Cathodic Protection of Aboveground Storage Tanks

Photo of Zach Johnson, Taylor Shelby, and Jess Randall Students: Zach Johnson, Taylor Shelby, and Jess Randall

Sponsor: Fluor Corporation

Date: Fall 2008

Requirements:
The main requirement is recreating a scaled version of a CP system of an AST bottom utilizing industry standards and equipment. The test msut be large enough in scale to accurately represent field conditions while not exceeding reasonable monetary and physical constraints (no more than 50lb/person). The test bed must be isolated from the outside environment. The experiment msut produce consistent repeatable The experiment variables include anode height, driving voltage, and distance from the anode.

Problem:
The United States currently spends approximately $276 billion on corrosion related damage and associated prevention systems. This project involves the design and implementation of an experiment to evaluate current NACE standards for anode spacing in impressed current corrosion prevention (CP) systems for aboveground storage tanks (ASTs). The objectives of this experiment are to observe the drop in current density as distance is increased from the anode and to identify an optimum anode spacing.

Solution:
The experiment is based on a 240 square-inch test coupon. Although the had problems due to lack of sensitivity of the measurement instruments, several valid data points were collected. The preliminary conclusion is that anode spacing in above-ground storage tank applications can be expanded from 3.5 times anode depth to at least 6 times anode depth. This projection suggests an actual anode throw of 80° in either direction, a 33% increase from NACE estimates. Furthermore, the application of these results could result in a drastic decrease in project costs. For a 200' diameter tank bottom, the new anode spacing would produce a 40% decrease in the total length of anodes implemented, with potential savings of ~$95,000.

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