A new integrated deck concept is presented which utilizes a single barge to transport the deck and a specially designed substructure. The details and advantages of the concept are discussed in detail. The concept, called HIDECK, is presently being used on the Maureen Field Development in the North Sea and details are inc1uded. Methods for accomplishing mating of a HIDECK to a previously installed substructure offshore are presented and potential future applications of the concept are discussed.
HIDECK, a new integrated deck concept, has been developed during the past three years to reduce the cost of offshore platform decks, reduce the time for field development and improve the constructability, operational characteristics and safety of decks.
Typically in the North Sea, offshore platform decks are composed of eight to twenty modules which must be set on a substructure by a large marine derrick barge and then hooked-up. The hook-up, together with rather extensive commissioning, has required an average of approximately 1,000,000 man-hours and ten months. HIDECK is completely fabricated and outfitted onshore, then towed and set on the substructure in one piece using a large transport barge. In this way, the derrick barge plus 90-95% of the offshore hook-up are eliminated.
The deep open truss structure of HIDECK permits a more orderly lay out of facilities and straighter piping and cabling runs which reduce onshore construction costs when compared with the construction cost of modules. Hence, not only is offshore hook-up cost nearly eliminated, but onshore construction cost is also reduced.
North Sea modular decks, including modules and module support frame, commonly consist of up to 60% structural steel, and this percentage generally trends upwards as modules are built larger. Much of the steel in a modular deck is required for structural integrity of the module during offshore transportation and lifting into place on the platform. Hence, during the operation of the deck, this steel is stressed to only a small proportion of the allowable stress. HIDECK, which is built and transported in one piece, utilizes a "balanced stress" design to reduce the percentage of steel required to approximately 30-40% of the total deck weight. The balanced stress concept makes most of the principle steel work at near its allowable stress during both transportation and operation of the deck.
As an example of the steel savings introduced by HIDECK, consider a modular deck and a HIDECK each containing 10,000 tonnes of equipment (dry). The modular deck would require approximately 15,000 tonnes of steel for a total deck weight (dry) of 25,000 tonnes. The HIDECK would require approximately 6,000 tonnes of steel for a total deck weight (dry) of 16,000 tonnes. Hence, HIDECK would save approximately 9,000 tonnes of steel.
On both levels of HIDECK, access lanes are provided for forklift trucks for accessing equipment during maintenance procedures. These access lanes also provide direct escape routes thus enhancing the safety of the deck. Such access lanes are impossible, of course, in a modular deck.