In today’s world of uncertainty, it becomes very important to maintain and manage current assets. Geodesic aluminum domes are an investment within our oil and gas industry that protects the product in the storage tank and has a service life of 50 plus years with some maintenance along the way.
What is a geodesic dome? A geodesic dome is a site specific, structurally engineered dome roof composed from an integrated aluminum system of interlocking panels, extruded struts, gusset plates, batten bars and hubs.
Why do I want a geodesic dome? One major reason is to seal the tank from the elements of nature such as rainfall and snow. Many open top tanks with carbon steel floating roofs have drainage issues with their roof drain systems in severe rain seasons, hurricanes and in severe snow seasons. Not having to worry about your roof drain system keeping up with the elements keeps your floating roof from sinking into the product. Other reasons are for the strength-to-span-ratio. This allows for a dome to span a large area without structural support columns, unlike a fixed cone roof. In today’s world where storage for your oil & gas products has led to larger and larger storage tanks, a clear-span aluminum dome allows for the columns that would be required on a typical cone style roof to be eliminated. These columns are called out as emission points. By removing them your tank system gains emission credits. Emission loss is also prevented by covering an open-top EFR style tank. The dome prevents this loss by deflection of the wind over the top of the dome, eliminating the vortex effect of wind passing over the top of a floating roof.
The dome’s ability to handle additional loads, such as cable suspending an aluminum internal floater from the dome roof, makes it possible to increase product capacity in a storage tank and provide tank maintenance benefits. This additional load of a suspended internal floating roof is considered during the design phase of the dome, just like live, snow, wind and other loads would be evaluated. The removal of the internal floating roof legs enables the floating roof to be set at the lowest possible point inside a tank. By not having legs, you can set a maintenance roof level of 10-ft above the floor so that you can drive equipment in/out of the tank during out-of-service work. Also, by having an aluminum internal floating roof suspended with the dome, you gain greater storage capacity versus a typical carbon steel pontoon style floater due to the thickness of the internal floating roof and the requirements for the seal system height.
Geodesic domes typically require less maintenance than a steel cone roof. Have you ever gone into a tank with a floater during inspection time and seen all the rusted material on your floater? This is from the rafter system and the underside of the steel cone roof plates. This corroded material accumulates on the secondary seal system and can create holes, ultimately causing emission leaks. One solution is the expensive and time-consuming task of sandblasting and coating the underside of the steel cone roof After taking the tank out of service. In addition, the top side of the steel roof must be sandblasted, repaired and coated to prevent corrosion-based breaching of the surface. Clear-span aluminum domes do not need to be painted for corrosion protection. Aluminum has a natural oxidation process that occurs, creating a thin layer of protection over time that will last the lifetime of the dome and most likely the tank. This is a major cost savings over the life of the storage tank, and it protects the stored product from UV and weather exposure.
How do I maintain a dome? An above-ground storage tank requires regularly scheduled preventative maintenance that will prolong your asset and keep it working correctly for your team. With a dome, we suggest an annual visual inspection from the platform. What is an inspector looking for during this visual?
- Look at the flashing connections where the dome meets the top of the tank, to make sure they are secured properly, and all fasteners are present.
- Look at the strut caps (batten bars) to see if there are any missing or loose screws. Is the gasket material fully compressed or wedged, is the gasket flexible/deteriorated? Is the gasket material missing?
- Visually inspect the sealant. Is the sealant adhering properly to the material? Is the sealant properly and neatly tooled? Is there sealant at all joints/splices around the interfaces of appurtenances?
- Visually inspect the hub covers to ensure they are present, sufficiently sealed, are there any dents or penetrations in them.
- Note if any of the appurtenances are missing or damaged – circulation vents, hatches, skylights, etc.
- Look at the mounting supports of the dome (dome shoes) and verify they are attached correctly.
- Note any customizations or modifications that have been done to the dome after it was originally installed.
- Unattended damage or defects to the existing dome should be noted. If there is a leak pattern on the floating roof, it should be documented to help facilitate future repairs.
Once all issues have been documented, a skilled contractor familiar with domes can suggest the proper repairs required to restore the dome as close as possible to its original condition. Beware of temporary fixes such as applying more sealant over the existing areas of sealant or covering with “flash band” style tape. These may temporarily remedy a leaking dome, but they do not offer a full cycle of protection and often require extensive cleaning or replacing of parts to properly get the dome back to a water-tight condition. If your dome has developed a leak, it is important to have an experienced dome contractor inspect and evaluate what is required to address the cause of the leaks and restore it to original condition.
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