Simplified Calculations of Impressed Current Anode Bed Resistance Underneath Tank Bottoms

• Published in: Corrosion (Houston, Tex.) Vol. 64; no. 2; pp. 138 - 142
• Main Authors: DEMOZ, A, FRIESEN, W. I
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.02.2008
• Subjects: Above ground tanks; Anode effect; Anodes; Anodic protection; Applied sciences; Calculators; Cathodic protection; Corrosion; Corrosion environments; Corrosion prevention; Exact sciences and technology; Finite element method; Historical account; History; Mathematical analysis; Metals. Metallurgy; Protection; Soil; Storage tanks; Cathodic protection; electrolyte resistance; anode bed; parallel grid anodes; Corrosion protection; anode spacing; tank bottom; Storage; Corrosion; ribbon anode; Impressed current; concentric circular anodes; distributed anode; Calculation; aboveground storage tank; Application; Storage tank
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3280682

Impressed current cathodic protection using uniformly distributed ribbon anodes has proven to be effective in controlling the corrosion of soil-side aboveground storage tank bottoms. Parallel and concentric ribbon anodes are two of the most common patterns of laying anode beds some distance underneath tank bottoms. At the design stage, the rule-of-thumb approach and historical data are used to determine the spacing between ribbon nodes. Computer-aided finite element analysis is potentially also available to assist in determining anode distributions. However, because of its complexity, this approach is not used frequently in practice. In this work, we address the design issue by taking a simplified approach based only on the geometries and the cathodic protection current requirement. The equations derived enable the determination (using a pocket calculator) of the number of concentric or parallel anodes, the spacing between them, and the anode bed resistances. Support of the derived resistance equations is established by comparing them with the well-known expressions for symmetrical geometries.