Simplified fatigue analysis of structural details of an ageing LPG carrier

Abstract

As the world gas carrier fleet is ageing, it is required to make sure that the transportation of oil and gas is carried out by quality vessels. Ship's conditions can remain of a good level throughout their service lives if they are operated in an appropriate manner, the current state of construction and equipment of each structure are clearly understood and inspections and maintenance are carried out regularly and properly. Fatigue is an important phenomenon that causes damage failure around the weld at member connections of ship structures. Fatigue happens due to high stress concentrations in the long term since loading conditions are time-dependent and continuous in dynamic sea environment. A fatigue crack starts at a localised spot and will with cyclic stress gradually increase over the cross section of the member. This study aims to calculate the fatigue life of longitudinal members amidships. These fatigue calculations are theoretical calculations that should be used as guidance for close-up inspections when ships are surveyed periodically to verify that they are maintained in an acceptable condition in accordance with international conventions, the Rules of Classification societies, etc.