Because of the complexity involved in the process of fatigue/corrosion fatigue and many variables contributing to the process, tests on large size steel tubular joints are essential to understand the fatigue/corrosion fatigue behavior of steel jacket structures. Structural Engineering Research Centre, Madras (SERC-M) have carried out, in the last twelve years, nearly 25 fatigue tests on large size steel tubular joints in air and seawater environments. Crack measurements were made during testing by using a crack microgauge, the functioning of which was based on ACPD technique. Crack initiation and propagation during the tests were monitored.

The first part of this paper briefly discusses the different methods of detection and measurement of cracks in steel offshore structures. In the second part, experimental investigations carried out by the authors on the fatigue behavior of large size steel tubular joints in air and seawater environments have been explained. The results of the fatigue tests and crack measurements are discussed. It is observed from the crack growth data that multiple cracks develop under corrosion fatigue conditions, resulting in accelerated crack growth and consequent reduction in fatigue life.