protection protection presentation plus image 5.ppt

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12-16 November, 2006

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Corrosion Control Techniques
5.Cathodic Protection

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2- Impressed current system
DC source
Ground bed
Fe
Anode
DC
Drain Point
I
Umbrella

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Basics of Impressed current system
Steel nails fixed to
dry battery terminals
The steel nails
immersed in saline
water
Results:
1- The nail at +ve
terminal Corrodes
2- The nail at –ve
terminal remains
Uncorroded

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Impressed current system
Nothing happens since
the nails are in different
electrolytes

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Transformer Rectifiers (T/R)
• AC input
Voltage, Single/ three phase, Frequency
• DC maximum output Amp, Volt
• Air Cooled: with sun-shade
Oil Cooled: with thermometer
• Location: according to area classification
• Explosion proof (hazardous area)
• Non-explosion proof (non-hazardous area)

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Transformer Rectifiers
T/R with sun-shade

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Transformer Rectifiers
Explosion-proof Wall-mounted/indoors Pole-mounted

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Transformer Rectifier
Alternating Current Direct Current

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Mixed Metal Oxide (MMO)
Platinized
Graphite
Common Impressed current anodes:
Si – Fe
Si – Cr – Fe
Consumable Anodes Non Consumable Anodes

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Si – Fe
Si – Cr – Fe

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 Are the most common impressed current anodes
 Are used in soil, water or sea water
 Come in two grades; FeSi and FeSiCr for sea water
applications
 Cable connection to anode shall be handled with great
care.
Fe Si Anodes

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Mixed Metal Oxide (MMO) Anodes
Solid Titanium
Core
Titanium
Substrate
with a Copper
Core
Titanium
Tubular
Titanium
Substrate Mesh
Titanium
Substrate
Ribbon
MMO is an electrically conductive
coating that is applied onto a
Titanium substrate in order to
make it act as an Anode

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Mixed Metal Oxide (MMO) Anodes
MMO Coating

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Graphite Anodes

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Platinized Anodes

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 Impressed current anodes are
some times packaged with the
Carbonaceous backfill.

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Impressed Current CP Systems

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Types of ground beds:
• Deep-well GB
• Horizontal shallow GB
• Distributed Anodes

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Deep well > 50m depth
Carbonaceous backfill
for anodes section
Sand topping
Non-metallic
vent tube

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Property 218-L 4518
 Resistivity,
ohm-inch
0.02 0.01
 Resistivity,
ohm-cm
0.05 0.03
 Carbon (L.O.I.
method)
99.0 99.9%
 Moisture 0.10% 0.02%
 Ash 0.35% 0.10%
 VCM 0.30% 0/22%
 Sulfur 3.75% 4.3%
 Bulk Density
(lbs/ft3)
46-50 62-66
 General Sizing
+ 4 Mesh
+ 8 Mesh
- 8 Mesh
+4M < 10%
+8M > 90%
-8M < 10%
4M 10%
+20M > 80%
-20M 10%
Carbonaceous backfill

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Deep-well ground beds
Non-metallic Perforated Casing

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Shallow Bed
Depth 3 – 5 m

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Distributed Impressed Current Anodes Arrangement

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Anode Connection :
Anodes cables are connected to anode / positive junction box
Each anode can be connected via a variable resistance to
control the current output
A header cable connects the PJB to e +ve terminal of T/R

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Anode Connection :
Direct connection to +ve bus bar
Anode
Cables
from
GB
Main Cable to +ve
Terminal of T/R
Positive Junction Box

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Anode Connection :
Connection via
variable resistance
Anode
Cables
from
GB
Main Cable to +ve
Terminal of T/R
Positive Junction Box

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Typical Impressed Current System Arrangement
Ground
Bed

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Positive current flux through soil to buried
pipeline and resulting distribution of current
density on pipe wall

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Pipeline attenuation and
multiple ground beds
V
vs
CSE
GB1 GB2 GB3

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Typical Under-Tank Cathodic Protection
System for New Tanks

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Under tank
cathodic protection
MMO anode grid

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Main Problem with Under-Tank CP
Systems
The protective +ve CP current
causes decomposition of water
Since water content of the soil
underneath the tank is very limited
As a result, the GB dries up – i.e. no
electrolyte – and the CP system is
aborted

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Laser Slotted PVC Tubes
Solution Installation of Under-Tank Watering System
Concrete Ring
Slotted PVC Pipes
Compacted
Soil

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Installation of Under-Tank Watering System
ICCP Anode Grit
Tank
PVC
Watering
Pipe
To T/R
Compacted Soil

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Peripheral Anode Cathodic Protection
System for Existing Tanks
Horizontal GB
MMO strip
anode
Existing Tank
Protecting outermost bottom

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Distributed Anode
Cathodic Protection
System

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Cathodic protection
installation for a well
casing

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Hanging
ICCP
anode
Impressed Current Cathodic
Protection for Tank Internals

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Impressed Current Cathodic
Protection for Tank Internals
ICCP anode
PVC Support
Anode Cable extended to
outside along vent tube

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ICCP for jackets
1- Hanging Anodes

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ICCP for jackets
2- Sub-sea Sleds

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Pourbaix diagram showing the
theoretical conditions for
corrosion, passivation, and
immunity of iron in water and
dilute aqueous solutions
Cathodic Protection Criteria
7 14
Potential
2.0
1.6
0.8
1.2
-0.4
0.4
0.0
-1.6
-0.8
-1.2
0
Immunity
Fe3+
Passivity
Corrosion
pH
Fe2+

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Fe-to-Soil Potential in
Low Resistivity Soils
showing the degree of
corrosion
The value – 850 mV is
the CP criterion for
protecting steel in
aggressive soils
Description
Potential vs Cu/CuSO4
mV
-500
Free Corrosion
-700
Zone of Cathodic Protection
-900
Intense Corrosion
-600
Sever Over-Protection
Problems
-1200
Increased Over-Protection
-1100
Some Over-Protection
-1000
Some Protection
-800

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Excessive negative potentials
can cause :
Cathodic Disbonding : i.e.
loss of adhesion between
the coating and the metal
surface
Hydrogen Damage : due
hydrogen evolution at –ve
potentials

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Potential criteria for cathodic protection of some metals
and alloys at 25º C (1)
(1) According to British code of practice No. CP 1021, August 1973.
(2) But not more negative than about -1.2 Volts.
Metal/ Alloy Potential criterion (mV)
vs Cu/ Cu SO4
Iron, steel, stainless steel:
Aerobic conditions
Anaerobic conditions
-850
-950
Lead -600
Copper -500
Aluminum -950 (2)

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According to ISO 15589-1 Part 1, 2003 concerning the
CP protection criteria of On-Land Pipelines :
“The CP system shall be capable of :
polarizing all parts of the buried pipeline to
potentials more negative than – 850 mV referred to
CSE,
&
to maintain such potentials throughout the design
life of the pipeline”.

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“For pipelines operating in soils with very resistivity,
a protection potential more positive than – 850 mV
referred to CSE may be considered, e.g. as follows”:
- 750 mV for 10,000 < p < 100,000 ohm.cm
- 650 mV for p 100,000 ohm.cm
>
According to ISO 15589-1 Part 1, 2003 concerning the
CP protection criteria of On-Land Pipelines :
i.e., the value of – 850 mV is only for soils with p < 10,000 ohm.cm
p = Soil Resistivity

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Cathodic protection monitoring
Potential Measurement
Structure/Electrolyte Potential is measure by means of a
reference electrode :
Copper / Copper Sulfate Soil
Silver / Silver Chloride Sea Water

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Copper / Copper Sulfate
reference electrode
Portable Type

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Copper / Copper Sulfate
reference electrode
In order to measure the structure – to – soil potential ,
the CSE must become part of the soil
This is fulfilled by inter-mixing of the CSE content with
the soil content due to diffusion down a concentration
gradient

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H2O (
SO4
2-
SO4
2-
Soil)
Copper Rod
CuSO4 Saturated
Water molecules
migrate into CSE
Sulfate ions migrate
from CSE to soil
Porous Disc
AVO meter
Typical Arrangement for Pipe
– to – Soil Measurement
Solution
HIGH WATER CONTENT
HIGH SO4
2- IONS
CONTENT
Pipe
Cu
Cu2+

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Typical Arrangement for Pipe – to – Soil Measurement
Icp umbrella
Icp umbrella
CSE

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Voltmeter
IR error
Ep
CP current
CSE @ soil
surface
Coating
Eon Reading
Eon = Ep + IR Error
Voltmeter

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Voltmeter
Ep
CSE @ soil
surface
Coating
Eoff Reading , instantaneous
Eoff = Ep
Voltmeter

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Permanent Copper / Copper Sulfate
reference electrode
Prepackaged CSE
Backfill :
Gypsum +
Bentonite clay +
Sodium sulfate

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Test Posts for CP Monitoring
Flush – to – ground

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Electrode Placement
For pipelines : on-the-line @ every 1- 2 Km destination
For tanks : preferred under tank or closest

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CP Permanent Monitoring ( Test ) Point
consists of :-
Permanent Reference Electrode ( or Portable type )
Test Post :
for pipelines : @ every 1- 2 Km intervals
for tanks : near the tank

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Structure-to-Soil potential measurement using Voltmeter.

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Permanently Installed Reference Electrode & Test Post

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Permanent Monitoring for
Under Tank Cathodic
Protection
Tank Diameter (m) No. of Electrodes
Required
5-10 1
10-23 2
23-36 3
45 and above 4

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Reference Electrodes Locations for
Under - Tank CP Systems
1/4D
1/6D
2/6D
2/8D
3/8D
1/8D
D=45m and above D=23-36m D=10.5-22.5m D=5-10m
Key : Reference Electrode

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PVC pipe installed through the
concrete ring @ different locations
for CSE placement.
Concrete Ring
Under Tank Soil
PVC Pipe – See Details
Top View
PVC Pipe
Under Tank Soil
Concrete
Ring
CSE

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CSE
Perforated PVC Pipe
Filled with Water
Tank
Perforated PVC Pipe Installed for Reference
Electrode Placement
AVO

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Correct method for measuring structure
potentials when surface is covered with
concrete or asphalt.
AVO
CSE in Wet Soil
Buried Pipe
Concrete / Asphalt

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For monitoring tank’s internal CP system use:
Hanging RE ( from roof )
Plug RE ( fixed on shell )
RE
RE
Hanging Reference Electrodes
Plug RE

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Diver with portable
reference electrode
Potential Measurement of jackets / platform legs

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Transponder CP
monitoring
Potential Measurement of jackets / platform legs

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Potential plot after data
analysis

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Potential Measurement of subsea pipelines
Trailing-wire
potential survey

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TP-3
TP-1 TP-2
well
TP
TP-3 TP-4
- 850 mV Min. protection level
Un protected
area
Pipe
to
soil
potential
-
mV
What about the potential
at any point ?
Buried pipeline ( 1.2 meter deep)
Well casing
8000 feet deep
The criterion most widely used on pipelines is based on measurements
of potential differences between the pipeline and its environment
.
ie: more negative than ( - 850 mv) reference to Cu/Cu So4 cell
Potential Measurement of well casing

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Up hole
Upper Centralizer
Upper Contactors
Spacer Bare
Lower Contactors
Lower Centralizer
Sinker Weight
Length
between
contactors
5
to
7
meters
V
Casing
Tool inside Casing
CASING POTENTIAL PROFILE TOOL
SPECIFICATIONS
8.5 m using 5.0 contactor spacing
10 m using 6.0 contactor spacing
length
Diameter 2.5/8 in. ( 6.5 cm) maximum
weight 440 lb.* (199.6 kg)
Max. temp. 300 deg.F (154 deg.C)
Max.
Pressure
10,000 psi (69 Mpa)
Casing
Size
4.5 in (11.4 cm) to 13.3/8 in (34 cm)
Hoisting
speed
80 ft/min (24.38 m/min
Recommended
Logging
reading
Stationary readings; average speed 25ft/
min (7.6 m/min) at 50 ft intervals
Logging
envirnment
Must be dray
Limitations
Not recommended for use in fresh
water
Typical Casing Potential Profile Tool (Courtesy of Atlas Industries, Inc.)

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+ -
T R
v
OUTPUT CURRENT
= ( I )
( I )
( i1 )
( i 2 )
( i3 )
( I-i1 )
( I-i1-i2 )
( I-i1-i2 -i3)
U1
U2
U3
Casing to soil
potential= (v)
Cu/Cu So4 cell v
U1
U2
U3
-700 -850 -900 -1000
Depth
in
feet
-850mv
min.protection
level
R
R
R Ohm’s Low:
V = I x R
U = Voltage drop
= I x R pipe

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Cable – to - cable connection
Cable – to - pipe connection
Cable – to - structure connection
Cable Connections

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Splice Kit : for cable-to-cable connection
Cable Connections
1 2
Araldite is poured
& let to dry

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For cable-to-pipe connection :
1- Thermite ( Cad / Exothermic ) Welding
2- Pin Brazing
3- Mechanical connection ( for gas pipelines )
Cable Connections

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For cable-to-pipe connection
1- Thermite Welding :
Cable Connections
Crucible
Disks
Cartridge
Spark Flint

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Thermite Weldment
Prior to welding :
The coating must be removed at
welding point ( 5x5 cm square )
Metal surface to be polished and
cleaned
Thermite Welding

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Self-adhesive
Handy-cap
1 2 3
Protecting the Thermite Weldment

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Cable Connections
2- Pin Brazing : emits less heat output
Pin Brazing Unit
Pistol / Gun
Pins & Ferrules
Lug
Grinder

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Cable Connections
2- Pin Brazing

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Cable Connections
2- Pin Brazing
1Clean the surface
2Load gun with pin
& ferrule
3pin braze
4Test connection

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Cable Connections
3- Mechanical Connection : recommended for drain point
connection of gas pipelines

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Cable Connections
Terminal Lugs :
for cable-to-structure ( tank )
connection

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Electrical isolation is made by :
Isolating flange kit ( IFK )
IFK is installed @ Aboveground / Underground Interface
Electrical Isolation
Structures to be protected shall be electrically isolated
from portions which do not require protection.

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Isolating flange kit ( IFK )

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Isolating flange kits
In hazardous areas , IFK’s are
protected by means of Spark Gaps
Spark Gap Fitted

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Monolithic Blocks

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Monolithic Blocks
+ Polarization Cell
The monolithic blocks are
protected against electrostatic
charges and lightening by
polarization cell

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Casings for Road Crossings

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Casings for Road Crossings
There should NOT be any contact
between the pipe & casing
Test posts usually installed @
crossings to monitor the potential
of pipe and casing separately

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Clamp Meter
Clamp Meters are used to
check:
electric cables integrity
current output of each anode
Clamp Meter

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Pipeline & Cable Warning Markers

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There are numerous codes and references that shall be
referred to when dealing with cathodic protection among
these are:
NACE RP 0169
NACE RP 0176
NACE RP 177
NACE RP 575
ISO 15589-1, PART I – 2003, “On-land Pipelines”
ISO 15589-2, PART II – 2004, “Offshore Pipelines”
DnV RP B 401
API 651
J. Morgan, “Cathodic Protection”
A.W. Peabody, “Control of Pipeline Corrosion”

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Terms & Definitions
Natural Potential:
Is potential of structure to be protected whenever no cathodic protection
system is applied.
Protection Potential:
Is the potential of structure to be protected whenever corrosion rate is
insignificant.
Anode Backfill:
Materials with low resistivity surrounding buried anode, may be moisture
retaining materials, used for decrease anode to electrolyte resistance and
prevent anode polarization.
5.Cathodic Protection Design

Terms & Definitions
Drain Point:
Location of negative cable connection to the structure to be protected through
which the cathodic protection current returns to its source.
Coating Break-down Factor:
Is the ration between the current density required to polarize coated surface
and density required to polarize bare surface.
Initial Current Density
Estimated current density required for polarization of structure to be protected
at the start of the lifetime.
Final Current Density:
Estimated current density required to maintain polarization at the end of the
lifetime.

Terms & Definitions
Mean Current Density:
Estimated current density for the entire of the lifetime
Anode Electro-chemical Capacity:
The amount of electricity expressed by (Amper.Hour/kg) that is produced due
to anode consumption.
Cathodic Protection Criteria:
Limits of protection potentials.

CP System Design :
Basic information for design considerations
1. Type of electrolyte (environment)
• Soil
• Fresh/ saline water.
2. Availability of power supply
3. Temperature
4. Type of coating
5. For pipelines:
• Pipeline route
• Crossings (foreign pipeline, roads, rivers, etc.)
• Presence of high transmission power lines
• Presence of foreign metallic structures.

Soil resistivity
Soil represents the electrolyte
Soils with low resistivity have high conductivity; i.e.
corrosive
NACE ranking :
Soil resistivity (ohm.cm) Corrosivity
up to 1,000 Severely corrosive
1,000-5,000 Corrosive
5,000-10,000 Moderately corrosive
10,000-20,000 Slightly corrosive
20,000 and above Non-corrosive

Four-Terminals (Wenner) Method :
For Measurement of Soil Resistivity.
Kit
Power Unit
Stainless Steel Pins
Cables

4-Terminals Arrangement
Ohm’s Low : R = V/I
R : Resistance (ohm)
V : Applied Voltage
I : Recorded Amperage
a a a
Depth = a

Current demand for CP:
Current density : it is the current required to polarize
(1 meter)2 of bare steel in a given electrolyte.
Current density increases with increasing temperature

Temperature : current demand shall be increased by 25% per
every 10º C incremental rise above 30º C. This requirement is
described by the following equation:
i = i0 + [i0 x 0.25 (t - t0)] / 10
Where,
i = current density at operating temperature, Amp/m2
i0 = base current density at standard temperature
t = operating temperature ºC
t0 = standard temperature (30ºC)

Current density determined in mA/m2 is dependant on the
media aggressivity.
Therefore if soil resistivity is low then current density shall be
high
Media Current Density
mA/m2
Aggressive Soil 10
Normal soil 5
Sea water 90
Fresh water 30

Power Supply :
The T/R is fed with AC current from the nearest power
supply.
If there is no power supply available, Solar Units to be
used instead of T/R.

240 Watt Solar Array
0-24 Volt

GB Pipe to be protected
Converter
Regulator
Batteries
Junction Box
Solar Modules
Structure
(-)
(+)
Typical Arrangement for ICCP Using Solar Energy
Sun

Typical Coating Resistances for various coating
qualities
Coating quality Range of specific
leakage resistance
(RC), ohm.m2
Poor 1,000-2,500
Fair 5,000-10,000
good 25,000-50,000
Excellent 100,000-500,000

Typical Coating Breakdown Values
Coating type % breakdown
Initial Mean Final
Thick coating ≤ 1 5 10
Epoxy coal tar ≤ 2 5-10 10-20
Fusion bonded
epoxy
1-2 5-10 5-20
Polypropylene (25
yrs)
0.5 2 5
Polyethylene (25 yrs) 0.5 1 3
CP
current

Recommended potential limits for different coatings
to avoid coating disbondment
Coating type Volt (vs Cu/ CuSO4)
Asphalt Enamel -2
Epoxy coal tar -1.5
Fusion bonded epoxy -1.5
Tape wrap -1.5
Polyethylene -1.0

Pipeline Route
Cross-country P/L’s pass through different types of soils,
i.e. different electrolytes
Presence of high voltage power transmission lines

Pipeline Route

Pipeline AC interference from
electromagnetic field

For protection against stray current
from high tension lines, zinc ribbon
and polarization cells are used

In case of pipe-crossing of cathodically
protected pipelines BONDING is
required by means of :
Solid boning, or
Resistance bonding
Stray current interference

Stray-current corrosion
Pipeline potential shifts in anodic
direction ( more positive values )
Possibility of high anodic current
densities , i.e. high corrosion rates
Pipeline potential shifts in cathodic
direction ( more negative values )
Possibility of coating disbondment
and hydrogen damage

Stray-current corrosion

CP Current Requirement
CD= S x a x CBDC
CD : Current Demand (A)
S : Design Current Density (A/m2)
a : Surface Area (m2)
CBDF : Coating Break-down Factor %
Current Rating : (1.5 times final CD)
Temperature (°C) 50 Initial Average Final
Current Density (mA/m2
) 5 CBDF (%) 0.01 2 3
Design Density (mA/m2
) 7.5 Current Demad (A) 0.0 5.7 8.6
Pipeline Length (km) 30
Pipeline Diameter (inch) 16 Current Rating (A) 13

Anodes Weight & Quantity Requirement
# of Anodes Required
Wt = Weight per anode (kg) Wt = 27.2 kg
CR = Consumption rate (kg/amp-year) CR = 0.34 kg/A-yr
DL = Desired life (years) DL = 20 yrs
Current = Current required (amps) Current = 5.70 A
UF = Utilization factor UF = 0.60
# anodes = 3.00
# of Anodes Required Based on Current Discharge
* from anode manufacturer data
MD = Maximum discharge per anode (amps) MD = 1.50 A
Current = Current required (amps) Current = 5.70 A
# anodes = 4.00
Impressed Current (On-land) Systems

CP Circuit Resistance : (ICCP systems)
R Gbed =Ground-bed resistance (ohms)
R C =Cable resistance (ohms)
R S =Pipeline/structure to earth resistance (ohms) 0.00 ohms
R T =Total circuit resistance (ohms) 0.00 ohms

CP Ground-Bed Resistance :
1) Dwight's Equation for Single Vertical Anode
ρ = Resistivity of backfill material (or earth) in ohm-cm 1,000 ohm-cm
L = Length of backfill (or anode) in meters 2.00 m
d = Diameter of backfill (or anode) in meters 0.30 m
R v = Resistance of one vertical anode to earth in ohms 2.366 ohms

2) Dwight's Equation for Multiple Vertical Anodes in Parallel
ρ = Soil (or Backfill) resistivity in ohm-cm 1,000 ohm-cm
N = Number of anodes in parallel 4 each
S = Anode spacing in meters 3.0 m
R = Resistance of vertical anodes in parallel to earth in ohms 0.8 ohms
CP Ground-Bed Resistance (cont’) :

3) Modified Dwight's Equation for Single (or Multiple) Anodes Installed Horizontally
ρ = Resistivity of Soil or (backfill) material 1,000 ohm-cm
S = Twice depth of anode in meters 3.0 m
RH = Resistance of horizontal anode (or multiple) to earth 0.9 ohms
CP Ground-Bed Resistance (cont’) :

CP Ground-Bed Resistance :
4) Dwight's Equation for Deep-Well Anodes
ρ = Effective Resistivity of earth in ohm-cm 1,000 ohm-cm
R v = Resistance of deep-well anode to earth in ohms 0.867 ohms

Cable Resistance
R CABLE = Resistance per km 0.833 ohms/km
L CABLE = Length in meters (sum of positive and negative cables) 150 m
R C = Cable resistance 0.125 ohms
CP Cables Resistance :

CP Circuit Resistance & Driving Voltage : (ICCP systems)
Driving Voltage = Max. Current x RT
R Gbed =Ground-bed resistance (ohms) 0.90 ohms
R C =Cable resistance (ohms) 0.125 ohms
R S =Pipeline/structure to earth resistance (ohms) 0.00 ohms
R T =Total circuit resistance (ohms) 1.03 ohms
Max. current (A) 13
Driving Voltage (v) 13.3

Transformer/Rectifier (T/R) Rating:
Max. current (A) 13.0
Driving Voltage (v) 13.3
T/R Output Rating:
Select near standard T/R rating:
(e.g. 12V, 24V, 36V, 48V, 5A, 10A, 15A, 20A…etc)
T/R output: 15A/24V DC
T/R Input Characteristics:
Check available electrical power characteristics:
Either 3PH, 400V AC, 50Hz Or 1PH, 230V AC, 50Hz
T/R Input: 3PH, 400V AC, 50Hz

CP Current Attenuation (Spread) Check
(for Pipelines)
En (v) Pipeline Natural Potential -0.55
∆Ea/∆Em = Cosh(αL) Ea (v) Pipeline Protective Potential at Drain Point -1.3
∆Ea (v) Pipeline Potential Shift at Drain Point -0.75
∆Ea = Ea - En Em (v) Pipeline Protective Potential at Distance (L) -0.95
∆Em = Em - En ∆Em (v) Pipeline Potential Shift at Distance (L) -0.4
α (m-1) Attenuation Constant 3.1623E-05
α = √ (Rs/Rlf) Rlf (ohm.m) Linear Coating Insulation Resistivity (final) 15664.8566
Rf (ohm.m2) Coating Insualtion Resistivity (final) 20000
Rlf = Rf/(π * D) Rs (ohm/m) Linear Pipeline Steel Conductivity 1.5665E-05
Rs = ρs/ (π * D * t) ρs (ohm.m) Pipeline Steel Specific Resistivity 0.00000019
D (m) Pipeline Diameter 0.4064
t (m) Pipeline Wall Thickness 0.0095
L (Km) Attenuation Distance 39.26

Typical Coating Resistance (for various coating qualities)
Coating quality Range of specific
leakage resistance
(Rl), ohm.m2
Poor 1,000-2,500
Fair 5,000-10,000
good 25,000-50,000
Excellent 100,000-500,000

CP Current Requirement
CD= S x a x CBDC
S : Design Current Density (A/m2)
a : Surface Area (m2)
CBDF : Coating Break-down Factor %
Temperature (°C) 50 Initial Mean Final
Current Density (mA/m2
) 90 CBDF (%) 0.01 2 3
Design Density (mA/m2
) 135 Current Demad (A) 0.5 103.4 155.1
Pipeline Length (km) 30
Pipeline Diameter (inch) 16
Coating 3PP
Sacrificial Anode Systems

Anode Material & Dimensions Selection
Anode Material Selection

Anodes Weight & Quantity Requirement
Total Mass Required
Icm = Mean Current Demand (A) 103.40 A
tdl = Design Lifetime (Year) 20 yrs
u = Utilization factor 0.80
ε = Design Electrochemical Capacity (A.hr/kg) 2500 A-hr/kg
m = Total Mass of Anodes (kg) 9057.8 kg
# of Anodes Required Based on Total Required Mass
ma = Standard Net Anode Mass (kg) 100.0 kg
n = Anodes Qty # anodes = 91

Sacrificial VS Impressed Current CP
Sacrificial Impressed current
No need for external power source Requires an external power source
Easy to design and install Requires skillful design and
installation
uncontrollable Can be controlled
Used only for limited surface areas
and well coated structures
Can be used for uncoated surfaces
and used for any surfaces
Has no detrimental effects Can cause serious problems if not
handled carefully
Is limited to low resistivity can be used at any resistivity
Low maintenance High maintenance

Sacrificial VS Impressed Current CP

Thank You and Good Luck

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