This paper presents the methodology used in calibrating the fatigue lives of primary tubular connections on a number of fixed offshore platforms in Bass Strait, Australia. The calibration was intended to produce a more realistic assessment of the probability of failure due to fatigue of primary tubular joints. This assessment was subsequently input into a risk based model for generating inspection programs on individual platforms, some of which have been in service for more than thirty years.
There are 14 steel jacket platforms in Bass Strait Australia operated by Esso Australia Ltd (Esso) for Esso Australia Resources Ltd and its joint venture partner BHP Australia. Water depths for the platforms range between 45 and 95 metres. The first five platforms installed in Bass Strait, also known as first generation platforms (FGP's), were installed between 1967 and 1969. The remaining steel jacket platforms were installed between 1976 and 1989. The potential for fatigue cracking in welded tubular joints is a key industry consideration with respect to assessing and maintaining the integrity of jacket structures. Fatigue analyses provide a basis for prioritising and selecting members for inspection purposes. However, fatigue analyses tend to produce very conservative predictions of joint fatigue lives. While this may be suitable for design purposes or for simple inspection prioritisation processes, it is overly conservative when assessing the risk of failure of in-service platforms. In order to quantify a probability of member failure, as is required in the development of a risk based inspection (RBI) program, more realistic fatigue data is required in order to better reflect the experience and data collected over the inspection history of the structure. To provide support to the development of an RBI methodology for underwater platform inspection (Barton & Descamps, 2000)
