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--
©20
03 B
rook
s/C
ole,
a d
ivis
ion
of T
hom
son
Lea
rnin
g, I
nc.
Tho
mso
n L
earn
ing ™
is a
trad
emar
k us
ed h
erei
n un
der
lice
nse.
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
Adextrusion
roll
AoAd
roll
tensile force
AoAddie
die
METAL FABRICATION METHODS-IMETAL FABRICATION METHODS-I
©20
03 B
rook
s/C
ole,
a d
ivis
ion
of T
hom
son
Lea
rnin
g, I
nc.
Tho
mso
n L
earn
ing ™
is a
trad
emar
k us
ed h
erei
n un
der
lice
nse.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©20
03 B
rook
s/C
ole,
a d
ivis
ion
of T
hom
son
Lea
rnin
g, I
nc.
Tho
mso
n L
earn
ing ™
is a
trad
emar
k us
ed h
erei
n un
der
lice
nse.
Figure 22.10 (a) Bacterial cells growing in a colony (x2700). (b) Formation of a tubercule and a pit under a biological colony.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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.
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
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
Corrosion possible with
oxygen reduction
Corrosion possible with
hydrogen evolution
Corrosion possible with
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?
Will iron corrode in
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
Will iron corrode in
neutral waters?
Will iron corrode in
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
Sources of Localized CorrosionSources of Localized Corrosion
MaterialMaterial• segregationsegregation• inclusionsinclusions• different phasesdifferent phases• grain boundariesgrain boundaries
Sources of Localized CorrosionSources of Localized Corrosion
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..
©20
03 B
rook
s/C
ole,
a d
ivis
ion
of T
hom
son
Lea
rnin
g, I
nc.
Tho
mso
n L
earn
ing ™
is a
trad
emar
k us
ed h
erei
n un
der
lice
nse.
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