2-Fundamnetals of Corrosion

Fundamentals of Corrosion By

Dr. Ir. Agus Solehudin

DEFINISI KOROSI

Korosi adalah Kerusakan material

karena bereaksi dengan lingkungannya

Corrosion is the destructive attack of a metal by chemical or

electrochemical reaction with its environment

MENGAPA LOGAM TERKOROSI?

LOGAM KEMBALI KE ALAM

E

KOROSI

LOGAM

MINERAL MINERAL

TEK.

ANTI KOROSI

t

IKATAN LOGAM

Ikatan logam adalah gaya tarik menarik antara ion-ion

positif dengan elektron-elektron pada kulit valensi dari

suatu atom unsur logam

KOROSI ?

PINDAHNYA ION LOGAM

DARI LOGAM KE LINGKUNGAN

Gcell = nFEcell

SUMBER HETEROGENITAS

HETEROGENITAS

STRATIFIKASI ENERGI

atau POTENSIAL

DI LOGAM

DI LINGKUNGAN

PERBEDAAN FASA PADA BAJA : FERIT (ANODIK), SEMENTIT (KATODIK)

BESI TUANG : DAERAH DEKAT GRAFIT

BUTIRAN HALUS = ANODIK

BUTIRAN KASAR = KATODIK

TERBENTUKNYA

DAERAH ANODIK

DAERAH DIMANA ADA TEGANGAN SISA KARENA

PENGERJAAN DINGIN (PEMBENGKOKAN, PEMUKULAN, PENGELASAN, DLL.

ANODIK (AKAN TERKOROSI)

Grafit

KOROSIF

e

BAGIAN YANG LEBIH PANAS (ANODIK)

AKAN TERKOROSI

T

LAJU KOROSI DENGAN V2 LEBIH BESAR DARI V1

BAGIAN SEDIKIT DIBAWAH PERMUKAAN ELEKTROLIT

KANDUNGAN OKSIGEN LEBIH RENDAH

O2 rendah

e

e

e

e

SEL KOROSI

K

A

A K

SEL LENGKAP

_

_

_

_ _

_

_ _

_

ANODA

KATODA

ELEKTROLIT

KONDUKTOR ANTARA ANODA DAN KATODA

SYARAT TERJADINYA KOROSI

di ANODA : TERKOROSI

TERJADI OKSIDASI

ARUS KELUAR LOGAM

di KATODA : TIDAK TERKOROSI

TERJADI REDUKSI

ARUS MASUK LOGAM

APA YANG TERJADI DI PERMUKAAN

LOGAM?

DI KATODA :

ASAM : 2e + 2H+ H2

BASA/NETRAL : 4e + O2 + H2O 4(OH)-

2e + 2H2O H

2 + 2(OH)-

REDUKSI ION : ne + Mn+ M

DI ANODA : M Mn+ + ne

4/13/2014 by asolehudin 23

Steel Corrosion

2 2 22 2 2Fe O H O Fe OH ( )

21

222 2 2 3Fe OH O H O Fe OH( ) ( )

Initial Oxidation Reaction

Secondary Oxidation Reaction

Rust

Cu /Cu++ Mulia 0,337 Volt

H2/H+ -0,000

Ni/Ni+ -0,250

Fe/Fe++ -0,440

Zn/Zn++ -0,763

Al/Al+++ -1,660

Mg/Mg++ Aktif -2,370

Corrosion potential calculation

Reduction Reaction must have higher potential than the oxidation reaction or

they will not form a cathodic cell

Fe e Fe 2 2 -0.440 V

Zn e Zn 2 2 -0.763 V

V V . . .440 763 0 323Relative measure of

corrosion

Zn Fe

+ + + +

+

+

+ + +

+ +

Apa Yang Terjadi?

Zn Zn++ + 2e 2H+ + 2e H2

Fe Fe++ + 2e

2H+ + 2e H2

Fe + 2H+ Fe++ + H2

Zn Zn++ + 2e

2H+ + 2e H2

2H+ + Zn Zn + H2

Oksidasi Oksidasi

Reduksi Reduksi

Net Net

REAKSI-REAKSI

Anoda Katoda

e

Ikor GALVANIK

di ANODA : TERKOROSI

TERJADI OKSIDASI

ARUS KELUAR LOGAM

di KATODA : TIDAK TERKOROSI

TIDAK TERKOROSI

ARUS MASUK LOGAM

APA YANG TERJADI?

BILA LOGAM DICELUPKAN

DALAM LARUTAN

TERKOROSI : LAMBAT

CEPAT

PASIF : LAPISAN PROTEKTIF (terkorosi sangat lambat)

LAPISAN BERPORI (terkorosi lebih cepat)

IMUN : TIDAK TERKOROSI

4/13/2014 by asolehudin

Ranks the reactivity of metals/alloys in seawater

Platinum

Gold

Graphite

Titanium

Silver

316 Stainless Steel

Nickel (passive)

Copper

Nickel (active)

Tin

Lead

316 Stainless Steel

Iron/Steel

Aluminum Alloys

Cadmium

Zinc

Magnesium

Based on Table 17.2, Callister 6e. (Source of Table 17.2 is M.G. Fontana, Corrosion Engineering, 3rd ed., McGraw-Hill Book Company,

1986.)

GALVANIC SERIES


Corrosion Mechanisms

3 primary mechanisms : Mechanical Chemical Electrochemical

Mechanical Corrosion is caused by stress and erosion.

Chemical Corrosion is caused by a direct chemical reaction of the metal with its surroundings.

Electrochemical Corrosion results from a chemical reaction involving the transfer of electrons.


Corrosion Mechanisms ELECTROCHEMICAL

GALVANIC

CREVICE - PITTING

INTERGRANULAR

STRAY CURRENT CORROSION.

CHEMICAL

H2S, Polysuphides, Sulphur

ACID

BIOLOGICAL EFFECTS - Sulphate Reducing Bacteria (SRB)

H2 (Hydrogen) EMBRITTLEMENT.

MECHANICAL

EROSION

CORROSION FATIGUE

STRESS - Sulphide Stress, Chloride Stress


Electrochemical Corrosion Electro-Chemical Corrosion needs:

An electrolyte ie. water with dissolved salts

A corrodent , usually a dissolved gas, acid.

Two separate simultaneous reactions occur :

Anodic Reaction (Oxidation):

Production of Electrons

M ---- M++ + 2e-

2 Cl- ------ Cl2 + 2e-

Cathodic Reaction (Reduction)

Consumption of Electrons

2 H+ + 2 e- -------- H2 Acid

2 H2O + 2 e- --------- H2 + 2 OH

- Alkaline / netral

O2 + 4 H+ + 4 e- ----------- 2H2O Acid

2 H2O + O2 + e- ------------- 4OH- Alkaline / netral


Galvanic Corrosion Galvanic (Two Metal) Corrosion occurs when two dis-

similar metals are immersed in a conductive medium.

Corroding tendency is determined by the relative position of the metals in the Galvanic series.

The metal with the larger tendency to corrode becomes the anode.

The anode continues to corrode as long as a circuit is maintained.

In a corrosion cell the anode and cathode may be on the same piece of metal. (Short circuited cell).


Galvanic Corrosion


Erosion Corrosion


Cavitation


Fretting


Pitting Corrosion


Crevice Corrosion


Intergranular Corrosion


SCC

soal

Example: A steel coupon of 4 x 2 x 1/8 inches is placed in an acid solution for one

week, and loses 90 mg. Calculate the rate

of corrosion in mpy. Assume that steel is

iron only.

d Fe = 7,8 gr/cm3


Dr. Yves Gunaltun, 2009,Corrosion Control in Oil and Gas Production, Total E&P, France

Denny A. Jones, 1992,Principles and Prevention of Corrosion, Macmillan Publishing Company, USA

R. Winston Revie and Herbert H. Uhlig, 2008, Corrosion and Corrosion Control, John Wiley & Sons, Inc. Canada

References

2-Fundamnetals of Corrosion

Documents

Transcript of 2-Fundamnetals of Corrosion