Corrosion analysis system and method

• US 6,195,624 B1
• Filed: 02/15/1995
• Issued: 02/27/2001
• Est. Priority Date: 06/15/1993
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Combustion Engineering Incorporated (ABB Limited)
• Inventors: Hall, John F., Woodman, Brian Wilder
• Primary Examiner(s): STAMBER, ERIC W
• Application Number:
  US08/389,545
• Time in Patent Office: 2,204 Days
• Field of Search: 395/911, 395/914, 395/920, 364/578, 364/551.01, 364/507, 735/98, 703/2, 703/7, 702/34, 706/911, 706/914, 706/920
• US Class Current: 703/7
• CPC Class Codes: G06F 2113/14 Pipes
• CPC Class Codes: G06F 2119/04 Ageing analysis or optimisation against ageing
• CPC Class Codes: G06F 2119/06 Power analysis or power optimisation
• CPC Class Codes: G06F 30/20 Design optimisation, verification or simulation optimisation, verification or simulation of circuit designs G06F30/30
• CPC Class Codes: G21C 17/00 Monitoring; Testing measuring in general G01; Maintaining
• CPC Class Codes: G21C 17/017 Inspection or maintenance of pipe-lines or tubes in nuclear installations
• CPC Class Codes: G21D 3/001 Computer implemented control
• CPC Class Codes: Y02E 30/00 Energy generation of nuclear origin
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors
• CPC Class Codes: Y10S 706/92 Simulation

Abstract

A system (10) and method (42,44,46,48,52,54) for generating an index (38,132,40,134) commensurate with the degree to which a tube array degrades over a period of time due to corrosion in a particular operating environment. A data array (62,114) is created defining the number of tubes in the tube array, a plurality of time points defining time intervals during which the degradation is to be assessed, and operating conditions that induce corrosion during each time interval. The expected degradation value of the array is computed over each of a plurality of time points using a deterministic failure model (88) having at least one parameter (102,104,106) that is assumed constant at each time point. For each time point and at least one parameter, a plurality of values of the parameter (108,110) that deviate from the assumed constant value, are generated. For each time point, a plurality of degradation values are computed using the deterministic model with each of the plurality of deviated values of the parameter, thereby defining a distribution (34) of degradation values at the time point surrounding the expected degradation value (36,130) at the time point. An index (38,132,40,134) is generated from the distribution of values, commensurate with the uncertainty at each time point, in the expected degradation value (36,130) as computed by the deterministic model.

Claims

1. A method for generating an index commensurate with a degree to which a tube array degrades over a period of time due to corrosion in a particular operating environment, comprising:

creating a data array defining a number of tubes in the tube array, a plurality of time points defining time intervals during which the degradation is to be assessed, and operating conditions that induce corrosion during each time interval;

computing an expected degradation value of the tube array over each of a plurality of time points using a deterministic failure model having at least one parameter that is assumed to have a constant value at each time point;

for each time point generating a plurality of values of said parameter that deviate from said assumed constant value;

for each time point, computing a plurality of degradation values using said deterministic failure model with each of said plurality of deviated values of said parameter, thereby defining a distribution of degradation values at said time point surrounding said expected degradation value at said time point; and

generating an index from said distribution of degradation values, commensurate with an uncertainty at each time point, in said expected degradation value as computed by said deterministic failure model.

2. The method of claim 1, wherein the step of generating a plurality of values of said parameter includes generating a plurality of random values of said parameter.

3. The method of claim 2, wherein the step of generating a plurality of random values of said parameter includes a Monte-Carlo simulation.

4. The method of claim 1, wherein the step of generating a plurality of values of said parameter includes treating the parameter as a probabilistic variable.

5. The method of claim 1 further comprising the steps of inspecting plant steam generator tubes, measuring a failure rate of the tubes, and from the measured failure rates empirically determining said parameter for use in said deterministic failure model.

6. A method for generating an index commensurate with an uncertainty in a failure rate of tubes in a tube array, modelled in a computer system having a platform including, data processor means for performing arithmetic and logic operations on digitized data, data storage means coupled to the data processor means, for storing digitized data including instruction data and operand data, data input means for supplying instruction and operand data to the data processor means, output means for recording at least some of the results of the arithmetic and logic operations of the data processor means, and monitor means for displaying information in response to the operation of the data processor means, wherein said data storage means contains a stored computer program for mathematically modelling an expected failure rate of tubes in a tube array, said model including at least one assumed constant parameter for characterizing corrosion effects on the tubes, the method comprising:

with said data input means,

creating a data array in said data storage means, defining a number of tubes in the tube array, a plurality of time points defining time intervals during which failures are to be modelled, and operating conditions that induce corrosion during each time interval, and

defining said at least one assumed constant parameter as a random variable having characteristics stored in said data storage means;

with said program stored in said data storage means, for mathematically modelling the expected failure rate of tubes in a tube array,

computing the expected failure rate of the tube array over a plurality of time points with said at least one assumed constant parameter,

for each time point, generating a plurality of values of said parameter that deviate from said at least one assumed constant parameter according to the random variable characteristics as defined with said data input means,

for each time point, computing a plurality of probabilistic failure rate values using said model with each of said plurality of deviated values of said parameter, thereby defining a distribution of probabilistic failure rate values at said time point surrounding said expected failure rate at said time point; and

from said distribution of probabilistic failure rate values surrounding the expected failure rate, generating and displaying on said monitor means, an index commensurate with the uncertainty at each time point, in said expected failure rate.

7. The method of claim 6, including the step of initiating from said data input means, a delivery of said index as presented on said monitor means, to said output means, for creating a permanent record of the uncertainty associated with each expected failure rate.

8. The method of claim 6 wherein said generating and displaying step further comprises the step displaying each said expected failure rate and wherein said displaying of an index displays a range of said distribution of probabilistic failure rate values surrounding each said expected failure rate.

9. A system for generating an index commensurate with a degree to which a tube array in a nuclear steam generator has degraded from multiple corrosion sources, comprising:

a computer platform including

data processor means for performing arithmetic and logic operations on digitized data,

data storage means coupled to the data processor means, for storing digitized data including instruction data and operand data,

data input means for supplying instruction and operand data to the data processor means,

output means, for recording at least some of the results of the arithmetic and logic operations of the data processor means, and

monitor means, for displaying information in response to the operation of the data processor means;

said data storage means containing a stored computer program including,

a first modelling means for modelling a number of tubes in said tube array, that fail with the passage of time due to a particular source of corrosion, said modelling means comprising a first series of instructions for defining a combination of inter-connected circuit elements and including at least one corrosion related parameter that is assumed to have a constant value,

a second modelling means defining a probabilistic model of deviation of each of said parameters, from the assumed constant value of the parameter, said second modelling means comprising a second series of instructions for defining a combination of inter-connected circuit elements,

execution means for executing said first modelling means with said parameter assumed to have a constant value and repeating execution of said first modelling means with said parameter deviated probabilistically from said assumed constant value, as generated by said second modelling means, said execution means comprising a third series of instructions for defining a combination of inter-connected circuit elements,

storing means for storing a probability distribution of the number of failed tubes as dependent on said probabilistic deviation of said parameter about the assumed constant value of the parameter, said storing means comprising a fourth series of instructions for defining a combination of inter-connected circuit elements, and

computing means for computing and displaying an uncertainty index commensurate with the probability distribution stored in said storing means.

10. A computerized system for plotting a probability of failure of tubes in a tube array due to corrosion over a series of future time intervals comprising a computer platform including a central processing unit, data storage means, a user interface, means for plotting a quantitative relationship between an independent variable and a dependent variable, and computer program means stored in said computer platform and defining instructions for executing digitized processes under control of said processing unit, wherein said computer platform and computer program means define a plurality of functional modules including:

a first functional module, for creating a data array defining a number of tubes in the tube array, a plurality of time points defining said time intervals during which degradation is to be assessed, and operating conditions that induce corrosion during each time interval, said first functional module comprising a first series of instructions for defining a combination of inter-connected circuit elements,

a second functional module, for computing expected degradation values of the tube array over a plurality of time points using a deterministic failure model having at least one parameter that is assumed to have a constant value at each time point, such that said expected degradation values are a computed dependent variable with time as an independent variable, said second functional module comprising a second series of instructions for defining a combination of inter-connected circuit elements,

a third functional module for creating a data array in which the assumed constant value of said parameter at each time point is a probabilistic variable that deviates probabilistically from said assumed constant value at said time point, said third functional module comprising a third series of instructions for defining a combination of inter-connected circuit elements,

a fourth functional module for computing a plurality of additional degradation values using said deterministic failure model at each of said time point, for each of said deviated value of the parameter, thereby generating a distribution of degradation values at said time point surrounding said expected degradation value at said time point, said fourth functional module comprising a fourth series of instructions for defining a combination of inter-connected circuit elements,

a fifth functional module for generating a quantitative representation from said distribution, commensurate with an uncertainty at each time point in said expected degradation value, said fifth functional module comprising a fifth series of instructions for defining a combination of inter-connected circuit elements, and

a sixth functional module for controlling said means for plotting, to plot the expected degradation value as a dependent variable against time as an independent variable as computed in said second functional module, and to plot said representation of the uncertainty in said expected degradation values as another dependent variable against time as the independent variable, said sixth functional module comprising a sixth series of instructions for defining a combination of inter-connected circuit elements.