2....impressed current -cathodic protection

Delta consultingDelta consulting 11

12-16 November, 2006


Corrosion Control Techniques5.Cathodic Protection



2- Impressed current system

DC source Ground bed

FeAnode

DC

Drain Point

I

Umbrella



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



Impressed current system

Nothing happens since the nails are in different electrolytes



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)



Transformer Rectifiers

T/R with sun-shade



Transformer Rectifiers

Explosion-proof Wall-mounted/indoors Pole-mounted



Transformer Rectifier

Alternating Current Direct Current



Mixed Metal Oxide (MMO)

Platinized

Graphite

Common Impressed current anodes:

Si – Fe

Si – Cr – Fe

Consumable AnodesConsumable Anodes Non Consumable AnodesNon Consumable Anodes




Si – Fe

Si – Cr – Fe


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





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




Mixed Metal Oxide (MMO) Anodes

MMO Coating




Graphite Anodes




Platinized Anodes


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




Impressed Current CP Systems



Types of ground beds:

• Deep-well GB• Horizontal shallow GB• Distributed Anodes



Deep well > 50m depth

Carbonaceous backfill Carbonaceous backfill for anodes sectionfor anodes section

Sand toppingSand topping

Non-metallic vent tube


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%


Carbonaceous backfill


Deep-well ground beds


Non-metallic Perforated Casing



Shallow Bed

Depth 3 – 5 m



Distributed Impressed Current Anodes Arrangement



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



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



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



Typical Impressed Current System Arrangement

Gro

un

d B

ed



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



Pipeline attenuation and multiple ground beds

V v

s C

SE

GB1 GB2 GB3



Typical Under-Tank Cathodic ProtectionSystem for New Tanks



Under tank cathodic protection

MMO anode grid



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



Laser Slotted PVC Tubes

Solution Installation of Under-Tank Watering System

Concrete Ring

Slotted PVC Pipes

Compacted

Soil



Installation of Under-Tank Watering System

ICCP Anode Grit

Tank

PV

C W

ater

ing

Pip

e

To T/R

Compacted Soil



Peripheral Anode Cathodic Protection System for Existing Tanks

Horizontal GBMMO strip anode

Existing Tank

Protecting outermost bottom



Distributed Anode Cathodic Protection

System



Cathodic protectioninstallation for a well

casing



Hanging ICCP anode

Impressed Current Cathodic Protection for Tank Internals



Impressed Current Cathodic Protection for Tank Internals

ICCP anodePVC Support

Anode Cable extended to outside along vent tube



ICCP for jackets

1- Hanging Anodes



ICCP for jackets

2- Sub-sea Sleds



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+



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



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



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(



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”.



“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



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



Copper / Copper Sulfate reference electrode

Portable Type



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



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+



Typical Arrangement for Pipe – to – Soil Measurement

Icp umbrella

Icp umbrella

CSE



Voltmeter

IR error

Ep

CP current

CSE @ soil surface

Coating

Eon Reading

Eon = Ep + IR Error

Voltmeter



Voltmeter

Ep

CSE @ soil surface

Coating

Eoff Reading , instantaneous

Eoff = Ep

Voltmeter



Permanent Copper / Copper Sulfate reference electrode

Prepackaged CSEBackfill :Gypsum +Bentonite clay +Sodium sulfate



Test Posts for CP Monitoring

Flush – to – ground



Electrode Placement

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



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



Structure-to-Soil potential measurement using Voltmeter.



Permanently Installed Reference Electrode & Test Post



Permanent Monitoring forUnder Tank Cathodic

Protection

Tank Diameter (m)No. of Electrodes Required

5-101

10-232

23-363

45 and above4



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



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



CSEPerforated PVC Pipe Filled with Water

Tank

Perforated PVC Pipe Installed for Reference Electrode Placement

AVO



Correct method for measuring structure potentials when surface is covered with concrete or asphalt.

AVOCSE in Wet Soil

Buried Pipe

Concrete / Asphalt



For monitoring tank’s internal CP system use:

Hanging RE ( from roof )

Plug RE ( fixed on shell )

RE

RE

Hanging Reference Electrodes

Plug RE



Diver with portable reference electrode

Potential Measurement of jackets / platform legs



Transponder CP monitoring

Potential Measurement of jackets / platform legs



Potential plot after data analysis



Potential Measurement of subsea pipelines

Trailing-wire potential survey



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




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.)




+ -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


Cable – to - cable connection

Cable – to - pipe connection

Cable – to - structure connection


Cable Connections


Splice Kit : for cable-to-cable connection


Cable Connections

1 2

Araldite is poured & let to dry


For cable-to-pipe connection :

1- Thermite ( Cad / Exothermic ) Welding

2- Pin Brazing

3- Mechanical connection ( for gas pipelines )


Cable Connections


For cable-to-pipe connection

1- Thermite Welding :


Cable Connections

Crucible

DisksCartridge

Spark Flint



Thermite WeldmentPrior to welding :

The coating must be removed at welding point ( 5x5 cm square )

Metal surface to be polished and cleaned

Thermite Welding



Self-adhesive Handy-cap

1 2 3

Protecting the Thermite Weldment



Cable Connections


2- Pin Brazing : emits less heat output

Pin Brazing Unit

Pistol / Gun

Pins & Ferrules

Lug

Grinder



Cable Connections


2- Pin Brazing



Cable Connections


2- Pin Brazing

1 Clean the surface2 Load gun with

pin & ferrule3 pin braze

4 Test connection



Cable Connections


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



Cable Connections

Terminal Lugs :

for cable-to-structure ( tank ) connection


Electrical isolation is made by :

Isolating flange kit ( IFK )

IFK is installed @ Aboveground / Underground Interface


Electrical Isolation Isolation

Structures to be protected shall be electrically isolated from portions which do not require protection.


Isolating flange kit ( IFK )


Electrical Isolation Isolation



Isolating flange kits

In hazardous areas , IFK’s are

protected by means of Spark Gaps

Spark Gap FittedSpark Gap Fitted


Monolithic Blocks


Electrical Isolation


Monolithic Blocks

+ Polarization Cell


The monolithic blocks are protected against electrostatic charges and lightening by charges and lightening by polarization cell polarization cell


Casings for Road Crossings



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




Clamp MeterClamp Meter

Clamp Meters are used to check:

electric cables integrity

current output of each anode

Clamp Meter



Pipeline & Cable Warning Markers



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”


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


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.



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 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.



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



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

MediaCurrent Density

mA/m2

Aggressive Soil10

Normal soil5

Sea water90

Fresh water30



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 Array0-24 Volt



GB Pipe to be protected

Converter

Regulator

Batteries

Junction Box

Solar ModulesStructure(-)(+)

Typical Arrangement for ICCP Using Solar Energy

Sun



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



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



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



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 CD= S xx a a xx CBDC 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) 30Pipeline Diameter (inch) 16 Current Rating (A) 13


Anodes Weight & Quantity Requirement


# 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


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-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



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’) :



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’) :


CP Ground-Bed Resistance :


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



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) 13Driving Voltage (v) 13.3


Transformer/Rectifier (T/R) Rating:


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


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 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


CP Current Requirement

CD= S CD= S xx a a xx CBDC 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) 30Pipeline Diameter (inch) 16

Coating 3PP

Sacrificial Anode SystemsSacrificial Anode Systems


Anode Material & Dimensions Selection

Anode Material Selection



Anodes Weight & Quantity Requirement


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


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




Sacrificial VS Impressed Current CP

141141

142142

143143


Thank You and Good Luck

2....impressed current -cathodic protection

Engineering

Transcript of 2....impressed current -cathodic protection