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Corrosion Management on Pipeline with Cathodic Protection

Corrosion Management on Pipeline with Cathodic Protection. Ilmu Bahan dan Korosi. Outline. Pipeline Risks and Corrosion Cp Technique : Galvanic Sacrificial Anode ( Principle , Installation ) Cp Technique : Impressed Current ( Principle , Installation )

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Corrosion Management on Pipeline with Cathodic Protection

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  1. Corrosion Management on Pipeline with Cathodic Protection Ilmu Bahan dan Korosi

  2. Outline • Pipeline Risks and Corrosion • Cp Technique : Galvanic Sacrificial Anode (Principle, Installation) • Cp Technique : Impressed Current (Principle, Installation) • Case Study : Sacrificial Anode • Case Study : Impressed Current

  3. Risks on Pipeline The product of the frequency with which an event is anticipated to occur and the consequence of the event outcome. RISK = PROBABILITY x SEVERITY

  4. Risks on Pipeline PRESSURE DROP LEAKAGE CORROSION

  5. Corrosion Control • Coating : insulation • Cathodic Protection: DC current injection towards pipeline, result: pipeline is “shifted” as cathode. • Sacrificial anode • Impressed current

  6. Galvanic Sacrificial Anode - Principle • Metal Driving voltage (Vd) • Negative Vd = active metal =tendency to corrode • Pipeline: connected with active metal • Anode: Mg, Zn Cathode: pipeline • Corrosion on Mg, Zn hence “sacrificial”

  7. Galvanic Sacrificial Anode-Principle

  8. Galvanic Sacrificial Anode-Installation (Source: Peabody’s Control of Pipeline Corrosion)

  9. Galvanic Sacrificial Anode-Installation (Source: Peabody’s Control of Pipeline Corrosion)

  10. Impressed Current • Minimum potential: -0.85V • Reference electrode: Copper Sulfate (Source: Peabody’s Control of Pipeline Corrosion)

  11. Galvanic Sacrificial Anode-Design • Calculate total area to be protected (Ap) • Determine the current density (ρ) • Calculate total protection current (Itot = ρ .Ap) • Calculate R per anode : R = f(d,l,ρ) • Calculate Ia per anode : (Vd-0.85/R) • Calculate total anode needed : • Initial : N=Itot/In • Lifetime: N = f(mass,lifetime,A/poundyear)

  12. Impressed Current-Principle • Rectifier • Variable voltage, variable current • Higher current density (> 1 A) • Higher soil resistivity (> 104 Ωcm)

  13. Impressed Current-Installation • Types of anode: • Graphite : big CR (pound/A/year) • High Silicon Cast Iron : medium CR • Platinum & niobium : small CR • Rectifier rating: • Voltage, Amperes, Watt, Freq. • Cooling System : Air, Oil • Efficiency CR: Consumption Rate

  14. Impressed Current - Installation (Source: Peabody’s Control of Pipeline Corrosion)

  15. Impressed Current - Design • Calculate total area to be protected (Ap) • Determine curent density (ρ) • Calculate total protection current (Ip) • Calculate total anode needed (N) • Initial • Lifetime • Calculate total anode resistance (Rtot = f(N,ρ,d,L,spacing)) • Calculate rectifier specification (Vdc, Idc, Pdc = f(Rtot,Ip)

  16. Pipeline Cathodic Protection– Case Study

  17. Galvanic Sacrificial Anode – Case Study

  18. Galvanic Sacrificial Anode – Case Study • Step 1: surface area of pipeline • Step 2: total protection area • Step 3: total protection current

  19. Galvanic Sacrificial Anode – Case Study • Step 4: Anode resistance (Dwight’s Equation) • Step 5: Current per Anode

  20. Galvanic Sacrificial Anode – Case Study • Step 6: Total Number of Anode • Initial • Lifetime Selected number of anodes: 31.

  21. Galvanic Sacrificial Anode – Case Study • Step 7: Distribution and Layout • Distribution • Layout

  22. Impressed Current Case Study

  23. Impressed Current Case Study • Step 1: surface area of pipeline • Step 2: total protection area • Step 3: total protection current • Step 4: determine type of anodes 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 = 20,32cm)

  24. Impressed Current Case Study • Step 5: total number of anodes • Current limit (silicon: 10.76 A/m2) • Lifetime Total anodes: 4.

  25. Impressed Current –Case Study • Step 6: groundbed resistance calculation Resistance limit: 2Ω (to limit rectifier’s spec) Spacing: S = 30 feet , Anode Length: L = 7 feet Anode Diameter: D = 0.8333 feet Groundbed resistance is below limit. If not, choose longer spacing.

  26. Impressed Current - Principle • Step 7: rectifier specification Specification: 21VDC, 302W . Final Results: • Anodes : Iron Silicon Chromium, 4 anodes. • Rectifier : 21VDC, 302W.

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