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Why Study Corrosion 1
Sheldon W. Dean
12/7/02
What is Corrosion?
What does it look like?
How do you know when you have it?
What is Corrosion?
• Metals made by smelting ( reduction of
ore)
• Metals in air want to return to their
oxidized state
• Corrosion is a natural process!
Is Corrosion Important?
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National issue?
International issue?
What industries are affected?
Does it affect us personally?
Importance to USA
• CC Technologies study – March 2002
• In 2000 about 3.1% of GDP spent on
corrosion repair and control
• Total cost $276Billion!
• Of industries analyzed, the cost was
$137.9 Billion
Examples of Corrosion
Damage
• Automotive problems - body rust
• Home examples- Plumbing fixtures
- Mail box
- Exterior fixtures and fasteners
• Concrete cracking
Corrosion Affects Our
Safety!
• Unexpected failures of equipment and
devices
• Need to replace damaged items
• Corrosion weakens structures
- Need to evaluate fitness for service
when corrosion occurs
What Does Corrosion Look
Like?
• Rust and tarnish, red blue or gray scale
• 8 types of damage – Fontana
• Several others also.
Most Common Forms of
Corrosion
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General attack (uniform wastage)
Pitting/ Crevice attack
Cracking (embrittlement)
Galvanic corrosion
Corrosion is
Electrochemical
• Two different reactions occur oxidation and reduction
• Electron transfer occurs
• Potential (voltage) driving force required
• Oxidation occurs at anode
• Reduction occurs at cathode
Corrosion Reactions
• Oxidation - e.g.
Fe  Fe++ + 2e
• Reduction – e.g.
O2 + 2H2O  4OH- - 4e
• Secondary - e.g.
4 Fe++ + O2  Fe2O3 + 8H+
Conclusions
• Corrosion rate depends upon the
corrosion products that form
• Solubility of corrosion products
determines the rate
• If solubility is high, the rate is high!
• If solubility is low, the rate is low
Potential/pH (Pourbaix)
Diagram
• Very useful way to present data
• Developed by Marcel Pourbaix (1966)
• Available for all metals and many other
elements
• Shows solubility and potential effects
• If solubility is < 10-6 M/l, no corrosion is
assumed
Characteristics of
Corrosion Products
• Very thin and dense: protective,e.g., Cr,
Al, Ti, 10 to 100 nm thick
• Thin: protective but some corrosion
occurs, e.g.,Cu, Zn, Pb 1 to 10 m
• Thick and porous, e.g., Fe, >100 m
Corrosion is a problem.
• Soluble, e.g., Na, K Not able to be
used.
Dealing with Corrosion
There are many ways to prevent
or minimize corrosion damage
Alloying to Resist
Corrosion - Steel
• Add >13% Cr (stainless steel)
• Add >2% Mo to stainless (to resist
pitting)
• Add Si, P, Cu, Cr ( and others) to obtain
weathering steel
Alloying to Resist
Corrosion - Copper
• Add Ni and Fe (cupronickel) sea water
• Add As, Sb, or P to prevent dealloying
of brass (Cu + 10 to 35% Zn)
• Add Al or Si to resist erosion
Metallic Coatings
• Widely used to protect steel and to
make other metals more attractive
• Zn and Zn alloys on steel – Galvanizing
• Ni + Cr on steel, brass or zinc to give a
bright finish
• Cu + Ni + Cr also used for bright finish
Organic Coatings - Paint
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Barrier layer to keep water away
Adhesion is key to success
Susceptible to thermal damage
Susceptible to UV damage
Electrochemical
Protection
• Cathodic protection – reduce the
potential and also corrosion rate widely used underground and in sea
water
• Anodic protection – increase potential to
produce a less soluble corrosion
product – used in some chemical plants
Corrosion Inhibitors
• Used in water systems:
- Automotive cooling systems
- Cooling towers
- Boilers, especially high pressure steam
• Temporary preservatives for metals
- Volatile corrosion inhibitors
• Paints and primers
Quiz Time!
• What is the most corrosive substance
we can think of?
• Corrosion damage only causes metals
to become thinner – True or False?
• How does corrosion affect me?
Answers!
• Water!!!
• False! Corrosion also causes cracking,
pitting, staining, wedging in crevices,
loss of electrical conductivity, and failure
of components
• What is your answer?
Break Time
Why Study Corrosion - 2
Sheldon Dean
12/7/02
Careers in Corrosion
Technician - Education
• High school diploma + interest in
chemistry or technology
• Associates degree – possible night
school - not required at entry level
- Chemistry
- Electrical technology
- Materials science
Careers in Corrosion
Technician-Work
• Lab technician
- Chemistry laboratory
- Materials laboratory
- Materials or chemical company
• Field technician – civil engineering
- Pipeline monitoring
- Bridges, tunnels etc.
Careers in Corrosion
Civil Engineer - Education
• Civil, mechanical or electrical SB
• MBA or MS (not required but often
helpful)
• PE license
• NACE Certification
Careers in Corrosion
Civil Engineer - Work
• Engineering firm or consultant
- Cathodic protection design
- System monitoring and evaluation
• State or local government
- Specify protection systems for
bridges, tunnels, other facilities
- Inspection and monitoring
Mat., Chem., Chem. Eng.
Education
• High School Diploma
• College SB, Major: Mat. Eng., Chem.,
Chem. Eng., or Mech.Eng.
• Grad school optional, MBA, MS or PhD
• Certification NACE (optional)
• PE License (optional)
Mat.,Chem.,Chem. Eng.
Work
• Chemical, materials, petroleum, auto
firm
- Engineering
- Safety
- Research (PhD)
- Plant Maintenance
• Engineering or consultant firm
NACE International
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Short courses, some with certification
Annual meeting and show
Standards development
Local sections
Symposia
Books, videos and computer products
NACE International
The Corrosion Society
• Address: P.O.Box218340,
Houston,TX77218-8340
• Phone: 281-228-6200
• Website: www.nace.org
ASTM International
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Standards development, Vol.03.02
Training courses
Symposia
Address:100 Barr Harbor Drive,
West Conshocken, PA 19428-2959
• Website: www.astm.org
• Corrosion committee: G-1
Corrosion Testing
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Used for a variety of purposes
Standard test methods available
Some tests are simple and easy to run
ASTM corrosion tests are in Volume
03.02 of the “Annual Book of ASTM
Standards”
Corrosion TestingPurposes
• Accelerated tests to demonstrate
products durability
• Acceptance tests to show that a
material meets standard
• Monitoring tests to show changes in a
system corrosivity
• Research tests to determine
mechanism of corrosion
Standard Tests
• Usually corrosion tests have many
parameters
• Corrosion tests often give results that
are difficult to reproduce –
Standardization helps reproducibility
• Consensus standard tests: ASTM and
NACE
Accelerated Test Example
• ASTM G48 Pitting and Crevice
Corrosion Resistance
• Ferric chloride, 6%solution
• 72Hrs at 22oC (room temperature)
• Report pitting or crevice corrosion
• Simulates sea water attack of stainless
steels
Acceptance Test - Al
Alloys
• ASTM G 69, Test of metallurgical
condition of Al alloys
• Measure potential,E, in salt solution
• Cu increases E, Zn reduces E
• Heat treatment determines condition
• Condition affects strength and corrosion
tendencies
ASTM G 69 Continued
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Solution: 1M Na Cl + 2.7%H2O2, 22oC
Surface preparation: 00 steel wool rub
1 Hour immersion
Measure potential every 5 minutes after
30 minutes against SCE electrode
• Average result: -750+/-10mV for pure Al
• Al foil is pure Al
Monitoring Test
ASTM C 876
• Corrosion of steel rebar in concrete
• Potential indicates when corrosion of
steel is occurring
• Copper/copper sulfate reference cell
• Chloride causes steel to corrode
• Deicing salt usually reason for problem
• Sea water also causes problems
Procedure ASTM C876
• Place electrode on concrete surface
• Measure potential with volt-meter
• If potential varies with time prewet
surface with 25ml/l detergent solution
• Record potential at several points on
the surface
Analyze Data
• Arrange values in ascending order and
number the values sequentially
• Determine plotting position,f
• f = r/(n +1) where r is the
measurement number, and n is the total
number of values
• Plot on probability paper
ASTM C876 Report
• Potential > -0.20 V, rebar is not
corroding
• Potential <-0.35V, rebar is corroding
• Potential in between then the rebar may
be corroding
Demonstration of
Corrosion
• A simple test to show local cathodes
and anodes with a corroding specimen
• Uses indicators to show where
reactions occur
• Phenolphthalein turns red at cathode
(OH– ion generated there)
• K3Fe(CN)6 turns blue at anode
Demonstration Test
Materials
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Agar agar
Salt (NaCl)
5%K3Fe(CN)6 solution
1% Phenolphthalein solution (in alcohol)
2 steel nails, bright finish (e.g.: 10d)
1 steel nail, galvanized (e.g.:10d)
Copper wires
Demonstration test
Procedure
• Prepare 250 ml of 3%salt (7.5g) and 2%
agar agar solution
• Boil to dissolve agar agar
• Add 5ml K3Fe(CN)6 solution and 1ml of
phenolphthalein solution
• Pour into 2 dishes, one with bright nail,
one with bright nail wired to galvanized
nail
Demonstration Test
Procedure Continued
• Allow the solutions to cool and watch
colors develop
• Where do are the red areas? (cathodes)
• Blue areas? (anodes)
• What does it mean when no blue areas
develop on the bright nail wired to the
galvanized nail?
Follow-up NACE
Foundation
• NACE Foundation wants to help high
schools with programs and information
• NACE local sections can provide
technical people to run field trips or lead
experimental demonstrations
• Contact Teri Elliott, phone 281-2286210
• Website: www.nace.foundation.org
Summary
• Corrosion is an important issue
• Corrosion technology shows where
chemistry can be used to prevent
problems
• Corrosion tests can provide good
hands-on experience for students
• Many opportunities for careers in
corrosion prevention
Thank You!
Questions please?