Reliability Analysis of Marine Platforms Subject to Fatigue Damage for Risk Based Inspection Planning

Abstract

The probability of failure of steel jacket platforms subjected to fatigue damage is computed by means of Monte Carlo simulations using limit state functions in which wave, wind, and deck loadings are expressed in terms of empirical functions of uncertain maximum wave height. Limit state functions associated with the base shear capacity of the jacket and the shear capacity of the deck legs were used. The sensitivity of the probability of failure to the coefficient of variation of resistance, of wave height, of resistance and loading biases, and to parameters in empirical loading functions, as well as the influence of the reserve strength ratio is analyzed using a simplified limit state function. Results from simulations are compared to those obtained with a formulation that relates the reserve strength ratio to the reliability index. An application to risk based inspection planning for extension of the service life of a platform is given.

A probabilistic approach to lifetime design of offshore platforms

“…( 12 ), is the annual probability of failure of the structure; it is the probability of lateral wave loading exceeding the ultimate resistance of the jacket in any given year. Assuming that a year is independent of another year, the cumulative probability of failure for t years can hence be calculated 17 . where is the annual probability of failure in year k .…”

“…Then the in year t can be expressed via Eq. ( 13 ) 17 . where is the annual conditional probability of failure given that there is no damage, is the annual conditional probability of failure given the state of damage i , is the probability of occurrence of damage state i , in year t ; and is the probability of no damage in the structure in year t as shown in Eq.…”

“…Finally, the annual reliability index ( ) throughout the design lifetime is calculated using Eq. ( 15 ) 17 . In Eqs.…”

“…Some studies have estimated wind speed and wave height with likelihood models. Heredia-Zavoni et al 17 determined the failure probability of steel jacket platforms under fatigue damage defining limit state functions for their applied loads. Lee et al 18 estimated extreme wind speed using Gumbel and Weibull distributions.…”

Fusing fleet in-service measurements using Bayesian networks

“…Heredia-Zavoni et al [17] presented a general framework for integrity management of offshore steel structures. This framework allows for risk-based planning of inspection and maintenance activities which accounts for both deterioration and damage processes using a Bayesian network for decision making.…”