FPSO Integrity: JIP on FPSO Fatigue Loads

Bluewater developed a hull fatigue strategy for her FPSOs. This strategy supports the decision process with respect to fatigue damage during the hull selection, hull modification and lifetime extension, hull monitoring/ inspection and offshore hull repair. The essential element in this process is the correct identification of the fatigue sensitive structural details and determination of their remaining fatigue life. As this remaining fatigue life can not be measured directly, a calculation procedure is necessary to estimate this remaining life.In the presented paper, the hull fatigue strategy is discussed and the side shell structure of FPSO Uisge Gorm is used as an example. After seven years of service as an FPSO, the applied strategy for the Uisge Gorm is evaluated. Using feedback from tank inspections, the predicted remaining fatigue life is compared with the actual cracks found. This information is used to improve the assessment procedure for fatigue sensitive structural details. The consequences for the hull fatigue strategy are discussed. Attention is given to improved models that predict the loading on the structural detail. In addition, some attention is given to (future) in-service monitoring systems that can determine this loading while the FPSO is at a field. Using such methods, the remaining hull fatigue life predictions will be updated continuously during the field lifetime.

Section: Crackmentioning

confidence: 99%

FPSO Fatigue Assessment: Feedback From In-Service Inspections

Hoogeland¹,

Nat²,

Kaminski

2003

“…A joint industry project on measurements of load effects on a floating production ship is presently going, see Bultema et al 16 .Therefore the aim of the project described in the present paper is to complement the ongoing JIP with emphasis on the capacity side to improve the basis for stress concentration factors and S-N data. Thus a minor error in determination of one parameter may lead to a significant deviation in predicted fatigue life.…”

Section: Motivationmentioning

confidence: 99%

Background and Status of the FPSO Fatigue Capacity JIP

Lotsberg

2000

A joint industry project on the Fatigue Capacity of FPSOs is being carried out with 19 participants from oil companies, designers, shipyards, classification soceieties and one university. This paper presents the background and the status of the project. The main objective of the project is to reduce the risk for fatigue cracks and fracture in FPSOs.Part of the work is carried out by a number of participants as work in kind. The project will provide small scale and full scale S-N data on typical fatigue sensitive details in FPSOs and tankers. It will also provide improved information on the important link between S-N data and finite element analyses for fatigue life assessment. Finally it will provide data to assess more reliable the risk for unstable fracture of FPSOs when fatigue cracks are present in the structure.

“…The background, objectives and structure of the project are described in further detail in ref [1]. The background, objectives and structure of the project are described in further detail in ref [1].…”

Section: Introductionmentioning

confidence: 99%

FPSO Integrity; Structural Monitoring of Glas Dowr

Boom¹,

Krekel²,

Aalberts³

2000

Self Cite

The objective of the Joint Industry project 'FPSO Integrity' is to provide insight in the fatigue loading of FPSO's and the accuracy and validity of computational models. The results should contribute to reliable life time prediction and site assessment studies for this relative new concept of production.Within the frame work of this JIP, 'Glas Dowr', a new build double hull FPSO operated by Bluewater for Amerada Hess at the Durward and Dauntless fields in the North Sea, has been instrumented extensively. The objective of the instrumentation was to measure sufficient signals to derive the fatigue loading on the vessel. The dedicated monitoring system comprised the instrumentation of two cross sections of the vessel with strain gauges, pressure transducers and wave height radar's. Also the deck and the turret were equipped with strain gauges. Both the wave induced motions and the low frequency positions and orientation of the vessel was recorded. For the analysis of the measured signals the wind, wave and current conditions have been recorded as well as the vessel parameters such as draft, trim and tank loads. Data from the Glas Dowr has been collected from October 1, 1997 to 1 August 1999. The data has been subjected to long term statistical analysis and for selected periods to more detailed spectral and statistical analysis as well as rain flow counts. The results have been used for validation of existing fatigue load calculation methods used by five classification societies and for the development of new fatigue load prediction software.