L52119 Comparative Consumption Rates of Impressed Current Cathodic Protection Anodes
Authors: Brossia  
Published: August 2023

There is a variety of impressed current anode materials available for onshore applications, including High Silicon Cast Iron (HSCI), Mixed Metal Oxides (MMO), graphite, platinum (or platinum coated titanium), and conductive polymers. Many end users simply select the anode material that they have experience with. What is lacking is a clear, direct comparison of relative anode consumption rates conducted under identical conditions. The present study examined the behavior of the various anode types under different current loads and soil conditions in an effort to establish baseline consumption rates under controlled conditions. Variables that were examined included soil resistivity, the presence of coke backfill, current load, and soil type (sand or 50/50 clay/sand mix).

The consumption rates of the anodes evaluated decreased in the order of: AnodeFlex, HSCI, Graphite, Pt, and MMO. A survey of field experiences yielded a slightly different order in terms of anode life with Graphite and HSCI lasting the longest. However, given the wide range of anode sizes used in the various field sites, it is difficult to directly link the field results to the consumption rates measured in the laboratory.

Soil composition and resistivity were not observed to have a significant influence on anode consumption rates. The presence of coke, however, led to a decrease in consumption for all anodes in some cases by as much as a factor of nearly 70. Utilizing anode cost estimates and neglecting installation costs, the life-cycle material costs for MMO and Pt anodes are much lower than the other anode materials. Furthermore, AnodeFlex was noted to be the highest cost system from a materials perspective. This may be slightly misleading since installation and replacement costs are not factored in. Given that the installation of AnodeFlex is often much easier and less expensive than the other anode types, this may prove to be a viable financial decision when the other factors are considered.

����������� The primary implications of the present study are:

Despite higher material costs, MMO and Pt anodes may offer significant long-term cost savings as compared to other anode types for many applications
Use of coke backfill is critical to ensure lower anode consumption rates for AnodeFlex, Graphite, and to a lesser extent HSCI; coke does not appear necessary for MMO or Pt
Soil composition (sand vs. clay/sand mix) and resistivity do not appear to significantly influence anode consumption rates, thus consideration of the soil environment (except groundwater chemistry) is not needed in selection of an appropriate anode
Because the influence of groundwater chemistry (as part of the soil environment) was not examined, the effects of sulfate, chloride, and pH will need to be evaluated in detail to better aid in anode material selection
Field use survey responses showed a wide range in observed anode lifespan, with graphite and HSCI experiencing the longest life and cable anodes the shortest
The field survey also revealed that a significant cause of anode failures was connector and cable problems