Corrosion Management on Corrosion Management on Pipeline with Cathodic Pipeline with Cathodic
ProtectionProtection
Ilmu Bahan dan KorosiIlmu Bahan dan Korosi
OutlineOutline• Pipeline Risks and CorrosionPipeline Risks and Corrosion
• Cp Technique : Cp Technique : Galvanic Sacrificial Galvanic Sacrificial Anode (Anode (PrinciplePrinciple, , InstallationInstallation))
• Cp Technique : Cp Technique : Impressed Current (Impressed Current (PrinciplePrinciple, , InstallationInstallation))
• Case StudyCase Study : : Sacrificial AnodeSacrificial Anode
• Case StudyCase Study : : Impressed Current Impressed Current
The product of the frequency with which an event is anticipated to occur and the consequence of the event outcome.
Risks on PipelineRisks on Pipeline
RISK = PROBABILITY x SEVERITY
LEAKAGE
CORROSION
PRESSURE DROP
Risks on PipelineRisks on Pipeline
Corrosion ControlCorrosion Control• CoatingCoating : insulation : insulation
• Cathodic Protection: DC current Cathodic Protection: DC current injection towards pipeline, result: injection towards pipeline, result: pipeline is “shifted” as cathode. pipeline is “shifted” as cathode.
Sacrificial anodeSacrificial anode
Impressed currentImpressed current
Galvanic Sacrificial Anode Galvanic Sacrificial Anode - Principle- Principle
• Metal Driving voltage (Metal Driving voltage (VdVd))
• Negative Negative VdVd = active metal = active metal =tendency to corrode=tendency to corrode
• Pipeline: connected with active Pipeline: connected with active metalmetal
• Anode: Mg, Zn Cathode: pipelineAnode: Mg, Zn Cathode: pipeline
• Corrosion on Mg, Zn hence Corrosion on Mg, Zn hence “sacrificial”“sacrificial”
Galvanic Sacrificial Galvanic Sacrificial Anode-PrincipleAnode-Principle
Material Driving Voltage (V)
Silver (Ag/Ag+) +0.8 (cathodic)
Copper (Cu/Cu2+) +0.34
Water (O2+H20+4e- = 4OH-) +0.401
Hydrogen (H2) 0 (reference)
Iron (Fe/Fe2+) -0.44
Zinc (Zn/Zn2+) -0.76
Magnesium (Mg2+) -2.36 (anodic)
Galvanic Sacrificial Galvanic Sacrificial Anode-InstallationAnode-Installation
(Source: Peabody’s Control of Pipeline Corrosion)
Galvanic Sacrificial Galvanic Sacrificial Anode-InstallationAnode-Installation
(Source: Peabody’s Control of Pipeline Corrosion)
Impressed CurrentImpressed Current
• Minimum potential: -0.85VMinimum potential: -0.85V• Reference electrode: Copper Sulfate Reference electrode: Copper Sulfate
(Source: Peabody’s Control of Pipeline Corrosion)
Galvanic Sacrificial Galvanic Sacrificial Anode-DesignAnode-Design
• Calculate total area to be protected (Ap)Calculate total area to be protected (Ap)• Determine the current density (Determine the current density (ρρ))• Calculate total protection current (Itot = Calculate total protection current (Itot =
ρρ .Ap) .Ap)• Calculate R per anode : R = f(d,l,Calculate R per anode : R = f(d,l,ρρ)) • Calculate Ia per anode : (Vd-0.85/R)Calculate Ia per anode : (Vd-0.85/R)• Calculate total anode needed : Calculate total anode needed :
Initial : N=Itot/InInitial : N=Itot/InLifetime: N = f(mass,lifetime,A/poundyear)Lifetime: N = f(mass,lifetime,A/poundyear)
Impressed Current-PrincipleImpressed Current-Principle
• RectifierRectifier
• Variable voltage, variable Variable voltage, variable currentcurrent
• Higher current density (> 1 A)Higher current density (> 1 A)
• Higher soil resistivity (> 10Higher soil resistivity (> 104 4
Ωcm)Ωcm)
Impressed Current-Impressed Current-InstallationInstallation
• Types of anode:Types of anode: Graphite : big CR (pound/A/year)Graphite : big CR (pound/A/year) High Silicon Cast Iron : medium CRHigh Silicon Cast Iron : medium CR Platinum & niobium : small CRPlatinum & niobium : small CR
• Rectifier rating:Rectifier rating: Voltage, Amperes, Watt, Freq.Voltage, Amperes, Watt, Freq. Cooling System : Air, OilCooling System : Air, Oil EfficiencyEfficiency
CR: Consumption Rate
Impressed Current - Impressed Current - InstallationInstallation
(Source: Peabody’s Control of Pipeline Corrosion)
Impressed Current - Impressed Current - DesignDesign
• Calculate total area to be protected (Ap) Calculate total area to be protected (Ap) • Determine curent density (Determine curent density (ρρ))• Calculate total protection current (Ip)Calculate total protection current (Ip)• Calculate total anode needed (N)Calculate total anode needed (N)
InitialInitial LifetimeLifetime
• Calculate total anode resistance (Rtot = Calculate total anode resistance (Rtot = f(N,f(N,ρρ,d,L,spacing)),d,L,spacing))
• Calculate rectifier specification (Vdc, Idc, Pdc Calculate rectifier specification (Vdc, Idc, Pdc = f(Rtot,Ip)= f(Rtot,Ip)
Pipeline Cathodic Pipeline Cathodic Protection– Case StudyProtection– Case Study
Galvanic Sacrificial Anode Galvanic Sacrificial Anode – Case Study– Case Study
Variabel Nilai
Pipe Diameter (d) a. 2 inch = 0.0508mb. 1 inch = 0.0254m
Pipe Length (l) a. 2 inch pipe: 300mb. 1 inch pipe: 1300m
Soil Resistivity (average) 4500 Ωcm
Current Density (ρ) 9mA/sqmm
Type of Anode Magnesium, weight 9 pon, r = 8.89cm, l = 53.54cm
Coating efficiency (n) 50%
Lifetime 20 years
Galvanic Sacrificial Anode Galvanic Sacrificial Anode – Case Study– Case Study
• Step 1: Step 1: surface area of pipelinesurface area of pipeline
• Step 2: Step 2: total protection areatotal protection area
• Step 3: Step 3: total protection currenttotal protection current
22 806,75613,151%50 mmApnAc
AmAmsqmmAAcIp 682,0254,682806,75/9 2
Galvanic Sacrificial Anode Galvanic Sacrificial Anode – Case Study– Case Study
• Step 4: Step 4: Anode resistance (Dwight’s Equation)Anode resistance (Dwight’s Equation)
• Step 5: Step 5: Current per AnodeCurrent per Anode
15,291
89,8
54,534ln
54,53
159,045001
4ln
159,0
r
L
LR
mARae
E
ctrolyteceAnodeElesis
eteelVoltagPolarisedstageDrivingVolIa 024,0
15,29
85,055,1
tanRe
Galvanic Sacrificial Anode Galvanic Sacrificial Anode – Case Study– Case Study
• Step 6: Step 6: Total Number of AnodeTotal Number of Anode
InitialInitial
LifetimeLifetime
Selected number of anodes: Selected number of anodes: 3131. .
anodesmA
A
Ia
IpN 41.28
024,0
682,0
anodestAnodeWeigh
IpLifetimeN 75.30
93,49
254,68220
3,49
Galvanic Sacrificial Anode Galvanic Sacrificial Anode – Case Study– Case Study
• Step 7: Step 7: Distribution and LayoutDistribution and Layout
DistributionDistribution
LayoutLayout
2445.231
806.75m
N
AcA
2935.233000508,05.0 m 10445,2:93,23
287.5113000254,05,0 m 21445,2:87.51
Type of Pipe Effective Surface (Ac) Number of Anode (Ac/A)
Diameter 2inch (0.0508m)
Diameter 1inch (0.0254m)
Total 31
Impressed Current Impressed Current Case StudyCase Study
Variabel Value
Pipe Diameter (d) 6 inch = 0,1524 m
Pipe Lengyth (l) 6800 feet = 2072 m = 2,072 km
Soil Resistivity (average) 2000 Ωcm
Current Density (ρ) 30mA/sqmm
Type of Anode Stated in next section
Coating Efficiency (n) 50%
Coating Impedance 25000Ω/m2
Maximum Groundbed Resistance
2Ω
Lifetime 15years
Impressed Current Impressed Current Case StudyCase Study
• Step 1: Step 1: surface area of pipelinesurface area of pipeline
• Step 2: total protection area
• Step 3: Step 3: total protection currenttotal protection current
• Step 4: Step 4: determine type of anodesdetermine type of anodesIron Silicon Chromium. Weight: 110 pon, cross section 4 sqft (0,371m2), Iron Silicon Chromium. Weight: 110 pon, cross section 4 sqft (0,371m2),
diameter 10 inch (0,833 feet = 2,54cm), length 84 inchi (7 feet = diameter 10 inch (0,833 feet = 2,54cm), length 84 inchi (7 feet = 20,32cm)20,32cm)
203,99220721524,0 mdlAp
22 015,49603,992%50 mmApnAc
AmAmsqmmAAcIp 88,1445,14880015,496/30 2
Impressed Current Impressed Current Case StudyCase Study
• Step 5: Step 5: total number of anodestotal number of anodes
• Current limit (silicon: 10.76 Current limit (silicon: 10.76 A/mA/m22))
• LifetimeLifetime
Total anodes: Total anodes: 44..
anode
mAm
A
IcAi
IpN 72,3
76,10371,0
88,14
22
anodepon
mA
tAnodeWeigh
IpLifetimeN 02,2
1101000
1488015
1000
Impressed Current –Case Impressed Current –Case StudyStudy
• Step 6: Step 6: groundbed resistance calculationgroundbed resistance calculation
Resistance limit: 2Ω (to limit rectifier’s spec)Resistance limit: 2Ω (to limit rectifier’s spec)
Spacing: Spacing: SS = 30 = 30 feetfeet , Anode Length: , Anode Length: LL = 7 = 7 feetfeet
Anode Diameter: Anode Diameter: DD = 0.8333 = 0.8333 feetfeet
Groundbed resistance is Groundbed resistance is below limitbelow limit. .
If not, If not, choose longer spacingchoose longer spacing..
36.1
4656.0ln30
721
833.0
78ln
47
200000521.0
)656.0ln2
18
(ln00521.0
NS
L
d
L
NLRg
Impressed Current - Impressed Current - PrinciplePrinciple
• Step 7: Step 7: rectifier specificationrectifier specification
Specification: Specification: 2121VDCVDC, 302, 302WW . .
Final ResultsFinal Results::
• Anodes : Anodes : Iron Silicon ChromiumIron Silicon Chromium, , 44 anodes. anodes.
• Rectifier : Rectifier : 21VDC, 302W21VDC, 302W..
WIpVrecSrec
VRgIpVrec
123,301
.237,2036.188,14