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ABSTRACT Recent development plans envisage the transport of hydrocarbons at temperature and pressure conditions far more severe than in past projects. Indeed, technical feasibility of certain inter field lines was put in doubt as a consequence of application of design guidelines currently in force. This fact gave rise to a critical review of design criteria. Statoil and Norske Agip have sponsored an R&D HOTPIPE project whose overall objective is to prepare a DNV Recommended Practice, to be used in the verification and design of high temperature/high pressure pipelines. The design guideline covers most practical cases where pipelines are subjected to high internal pressure and temperature. The design criteria are based on the application of reliability methods to calibrate the partial safety factors involved. This paper describes the main structure of the design guideline, focusing on pipeline scenarios and design procedures. Further, draft design criteria for handling snaking of a pipeline on a flat seabed are given for illustration. BACKGROUND The characteristic behaviour of HP/HT pipelines from a structural point of view is the potential high effective compressive force that arises when it is totally restrained. This may cause global (Euler-) buckling and may be a potential hazard for in-service pipelines/flowlines at high pressure-temperature conditions. The Eulerbar buckling is induced by the frictional restraint of thermal expansion due to the change in temperature or internal pressure and may occur for both buried and unburied pipelines. Lines placed above ground or buried in relatively shallow trenches present two different modes of buckling: lateral/snaking and vertical/upheaval. A number of unexpected mishaps occurred in the second half of the 80's in the North Sea, causing considerable economic drawbacks from remedial measures and lost transmission availability. At least five upheaval buckling incidents in the North Sea are known, three of which occurred in 1989.
- Europe > United Kingdom > North Sea (0.45)
- Europe > Norway > North Sea (0.45)
- Europe > North Sea (0.45)
- (2 more...)
Design of Deepwater Metallic Risers
Kirkemo, Finn (Seaflex) | Mørk, Kim J. (Det Norske Veritas) | Sødahl, Nils (Det Norske Veritas) | Leira, Bernt (SINTEF)
ABSTRACT This paper gives an introduction to the results from a 4 year Joint Industry Project (JIP) named "Design procedures and acceptance criteria for deep water risers". The objective of the JIP is to provide the Oil & Gas industry with practical guidelines for the design and analysis of metallic risers with focus on deepwater application. The design and analysis guideline includes the following: safety classes linked to consequence of failure, limit state design method, load effect and resistance design format (LRFD) and recommended analysis procedures. INTRODUCTION The riser system constitutes a key element in relation to availability and safety in all phases spanning from drilling to production/export/import. Exploration and production of hydrocarbons in deepwater represents a new challenge to design and analysis of riser systems compared to shallow water applications. Standard industry practice for riser design, e.g. API RP 2RD (1998), apply the traditional working stress design (WSD) format where structural safety is taken care of by using a single usage (safety) factor. One of the limitations of WSD is that a single safety factor leads to a safety level that is strongly dependent on the load conditions. Design codes gives also normally limited guidance on how to establish extreme and fatigue load effects to be used in the code checks. In response to the above situation, DNV, SINTEF and SeaFlex initiated a Joint Industry Project (JIP) called "Design Procedures and Acceptance Criteria for Deepwater Risers" in December 1995. The main objective of the JIP is to assist exploration and development of deepwater fields, by providing safe and efficient design and analysis procedures for metallic risers. The JIP has 3 phases, where phase 3 is ending 1999. The product of Phase 3 will be a guideline for design and analysis of metallic risers.