High Silicon Cast Iron (HSCI) Anodes for use in Impressed Current Cathodic Protection Applications
High Silicon Cast Iron (HSCI)
Chemistry ASTM A518 Grade 3
Chill Cast in Metal Molds
Anotec uses a proprietary manufacturing process called "Chill Cast in Metal Molds" to manufacture its high silicon cast iron (HSCI) anodes. This process assures more consistent weight, greater density, less flake graphite grain boundary, and lower chemical segregation than sand cast anodes or spin cast tubular anodes.
The consumption rate of high silicon cast iron anodes has been found to be between 0.2 and 1.2 pounds
per ampere-year. For anodes of the same chemistry and microstructure, variance in consumption is
primarily due to the chemical and physical characteristics of the anode environment. The consumption
rate does not appear to be significantly affected by current density (amperes per unit area of
anode surface). The use of coke breeze around the anode in soil ground beds will tend to lower the
consumption rate. A generally accepted design guideline for anodes buried in coke breeze is 0.75 pounds
per amp year.
The utilization of an anode represents the percentage of the anode weight that can be consumed before the cable connection area becomes compromized. It is not possible to utilize 100% of the anode weight. Since current preferentially discharges from the ends of anodes, the utilization is different for solid stick anodes (where the cable connection is made at one end) and a tubular anode (where the cable connection is made in the middle.
As a guideline, one can use a utilization of 65% for solid stick anodes and 85% for tubular anodes.
The maximum stable current density discharge may be limited by the environment regardless of the anode type. In free flowing water or in very wet soil ground beds, there is very little restriction on current density. However, anodes buried in clay soils tend to suffer “electro-osmotic drying”, a phenomenon of magnitude directly proportional to current density. For any particular soil with electro-osmotic characteristics, there will tend to be a critical maximum current density at the anode-to-soil (or coke breeze-to-soil) interface, above which progressive drying occurs, with corresponding increases in anode-soil resistance. Drying is usually reversible by increasing soil moisture and/or lowering current density.
Table: Guideline Values to Minimize Electro-osmotic Drying of Groundbeds Installed in Clay Soils
Average Soil Resistivity Along Ground Bed (ohm-cm)
Maximum Amps Per Anode in a Coke Breeze Column 12″ OD by 60″ Long
Equivalent Current Density on Surface of Coke Breeze Column (mA/sq. ft.)
Less than 1,000
1,000 – 1,500
1,500 – 2,000
2,000 – 3,000
Note: For greater success, limit current density to less than 100 mA/sq.ft. for soils of less than 1,500 ohm-cm resistivity.