Retrofitting analysis of tanker ship hull structure subjected to corrosion

Abstract

The objective of the study presented here is to investigate the efficiency in recovering the structural capacity of a double bottom side girder plate of an oil tanker, accounting for the probability of failure and cost associated with the retrofit or substitution of the plate. The side girder includes a manhole shape opening, and it is subjected to a uniaxial compressive load and random non-uniform corrosion degradation. The Monte Carlo simulator models the non-uniformity of the corrosion degradation. Four cases are considered for the retrofitting process: the replacement of the entire plate, reinforcement by two longitudinal stiffeners, two longitudinal and two transversal stiffeners, a flange on the opening. Twelve scenarios are selected and analysed. Four strategies of accessing the space where the side girder is located to perform the retrofit and replacement are considered: no opening, access from the deck of the vessel, access from the side of the vessel, access from the bottom of the vessel. The First Order Reliability Method is used to estimate the reliability of the different solutions towards time. The cost and associated risk assessment are performed to compare the scenarios and determine the most convenient one. A comparison of the most advantageous solutions and the worst one is conducted considering the probability of failure, cost and associated risk.