1.Kriteria Pk

KRITERIA PK

• BANYAK PIHAK BELUM MEMAHAMI DASAR

KRITERIA.

• IMBASNYA KE PRAKTIS LAPANGAN.

• DAPAT MENIMBULKAN SELISIH PENDAPAT

YANG PERLU MENDAPAT PERHATIAN.

• PERLU MEMAHAMI PROSES KOROSI, PRINSIP

PK, FAKTOR2 YANG MEMPENGARUHI, DLL.

• PERLU PERSAMAAN PANDANGAN ANTARA

PARA PRAKTISI LAPANGAN DAN PARA

PENGGUNA.

MASALAH

YANG PERLU DIFAHAMI

•DASAR KRITERIA

•IR DROP

•PENGARUH LINGKUNGAN

•PENGARUH JENIS COATING

•PENGARUH APLIKASI CIATING.

•PENGARUH SUHU

•DLL.

APAKAH PK?

1. PK ADALAH TEKNIK PENGENDALIAN KOROSI LOGAM

DALAM ELEKTROLIT DENGAN JALAM MENGALIRI

ARUS LISTRIK SEARAH KE ARAH MELELAUI

ELEKTROLIT SELURUH PERMUKAAN LOGAM.

2. PERMASALAHN TEKNIS UTAMA ADALAH ARUS

PROTEKSI HARUS TERSEBAR SEMERATA MUNGKIN DI

SELURUH PERMUKAAN LOGAM.

3. INI ADALAH PERMASALAHAN TEKNIS YANG RUMIT

YANG MEMERLUKAN PENGALAMAN.

4. CATHODIC PROTECTION IS MORE ART THAN

SCIENCE.

I

V

Re

Ra

Rc

V = I(Ra + Re + Rc)

E

KUHN 1933

ARUS PROTEKSI

1. BILA POTENSIA BAJA DITURUNKAN 0.4 V MAKA KOROSI

AKAN TERPPROTEKSI DARI KOROSI.

2. ARUS PROTEKSI YANG DIPERLUKA SEKTITAR :

3. R = TAHANAN PIPA DALAM TANAH. TAHANAN JALUR

PIPA TERHADAP TANAH DAPAT DITENTUKAN DENGAN

PENGKURAN. MAKIN TINGGI TAHANAN MAKIN

RENDAH RENDAH KEPERLUAN ARUS PROTEKSI.

I = 0.4/R

KRITERIA ARUS PROTEKSI

1. SANGAT RUMIT UNTUK DIAPLIKASIKAN.

2. RAPAT ARUS PROTEKSI BAJA BERKISAR

ANTARA 10 MA/M2 SAMPAI 1500 MA/M2.

3. KEPERLUAN ARUS PROTEKSI INI

TERGANTUNG DARI KONDISI COATING,

KONDISI LINGKUNGAN, SUHU OPERASI,

DLL.

BROWN

WHERE CORROSION IS ENTIRELY

ELECTROCHEMICAL IN NATURE IT IS

NECESSARY TO POLARIZE THE

CATHODES IN THE CORROSION CELL TO

THE OPEN CIRCUIT POTENTIAL OF THE

LOCAL ANODES IN ORDER TO OBTAIN

COMPLETE CATHODIC PROTECTION

e

e

e

K

A

OPEN CIRCUIT POTENTIAL?

Ea

Ec

Ex

Rx

Ra

Rc

Ia

Ic

Ix

ia + ix = ic ia = 0 Ea = Ec + Rxix

ix = ic

log i

E

A

K

CP CRIT. BROWN

APPLIED CURRENT

POTENSIAL PADA OPEN

CIRCUIT ANODE?

1. PADA OPEN CIRCUIT ANODE POTENTIAL,

TERJADI EXCHANGE CURRENT DENSITY,

DIMANA KONSENTRASI ION Fe++ = 10-6 MOL/L

2. DENGAN RUMUS NERNST :

Fe Fe++ + 2e (Fe++= 10-6 MOL)

E = E0 – 0.059/n log (Red/Ox)

E = -0.44 –0.059/2 x 6 = -0.62 V(SHE)

E = 0.95 V (CSE) (TEORI BROWN)

NBS SURVEY

NBS mengadakan survey sekitar 15 tahun, dan

berkesimpulan bahwa proteksi sempurna dapat

dapat dicapai bila baja dipolarisasi sampai

- 0.85 V (CSE)

Kalau kita kembalikan ke persamaan Nernst, maka

potensial tersebut mencerminkan aktivitas

(konsentrasi) ion (Fe++) = 10-3 mol/L

Nini kriteria – 0,85 V, CSE secara umum pada saat

ini diaplikasikan di seluruh dunia.

NACE 0169-96 (PEABODY)

1. - 850 MV, CSE, WITH CP APPLIED

2. A POLARIZED POTENTIAL – 850 Mv, CSE

3. 100 MV OF POLARIZATION

4. NET PROTECTIVE CURRENT FLOWS

TOWARD PROTECTED STRUCTURE

FOR STEEL AND CAST IRON

MOST COMMON

1. The most common criteria used is the potential of -850

mV(CSE) with CP applied, by contacting the reference

electrode to electrolyte for coated structures/pipeline.

2. The limitation is that it may vary with soil condition,

especially the resistivity. The higher the resistivity the

more negative potential will be resulted.

3. The forth criterion is used when the steel is heavily

corroded, where it is impossible to achieved potential

as described in (1).

BS 7361 - 1992

Metal/Alloy

Protection potential, mV

Cu/CuSO4 Ag/AgCl Zn/seawater

Iron/steel :- aerobic- anaerobic

LeadCu alloysAluminum - Upper limit- Lower limit

-850-950-600-500 to –600

-950-1200

-750-850-500-400 to –550

-850 -1100

+250+150+500+600 to +450

+150-100

Morgan p. 25

1. Potential of the structure is polarized to be more negative than open circuit anode potential.

2. Potential change of the metal greater than corrosion potential and the open circuit anode potential.

3. External current flow through electrolyte on to the structure receiving protection.

Morgan p. 37 for steel

1. - 850 mV, CSE, + 2mV/oC for elevated

temp.

2. Anaerobic 100 mV less negative.

3. Potential shift negative 300 mV, or 400

mV foe anaerobic.

4. Cathodic Polarization decay 100 mV

or 150 mV for anaerobic

CP CRITERIA

ISO 15589-1

WHAT IS CP ISO

1. A METHOD OF CONTROLING CORROSION RATE BY FLOWING DIRECT CURRENT TRHOUGH ELECTROLYTE ONTO THE METAL SURFACE TO BE PROTECTED’

2. THIS WILL BRING THE METAL POTENTIAL DOWN.

CP CRITERIA FOR STEEL

ISO

1. COROSION RATE SHOULD BE

BROUGHT TO LESS THAN

0.01 mm PER YEAR.

2. THIS CAN BE REACHED IF THE

POTENTIAL IS LOWERED TO –

850 MV AGAINST Cu/CuSO4 OR

LESS NEGATIVE.

ISO vs NACE and BS for

STEEL CP CRITERIUM

- mV, vs CSE

ISO NACE BS

850 850 850 aerobic

950 anaerobic