The benefit of internal floating roofs (IFR) is widely known. IFRs provide a very good cost-to-benefit ratio in terms of vapor emission reduction compared to other solutions. Also, IFRs need very little maintenance during their operating life cycle, especially when they are made of aluminum or stainless steel. This article will discuss the various options for end users who opt for a low maintenance IFR made of aluminum or stainless steel.
1. There is a choice of material to be made among stainless steel, aluminum and lately glass fiber reinforced epoxy (GRE). Aluminum, being the lightest and cheapest option, is suitable for almost all storage products used in the industry. But there are limitations in terms of corrosion resistance against certain aggressive chemicals. GRE can be provided in various qualities to comply with the stored product. The most adaptive material to potentially changing storage products is of course stainless steel. But then, the important difference in price often scares users away from this material.
2. A basic choice in design has to be made between full contact decks and pontoon-type decks. Full contact decks (FCD) are fully immersed into the product. Pontoon-type decks only have their floating pontoons wetted in the product with the skin that acts as a vapor barrier a few inches over the product level, thus leaving a certain amount of vapor space between the deck and the product.
Most skin and pontoon decks offer proven clamping systems good enough to withstand the low vapor pressure very well, but FCDs eliminate the vapors completely. FCDs usually are more solid and stiff, giving an overall tough impression close to what you would expect from car-bon steel.
The concept of skin and pontoon is more to be flexible and adaptive to movements of the product. But as they are built according to the same API 650 App H, they must of course comply with the respective and structural requirements. The main advantage of skin and pontoon decks is probably the low material and installation cost, as it can usually be brought into the tank through the tank manhole, whereas full contact IFRs usually have much larger parts that need additional entry doors or roof openings.
Another important design aspect is the ability to verify if the floaters are gas free when a tank inspection is due with hot work in the tank. Different manufacturers have introduced different designs, especially for the full contact decks. Foam-filled panels make it nearly impossible to properly identify gas in them. The so-called honeycomb aluminum panels need special vapor permeable honeycomb cells to make a certification possible.
The best option would be empty floaters where no gas can be trapped. This would apply for pontoons as well as for certain makes of aluminum or stainless steel FCDs. Single deck, open top IFRs can also be found made from aluminum. They provide ultimate visibility for trapped product but are subject to flooding from the top.
One aspect that has emerged rather recently and mainly in the U.S. is the focus on welded versus clamped deck seams. The potential leak from clamped seams is regarded as quite important by EPA which defines the emissions for IFRs. This requires field welding of aluminum where the strength of aluminum IFRs was the weld-free installation.
From a manufacturer’s point of view, this development goes in the wrong direction as it forces both users and suppliers to adopt solutions that lack a proper quality control just to improve the permitting situation.
As a conclusion, you will find as a user there are choices to be made beyond price or installation time and cost. The expected operating life of an IFR should equal the tank’s life cycle. So it is quite worthwhile to invest some time to find out what the requirements really are today and tomorrow.
Serious and reasonable IFR manufacturers should be able and competent partners to discuss suitable options before the budgets are made. In the end, every solution bears its ups and downs, and there is no such thing as black and white for this choice. Grey (aluminum) is a beautiful color!
Marco Micelli is CEO of Vacono Aluminium Covers located in Germany.
For more information, contact Micelli at marco.micelli@vacono.com or visit www.vacono.com.
