kuliah korosi 2008

Korosi dan PencegahanKorosi dan Pencegahan

Prof. Dr. Ir. Johny Wahyuadi Soedarsono, DEAProf. Dr. Ir. Johny Wahyuadi Soedarsono, DEA

Departemen Metalurgi dan Material FTUIDepartemen Metalurgi dan Material FTUI20082008

Completing the Materials CycleCompleting the Materials Cycle

What is Corrosion?What is Corrosion?

Metals made by smelting Metals made by smelting (reduction of ore) (reduction of ore)

Metals in air want to return to Metals in air want to return to their oxidized statetheir oxidized state

Corrosion is a natural process!Corrosion is a natural process!

What is Corrosion?What is Corrosion?

Reaction of a metal with its Reaction of a metal with its environmentenvironment

Aqueous corrosionAqueous corrosion•reaction with water (usually containing reaction with water (usually containing dissolved ions)dissolved ions)

High temperature oxidationHigh temperature oxidation•reaction with oxygen at high temperaturereaction with oxygen at high temperature

High temperature corrosionHigh temperature corrosion•reaction with other gasesreaction with other gases

Corrosion CycleCorrosion Cycle

Iron Ore FeIron Ore Fe22OO33

Blast Furnace – Reduction to FeBlast Furnace – Reduction to Fe

Steelmaking FurnaceSteelmaking Furnace

Structural SteelStructural SteelOxidation of Fe – Rust - FeOxidation of Fe – Rust - Fe22OO33

Examples of CorrosionExamples of Corrosion

Rusting of steelRusting of steel•corrosion product (rust) is solid but not corrosion product (rust) is solid but not protectiveprotective

Reaction of aluminium with waterReaction of aluminium with water•corrosion product is insoluble in water, so corrosion product is insoluble in water, so may be protectivemay be protective

Burning of magnesium in airBurning of magnesium in air•high temperature oxidationhigh temperature oxidation

Examples of CorrosionExamples of Corrosion

Korosi yang terjadi pada Pipe Line

Figure : Three types of oxides may form, depending on the volume ratio between the metal and the oxide:

(a) magnesium produces a porous oxide film,

(b) aluminum forms a protective, adherent, nonporous oxide film, and

(c) iron forms an oxide film that spills off the surface and provides poor protection.

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

““Rust Never Sleep”Rust Never Sleep”

Kerugian Akibat KorosiKerugian Akibat Korosi

Sekitar 1 – 5 % dari Pendapatan Sekitar 1 – 5 % dari Pendapatan Domestik Nasional / Gross Domestik Nasional / Gross Domestic Product (GDP).Domestic Product (GDP).

Amerika Serikat pada tahun 1998 Amerika Serikat pada tahun 1998 kerugian akibat korosi adalah kerugian akibat korosi adalah sebesar US $ 276 Milyar yang sebesar US $ 276 Milyar yang merupakan 3,15 % dari GDPmerupakan 3,15 % dari GDP

Penyebab Besarnya Biaya Korosi Penyebab Besarnya Biaya Korosi

Disain yang berlebihan (Corrosion Disain yang berlebihan (Corrosion allowance yang terlalu besar)allowance yang terlalu besar)

Kehilangan produksi (shutdowns)Kehilangan produksi (shutdowns) Kerusakan komponenKerusakan komponen Biaya pemeliharaanBiaya pemeliharaan Kontaminasi terhadap produkKontaminasi terhadap produk Kerusakan lingkunganKerusakan lingkungan

Data Kerugian Akibat KorosiData Kerugian Akibat KorosiNo Sektor Industri / Negara Kerugian (US $)

1 Industri pesawat terbang (USA) 13 M / tahun

2 Pesawat militer (USA) 3 M/ tahun

3 Pesawat (tidak bisa terbang) 100.000 / hari

4 Angkatan Udara dan Laut (Australia) 50 juta / tahun

5 Otomotif (Finlandia) 300 Juta / tahun

6 Otomotif (USA) 0,25 % GNP tahun 1998

7 Menara Eiffel (Perancis) 40 juta / 7 tahun

8 Minyak dan gas (AGIP) 0,40 / barrel produksi tahun 1999

9 Minyak dan Gas (Laut Utara) 60% biaya pemeliharaan tahun 1999

10 Swiss 3 – 5 % GNP

80 % kerusakan material pada industri 80 % kerusakan material pada industri minyak dan gas diakibatkan oleh minyak dan gas diakibatkan oleh

korosi (US $ Milyar)korosi (US $ Milyar)

1.43.7

75

0.9

7 Eksplorasi

Refining

Pipa transmisi

Distribusi gas

Transport

Penyimpanan

Problem Keselamatan dan Problem Keselamatan dan Lingkungan Akibat KorosiLingkungan Akibat Korosi

Pengangkutan maupun penanganan Pengangkutan maupun penanganan bahan beracun dan berbahaya yang bahan beracun dan berbahaya yang menggunakan material / logammenggunakan material / logam

Kontaminasi pada pipa saluran air Kontaminasi pada pipa saluran air minum atau industri makanan. minum atau industri makanan.

Contoh Kerugian Akibat KorosiContoh Kerugian Akibat Korosi

Kejadian tahun 1987 di Minnesota Kejadian tahun 1987 di Minnesota korosi selektif pada lasan pipa bahan korosi selektif pada lasan pipa bahan bakar, terjadi kebakaran korban bakar, terjadi kebakaran korban tewas 2 orangtewas 2 orang

Korosi pipa uap Pembangkit Listrik Korosi pipa uap Pembangkit Listrik Nuklir di Virginia, terjadi korosi dan Nuklir di Virginia, terjadi korosi dan erosi, uap panas mengakibatkan 8 erosi, uap panas mengakibatkan 8 orang meninggal dunia.orang meninggal dunia.

Strategi Untuk Penghematan Biaya Strategi Untuk Penghematan Biaya Korosi (Save 25 – 30 %)Korosi (Save 25 – 30 %)

Kepedulian semua pihak terhadap Kepedulian semua pihak terhadap korosikorosi

Merubah persepsi korosi tidak bisa Merubah persepsi korosi tidak bisa diatasidiatasi

Perubahan kebijakan perusahaan Perubahan kebijakan perusahaan menerapkan management korosimenerapkan management korosi

Peningkatan pendidikan, pendidikan Peningkatan pendidikan, pendidikan terstruktur maupun training untuk para terstruktur maupun training untuk para stafstaf

Peningkatan keahlian disainPeningkatan keahlian disain Peningkatan pengkajian dan prediksi umur Peningkatan pengkajian dan prediksi umur

pakai bahan / materialpakai bahan / material Pengembangan teknologi pencegahan Pengembangan teknologi pencegahan

korosi melalui penelitian, pengembangan korosi melalui penelitian, pengembangan dan implementasidan implementasi

Mekanisme Korosi :Mekanisme Korosi :

Korosi Korosi : : peristiwa elektrokimia antara peristiwa elektrokimia antara logam dengan lingkungannya, syarat logam dengan lingkungannya, syarat terjadinyaterjadinya : :

anoda, terjadi reaksi oksidasi,anoda, terjadi reaksi oksidasi, katoda, terjadi reaksi reduksi,katoda, terjadi reaksi reduksi, elektrolit, penghantar arus listrik, elektrolit, penghantar arus listrik, ada hubungan anoda dengan katoda.ada hubungan anoda dengan katoda.

Mekanisme korosi : ada beda Mekanisme korosi : ada beda potensial potensial

Contoh Zn dlm asam, potensial Contoh Zn dlm asam, potensial Zn lebih rendah dari potensial Zn lebih rendah dari potensial HH22..

Zn Zn Zn Zn2+2+ + 2e + 2e-- pada permukaan logam pada permukaan logam

membentuk gas Hmembentuk gas H22.. 2H2H++ + 2e + 2e-- H H22

Reaksi umum :Reaksi umum :

AAnodanoda :: M M M Mn+n+ + ne + ne--

KatodaKatoda ::evolusi hidrogen (asam):evolusi hidrogen (asam): 2H2H++ + 2e + 2e-- H H22

reduksi air (netral/basa):reduksi air (netral/basa): H H22O + 2O + 2ee-- H H22 + 2 OH + 2 OH--

reduksi oksigen (asam)reduksi oksigen (asam) :O:O22 + 4H + 4H++ + 2 + 2ee-- 2 H 2 H22OO

Reduksi oksigen (netral/basa) :OReduksi oksigen (netral/basa) :O22 + 2 H + 2 H22O + 4O + 4e- e- 4OH4OH--

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Figure The half-cell used to measured the electrode potential of copper under standard conditions. The electrode potential of copper is the potential difference between it and the standard hydrogen electrode in an open circuit. Since E0 is great than zero, copper is cathodic compared with the hydrogen electrode.

Crystal Structure of MetalsCrystal Structure of Metals

Crystal Structure of MetalsCrystal Structure of Metals Atoms arrange themselves into various orderly configuration, Atoms arrange themselves into various orderly configuration,

called called crystals.crystals. The arrangement of the atoms in the crystal is called The arrangement of the atoms in the crystal is called

crystalline structurecrystalline structure.. The smallest group of atoms showing the characteristic The smallest group of atoms showing the characteristic lattice lattice

structurestructure of a particular metal is known as a of a particular metal is known as a unit cellunit cell. .

Ao Ad

force

dieblank

force

• Forging (wrenches, crankshafts)

CASTING JOININGFORMING

• Drawing (rods, wire, tubing)

often atelev. T

• Rolling (I-beams, rails)

• Extrusion (rods, tubing)

ram billet

container

containerforce

die holder

die

Ao

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roll

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roll

tensile force

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METAL FABRICATION METHODS-IMETAL FABRICATION METHODS-I

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Figure The Fe-Fe3C phase diagram ( a portion of the Fe-C diagram). The vertical line at 6.67% C is the stoichiometric compound Fe3C.

A phase diagram, also called equilibrium diagram or a constitutional diagram, graphically illustrates the relationships among temperature, composition, and the

phases present in a particular alloy system.

400 C

1400 C

1200 C

1000 C

800 C

600 C

1600 C

Fe 1% C 2% C 3% C 4% C 5% C 6% C 6.70% C

L

Steel Cast Iron

Pure Metal SolidificationPure Metal Solidification

• Temperature remains constant while grains grow.

• Some metals undergo allotropic transformation in solid state.

• For example on cooling bcc -iron changes to fcc -iron at 1400 C, which again to bcc -iron at 906 C.

Crystal Nucleation and GrowthCrystal Nucleation and Growth

Nucleation and Grain GrowthNucleation and Grain Growth

Nucleation;Nucleation;• Homogeneous nucleation: very pure metal, substantial Homogeneous nucleation: very pure metal, substantial

undercooling (0.2Tm)undercooling (0.2Tm)• Heterogeneous nucleation: nucleation agents (5ºC Heterogeneous nucleation: nucleation agents (5ºC

undercooling)undercooling) Grain growthGrain growth

• Planar: pure metalPlanar: pure metal• Dendritic: solid solutionDendritic: solid solution

Grain size Grain size • depends on number of nuclei and cooling rate. depends on number of nuclei and cooling rate.


Figure 11.17 The evolution of the microstructure of hypoeutectoid and hypereutectoid steels during cooling. In relationship to the Fe-Fe3C phase diagram.

Figure 11.16 Growth and structure of pearlite: (a) redistribution of carbon and iron, and (b) photomicrograph of the pearlite lamellae (2000). (From ASM Handbook, Vol. 7, (1972), ASM International, Materials Park, OH 44073.)

Figure : Example of microgalvanic cells in two-phase alloys: (a) In steel, ferrite is anodic to cementite. (b) In austenitic stainless steel, precipitation of chromium carbide

makes the low Cr austenite in the grain boundaries anodic.


Figure 7.20 The structure and properties surrounding a fusion weld in a cold-worked metal. Note: only the right-hand side of the heat-affected zone is marked on the diagram. Note the loss in strength caused by recrystallization and grain growth in the heat-affected zone


Figure 7.21 During hot working, the elongated anisotropic grains immediately recrystallize. If the hot-working temperature is properly controlled, the final hot-worked grain size can be very fine

Differential AerationDifferential Aeration

Fe

O2

Fe2+ Fe

Fe2+

O2

ElectronsConventional

current

Fe2+

Aerated Deaerated

pH goes acid byFe2+ + H2O FeOH+ + H+

pH goes alkaline byO2 + 2H2O + 4e- 4OH+

Steel corrodes actively

Steel passivates

7 14

Pot

enti

al

2.01.6

0.81.2

-0.4

0.40.0

-1.6

-0.8-1.2

0

Fe metal stable

Fe3+

Fe oxidesstable

Fe2+ stable

pH


Figure : Concentration cells: (a) Corrosion occurs beneath a water droplet on a steel plate

due to low oxygen concentration in the water. (b) Corrosion occurs at the tip of a crevice because of limited

access to oxygen.


Figure 22.8 Examples of stress cells. (a) Cold work required to bend a steel bar introduces high residual stresses at the bend, which then is anodic and corrodes. (b) Because grain boundaries have a high energy, they are anodic and corrode.


Figure : Concentration cells: (a) Corrosion occurs beneath a water droplet on a steel plate

due to low oxygen concentration in the water. (b) Corrosion occurs at the tip of a crevice because of limited

access to oxygen.

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Figure 22.10 (a) Bacterial cells growing in a colony (x2700). (b) Formation of a tubercule and a pit under a biological colony.


Figure 22.11 Alternative methods for joining two pieces of steel: (a) Fasteners may produce a concentration cell, (b) brazing or soldering may produce a composition cell, and (c) welding with a filler metal that matches the base metal may avoid the formation of galvanic cells (for Example 22.8)

Galvanic CorrosionGalvanic CorrosionTable 1 Standard emf series Table 2 Galvanic Series in Seawater

Reaction Eo at 25oC,(V vs NHE)

Au-Au3+

Pt-Pt2+

Ag-Ag+

Hg-Hg22+

Cu-Cu2+

H2-H+

Ni-Ni2+

Fe-Fe2+

Cr-Cr3+

Zn-Zn2+

Al-Al3+

Mg-Mg2+

Na-Na+

+1.498+1.2

+0.799+0.788+0.337

0.000

-0.250-0.440-0.744-0.763-1.662-2.363-2.714

Noble orcathodic

Active oranodic

PlatinumGoldSilver18-8 Mo stainless steel (passive)Nickel (passive)Cupronickels (60-90 Cu, 40-10 Ni)CopperNickel (active)18-8 Mo stainless steel (active)Steel or iron2024 aluminium (4.5 Cu, 1.5 Mg, 0.6 Mn)CadmiumCommercially pure aluminium (1100)ZincMagnesium and magnesium alloys

After de Bethune and Loud from INCO test results

Which is better?Which is better?

Brass bolt in a steel structureSteel bolt in a brass structure

Small brass cathode will cause small increase in corrosion of steel structure. Bolt will be protected from corrosion by coupling to steel

Small steel anode will suffer large increase in corrosion due to coupling with brass structure.


Figure 22.12 Zinc-plated steel and tin-plated steel are protected differently. Zinc protects steel even when the coating is scratched, since zinc is anodic to steel. Tin does not protect steel when the coating is disrupted, since steel is anodic with respect to tin.


Figure : Cathodic protection of a buried steel pipeline: (a) A sacrificial magnesium anode assures that the galvanic

cell makes the pipeline the cathode. (b) An impressed voltage between a scrap iron auxiliary anode

and the pipeline assures that the pipeline is the cathode.

Relevant RustingRelevant RustingResultsResults

Unprotected iron in agar mediaUnprotected iron in agar media

Relevant RustingRelevant RustingResultsResults

Iron wrapped withIron wrapped with zinc wirezinc wire

Iron wrapped withIron wrapped with copper wirecopper wire

Material :Material : Logam / paduanLogam / paduan Polimer / plastikPolimer / plastik Keramik /non logamKeramik /non logam

Sifat logam, KorosiSifat logam, Korosi Batas butir, energi tinggi, mudah terkorosi (intergranular, Batas butir, energi tinggi, mudah terkorosi (intergranular,

pitting)pitting) Laku mekanik ; tegangan dalam / tegangan sisa (SCC)Laku mekanik ; tegangan dalam / tegangan sisa (SCC)

Faktor yang mempengaruhi sifat korosiFaktor yang mempengaruhi sifat korosi : : TeganganTegangan Konsentrasi Hidrogen / OksigenKonsentrasi Hidrogen / Oksigen Homogenitas kimia (impurities, segregasi dll) dan fisik Homogenitas kimia (impurities, segregasi dll) dan fisik

(roughness, scale, kotor dll)(roughness, scale, kotor dll) Protective film (pasivasi, lapisan oksida) Protective film (pasivasi, lapisan oksida)

impermeable, kuat, tidak mudah retak, adhesi, mudah impermeable, kuat, tidak mudah retak, adhesi, mudah terbentuk)terbentuk)

Pengaruh unsur paduan terhadap Pengaruh unsur paduan terhadap korosikorosi

Stabilitas alpha (Cr, Si, Mo, W dll.)Stabilitas alpha (Cr, Si, Mo, W dll.) Stabilitas gamma (Cu, Ni, Mn, Co dll)Stabilitas gamma (Cu, Ni, Mn, Co dll) Pembentuk karbida (Fe, Mn, Nb, Ti dll)Pembentuk karbida (Fe, Mn, Nb, Ti dll) Menurunkan titik eutectoid ( Mn, V, Ta, W dll)Menurunkan titik eutectoid ( Mn, V, Ta, W dll) Tahan korosi (Tahan korosi (Cr, Ni, MoCr, Ni, Mo, Ti, Nb, Mn, Cu, Si), Ti, Nb, Mn, Cu, Si)

Produk korosi tidak mudah larutProduk korosi tidak mudah larut Pasivasi Pasivasi

stabilitas karbidastabilitas karbida

Korosi di atmosfer dan air lautKorosi di atmosfer dan air laut

Korosi atmosferik disebabkan :Korosi atmosferik disebabkan : Gas oksigenGas oksigen Uap airUap air PengotorPengotor Pengaruh atmosfer (kering, lembab, laut, Pengaruh atmosfer (kering, lembab, laut,

tropis, pedesaan, kota, industri)tropis, pedesaan, kota, industri)

Korosi lingkungan laut :Korosi lingkungan laut : pHpH Oksigen Oksigen Kecepatan gerak air lautKecepatan gerak air laut TemperaturTemperatur Biota laut (biofouling / pelekatan material, Biota laut (biofouling / pelekatan material,

over loaded)over loaded)

Biota laut :Biota laut : Bernacles (menimbulkan celah, mempercepat Bernacles (menimbulkan celah, mempercepat

korosi)korosi) Sebagai penghalang / turbulensi lokalSebagai penghalang / turbulensi lokal Mampu menembus lapisan pelindungMampu menembus lapisan pelindung Bakteri pereduksi sulfat (menghasilkan asam sulfat)Bakteri pereduksi sulfat (menghasilkan asam sulfat)

Lingkungan laut :Lingkungan laut : Daerah percikan (serangan korosi sangat kuat, no Daerah percikan (serangan korosi sangat kuat, no

fouling)fouling) Daerah Pasang (fouling mulai ada, air laut jenuh Daerah Pasang (fouling mulai ada, air laut jenuh

udara)udara) Daerah laut dangkal (air laut jenuh oksigen, Daerah laut dangkal (air laut jenuh oksigen,

pengotor, fouling, gerakan arus)pengotor, fouling, gerakan arus) Laut dalam (korosi karena pengaruh oksigen, chlor Laut dalam (korosi karena pengaruh oksigen, chlor

dll)dll) Daerah lumpur (komplex, korosi agak rendah / Daerah lumpur (komplex, korosi agak rendah /

oksigen terbatas)oksigen terbatas)

Corrosion of Zinc in AcidCorrosion of Zinc in Acid

Zinc dissolves with hydrogen evolutionZinc dissolves with hydrogen evolution

Zn + 2HCl Zn + 2HCl ZnCl ZnCl22 + H + H22

Zinc known as a base or active metalZinc known as a base or active metalZinc known as a base or active metalZinc known as a base or active metal

One atom of zinc metalOne atom of zinc metalplus two molecules of hydrogen

chloride (hydrochloric acid)

plus two molecules of hydrogenchloride (hydrochloric acid)

reacts to formgoes to

reacts to formgoes to

one molecule of zinc chlorideone molecule of zinc chlorideplus one molecule of hydrogen gasplus one molecule of hydrogen gas

Corrosion of Platinum in AcidCorrosion of Platinum in Acid

Platinum does not react with acidsPlatinum does not react with acids Platinum is known as a Platinum is known as a noblenoble metal metal

Connection of Platinum to ZincConnection of Platinum to Zinc

Zn Pt

HCl

Zinc and platinum not connected, no

reaction on platinum

Zinc and platinum not connected, no

reaction on platinum

Zinc and platinum connected, current

flows and hydrogen is evolved on platinum

Zinc and platinum connected, current

flows and hydrogen is evolved on platinum

Zn + 2HCl ZnCl2 + H2

metal + acid salt + hydrogen

Zn + 2HCl ZnCl2 + H2

metal + acid salt + hydrogenZn Zn2+ + 2e-

metal metal ions + electrons

Zn Zn2+ + 2e-

metal metal ions + electrons 2H+ + 2e- H2

hydrogen ions + electrons hydrogen gas

2H+ + 2e- H2

hydrogen ions + electrons hydrogen gas

electronselectrons

Connection of Platinum to ZincConnection of Platinum to Zinc

Zn + 2HCl Zn + 2HCl ZnCl ZnCl22 + H + H22

But we can separate metal But we can separate metal dissolution and hydrogen evolutiondissolution and hydrogen evolution

Zn Zn Zn Zn2+2+ + 2e + 2e- -

Reactions that involve both chemical change and the

transfer of charge

Reactions that involve both chemical change and the

transfer of charge

2H2H++ + 2e + 2e-- H H22

These are known as These are known as electrochemical electrochemical reactionsreactionsOne atom of zinc metalOne atom of zinc metal

one zinc ion in solutionone zinc ion in solutiontwo electrons in the metaltwo electrons in the metal

ElectrodesElectrodes

Electrodes are pieces of metal on Electrodes are pieces of metal on which an electrochemical reaction is which an electrochemical reaction is occurringoccurring

An An anodeanode is an electrode on which an is an electrode on which an anodicanodic or oxidation reaction is or oxidation reaction is occurringoccurring

A A cathodecathode is an electrode on which a is an electrode on which a cathodiccathodic or reduction reaction is or reduction reaction is occurringoccurring

Anodic ReactionsAnodic Reactions ExamplesExamples

ZnZn Zn Zn2+2+ + 2e + 2e-- zinc corrosionzinc corrosion

FeFe Fe Fe2+2+ + 2e + 2e-- iron corrosioniron corrosion

AlAl Al Al3+3+ + 3e + 3e-- aluminium corrosionaluminium corrosion

FeFe2+2+ Fe Fe3+3+ + e + e-- ferrous ion oxidationferrous ion oxidation

HH22 2H 2H++ + 2e + 2e-- hydrogen hydrogen oxidationoxidation

2H2H22OO O O22 + 4H + 4H++ + 4e + 4e-- oxygen evolutionoxygen evolution OxidationOxidation reactions reactions ProduceProduce electrons electrons

Cathodic ReactionsCathodic Reactions ExamplesExamples

OO22 + 2H + 2H22O + 4eO + 4e--4OH4OH-- oxygen reductionoxygen reduction

2H2H22O + 2eO + 2e-- H H22 + 2OH + 2OH-- hydrogen hydrogen evolutionevolution

CuCu2+2+ + 2e + 2e-- Cu (copper plating) Cu (copper plating)

FeFe3+3+ + e + e-- Fe Fe2+ 2+ (Ferric ion reduction)(Ferric ion reduction) ReductionReduction reactions reactions ConsumeConsume electrons electrons

Effect of pH on reaction rateEffect of pH on reaction rate Consider hydrogen evolution reaction :Consider hydrogen evolution reaction :

2H2H++ + 2e + 2e-- H H22

The concentration of hydrogen ions will The concentration of hydrogen ions will influence the rate of the reactioninfluence the rate of the reaction

As the hydrogen ion concentration is As the hydrogen ion concentration is increased (i.e. the solution made more increased (i.e. the solution made more acid), so the rate of the reaction acid), so the rate of the reaction increasesincreases

Similarly the potential will influence the Similarly the potential will influence the reaction - the more negative the reaction - the more negative the potential the faster the reactionpotential the faster the reaction

Effect of pH and potential on rate Effect of pH and potential on rate of hydrogen evolutionof hydrogen evolution

pH

Potential

Faster

Slower

Effect of pH on reaction rateEffect of pH on reaction rate On platinum no metal dissolution will On platinum no metal dissolution will

occur, but to balance the charge a occur, but to balance the charge a reaction which creates electrons must reaction which creates electrons must occuroccur

If the solution contains dissolved If the solution contains dissolved hydrogen, the reverse of the hydrogen, the reverse of the hydrogen evolution reaction can hydrogen evolution reaction can occur:occur:

HH2 2 2H2H++ + 2e + 2e--

Effect of pH on reaction rateEffect of pH on reaction rate

HH2 2 2H2H++ + 2e + 2e--

This reaction will go faster in alkaline This reaction will go faster in alkaline solution (since Hsolution (since H++ will be removed by H will be removed by H++ + OH+ OH-- H H22O)O)

This reaction will go faster at more This reaction will go faster at more positive potentials (because electrons positive potentials (because electrons will be removed from metal)will be removed from metal)

Effect of pH and potential on rate Effect of pH and potential on rate of hydrogen oxidationof hydrogen oxidation

pH

Potential

OxidationFaster

OxidationSlower Reduction

Faster

ReductionSlower

Rates equalElectrochemical

Equilibrium

Corrosion of zinc in acidCorrosion of zinc in acid

When zinc is placed in acid the metal When zinc is placed in acid the metal will start to dissolve and hydrogen will start to dissolve and hydrogen will start to be liberated according to will start to be liberated according to the potential of the metal the potential of the metal

Consider the anodic zinc dissolution Consider the anodic zinc dissolution reactionreaction

Zn Zn Zn Zn2+2+ + 2e + 2e--

PolarisasiPolarisasiLogam dlm lar setimbang, reaksi anodik dan katodikLogam dlm lar setimbang, reaksi anodik dan katodik

Tidak dalam kesetimbangan, selisihnya : overpotensial (Tidak dalam kesetimbangan, selisihnya : overpotensial () atau ) atau polarisasipolarisasi

Klasifikasi :Klasifikasi :Polarisasi aktivasiPolarisasi aktivasi : terdiri dari 3 tahapan utama. : terdiri dari 3 tahapan utama. Pertama : H+ + e- Pertama : H+ + e- H ads H ads KeduaKedua : H ads + H ads : H ads + H ads H2 H2Ketiga : gelembung H2Ketiga : gelembung H2

Hubungan antara polarisasi / overpotensial dengan laju reaksi Hubungan antara polarisasi / overpotensial dengan laju reaksi

untuk polarisasi anodik, dan polarisasi katodiknya adalah :untuk polarisasi anodik, dan polarisasi katodiknya adalah :

i0 : i0 : exchange current densityexchange current density, , a dan a dan c tetapan anoda dan katoda Tafel.c tetapan anoda dan katoda Tafel.

o

aaa i

ilog

o

ccc i

ilog

Kurva TafelKurva Tafel

Kecepatan korosi material dalam Kecepatan korosi material dalam mpympy (mils per year; 1 mil = 0,001 (mils per year; 1 mil = 0,001 inchi), inchi),

di mana : Ddi mana : D = densitas (g/cm3)= densitas (g/cm3) icoricor = rapat arus korosi (A/cm2)= rapat arus korosi (A/cm2) MM = berat ekivalen (g/mol.equ)= berat ekivalen (g/mol.equ)

D

Mi129,0 mpy cor

Polarisasi konsentrasiPolarisasi konsentrasi akibat kecepatan reaksi terhadap akibat kecepatan reaksi terhadap

koefisien difusi ion terlarut (Dz) dan koefisien difusi ion terlarut (Dz) dan konsentrasinya dlm larutan (CB). konsentrasinya dlm larutan (CB).

Hubungan koefisien difusi, konsentrasi Hubungan koefisien difusi, konsentrasi larutan dengan kecepatan reaksi larutan dengan kecepatan reaksi disebut rapat arus batas (disebut rapat arus batas (iLiL) :) :

: ketebalan gradien konsentrasi dlm lar.: ketebalan gradien konsentrasi dlm lar.

Jika tanpa polarisasi aktivasi, polarisasi Jika tanpa polarisasi aktivasi, polarisasi konsentrasi :konsentrasi :

RR : konstanta gas (8,314 J/mol.K): konstanta gas (8,314 J/mol.K)TT : temperatur absolut (273 K): temperatur absolut (273 K)

Bz

L

nFCDi

Lk i

i1log

nF

RT2,3

PassivationPassivation

definisi sebagai sebuah bentuk definisi sebagai sebuah bentuk ketahanan korosi akibat ketahanan korosi akibat pembentukan lapisan pelindung pembentukan lapisan pelindung

Jika lapisan pelindung terbentuk, hal Jika lapisan pelindung terbentuk, hal ini akan menyebabkan rapat arus ini akan menyebabkan rapat arus turun akibat tahanan lapisan film turun akibat tahanan lapisan film dan pengaruh lapisan difusidan pengaruh lapisan difusi

Kurva disolusi anodik dari logam aktif-pasifKurva disolusi anodik dari logam aktif-pasif

PassivationPassivation

log |current density|

Ele

ctro

de P

oten

tial

Active corrosion gives normal activation polarization

Active corrosion gives normal activation polarization

Current falls as the passive film starts to form - the

active-passive transition

Current falls as the passive film starts to form - the

active-passive transition

When a stable passive film has formed, the current has

a steady, low value - the passive current density

When a stable passive film has formed, the current has

a steady, low value - the passive current density

The rate of corrosion will be critically affected by the

cathodic curve

The rate of corrosion will be critically affected by the

cathodic curve

Rapid rate of cathodic reaction leads to passivation,

and low rate of corrosion

Rapid rate of cathodic reaction leads to passivation,

and low rate of corrosionLower rate of cathodic reaction leads to activity, and

high rate of corrosion

Lower rate of cathodic reaction leads to activity, and

high rate of corrosionBut it may also lead to low

rate of corrosion?

But it may also lead to low rate of corrosion?Very slow cathodic reaction

leads to low rate of corrosion

Very slow cathodic reaction leads to low rate of corrosion

The Pourbaix (E-pH) DiagramThe Pourbaix (E-pH) DiagramThe Pourbaix (E-pH) DiagramThe Pourbaix (E-pH) Diagram

Pot

enti

al

H2O is stable

H2 is stable

7 14

pH = - log [H+]pH = - log [H+]

2H+ + 2e- = H2 Equilibrium

potential falls as pH increases

2H+ + 2e- = H2 Equilibrium

potential falls as pH increases

2.01.6

0.81.2

-0.4

0.40.0

-1.6

-0.8-1.2

0

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

Equilibrium potential falls as pH increases

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

Equilibrium potential falls as pH increasesO2 is stable

Pitting Resistance IndexPitting Resistance Index

PittingPitting

Pot

enti

al

7 14

2.01.6

0.81.2

-0.4

0.40.0

-1.6

-0.8-1.2

0

Pourbaix Diagram for ZincPourbaix Diagram for Zinc

Zn metal stable

Zn2+ stable

in solution

Zn(OH)2

stable

solidZnO2

2-

stable in

solution

Corrosion

Cor

rosi

on

ImmunityP

assi

vity

Corrosion possible with

oxygen reduction


oxygen reduction


hydrogen evolution


hydrogen evolution

Corrosion requires strong oxidising

agent

Corrosion requires strong oxidising

agent

Corrosion is thermodynamically

impossible

Corrosion is thermodynamically

impossible

Corrosion is possible, but likely

to be stifled by solid corrosion product

Corrosion is possible, but likely

to be stifled by solid corrosion product

Pourbaix Diagram for GoldPourbaix Diagram for Gold

Pot

enti

al

7 14

2.01.6

0.81.2

-0.4

0.40.0

-1.6

-0.8-1.2

0

Gold metal stable

Immunity

CC

Passivity

Gold can’t corrode with oxygen reduction or hydrogen evolution

Gold can’t corrode with oxygen reduction or hydrogen evolution

Pourbaix Diagram for IronPourbaix Diagram for Iron

Pot

enti

al

7 14

2.01.6

0.81.2

-0.4

0.40.0

-1.6

-0.8-1.2

0

Fe metal stable

Fe3+

Fe oxidesstable

Will iron corrode in

acid?


acid?

Fe2+ stable

Yes - there is a reasonably wide

range of potentials where hydrogen

can be evolved and iron dissolved

Yes - there is a reasonably wide

range of potentials where hydrogen

can be evolved and iron dissolved


neutral waters?


neutral waters?Yes - although iron can form an oxide in neutral solution, it tends not to

form directly on the metal, as the potential

is too low, therefore it is not protective.

Yes - although iron can form an oxide in neutral solution, it tends not to

form directly on the metal, as the potential

is too low, therefore it is not protective.

Will iron corrode in alkaline solution?

Will iron corrode in alkaline solution?

No - iron forms a solid oxide at all potentials,

and will passivate

No - iron forms a solid oxide at all potentials,

and will passivate

Pourbaix diagram for AluminiumPourbaix diagram for Aluminium

Pot

enti

al

Pot

enti

al

77 1414

1.21.2

0.80.8

0.00.00.40.4

-1.2-1.2

-0.4-0.4

-0.8-0.8

-2.4-2.4

-1.6-1.6

-2.0-2.0

00

Al

Al3+

Al2O3AlO2

-

Limitations of Pourbaix Limitations of Pourbaix DiagramsDiagrams

Tell us what Tell us what cancan happen, not happen, not necessarily what necessarily what willwill happen happen

No information on rate of reactionNo information on rate of reaction Can only be plotted for pure metals Can only be plotted for pure metals

and simple solutions, not for alloysand simple solutions, not for alloys

Bentuk korosiBentuk korosi

Sources of Localized CorrosionSources of Localized Corrosion

EnvironmentEnvironment• oxygen concentrationoxygen concentration• chloride ion concentrationchloride ion concentration• pHpH• flow rateflow rate


MaterialMaterial• segregationsegregation• inclusionsinclusions• different phasesdifferent phases• grain boundariesgrain boundaries


MechanicalMechanical• static stressstatic stress• fluctuating stressfluctuating stress

Bentuk-bentuk korosi sumuran : Bentuk-bentuk korosi sumuran :

(a) narrow,deep, (b )eliptical, (c) wide, shallow, (d) (a) narrow,deep, (b )eliptical, (c) wide, shallow, (d) subsurface, (e) undercutting, (f) subsurface, (e) undercutting, (f) hhorizontal, (g) verticalorizontal, (g) vertical

Gambar Skematis proses pertumbuhan Gambar Skematis proses pertumbuhan pitpit pada besi pada besi

Contoh : Produk yang terkorosi merataContoh : Produk yang terkorosi merata

Galvanic CorrosionGalvanic Corrosion

Fe

O2

Cu

Fe2+

ElectronsConventionalcurrent

Fe2+

O2

Galvanic CorrosionGalvanic Corrosion

Important factors in galvanic Important factors in galvanic corrosioncorrosion• relative areas of anode and cathoderelative areas of anode and cathode• difference in potential between anode difference in potential between anode

and cathodeand cathode• effect of anodic polarization on anode effect of anodic polarization on anode

(some may passivate)(some may passivate)

Crevice CorrosionCrevice CorrosionMetalO2

O2 Cr3+

1 Oxygen is consumed in crevice by slow passive corrosion

Metal

2 Passive corrosion continues, and pH falls by Cr3+ hydrolysis

3 Passive film breaks down in acid and rapid active corrosion starts

Active corrosion is corrosion occurring in the absence of an oxide film

Cr3+Hydrolysis is a reaction with water, in this case

2Cr3+ + 6H2O Cr2O3 + 6H+

4 The active corrosion causes even stronger acidification andstabilises the crevice corrosion

Crevice CorrosionCrevice Corrosion

Crevice corrosion

under washers

Pitting corrosion on free surface

Gambar Gambar 1. 1. Tahap awal korosi celahTahap awal korosi celah2. Tahap lanjut2. Tahap lanjut

1 2

Other anions (e.g. OH- and SO42-) can

inhibit pitting, either by buffering the pH in the pit or by causing the precipitation of a salt film

PittingPitting

O2 O2

Cr3+ Cr3+

Inside the growing pit the hydrolysis of Cr3+ lowers the pH and breaks down the passive film. The cathodic oxygen reduction reaction continues outside the pit

e e

Cl- Cl-

The presence of chloride is important, as it allows a pH of about 1 to be achieved (HCl is a strong acid, and does not associate) and the metal chlorides are very soluble

Mechanical Aspects of CorrosionMechanical Aspects of Corrosion

Static stressStatic stress• stress-corrosion crackingstress-corrosion cracking• hydrogen embrittlementhydrogen embrittlement• liquid metal embrittlementliquid metal embrittlement

Dynamic stressDynamic stress• corrosion fatiguecorrosion fatigue• fretting corrosionfretting corrosion

The Effect of Stress and Strain The Effect of Stress and Strain on Corrosionon Corrosion Stress Stress per seper se does not affect does not affect

corrosion processes muchcorrosion processes much Plastic strain can have a large effect:Plastic strain can have a large effect:

• increased dislocation densityincreased dislocation density• rupture of passive filmsrupture of passive films

Stress-Corrosion CrackingStress-Corrosion Cracking

Cracking of a metal under the Cracking of a metal under the combined effects of a static stress combined effects of a static stress and a specific chemical environmentand a specific chemical environment

Several possible mechanisms, still Several possible mechanisms, still not fully understoodnot fully understood

Cause of major industrial costs and Cause of major industrial costs and safety hazardssafety hazards

Stress-Corrosion CrackingStress-Corrosion Cracking

MechanismsMechanisms• Anodic dissolutionAnodic dissolution• Hydrogen embrittlementHydrogen embrittlement• Film-induced cleavageFilm-induced cleavage

DealloyingDealloying

‘Plug-type’ dealloying of a brass tube

Intergranular CorrosionIntergranular Corrosion

When grain boundary chromium When grain boundary chromium carbide precipitation has occurred, carbide precipitation has occurred, the stainless steel is said to be the stainless steel is said to be sensitisedsensitised..

Sensitisation frequently occurs in the Sensitisation frequently occurs in the heat-affected zone during welding, heat-affected zone during welding, and the resultant corrosion is called and the resultant corrosion is called weld decayweld decay..

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03 B

rook

s/C

ole,

a d

ivis

ion

of T

hom

son

Lea

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Tho

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earn

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Figure 22.15 The peak temperature surrounding a stainless-steel weld and the sensitized structure produced when the weld slowly cools (for Example 22.10)

Figure 22.14 (a) Intergranular corrosion takes place in austenitic stainless steel. (b) Slow cooling permits chromium carbides to precipitate at grain boundaries. (c) A quench anneal to dissolve the carbides may prevent intergranular corrosion.

Concentration of Cr decreases near the precipitates

Cr23C6

Grain boundaries will be depleted in Cr and will corrode

Intergranular CorrosionIntergranular CorrosionWhen stainless steel is heated to about 650oC, Cr carbides form at the grain boundaries

C

C C

CBecause of its high diffusion rate, carbon can diffuse a long way to form the precipitate

However, chromium can only diffuse a short distance, and this reduces the matrix concentration of chromium at the grain boundary

CrCr

Cr

Cr

If the grain boundary Cr oncentration falls low enough (below about 9%), then it will no longer remain passive, and grain boundary corrosion will occur

Gambar Mekanisme korosi erosi oleh partikel padatGambar Mekanisme korosi erosi oleh partikel padat

Flow EffectsFlow Effects

Perhitungan kecepatan korosiPerhitungan kecepatan korosi

WW = massa yang hilang (mg)= massa yang hilang (mg)

DD = densitas (g/cm3)= densitas (g/cm3)

AA = luas permukaan (in2)= luas permukaan (in2)

TT = waktu penetrasi (jam)= waktu penetrasi (jam)

DAT

W534mpy

Corrosion RatesCorrosion Rates

Nomograph for Calculation of Corrosion Rate

Parameter Air Sedimen Parameter Air Sedimen BakuBaku

1.1. KationKation- - KalsiumKalsium - Besi- Besi- Magnesium- Magnesium - Barium- Barium- Natrium- Natrium - Strontium- Strontium

2.2. AnionAnion- Klorida- Klorida - Karbonat dan Bikarbonat- Karbonat dan Bikarbonat- Sulfat- Sulfat

3.3. Sifat-Sifat FisikSifat-Sifat Fisik- - pHpH - - TemperaturTemperatur- - TDSTDS - Oksigen terlarut- Oksigen terlarut- - AlkalinitasAlkalinitas - Karbon Dioksida terlarut- Karbon Dioksida terlarut

Parameter Air Sedimen Parameter Air Sedimen BakuBaku

Kalsium (CaKalsium (Ca2+2+) ) : Sebagai unsur utama pada : Sebagai unsur utama pada oilfield brinesoilfield brines dan dapat berperan sebagai pembentuk endapan.dan dapat berperan sebagai pembentuk endapan.

pHpH : Kelarutan senyawa CaCO3 dan besi sangat tergantung : Kelarutan senyawa CaCO3 dan besi sangat tergantung pada besarnya pH. pada besarnya pH.

TDSTDS : Jumlah total zat yang larut dalam air (kation dan : Jumlah total zat yang larut dalam air (kation dan anion).anion).

AlkalinitasAlkalinitas : Ditandai dengan kehadiran ion HCO : Ditandai dengan kehadiran ion HCO33--, CO, CO33

2-2- dan dan OHOH--

TemperaturTemperatur : Berpengaruh terhadap kecenderungan : Berpengaruh terhadap kecenderungan pembentukan endapan, pH dan kelarutan gas di dalam air pembentukan endapan, pH dan kelarutan gas di dalam air serta berat jenis air itu sendiri.serta berat jenis air itu sendiri.

pHpH Ion Penyebab AlkalinitasIon Penyebab Alkalinitas

9,6 - 149,6 - 14 OHOH-- dan CO dan CO332-2-

8,3 - 9,68,3 - 9,6 HCOHCO33-- dan CO dan CO33

2-2-

4,5 - 8,34,5 - 8,3 HCOHCO33--

Indeks KorosifitasIndeks Korosifitas

1.1. Langelier (LI)Langelier (LI)

LI = pH - pHLI = pH - pHss

2.2. Ryznar (RI)Ryznar (RI)

RI = 2pHRI = 2pHss - pH - pH

pHpHss = (9,3 + A + B) - (C + D) = (9,3 + A + B) - (C + D) Dimana:Dimana:AA = (log TDS (mg/L atau ppm) - 1)/10= (log TDS (mg/L atau ppm) - 1)/10BB = -13,12 log (T (= -13,12 log (T (°°C)C)+ 273) + 34,55+ 273) + 34,55CC = log (Ca= log (Ca2+2+ (mg/L atau ppm)) - 0,4 (mg/L atau ppm)) - 0,4DD = log (alkalinitas (mg/L atau ppm))= log (alkalinitas (mg/L atau ppm))

KriteriaKriteria Sifat Korosifitas Sifat Korosifitas

Interpretasi LI:Interpretasi LI: LILI > 0 > 0 → Air akan membentuk endapan→ Air akan membentuk endapan LILI = 0 = 0 → Air bersifat netral→ Air bersifat netral LILI < 0 < 0 → Air bersifat korosif→ Air bersifat korosif

Interpretasi RI:Interpretasi RI: RIRI < 5,5 < 5,5 → → Heavy scaleHeavy scale akan terbentuk akan terbentuk 5,5 < 5,5 < RIRI < 6,2 < 6,2 → Endapan akan terbentuk→ Endapan akan terbentuk 6,2 < 6,2 < RIRI < 6,8 < 6,8 → Air bersifat netral→ Air bersifat netral 6,8 < 6,8 < RIRI < 8,5 < 8,5 → Air bersifat korosif→ Air bersifat korosif RIRI > 8,5 > 8,5 → → Air bersifat sangat korosifAir bersifat sangat korosif

Dealing with CorrosionDealing with Corrosion

There are many ways to prevent or There are many ways to prevent or minimize corrosion damage.minimize corrosion damage.

AlloyingAlloying Coating - metallicCoating - metallic Coating – organicCoating – organic ElectrochemicalElectrochemical InhibitorsInhibitors

SteelSteel Alloying to Provide Alloying to Provide Corrosion ResistanceCorrosion Resistance

Add >11% Cr (stainless steel)Add >11% Cr (stainless steel)

Add >2% Mo to stainless (resist Add >2% Mo to stainless (resist pitting)pitting)

Add Si, P, Cu, Cr ( and others) to Add Si, P, Cu, Cr ( and others) to obtain weathering steel obtain weathering steel

Metallic CoatingsMetallic Coatings

Widely used to protect steel and Widely used to protect steel and to make other metals more to make other metals more attractiveattractive

Zn and Zn alloys on steel: Zn and Zn alloys on steel: GalvanizingGalvanizing

Al on steel: AluminizingAl on steel: Aluminizing Ni + Cr on steel, brass or zinc to Ni + Cr on steel, brass or zinc to

give a bright finishgive a bright finish Cu + Ni + Cr also used for bright Cu + Ni + Cr also used for bright

finishfinish

Organic Coatings - PaintOrganic Coatings - Paint Barrier layer to keep water Barrier layer to keep water

awayaway

Adhesion is key to successAdhesion is key to success

Susceptible to thermal Susceptible to thermal damagedamage

Susceptible to UV damageSusceptible to UV damage

Inhibitors - Additions to the electrolyte that preferentially migrate to the anode or cathode, cause polarization, and reduce the rate of corrosion.

Sacrificial anode - Cathodic protection by which a more anodic material is connected electrically to the material to be protected. The anode corrodes to protect the desired material.

Passivation - Producing strong anodic polarization by causing a protective coating to form on the anode surface and to thereby interrupt the electric circuit.

Protection Against Electrochemical Corrosion

InhibitorInhibitor

Inhibitor senyawa kimia Inhibitor senyawa kimia ditambahkanditambahkan dalam jumlah kecil dalam jumlah kecil

Interface inhibisi : interaksiInterface inhibisi : interaksi inhibitor inhibitor dengan permukaan logam membentuk dengan permukaan logam membentuk lapisan tipis (presipitasi).lapisan tipis (presipitasi).

Interphase inhibisi : yaitu modifikasi Interphase inhibisi : yaitu modifikasi lingkungan yang korosif lingkungan yang korosif , , misal : misal : penangkapan oksigen, netralisasi gas penangkapan oksigen, netralisasi gas yang bersifat asam, pengaturan pH dan yang bersifat asam, pengaturan pH dan lain sebagainya.lain sebagainya.

MekanismeMekanisme

mekanisme inhibitor mekanisme inhibitor dibedakan 4 jenis :dibedakan 4 jenis :

1.1. OxidizerOxidizer

2.2. Oxygen scavengersOxygen scavengers

3.3. Precipitation Precipitation inhibitorsinhibitors

4.4. Adsorpsion inhibitorAdsorpsion inhibitor

Corrosion InhibitorsCorrosion Inhibitors

Used in water systems:Used in water systems:

Automotive cooling systemsAutomotive cooling systems

Cooling towersCooling towers

Boilers, especially high pressure Boilers, especially high pressure steamsteam

Temporary preservatives for metalsTemporary preservatives for metals

Volatile corrosion inhibitorsVolatile corrosion inhibitors Paints and primers Paints and primers

Pencegahan dan perlindungan korosiPencegahan dan perlindungan korosi

Perlindungan katodikPerlindungan katodik

1.1. Arus tanding (impressed current)Arus tanding (impressed current)

2.2. Anoda korban (sacrificed anode)Anoda korban (sacrificed anode)

Kriteria material anoda korbanKriteria material anoda korban

• logam aktif dengan potensial korosi lebih logam aktif dengan potensial korosi lebih kecil/negatif dari potensial korosi yang kecil/negatif dari potensial korosi yang diproteksidiproteksi

• potensial korosi harus mampu melawan potensial korosi harus mampu melawan hambatan elektrolithambatan elektrolit

• polarisasinya rendah,polarisasinya rendah,• tidak dalam kondisi pasif pada lingkungan tidak dalam kondisi pasif pada lingkungan

kerjakerja• efisiensi tinggiefisiensi tinggi• nilai ekonomis tinggi.nilai ekonomis tinggi.

Kriteria Proteksi KatodikKriteria Proteksi Katodik Kriteria proteksi NACE Standard RP 0169-83:Kriteria proteksi NACE Standard RP 0169-83: potensial terukur terhadap Cu/CuSO4 potensial terukur terhadap Cu/CuSO4

maksimal –850 mV (untuk baja),maksimal –850 mV (untuk baja), polarisasi katodik lebih dari 300 mV aktif polarisasi katodik lebih dari 300 mV aktif

terhadap potensial korosi struktur (dengan terhadap potensial korosi struktur (dengan faktor IRfaktor IR),),

polarisasi katodik lebih dari 100 mV aktif polarisasi katodik lebih dari 100 mV aktif terhadap potensial korosi struktur (tanpa terhadap potensial korosi struktur (tanpa faktor IRfaktor IR),),

besar potensial polarisasi katodik besar potensial polarisasi katodik berdasarkan sifat yang diinginkan menurut berdasarkan sifat yang diinginkan menurut kurva Tafel (E-log I), dankurva Tafel (E-log I), dan

arus proteksi yang mencapai struktur arus proteksi yang mencapai struktur merupakan nilai bersih.merupakan nilai bersih.

Terima KasihTerima Kasih

kuliah korosi 2008

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