corrosion

CORROSION

Introduction

Forms of Corrosion o Uniform Corrosion o Pitting Corrosion o Stress Corrosion Crackingo Crevice Corrosiono Erosion Corrosiono Intergranular Corrosiono Hydrogen Damage

o Corrosion Fatigueo Concentration Cell Corrosion

o Fretting Corrosion o Dealloying o Corrosion in Concrete

CONTENTS

Electrochemical cell

The components in an electrochemical cell

A cell in which electrons and ions can flow by separate paths between two materials, producing a current which, in turn, leads

to corrosion or plating.

Electrochemical corrosion

Corrosion produced by the development of a current in an electrochemical

cell that removes ions from the material.

CORROSION :

Degradation of metals and is often called RUST

Car Corrosion

Examples

Corrosion of Implants

Portion Of Different Forms Of Corrosion

Uniform Corrosion

Pitting Corrosion

Potential (Volts)

Current Density

A/cmicrit2

a - activation control

Epp

Passive region

Transpassive region

101

Examples of stress cells

Cold work required to bend a steel bar introduces high residual stresses at the bend, which then is anodic and corrodes.

Stress Corrosion Cracking

Because grain boundaries have a high energy, they are anodic and corrode.

River Branching Pattern

Intergranular SCC Of An Aluminum Aerospace Part

The arrows indicate the primary crack shown in both pictures

Changes in alloy heat treatment recommended

Corrosion occurs at the tip of a crevice because of limited access to oxygen.

Crevice Corrosion

Erosion Corrosion

In austenitic stainless steel, precipitation of chromium carbide makes the low Cr austenite in the grain boundaries anodic.

Intergranular Corrosion

Exfoliation Corrosion

Example of microgalvanic cells in two-phase alloys :

In steel, ferrite is anodic to cementite

Galvanic Corrosion

Hydrogen Damage

Hydrogen Embrittlement of Valve Capscrew Fasteners

Corrosion Fatigue

Corrosion fatigue cracks on the I.D. of a Admiralty brass exchanger tube

Corrosion Fatigue Cracks In AISI 1020 Steel In Oil And Gas

Downhole Service

Concentration Cell Corrosion

Corrosion occurs beneath a water droplet on a steel plate due to low oxygen concentration in the water.

Fretting Corrosion

Dealloying

Photomicrograph of a copper deposit in brass, showing the effect of dezincification (x50).

Filiform Corrosion

Corrosion in Concrete

THANK YOU FOR YOUR KIND ATTENTION

References :

1. http://corrosion.ksc.nasa.gov

2. http://www.corrosion-doctors.org

3. http://www.hghouston.com

4. The Science and Engineering of Materials, 4th ed Donald R. Askeland

– Pradeep P. Phuile’