Extreme growth behaviour of corrosion pit in hydrocarbon pipeline (case study of ø242.1mm pipeline)

Abstract

Inspection data obtained from in-line inspection is useful to assess present integrity as well as to predict future integrity of pipeline by using statistical and probabilistic analyses and simulation process. However, numerical errors arise when all the inspection data are used in the analysis. Numerical error arises because failure probability due to a single extreme corrosion out of huge quantity of corrosion data has been greatly reduced. Thus, in this study, extreme values analysis using extreme value theory, peaks-over-threshold method or combination of both methods is adopted to analyze the inspection data. This aims to eliminate the “low-risk” data in the analysis in order for extreme values to be emphasized. Based on the result, high threshold value will lead to high failure probability. However, the optimum threshold value is limited by the number of remaining data. Meanwhile, extreme value distribution is also efficient in indicating an early failure probability. Instead, combination of both methods results an overestimated failure probability.