A. Current requirement ( I ) = SA x CD
Where :
SA = Surface area (taken from Norton Corrosion calculation)
CD = Current density (taken from NACE standard RP 0176-83)
(Standard Recommended Practice Corrosion Control of Steel, fixed Offshore Platform
Associated with Petroleum Production)
Sea water = 55 mA.sq.m
Seabed = 11 mA/sq.m
B. Anode Weight = N
N = (I x Con x L) : U
Where,
I = Current requirement (Amp)
Con = Consumption rate of aluminium anode = 3.35 Kg/AY
Consumption rate of magnesium anode = 7.7 Kg/AY
L = Life time = 10 years
U = Utilization factor = 0.9
C. Example
Data:
Atmospheric Storage Tank:
- Length (L) : 5.54 m
- Diameter (D) : 9.058 m
- Water level Assume : 1 m
Current Density (CD) : 55 mA/m2
Consumption Rate of Aluminum Anode : 3.5 kg/Amp Year
Years design : 10 tahun
Utility Factor : 0.9
Calculation:
1 Surface Area (SA)
- Surface Area of Ground = pi x D2 = 3.14 x 82.047 = 257.62 m2
- Surface Area of wall = pi x D x L = 3.14 x 9.058 x 5.54 = 157.56 m2
Total Surface Area = 415.18 m2
2 Current Requirement (Ip)
Ip = SA x CD
= 415.18 m2 x 55 mA/m2
= 22,834.9 mA = 22.835 Amp
3 Weight of Anode (W)
W.Al = Ip x Y x 3.5 kg/Amp Year
U = 22.835 Amp x 10 years x 3.5 kg/Amp Year : 0.9
= 799.225 kgs
4 Number of Aluminium Anode (N)
Proposed Aluminium Anode type 50 kg - Net weight = 50 kg/ea
N.Al = W.Al : 50 kg
= 799.225 kgs : 50 kg
= 15.985 pcs = 16 pcs
Total = 16 pcs Aluminum Anode type 50 kg
regards
bajakz
email : bajakz@gmail.com
note : if you need more of calculation for cathodic protection, please contact me
