CATHODIC PROTECTION – DESIGN:
The cathodic protection system is generally designed to meet the following requirements:
The pipe-to-soil potential will be between (-) 0.85 Volt and (-) 1.5 Volts with respect to Copper / Copper Sulfate reference electrode.
The pipeline will be considered protected when a minimum (-) 250 millivolt potential shift has been achieved from the initial native potential to the “CURRENT DRAINAGE” (C.D.) potentials.
A minimum polarization shift of (-)100 millivolts will indicate adequate levels of Cathodic Protection on the pipeline.
DESIGN CALCULATIONS :
MINIMUM CURRENT REQUIREMENT:
|It||= Sa x Cd x Sf|
|= Total current for coated pipeline|
|Sa||= Total Surface Area|
|Sf||= Safety Factor= 1.3|
|Cd||=Current Density (Protective Current required per Sq. mtr.)|
ANODE WEIGHT AND NUMBER REQUIRED:
W = I x Q x Y /Uf
|where W||anode weight required (Kg)|
|I||= total current|
|Q||= anode consumption rate (Kg / Amp-year)|
|Y||= design life (15 to 20 years)|
|Uf||= Utilization Factor (0.7 to 0.85)|
Thus knowing the total current of the anode material required the C.P. System can be designed.
CATHODIC PROTECTION SYSTEM FOR PIPELINE :
1. Impressed Current Cathodic Protection System.
2. By using Sacrificial Anodes
1. SPECIFICATIONS / REQUIREMENTS FOR ICCP SYSTEM:
The requirements for ICCP for the pipelines shall be as per following specifications.
Each ICCP station shall consist of the following :
Transformer Rectifier Unit.
Anode Ground Bed comprising of Hi-Silicon Ferro Alloy Anodes
Anode Header Cable from Anode Bed to T.R.Unit
Cathode Header Cable from pipeline to T.R.Unit
Anode Junction Box
Permanent PSP measurement system comprising of
1 2 Nos Cu-CuSO4 or Zinc Permanent Ref. Electrode installed close to the pipeline
2 1 No. Measurement Cable from pipeline to T.R.unit
3 1 No. Measurement Cable from Ref. electrode to T.R.Unit
ANODE GROUND BED :
Anode Ground bed shall be of horizontal or vertical type for the specified ICCP stations. The type and location of the ground bed shall depend on availiability of space and other requirements.
2.SPECIFICATIONS / REQUIREMENTS FOR CATHODIC PROTECTION SYSTEM USING SACRIFICIAL ANODES:
The anodes that are generally used are :
1. Magnesium anodes
2. Zinc Anodes
3. Aluminium Anodes
4. Other Types.