TANK BOTTOM LIFE, RISK BASED INSPECTION AND CORROSION: PART 2

IN PART 1, we established a foundation for determining what a corrosion rate is and how it is used to establish tank internal inspection intervals. In this part we provide the methodology for using survival analysis (Sidebar 1) to properly quantify the useful tank bottom life which may then be applied to managing the inspection protocols of tank populations. [SIDEBAR 1: SURVIVAL ANALYSIS Survival analysis is a branch of statistics that is best suited to technically address rates of mortality and lifespan. This idea might be applied to: Cancer studies of patient survival time Equipment failure and failure time analysis Event history analysis The two most important variables in survival analysis are time to failure and relapse-free survival time which corresponds to survival time after a treatment (in the case of tanks this would be survival time after repairs). Another important aspect of survival time is censoring, which means that the data or study are not available to show when the failure occurred. In tank bottoms this would be cases where the data were collected but the tank failed prior to the inspection (e.g. holes in the tank bottom discovered during internal...