Operators of marine structures have to ensure that structural integrity is maintained at a sufficient level during in-service life or in the case of the structure life prolongation. This can be achieved by Inspection, Maintenance and Repair plans (IMR), as rational aid-tools for decisional purposes. Such plans are complex and can be expensive. This leads to their global optimization, particularly regarding inspections. In this context, original results on inspections data in IMR plans are presented. The approach is based on decision and detection theories and include both the probability of false alarm and the probability of detection. It is shown how to introduce these probabilities in a decision scheme. The effect of false alarms and miss detections on the global cost of inspection planning is underlined through a basic example.

This paper is the first part of a report dealing with industrial implementation of Risk Based Inspection planning methods to offshore facilities. The first part deals with FPSO/FSO while the second deals with fixed steel offshore structures. The objective of the report is to convey “lessons learned” from experience using RBI methods. Theses methods aim at establishing inspection planning based on optimization procedures derived from specific risk assessments. Experience of the three authors is based on the last methodological developments in the area of RBI planning for structural components subject to fatigue degradation and on application of these methods to various types of offshore facilities. The main steps of the RBI methodology are summarized in the first paper. General conclusions related to the two types of facilities are given at the end of the second paper.

Survey and inspection campaigns are important inputs in the Asset Integrity Management System (AIM) of FPSOs and other floating offshore facilities. Considering that the unit shall stay at site during the whole life of the field where the disconnection or the removal of the mooring system are not planned, a comprehensive methodology for the survey and inspection of the unit during this period shall be provided and subject to review based on the results of the scheduled inspections. So further than subjected to class and statutory requirements, inspection and survey plans shall reflect the required availability and durability of the unit regarding the field life. Among the several degradation mechanisms covered by the inspection and survey plans, fatigue is an important issue to check carefully. Risk Based Inspection Methodology has been adopted in several projects and is an important tool to establish rational inspection campaign for structural components, mainly for those located in areas where access is critical and operational constraints are an important parameter. The aim of this paper is to present the methodology to establish inspection and survey plans, combining RBI analysis and the industry expertise. The several steps to achieve the final inspection campaign are described based on the experience on new-built but also converted FPSOs.

SUMMARYThis paper deals with the problem of a through-cracked tubular joint behaviour modelling. A new beam ÿnite element has been created, in order to take into account the loss of sti ness of the joint due to through-thickness crack presence, and the coupling between axial force and bending momentum. This allows to study at a low computing time large damaged o shore structures, using beam elements. The mechanical model used to build the ÿnite element is ÿrst described. An analytical identiÿcation of its internal parameters (eccentricity and sti ness) is then performed. Finally, some results are presented.

The paper presents a Probabilistic System Approach for Risk Based Inspection (RBI) of FPSOs. This approach is based on a hierarchical model of the hull and uses Bayesian Probabilistic Networks to propagate probabilities from component level to system level. The system approach makes risk analysis more tractable because consequence analysis, including evaluation of direct and indirect consequences of damages to the constituents of the system, may be developed in an exhaustive and systematic way. This approach is new as consequences of failure and damages are usually considered only in setting crudely acceptable failure probabilities at component level. A model example is given for illustration. The paper gives also some insights regarding the owner and class point of views in terms of RBI. This paper explained also how Risk Based Inspection may be developed within the Class regime. Introduction Floating Production, Storage and Offloading Units (FPSOs) are specific installations regarding their operating conditions and functions in comparison with classic ships. One of these specificities is the lack of opportunity to dry-dock. Operating FPSOs continuously whilst at the same time safely presents therefore a particular challenge which ultimately led to the development of new Inspection, Maintenance and Repair (IMR) procedures to be applied to FPSOs. This has encouraged major companies and class societies to adopt Risk Based Inspection (RBI) as the most appropriate procedure for IMR planning of FPSOs. As a consequence, the challenge of both parties during the last decade was to develop and implement RBI methodologies which guarantee profitability and competitiveness of FPSOs while ensuring the required structural integrity level throughout the service life. Bureau Veritas has developed, since the beginning of this period, RBI methodologies which have then been applied to a significant number of offshore units and can also be used within Class regime. Bureau Veritas thus acquired major knowledge and competency in the field of RBI. In parallel, many major' oil companies decided to implement risk based IMR plans to some of their FPSOs. Advantages and benefits of RBI are first presented. It is shown how RBI may be a key issue to ensure the success of a Structural Integrity Management program for FPSOs. General principles of RBI are then reminded and a new RBI approach based on system considerations is presented: the approach uses a hierarchical representation of the hull and Bayesian Probabilistic Networks (BPNs) to compute at system level the risks associated to any inspection planning. A model example is given as illustration. The last part of the paper reverts on the challenge of the development of system approaches for RBI.