TANK BOTTOM LIFE, RISK BASED INSPECTION AND CORROSION: PART 3

What it takes to implement corrosion prediction of tank bottoms. IN PART 1, we established a foundation for determining what a corrosion rate is, how care is required in defining a corrosion rate, and how it is used to establish tank internal inspection intervals. In Part 2, we provided the methodology for using survival analysis to properly quantify the useful tank bottom life. Part 3 will look at the details of how the gamma process model can work and show the kinds of results returned by simulated examples. THE CORROSION PROCESS The gamma model of corrosion has been applied to degradation of structures and corrosion by various researchers. One of the reasons that it has been applied is that the damage mechanisms are monotonically increasing with time and the model accounts for the random and independent increments of corrosion depth. The model works well with observed corrosion depths we investigated. The unique corrosion history varies randomly around the expected pit depth, as shown in Part 2. In a gamma process model1, pit depth at time t has a gamma distribution2 with constant scale, s , and mean equal to the power law for pit depth, as shown in Figure 2. The...