![]() ![]() Though many floating-roof tanks provide long life, problems with the service history of internal floating tanks has prompted an American Petroleum Institute subcommittee on pressure vessels and tanks to revise the design standard for internal floating roofs (IFRs), says Robert Ferry, The TGB Partnership, Hillsborough, North Carolina. When properly designed and constructed, a floating-roof tank should provide from 15 to 30 years of service with a minimum level of preventive maintenance. A life cycle cost analysis represents the true cost and should be the primary consideration when selecting a storage system. The initial cost of a floating-roof storage tank does not represent the true cost of operation, Gallagher notes. Operators should look for indications of product on the deck, unusual water ponding, deck ballooning, manhole covers out of place, shunts contacting the tank shell above the secondary seal, trash in the drain, out-of-place roof support and bleeder vent locks, and bird nests in foam chambers. Periodic visual inspections of the floating roof will help eliminate surprises, Gallagher says. Many tanks built more than 45 years ago are still in operation. Tank Maintenanceįloating-roof tanks are not maintenance free, Gallagher adds, but with the proper roof selection and use of well-designed rim seals, fittings, and related equipment, the new floating roof can provide many years of trouble-free operation. Rolling ladders, roof drains, and fire foam systems must be designed and installed so that the floating roof remains in a balanced operating condition. Floating-roof primary and secondary seals, adjustable roof supports, mixers, swing-lines, special fitting details, and rolling ladders all must be designed to operate with the floating roof without compromising the integrity of the storage tank. In many cases, these components can be implemented economically and without removing the tank from product service.”įloating-roof tanks use a significant amount of mechanical equipment to ensure safe and efficient operation, he says. They have been available for several years and have proven performance records. “New equipment such as low-loss slotted guide poles is available. ![]() “We expect that there will be a need to modify many of the external floating roof tanks currently in operation in the US refinery and terminal facilities over the next few years,” Gallagher says. The opening in the storage tank roof through which the guide pole passes, as well as the slots in the guide pole, constitutes “visible gaps: that must be maintained in a closed position at all times except when the device is in actual use. These sub-parts comprise the regulations for storage tanks. The announcement reaffirms that slotted guide poles for petroleum and volatile organic liquid storage tanks are subject to the “no visible gap” clause of EPA Regulations on Standards of Performance for New Stationary Sources Title 40, Part 60, sub-parts K, Ka, and Kb. The US Environmental Protection Agency (EPA) in the January 14, 2000, edition of the Federal Register announced a regulation that will require industry action, says Terry Gallagher, product design manager for Chicago Bridge & Iron Company, Plainfield, Illinois. Though recent regulations don't affect the main characteristics of floating roofs for storage tanks, they do impact details such as rim seals. Environmental regulations continue to be a driving force for change in the way storage tanks are managed by the petroleum industry.
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