Cryogenic Flexible for Offshore LNG Transfer

Abstract

Abstract This paper addresses the conception, development and testing of a cryogenic flexible, and its integration and qualification as part of an overall offshore transfer system. This technological advance has been made possible by Joint Industry Projects (J.I.P.), sponsored by both major Oil & Gas companies, and shipping & service companies. Development is ongoing and an industry Specification is one of the main aims. Introduction The industry trend towards the offshore production and transfer of LNG has lead to the requirement for innovative solutions to ensure safety in a marine environment and acceptable operating envelopes between the production units and the shuttle tankers. One solution is the use of a cryogenic flexible as part of an integrated transfer system, for both loading and offloading. The main part of this paper is dedicated to the cryogenic flexible itself, whilst a short second part discusses the system approach. 1.0 Cryogenic Flexible 1.1 Design Basis The characteristics of Liquefied Natural Gas, in particular its temperature of -163°C and the large volumes involved, means that the traditional methods and materials used for the manufacturing of flexibles for offshore use in the Oil and Gas Industry are not acceptable, and that alternative techniques must be used. At the initial stage of its development, no industry standard existed, however in order for one of the recognised Certification authorities to have a basis upon which to eventually propose such a standard, reference was made to the following:Oil Companies International Marine Forum (OCIMF) "Guide to Purchasing Manufacturing and Testing of Loading and Discharge Hoses for Offshore Moorings", 1991 (OCIMF 91)British Standards (BS), "Specifications for Hose and Hose Assemblies for Liquefied Petroleum Gas", BS 4089, 1989.British Standards (BS), "Flexible Metallic Hose Assemblies", BS 6501, 1991Expansion Joint Manufacturers AssociationCode des Appareils et Pression These parameters cover both the loading and gas return conditions. The prototype design, whilst being a 16- full bore flexible, allows full extrapolation of all results up to an internal diameter of 24-. The minimum service life is set at 5 years with a safety factor of 10 relative to fatigue life. Where possible, materials with a proven track record within cryogenic applications were chosen.