Fatigue design of steel containment cylinders for CNG ship application

A reliable methodology is required for fatigue design of steel cylinders for Compressed Natural Gas (CNG) carriers in order to meet target safety level at an acceptable cost. This includes description of physical models that represents actual long term fatigue capacity of the Cargo Containment cylinders. The design methodology includes length of welds, fabrication tolerances, fabrication methodology and non destructive testing. It also involves definition of characteristic values for loading and capacity in addition to recommended Design Fatigue Factors. Three alternative fatigue design procedures requiring different Design Fatigue Factors to achieve a system target safety level of annual probability of failure less or equal to 10−5 are presented.