COLVIN MANN, P.E., NACE 38623 ALABAMA ......The steel, whether rebar, wire or cylinder, embedded in...

COLVIN MANN, P.E. , NACE 3862 3

ALABAMA/MISSISSIPPI SECTION

AMERICAN WATER WORKS ASSOCIATION

M A Y , 2 0 1 6

External Corrosion Control

Iron Pipe Manufacturing

Melting Furnace (Cupola) ENERGY GAINED

Raw Materials

TransferLadle

CastingMachine

External Corrosion Control

Steel Pipe Manufacturing

Electric Arc FurnaceENERGY GAINED

Raw Materials

TransferLadle

Hot Rolling Machine

External Corrosion Control

Prestressed Concrete Cylinder Pipe

External Corrosion Control

Prestressed Concrete Cylinder PipeLined Cylinder Pipe

External Corrosion Control

Prestressed Concrete Cylinder PipeEmbedded Cylinder Pipe

External Corrosion Control

Ductile Iron Pipe

External Corrosion Control

Ductile Iron Joints

External Corrosion Control

Push-on Joint Mechanical Joint

Corrosion Mechanisms Oxygen Concentration (Iron and PCCP)

High Oxygen to Low Oxygen

Sulfate Reducing Anaerobic Bacteria (Iron and PCCP) Produces Sulfides – H SO – highly corrosive

Dissimilar Metals (Iron and PCCP) Galvanic Cell

Stray Current (Iron and PCCP)

Chlorides (PCCP)

Moisture Variations(Iron and PCCP) Fluctuating Water Table

External Corrosion Control

Corrosion Mechanisms High Sulfates (Iron and PCCP)

Sulfate Reducing Bacteria

Soil Chemistry(Iron and PCCP) Low Resistivity

Low PH

Alternating Current (Iron and PCCP) Hard To Mitigate

External Corrosion Control

Stray Current Interference

External Corrosion Control

Stray Current Interference

External Corrosion Control

External Corrosion Control

External Corrosion Control

External Corrosion Control

External Corrosion Control

Galvanic Series

Referenced to Copper-Copper Sulfate

Metal Volts

Magnesium -1.60 to -1.75

Zinc -1.10

Aluminum -1.05

Carbon Steel -0.50 to -0.80

Cast/Ductile Iron -0.50

Lead -0.50

Copper -0.20

Carbon, Graphite +0.30

Corrosion Cell Elements

All Corrosion Cells Have The Following:

ANODE

CATHODE

ELECTRONIC PATH

ELECTROLYTE

External Corrosion Control

Current

Electron

Fe++

Fe+++

e-

e-

e-

e-

e-

H+

H+

H+

H+

OH-

OH-

OH-

OH-

AnodeCathode

Electrolyte

Return current path

Galvanic Corrosion Cell

The Underground Pipe Corrosion Cell

AnodeCathode

Electrolyte

Return Current Path

Resistivity

Redox

pH

Sulfides

Moisture

Chlorides

Soil Evaluation Parameters

External Corrosion Control

10-Point Soil EvaluationResistivity - ohm-cm (based on water-saturated soil box):

< 1,500 1,500 - 1,800> 1,800 - 2,100> 2,100 - 2,500> 2,500 - 3,000> 3,000

pH:0 - 22 - 44 - 6.56.5 - 7.57.5 - 8.5> 8.5

Redox potential:> +100 mV+50 to +100 mV0 to +50 mVNegative

Sulfides:PositiveTraceNegative

Moisture:Poor drainage, continuously wetFair drainage, generally moistGood drainage, generally dry

1085210

5300*03

03.5

45

3.520

210

*3 points should be added

if low or negative redox

and sulfides are present

External Corrosion Control

ph = 3.94; resistivity = 230 ohm-cm;sulfates = 5440 ppm

External Corrosion Control

The steel, whether rebar, wire or cylinder, embedded inPortland cement concrete, forms a passive film due to the phof the cement, around 12. This film slows corrosion to a verysmall rate. The intrusion of the water soluble chloride ionfound in some ground water attacks the film and exposes thesteel to a galvanic corrosion condition. As corrosion builds, itoccupies more space than the original steel and eventuallyresults in spalling and delamination of the mortar. With thisincreased exposure, corrosion can increase to failure.

Chlorides

External Corrosion Control

Prestress

External Corrosion Control

Bar Wrap

External Corrosion Control

Polyethylene Encasement

Coatings

Sacrificial Cathodic Protection

Impressed Current Cathodic Protection

Protection

External Corrosion Control

Polyethylene Encasement

External Corrosion Control

Polyethylene Encasement

External Corrosion Control

Polyethylene Encasement

External Corrosion Control

Fusion Bonded Epoxy

External Corrosion Control

80 Mil Tape Wrap

External Corrosion Control

Cathodic Protection Principle

External Corrosion Control

Cathodic Protection Sacrificial Anode

AnodeProtectedPipe Mg

or

Zn

Maximum Driving Potential: - Mg ( -1.7 V )

Steel ( - 0.6 V )

1.1 V

External Corrosion Control

Galvanic Anode

External Corrosion Control

Magnesium Anode

External Corrosion Control

Galvanic Anodes at Every Other Joint

External Corrosion Control

Distributed Galvanic Sacrificial System

External Corrosion Control

Grouped Sacrificial Galvanic System

External Corrosion Control

Ribbon Type Galvanic Anode

External Corrosion Control

Galvanic Anode Installation

External Corrosion Control

Galvanic Anodes In Repair Conditions

External Corrosion Control

Impressed Current System Rectifier

External Corrosion Control

Impressed Current System Rectifier

External Corrosion Control

Impressed Current System Rectifier

External Corrosion Control

Impressed Current Anodes

External Corrosion Control

Impressed Current Deep Anode Installation

External Corrosion Control

Impressed Current Deep Anode Installation

External Corrosion Control

Impressed Current System

External Corrosion Control

Caution is required with CP potentials over 1100 mv withPCCP as the hydrogen production at the cathode can result inatomic hydrogen which permeates the high strength, highstress wire causing hydrogen embrittlement. The result canbe loss of ductility and tensile strength and ultimately, failure.

Impressed Current Cathodic Protection

External Corrosion Control

Stray Current DC

External Corrosion Control

Stray Current DC

External Corrosion Control

Consumed Galvanic Anode

External Corrosion Control

Consumed Galvanic Anode Origin

External Corrosion Control

Questions

Contact Information

.

Colvin Mann, P.E., NACE 38623

Neel-Schaffer, Inc.

601 948-3071

colvin.mann@neel-schaffer.com