

[0041] As preferred, the specific step of step (3) is:

[0042] (31) Determine the residual service life t1of the concrete, wherein when the concrete strength decreases to the design allowable value f min1 , the concrete bearing capacity is considered to fail, and then the residual life t strength dominated by strength decay can be calculated in combination with formula (1).

[0043] t strength = -ln(f c0 / f min1 ) / λ (8)

[0044] where t strength is the residual life dominated by strength decay; f min1 is the design allowable value of the concrete strength; the remaining symbols are consistent with formula (1);

[0045] (32) When the chloride ion concentration reaches the critical concentration C crit at time d c , that is, C(d crit , t) = C crit , the concrete bearing capacity is considered to fail, and then the residual life t c of the concrete can be calculated in combination with formula (1).c For the concrete protection thickness, it is explained that the chloride ion penetrates the protective layer, and it is considered that the concrete structure loses its bearing capacity, and then combined with formula (2), the remaining life t dominated by chloride ion erosion can be calculated Cl The calculation expression is

[0046] (9)

[0047] In the formula, t Cl is the remaining life dominated by chloride ion erosion; d c is the concrete protection thickness; C crit is the critical concentration of chloride ion concentration; the remaining symbols are consistent with formula (2), wherein D(t) is a time-varying function, which needs to be solved iteratively;

[0048] (33) When the carbonation depth of concrete reaches the thickness of the protective layer, it is considered that the concrete loses its bearing capacity, and then combined with formula (3), the remaining life t dominated by carbonation can be obtained carb The calculation expression is

[0049] t carb =(d c / k) 2 (10)

[0050] In the formula, t carb is the remaining life dominated by carbonation; d c is the concrete protection thickness; k is the environmental coefficient;

[0051] (34) In the actual environment, the chloride ion erosion, carbonation and strength decay of concrete may occur at the same time, and the most unfavorable principle is adopted to calculate the remaining life of concrete, and then the calculation expression of the remaining life t1 of concrete is

[0052] t1=min(t strength , t Cl , t carb ) (11)

[0053] In the formula, t1 is the remaining life of concrete; t strength is the remaining life dominated by strength decay; t Cl is the remaining life dominated by chloride ion erosion; t carb is the remaining life dominated by carbonation;

[0054] (35) Determine the remaining service life t2 of the prestressed steel wire: when the tensile strength of the prestressed steel wire decays to the design allowable strength f min2 , it is considered that the bearing capacity of the steel wire loses its bearing capacity, and then combined with formula (4), the remaining life t based on the remaining tensile strength can be obtained s The calculation expression is

[0055] t s=- ln(f p0 / f min2 ) / ω (12)

[0056] In the formula, t s The remaining life is based on the remaining tensile strength; f min2 The design allowable strength of the prestressed steel wire; the other symbols are consistent with equation (4);

[0057] When the corrosion depth of the steel wire reaches the critical corrosion depth d crit If the steel wire fails to bear the load, then by combining equation (5), the remaining life t based on the corrosion depth can be obtained. corr The calculation expression is

[0058] t corr = ( d crit / r p ) 1 / b (13)

[0059] In the formula, t corr Remaining lifetime based on corrosion depth; d crit is the critical corrosion depth of the steel wire; the other symbols are consistent with equation (5);

[0060] When the wire breakage rate reaches the design allowable wire breakage rate η allow If the steel wire fails to bear the load, then by combining equation (6), the remaining life t based on the wire breakage rate can be obtained. break The calculation expression is

[0061] t break = β• [-ln(1-η allow )] 1 / α (14)

[0062] In the formula, t break η is the remaining life based on the wire breakage rate. allow The allowable wire breakage rate is determined by the design; the remaining symbols are consistent with equation (6);

[0063] In practical engineering, the synergistic effect of corrosion and strength, as well as the randomness of wire breakage rate, need to be considered. The remaining life of the steel wire is calculated using the worst-case scenario principle. Therefore, the remaining life of the steel wire is t2.

[0064] t2=min(t s , t corr ,t break (15)

[0065] In the formula, t2 is the remaining life of the steel wire; the other symbols are consistent with those in formulas (12), (13) and (14), respectively.

[0066] (36): The critical thickness for steel cylinder failure is δcrit Then, combined with equation (7), the expression for calculating the remaining life t3 of the steel cylinder is obtained as follows:

[0067] t3= [(δ0-δ crit ) / r s ] 1 / b (16)

[0068] In the equation, t3 is the remaining life of the steel cylinder; δ crit is the critical thickness of the failure of the steel cylinder; and the remaining symbols are consistent with equation (7).

[0069] As a preferred, the step (4) is specifically as follows: determining the remaining service life t1, t2, t3 of each part, and taking the minimum value as the PCCP reference remaining service life according to the most unfavorable principle, and the value of the material corresponds to the material that dominates the failure of the PCCP. That is, the calculation expression of the PCCP reference remaining service life t0 is as follows:

[0070] t0= min(t1, t2, t3) (17)

[0071] In the equation, t0 is the PCCP reference remaining service life; t1 is the remaining life of the concrete; t2 is the remaining life of the steel wire; and t3 is the remaining life of the steel cylinder.

[0072] As a preferred, the step (5) is specifically as follows:

[0073] (51) In the calculation of the reference value t0 of the life, it is usually assumed that the other two materials and the other system are in a certain "reference state", that is, an invariant. However, in the actual service process of the PCCP, the material performance is always evolving, and the influence of the other two materials and the system factors on the reference life of the dominant material needs to be considered. In the actual calculation, after obtaining the reference remaining service life t0, the corresponding material is the dominant material, and the remaining two materials are considered as correction factors. Here, three methods for evaluating and quantifying the state of the material and the system factors and determining the correction coefficient are given.

[0074] As a preferred, the step (51) is specifically as follows:

[0075] (511) Evaluate and quantify the state of the concrete to determine the correction coefficient u c . The state of the concrete protective layer needs to be investigated on site and quantified. First, the on-site state is evaluated and quantified by scoring, and a check table is developed to score the concrete state of the pipeline (or a representative pipe section). The specific evaluation indexes and state descriptions and scores are shown in Table 1. It should be noted that the operating environments of different PCCPs are quite different, and the evaluation index content of Table 1 can be added, deleted or adjusted according to the specific circumstances.

[0076] Table 1

[0077]

[0078] Then the total score is calculated and mapped to the correction factor u c The above scores are added to obtain the total score S (e.g. 8 full marks). According to the total score, the correction factor u c is determined, as follows:

[0079] When S ≥ 7, the state is good, and the protection function is intact; u c takes 1.0 (no need to reduce).

[0080] When 5 ≤ S < 7, the state is medium, and the protection function has decreased; u c takes 0.7 ~ 0.9.

[0081] When 3 ≤ S < 5, the state is poor, and the protection function is severely lost; u c takes 0.4 ~ 0.6.

[0082] When S < 3, the state is extremely poor, and the steel wire is in a direct exposure state. u c takes 0.1 ~ 0.3.

[0083] (512) Evaluate and quantify the state of the steel wire to determine the correction factor u s The residual prestress of the prestressed steel wire, the number of broken wires, the corrosion degree, and the mechanical properties of the steel wire are evaluated to obtain the state grade of the steel wire system. The correction factor u s corresponding to different grades is shown in Table 2.

[0084] Table 2

[0085]

[0086] (513) Evaluate the state of the steel cylinder to determine the correction factor u cs The inspection method uses internal visual inspection (CCTV), leakage monitoring, and ultrasonic thickness measurement for comprehensive detection and evaluation. The evaluation criteria include intact, slight corrosion, and severe corrosion / perforation, as follows:

[0087] When the steel cylinder is in good condition, there is no leakage, and no obvious corrosion; u cs takes 1.0;

[0088] When the steel cylinder is slightly corroded, there are rust spots but no perforation leakage; u cs takes 0.9;

[0089] When the steel cylinder is severely corroded / perforated, it has leaked and will continue to introduce moisture and corrosive substances, worsening the steel wire environment; u csTake 0.5~0.7.

[0090] (514) evaluate other system factor state, determine correction coefficient w. Other factors include cathodic protection system and operating pressure. Specific cathodic protection system effectiveness evaluation criteria and correction coefficient w1 are:

[0091] When the cathodic protection system is effectively operated and the data meets the standard, the service life can be slightly extended, w1 takes 1.1;

[0092] When the cathodic protection system is invalid or does not exist, w1 takes 1.0;

[0093] When the cathodic protection system is abnormally operated (such as overprotection, which may produce hydrogen embrittlement and is harmful), w1 takes 0.8.

[0094] Operating pressure evaluation criteria and correction coefficient w2 are: when PCCP is operated below 0.8P_design (design pressure), w2 takes 1.0~1.2, wherein the lower the pressure, the smaller the stress on the steel wire, and the less the reduction; when PCCP is operated at 0.8P_design~P_design, w2 takes 1.0; when PCCP is operated above P_design, w2 takes 0.8~0.9, wherein P_design represents the design operating pressure.

[0095] Calculate the correction coefficient w of other system factors:

[0096] w = w1 · w2 (18)

[0097] In the formula, w is the correction coefficient of other system factors; w1 is the correction coefficient of the cathodic protection system; and w2 is the correction coefficient of the operating pressure.

[0098] (52) Calculate the remaining service life of PCCP. Through step (51), the influence degree and correction coefficient of the other two materials and system factors on the dominant material are determined, and then the remaining service life of the dominant failure material is corrected and calculated based on the life assessment correction method of the dominant failure mode, and the calculation result is the remaining service life t of PCCP PCCP , the expression is:

[0099] t PCCP = t0× u1×u2×w (19)

[0100] In the formula, t PCCP is the remaining life of PCCP; t0 is the reference remaining service life of PCCP; u1 and u2 are the correction coefficients of the other two materials; and w is the correction coefficient of other system factors.

[0101] A re-inspection is conducted every 3 years, with a focus on monitoring the breakage of prestressed steel wires. The correction factor is updated based on the re-inspection results, and the life prediction is dynamically adjusted.

[0102] Beneficial Effects: This invention provides a comprehensive PCCP life assessment method that considers the degradation of interface material properties. By combining PCCP on-site monitoring and testing data, it obtains the main degradation parameters of each material's performance degradation model (concrete, prestressed steel wire, and steel cylinder), improving the fitting accuracy of each material degradation model. This allows for the determination of the PCCP's baseline remaining life based on the lifespan of the dominant material. Further adjustments to the baseline remaining life by incorporating the performance of other materials and the system's operational status further enhance the accuracy of the PCCP's remaining life calculation. This clarifies the current performance status of each material and enables a comprehensive assessment of the remaining lifespan of each PCCP segment. This life calculation model overcomes the limitations of traditional single-prestressed steel wire performance assessment methods, which cannot fully grasp the degradation status of key interface materials in the PCCP. It also avoids the inaccurate lifespan predictions of traditional methods. Based on the degradation status of each material, PCCP maintenance strategies can be optimized, providing a basis for decision-making regarding reinforcement measures for weak segments in the project. Attached Figure Description

[0103] Figure 1 This is a flowchart of the present invention.

[0104] Figure 2 This is a structural diagram of the PCCP material. Detailed Implementation

[0105] The invention will now be further described with reference to the accompanying drawings.

[0106] like Figure 1 As shown, the PCCP lifetime assessment method of the present invention, which comprehensively considers the degradation of interface material properties, includes the following steps:

[0107] (1) Collect and organize PCCP structural design parameters, on-site monitoring and testing data, determine that the main load-bearing structure of PCCP is concrete material, prestressed steel wire and steel cylinder, clarify the main influencing factors of performance degradation of each material, and determine the key quantitative time-varying evaluation indicators of performance degradation of each material;

[0108] Step 1.1: Collect and organize PCCP structural design parameters, on-site monitoring, and test data to determine that the main load-bearing structure of the PCCP consists of concrete, prestressed steel wire, and steel cylinder. This requires collecting PCCP structural design parameters, on-site monitoring, and test data. Basic information on PCCP structural design parameters, on-site monitoring, and test data is shown in Table 3.

[0109] Table 3

[0110]

[0111] Step 1.2: Since concrete material, prestressed steel wire and steel cylinder are the main load-bearing materials of PCCP, it is necessary to clarify the main influencing factors of performance degradation of each material (concrete material, prestressed steel wire and steel cylinder).

[0112] Step 1.2.1: According to the load bearing condition of the concrete of PCCP, the influencing factors of performance degradation of concrete material are clarified. The main influencing factors of degradation of concrete material include freeze-thaw cycle, sulfate corrosion, chloride ion corrosion, carbonation (CO2permeation).

[0113] Step 1.2.2: According to the load bearing condition of the prestressed steel wire of PCCP, the influencing factors of performance degradation of prestressed steel wire are clarified. The main influencing factors of degradation of prestressed steel wire include stress corrosion cracking (SCC), hydrogen embrittlement, uniform / local corrosion.

[0114] Step 1.2.3: According to the load bearing condition of the steel cylinder of PCCP, the influencing factors of performance degradation of steel cylinder are clarified. The main influencing factors of degradation of steel cylinder include electrochemical corrosion, fatigue damage, and the performance degradation parameters of each material are shown in Table 4.

[0115] Table 4

[0116]

[0117] Step 1.3: According to the main influencing factors of performance degradation of each material (concrete material, prestressed steel wire and steel cylinder), the key quantitative time-varying evaluation indexes of performance degradation of each material are determined.

[0118] Step 1.3.1: Clarify the time-varying evaluation indexes of performance degradation of concrete material. According to the main influencing factors of degradation of concrete material, the main time-varying evaluation indexes of performance degradation of concrete material are proposed, which specifically include the compressive strength f c (t), the chloride ion diffusion coefficient D Cl (t) and the carbonation depth x c (t).

[0119] Step 1.3.2: Clarify the time-varying evaluation indexes of performance degradation of prestressed steel wire. According to the main influencing factors of degradation of prestressed steel wire, the main time-varying evaluation indexes of performance degradation of prestressed steel wire are proposed, which specifically include the residual tensile strength f p (t), the corrosion depth d p (t) and the wire breakage rate η(t).

[0120] Step 1.3.3: Clarify the time-varying evaluation indexes of performance degradation of steel cylinder. According to the main influencing factors of degradation of steel cylinder, the main time-varying evaluation indexes of performance degradation of steel cylinder are proposed, which specifically include the residual thickness t s (t), which is related to the corrosion rate r s of steel cylinder.

[0121] Step 2: Based on the time-varying evaluation indices for the performance degradation of each material (concrete, prestressed steel wire, and steel cylinder), determine the time-varying degradation functions of each material's performance. Combining PCCP design data with field testing and monitoring data, model the time-varying degradation functions of each key evaluation index of the PCCP mentioned above.

[0122] Step 2.1: Establish a concrete performance degradation model. The concrete performance degradation model includes a compressive strength attenuation model (based on damage mechanics), a chloride ion diffusion time-varying function, and a carbonation depth model. The compressive strength attenuation model (based on damage mechanics) is as follows:

[0123] f c (t)=fc0• exp(-λt) (1)

[0124] In the formula, f c λ is the compressive strength; fc0 is the initial compressive strength of the concrete; λ is the degradation rate parameter (determined through regression test data); t is time.

[0125] The time-varying function of chloride ion diffusion is

[0126] C(x,t)=C0+(C s -C0)• [1-erf(x / 2(D(t)• t) 0.5 (2)

[0127] In the formula, C s denoted as chloride ion concentration; C0 as initial concentration; x as protective layer thickness; t as time; and D(t) as time-varying diffusion coefficient, where D(t) = D0• t n D0 is the initial diffusion coefficient (determined by the rapid chloride ion migration test), which is the unsteady-state migration coefficient D measured by accelerating chloride ion penetration through electromigration. RCM Then convert it to D0; n is the aging coefficient (usually 0.2~0.6), which can be obtained by accelerating aging through damp heat cycling or electromigration, combined with the time scaling factor.

[0128] Carbonization depth model is

[0129] x c (t)=k(t) 0.5 (3)

[0130] In the formula, x cwhere k is the environmental coefficient (related to humidity, CO2 concentration); t is time. The value of k is obtained by fitting the carbonation depth measured by periodically spraying phenolphthalein reagent on the concrete specimen placed in the actual environment (e.g. soil or atmosphere environment where PCCP is laid). Alternatively, accelerated carbonation in laboratory under high CO2 concentration (usually 3%~20%) and constant temperature and humidity conditions is used to measure the carbonation depth, which is then converted to the k value in the actual environment by time scaling factor.

[0131] Step 2.2: Establish the degradation model of prestressed steel wire. The degradation model of prestressed steel wire includes time-varying function of residual tensile strength, time-varying function of corrosion depth and probability model of wire breakage rate. The time-varying function of residual tensile strength is

[0132] f p (t) = f p0 • (1-D p (t)) (4)

[0133] where f p is the residual tensile strength; f p0 is the initial tensile strength of steel wire (design value); D(t) is the damage factor (value range 0~1) representing the strength degradation over time t, D p (t) can be calculated by 1-e -ωt , where ω is the fitting parameter related to material and environment (calibrated by experiment or field data); t is time.

[0134] The time-varying function of corrosion depth is

[0135] d p (t) = r p • t b (5)

[0136] where d p is the corrosion depth; r p is the corrosion rate (related to chloride ion concentration, humidity); b is the time index (usually 0.5~1.0); t is time. The high-chloride salt environment is simulated by salt spray test, and the corrosion current density i corr of steel wire is measured by electrochemical method (such as polarization resistance), and then the corrosion rate is converted according to Faraday's law.

[0137] The probability model of wire breakage rate is established by Weibull distribution, which is expressed as

[0138] η(t) = 1- exp[-(-t / α) β ] (6)

[0139] In the formula, η is the cumulative wire breakage rate; α is the shape parameter, characterizing the controlled failure mode (early failure, random failure, or aging failure); and β is the scale parameter, characterizing the characteristic life. If PCCP detection data (such as the number and time of wire breakage recorded by electromagnetic detection and acoustic emission monitoring) is available, α and β are fitted by linear regression based on historical wire breakage data. If long-term service data is lacking, accelerated corrosion tests can be conducted, and α and β can be fitted according to the Arrhenius model or corrosion rate ratio.

[0140] Step 2.3: Establish a performance degradation model for the steel cylinder. The performance degradation model for the steel cylinder adopts a corrosion model and is calculated using a time-varying function of the remaining thickness. Its expression is as follows:

[0141] δ(t) = δ0 - r s • t b (7)

[0142] In the formula, δ is the thickness of the steel cylinder; r s δ0 represents the corrosion rate (related to soil resistivity and pH); δ0 represents the remaining thickness at the initial time; t represents time; b represents the time exponent (usually b=1 for linear corrosion, b=0.5 for diffusion-controlled corrosion). The corrosion rate r0 is... s The time index b can be obtained from laboratory accelerated corrosion tests or long-term exposure tests.

[0143] Step 3: Based on the time-varying degradation function of each material's properties and its design load-bearing capacity, determine the expected remaining service life of the concrete material, prestressed steel wire, and steel cylinder of each component of the PCCP. The indices and parameters for calculating the remaining service life of each component are shown in Table 2.

[0144] Step 3.1: Determine the remaining service life t1 of the concrete. This includes determining the service life when the concrete strength drops to the design allowable value f. min If the concrete bearing capacity fails, then by combining equation (1), the remaining life t dominated by strength decay can be calculated. strength The calculation expression is

[0145] t strength = -ln(f c0 / f min ) / λ (8)

[0146] In the formula, t strength Remaining lifetime is dominated by intensity decay; f min is the allowable value for concrete strength design; the other symbols are consistent with equation (1).

[0147] When the chloride ion concentration reaches the critical concentration C crit The time, i.e., C(d) c ,t)=C crit , where dc For the concrete protection thickness, it is considered that the chloride ion penetrates the protective layer and the concrete structure loses its bearing capacity. Then, combined with equation (2), the remaining life t dominated by chloride ion erosion can be calculated Cl The calculation expression is

[0148] (9)

[0149] In the formula, t Cl is the remaining life dominated by chloride ion erosion; d c is the concrete protection thickness; C crit is the critical concentration of chloride ions; and the remaining symbols are consistent with equation (2), wherein D(t) is a time-varying function, which needs to be solved iteratively.

[0150] When the carbonation depth of concrete reaches the protection layer thickness, it is considered that the concrete loses its bearing capacity, and then, combined with equation (3), the remaining life t dominated by carbonation can be obtained carb The calculation expression is

[0151] t carb = (d c / k) 2 (10)

[0152] In the formula, t carb is the remaining life dominated by carbonation; d c is the concrete protection thickness; and k is the environmental coefficient.

[0153] In the actual environment, concrete chloride ion erosion, carbonation and strength decay may occur at the same time, and the most unfavorable principle is adopted to calculate the remaining life of concrete. Then, the calculation expression of the remaining life t1 of concrete is

[0154] t1=min(t strength , t Cl , t carb ) (11)

[0155] In the formula, t1 is the remaining life of concrete; t strength is the remaining life dominated by strength decay; t Cl is the remaining life dominated by chloride ion erosion; and t carb is the remaining life dominated by carbonation.

[0156] Step 3.2: Determine the remaining service life t1 of the prestressed steel wire. When the tensile strength of the prestressed steel wire decays to the design allowable strength f min , it is considered that the steel wire loses its bearing capacity, and then, combined with equation (4), the remaining life t based on the remaining tensile strength can be obtained s The calculation expression is

[0157] t s =- ln(fp0 / f min ) / ω (12)

[0158] where t s is the remaining life based on the remaining tensile strength; f min is the design allowable strength of the prestressed steel wire; and the remaining symbols are consistent with equation (4).

[0159] When the corrosion depth of the steel wire reaches the critical corrosion depth d crit , the steel wire is considered to have failed in carrying capacity, and then, based on equation (5), the remaining life t corr based on the corrosion depth can be obtained, and the calculation expression is

[0160] t corr = ( d crit / r p ) 1 / b (13)

[0161] where t corr is the remaining life based on the corrosion depth; d crit is the critical corrosion depth of the steel wire; and the remaining symbols are consistent with equation (5).

[0162] When the wire breakage rate of the steel wire reaches the design allowable wire breakage rate η allow , the steel wire is considered to have failed in carrying capacity, and then, based on equation (6), the remaining life t break based on the wire breakage rate of the steel wire can be obtained, and the calculation expression is

[0163] t break = β• [-ln(1-η allow )] 1 / α (14)

[0164] where t break is the remaining life based on the wire breakage rate of the steel wire; η allow is the design allowable wire breakage rate; and the remaining symbols are consistent with equation (6).

[0165] In actual engineering, the synergistic effect of corrosion and strength and the randomness of the wire breakage rate need to be considered, the remaining life of the steel wire is calculated by using the most unfavorable principle, and then the remaining life t2 of the steel wire is

[0166] t2=min(t s , t corr ,t break ) (15)

[0167] where t2 is the remaining life of the steel wire; and the remaining symbols are consistent with equations (12), (13) and (14), respectively.

[0168] Step 3.3: The critical thickness of the steel cylinder failure is δ crit, then combined with equation (7), the expression for calculating the remaining life t3 of the steel cylinder is

[0169] t3= [(δ0-δ crit ) / r s ] 1 / b (16)

[0170] where t3 is the remaining life of the steel cylinder; δ crit is the critical thickness of the steel cylinder failure; and the remaining symbols are consistent with equation (7).

[0171] Step 4: According to the calculation of step 3, determine the remaining service life t1, t2, t3 of each part, and according to the most unfavorable principle, take the minimum value as the PCCP reference remaining service life, and the value of the material corresponds to the material that dominates the PCCP failure. That is, the expression for calculating the PCCP reference remaining service life t0 is

[0172] t0= min(t1, t2, t3) (17)

[0173] where t0 is the PCCP reference remaining service life; t1 is the remaining life of the concrete; t2 is the remaining life of the steel wire; and t3 is the remaining life of the steel cylinder.

[0174] Step 5: In actual calculation, after obtaining the reference remaining service life t0, the corresponding material is the dominant material, and the remaining two other materials are considered as correction factors. Here, three material states and system factors are evaluated and quantified, and a method for determining the correction coefficient is given to calculate the PCCP remaining service life

[0175] Step 5.1: Evaluate and quantify the concrete state to determine the correction coefficient u c . The state of the concrete protective layer needs to be investigated on site and quantified. First, evaluate and quantify the score on site, develop a checklist, and score the concrete state of the pipeline (or representative pipe section). The specific evaluation indicators and state descriptions and scores are shown in Table 3. It should be noted that the operating environment of different PCCPs differs greatly, and the evaluation indicators in Table 3 can be added, deleted, or adjusted according to specific circumstances.

[0176] Then calculate the total score and map it to the correction coefficient u c . Add the scores of the above items to get the total score S (for example, 8 points for full score). According to the total score, determine the correction coefficient u c , as follows:

[0177] When S ≥ 7, the state is excellent and the protection function is intact; u c takes 1.0 (no need to reduce).

[0178] When 5 ≤ S < 7, the state is medium, and the protection function has decreased; u c Take 0.7 ~ 0.9.

[0179] When 3 ≤ S < 5, the state is poor, and the protection function is seriously lost; u c Take 0.4 ~ 0.6.

[0180] When S < 3, the state is extremely poor, and the steel wire is in a direct exposure state. u c Take 0.1 ~ 0.3.

[0181] Table 5

[0182]

[0183] Step 5.2: Evaluate and quantify the state of the steel wire to determine the correction coefficient u s The state grade of the steel wire system is obtained by comprehensive evaluation of the residual prestress, the number of broken wires, the corrosion degree, and the mechanical property test of the prestressed steel wire. The correction coefficient u s corresponding to different grades is shown in Table 6.

[0184] Table 6

[0185]

[0186] Step 5.3: Evaluate the state of the steel cylinder to determine the correction coefficient u cs The inspection method adopts internal visual inspection (CCTV), leakage monitoring, and ultrasonic thickness measurement for comprehensive detection and evaluation. The judgment criteria include intact, slight corrosion, and severe corrosion / perforation, as follows:

[0187] When the steel cylinder is in good condition, there is no leakage, and no obvious corrosion; u cs Take 1.0;

[0188] When the steel cylinder is slightly corroded, there are rust spots but no perforation leakage; u cs Take 0.9;

[0189] When the steel cylinder is severely corroded / perforated, it has leaked and will continue to introduce moisture and corrosive substances, worsening the steel wire environment; u cs Take 0.5 ~ 0.7.

[0190] Step 5.4: Evaluate the state of other system factors to determine the correction coefficient w. Other factors include the cathodic protection system and the operating pressure. The specific cathodic protection system effectiveness evaluation criteria and correction coefficient w1 are:

[0191] When the cathodic protection system is effective and the data is up to standard, the service life can be slightly extended, w1 is 1.1;

[0192] When the cathodic protection system is ineffective or does not exist, w1 is 1.0;

[0193] When the cathodic protection system is abnormally running (such as over-protection, which may produce hydrogen embrittlement and is harmful), w1 is 0.8.

[0194] The running pressure evaluation standard and the correction coefficient w2 are as follows: when the PCCP is running below 0.8P design (design pressure), w2 is 1.0-1.2, wherein the lower the pressure, the smaller the stress on the steel wire, and the less the reduction; when the PCCP is running at 0.8P design-P design, w2 is 1.0; when the PCCP is running above P design, w2 is 0.8-0.9, wherein P design represents the design running pressure.

[0195] The correction coefficient w of other system factors is calculated as follows:

[0196] w = w1 · w2 (18)

[0197] In the formula, w is the correction coefficient of other system factors; w1 is the correction coefficient of the cathodic protection system; and w2 is the correction coefficient of the running pressure.

[0198] Step 5.5: Calculate the remaining service life of the PCCP. The influence degree and the correction coefficient of the other two materials and system factors on the dominant material are determined through step 5.4, and then the remaining service life of the dominant failure material is corrected and calculated based on the life evaluation correction method of the dominant failure mode, and the calculation result is the remaining service life t of the PCCP. PCCP , the expression of which is:

[0199] t PCCP = t0× u1×u2×w (19)

[0200] In the formula, t PCCP is the remaining life of the PCCP; t0 is the baseline remaining service life of the PCCP; u1 and u2 are the correction coefficients of the other two materials; and w is the correction coefficient of other system factors.

[0201] In addition, re-inspection needs to be carried out every 3 years, the prestressed steel wire breakage is monitored, and the correction coefficient is updated according to the re-inspection result to dynamically adjust the life prediction.

[0202] Example 1

[0203] The PCCP lifetime assessment method of the present invention, which comprehensively considers the degradation of interface material properties, includes the following steps:

[0204] Step 1: Determine the project overview and operational status. A PCCP pipeline for a city's water supply trunk line has a diameter of DN2400mm, a prestressed steel wire diameter D of 5mm, a single pipe length of 8 meters, a design pressure of 1.0MPa, and has been in service for 39 years. Through wire breakage monitoring, it was found that some pipe sections exhibited varying degrees of wire breakage. The remaining service life of the selected pipe sections with more severe wire breakage was estimated and calculated.

[0205] Step 2: Determine the parameters of the material performance degradation model or the time-varying function of material degradation. Based on Tables 1 and 2, determine the remaining life calculation parameters for concrete materials, prestressed steel wires, and steel cylinders.

[0206] Step 2.1: Determine the remaining service life calculation parameters for concrete. Relevant parameters for the concrete compressive strength decay model include the initial compressive strength f. c0 The strength is 50 MPa, the strength degradation rate λ is 0.005 / year, and f min The pressure is 30 MPa; relevant parameters of the chloride ion diffusion time-varying function include the critical chloride ion concentration C. crit The content is 0.05%, and the thickness of the protective layer is d. c The diameter is 50 mm, and the initial diffusion coefficient D0 is 1.0 × 10⁻⁶. -12 m 2 / s, aging coefficient n is 0.3; carbonization depth model related parameter carbonization coefficient k is 3.0 mm / year.

[0207] Step 2.2: Determine the remaining life calculation parameters for the prestressed steel wire. Relevant parameters for the degradation model of the prestressed steel wire include the initial tensile strength of the wire being 1860 MPa, and the design allowable tensile strength f. min The damage factor is 1488 MPa. p (t) is 1-e -0.03t The time-varying parameters of the corrosion depth function include the corrosion rate r. p The corrosion rate is 0.02 mm / year, the time index b is 0.6, and the critical corrosion depth d is... crit The wire breakage rate is 0.5 mm; the Weibull parameters α and β of the wire breakage rate probability model are 1.8 and 45, respectively, and the allowable wire breakage rate η is... allow It is 5%.

[0208] Step 2.3: Determine the remaining service life calculation parameters for the steel cylinder. Relevant parameters for the steel cylinder performance degradation model include the initial cylinder thickness δ0 of 6 mm and the corrosion model r. s The annual precipitation is 0.05 mm / year, the time exponent b is 0.8, and the critical thickness δ is... crit =2mm.

[0209] Step 3: Calculate the remaining life t1 of the concrete material.

[0210] Step 3.1: Calculate the remaining life t strength dominated by strength degradation. Combining the parameters related to the compressive strength degradation model of concrete and the above equation (8), t strength = -0.0051 x ln(30 / 50) ≈ 102 years.

[0211] Step 3.2: Calculate the remaining life t Cl dominated by chloride ion erosion. Combining the parameters related to the chloride ion diffusion time-varying function of concrete and the above equation (9), the numerical iteration solution is t Cl ≈ 45 years.

[0212] Step 3.3: Calculate the remaining life t carb dominated by carbonation. Combining the carbonation coefficient of concrete and the above equation (10), t carb = (50 / 3.0) 2 = 278 years.

[0213] Step 3.4: Calculate the remaining life t1 of the concrete material, then t1 = min(t strength , t Cl , t carb ) = min(45, 278, 102) = 45 years.

[0214] Step 4: Calculate the remaining life t2 of the prestressed steel wire.

[0215] Step 4.1: Calculate the remaining life t s based on the remaining tensile strength. Combining the parameters related to the degradation model of the prestressed steel wire and the above equation (12), t s = -1 x ln(1488 / 1860) / 0.03 ≈ 7 years.

[0216] Step 4.2: Calculate the remaining life t corr based on the corrosion depth. Combining the parameters related to the corrosion depth time-varying function of the prestressed steel wire and the above equation (13), t corr = (0.5 / 0.02) 1 / 0.6 ≈ 27 years.

[0217] Step 4.3: Calculate the remaining life t break based on the steel wire breakage rate. Combining the parameters related to the breakage rate probability model of the prestressed steel wire and the above equation (14), t break = 45 x [-ln(0.95)] 1 / 1.8 ≈ 12 years

[0218] Step 4.4: Calculate the remaining life of the prestressed steel wire t2, then t2 = min(t s , t corr , t break ) = min(7, 27, 12) = 7 years.

[0219] Step 5: Calculate the remaining life of the steel cylinder t3. Combining the performance degradation model related parameters of the steel cylinder and the above formula (16), t3 = [(6-2) / 0.05] 1 / 0.8 ≈ 33 years.

[0220] Step 6: Calculate the reference value of the remaining service life of the PCCP t0= min(t1, t2, t3) = min(45, 7, 33) = 7 years.

[0221] Step 7: From step 6, the dominant failure material of the PCCP is the prestressed steel wire. Through the inspection of the concrete, steel cylinder and other system factors, the correction coefficients are determined respectively by comparing the scoring standards.

[0222] Step 7.1: Calculate the correction coefficient u1. The concrete state S scores 6 points, which is in the range of 5 ≤ S < 7, the state is medium, and the protection function has decreased; u c takes 0.80, i.e. the correction coefficient u1 is 0.80.

[0223] Step 7.2: Calculate the correction coefficient u2. The steel cylinder is slightly corroded with rust spots but no perforation leakage, u cs takes 0.90, i.e. the correction coefficient u2 is 0.90.

[0224] Step 7.3: Calculate the system factor correction coefficient w. The cathodic protection system of the PCCP is effectively running and the data is up to standard, which can slightly extend the life, w1 takes 1.1; and the PCCP has been running for a long time (more than two years) at less than 0.8P_design, then w2 takes 1.05. Thus, w = w1 × w2 = 1.1 × 1.05 = 1.155

[0225] Step 8: Calculate the remaining life t PCCP of the PCCP. The t PCCP calculation expression is as follows:

[0226] t PCCP = t0× u1×u2×w= 7× 0.80×0.90×1.155=5.8 years.

[0227] From the above calculation results, the weak link of the PCCP is the prestressed steel wire, and the prestressed steel wire needs to be strengthened monitoring, and a set of reinforcement measures for the prestressed steel wire is proposed according to the environment and load conditions of the project to ensure the safety and benefit of the project.

[0228] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A PCCP life assessment method considering degradation of interface material performance in an integrated manner, characterized by, The method comprises the following steps: (1) collecting and collating PCCP structure design parameters, field monitoring and detection data, determining that the main bearing force structure of PCCP is concrete material, prestressed steel wire and steel cylinder, clearly defining the main influencing factors of the performance degradation of each material, and determining the key quantitative time-varying evaluation indexes of the performance degradation of each material; (2) determining the degradation time-varying function of the performance of each material according to the time-varying evaluation indexes of the performance degradation of each material; (3) determining the predicted residual service life of the concrete material, the prestressed steel wire and the steel cylinder of each component material of PCCP according to the degradation time-varying function of the performance of each material and the bearing force design requirement value thereof; (4) Calculate the remaining service life of each part according to step (3) t 1、 t 2、 t 3, according to the principle of most unfavorable, the minimum value is the PCCP remaining service life reference value t0, and the corresponding material is the PCCP leading failure material; (5) The dominant failure mode-based life assessment correction method is proposed to correct and calculate the residual service life benchmark value t0 of the dominant failure material, and the calculation result is the residual service life t of the PCCP PCCP； The step (5) comprises the following steps: (51) Assess and quantify the state of concrete to determine the correction factor u c : On-site investigation of the state of the concrete cover and quantification thereof, development of a checklist, scoring of the state of the concrete of the pipe, addition of the scores of the above items to obtain a total score S, maximum score of 8, determination of the correction factor u c according to the total score, as follows: When S ≥ 7, the state is good, and the protection function is perfect; u c Take 1.0; When 5 ≤ S < 7, the state is medium, and the protection function has decreased; u c Take 0.7 ~ 0.9; When 3 < S < 5, the state is poor, and the protection function is seriously lost;u c Take 0.4 ~ 0.6; When S < 3, the state is very poor, and the steel wire is in a directly exposed state, u c Take 0.1 ~ 0.3; (52) Evaluate and quantify the state of steel wire, determine the correction coefficient u s : Through the assessment of the residual prestress of prestressed steel wire and the number of broken wires, the assessment of corrosion degree and the mechanical property test of steel wire, the state grade of steel wire system is obtained comprehensively, wherein different grades correspond to different correction coefficients u s ; if the steel wire is intact, the ability of the restrained concrete is strong, the deterioration of the structure is delayed, the correction coefficient u s is 1.0-1.2; when the steel wire state has no significant influence on the deterioration of the concrete, the correction coefficient u s is 1.0; when the broken wire or corrosion causes local stress concentration, accelerates the cracking and spalling of the concrete, the correction coefficient u s is 0.7-0.9; (53) Assess the condition of the steel cylinder and determine the correction factor u cs The inspection method uses internal visual inspection, leak monitoring and ultrasonic thickness measurement for comprehensive detection and evaluation, and the evaluation criteria include intact, slight corrosion and severe corrosion / perforation, as follows: When the steel cylinder is in good condition, no leakage, no obvious corrosion; u cs Take 1.0; When the steel cylinder is slightly corroded, with rust spots but no perforation leakage; u cs Take 0.9; When the steel cylinder is seriously corroded / perforated, it has leaked, and will continue to introduce moisture and corrosion, worsening the environment of the steel wire;u cs Take 0.5 ~ 0.7; (54) evaluating the state of other system factors to determine a correction coefficient w: other factors include a cathodic protection system and operating pressure, and the specific cathodic protection system effectiveness evaluation standard and the correction coefficient w1 are as follows: When the cathodic protection system is effectively operated and the data meets the standard, w1 is 1.1; When the cathodic protection system is invalid or does not exist, w1 is 1.0; When the cathodic protection system is abnormally operated, w1 is 0.8; The operating pressure evaluation standard and the correction coefficient w2 are as follows: when PCCP is operated below 0.8P_design, w2 is 1.0-1.2; when PCCP is operated at 0.8P_design-P_design, w2 is 1.0; and when PCCP is operated above P_design, w2 is 0.8-0.9, wherein P_design represents the design operating pressure; The correction coefficient w of other system factors is calculated as follows: w = w1 · w2 (18) In the formula, w is the correction coefficient of other system factors; w1 is the correction coefficient of the cathodic protection system; and w2 is the correction coefficient of the operating pressure; (55) Calculate the PCCP remaining service life: the above steps determine the influence degree and correction coefficient of other two materials and system factors on the dominant material, and then the remaining service life benchmark value t0 of the dominant failure material is corrected and calculated based on the life assessment correction method of the dominant failure mode, and the calculation result is the PCCP remaining service life t PCCP The expression is: t PCCP = t0× u1×u2×w (19) In the formula, t PCCP is the PCCP remaining life; t0 is the PCCP reference remaining service life; u1, u2 are correction coefficients of two materials other than material A; w is a correction coefficient of other factors of the system.

2. The PCCP life assessment method considering degradation of interface material performance according to claim 1, wherein, The step (2) comprises the following steps: (21) establishing a concrete performance degradation model; (22) establishing a prestressed steel wire degradation model; (23) establishing a steel cylinder performance degradation model.

3. The PCCP life assessment method considering degradation of interface material performance according to claim 2, characterized in that, The step (21) comprises the following steps: (211) the compressive strength attenuation model is f c (t) = fc0• exp(-λt) (1) where f c is the compressive strength; fc0is the initial compressive strength of the concrete; λ is a degradation rate parameter determined by regression of test data; and t is time. (212) the chloride ion diffusion time-varying function is C(x, t) = Co + (C s - Co) • [1 - erf(x / (2(D(t) • t) 0.5 )] (2) In the formula, C s denoted as chloride ion concentration; C0 as initial concentration; x as protective layer thickness; t as time; and D(t) as time-varying diffusion coefficient, where D(t) = D0• t n D0 is the initial diffusion coefficient, which is the unsteady-state migration coefficient D obtained by accelerating chloride ion penetration through electromigration. RCM Then convert to D0; n is the aging coefficient, usually 0.2~0.6, which is derived by accelerating aging through damp heat cycling or electromigration, combined with the time scaling factor; (213) the carbonation depth model is x c (t)=k(t) 0.5 (3) where x c is the carbonization depth; k is the environmental coefficient, and t is the time.

4. The PCCP life assessment method considering degradation of interface material performance according to claim 2, wherein, The step (22) comprises the following steps: (221) the residual tensile strength time-varying function is f p (t) = f p0 • (1-D p (t)) (4) where f p is the residual tensile strength; f p0 is the initial tensile strength of the steel wire; D p (t) is a damage factor, taking values in the range 0-1, representing the strength degradation over time t, D p (t) is given by 1-e -ωt where ω is a material and environment dependent fitting parameter; t is the time; (222) the corrosion depth time-varying function is d p (t) = r p • t b (5) where d p is the corrosion depth; r p is the steel wire corrosion rate; b is the time exponent, typically 0.5-1.0; t is the time, where the high-chloride salt environment is simulated by a salt spray test, and the steel wire corrosion current density i corr is measured by electrochemical methods, and is converted to the corrosion rate according to Faraday's law; (223) the broken wire rate probability model is established through Weibull distribution, and the expression is η(t) = 1 - exp[-(t / α) β ] (6) In the formula, η is the cumulative broken wire rate; α is a shape parameter representing a control failure mode; and β is a scale parameter representing a characteristic life. If there is PCCP detection data, α and β are fitted based on the historical broken wire data through linear regression. If there is a lack of long-term service data, an accelerated corrosion test is performed, and α and β are fitted according to the Arrhenius model or the corrosion rate ratio.

5. The PCCP life assessment method considering degradation of interface material performance according to claim 2, wherein, The step (23) comprises the following steps The steel cylinder performance degradation model adopts a steel cylinder corrosion model, and the residual thickness time-varying function is calculated, and the expression is δ(t) = δ0- r s • t b (7) where δ is the thickness of the steel cylinder; r is the corrosion rate of the steel cylinder; δ0is the remaining thickness at the initial time; t is the time; and b is the time exponent, where the corrosion rate r and the time exponent b are obtained from laboratory accelerated corrosion tests or long-term exposure tests. s where δ is the thickness of the steel cylinder; r is the corrosion rate of the steel cylinder; δ0is the remaining thickness at the initial time; t is the time; and b is the time exponent, where the corrosion rate r and the time exponent b are obtained from laboratory accelerated corrosion tests or long-term exposure tests. s where δ is the thickness of the steel cylinder; r is the corrosion rate of the steel cylinder; δ0is the 6. The PCCP life assessment method considering degradation of interface material performance according to claim 1, wherein, The step (3) comprises the following steps: (31) determining the remaining service life t1 of the concrete, wherein when the concrete strength decreases to the design allowable value f min1 , it is considered that the concrete bearing capacity fails, then combining formula (1), the strength attenuation dominant remaining life t strength The calculation expression is t strength = -ln(f c0 / f min1 ) / λ (8) In the formula, t strength is the remaining life dominated by strength degradation; f min1 is the allowable value of concrete strength design; (32) When the chloride ion concentration reaches the critical concentration C crit at time d c , t) = C crit , where d c is the concrete protection thickness, it indicates that the chloride ion penetrates the protection layer, and it is considered that the concrete structure bearing capacity fails, then combined with formula (2), the remaining life t Cl of the chloride ion erosion dominated is calculated. （9） where t Cl is the remaining service life dominated by chloride ion attack; d c is the concrete cover; C crit is the critical concentration of chloride ion concentration; n is the aging coefficient; (33) When the carbonation depth of concrete reaches the thickness of the protective layer, the concrete bearing capacity is considered to be invalid, and combined with formula (3), the remaining life t dominated by carbonation can be obtained carb The calculation expression is t carb = (d c / k) 2 (10) where t carb is the carbonation dominated remaining life; d c is the concrete protection thickness; k is the environmental coefficient; (34) In the actual environment, concrete chloride ion erosion, carbonation and strength decay may occur simultaneously, and the most unfavorable principle is used to calculate the remaining life of concrete, and the remaining life of concrete t1 calculation expression is t1 = min(t strength , t Cl , t carb ) (11) In the formula, t1 is the remaining life of concrete; (35) Determination of the remaining service life t2 of the prestressing steel wire: when the tensile strength of the prestressing steel wire decays to the design allowable strength f min2 , the steel wire is considered to have failed in load bearing capacity. In combination with equation (4), the remaining life t s The calculation expression is t s =- ln(f p0 / f min2 ) / ω (12) where t s is the remaining life based on the remaining tensile strength; f min2 is the design allowable strength of the prestressing steel wire; When the corrosion depth of the steel wire reaches the critical corrosion depth d crit , it is considered that the steel wire bearing capacity fails, and then combined with formula (5), the remaining life t corr based on the corrosion depth can be obtained The calculation expression is t corr = ( d crit / r p ) 1 / b (13) In the formula, t corr is the remaining life based on the corrosion depth; d crit is the critical corrosion depth of the steel wire; When the wire breakage rate reaches the design allowable breakage rate η allow , it is considered that the wire bearing capacity fails, and combined with formula (6), the remaining life t break of the wire based on the wire breakage rate can be obtained t break = β• [-ln(1-η allow )] 1 / α (14) In the formula, t break is the remaining life based on the wire breakage rate; η allow is the design allowable breakage rate; In actual engineering, the synergistic effect of corrosion and strength, as well as the randomness of broken wire rate, should be considered, and the remaining life of steel wire t2 is calculated by the most unfavorable principle t2 = min(t s , t corr , t break ) (15) In the formula, t2 is the remaining life of steel wire; (36) The critical thickness of the steel cylinder failure is δ crit Then, combining equation (7), the residual life t3 of the steel cylinder can be calculated as follows: t3= [(δ0-δ crit ) / r s ] 1 / b (16) In the formula, t3 is the remaining life of the steel cylinder; δ crit is the critical thickness of the steel cylinder failure.

7. The PCCP life assessment method considering degradation of interface material performance according to claim 6, wherein: The specific steps of the step (4) are as follows: determining the remaining service life t1, t2, t3 of each part, and taking the minimum value as the reference value of the remaining service life of PCCP according to the most unfavorable principle, that is, the reference value t0 of the remaining service life calculation expression is t0= min(t1, t2, t3) (17) In the formula, t0 is the reference value of the remaining service life of PCCP, and the corresponding material is A; t1 is the remaining life of concrete; t2 is the remaining life of steel wire; t3 is the remaining life of steel cylinder.

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