Placement of Sacrificial Anode in Trench Side Pocket

training courses

1. Haward Technology Middle East 1Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Section 20
Corrosion Management on Pipeline
with Cathodic Protection

2. Haward Technology Middle East 2Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 3Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 4Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Risks on Pipeline

5. Haward Technology Middle East 5Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Corrosion Control
Coating : insulation
Cathodic Protection: DC current injection towards
pipeline, result: pipeline is “shifted” as cathode.
•Sacrificial anode
•Impressed current

6. Haward Technology Middle East 6Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 7Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode - Principle

8. Haward Technology Middle East 8Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode - Installation

9. Haward Technology Middle East 9Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode - Installation

10. Haward Technology Middle East 10Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current
•Minimum potential: -0.85V
•Reference electrode: Copper Sulfate

11. Haward Technology Middle East 11Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 12Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current - Principle
Rectifier
Variable voltage, variable current
Higher current density (> 1 A)
Higher soil resistivity (> 10
4
Ωcm)

13. Haward Technology Middle East 13Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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

14. Haward Technology Middle East 14Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current - Installation

15. Haward Technology Middle East 15Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 16Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Pipeline Cathodic Protection
Case Study

17. Haward Technology Middle East 17Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode – Case Study
d = 2 inch, length 300m
d = 1 inch,
length 260m
d = 1 inch,
length 260m
d = 1 inch,
length 260m
d = 1 inch,
length 260m
d = 1 inch,
length 260m

18. Haward Technology Middle East 18Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode – Case Study
Step 1: surface area of pipeline
Step 2: total protection area
Step 3: total protection current

19. Haward Technology Middle East 19Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode – Case Study
Step 4: Anode resistance (Dwight’s Equation)
Step 5: Current per Anode

20. Haward Technology Middle East 20Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode – Case Study
Step 6: Total Number of Anode
•Initial
•Lifetime
Selected number of anodes: 31

21. Haward Technology Middle East 21Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Galvanic Sacrificial Anode – Case Study
Step 7: Distribution and Layout
•Distribution
•Layout

22. Haward Technology Middle East 22Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current Case Study

23. Haward Technology Middle East 23Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 24Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current Case Study
•Step 5: total number of anodes
‐Current limit (silicon: 10.76 A/m
2
)
‐Lifetime
Total anodes: 4.

25. Haward Technology Middle East 25Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
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. Haward Technology Middle East 26Section 20
Cathodic Protection Systems: Design,
Fabrication, Installation, Operation and Repair
Impressed Current - Principle
•Step 7: rectifier specification
Specification: 21VDC, 302W
Final Results:
‐Anodes : Iron Silicon Chromium, 4 anodes.
‐Rectifier : 21VDC, 302W.