Risk Based Inspection Approach for Topside Structural Components
Authors: Truchon Michel , Rouhan Antoine , Goyet Jean 
Published: October 2008

The fleet of Total floating production units is at present highly increasing. They range from converted tankers to new built mega-FPSO projects as Girassol or Dalia (Angola). In order to better assess for the safety, environmental and economic aspects in these developments, it has been decided to develop and use Risk Based Inspection methodologies for all systems and sub-systems of the units. In the past decade, RBI methodologies have been developed and applied for the Hull part and the Process part of the FPSO's. This paper presents the Risk Based Inspection planning approach that has been developed and implemented for defining the inspection plan of Topsides Structural Components of FPSO's.

This approach has been applied to the topsides modules of a specific FPSO used as reference and will be applied in the future to the full Total fleet of FPSO's.

Due to the large variety of components types, a qualitative risk approach has been developed and applied. In this approach, failure modes are described and probabilities and consequences of failure are assessed. Risk level and corresponding inspection effort are estimated. An overall inspection plan is then provided for all structural components of the topside process modules: basic modules, pipe racks modules and manifolds. Such a methodology has the benefit to rank the components and results in the optimising of the inspection and maintenance effort. Typical input data and results of the application on the reference FPSO are included in the paper.

Very few publications on RBI methodologies for Topsides Structural components exist and have been actually applied. The work presented in the paper allows now to provide such methodology. Redundancy analyses are used and Risk Analysis is performed taking into account the consequences of failures of Topsides Structural Components in terms of Physical injury, Environment and Asset (Loss of production, Unavailability, Costs of repair). The development of RBI approach for Topsides Structural Components, in addition to specific RBI methodologies already developed for Hull and Process, provide a full consistent approach for the maintenance and the inspection of offshore facilities, where all systems and sub-systems are addressed.

Introduction

Total is now operating and will operate in the future almost a dozen of assets having the function of storage, and/or production, and/or offloading - in short FPSO. Paper OTC- 18563 (this Conference) is giving an extensive panorama of this fleet [1].

These Floating Units can be ship-shaped or box-shaped or any other shape such as TLPs, SPARs, SEMIs, etc. They can be in steel or concrete and can handle various types of hydrocarbon products (oil, condensates, gas, LPG, LNG..). What are common to all are the topsides that are built in separate modules which are then put together on the main support in the construction yard. Each module is made of a structure that supports all process equipment.

The inspection issue

In conventional offshore development, i.e. jacket based, the inspection of topside structure is mainly driven by the painting deterioration and the subsequent corrosion issue.