DISCUS OpenRaft™ — A breakthrough design in aluminium internal floating covers

Since the 1970s, the design principles used in the fabrication, installation and upkeep of internal floating covers (IFC) have essentially remained the same, while the issues of reliability, life expectancy, time and costs associated with maintenance, testing, cleaning and repairing, as well as the hazards posed by life-threatening vapour leakage, have persisted.

Poor design has persisted in the industry

The skin and pontoon tank cover model developed in the ’70s is still widely used today, despite the fact this type of roof frequently fails due to inadequate flotation, poor design, improperly assembled components, structural members spaced across a large grid, poor test port design and the use of plated fasteners.

In the mid-1990s, tank cover designs for the petrochemical industry took a step forward with the invention of enclosed welded honeycomb ‘sandwich’ panel roofs. However, neither the pontoon nor the honeycomb compartment covers really solved the problem of leaks and emissions. Moreover, both pontoon and sandwich panel roofs have enclosed compartments that often trap gasses and liquids and become ‘hot’.

What’s more, each pontoon or compartment, as well as the internal connections and perimeter seals, must be individually checked, tested, cleaned and maintained, which is time consuming, costly and often dangerous. The process involves significant labour and tank downtime.

A number of incremental improvements took place over the years, as bolted seams gave way to welded seams and steel was replaced with aluminum fabrication in order to accommodate cable suspension systems.

At last, A new and better idea

David Rosenkrantz, founder of DISCUS Engineered Products, wanted to come up with an improved design. He thought hard about all the issues and of tank economics. He began with the premise that an aluminum IFC should not contain enclosed spaces. ‘We know that enclosed pontoons or enclosed compartments trap noxious gasses that are explosive, carcinogenic and dangerous. They could become bombs,’ he says. ‘A better design would eliminate pontoons and enclosed compartments altogether.’

DISCUS IFR in Tank 337The DISCUS model features an open raft design instead of enclosed flotation compartments.

The rafts are comprised of aluminum panels that are open at the top. A technician can do a visual check and see if there is liquid or staining that indicates leakage, rather than examine and test each individual pontoon or enclosed compartment.

The DISCUS’ optional bolted or welded seams are designed to be as impervious as possible to leakage. The structure is strong enough that it does not require drains and so eliminates them as known emissions leak points. It minimises leakage and evaporation to a degree that it redefines the federal EPA’s Lowest Achievable Emission Rate standard.

DISCUS OpenRaft™ AIFC arrives

Colonial Pipeline was the first company to purchase and install a DISCUS AIFC last year at its facility in Atlanta. ‘With the DISCUS new seal design, we are able to inspect the seals from the top side of the deck so it saves time and money,’ Alan Geis, tank program coordinator for Colonial Pipeline says. ‘Also, since it contains only one sheet of material and has no compartments, it does not trap vapours and free product so it doesn’t become hot. That’s one less thing for me to worry about.’

‘When you factor in the short-term advantages and long-term cost benefits, our product becomes cost-effective,’ notes Rosenkrantz. ‘Think: less risk; fewer accidents, injuries and deaths. Then consider: reduced downtime for cleaning, maintenance and testing, with tanks back in service much quicker. These are factors with huge savings and the industry has evolved to a point where that is recognised.’

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