Reliability Analysis of Tank Car General Corrosion

As is well documented in the literature, corrosion behavior is sensitive to both material characteristics and environmental variables. Different corrosion behaviors occur for different combinations of material/environment systems, as dictated by thermodynamic conditions and kinetic laws for specific operating situations. Not being limited to a specific corrosion mechanism, the current work for corrosion reliability analysis is based on a phenomenon that is common to tank car general corrosion process. This common phenomenon is the material loss (tank wall thinning) as a function of time. A phenomenon-based general corrosion model is proposed as shown in the lower left figure for a schematic of tank wall cross section, where B0 is the original tank wall thickness; the area designated “corroded” is the material loss (tank wall thinning) at time t; B(t) is remaining thickness at a corrosion site at time t, Bc is a critical tank wall thickness below which leakage or rupture may occur. The lower right figure shows failure probability as a function of sevice time for five cases with different corrosion rate/corrosion initiation time to illustrate the effects of major parameters.

Although it is phenomenon-based, specific corrosion mechanisms and the corresponding material and electrochemical variables can readily enter into the model through kinetic laws dictating the corrosion rate and the corrosion initiation time. Thus, the phenomenon-based model retains sufficient generality to accommodate specific corrosion mechanisms and the corresponding parameters.