cathodic protection system for internal tank

Basic calculation for cathodic protection system for internal tank

Data:
Atmospheric Storage Tank:
 - length                                                : 11 m
 - Diameter (D)                                      : 38 m
 - high of water level (L)                         : 9 m
Current Density (CD)                              : 55 mA/m2
Consumption Rate of Aluminum Anode     : 3.5 kg/Amp Year
life time design                                       : 0.2 tahun
Utility Factor                                          : 0.8

Calculation:

1      Surface Area (SA)                  
             - SA bottom     = p x D2                            = 3.14 x 382                   = 1134.1 m2
                                         4                                      4 
             - SA wall  =
p x D x L                    = 3.14 x 38  x 9 = 1074.4 m2 
                                                 Total Surface Area                                          = 2208.5 m2
                       
2      Current Requirement (Ip)
Ip         = SA x CD
            = 2208.5 m2  x 55 mA/m2
            = 121467.5 mA = 121.5 Amp

3    Weight of Anode (W)
WAl       =  Ip x Y x 3.5 kg/Amp Year
                                U
            =  121.5 Amp x 0.2 years x 3.5 kg/Amp Year
                                           0.8
                        = 106.3 kgs

4          Number of Aluminium Anode (N)
Proposed Aluminium Anode type 120 ADFB - Net weight = 12 kg/ea
NAl          = WAl : 12 kg
                          = 106.3 kgs : 12 kg
              = 8.86 pcs » 9 pcs

Total = 9 pcs Aluminium  Anode type  120 ADFB