Corrosion Fatigue of Stiffened Offshore Steel Tubular Joints

Abstract

Corrosion fatigue is a complex phenomenon involving many variables. Welded‐steel tubular joints of offshore structures are subjected to corrosion fatigue due to the combined action of corrosive seawater environment and cyclic wave forces. This paper addresses the aforementioned problem, mainly with respect to internally ring stiffened steel tubular joints. The studies were made with respect to tropical seawater environment similar to that in the Bombay High offshore region where bulk of the Indian oil is produced. Corrosion‐fatigue tests were conducted on five welded‐steel tubular T and Y joints under constant amplitude axial‐brace loading at a frequency of 0.2 Hz. The studies have shown reduction in fatigue life when compared to S‐N curves recommended by the codes that are mainly based on air fatigue tests. Based on crack‐growth data obtained from the tests, a model has been proposed to predict the remaining life of stiffened tubular joints under corrosion fatigue.