NDLI: Integrated Fatigue Analysis of the GAP Structural System

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Melis, Cecile Laymond, Stephane Jean, Philippe
Copyright Year	2008
Abstract	MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. The GAP is an interesting combination of mooring (tether chains), dynamic steel riser (carrier pipe and flowlines) and steel structures (towheads). Design codes and standards usually address the design of these components separately. One of the challenges of the GAP project is to have a consistent design philosophy for all the components so that the GAP can be treated as an integrated system with homogeneous quality and safety levels. GAP component fatigue analysis is a good example of integrated system design. In the GAP, fatigue loading is applied by the floaters, through the tether chains, to the towheads into the carrier pipe. The fatigue analysis of individual GAP components cannot be performed in isolation — it must be the result of an integrated GAP fatigue analysis. A global model of the GAP is built with towheads modelled as rigid bodies and tether chains and carrier pipe modelled as dynamic lines. This model is used to obtain time series of loads on all components of the GAP. The fatigue of each component is calculated using the same methodology based on stress Response Amplitude Operators (RAOs) for a selected number of combinations of FPSO headings, wave directions, FPSO drafts and fluid densities. This methodology is classical for chains and steel pipes. It is less classical to apply such a detailed methodology for large structures like towheads. The towhead structures are key components that provide connection between tether chains and carrier pipe, flexible jumpers and steel flow lines, carrier pipe and decoupling overhead buoyancy tank. As such, the fatigue analysis of the towhead is as critical as for the tether chains and the carrier pipe. Finite element models of the towheads have been subjected to unit loads from all components attached to them and from the dynamic fluid pressures generated by unit towhead accelerations. Using the loads extracted from hydrodynamics calculations on the global GAP model and the matrix of stress for unit loads, the time domain approach is kept throughout the complete structural assessment of the towheads. This is in order to maintain a high degree of accuracy in the stress prediction. Given the criticality of the carrier pipe, a very detailed Engineering Criticality Assessment (ECA) is performed to define flaw acceptance criteria to be used during the Non Destructive Examination (NDE) campaign.
Sponsorship	Ocean, Offshore and Arctic Engineering Division
Starting Page	531
Ending Page	540
Page Count	10
File Format	PDF
ISBN	9780791848180
DOI	10.1115/OMAE2008-57534
e-ISBN	0791838218
Volume Number	Volume 1: Offshore Technology
Conference Proceedings	ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering
Language	English
Publisher Date	2008-06-15
Publisher Place	Estoril, Portugal
Access Restriction	Subscribed
Subject Keyword	Dynamic riser Fluid transfer system Fatigue Eca Bundle Gap Water Chain Seas Gravity (force) Buoyancy Fatigue analysis Waves Design Fluids Nondestructive evaluation Finite element model China Engineering standards Safety Risers (casting) Acceptance criteria Integrated systems Mooring Fpso Time series Hydrodynamics Fluid density Steel Flow (dynamics) Stress Fluid pressure Spar platforms Pipeline risers Ocean engineering Pipes Wing spars
Content Type	Text
Resource Type	Article

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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GAP Launch: Methodology, Constraints and Challenges

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