Post on 14-Jan-2016
description
transcript
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