impressed current cathodic protection
TRANSCRIPT
IMPRESSED CURRENT CATHODIC
PROTECTION
By: Shailesh ShuklaM.Tech - D&H13400102004
Under the Guidance of:Mrs. Madhu JoshiScientist - BIMU Visakhapatnam
April 15, 2023
What is Corrosion ? The word “Corrosion” is made from Latin word
“Corroder” = To gnaw
It is the gradual destruction of materials (usually metals), by chemical reaction with its environment.
It means electrochemical oxidation of metals in reaction with an oxidant such as oxygen.
It also occurs in non-metals like polymers & ceramics.
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Cathodic Protection is a method of corrosion control that can be applied to buried and submerged metallic structures.
The material to be protected is supplied with an external cathodic current.
The electrochemical potential of the protected material is moved in a negative direction to the immune area.
The material is completely protected when it reaches the Protection Potential.
What is Cathodic Protection ?
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HISTORYCathodic Protection was first described by Sir
Humphry Davy in a series of papers presented to the Royal Society in London in 1824.
Thomas Edison experimented with impressed current cathodic protection on ships in 1890 but was unsuccessful due to lack of a suitable current source and anode material.
In USA by 1945 CP was applied to oil & natural gas industry.
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DISCRIPTION The simplest method to apply CP is by connecting the metal to be
protected with another more easily corroded “Sacrificial Metal” to act as the anode of the electrochemical cell.
The sacrificial metal then corrodes instead of the protected metal. When passive galvanic CP is not adequate, then we provide an external Dc source.
Common applications are: Steel water or oil pipe lines, storage tanks, ship & boat hulls, offshore platforms, metal reinforcement bars in concrete buildings.
In galvanized steels , in which a sacrificial coating of zinc on steel parts protect them from rust.
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Why it is important ?
Corrosion costs money.
Corrosion of metals cost USA economy almost $300 billion per year and it is estimated that 1/3 of it can be controlled by better techniques like this.
Our country has been losing around ₹1.52 lakh crore every year due to corrosion in various sectors like; infrastructure, manufacturing, production, defense & nuclear waste.
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Reaction
The basic process at an anodic site is the release of iron (Fe) from the steel surface into the environment and can be expressed as:
Fe Fe2+ + 2e-
During the process two electrons are generated which must be consumed by the environment.
4H++ O2 + 4e- 2H2O
2Fe + 2H2O + O2 2Fe(OH)2
The term Fe(OH)2 is iron oxide which can be oxidized to form the Red-brown Fe(OH)3 called Rust.
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SACRIFICIAL ANODE In the usual application, a galvanic anode, a piece of a more
electrochemically active metal, attached to the vulnerable metal surface where it is exposed to the corrosive liquid. Galvanic anodes have more active voltage that the target material usually steel.
For effective CP, the potential of the steel surface is polarized more negative until the surface has a uniform potential.
Metals like Zn, Al & Mg are used for making anodes.
For increasing electrical contact the active metal is placed in back fill (Coal & NaCl).
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IMPRESSED CURRENT CATHODIC PROTECTION
For larger structures, galvanic anodes can’t economically deliver enough current to provide complete protection.
In this method, an impressed current is applied in opposite direction to nullify the corrosion current and convert the corroding metal from anode to cathode.
ICCP systems use anodes connected to a DC source.
This current is given to insoluble anode like graphite, stainless steel or scrap iron buried in soil.
The negative terminal of DC is connected to pipeline to be protected. The anode is kept in back fill to increase the electrical contact with the surrounding soil.
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Impressed Cathodic ProtectionCathodic Protection
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Example of Impressed Current Installation
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Applications of Impressed Current
Applied on steel in seawater or soilOil Platforms in steel and concreteSubsea PipelinesHullQuay structures and sheet pile curtainsConcrete bridges placed in seawaterPipelines buried in soilVessels/tanks buried in soil
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PIPE LINES
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SHIPS
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OFFSHORE PLATEFORMS
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GALVANIZED STEEL
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IMPRESSED CURRENTAdvantages:
High driving voltage (30 V)Few anodes – reduced resistance
Disadvantages:Vulnerable componentsNeed for regulation/control system
Risk of overprotection of highly charged materials Coating damages – cathodic accouplement
Need for/recommended protection shield around the anodes
Need for maintenance
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Problems Arised Due To CP
Production of hydrogen ions
Cathodic Disbonding
Cathodic Shielding
Safety
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