|Content Type||Conference Paper|
|Title||The Design And Performance Of Polymeric Anode, Cathodic Protection Systems On Burmed Lpg Bullet Tanks And Above Ground Storage Tank Bottoms|
|Authors||Robin C. John, Tyco Electronics; K.B. Singh, Tyco Adhesives|
|Source||CORROSION 2004, March 28 - April 1, 2004 , New Orleans, La|
|Copyright||2004. NACE International|
|Keywords||cathodic protection, storage tanks, LPG tanks, polymeric anodes, voltage gradient|
For both safety and environmental reasons, external protection of burned bullet tanks and above ground storage tank bottoms is now at the top of our industry?s worldwide priorities. To protect these buried structures it is essential to provide efficient cathodic protection systems, combined with external coatings. In fact, regulations in many countries now require the use of both active and passive protection. Cathodic protection for these buried structures presents a real challenge due to the large and complex geometries involved and the proximity of the anodes to the target structure.
This paper details new design criteria for protecting these structures and providing a more efficient engineered solution that will ensure long-term corrosion-free service. It also discusses the field performance assessment of polymeric anode systems installed on both above ground storage tanks and LPG bullet tanks that have been in service for more than five years.
Above ground storage tank (AST) bottom plates are usually coated on the soil-side and then welded together until the entire tank bottom is assembled. An effective cathodic protection system must be installed for the following reasons:
(1) The heat of welding will destroy the coating in the vicinity of the welds, leaving, these now unprotected areas in contact with the soil and in a place where they cannot be repaired;
(2) Welding can cause differences in the microstructure of the steel plate, with preferential corrosion possibly occurring at the heat-affected zones (HAZ) of the base metal near welds. This type of corrosion can cause significant localized metal loss1;
(3) The remaining areas of undamaged coating cannot be relied upon to fully protect the bottomplate for its desired lifetime. This is due to normal coating breakdown over time, as well as the impossibility of gaining access to repair such coating defects.
Applying a good quality, external, anti-corrosion coating to the bottom plates will significantly reduce the total CP current requirement and greatly extend the lifetime of the tank. Since the coating will have to perform over many years, it is best to use a high performance material such as fusionbonded epoxy or a solvent-free, liquid epoxy, applied to a minimum thickness of 350 microns.
|File Size||537 KB||11|