CATHODIC PR

OTECTION

SYSTEM

T A K O R A D I TH E R M A L P

O W E R ST A T I O

N

CORROSION BASICS• Corrosion is the degradation or destructive attack of

a metal by chemical or electrochemical reaction with its environment.

Fe ------- Fe++ + 2e- (1) O2 + 2H2O + 4e- ------- 4OH- (2) 2H2O + 2e- -------- H2 + 2OH- (3)

• Return of metal to the low energy oxide form in which it originally existed as an ore with complete loss of its metallic properties.

THE IMPACT OF CORROSION ON PIPELINES

WHY CORROSION IS IMPORTANT TO COMBAT?Corrosion Effects:• The world is loosing 2.2 trillion dollars every year – equivalent

to 3% of the world’s GDP.

• The plants spends more than 600 thousand dollars each year and corrosion control.

• Watching corrosion is like watching grass grow – slower in motion, but it definitely grows, and it grows in such an extent, that one day, it will become disaster and starts giving sleepless nights to operators of plants, pipelines and other structures affected by corrosion.

CORROSION CONTROL• Protective Coatings

• Environmental Control

BASIC ELECTRICITYVOLTAGE• Voltage is an electromotive force or a difference in

potential expressed in volts.

CURRENT• Current is the flow of charges along a conducting path

and is measured in amperes.

RESISTANCE• Resistance is the opposition to current flow through a

material.

• Current flows in only one direction

DIRECT CURRENT

ALTERNATING CURRENT

• Current reverses direction on a cyclic basis.

• A full cycle is completed in 50th or 60th of a second, represented in Hertz.

UNDERGROUND CORROSION AND ITS CONTROL

CATHODIC PROTECTION• The concept of cathodic protection involves

reducing the potential difference between local anodic and cathodic sites on a metal surface to zero, resulting in zero corrosion current flow.

CORROSION CELL (CONSTITUENTS OF CP)

CRITERIA FOR CATHODIC PROTECTION• A negative (Cathodic) potential of at least

850mV

• A minimum of 100mV of Cathodic polarization

TYPES OF CATHODIC PROTECTIONG A L V A N I C A N O D E S Y S T E M

I M P R E S S E D C U R R E N T S Y S T E M

GALVANIC SERIESMetal Potential wrt Cu:CuSO4

reference electrode (Volts)Carbon, Graphite, Coke +0.3

Platinum 0 to -0.1Mill scale on Steel -0.2

High Silicon Cast Iron -0.2Copper, Brass, Bronze -0.2Mild Steel in Concrete -0.2

Lead -0.5Cast Iron (not Graphitized) -0.5

Mild Steel (Rusted) -0.2 to -0.5Mild Steel (Clean) -0.5 to -0.8

Commercially Pure Aluminium -0.8Aluminum Alloy (5% Zinc) -1.05

Zinc -1.1Magnesium Alloy (6% Al, 3% Zn, 0.15% Mn) -1.6

Commercially Pure Magnesium -1.75

CONNECTION DIAGRAM

G C P I C C P

ADVANTAGES OF GCP/SACP SYSTEM• No external power source required.

• Low maintenance requirements.

• Easy to install.

LIMITATIONS OF GCP/SACP SYSTEM• Low driving voltage/current output.

• May be ineffective in high – resistivity environments.

• Higher cost per unit ampere than impressed current due to lower efficiency (self – consumption).

• May be difficult or expensive to replace spent anodes.

ADVANTAGES OF ICCP SYSTEM• Flexible with capability to handle a wide range of

voltage and current outputs.

• Satisfy high current requirements with a single installation.

• Effective in high – resistivity environments.

• Less anode consumption than with galvanic anodes.

LIMITATIONS OF ICCP SYSTEM• Higher inspection and maintenance cost than with

galvanic system.

• Requires external power.

• Constant power supply cost.

• May cause overprotection resulting in hydrogen embrittlement and coating damage.

TTPS CATHODIC PROTECTION (TANK FARM)

PERMANENT RE PORTABLE RE

CU/CUSO4 REFERENCE CELL/ELECTRODE

TRANSFORMER RECTIFIER UNIT

COOLING TOWER BURRIED PIPES

GAS TURBINE BURIED CCW PIPES

UNDERGROUND GAS PIPELINE

THANK YOU