Cathodic Protection Impressed Current

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14 DES 2011

PT PERTAMINA (PERSERO)

Cathodic Protection

Impressed Current

Agustus 2013

Pelatihan Basic Electrical

CONFIDENTIAL AND PROPRIETARY

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CATHODIC PROTECTION

Cathodic Protection adalah salah satu teknik yang

digunakan untuk mengontrol korosi pada

k

l

permukaan logam.

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APA ITU KOROSI ???

• Korosi = karat = Kerusakan material dikarenakan reaksi

dengan lingkungannya.

• Karat = Zat berwarna merah kecoklatan pada

permukaan besi / baja

.

• Akibat : Adanya proses elektrokimia atau fenomena

elektrikal.

Kriteria terjadinya peristiwa

korosi akibat pengaruh

elektrikal :

1. Anoda dan Katoda

2. Berada dalam media elektrolit

yang sama

3. Hubungan listrik antara anoda

dan katoda

4 Adanya O

₂

PERTAMINA

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PENDAPAT LAIN :

Korosi

:

- Akibat reaksi elektrokimia

Sebab

:

- Perbedaan potential pada permukaan besi/baja

KOMBINASI REAKSI “OKSIDASI” DAN “REDUKSI” = REAKSI ‘REDOKS’

dengan produk akhir yang disebut RUST atau KARAT Reaksi korosi lain yang terjadi adalah terbentuknya Fe₂O₃ (hematit) :

PERTAMINA 3Fe(OH)₂ + 2OH¯ ----> Fe₃O₄ + 4 H₂O

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KERUGIAN AKIBAT KOROSI

Kerugian karena korosi pada banyak

instalasi besi baja yang “rusak”

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• Akibat Langsung

Kerugian di USA pada tahun 1975

adalah US$ 70 billion atau 3 – 5%

d i GNP k

k

dari GNP karena kerusakan

material.

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• Akibat Tidak Langsung

* Kematian dan kecelakaan

* Kematian dan kecelakaan.

* Produksi yang berkurang.

* Plant shut down.

* Over design

Over design.

* Kontaminasi produk.

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METODA PENCEGAHAN

KOROSI

Penyelidikan pencegahan korosi diantaranya oleh :



National Association of Corrosion Engineers (NACE)



Federation of Societies for Paint Technology



Federation of Societies for Paint Technology



Steel Structure Painting Council (SSPC)



Dll.

Metoda antara lain :

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APA ITU CATHODIC PROTECTION ?

CATHODIC PROTECTION adalah :

Proses pencegahan karat / korosi yang

memanfaatkan proses / peristiwa korosi

itu sendiri

itu sendiri.

CATHODIC PROTECTION didapat dengan 2 cara :

1. SACRIFICIAL ANODE SYSTEM

2 IMPRESSED CURRENT SYSTEM

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CATHODIC PROTECTION

SISTEM PERLINDUNGAN KATODIK

Cara bekerja :

Mengubah potensial permukaan besi / baja menjadi katoda

Arus proteksi luar yang menekan / menahan arus keluar

D

h k t d

Daerah katoda

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SACRIFICIAL SYSTEM

Mg

-1.50

PER

T

A

M

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PRINCIPLES OF

CORROSION

Dimana 2 atau lebih metal yang terhubung

PRINCIPLES OF

CORROSION

Dimana 2 atau lebih metal yang terhubung Dimana 2 atau lebih metal yang terhubung

electrically, salah satu metal akan cenderung terkorosi terhadap metal lainnya.

Metal yang terletak di atas akan cenderung Dimana 2 atau lebih metal yang terhubung

electrically, salah satu metal akan cenderung terkorosi terhadap metal lainnya.

Metal yang terletak di atas akan cenderung Metal yang terletak di atas akan cenderung terkorosi dan akan melindungi metal di bawahnya.

Contoh:

Metal yang terletak di atas akan cenderung terkorosi dan akan melindungi metal di bawahnya.

Contoh:

Cooper dan Zinc terhubung satu sama lain, Zinc akan terkorosi sehingga akan memproteksi Copper.

Corrosion rate tergantung pada relative area Cooper dan Zinc terhubung satu sama lain,

Zinc akan terkorosi sehingga akan memproteksi Copper.

Corrosion rate tergantung pada relative area g g p antara anode dan cathode.

g g p antara anode dan cathode.

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CONTOH PEMASANGAN SACRIFICIAL ANODE SYSTEM

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Impressed Current Anodes

a)

Impressed current anodes must be able to pass d.c. current with

negligible metal loss

b)

Steel will lose 9kg per amp year.

c)

Impressed current anodes cause electrolysis of water and only a

few materials are suitable for this application.

2H

₂

O



4H

+

_{+ ½O}

2 +

4e

d)

In sea water chlorine evolution will also take place

2Cl

- _

_{½ Cl}

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Anodes

• Platinised Titanium

a)

Inert Titanium substrate coated with 2.5, 5 or even 7.5 microns

of platinum.

b)

Can operate at high current densities in the range 100 to 5000

b)

Can operate at high current densities in the range 100 to 5000

Am

-2

_.

c)

Low consumption rate of 10 mg per amp per year.

c)

Low consumption rate of 10 mg per amp per year.

d)

Long Life if left energised, if not energised for 3 to 6 months

failure of the anode can occur.

e)

Limited operating voltages in seawater (12V)

f)

Need to be of robust construction when used on jetties

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Other Anode Materials

• Silicon Iron Chrome

▫

These are extremely brittle materials

▫

Operate at low current densities 10 to 40 Am 2

▫

Operate at low current densities 10 to 40 Am-2

▫

Consumption rate 0.2 to 0.5 kg A-1y-1

▫

Cheap and proven track record

• Magnetite

▫

These are light and brittle

▫

Quite expensive

▫

Low consumption rate

▫

Relatively new anode material

L

d Sil

• Lead Silver

▫

Only used in seawater

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TYPES OF REFERENCE ELECTRODE

• Copper/Copper Sulphate (Cu/CuSO

₄

) (For onshore

cathodic protection systems only)

• Zinc

• Silver/Silver Chloride/Seawater (Ag/AgCl)

Silver/Silver Chloride/Seawater (Ag/AgCl)

• Specialist electrodes for cathodic protection in concrete

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GROUNDBED

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Effectivitas Cathodic Protection

Menurut NACE Standard :

Most commonly accepted criteria if

Effectivitas Cathodic Protection

Menurut NACE Standard :

Most commonly accepted criteria if

a negative potential of at least

0.85 volt ( or More negative )

as measured between structure

Most commonly accepted criteria if

a negative potential of at least

0.85 volt ( or More negative )

as measured between structure

surface and saturated copper /

copper sulfate reference

electrode in contact with

electrolyte

surface and saturated copper /

copper sulfate reference

electrode in contact with

electrolyte

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Effectivitas Cathodic Protection

Menurut BS 7361 Part 1 : Minimum protection criteria for Cathodic Protection.

• If the structure to seawater potential is more negative than -850mV vs a Cu/CuSOp g ₄₄ electrode (or -800mV vs an Ag/AgCl) then full levels of cathodic protection are achieved in an aerobic environment.

• If the structure to seawater potential is more negative than -950mV vs a Cu/CuSOp g ₄₄ electrode (-900 mV vs an Ag/AgCl electrode) then full levels of cathodic protection are achieved in an anaerobic environment.

• The maximum level of potential is determined by the structure coating CathodicThe maximum level of potential is determined by the structure coating Cathodic Disbondment of the coating can occur if a high negative potential is applied.

• The maximum negative potential is -1.10 to -1,15V vs Ag/AgCl. There is also the possibility of hydrogen embrittlement

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T

ZONE OF CATHODIC PROTECTION

-0.9 -0.85 + 0.2

INCREASED OVERPROTECTION

PRODUCING BLISTERING OF PAINTS

-1.2

PRODUCING BLISTERING OF PAINTS

INCREASING DANGER OF

THE RELATIONSHIP BETWEEN THE

-1.4 EMBRITTLEMENT

-1.3 AND SPALLING

-0.3 -1.35

-0.2 -1.25

THE RELATIONSHIP BETWEEN THE CORROSION/CATHIODIC PROTECTION

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Summary of Typical Maintenance Requirements Extracted

from BS 7361: Impressed Current CP Systems

Test Frequency: Test Description

Every 3 Months 1. At maximum intervals of 3 months check the satisfactory operation of transformers rectifiers.

satisfactory operation of transformers rectifiers.

Rectifier output voltages and currents should be recorded and pipe to soil potential recorded at the extremities of the pipeline and at test facilities midway

f f

between the transformer rectifier locations.

Every 12 Months 1. At maximum intervals of 12 months the pipe to soil potential should be recorded at all measuring locations and at other locations where a low potential has been recorded.

2. Potentials on secondary structures bonded into the CP system or with sacrificial anodes fitted should be recorded.

3 All transformer rectifiers and test facilities should be

PERTAMINA

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Summary of Typical Maintenance Requirements Extracted

from BS 7361: Impressed Current CP Systems

Every 5 to 10 years 1. Close interval potential surveys should be conducted. These tests are primarily concerned with impressed current systems but should also be considered for sacrificial anode systems.

2. Repeat interference testing.

3 B di h k

3. Bonding checks.

Annual

▪

Carry out tests normally carried out at monthly and six monthly intervals.y y y y

▪

Carry out Electrical Performance Tests on Transformer Rectifiers to comply with BS 7671.

Specialist Checks Inspection Frequency to be agreed

▪

Check condition of all reference electrode, anode and bonding cable connections from surface.