A new innovation has been invented that will benefit many tank owners/operators that have double-bottom tanks without a high-density polyethylene, or nonconductive, liner between the old and new tank bottoms. Once the old tank bottom and dead shell are electrically isolated away from the new upper tank bottom, cathodic protection (CP) current from conventional CP systems and/or deep-anode beds will flow to the new upper tank bottom, providing CP (see drawing). On a present-day tank without this new concept, CP current will flow to the lower tank bottom with no CP benefits to the newer upper bottom. This method will work on tanks with sand tank pads as well as double-bottom tanks with existing concrete pads. With the new invention, the old tank bottom becomes essentially transparent, allowing CP current to flow right through the old tank bottom to protect the new tank bottom.
Extend API 653 inspection intervals
API 653 internal inspection intervals can be extended for five years by adding CP for each tank in which the old tank bottom is isolated from the new tank bottom, helping to prevent soil-side corrosion and protect the environment.
New double-bottom tanks
Eliminator isolator installed on existing double-bottom tank.
If a new tank bottom has to be installed, simply utilize the invention prior to installing the new bottom to electrically isolate the old bottom and dead shell away from the new upper bottom. The recommended clean sand pad per NACE and API and a closely installed CP system with anodes between the tank bottoms can be used, and/or your existing CP conventional or deep-anode groundbeds can be used to protect the new tank bottom. If a concrete pad is utilized, a layer of sand can be installed on top of the concrete pad, in accordance with NACE RP0193-2016 section 5.7.1, to provide an improved path for CP current to flow to the tank bottom through the concrete pad. The new concept may also include the use of a conductive, or clay, liner to be installed over the old tank bottom as a release prevention barrier (RPB). A conductive RPB may or may not be used in combination with the new concept. The concern about depleted CP systems between the tank bottoms has been eliminated, as CP current can now flow through the old tank bottom to the new upper tank bottom indefinitely. The next generation of double-bottom tanks has arrived!
For more information, email lou@ ustankprotectors.com or call (630) 719-9754.
