Corrosion analysis system and method

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.

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.

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.