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ConocoPhillips LNG tank design approved ABS okays design in principle; new semi-pyramid-shaped ship-board tank would help reduce sloshing loads as ocean-going LNG tankers grow in size Allen Baker Petroleum News Contributing Writer
A unique design for a semi-pyramid-shaped shipboard LNG tank has been approved in principle by the American Bureau of Shipping, the bureau announced March 14.
The design submitted to ABS by ConocoPhillips looks a bit like a short and squat pencil sitting on the eraser end. The unique shape reduces free surface area, and thus cuts the high-impact sloshing of loads in the container, ABS said after its testing.
Hydrodynamic experts at ABS say impact pressure due to sloshing is one of the critical factors in design for the tanks carrying the super-cold liquefied natural gas, which is stored at around 250 degrees below zero Fahrenheit. The ConocoPhillips design also reduces the resonance period since the tank is smaller at the top due to the sloped sides.
Tanks on LNG carriers have traditionally been spherical, but with huge new tankers on the drawing board, makers have been looking for designs that save space in the hulls. In November, ABS gave approval in principal for a cylindrical tank with spherical dished ends designed by Houston-based Ocean LNG Inc. The company suggested five of the tanks, each about 117 feet in diameter and 130 feet high, could provide a ship with a capacity of 180,000 cubic meters. Demand, vessel sizes have grown As demand for LNG carriers has grown, vessels have grown as well, with the newest generation holding 200,000 to 250,000 cubic meters. That’s about 112,000 metric tons at the high end, or the equivalent of 5.4 billion cubic feet once the cargo has been regasified.
The designs by ConocoPhillips Marine involve a four-tank setup for a theoretical LNG vessel having a capacity of about 235,000 cubic meters. Test results showed the design was acceptable and the loads were equal to or less than the loads on a traditional ship carrying 138,000 cubic meters, according to ABS.
ConocoPhillips contracted for model tests on its design at the Marine Technological Research Institute in Norway, with engineers from ABS and ConocoPhillips on hand for the testing. The ship motion and sloshing impact simulations were calculated based on conditions in the North Atlantic.
Peter G. Noble, manager of marine transportation for ConocoPhillips, said that several other technological development initiatives are under way at the company in the field of LNG carriers and terminals. Phillips Petroleum, a predecessor to ConocoPhillips, was a pioneer in gas liquefaction technology, and its liquefaction plant in Nikiski, Alaska, has been operating since 1967.
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