The Institute of Concrete Technology

A group of American companies and Pertamina, the Indonesian state-owned oil company, have joined together in constructing the world's first offshore facility for the recovery, processing and export of natural gas liquids. Although the producing complex, located in the Java Sea, is only some 20 miles from the nearest coastline, the low marshy coastal terrain would require costly pile foundations and extensive road construction. Also, the coastal waters are too shallow for tanker access, and would require considerable dredging and long cargo-loading pipelines. The Atlantic Richfield Company is the operator for the Pertamina group in a 10,500 square mile area known as the Ardjuna Field, Fig. 1. Gas and crude oil facilities at locations "L", "K", "U" and "E" (Fig. 1) include platforms located in water depths from 95 to 135 feet. The site is located in an earthquake belt, and the area is also subjected to gales up to 75 mph which result in sea waves up to 27 feet in height. The oil and gas production platforms rest on the sea bottom. An extensive network of oil and gas pipelines resting on the sea floor transmit the oil and gas from points "L", "K", "U" and "E" to junction platform "B", where the crude oil is collected in steel storage barges and the liquid petroleum gas is collected, refrigerated and stored aboard a prestressed concrete barge, Fig. 2. The prestressed concrete barge, considered one of the most unique features of the project, is being built by Concrete Technology Corporation in Tacoma, Washington. The vessel's measurements 461 ft. long, 135.ft. wide, and 56 ft. deep permit a total storage of 375,000 barrels, or approximately 30,000 metric tons of liquid petroleum gas (LPG). A floating storage facility was selected over fixed platform LPG storage tanks on the basis of lower cost. Had seismic design criteria been reflected, the cost differential would have been greater. Concrete was selected over steel primarily on account of an earlier delivery date at a time when steel shipyards were heavily backlogged with orders. According to the purchaser of the vessel, an early obstacle to the use of concrete was removed when the American Bureau of Shipping gave its assurance that it would classify the vessel for insurance purposes. Concrete has long been considered inferior to steel not only for ships but also for important land structures. George F. Swain, Hon.M. and ASCE Past President, once said: "Steel does not change after it is put into a structure. It does not crystallize under repeated loads. It is not porous. As compared with these qualities of steel, the first peculiarity of concrete to be noted is that it is not a finished product. It is made on the job. The engineer must design the material. It seems to me also that too much attention has been given to strength, and not enough to imperviousness, which is more important from the point of view of durability.