CALCULATION CATHODIC PROTECTION SYSTEM FOR PIPELINE

Under Ground Surface Pipe Area

The surface pipeline to be protected, as follows:

• Length pipeline (L): 4.875 km
• Pipeline Diameter (d) :  ∅ 12 inch = 323.85 mm = 0.32385 m

Total surface to be protected (A) = π * d * L

A =  4957.33 m2

Demand of Current

Total demand current to given formula:

Where :

= Demand Current (Amp)

= Surface area to be protected (m2)

= Current density per m2 (mA)

= Coating breakdown factor

Therefore:

mA = 0.992 Amp

3. Resistance of Magnesium Anode for Kp 4+500

Rmg : Magnesium anode resistance (Ohm)

Lmg : Length of prepacked magnesium anode 32lbs (m) 0,9 m

Dmg : Diameter of prepacked magnesium anode 32lbs (m) 0,195 m

ρ : Layer Soil resistivity data at depth from survey  (Ohm cm) 5500 ohm.cm

Rmg = 25.3739 ohm

4. Driving Voltage Anode

Net Driving Voltage The net driving voltage between Magnesium anode of -1.6  V

(Cu/CuSO4 reference) is 0.75 V (1.6 - 0.85).

 Close circuit potential (Volt) of magnesium is -1.6 volt

5. Current of anode For Kp 4+500

Ia : Magnesium anode current output (Amp) = (Ec - Ea) : Rmg

Ipf : Required current

Ec : Protective potential (Volt) -0,85 Volt

Ea : Close circuit potential (Volt) -1,6 Volt

I = -0.85 – (-1.6) : 25.3739

I = 0.0296 A

6. Sacrificial anode requirement

1. Mass Metode

Total Sacrificial Anode weight to be given formula:

Where:

Y = Design Live Period (year)

S = Consumption rate (kg/amp-year)

= demand current (Amp)

f  = Utility factor

So, total weight;

kg

N = 13.68 ≈ 14 Pcs

2. Current Output Method for Kp 4+500

Ip = Current Protective

Ia = Current Anode

N = 2.6 ≈ 3 Pcs

7. Lifetime of anode

Current capacity = mass anode : Consumtion rate

Current capacity = 14.5 kg : 8 kg/amp.year = 1.8125 A.Y

Life of anode = Current Capacity (A.Y) x N  x f    :     IR

Life of anode = 1.8125 A.Y x 14  x 0.8 : 0.992 A

Life of anode = 20.46 Years > 20 Years

8. Total Anode Required

The total Anode required is 40 Pcs, weight is 32 lbs or 14.5kg for each. Uses Current Method for better distribution.