Post on 19-Jun-2015
description
Delta consultingDelta consulting 11
12-16 November, 2006
Delta consultingDelta consulting 22
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 33
Corrosion Control Techniques5.Cathodic Protection
2- Impressed current system
DC source Ground bed
FeAnode
DC
Drain Point
I
Umbrella
Delta consultingDelta consulting 44
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 55
Corrosion Control Techniques5.Cathodic Protection
Impressed current system
Nothing happens since the nails are in different electrolytes
Delta consultingDelta consulting 66
Corrosion Control Techniques5.Cathodic Protection
Transformer Rectifiers (T/R)
• AC inputVoltage, Single/ three phase, Frequency
• DC maximum output Amp, Volt
• Air Cooled: with sun-shadeOil Cooled: with thermometer
• Location: according to area classification • Explosion proof (hazardous area)• Non-explosion proof (non-hazardous area)
Delta consultingDelta consulting 77
Corrosion Control Techniques5.Cathodic Protection
Transformer Rectifiers
T/R with sun-shade
Delta consultingDelta consulting 88
Corrosion Control Techniques5.Cathodic Protection
Transformer Rectifiers
Explosion-proof Wall-mounted/indoors Pole-mounted
Delta consultingDelta consulting 99
Corrosion Control Techniques5.Cathodic Protection
Transformer Rectifier
Alternating Current Direct Current
Delta consultingDelta consulting 1010
Corrosion Control Techniques5.Cathodic Protection
Mixed Metal Oxide (MMO)
Platinized
Graphite
Common Impressed current anodes:
Si – Fe
Si – Cr – Fe
Consumable AnodesConsumable Anodes Non Consumable AnodesNon Consumable Anodes
Delta consultingDelta consulting 1111
Corrosion Control Techniques5.Cathodic Protection
Common Impressed current anodes:
Si – Fe
Si – Cr – Fe
Delta consultingDelta consulting 1212
Are the most common impressed current anodesAre the most common impressed current anodes
Are used in soil, water or sea waterAre used in soil, water or sea water
Come in two grades; FeSi and FeSiCr for sea water Come in two grades; FeSi and FeSiCr for sea water applicationsapplications
Cable connection to anode shall be handled with great Cable connection to anode shall be handled with great care.care.
Fe Si Anodes
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 1313
Corrosion Control Techniques5.Cathodic Protection
Common Impressed current anodes:
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
Delta consultingDelta consulting 1414
Corrosion Control Techniques5.Cathodic Protection
Common Impressed current anodes:
Mixed Metal Oxide (MMO) Anodes
MMO Coating
Delta consultingDelta consulting 1515
Corrosion Control Techniques5.Cathodic Protection
Common Impressed current anodes:
Graphite Anodes
Delta consultingDelta consulting 1616
Corrosion Control Techniques5.Cathodic Protection
Common Impressed current anodes:
Platinized Anodes
Delta consultingDelta consulting 1717
Impressed current anodes are Impressed current anodes are some timessome times packaged packaged with the with the Carbonaceous backfill.Carbonaceous backfill.
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 1818
Corrosion Control Techniques5.Cathodic Protection
Impressed Current CP Systems
Delta consultingDelta consulting 1919
Corrosion Control Techniques5.Cathodic Protection
Types of ground beds:
• Deep-well GB• Horizontal shallow GB• Distributed Anodes
Delta consultingDelta consulting 2020
Corrosion Control Techniques5.Cathodic Protection
Deep well > 50m depth
Carbonaceous backfill Carbonaceous backfill for anodes sectionfor anodes section
Sand toppingSand topping
Non-metallic vent tube
Delta consultingDelta consulting 2121
Property218-L4518
Resistivity, ohm-inch
0.020.01
Resistivity, ohm-cm
0.05 0.03
Carbon (L.O.I. method)
99.099.9%
Moisture0.10%0.02%
Ash0.35%0.10%
VCM0.30% 0/22%
Sulfur3.75% 4.3%
Bulk Density (lbs/ft3)
46-5062-66
General Sizing + 4 Mesh + 8 Mesh - 8 Mesh
+4M < 10%+8M > 90%-8M < 10%
4M 10%
+20M > 80%-20M 10%
Corrosion Control Techniques5.Cathodic Protection
Carbonaceous backfill
Delta consultingDelta consulting 2222
Deep-well ground beds
Corrosion Control Techniques5.Cathodic Protection
Non-metallic Perforated Casing
Delta consultingDelta consulting 2323
Corrosion Control Techniques5.Cathodic Protection
Shallow Bed
Depth 3 – 5 m
Delta consultingDelta consulting 2424
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 2525
Corrosion Control Techniques5.Cathodic Protection
Distributed Impressed Current Anodes Arrangement
Delta consultingDelta consulting 2626
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 2727
Corrosion Control Techniques5.Cathodic Protection
Anode Connection :
Direct connection to +ve bus bar
An
od
e C
able
s fr
om
GB
Main Cable to +ve Terminal of T/R
Positive Junction Box
Delta consultingDelta consulting 2828
Corrosion Control Techniques5.Cathodic Protection
Anode Connection :
Connection via variable resistance
An
od
e C
able
s fr
om
GB
Main Cable to +ve Terminal of T/R
Positive Junction Box
Delta consultingDelta consulting 2929
Corrosion Control Techniques5.Cathodic Protection
Typical Impressed Current System Arrangement
Gro
un
d B
ed
Delta consultingDelta consulting 3030
Corrosion Control Techniques5.Cathodic Protection
Positive current flux through soil to buriedpipeline and resulting distribution of current density on pipe wall
Delta consultingDelta consulting 3131
Corrosion Control Techniques5.Cathodic Protection
Pipeline attenuation and multiple ground beds
V v
s C
SE
GB1 GB2 GB3
Delta consultingDelta consulting 3232
Corrosion Control Techniques5.Cathodic Protection
Typical Under-Tank Cathodic ProtectionSystem for New Tanks
Delta consultingDelta consulting 3333
Corrosion Control Techniques5.Cathodic Protection
Under tank cathodic protection
MMO anode grid
Delta consultingDelta consulting 3434
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 3535
Corrosion Control Techniques5.Cathodic Protection
Laser Slotted PVC Tubes
Solution Installation of Under-Tank Watering System
Concrete Ring
Slotted PVC Pipes
Compacted
Soil
Delta consultingDelta consulting 3636
Corrosion Control Techniques5.Cathodic Protection
Installation of Under-Tank Watering System
ICCP Anode Grit
Tank
PV
C W
ater
ing
Pip
e
To T/R
Compacted Soil
Delta consultingDelta consulting 3737
Corrosion Control Techniques5.Cathodic Protection
Peripheral Anode Cathodic Protection System for Existing Tanks
Horizontal GBMMO strip anode
Existing Tank
Protecting outermost bottom
Delta consultingDelta consulting 3838
Corrosion Control Techniques5.Cathodic Protection
Distributed Anode Cathodic Protection
System
Delta consultingDelta consulting 3939
Corrosion Control Techniques5.Cathodic Protection
Cathodic protectioninstallation for a well
casing
Delta consultingDelta consulting 4040
Corrosion Control Techniques5.Cathodic Protection
Hanging ICCP anode
Impressed Current Cathodic Protection for Tank Internals
Delta consultingDelta consulting 4141
Corrosion Control Techniques5.Cathodic Protection
Impressed Current Cathodic Protection for Tank Internals
ICCP anodePVC Support
Anode Cable extended to outside along vent tube
Delta consultingDelta consulting 4242
Corrosion Control Techniques5.Cathodic Protection
ICCP for jackets
1- Hanging Anodes
Delta consultingDelta consulting 4343
Corrosion Control Techniques5.Cathodic Protection
ICCP for jackets
2- Sub-sea Sleds
Delta consultingDelta consulting 4444
Corrosion Control Techniques5.Cathodic Protection
Pourbaix diagram showing the theoretical conditions for corrosion, passivation, and immunity of iron in water and dilute aqueous solutions
Cathodic Protection Criteria
7 14P
ote
nti
al
2.01.6
0.81.2
-0.4
0.40.0
-1.6
-0.8-1.2
0
Immunity
Fe3+
Passivity
Corrosion
pH
Fe2+
4545
Delta consultingDelta consulting 4646
Corrosion Control Techniques5.Cathodic Protection
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
DescriptionPotential vs Cu/CuSO4
mV
-500
Free Corrosion-700
Zone of Cathodic ProtectionZone of Cathodic Protection-900
Intense Corrosion-600
Sever Over-Protection
Problems
Sever Over-Protection
Problems-1200
Increased Over-Protection-1100
Some Over-Protection-1000
Some Protection-800
Delta consultingDelta consulting 4747
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 4848
Corrosion Control Techniques5.Cathodic Protection
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/ AlloyPotential criterion (mV)
vs Cu/ Cu SO4
Iron, steel, stainless steel :
Aerobic conditions
Anaerobic conditions
-850
-950
Lead -600
Copper-500
Aluminum -950 )2(
Delta consultingDelta consulting 4949
Corrosion Control Techniques5.Cathodic Protection
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”.
Delta consultingDelta consulting 5050
Corrosion Control Techniques5.Cathodic Protection
“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
Delta consultingDelta consulting 5151
Corrosion Control Techniques5.Cathodic Protection
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
5252
Delta consultingDelta consulting 5353
Corrosion Control Techniques5.Cathodic Protection
Copper / Copper Sulfate reference electrode
Portable Type
Delta consultingDelta consulting 5454
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 5555
Corrosion Control Techniques5.Cathodic Protection
H2O (
SO42-
SO42-
Soil)
Copper RodCuSO4 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 SO42- IONS
CONTENT
Pipe
Cu
Cu2+
Delta consultingDelta consulting 5656
Corrosion Control Techniques5.Cathodic Protection
Typical Arrangement for Pipe – to – Soil Measurement
Icp umbrella
Icp umbrella
CSE
Delta consultingDelta consulting 5757
Corrosion Control Techniques5.Cathodic Protection
Voltmeter
IR error
Ep
CP current
CSE @ soil surface
Coating
Eon Reading
Eon = Ep + IR Error
Voltmeter
Delta consultingDelta consulting 5858
Corrosion Control Techniques5.Cathodic Protection
Voltmeter
Ep
CSE @ soil surface
Coating
Eoff Reading , instantaneous
Eoff = Ep
Voltmeter
Delta consultingDelta consulting 5959
Corrosion Control Techniques5.Cathodic Protection
Permanent Copper / Copper Sulfate reference electrode
Prepackaged CSEBackfill :Gypsum +Bentonite clay +Sodium sulfate
Delta consultingDelta consulting 6060
Corrosion Control Techniques5.Cathodic Protection
Test Posts for CP Monitoring
Flush – to – ground
Delta consultingDelta consulting 6161
Corrosion Control Techniques4.Cathodic Protection
Electrode Placement
For pipelines : on-the-line @ every 1- 2 Km destination For tanks : preferred under tank or closest
Delta consultingDelta consulting 6262
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 6363
Corrosion Control Techniques5.Cathodic Protection
Structure-to-Soil potential measurement using Voltmeter.
Delta consultingDelta consulting 6464
Corrosion Control Techniques5.Cathodic Protection
Permanently Installed Reference Electrode & Test Post
Delta consultingDelta consulting 6565
Corrosion Control Techniques5.Cathodic Protection
Permanent Monitoring forUnder Tank Cathodic
Protection
Tank Diameter (m)No. of Electrodes Required
5-101
10-232
23-363
45 and above4
Delta consultingDelta consulting 6666
Corrosion Control Techniques5.Cathodic Protection
Reference Electrodes Locations for Under - Tank CP Systems
1/4D1/6D
2/6D2/8D
3/8D
1/8D
D=45m and above D=23-36m D=10.5-22.5m D=5-10m
Key : Reference Electrode
Delta consultingDelta consulting 6767
Corrosion Control Techniques5.Cathodic Protection
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
Co
ncr
ete
Rin
g
CSE
Delta consultingDelta consulting 6868
Corrosion Control Techniques5.Cathodic Protection
CSEPerforated PVC Pipe Filled with Water
Tank
Perforated PVC Pipe Installed for Reference Electrode Placement
AVO
Delta consultingDelta consulting 6969
Corrosion Control Techniques5.Cathodic Protection
Correct method for measuring structure potentials when surface is covered with concrete or asphalt.
AVOCSE in Wet Soil
Buried Pipe
Concrete / Asphalt
Delta consultingDelta consulting 7070
Corrosion Control Techniques5.Cathodic Protection
For monitoring tank’s internal CP system use:
Hanging RE ( from roof )
Plug RE ( fixed on shell )
RE
RE
Hanging Reference Electrodes
Plug RE
Delta consultingDelta consulting 7171
Corrosion Control Techniques5.Cathodic Protection
Diver with portable reference electrode
Potential Measurement of jackets / platform legs
Delta consultingDelta consulting 7272
Corrosion Control Techniques5.Cathodic Protection
Transponder CP monitoring
Potential Measurement of jackets / platform legs
Delta consultingDelta consulting 7373
Corrosion Control Techniques5.Cathodic Protection
Potential plot after data analysis
Delta consultingDelta consulting 7474
Corrosion Control Techniques5.Cathodic Protection
Potential Measurement of subsea pipelines
Trailing-wire potential survey
Delta consultingDelta consulting 7575
Corrosion Control Techniques5.Cathodic Protection
TP-3TP-1 TP-2
wellTP
TP-3 TP-4
- 850 mV Min. protection levelUn protected
area
Pip
e to
soi
l pot
entia
l-
mV
What about the potential at any point ?
Buried pipeline ( 1.2 meter deep)
Well casing8000 feet deep
The criterion most widely used on pipelines is based on measurementsof 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
Delta consultingDelta consulting 7676
Corrosion Control Techniques5.Cathodic Protection
Potential Measurement of well casing
Up hole
Upper Centralizer
Upper Contactors
Spacer Bare
Lower Contactors
Lower Centralizer
Sinker Weight
Leng
th b
etw
een
c ont
acto
rs5
to 7
met
ers
V
Casing
Tool inside Casing
CASING POTENTIAL PROFILE TOOLSPECIFICATIONS
8.5 m using 5.0 contactor spacing10 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)
CasingSize
4.5 in (11.4 cm) to 13.3/8 in (34 cm)
Hoistingspeed
80 ft/min (24.38 m/minRecommended
Loggingreading
Stationary readings; average speed 25ft/min (7.6 m/min) at 50 ft intervals
Loggingenvirnment
Must be dray
LimitationsNot recommended for use in fresh
water
Typical Casing Potential Profile Tool (Courtesy of Atlas Industries, Inc.)
Delta consultingDelta consulting 7777
Corrosion Control Techniques5.Cathodic Protection
Potential Measurement of well casing
+ -T RvOUTPUT CURRENT
= ( I )
( I )
( i1 )
( i 2 )
( i3 )
( I-i1 )
( I-i1-i2 )
( I-i1-i2 -i3)
U1
U2
U3
Casing to soilpotential= (v)
Cu/Cu So4 cell v
U1
U2
U3
-700 -850 -900 -1000
Dep
th in
feet -8
50 m
v m
i n. p
rot e
ctio
n le
vel
R
R
R Ohm’s Low: V = I x R U = Voltage drop = I x R pipe
Delta consultingDelta consulting 7878
Cable – to - cable connection
Cable – to - pipe connection
Cable – to - structure connection
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
Delta consultingDelta consulting 7979
Splice Kit : for cable-to-cable connection
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
1 2
Araldite is poured & let to dry
Delta consultingDelta consulting 8080
For cable-to-pipe connection :
1- Thermite ( Cad / Exothermic ) Welding
2- Pin Brazing
3- Mechanical connection ( for gas pipelines )
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
Delta consultingDelta consulting 8181
For cable-to-pipe connection
1- Thermite Welding :
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
Crucible
DisksCartridge
Spark Flint
Delta consultingDelta consulting 8282
Corrosion Control Techniques5.Cathodic Protection
Thermite WeldmentPrior to welding :
The coating must be removed at welding point ( 5x5 cm square )
Metal surface to be polished and cleaned
Thermite Welding
Delta consultingDelta consulting 8383
Corrosion Control Techniques5.Cathodic Protection
Self-adhesive Handy-cap
1 2 3
Protecting the Thermite Weldment
Delta consultingDelta consulting 8484
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
For cable-to-pipe connection
2- Pin Brazing : emits less heat output
Pin Brazing Unit
Pistol / Gun
Pins & Ferrules
Lug
Grinder
Delta consultingDelta consulting 8585
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
For cable-to-pipe connection
2- Pin Brazing
Delta consultingDelta consulting 8686
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
For cable-to-pipe connection
2- Pin Brazing
1 Clean the surface2 Load gun with
pin & ferrule3 pin braze
4 Test connection
Delta consultingDelta consulting 8787
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
For cable-to-pipe connection
3- Mechanical Connection : recommended for drain point connection of gas pipelines
Delta consultingDelta consulting 8888
Corrosion Control Techniques5.Cathodic Protection
Cable Connections
Terminal Lugs :
for cable-to-structure ( tank ) connection
Delta consultingDelta consulting 8989
Electrical isolation is made by :
Isolating flange kit ( IFK )
IFK is installed @ Aboveground / Underground Interface
Corrosion Control Techniques4.Cathodic Protection
Electrical Isolation Isolation
Structures to be protected shall be electrically isolated from portions which do not require protection.
Delta consultingDelta consulting 9090
Isolating flange kit ( IFK )
Corrosion Control Techniques4.Cathodic Protection
Electrical Isolation Isolation
Delta consultingDelta consulting 9191
Corrosion Control Techniques4.Cathodic Protection
Isolating flange kits
In hazardous areas , IFK’s are
protected by means of Spark Gaps
Spark Gap FittedSpark Gap Fitted
Delta consultingDelta consulting 9292
Monolithic Blocks
Corrosion Control Techniques4.Cathodic Protection
Electrical Isolation
Delta consultingDelta consulting 9393
Monolithic Blocks
+ Polarization Cell
Corrosion Control Techniques4.Cathodic Protection
The monolithic blocks are protected against electrostatic charges and lightening by charges and lightening by polarization cell polarization cell
Delta consultingDelta consulting 9494
Casings for Road Crossings
Corrosion Control Techniques4.Cathodic Protection
Delta consultingDelta consulting 9595
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
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 9696
Corrosion Control Techniques4.Cathodic Protection
Clamp MeterClamp Meter
Clamp Meters are used to check:
electric cables integrity
current output of each anode
Clamp Meter
Delta consultingDelta consulting 9797
Corrosion Control Techniques5.Cathodic Protection
Pipeline & Cable Warning Markers
Delta consultingDelta consulting 9898
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 9999
Corrosion Control Techniques5.Cathodic Protection
There are numerous codes and references that shall beThere are numerous codes and references that shall bereferred to when dealing with cathodic protection among referred to when dealing with cathodic protection among these are:these are:
NACE RP 0169NACE RP 0169NACE RP 0176NACE RP 0176NACE RP 177NACE RP 177NACE RP 575NACE RP 575
ISO 15589-1, PART I – 2003, “On-land Pipelines”ISO 15589-1, PART I – 2003, “On-land Pipelines” ISO 15589-2, PART II – 2004, “Offshore Pipelines”ISO 15589-2, PART II – 2004, “Offshore Pipelines”
DnV RP B 401DnV RP B 401API 651API 651J. Morgan, “Cathodic Protection”J. Morgan, “Cathodic Protection”A.W. Peabody, “Control of Pipeline Corrosion”A.W. Peabody, “Control of Pipeline Corrosion”
Delta consultingDelta consulting 100100
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.
Corrosion Control Techniques5.Cathodic Protection Design
Delta consultingDelta consulting 101101
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 DensityEstimated 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.
Corrosion Control Techniques5.Cathodic Protection Design
Delta consultingDelta consulting 102102
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.
Corrosion Control Techniques5.Cathodic Protection Design
Delta consultingDelta consulting 103103
Corrosion Control Techniques5.Cathodic Protection
CP System Design :
Basic information for design considerations1. Type of electrolyte (environment)
• Soil• Fresh/ saline water.
2. Availability of power supply3. Temperature 4. Type of coating5. For pipelines:
• Pipeline route• Crossings (foreign pipeline, roads, rivers, etc.)• Presence of high transmission power lines• Presence of foreign metallic structures.
Delta consultingDelta consulting 104104
Corrosion Control Techniques5.Cathodic Protection
Soil resistivity
Soil represents the electrolyteSoils with low resistivity have high conductivity; i.e.
corrosive
NACE ranking :
Soil resistivity (ohm.cm)Corrosivityup to 1,000Severely corrosive
1,000-5,000Corrosive
5,000-10,000Moderately corrosive
10,000-20,000Slightly corrosive
20,000 and aboveNon-corrosive
Delta consultingDelta consulting 105105
Corrosion Control Techniques5.Cathodic Protection
Four-Terminals (Wenner) Method :For Measurement of Soil Resistivity.
Kit
Power Unit
Stainless Steel Pins
Cables
Delta consultingDelta consulting 106106
Corrosion Control Techniques5.Cathodic Protection
4-Terminals Arrangement
Ohm’s Low : R = V/I
R : Resistance (ohm)V : Applied Voltage I : Recorded Amperage
a a a
Depth = a
Delta consultingDelta consulting 107107
Current demand for CP:
Current density : it is the current required to polarize (1 meter)2 of bare steel in a given electrolyte.
Corrosion Control Techniques5.Cathodic Protection Design
Current density increases with increasing temperature
Delta consultingDelta consulting 108108
Corrosion Control Techniques5.Cathodic Protection Design
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)
Delta consultingDelta consulting 109109
Corrosion Control Techniques5.Cathodic Protection
Current density determined in mA/m2 is dependant on the
media aggressivity.
Therefore if soil resistivity is low then current density shall be
high
MediaCurrent Density
mA/m2
Aggressive Soil10
Normal soil5
Sea water90
Fresh water30
Delta consultingDelta consulting 110110
Corrosion Control Techniques5.Cathodic Protection
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.
Delta consultingDelta consulting 111111
Corrosion Control Techniques5.Cathodic Protection
240 Watt Solar Array0-24 Volt
Delta consultingDelta consulting 112112
Corrosion Control Techniques5.Cathodic Protection
GB Pipe to be protected
Converter
Regulator
Batteries
Junction Box
Solar ModulesStructure(-)(+)
Typical Arrangement for ICCP Using Solar Energy
Sun
Delta consultingDelta consulting 113113
Corrosion Control Techniques5.Cathodic Protection
Typical Coating Resistances for various coating qualities
Coating qualityRange of specific leakage resistance
(RC), ohm.m2
Poor1,000-2,500
Fair5,000-10,000
good25,000-50,000
Excellent 100,000-500,000
Delta consultingDelta consulting 114114
Corrosion Control Techniques5.Cathodic Protection
Typical Coating Breakdown ValuesTypical Coating Breakdown Values
Coating type %breakdown
Initial Mean Final
Thick coating ≤ 1510
Epoxy coal tar≤ 25-1010-20
Fusion bonded epoxy
1-25-105-20
Polypropylene (25 yrs)
0.525
Polyethylene (25 yrs)0.513
CP
curren
t
Delta consultingDelta consulting 115115
Corrosion Control Techniques5.Cathodic Protection
Recommended potential limits for different coatingsto avoid coating disbondment
Coating typeVolt (vs Cu/ CuSO4)
Asphalt Enamel-2
Epoxy coal tar-1.5
Fusion bonded epoxy-1.5
Tape wrap-1.5
Polyethylene -1.0
Delta consultingDelta consulting 116116
Corrosion Control Techniques5.Cathodic Protection
Pipeline Route
Cross-country P/L’s pass through different types of soils, i.e. different electrolytes
Presence of high voltage power transmission lines
Delta consultingDelta consulting 117117
Corrosion Control Techniques5.Cathodic Protection
Pipeline Route
Delta consultingDelta consulting 118118
Corrosion Control Techniques5.Cathodic Protection
Pipeline AC interference from electromagnetic field
Delta consultingDelta consulting 119119
For protection against stray current
from high tension lines, zinc ribbon
and polarization cells are used
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 120120
In case of pipe-crossing of cathodically protected pipelines BONDING is required by means of :
Solid boning, or
Resistance bonding
Corrosion Control Techniques5.Cathodic Protection
Stray current interference
Delta consultingDelta consulting 121121
Stray-current corrosion
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 122122
Corrosion Control Techniques5.Cathodic Protection
Stray-current corrosion
Delta consultingDelta consulting 123123
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 124124
CP Current Requirement
CD= S CD= S xx a a xx CBDC CBDC
Corrosion Control Techniques5.Cathodic Protection
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) 30Pipeline Diameter (inch) 16 Current Rating (A) 13
Delta consultingDelta consulting 125125
Anodes Weight & Quantity Requirement
Corrosion Control Techniques5.Cathodic Protection
# of Anodes Required
Wt = Weight per anode (kg) Wt = 27.2 kgCR = Consumption rate (kg/amp-year) CR = 0.34 kg/A-yrDL = Desired life (years) DL = 20 yrs
Current = Current required (amps) Current = 5.70 AUF = Utilization factor UF = 0.60
# anodes = 3.00
# of Anodes Required Based on Current Discharge
* from anode manufacturer dataMD = 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
Delta consultingDelta consulting 126126
CP Circuit Resistance : (ICCP systems)
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 127127
CP Ground-Bed Resistance :
Corrosion Control Techniques5.Cathodic Protection
1) Dwight's Equation for Single Vertical Anode
ρ = Resistivity of backfill material (or earth) in ohm-cm 1,000 ohm-cmL = Length of backfill (or anode) in meters 2.00 md = Diameter of backfill (or anode) in meters 0.30 m
R v = Resistance of one vertical anode to earth in ohms 2.366 ohms
Delta consultingDelta consulting 128128
Corrosion Control Techniques5.Cathodic Protection
2) Dwight's Equation for Multiple Vertical Anodes in Parallel
ρ = Soil (or Backfill) resistivity in ohm-cm 1,000 ohm-cmN = Number of anodes in parallel 4 eachL = Length of backfill (or anode) in meters 2.0 md = Diameter of backfill (or anode) in meters 0.3 mS = Anode spacing in meters 3.0 mR = Resistance of vertical anodes in parallel to earth in ohms 0.8 ohms
CP Ground-Bed Resistance (cont’) :
Delta consultingDelta consulting 129129
Corrosion Control Techniques5.Cathodic Protection
3) Modified Dwight's Equation for Single (or Multiple) Anodes Installed Horizontally
ρ = Resistivity of Soil or (backfill) material 1,000 ohm-cmL = Length of backfill (or anode) in meters 8.00 m
S = Twice depth of anode in meters 3.0 md = Diameter of backfill (or anode) in meters 0.3 m
RH = Resistance of horizontal anode (or multiple) to earth 0.9 ohms
CP Ground-Bed Resistance (cont’) :
Delta consultingDelta consulting 130130
CP Ground-Bed Resistance :
Corrosion Control Techniques5.Cathodic Protection
4) Dwight's Equation for Deep-Well Anodes
ρ = Effective Resistivity of earth in ohm-cm 1,000 ohm-cmL = Length of backfill (or anode) in meters 8.00 md = Diameter of backfill (or anode) in meters 0.30 m
R v = Resistance of deep-well anode to earth in ohms 0.867 ohms
Delta consultingDelta consulting 131131
Corrosion Control Techniques5.Cathodic Protection
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 :
Delta consultingDelta consulting 132132
CP Circuit Resistance & Driving Voltage : (ICCP systems)
Corrosion Control Techniques5.Cathodic Protection
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) 13Driving Voltage (v) 13.3
Delta consultingDelta consulting 133133
Transformer/Rectifier (T/R) Rating:
Corrosion Control Techniques5.Cathodic Protection
Max. current (A) 13.0Driving 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
Delta consultingDelta consulting 134134
CP Current Attenuation (Spread) Check
(for Pipelines)
Corrosion Control Techniques5.Cathodic Protection
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
Delta consultingDelta consulting 135135
Corrosion Control Techniques5.Cathodic Protection
Typical Coating Resistance (for various coating qualities)
Coating qualityRange of specific leakage resistance
(Rl), ohm.m2
Poor1,000-2,500
Fair5,000-10,000
good25,000-50,000
Excellent 100,000-500,000
Delta consultingDelta consulting 136136
CP Current Requirement
CD= S CD= S xx a a xx CBDC CBDC
Corrosion Control Techniques5.Cathodic Protection
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) 30Pipeline Diameter (inch) 16
Coating 3PP
Sacrificial Anode SystemsSacrificial Anode Systems
Delta consultingDelta consulting 137137
Anode Material & Dimensions Selection
Anode Material Selection
Corrosion Control Techniques5.Cathodic Protection
Delta consultingDelta consulting 138138
Anodes Weight & Quantity Requirement
Corrosion Control Techniques5.Cathodic Protection
Total Mass Required
Icm = Mean Current Demand (A) 103.40 Atdl = Design Lifetime (Year) 20 yrsu = Utilization factor 0.80ε = 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
m a = Standard Net Anode Mass (kg) 100.0 kg
n = Anodes Qty # anodes = 91
Delta consultingDelta consulting 139139
Sacrificial Sacrificial VSVS Impressed Current CP Impressed Current CP
Sacrificial Impressed current
No need for external power sourceRequires an external power source
Easy to design and installRequires skillful design and installation
uncontrollableCan 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 effectsCan cause serious problems if not handled carefully
Is limited to low resistivitycan be used at any resistivity
Low maintenanceHigh maintenance
Corrosion Control Techniques4.Cathodic Protection
Delta consultingDelta consulting 140140
Corrosion Control Techniques5.Cathodic Protection
Sacrificial VS Impressed Current CP
141141
142142
143143
Delta consultingDelta consulting 144144
Thank You and Good Luck