ABSTRACT

This paper provides an overview of the Monitas project, aspects of which are further detailed in accompanied OTC 2010 papers. The Monitas project is a Joint Industry Project that was presented to the offshore industry in 2005 and now the project is close to its completion. The Monitas project has developed the Advisory Monitoring System (AMS) that presents, explains and advises on the fatigue lifetime consumption of FPSO's hulls. The advice is based on comparisons between the design and the actual fatigue lifetimes predicted by replacing the design factors like operational settings, environmental conditions and hydro-structural response by the measured ones. The name Monitas stands for Monitoring Advisory System.

The project has demonstrated that the Monitas system installed on board an FPSO enhances the safety of the crew, the asset and the environment by controlling the lifetime consumption of the hull. Deviations from the design conditions can be timely identified and actions can be undertaken to secure sufficient lifetime in case it is being consumed too fast. The beauty of the system lies in the fact that the system identifies which factor contributes mostly to faster lifetime consumption. The project recommends including the requirement for such a system in the contract specification. This allows for a proper documentation of the fatigue lifetime calculations and cost-effective implementation of the system without expensive change orders.

The project results are applicable directly to all FPSOs and with some modifications to all floating structures. The Monitas system, when installed, can give justification for lifetime extension. The paper ends with plans for improving the system.

Introduction

The background of the Monitas project was presented by Kaminski (2007). Based on discussion of fatigue design practice applied for FPSOs and associated uncertainties he concluded that the industry record showing fatigue failures in many FPSOs is understandable. This is because fatigue is a very complex phenomenon depending on multiple variables with large uncertainties and relatively low safety factors which are unfortunately defined on fatigue lifetime. His conclusion is well supported by the following clause added to a report on fatigue design analysis carried out by an offshore yard:

" It should be noted that the accuracy of fatigue life estimates is dependent upon many factors related to original construction, structural maintenance and the FPSO's operational profile as well as to the application of the method, assumptions and statistical distribution of environmental data of the assessment procedure. Hence, such estimates should be considered as a qualitative indicator of the capability of the structure rather than an absolute prediction of service life limitation??

In 2005, MARIN as an independent and not-for-profit research foundation presented together with Total a proposal to the FPSO industry for the Monitas Joint Industry Project (JIP). The Monitas name stands for Monitoring Advisory System. The goal of the project was to develop an Advisory Monitoring System that will explain why the actual fatigue lifetime differs from the predicted one. Such an explanation was meant to give a rational basis for actions assuring desired fatigue lifetime when the fatigue lifetime is consumed too fast. This is contrary to existing Hull Monitoring Systems (HMS) which only shows the consumed fatigue lifetime (or equivalently the accumulated fatigue damage).

The industry responded very positively to this proposal. At the moment sixteen companies form the Monitas consortium and support the project. They are listed in the Acknowledgement and include major Class Societies, major gas & oil companies, FPSO designers & operators and shipyards.

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