Design and Installation Aspects of Cathodic Protection

Design and Installation Aspects of Cathodic Protection on Storage Tanks & Pipelines for safe operation of the plant.
Design Aspects of Cathodic Protection
Sacrificial Anode System
Sacrificial anodes design calculations centre around two basic requirements:
There must be enough sacrificial anode material to last the design life.
The current output of the system must be sufficient to initially polarize and then maintain protection throughout the design life.
Design optimization is about meeting these two requirements at the lowest cost i.e. with the least amount of sacrificial anode material
Maintenance cost is also a contributing factor
Steps in designing sacrificial anode system
Establish soil resistivity
Determine current density requirement on the basis of soil resistivity and type of soil
Electrical continuity of structure
Select requirement of electrical isolation
Select suitable anode material on the basis of soil resistivity and soil type
Calculate total mass of anode required for design life
Calculate anode resistance to deliver output current
Calculate current output of each anode and its weight
Calculate total number of anodes required to satisfy mass and their configuration that is horizontal or vertical
Consider facilities for monitoring performance
Proper project drawing & specifications
Current requirement for steel for 3LPE coating

Soil Resistivity Current density µA/m²
< 10 ?-m for marshy soil 50
10 ?-m to 100 ?-m for normal 25
> 100 ?-m dry high resistivity 15
Safety margin of 30% to be provided on the above current densities
• Step 1: Surface Area
Sa = pd l
• Step 2: Current Requirement
It = Sa x Cd x 1.3
It = Protective current requirement(Amp)
Cd = Protective current density (A/m2) l = length of the pipeline(meter)
d = diameter of pipeline(meter)
Sa = Surface Area (m2 )
Safety margin is taken 1.3
Anode weight requirement
Step 3 : Anode weight requirement