Temporal variability in corrosion modeling and reliability updating

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.