Cathodic Protection Technique to Control Galvanic Corrosion

SUBMITTED BY

Mahmoud Saleh Elkaffas Ahmed Shawky Said Waleed Mohamed Awny Abdelhamid Saleh Abdelhamid Mohamed Mamdouh Ahmed Ahmed Nagdy Arafa Marwan Ahmed Abou-Salem Omar Mahmoud Moustafa Mahmoud El-Sayed Mahmoud Mohamed Nabil Zein El-din

SAFETY OF ELECTROMECHANICAL SYSTEMS

SUBMITTED TO: DR/ MOHAMED MOHAMED ZAKARIA

Cathodic Protection

Introduction -Corrosion is a process of formation of the compound of pure

metal by the chemical reaction between metallic surface and its environment .

--It is an oxidation process .

--It causes loss of metal .

-Hence, disintegration of a metal by its surrounding chemicals through a chemical reaction on the surface of

the metal is called corrosion.

Galvanic Corrosion(Electrochemical

Corrosion)

A process that degrades metals electrochemically. It occurs in two cases.

Case IOccurs

between two dissimilar

metals

Case IIOccurs

between same metals exposed to electrolyte

with different concentration

s

In a galvanic cell, the more active metal (the anode) corrodes at an accelerated rate and the more noble metal (the cathode) corrodes at a retarded rate.

Case I (Corrosion occurs between two dissimilar metals)

What happens inside the galvanic cell?

Zinc atoms are losing two electrons, forming Zinc ions (Zn⁺⁺) which enter the solution.The two electrons (e⁻) lost by Zinc metal flow through the wire to the copper electrode

Two electrons (e⁻) combine with each cupper ion (Cu⁺⁺) in the solution to produce cupper metal.

Galvanic Series -The galvanic series (or electro potential series) determines the

nobility of metals and semi-metals. When two metals are submerged in an electrolyte, while electrically connected, the less noble (base) will experience galvanic corrosion. The rate of corrosion is determined by the electrolyte and the difference in nobility.

Case II (Corrosion occurs between same metals)

What happens at the anode part?

What happens at the cathode part?

The end of the corrosion process on the pipeline. (WatchVideo: http://www.youtube.com/watch?v=hfmD1RyUWgY)

Causes and Effects of Corrosion

The impact of corrosion on pipelines

(Video: http://www.youtube.com/watch?v=zeNtWvsmXAY)

The impact of corrosion on structure

(Video:http://www.youtube.com/watch?v=JweyK4rs6TE)

Cathodic Protection

1- Sacrificial Anode

2- Impressed Current

WHAT IS CATHODIC PROTECTION?

CP is a technique used to control the corrosion of a metal surface.

The principle of CP is to prevent anodic sites occurring on the structure under protection by allowing the anodic reactions to occur on specially designed and installed anodes.

1 -SACRIFICIAL ANODE

A piece of more active metal is attached to the vulnerable “less active” where it is exposed to the corrosive liquid.

Metals like (Zn, Mg, Al) are used for making anode because they are more active “low electrochemical potential” as compared to steel.

When it is consumed completely, it will be replaced by a newer one.

How the sacrificial anode works?

What happens at both the cathode and the anode?

(Video: http://www.youtube.com/watch?v=RAlC75xG4qU)

Cathodic Protection

1- Sacrificial Anode

2- Impressed Current

2 -IMPRESSED CURRENT For larger structures, sacrificial anode type

can not economically deliver enough current to provide complete protection.

An impressed current is applied in opposite direction to nullify the corrosion current and convert the corroding metal from anode into cathode.

ICCP systems are rectifiers which are connected to an AC supply source and convert it into DC.

In ICCP, the impressed current is given to insoluble anode like graphite, stainless steel or scrap iron buried in soil.

How the ICCP works?

(Video: http://www.youtube.com/watch?v=QYd9ENn1nP0 )

When to use ICCP?

Stray current: is a flow of electricity through equipment, buildings or the ground due to imbalances in electrical supply systems or because of wiring damage. It may cause electrochemical corrosion.

(Video: http://www.youtube.com/watch?v=fUv9eGp5AUM)

When to use sacrificial anode cathodic protection?

(Video: http://www.youtube.com/watch?v=9I5tMKqFXXo)

ANY QUESTIONS?

http://www.youtube.com/user/CorrConnect/videos

http://www.slideshare.net/abhishekwantsyou/cathodic-protection-14917643?from_search=1

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

References: