Structural Fatigue of Process Plant Modules during Ocean Transport

Increasingly, process plant modules are transported by sea from a module assembly yard to the plant site. Structural engineers and naval architects routinely collaborate to ensure that the module has sufficient structural strength to withstand inertial forces imposed by probable extreme motions during ocean transport. However, it is not only extreme motions that must be considered, because all motions will contribute to accumulation of structural fatigue damage. The module must be detailed to ensure that it has adequate fatigue resistance. This paper describes a relatively simple procedure by which the fatigue resistance of a module’s structural details can be assessed. The paper briefly describes the basics of fatigue damage assessment. It describes the data required from a naval architect for a simplified fatigue assessment of a module structure subject to vessel motions and includes results of such an assessment using criteria from AISC 360-10.