Download - 1.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.
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
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
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
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