corrosion management on pipeline with cathodic protection

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