Corrosion and Corrosion Control

FundamentalsJeff Knauer, PE, ME, NACE CP Specialist

Engineering Manager, Corrpro San Leandro, CA

(510)614-8800, JKnauer@corrpro.com

American Water Works Association, October 2, 2013

What is Corrosion?

• Corrosion is the unwanted degradation of

a material or metal due to a reaction with

its environment

• In other words, rust

Corrosion has Impact On:

• Pipelines

• Tanks

• Reinforced Concrete

• Sheet Piles

• Transit Systems

• Treatment Facilities

Pitting of Steel Pipe

Failure of a UST

Just a Small Leak…

Why is Corrosion Control

Important?

• Preserve Assets, $

• Reduce Maintenance Costs, $

• Reduce Inspection Costs, $

• Regulation / Compliance

• Preserve The Environment

Corrosion is a Natural Process

Iron

Oxide

Iron

Oxide

Refining &

Milling

Steel

Steel Corrosion

+

+

=

=

Requirements for Corrosion

• Anode

• Cathode

• Electrolyte

• Metal Path

Factors Contributing to Corrosion

- Coupling to Dissimilar Metals

- Differential Aeration

- Differential Soils

- Coupling of Old Pipe / New Pipe

- Dissimilar Surface Conditions

- Temperature Difference

- Stray Current

Galvanic Series

• Material Potential*

• Magnesium Alloy -1.75

• Zinc -1.10

• Aluminum Alloy -1.00

• Cadmium -0.80

• Mild Steel (New) -0.60

• Mild Steel (Old) -0.45

• Cast Iron -0.50

• Stainless Steel up to +0.10

• Copper, Brass, Bronze -0.20

• Titanium -0.20

• Gold +0.20

• Carbon, Graphite +0.30

• * Potentials With Respect to Saturated Cu-CuSO4 Electrode

AnodeCathode

Pipeline Corrosion Cell

Dissimilar Surface Conditions

(Potential differences on a steel surface)

-530mV

-512mV

-499mV

-561mV

-530mV

-505mV

-487mV

-521mV

-500mV

-558mV

-504mV

Corrosion

Steel or Ductile Iron

Copper

Dissimilar Metals at Service Lateral

Old Pipe

(Cathode)New Pipe

(Anode)

Coupling of Old Pipe / New Pipe

Hot Gas

Cooler

Gas

CATHODE

Temperature Difference

Compressor

Station

DRY

SAND

MOIST SAND

WATER

Differential Aeration - Caused by Poor

Drainage Under Water Storage Tank

SANDCURRENT FLOW

Differential Soils - Caused by Foreign

Material

CLAY

Steel Tank Floor

Corrosion Control Methods

• Material Selection

• Environmental Modifications

• Coatings

• Cathodic Protection

How Cathodic Protection Works

• Corrosion occurs where current

discharges from metal to electrolyte

• The objective of cathodic protection is to

force the entire surface to be cathodic to

the environment

AnodeCathode

Pipeline Corrosion Cell,

Revisted

AnodeCathode

Metallic

Connection

Electrolyte

Cathodic Protection Anode

Cathodic Protection

Current

Corrosion of the Metal Will Cease Once the Applied

CP Current Equals the Corrosion Current

Cathodic Protection

Cop

per

-3

00m

V

Ste

el

-600

mV

Ma

gne

siu

m

-1.7

V1) ANODE

2) CATHODE

3) ELECTROLYTE

4) METAL PATH

Cathodic Protection

Cat

hod

e

Cat

hod

e

An

ode

1) ANODE

2) CATHODE

3) ELECTROLYTE

4) METAL PATH

Cathodic Protection Current Requirements

• Surface area to be protected

• Polarization behavior of the structure in

its environment

• Presence of barrier coatings

Coatings Reduce Exposed Metal Area

CORRPROC O M P A N I E S I N C

Bonding Across a Bell and Spigot

or Slip-joint

Pipe

Copper wire with

direct burial insulation

Thermite brazed

connection coated with

bitumous compound

Electrical Continuity

Common Types of Galvanic Anodes

• Magnesium

• Zinc

• Aluminum

Magnesium Anodes

Zinc Soil & Ribbon Anodes

Bracelet Anodes

Impressed Current Cathodic Protection Schematic

Impressed Current Cathodic Protection

Components

• Anodes

• Rectifier

• Wiring

O&M Considerations

• Galvanic Systems

• Impressed Current Systems

• Monthly

• Annually

Questions