Design Standard for Concrete LNG Terminals Offshore
Authors: Waagaard Knut 
Published: October 2008

Investors and oil companies have lately shown an interest in concept development, design and construction of reinforced concrete structures in the marine environment. Examples of such concepts are fixed and floating concrete platform to be used as terminals for LNG/LPG.

Based on this interest, DNV has developed an Offshore Standard for Classification of Concrete LNG Terminal. The DNV Offshore standard for " Offshore Concrete Structures " is based on the earlier Rules for Design of Concrete in the marine environment, i.e. the 1974 Rules, the 1977 Rules and the 1993 FOI Rules. The Offshore standard is further founded on the experience gained with the used of these standards and the durability of existing platforms built in the period after the installation of the first concrete platform at Ekofisk in 1973. The LNG containment is incorporating the requirements of IGC and EN1473 into the general design approach for offshore concrete structures.

The DNV Offshore standard for offshore concrete structures can be used for material selection, design, construction supervision and in-service inspection of Offshore Concrete Structures of any type and with the new DNV-OSC503 Offshore LNG/LPG terminals in concrete is also covered by a DNV Offshore Standard. The focus in this paper is directed toward LNG terminal due to the current need for a concrete standard associated with new terminal concepts. DNV Offshore Standard C502 " Offshore Concrete Structures" and DNV OS-C503 " Offshore Concrete LNG Terminals" will be issued in spring 2004 and can be applied for design, verification and classification of offshore Concrete Structures where DNV is acting as classification company or DNV is performing verification work for compliance with specific standard.

The standard is considered to be of significant assistance to both the owner, the designer and the National Authorities (US Coast Guard) in quality assurance of the New Terminal Structures, as currently no comprehensive standard exist covering the design of these new innovative structures in concrete.

Introduction

AkerKvarner's website annonced on October 31 2003 "AkerKvarner has been awarded a contract to perform engineering, procurement and construction management (EPCm) services for concrete structures placed on the seabed for ChevronTexaco's proposed Port Pelican and Baja California offshore terminals in North America." The proposed terminals will be placed on concrete substructures on the seabed many miles off the coast. Similar large concrete structures have been designed, built and installed by North Sea Contractors for offshore oil and gas production platforms since early nineteen seventies, most of which in hash weather regions in the North Sea and North Atlantic.

These two LNG terminals for gas import may be the first import terminals to be built offshore in concrete. Interests in the concept, however, indicate that this may be the first out of a series of this type of LNG offshore terminals. From literature it is speculations that only in North America 10-12 LNG terminals are planned either in Canada, US or in Mexico. It is expected that at least seven of these terminals will be contracted.