Corrosion Management on Pipeline with Cathodic Protection

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
Material Driving Voltage (V)
Silver (Ag/Ag) 0.8 (cathodic)
Copper (Cu/Cu2) 0.34
Water (O2H204e- 4OH-) 0.401
Hydrogen (H2) 0 (reference)
Iron (Fe/Fe2) -0.44
Zinc (Zn/Zn2) -0.76
Magnesium (Mg2) -2.36 (anodic)
8
Galvanic Sacrificial Anode-Installation
(Source Peabodys Control of Pipeline Corrosion)
9
Galvanic Sacrificial Anode-Installation
(Source Peabodys Control of Pipeline Corrosion)
10
Impressed Current
(Source Peabodys Control of Pipeline Corrosion)

• Minimum potential -0.85V
• Reference electrode Copper Sulfate

11
Galvanic Sacrificial Anode-Design

• Calculate total area to be protected (Ap)
• Determine the current density (?)
• Calculate total protection current (Itot ? .Ap)
• Calculate R per anode R f(d,l,?)
• Calculate Ia per anode (Vd-0.85/R)
• Calculate total anode needed
• Initial NItot/In
• Lifetime N f(mass,lifetime,A/poundyear)

12
Impressed Current-Principle

• Rectifier
• Variable voltage, variable current
• Higher current density (gt 1 A)
• Higher soil resistivity (gt 104 ?cm)

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 Peabodys Control of Pipeline
Corrosion)
15
Impressed Current - Design

• Calculate total area to be protected (Ap)
• Determine curent density (?)
• Calculate total protection current (Ip)
• Calculate total anode needed (N)
• Initial
• Lifetime
• Calculate total anode resistance (Rtot
  f(N,?,d,L,spacing))
• Calculate rectifier specification (Vdc, Idc, Pdc
  f(Rtot,Ip)

16
Pipeline Cathodic Protection Case Study
17
Galvanic Sacrificial Anode Case Study
Variabel Nilai
Pipe Diameter (d) a. 2 inch 0.0508m b. 1 inch 0.0254m
Pipe Length (l) a. 2 inch pipe 300m b. 1 inch pipe 1300m
Soil Resistivity (average) 4500 ?cm
Current Density (?) 9mA/sqmm
Type of Anode Magnesium, weight 9 pon, r 8.89cm, l 53.54cm
Coating efficiency (n) 50
Lifetime 20 years
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 (Dwights 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

Type of Pipe Effective Surface (Ac) Number of Anode (Ac/A)
Diameter 2inch (0.0508m)
Diameter 1inch (0.0254m)
Total 31
22
Impressed Current Case 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 ?cm
Current Density (?) 30mA/sqmm
Type of Anode Stated in next section
Coating Efficiency (n) 50
Coating Impedance 25000?/m2
Maximum Groundbed Resistance 2?
Lifetime 15years
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 2? (to limit rectifiers 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.