Why Study Corrosion 1

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Why Study Corrosion 1

• Sheldon W. Dean
• 12/7/02

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What is Corrosion?

• What does it look like?
• How do you know when you have it?

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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!

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Is Corrosion Important?

• National issue?
• International issue?
• What industries are affected?
• Does it affect us personally?

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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

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Examples of Corrosion Damage

• Automotive problems - body rust
• Home examples-
• - Plumbing fixtures
• - Mail box
• - Exterior fixtures and fasteners
• Concrete cracking

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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

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What Does Corrosion Look Like?

• Rust and tarnish, red blue or gray scale
• 8 types of damage Fontana
• Several others also.

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Most Common Forms of Corrosion

• General attack (uniform wastage)
• Pitting/ Crevice attack
• Cracking (embrittlement)
• Galvanic corrosion

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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

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Corrosion Reactions

• Oxidation - e.g.
• Fe ? Fe 2e
• Reduction e.g.
• O2 2H2O ? 4OH- - 4e
• Secondary - e.g.
• 4 Fe O2 ? Fe2O3 8H

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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

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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 lt 10-6 M/l, no corrosion is
  assumed

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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, gt100 ?m Corrosion is
  a problem.
• Soluble, e.g., Na, K Not able to be used.

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Dealing with Corrosion

• There are many ways to prevent or minimize
  corrosion damage

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Alloying to Resist Corrosion - Steel

• Add gt13 Cr (stainless steel)
• Add gt2 Mo to stainless (to resist pitting)
• Add Si, P, Cu, Cr ( and others) to obtain
  weathering steel

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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

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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

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Organic Coatings - Paint

• Barrier layer to keep water away
• Adhesion is key to success
• Susceptible to thermal damage
• Susceptible to UV damage

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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

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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

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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?

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Answers!

• Water!!!
• False! Corrosion also causes cracking, pitting,
  staining, wedging in crevices, loss of electrical
  conductivity, and failure of components
• What is your answer?

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Break Time
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Why Study Corrosion - 2

• Sheldon Dean
• 12/7/02

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Careers in CorrosionTechnician - Education

• High school diploma interest in chemistry or
  technology
• Associates degree possible night school - not
  required at entry level
• - Chemistry
• - Electrical technology
• - Materials science

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Careers in CorrosionTechnician-Work

• Lab technician
• - Chemistry laboratory
• - Materials laboratory
• - Materials or chemical company
• Field technician civil engineering
• - Pipeline monitoring
• - Bridges, tunnels etc.

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Careers in CorrosionCivil Engineer - Education

• Civil, mechanical or electrical SB
• MBA or MS (not required but often helpful)
• PE license
• NACE Certification

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Careers in CorrosionCivil 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

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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)

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Mat.,Chem.,Chem. Eng.Work

• Chemical, materials, petroleum, auto firm
• - Engineering
• - Safety
• - Research (PhD)
• - Plant Maintenance
• Engineering or consultant firm

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NACE International

• Short courses, some with certification
• Annual meeting and show
• Standards development
• Local sections
• Symposia
• Books, videos and computer products

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NACE InternationalThe Corrosion Society

• Address P.O.Box218340, Houston,TX77218-8340
• Phone [phone]
• Website www.nace.org

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ASTM International

• Standards development, Vol.03.02
• Training courses
• Symposia
• Address100 Barr Harbor Drive, West
  Conshocken, PA 19428-2959
• Website www.astm.org
• Corrosion committee G-1

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Corrosion Testing

• 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

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Corrosion Testing-Purposes

• 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

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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

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Accelerated Test Example

• ASTM G48 Pitting and Crevice Corrosion Resistance
• Ferric chloride, 6solution
• 72Hrs at 22oC (room temperature)
• Report pitting or crevice corrosion
• Simulates sea water attack of stainless steels

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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

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ASTM G 69 Continued

• Solution 1M Na Cl 2.7H2O2, 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

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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

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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

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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

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ASTM C876 Report

• Potential gt -0.20 V, rebar is not corroding
• Potential lt-0.35V, rebar is corroding
• Potential in between then the rebar may be
  corroding

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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

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Demonstration TestMaterials

• Agar agar
• Salt (NaCl)
• 5K3Fe(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

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Demonstration testProcedure

• Prepare 250 ml of 3salt (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

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Demonstration TestProcedure 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?

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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 [phone]
• Website www.nace.foundation.org

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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

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Thank You!

• Questions please?