Floating production systems asset integrity management programs are dependent on a combination of inspection, analysis and measured data. These tasks are often labor intensive to perform. A digital twin model combines data and computer models, which can significantly increase the efficiency of these integrity management tasks. A digital twin model has been developed that utilizes typical floating systems measured data and a global performance model. This digital twin model provides an automated continuous assessment of the asset. Eliminating many of the labor intensive activities allows personnel to focus on applying the outcomes of the floating systems assessments rather than performing the assessments. The automated and continuous nature of the digital twin model also allows for a much greater understanding of the behavior of the system, which is the fundamental basis of a successful integrity management program.

This paper describes the experience of Petrobras in the design, installation and operation of deepwater mooring systems incorporating high efficiency polyester fiber ropes. These ropes have been used now for more than 12 years in catenary and taut configurations to moor drilling and production units as well as storage and offloading facilities. The paper provides a history of the development of this technology, highlighting the key issues involved in introducing in mooring systems a component that has non-linear visco-elastic behavior. Differences to all steel systems in terms of: behavior, failure modes and design criteria and procedures are discussed. The paper presents the life cycle management strategy adopted by Petrobras in the early years of the use of this technology and its evolution that have guaranteed that the only failure mode observed over all these years was mechanical damage. It is expected that this paper shows that the use of polyester (polyethylene terephthalate) ropes in deepwater moorings is a mature technology.

Following the warning of a flooded bow horizontal brace of a semi-submersible production platform, an inspection diving team was mobilized and cracks were found at both bow and aft K-joints. Analysis of the service life of the platform, together with the results of structural analysis and local strain measurements, concluded that cracking was caused by fatigue initiated at high stress concentration points on the gusset plates inserted in the tubular joints. As a consequence of the fractured plates other cracks were nucleated close to the intersection lines of the braces that compose the K-joints. Based on this analysis different repair possibilities were proposed. To comply with the production goals of the Business Unit it was decided to repair the platform on-site and in production in agreement with the Classification Society. The proposed repair contemplated the installation of two flanges on the gusset plates between the diagonal braces by underwater wet (UWW) welding. Cracks at the gusset plates were also removed by grinding and wet welding. Defects located at the braces are being monitored and repaired by the installation of backing bars, by wet welding, followed by grinding and welding from the inside. To carry out the job two weld procedures and ten welder-divers were qualified.

Life extension of ageing floating production facilities can be an effective way to maximize profitability of mature assets by extending production and offset decommissioning expenditures, increasing profitability. Utilizing existing assets can be also an option to develop and tie-back new marginal fields in a more economical way rather than develop new large greenfield facilities. Nonetheless, the benefits of extending the life of the production system might be reverted not only due to the installed capital cost of replacement of a mooring system, but also due to loss or deferred production. The present paper proposes a holistic approach for assessment of the mooring system in order to achieve the intended performance of the asset, taking into consideration not only the system design but also the knowledge accumulated during the original operational life of the legacy system.

The primary goal of floating systems life extension efforts is to project how the system or components will behave in the future beyond the original design life. This predicted behavior can then be used to determine the practicality of the proposed life extension in terms of safety, environmental and economic risk. Often, these predictions are limited to reviewing inspection data (which has a limited ability to predict future response) or analysis (which is dependent on various assumptions). Measured data from in-situ monitoring systems provides accurate system response information which, in conjunction with mathematical modeling and inspection data, can be used to determine past and future behavior. The full potential of measured data for life extension activities has not been realized thus far. Some uses of measured data in life extension efforts are illustrated through examples in this paper. The first example highlights ongoing fatigue assessment of a mooring line chain jack system using line tension measurements. The second example describes how uncertainty was greatly reduced in a polyester rope fatigue assessment by utilizing measured mooring line tension data. The third example demonstrates use of measured vortex induced motion response of a floating system to reduce the conservative assumptions provided during the design phase. The results of all of these examples show that measured data can provide insight into floating production system (FPS) response that cannot be attained otherwise, allowing for significantly reduced conservatism in life extension engineering assessments. Without the availability and use of this data it would be difficult to demonstrate the fitness for service of these facilities. The examples of utilizing measured data to enhance life extension efforts provide concrete demonstrations as to how life extension of FPS components can be justified where uncertainty in analytical prediction is high. In such situations, demonstrating fitness for service beyond the design life would prove exceedingly difficult if measured data was not available. Continued service feasibility is most effectively demonstrated by augmenting inspection and analysis efforts with field monitoring data.

The Perdido platform is a spar located in a water depth of 7,825 feet in the Alaminos Canyon Block 857in the Gulf of Mexico. The mooring system consists of nine mooring lines in three groups of three, spacedapproximately 120 degrees apart between each group. Each mooring line is composed of a platform chain,a multi-segment polyester rope including a 120 feet long test insert at the top, a ground chain, a pile chainand other associated connectors. The mooring lines are connected to suction piles. The Minimum BreakStrength for the Perdido polyester mooring line is 4,000 kips. Installation of the spar hull was completed inSeptember 2008 and the topsides was set in March 2009. The spar and its mooring system were originallydesigned for a twenty (20) year life. On May 4, 2019, mooring line # 6 (ML6) was contacted by a marine vessel down line and was severed.Contact occurred along the polyester test insert. A recovery effort was planned, and the mooring line wasreplaced in early June. The original ML6 was recovered from the seafloor on June 4, 2019 as a part of thatcampaign and submitted to an initial inspection. This paper is not intended to go into either the cause of the incident or the replacement of ML6 but willlook to the inspection of the recovered mooring line and explore its suitability for reuse. Initial inspection ofthe lines suggested minimal damage to the polyester rope segments and raised questions to the impacts of 10years of use. Testing was envisioned as a learning opportunity for the impact of service on polyester mooringand was reinforced by the potential cost savings that could be attained though reuse. A methodology wasdeveloped, supported by initial inspections and a suite of testing was performed. The results of these testsare presented in the following, along with a proposed process for assessing and considering reuse of a linefollowing a drop. Additionally, conclusions will be shared for the process, the results, and the potentialramifications for the industry.