Impressed Current Cathodic Protection (ICCP) anode life is a designing parameter. The most common anode in ICCP is Dimensionally Stable Anode (DSA). DSA means the changes in the dimension are low but not zero. This group includes High Silicon Cast Iron (HSCI) and Ti-MMO (Titanium-Mixed Metal Oxide). Carbon steel is also sometimes considered an ICCP anode. However, its consumption rate is relatively high, and it is not a DSA. There are other types, but their consumption rate is not mentioned in the first version of CCPTools.
Ti-MMO Anode Life
The Ti-MMO anode is a Mixed Metal Oxide (MMO) layer at the surface of Titanium. The shape of the anode can change by changing the substrate shape. As a result, the Ti-MMO anode has a wide range of shapes. Moreover, since the substrate is lightweight Ti, the final anode is light too, while the oxide coating is conductive and stable in tough conditions. The coating of Ti-MMO is in the order of a few micrometers thick, and the typical color is black. Increasing the current can reduce the MMO life, but this increase/decrease relationship is not entirely linear. However, we can consider it a linear relation for the sake of simplicity, as we do in CCPTools. Generally, MMO anode suppliers give you a design life and a current (or current density) output, depending on the coating and anode backfill or contact electrolyte. In CCPTools, you can translate the numbers for MMO design life and design current to the minimum anode number you need for your system design life.
Anode Life/Number Calculation
In CCPTools, we assume the Ti-MMO anode life is linear to the current output. Meanwhile, we calculate the minimum anode number from a roundup of PC x DL / ADL x ADC
where PC is the protection current or average of protection current, DL is the design life of the CP system, ADL is the anode design life, and ADC is the anode design current. The last two items come from the producer. For example PC = 100 A, DL = 30 year, ADL = 25 year, and ADC = 7.8 A, so the minimum anode number is 16.
If your design life is very different from the anode design life, we recommend that you check the linear assumption’s validity. This is valid for all the ICCP anode life calculations. If you have any comments or experiences you would like to share on this topic, we would be happy to hear from you in CCPTools.