In a Tank Storage magazine article, Stay Afloat Using Radar Technology, Emerson’s Ulf Johannesson describes how radar technology is used to improve safe and reliable operation on storage tanks with floating roofs.
…than half of the world’s larger tanks used for storing common petroleum products have floating roofs, and this proportion is likely to rise due to tightening demands for reduced vapour emissions.
Floating roofs have an advantage over fixed-roof tanks in cost and vapor balancing and recovery. They also come with their own set of issues:
…such as sinking, tilting, leaking and sticking decks can affect the performance of floating roofs – potentially leading to costly structural damage and major environmental and safety risks.
Traditionally, manual inspection of these floating roofs has been the way to try to spot these issues. Not only does this practice put operating personnel in hazardous areas, this inspection can be only performed on a periodic basis, it may also not find the issues in time before an abnormal situation develops.
Tank farm operators:
…are increasingly favouring a continuous and automated roof monitoring solution that offers greater efficiency and reliability, and keeps personnel out of harm’s way as much as possible.
Ulf cites other problems that may occur with floating roof such as excessive water or snow buildup, tilt from strong winds and unbalanced weights, leaking pontoons or a punctured deck, and rim seals that are either too loose or too tight.
He describes two automated approaches to continuous floating roof tank monitoring—tank top monitoring and on floating roof monitoring.
For tank top monitoring [hyperlinks added]:
…typically three non-contacting radars such as Emerson’s Rosemount 5400 series or Rosemount 5900 series are installed, mounted at 120 degrees from each other. A reflector plate on the roof enables accurate measurements to be performed without being affected by any protruding objects on the roof surface.
This installation arrangement provides continuous monitoring to detect conditions such as roof tilt, buoyancy, roof sticking and overfill conditions.
For measurement devices on the floating roof itself [hyperlinks added]:
…wireless and battery-powered guided wave radars (GWR), such as Emerson’s Rosemount 3308, are installed in existing nozzles, with rigid probes penetrating through the roof and into the liquid below. The wireless devices enable installation without the need for flexible wiring that can cope with the movement of the roof. A wireless repeater mounted at the top of the tanks ensures that when the roof is at a low point the radars can still transmit uninterrupted data back to the control room despite the devices being below the upper edge of the tank shell.
The advantage of the second method is [hyperlink added]:
…ease of installation, configuration and communication. Installation can be done in just two hours and with the tank still in operation. The configuration of the GWR can be performed remotely via wireless on an easy-to-use configuration screen, and the roof tilt data will be available in the TankMaster software in the control room.