KR101656672B1 - Evaluating method for degree of risk using creep and wall thinning of heat exchanger steam tube - Google Patents

Abstract

The present invention relates to a method for evaluating the risk of a boiler tube in consideration of both fatigue and creep.
The present invention relates to a shape information collecting step of collecting information on a shape of a boiler tube; A creep risk assessment process to assess creep risk from boiler tube stresses and temperatures; A thinning risk assessment process that evaluates the risk of thinning from the thickness of the boiler tube; And a boiler tube risk determination step of determining a risk of a boiler tube based on the results of the creep risk assessment step and the thinning risk evaluation step. The present invention also provides a risk evaluation method of a boiler tube considering creep and thinning.
According to the present invention, it is possible to evaluate the reliability of the tube risk, and thereby, it is possible to prevent the unexpected failure and to utilize it to determine the optimum maintenance cycle.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of evaluating a risk of a boiler tube having a creep and a thin wall,

The present invention relates to a method for evaluating the risk of a boiler tube in consideration of both fatigue and creep.

In the case of standard coal-fired power generation, the generation capacity is very large. Therefore, if a large-scale accident occurs, the cost of power generation loss due to long-term shutdown is larger than the cost of damage recovery.

In case of low pressure steam turbine, it is necessary to establish a system that can effectively prevent failure because a long term suspension is required in case of failure.

The sudden breakdown of boiler tubes, one of the key components in determining the risk of a boiler, is one of the main causes of unexpected shutdown of coal-fired power plants. A quasi-quantitative risk assessment technique is used to analyze the failure probability and failure damage in order to reduce the unexpected damage of the boiler tube and to predict the optimal maintenance time. At this time, the life factor consumption rate, which is a key factor in evaluating the failure probability, is determined by a typical damage mechanism of the boiler tube such as creep, fatigue or fatigue.

Here, in the case of creep and fatigue, a methodology of statistically analyzing experimental data of a material, determining the degree of deterioration with time using temperature and stress, and calculating the average lifetime is commonly used.

However, no method exists to date to assess the risk associated with tube thickening.

In the past, although thinning was considered in the case of tube damage, it was only used to calculate the real-time tube stress from the estimated reduction rate of the tube by estimating the tube hourly rate and did not evaluate the risk of tube thinning.

However, in actual power generation sites, damage due to thinning has been continuously reported. Therefore, it is necessary to accurately evaluate the thinning which directly affects the risk of the equipment in actual operation.

Korean Patent Publication No. 2011-0015258 (Published on February 15, 2011)

The present invention has been made to overcome at least some of the problems of the prior art as described above, and it is an object of the present invention to provide a risk evaluation method of a boiler tube considering creep and thinning, which can evaluate a reliable tube risk by considering both creep and thinning The purpose.

According to an aspect of the present invention, there is provided a boiler tube including: a shape information collecting step of collecting information on a shape of a boiler tube; A creep risk assessment process to assess creep risk from boiler tube stresses and temperatures; A thinning risk assessment process that evaluates the risk of thinning from the thickness of the boiler tube; And a boiler tube risk determination step of determining a risk of a boiler tube based on the results of the creep risk assessment step and the thinning risk evaluation step. The present invention also provides a risk evaluation method of a boiler tube considering creep and thinning.

At this time, the boiler tube risk assessment process can determine the risk of the boiler tube based on the higher risk value among the creep risk and the thinning risk.

In addition, the boiler tube risk determination process selects a risk of a boiler tube based on a higher risk value among the creep risk and the thinning risk, and then calculates a failure probability correction factor (POF _i ) (PDF _e ) for the method.

The thinning risk evaluation step may include an initial thickness estimation step of estimating an initial thickness of the boiler tube based on the measured value of the thickness of the boiler tube collected in the shape information collection step, A thinning fatigue life consumption rate calculating step of calculating a thinning fatigue life consumption rate by using the thickness of the fatigue fatigue fatigue life estimation step and a fatigue failure probability calculating step of estimating a fatigue failure probability based on the fatigue fatigue life consumption rate calculated in the fatigue fatigue life rate calculating step.

The creep risk assessment step includes a stress calculation step of calculating stress using the shape and pressure condition of the boiler tube, a temperature calculation step of calculating the temperature of the tube in consideration of the operation temperature, A creep life span consumption rate calculation step of calculating a creep life span consumption rate from the calculation process and a process of determining a creep failure probability and a risk degree from the calculated creep life span rate.

According to one embodiment of the present invention having such a configuration, a reliable tube risk assessment can be performed by considering the risk due to thinning as well as creep, and selecting a higher risk (or failure probability) In this way, it is possible to prevent an unexpected failure and to utilize it to determine an optimum maintenance cycle.

In particular, although the probability of failure due to thinning has not been taken into consideration in the past, damage due to thinning has been continuously reported in actual field inspection and maintenance. According to the present invention, it is possible to accurately evaluate the thinning which directly affects the risk of a facility in actual operation, thereby improving the efficiency and stability in maintenance of the facility.

According to the embodiment of the present invention, in addition to the creep risk and the thinning risk, the failure probability correction factor (POF _i ) and the utility factor correction factor (PDF _e ) A more reliable risk assessment can be made.

According to an embodiment of the present invention, reliable estimation of the initial thickness can ensure reliability in the rate of thinning-life-time consumption and in the probability of failure of thinning or risk assessment.

1 is a flowchart of a method for evaluating a risk of a boiler tube considering creep and thinning according to an embodiment of the present invention.
FIG. 2 is a graph showing the permissible stresses for each material in consideration of the operating temperature. FIG.
3 is a schematic view of a boiler tube;
4 is a cross-sectional view schematically showing a section of a boiler tube;
Figure 5 is a Mollier chart for water and steam.
FIG. 6 is a Gumbel probability distribution diagram according to the measured thickness of a boiler tube. FIG.
7 is a cumulative probability density curve of the probable probability distribution diagram shown in Fig.
8 is a graph showing a curve of the tube thickness according to the operation time.
9 is a system screen configuration diagram illustrating an example of a system for implementing a method for evaluating a risk of a boiler tube considering creep and thinning according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. The shape and size of elements in the drawings may be exaggerated for clarity.

Furthermore, the singular forms "a", "an," and "the" include plural referents unless the context clearly dictates otherwise.

The present invention relates to a method for evaluating the risk of a boiler tube in consideration of both fatigue and creep.

This risk assessment can be evaluated as failure probability and failure damage. In this case, the failure probability is the theoretical (general) Probability of Failure considering the material destruction test data and the operating conditions, and may differ from the actual equipment status during use.

Therefore, in order to calculate the failure probability, it is necessary to calculate the correction failure probability considering the state of the plant in the theoretical failure probability, and it can be corrected by the following [Equation 1].

[Expression 1] POF = PDF _g + POF _i + PDF _e

Here, POF: failure probability

PDF _g : Theoretical (general) probability of failure

POF _i : Probability correction factor by test result

PDF _e : Utility Correction Factor for Detecting Damage of Inspection Methods

As shown in Table 1 below, the failure probability correction factor (POF _i ) according to the inspection result is evaluated according to a table in which a predetermined correction rate is set according to each item (damage mode) .

[Table 1] Failure probability correction criteria based on test results

The utility factor correction factor (PDF _e ) for damage detection of the inspection method is, for example, as shown in the following Table 2, with respect to each damage mode (inspection item) A predetermined correction rate can be evaluated according to the designated table.

[Table 2] Failure probability correction standard based on inspection utility of inspection method

In Table 2, if there are two or more inspection methods for one damage mode, it can be set to reflect only the lowest score.

In Table 2, VI is used for Visual Inspection, UT for Ultrasonic Testing, UTT for Ultrasonic Thickness Testing, MT for Magnetic Particle Testing, PT for Ultrasonic Thickness Testing, Penetration testing (Penetration Testing), and RT is Radiographic Testing.

On the other hand, when establishing the inspection plan at the time of preventive maintenance, there are cases where the whole inspection is performed considering the condition of the equipment and the site conditions, and the inspection range is determined at a certain ratio.

Therefore, the inspection method is selected when calculating the inspection utility, and as an example, the POF _e can be finally calculated by adding the score according to the inspection ratio to the inspection utility by referring to the following [Table 3].

[Table 3] Failure probability correction standard

Basically, in the case of the failure probability correction, the risk determined by the POF _g is designed in consideration of a rise or a fall in the level, and it can be corrected and supplemented based on the operating characteristics and management standards of the development company.

1 is a flowchart of a method for evaluating a risk of a boiler tube considering creep and thinning according to an embodiment of the present invention.

Referring to FIG. 1, a boiler tube risk assessment method (S100) considering creep and thinning according to an embodiment of the present invention includes a shape information collecting step (S200) for collecting information on the shape of a boiler tube, (S300) for evaluating creep risk from stress and temperature, a thinning risk evaluation process (S400) for evaluating the risk of thinning from the thickness of the boiler tube, a creep risk evaluation process (S300) and the thinning risk evaluation process And a boiler tube risk determination process (S500) that determines the risk of the boiler tube based on the result of the process (S400).

In this case, the apparatus may include a step S110 for selecting a facility and a location for evaluating the risk before the shape information collection step S200.

Particularly, in the boiler tube risk assessment method (S100) considering creep and thinning according to an embodiment of the present invention, an optimal probability distribution curve is found based on measurement data on the tube thickness, and an initial thickness is predicted at a cumulative distribution probability And evaluating the risk of the facility by calculating the lifetime consumption rate and the reduction rate using the average and the standard deviation.

The details of the boiler tube risk assessment method (S100) considering creep and thinning according to an embodiment of the present invention are as follows.

Equipment and location selection process ( S110 )

First, the power plant and location to assess risk are determined. That is, the position of the boiler tube to be subjected to the risk assessment is determined in the target power generation facility.

Shape measurement process S200 )

Next, data on the outer diameter, scale thickness, and tube thickness of the tube are acquired with respect to the position determined in the facility and position selection step (S110). Since the data acquisition process and the types of data that can be obtained through the data acquisition process are well known, a detailed description thereof will be omitted.

Thus, when the shape measuring step S200 is completed, the creep risk evaluation step S300 and the thinning risk evaluation step S400 are performed. The creep risk evaluation step (S300) and the thinning risk evaluation step (S400) may be performed simultaneously regardless of the order.

Creep risk assessment process ( S300 )

The creep risk assessment process (S300) evaluates the creep risk from the stresses and temperatures of the boiler tubes.

The creep risk assessment step S300 includes a stress calculation step S310, a temperature calculation step S320, a creep life span rate calculation step S330, and a step S340 and S350 for evaluating a creep failure probability and a risk degree .

The concrete content of the risk assessment process (S300) is as follows.

Stress calculation process ( S310 )

The computational process is very complicated because the mechanical stresses considered for calculating the lifetime consumption rate change with the progress of the thinning and the tube temperature changes with the growth of the oxide layer. For the sake of simplicity, the operating time to the present should be divided into units of time that can be assumed to be constant with respect to internal pressure, tube temperature, and thickness reduction rate. For superheaters and reheating tubes, the stress can be calculated using the following formula 2 according to KEPIC-MBB (ASME Sec. I).

[Equation 2]

In Equation 2, e is a thickness-related factor, typically 0, and 0.04 can be used in consideration of the outer diameter and thickness conditions when a detailed tube standard is used. On the other hand, when evaluating the risk, a relatively large stress value is used as compared with the allowable stress for each material considering the operation temperature as illustrated in FIG.

Temperature calculation process ( S320 )

Temperature is an important parameter of the damage model in the assessment of tube risk considering creep damage. Since the temperature of the tube is not directly measured at the plant site, it is estimated thermodynamically using the operating parameters or corrected by the outlet header according to the boiler design standard.

Referring to FIG. 3, an example of a boiler tube for performing heat exchange includes a plurality of tube heat bundles 10 between the inlet header 110 and the outlet header 120 in the traveling direction of the high temperature fluid, And a temperature sensor 111 for measuring the temperature and the pressure of the inlet header 110 adjacent to the inlet header 110, respectively, in a non-heated area outside the heating wall 11, A pressure sensor 112 and a temperature sensor 121 and a pressure sensor 122 are provided adjacent to the outlet header 120 to measure the temperature and pressure on the outlet header 120 side. The flow rate sensor 130 is provided to measure the flow rate of the refrigerant flowing into the compressor 110.

The temperature sensors 111 and 121 and the pressure sensors 112 and 122 may be installed corresponding to three to five tube bundles 10 out of several tens of tube bundles, Or only one location on the inlet header 110 or outlet header 120 side to be able to measure the total steam flow rate rather than the vapor flow rate per tube bundle.

In order to calculate the surface temperature thermodynamically, as shown in FIG. 3, temperature and flow analysis of an inlet (inlet header) and an outlet (outlet header) measured using temperature sensors 111 and 121 such as a thermocouple The calculated pressure is used.

When the surface temperature inside and outside the tube is calculated, the surface temperature (T) of the tube used for the life consumption rate is calculated by the average value of the two values as shown in the following equation (3).

[Equation 3]

Here, the surface temperature (T _ro ) at the outside of the tube can be calculated by using a thermal conductivity equation with the surface temperature (T _ri ) inside the tube (tube-oxide scale interface) as shown in [Equation 4].

[Equation 4]

4, q _r is the heat generation rate, r _o is the outer diameter of the tube, r _i is the inner diameter of the tube, and k is the thermal conductivity of the tube. 4, T _s is the temperature of the steam (steam), and T _g is the temperature of the combustion gas.

This heat generation rate q _r can be calculated using the enthalpy at the inlet and outlet of the tube. As an example, the following [Equation 5] can be used.

[Equation 5]

는 스팀의 질량유량으로서 실제 측정한 유량 정보를 이용하며, ΔH_s는 입구부{입구헤더(110)}의 엔탈피(H_{steam , in})와 출구부{출구헤더(120)}의 엔탈피(H_{steam , out}) 사이의 엔탈피 변화량으로 다음의 [수식 6]으로 표현될 수 있다.In Equation 5,

Utilizes an actual flow rate information measured as the mass flow rate of steam, ΔH _s is the inlet portion {inlet header (110) of the enthalpy (H _{steam, in)} and an outlet portion {outlet header 120} enthalpy (H _steam of _{, out} can be expressed by the following equation (6).

[Equation 6]

The enthalpy is determined by the temperature and pressure of the steam. In the case of the large-capacity thermal power boiler, as shown in FIG. 3, by using the measured values of the temperature sensors 111 and 121 and the pressure sensors 112 and 122 installed at the inlet and the outlet of the tube The tube inlet enthalpy (H _{steam , in} ) and outlet enthalpy (H _{steam , out} ) can be obtained.

If the enthalpy has information on the temperature and the pressure, the enthalpy value in the superheated steam condition above the critical point can be obtained by using the Mollier chart (Mollier diagram) shown in FIG.

The convective heat transfer coefficient (h _s ) used for the heat transfer between the oxide scale and the tube surface is expressed by the Nusselt number and the tube dimension (D) as shown in the following equation (7). Here, the number of nucels is the ratio of the size of the heat transfer caused by the convection through the fluid layer, such as the size of the heat transfer caused by convection through a certain fluid layer. The larger the number of nucels, the larger the effect of convection. In Equation 7, k is the thermal conductivity of the fluid.

[Equation 7]

In addition, the Nusselt number can be expressed as a function of the Reynolds number Re and the Prandtl number Pr as a dimensionless number representing the ratio of heat transferred between the fluid and the solid surface. Here, the Reynolds number Re is related to the ratio of the inertial force to the viscous force. The Prandtl number is a characteristic of the fluid and is defined as a ratio of molecular diffusivity of heat to kinetic viscosity.

Meanwhile, the empirical formula relating to the Nusselt number in the single-phase flow can be expressed as [Equation 8].

[Equation 8]

On the other hand, when calculating the temperature (T _ri ) inside the tube, the temperature (T _ox ) at the oxide scale surface must be considered. Therefore, heat transfer between the oxide scale and the tube surface is considered. The temperature inside the tube (T _ri ) can be calculated using the following equation (9).

In addition, the temperature (T _ri ) inside the tube considering the temperature (T _ox ) at the oxide scale surface can be calculated by the following equation (10).

[Equation 9]

[Equation 10]

Referring to FIG. 4, T _s is the temperature of steam (vapor), and? _Ox is the thickness of the scale in the above-mentioned Equations (9) and (10). K _ox is the thermal conductivity coefficient of the scale.

Although not described in detail above, it is also possible to calculate the temperature of the tube in consideration of the tube bundle number, the bending portion number, and the like, as well as the above-described inlet portion and outlet portion pressure and steam flow rate.

Creep Life Time Consumption Rate Estimation Process ( S330 )

The factors affecting creep damage are stress, temperature, and time. The most commonly used model for predicting creep life is the Larson-Miller parameter, which represents the stress as a function of the three parameters, temperature and time.

The Larson-Miller parameter P _LM can be determined from the Larson-Miller diagram. At this time, if there are other similar parameters that can suggest changes related to lifetime, it can be used for the calculation. The Larson-Miller parameter can be expressed as an empirical formula involving the material constant C as a function of the temperature T and the expected lifetime L _e , as follows:

[Equation 11]

Using Equation 11 on the basis of the temperature and stress of the tube calculated above, the expected lifetime L _e under the same operating condition can be obtained, and the lifetime consumption rate D for the failure probability evaluation can be obtained by multiplying the current operating time L ₀ and the expected lifetime L _e Is obtained from the following equation (12).

[Equation 12]

Creep Failure Probability Estimation Process S340 ) And creep risk assessment process ( S350 )

The failure probability is calculated quantitatively, but the failure probability class can be determined according to the magnitude of the quantitative failure probability to indicate the severity of the failure probability.

The actual failure probability is determined by using 50% of the probability distribution curve determined based on the creep test data as the final life, but 50% of the life consumption rate can be used as the failure probability for convenience in consideration of conservatism.

Then, the failure probability class of the life span rate is used in the risk matrix to evaluate the severity of the failure risk together with the failure class.

The criterion that shows the probability of quantitative failure as a failure class is, for example, as shown in [Table 4].

[Table 4]

Thinning  Risk Assessment Process ( S400 )

Meanwhile, in the thinning risk evaluation step (S400), the risk of thinning is evaluated from the thickness of the boiler tube.

The thinning risk assessment step 400 includes an initial thickness estimation step S420 for estimating an initial thickness of the boiler tube based on the measured value of the thickness of the boiler tube collected in the shape information collection step S200, (S430) for calculating a thinning lifetime consumption rate using the initial thickness estimated in the estimation process, and a probability of thinning failure based on the thinning lifetime consumption rate calculated in the thinning lifetime consumption rate calculation step (S430) And a thinning risk evaluation process S450 for evaluating the thinning risk from the thinning failure probability calculated in the thinning failure probability calculation process S440.

At this time, in order to perform the initial thickness estimation process (S420), a probability distribution calculation process S410 for calculating a probability distribution of the boiler tube thickness may be further included.

The details of the process included in the thinning risk assessment process (S400) are as follows.

Probability distribution calculation process S410 )

The thickness measurement data of the boiler tube collected in the shape information collecting step (S200) is extracted to determine an appropriate probability distribution curve and an average and a standard deviation are obtained.

At this time, in order to evaluate the risk of tube thinning, data related to the initial thickness can be estimated using the Gumbel probability distribution among the extreme distributions as shown in FIG.

Initial thickness estimation process ( S420 )

In actual boilers, thicker tubes are often installed and operated compared to the design geometry, and basic information about the initial thickness is not managed.

However, the initial thickness is very important for the lifetime consumption rate and the stress calculation due to the thinning.

If it is necessary to consider the initial thickness, it is necessary to consider the tube thickness at design time as the initial thickness, though there is a difference in the tube thickness at the time of design and at the time of construction, and the minimum thickness or average thickness The reliability of the initial thickness was not ensured such that the initial thickness was conservatively used.

However, in the case of thinning, since the measured thickness data have a non-uniform distribution, the result is inaccurate when a simple average value is used. When the thickness information is different from the design information, the initial thickness information is unknown. It is difficult to do.

In consideration of this point, in the initial thickness estimation step (S420), a method of measuring the thickness of the non-reduced portion and a method of estimating the thickness corresponding to a preset value in the cumulative probability density function may be used.

At this time, there may be cases in which the method of measuring the thickness of the non-sensitive portion is not available or inaccurate. Therefore, according to an embodiment of the present invention, a method using a cumulative probability density function can be used to estimate the initial thickness.

In other words, the initial thickness can be estimated by the probabilistic distribution using the measured values of the tube thickness, and the life and the risk can be evaluated by using the mean and the deviation in the distribution.

FIG. 7 shows a cumulative probability density curve according to the probablistic distribution of the measured tube thicknesses shown in FIG. 6 to illustrate a method of using the cumulative probability density function.

At this time, the initial thickness estimation method using the cumulative probability density function can estimate the thickness corresponding to a certain value (for example, a value selected from 90 to 97%) in the probable probability distribution as the initial thickness of the boiler tube. In addition, 95% of the probable probability distribution can be estimated as the initial thickness of the boiler tube, which is more advantageous for ensuring reliability.

Thinning  Lifetime Consumption Rate Estimation Process ( S430 )

The design residual life due to thinning is defined as the operating time from the original installation thickness δ for enclosing the process material in the equipment to the minimum thickness δ _α at which leakage can occur and the evaluation residual life is defined as the It is defined as the operating time to the minimum thickness.

[Equation 13]

The minimum allowable thickness of the device can be calculated by KEPIC-MGE (ASME B3.1.1), taking into account the type of material to be manufactured, the process material filling pressure and temperature in the device. The following formula (14) can be used for the calculation of the reduction ratio TR.

[Equation 14]

The definitions of the respective variables in the above-described [Equation 13] and [Equation 14] are as follows.

R _t : Residual life due to thinning

δ: thickness of the device

δ _α : Minimum allowable thickness for enclosing process material in the equipment

TR:

t ₀ : Operating time for initial thickness measurement

t ₁ : Operating time for second thickness measurement

Meanwhile, the curve of the tube thickness according to the operation time is shown in FIG.

That is, as the operating time elapses from the beginning, the tube becomes thinner gradually. Also, the thinning rate may vary with the passage of the operating time. In consideration of this point, when determining the life of the tube, it is possible to calculate the rate of reduction according to the inspection period by reflecting the presence or absence of the previous inspection. That is, the remaining life can be evaluated by reflecting the reduction ratio after the previous inspection as in [Equation 14].

The lifetime consumption rate D for the failure probability evaluation can be obtained from the current operation time (L ₀ ) and the remaining service life (R _t ) using the following equation (15).

[Equation 15]

Thinning  Failure probability evaluation process ( S440 ) And Thinning  Risk Assessment Process ( S450 )

The failure probability and the risk evaluation according to the thinning can be performed in the same manner as the creep failure probability evaluation step S340 and the creep risk assessment step S350 described above.

That is, 50% of the probability distribution curve determined based on the thinning test data is used as the final life, but 50% of the life consumption rate can be used as the failure probability for convenience in consideration of conservatism.

The failure probability class of the life span rate is shown in the risk matrix together with the failure class, and is used to evaluate the severity of the failure risk. As a criterion that shows the failure probability as the quantitative failure probability, .

Risk Assessment Process ( S500 )

Since the risk of the tube may be caused by creep and thinning, the probability of failure (POF _g ) is determined as a large value among the risk evaluation results of the creep and thinning in the tube risk assessment process (S500) The final risk is determined by reflecting the failure probability correction factor (POF _i ) based on the result and the utility factor (PDF _e ) for damage detection of the inspection method.

At this time, the failure probability correction factor (POF _i ) based on the result of the field inspection and the utility factor correction factor (PDF _e ) for the damage detection of the inspection method can be calculated in accordance with the above-described theoretical (general) failure probability (POF _g ) Correction can be used. For example, the risk by correction may be adjusted according to the sum of the failure probability correction factor (POF _i ) due to the field inspection result and the correction ratio (correction%) according to the utility factor correction factor (PDF _e ) .

Meanwhile, the method for evaluating the risk of boiler tubes considering creep and thinning according to an embodiment of the present invention can be implemented by a system as shown in FIG. 9 as an example. That is, when the operation / measurement information is input, the remaining life and failure probability for creep and thinning can be calculated.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

110 ... entrance header 120 ... exit header
111, 121 ... temperature sensors 112, 122 ... pressure sensors
130 ... flow sensor
S100 ... Boiler tube risk assessment method
S200 ... shape measuring process
S300 ... creep risk assessment process
S400 ... thinning risk assessment process
S500 ... Risk assessment process

Claims (10)

A shape information collecting step of collecting information on the shape of the boiler tube;
A creep risk assessment process to assess creep risk from boiler tube stresses and temperatures;
A thinning risk assessment process that evaluates the risk of thinning from the thickness of the boiler tube; And
A boiler tube risk determination process for determining a risk of a boiler tube based on the creep risk assessment process and the result of the thinning risk assessment process;
/ RTI >
The boiler tube risk assessment process determines the risk of the boiler tube based on the higher risk value among the creep risk and the thinning risk,
The thinning risk assessment step includes:
An initial thickness estimating step of estimating an initial thickness of the boiler tube based on a measured value of the thickness of the boiler tube collected in the shape information collecting step,
A thinning longevity consumption rate calculating step of calculating a thinning longevity consumption rate using an initial thickness estimated in the initial thickness estimating step;
And a thinning failure probability calculating step of calculating a thinning failure probability based on the thinning lifetime consumption rate calculated in the thinning life consumption rate calculating step,
Wherein the thinning-life-time consumption rate calculation step reflects the presence or absence of the previous inspection and calculates and reflects the reduction rate according to the inspection period, thereby reflecting the creep and thinning. delete The method according to claim 1,
The boiler tube risk determination process selects a risk of a boiler tube based on a higher risk value among the creep risk and the thinning risk, and then calculates a failure probability correction factor (POF _i ) and an inspection method A method for evaluating the risk of a boiler tube considering creep and thinning, characterized by correcting the risk by considering the utility factor (PDF _e ). The method of claim 3,
The boiler tube risk determination process includes a step of correcting the risk level by taking into account the failure probability correction factor (POF _i ) and the utility efficiency correction factor (PDF _e ) A Risk Assessment Method for Boiler Tube Considering. delete The method according to claim 1,
Wherein the initial thickness estimation process estimates the initial thickness of the boiler tube using a Gumbel probability distribution based on a measured value of the thickness of the boiler tube. The method according to claim 6,
Wherein the initial thickness estimating step estimates the initial thickness of the boiler tube to a thickness corresponding to a value selected from 90 to 97% in the Gumbel probability distribution. The method according to claim 1,
The method of claim 1, wherein the step of estimating the thickness of the boiler tube is based on the assumption of 50% of the life consumption rate calculated in the step of calculating the thickness of the boiler tube. delete The method according to any one of claims 1, 3, and 4,
The creep risk assessment step includes:
A stress calculation step of calculating stress using the shape and pressure condition of the boiler tube,
A temperature calculation step of calculating the temperature of the tube in consideration of the operation temperature,
A creep life span consumption rate calculation step of calculating a creep life span consumption rate from the stress calculation step and the temperature calculation step,
And determining a creep failure probability and a risk level from the estimated creep life time consumption rate.

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