Temporal Variability in Corrosion Modeling and Reliability Updating

[+] Author and Article Information
Daniel Straub

Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710straub@ce.berkeley.edu

Michael Havbro Faber

 Institute of Structural Engineering (IBK), ETH Zurich, 8093 Zurich, Switzerlandfaber@ibk.baug.ethz.ch

J. Offshore Mech. Arct. Eng 129(4), 265-272 (May 26, 2006) (8 pages) doi:10.1115/1.2355517 History: Received July 21, 2005; Revised May 26, 2006

Many parameters influencing corrosion degradation are time variant and the corrosion process is thus subject to temporal variability, the real characteristics of which are commonly neglected in reliability assessment. After a short overview on the quantitative modeling of corrosion loss, a comparison is made between different temporal models of corrosion degradation and the consequences of applying an inappropriate model are investigated. The effect of temporal variability is then investigated in detail and illustrated in an example considering CO2 corrosion in pipelines. It is demonstrated how the time-variant corrosion process can be consistently represented by time-invariant random variables, using equivalent values of the corrosion rate. Finally, the influence of temporal variability on reliability updating following inspections is investigated and it is shown how this effect can be accounted for in inspection planning.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Common quantitative temporal corrosion models

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Figure 2

Comparing two corrosion models. The shaded areas represent the 95% confidence interval.

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Figure 3

Reliability index obtained with the two corrosion models, with and without inspection

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Figure 4

One realization of the two random processes and the consequent corrosion rate

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Figure 5

The distribution of re(t=5year)

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Figure 6

The standard deviation of the equivalent corrosion rate σre as a function of νt

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Figure 7

Correlation of the equivalent corrosion rate in the period before the inspection and the total time period t



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