Corrosion of Buried Steel at New and In-Service Infrastructure (2023) / Chapter Skim
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8 Predictive Modeling
8 Predictive Modeling
Pages 93-104
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From page 93... ...
The geo-civil industries tend to use models prior to design to predict metal loss with time and therefore to determine the additional steel necessary in design to compensate for that metal loss due. The oil and gas pipeline industries tend to emphasize modeling of the steel infrastructure during operations and maintenance, using data collected from indirect or in-line inspection (ILI)
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From page 94... ...
EMPIRICAL MODELS FOR CORROSION RATE BASED ON SUBSURFACE PROPERTIES One type of empirical model estimates corrosion rates based on subsurface characterization measurements (see Chapter 6)
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From page 95... ...
PREDICTIVE MODELING 95 TABLE 8.1 Types of Models Applied to Problems Related to Corrosion of Buried Steel Example Outputs for Example Inputs for Corrosion Model Type Definition Typical Use Corrosion Applications Applications Deterministic Models Empirical Directly relate Research and the geo- Corrosion rate Measured soil resistivity and pH input to a database civil industries of observations or Metal loss Experimentally derived estimates experimental data describing corrosion rate in 1 year and a time constant describing change of corrosion rate over time Semiempirical Use simplified Academia and industry Metal loss due to Difference in the respective calculations to use galvanic corrosion corrosion potentials; kinetics of the relate input to electrochemical reactions on each a database of metal, areas of each metal, and the observations or ohmic resistance of the electrolyte to experimental which they are exposed results to obtain an answer Analytical Mathematical Used in research and Effectiveness of cathodic Measurements of a corrosion defect models that rarely in oil and gas protection and the and of potential, current, and describe an exact industries likelihood of corrosion impedance profiles change in a Corrosion rate Measured electrochemical potential system through at surface, measured or calculated solution of a thermodynamic and kinetic mathematical parameters analytic function Numerical Computation of Used in research and Finite element modeling a large number rarely in oil and gas to predict corrosion of mathematical industries anomalies for cathodic equations to find protection systems an approximate Predictions of galvanic Electrical or thermal field given solution corrosion for components conductivity and appropriate with complex shapes boundary conditions Nondeterministic Models Statistical Mathematical Used in research and in Probability of pipeline Defect measurements model oil and gas industriesa failure, uncertainty incorporating of corrosion rate, set of statistical uncertainty of corrosion assumptions depth about sampling of corrosion processes or corrosion damage Stochastic Mathematical Used in research and in Spatial distribution or Historical inspection data; soil survey model to estimate oil and gas industriesb occurrence of corrosion results; climate, geological, and spatial/temporal defects or events, geotechnical data variation of temporal fluctuation of possible outcomes; corrosion rate or current variation usually based on historical data continued
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From page 96... ...
concluded that buried steel corrosion rates attenuate with time, depending on the degree to which the soil is aerated, which, in turn, is dependent largely on drainage. He found this observation applied to general corrosion as well as localized corrosion from pitting.
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From page 97... ...
The protective scale formed in this manner tends to decrease corrosion rates with time, and this is modeled using lower values of n1 and n2. In poorly aerated soils, the products of corrosion remain as ferrous ions with a lower oxidation state and tend to diffuse outward into the soil, offering little or no protection to the buried steel, such that the initial corrosion rates decrease slowly with respect to time, if at all.
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From page 98... ...
But for longer service lives (e.g., 75 or 100 years) , the linearized AASHTO model renders more metal loss compared to the power law implemented for the Darbin model (Fishman and Withiam, 2011)
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From page 99... ...
But for longer service lives (e.g., 75 or 100 years) , the linearized AASHTO model renders more metal loss compared to the power law implemented for the Darbin model (Fishman and Withiam, 2011)
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From page 100... ...
that "defines and classifies galvanic compatibility of electrically conductive materials and establishes requirements for protecting electrically conductive materials in a dissimilar couple against galvanic corrosion." The standard replaces an older standard based only on corrosion potentials, which can result in incorrect recommendations. The new standard is based on polarization curves using predictions of the sort provided by the commercial software listed above.
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From page 101... ...
Probabilistic Modeling for Corrosion Rate and Severity Recent efforts in corrosion science have attempted to try to implement probabilistic reliability-based models, instead of "go/no-go" models that are based on factors of safety. This has been more successful in recent years in the oil and gas pipeline industries that utilize ILI data from "smart pigs" to measure size, shape, and locations of defects (see Chapter 7)
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From page 102... ...
Effective ML requires large, high-fidelity datasets to allow accurate training as well as validation and testing of the algorithms. The oil and gas pipeline industries have generated large volumes of data as a result of regulatory requirements for active integrity programs and the ability to collect pipe corrosion data using sensors in smart pigs.
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From page 103... ...
One approach, known as density functional theory, solves an equation similar to the Schrodinger equation for a small cluster of atoms to determine factors such as the electron density distribution, system potential energy, band structure, and the equilibrium atomic structure. These parameters can be used for a variety of fundamental applications relevant to corrosion, such as assessing chemical bond strength, reaction mechanisms, activation energies and reaction kinetics, and mechanical properties (Ke and Taylor, 2019)
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