COLVIN MANN, P.E., NACE 38623 ALABAMA ......The steel, whether rebar, wire or cylinder, embedded in Portland cement concrete, forms a passive film due to the ph of the cement, around

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


Steel Pipe Manufacturing

Electric Arc FurnaceENERGY GAINED

Raw Materials

TransferLadle

Hot Rolling Machine


Prestressed Concrete Cylinder Pipe


Prestressed Concrete Cylinder PipeLined Cylinder Pipe


Prestressed Concrete Cylinder PipeEmbedded Cylinder Pipe


Ductile Iron Pipe


Ductile Iron Joints


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


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


Stray Current Interference


Stray Current Interference






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


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


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


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


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


Prestress


Bar Wrap


Polyethylene Encasement

Coatings

Sacrificial Cathodic Protection

Impressed Current Cathodic Protection

Protection








Fusion Bonded Epoxy


80 Mil Tape Wrap


Cathodic Protection Principle


Cathodic Protection Sacrificial Anode

AnodeProtectedPipe Mg

or

Zn

Maximum Driving Potential: - Mg ( -1.7 V )

Steel ( - 0.6 V )

1.1 V


Galvanic Anode


Magnesium Anode


Galvanic Anodes at Every Other Joint


Distributed Galvanic Sacrificial System


Grouped Sacrificial Galvanic System


Ribbon Type Galvanic Anode


Galvanic Anode Installation


Galvanic Anodes In Repair Conditions


Impressed Current System Rectifier






Impressed Current Anodes


Impressed Current Deep Anode Installation


Impressed Current Deep Anode Installation


Impressed Current System


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


Stray Current DC


Stray Current DC


Consumed Galvanic Anode


Consumed Galvanic Anode Origin


Questions

Contact Information

.

Colvin Mann, P.E., NACE 38623

Neel-Schaffer, Inc.

601 948-3071

[email protected]

mailto:[email protected]

Documents

COLVIN MANN, P.E., NACE 38623 ALABAMA ......The steel, whether rebar, wire or cylinder, embedded in Portland cement concrete, forms a passive film due to the ph of the cement, around