8/2/2019 Different Forms of Corrosion 2

1/42

CORROSION

http://www.corrosion-doctors.org/picture.htm

8/2/2019 Different Forms of Corrosion 2

2/42

Introduction

Forms of Corrosiono Uniform Corrosion

o Pitting Corrosion

o Stress Corrosion Cracking

o Crevice Corrosiono Erosion Corrosion

o Intergranular Corrosion

o Hydrogen Damage

o Corrosion Fatigueo Concentration Cell Corrosion

o Fretting Corrosion

o Dealloying

o Corrosion in Concrete

CONTENTS

8/2/2019 Different Forms of Corrosion 2

3/42

Electrochemical cell

The components in an electrochemicalcell

A cell in which electrons and ions can flow by separate pathsbetween two materials, producing a current which, in turn, leadsto corrosion or plating.

8/2/2019 Different Forms of Corrosion 2

4/42

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

8/2/2019 Different Forms of Corrosion 2

5/42

Car Corrosion

Examples

8/2/2019 Different Forms of Corrosion 2

6/42

Corrosion of Implants

http://www.corrosion-doctors.org/Aircraft/mullin.htm

8/2/2019 Different Forms of Corrosion 2

7/42

Portion Of Different Forms Of Corrosion

8/2/2019 Different Forms of Corrosion 2

8/42

Uniform Corrosion

8/2/2019 Different Forms of Corrosion 2

9/42

Pitting Corrosion

Potential(Volts)

Current Densit

A/cmicrit2

a - activation control

Epp

Passive region

Transpassive region

101

8/2/2019 Different Forms of Corrosion 2

10/42

8/2/2019 Different Forms of Corrosion 2

11/42

http://corrosion.ksc.nasa.gov/images/pit4.jpghttp://corrosion.ksc.nasa.gov/images/pit3.jpg

8/2/2019 Different Forms of Corrosion 2

12/42

http://corrosion.ksc.nasa.gov/images/pit5.jpghttp://corrosion.ksc.nasa.gov/images/pit1.jpg

8/2/2019 Different Forms of Corrosion 2

13/42

Examples of stress cells

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

Stress Corrosion Cracking

8/2/2019 Different Forms of Corrosion 2

14/42

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

8/2/2019 Different Forms of Corrosion 2

15/42

River Branching Pattern

http://corrosion.ksc.nasa.gov/images/scc1.jpghttp://corrosion.ksc.nasa.gov/images/scc2.jpg

8/2/2019 Different Forms of Corrosion 2

16/42

Intergranular SCC Of An Aluminum Aerospace Part

The arrows indicate the primary crack

shown in both pictures

Changes in alloy heat treatment recommended

http://corrosion.ksc.nasa.gov/images/scc4.jpghttp://corrosion.ksc.nasa.gov/images/scc3.jpg

8/2/2019 Different Forms of Corrosion 2

17/42

8/2/2019 Different Forms of Corrosion 2

18/42

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

Crevice Corrosion

8/2/2019 Different Forms of Corrosion 2

19/42

http://corrosion.ksc.nasa.gov/images/crev1.jpg

8/2/2019 Different Forms of Corrosion 2

20/42

Erosion Corrosion

8/2/2019 Different Forms of Corrosion 2

21/42

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

Intergranular Corrosion

8/2/2019 Different Forms of Corrosion 2

22/42

8/2/2019 Different Forms of Corrosion 2

23/42

Exfoliation Corrosion

http://corrosion.ksc.nasa.gov/images/guardrail.jpg

8/2/2019 Different Forms of Corrosion 2

24/42

http://corrosion.ksc.nasa.gov/images/stairs.jpg

8/2/2019 Different Forms of Corrosion 2

25/42

Example of microgalvanic cells in two-phase alloys :

In steel, ferrite is anodic to cementite

Galvanic Corrosion

8/2/2019 Different Forms of Corrosion 2

26/42

http://corrosion.ksc.nasa.gov/images/gal2.jpghttp://corrosion.ksc.nasa.gov/images/gal1.jpg

8/2/2019 Different Forms of Corrosion 2

27/42

http://corrosion.ksc.nasa.gov/images/fili.jpg

8/2/2019 Different Forms of Corrosion 2

28/42

Hydrogen Damage

Hydrogen Embrittlement of ValveCapscrew Fasteners

8/2/2019 Different Forms of Corrosion 2

29/42

http://corrosion.ksc.nasa.gov/images/hydro2.jpghttp://corrosion.ksc.nasa.gov/images/hydro1.jpg

8/2/2019 Different Forms of Corrosion 2

30/42

Corrosion Fatigue

8/2/2019 Different Forms of Corrosion 2

31/42

http://corrosion.ksc.nasa.gov/images/fat2.jpghttp://corrosion.ksc.nasa.gov/images/fat1.jpg

8/2/2019 Different Forms of Corrosion 2

32/42

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

Corrosion Fatigue Cracks In AISI1020 Steel In Oil And GasDownhole Service

8/2/2019 Different Forms of Corrosion 2

33/42

Concentration Cell Corrosion

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

8/2/2019 Different Forms of Corrosion 2

34/42

Fretting Corrosion

http://corrosion.ksc.nasa.gov/images/fret4.jpg

8/2/2019 Different Forms of Corrosion 2

35/42

http://corrosion.ksc.nasa.gov/images/fret2.jpghttp://corrosion.ksc.nasa.gov/images/fret1.jpg

8/2/2019 Different Forms of Corrosion 2

36/42

Dealloying

8/2/2019 Different Forms of Corrosion 2

37/42

Photomicrograph of a copperdeposit in brass, showing theeffect of dezincification (x50).

8/2/2019 Different Forms of Corrosion 2

38/42

Filiform Corrosion

http://corrosion.ksc.nasa.gov/images/filiform.jpghttp://corrosion.ksc.nasa.gov/images/filiform2.jpg

8/2/2019 Different Forms of Corrosion 2

39/42

http://corrosion.ksc.nasa.gov/images/worms.jpg

8/2/2019 Different Forms of Corrosion 2

40/42

Corrosion in Concrete

http://corrosion.ksc.nasa.gov/images/con1.jpg

8/2/2019 Different Forms of Corrosion 2

41/42

THANK YOU FOR YOUR KIND ATTENTION

8/2/2019 Different Forms of Corrosion 2

42/42

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. AskelandPradeep P. Phuile