HSCI Impressed Current Anodes

High Silicon Cast Iron (HSCI) Anodes for use in Cathodic Protection Applications

Anode Design, Features and Specifications

Anode Composition

High Silicon Cast Iron (HSCI)
Chemistry ASTM A518 Grade 3

Element
Minimum %
Maximum %
Silicon
14.20
14.75
Chromium
3.25
5.00
Carbon
0.70
1.10
Manganese
1.50
Copper
0.50
Molybdenum
0.20

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.

Visual comparison of anodes made with chill cast manufacturing versus competitor's sand cast manufacturing

Special Features

Accelerated corrosion tests confirm that Anotec chill cast anodes yield more ampere-years per pound than anodes manufactured by sand cast or spin cast processes

NSF International Certifies that these anode products conform to the requirements of NSF/ANSI Standard 61 – Drinking Water System Components – Health Effects

Anodes are manufactured, inspected and tested in accordance with documented procedures.

Design Parameters

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
2.00
127
1,000 – 1,500
1.75
111
1,500 – 2,000
1.50
96
2,000 – 3,000
1.25
80
Over 3,000
1.00
64
Note: For greater success, limit current density to less than 100 mA/sq.ft. for soils of less than 1,500 ohm-cm resistivity.
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Material
Voltage Range
Relative Position
Least Noble (More Anodic)
Magnesium
-1.60V to -1.67V
Zinc
-1.00V to -1.07V
Beryllium
-0.93V to -0.98V
Aluminum Alloys
-0.76V to -0.99V
Cadmium
-0.66V to -0.71V
Mild Steel
-0.58V to -0.71V
Cast Iron
-0.58V to -0.71
Low Alloy Steel
-0.56V to -0.64V
Austenitic Cast Iron
-0.41V to -0.54V
Aluminum Bronze
-0.31V to -0.42V
Brass (Naval, Yellow, Red)
-0.31V to -0.40V
Tin
-0.31V to -0.34V
Copper
-0.31V to -0.40V
50/50 Lead/Time Solder
-0.29V to -0.37V
Admiralty Brass
-0.24V to -0.37V
Aluminum Brass
-0.24V to -0.37V
Manganese Bronze
-0.24V to -0.34V
Silicon Bronze
-0.24V to -0.30V
Stainless Steel (410, 416)
-0.24V to -0.37V
(-0.45V to -0.57V)
Nickel Silver
-0.24V to -0.30V
90/10 Copper/Nickel
-0.19V to -0.27V
80/20 Copper/Nickel
-0.19V to -0.24V
Stainless Steel (430)
-0.20V to -0.30V
(-0.45V to -0.57V)
Lead
-0.17V to -0.27V
70/30 Copper Nickel
-0.14V to -0.25V
Nickel Aluminum Bronze
-0.12V to -0.25V
Nickel Chromium Alloy 600
-0.09V to -0.15V
(-0.35V to -0.48V)
Nickel 200
-0.09V to -0.20V
Silver
-0.09V to -0.15V
Stainless Steel (302, 304, 321, 347)
-0.05V to -0.13V
(-0.45V to -0.57V)
Nickel Copper Alloys (400, K500)
-0.02V to -0.13V
Stainless Steel (316, 317)
0.00V to -0.10V
(-0.35V to -0.45V)
Alloy 20 Stainless Steel
0.04V to -0.12V
Nickel Iron Chromium Alloy 825
0.04V to -0.10V
Titanium
0.04V to -0.12V
Gold
0.20V to 0.07V
Platinum
0.20V to 0.07V
Graphite
0.36V to 0.19V
Most Noble (More Cathodic)

Primary voltage range for material
Voltage range in crevices or stagnant and poorly aerated water