why study corrosion 1 sheldon w. dean 12/7/02. what is corrosion? what does it look like? how do you...
Post on 24-Dec-2015
213 Views
Preview:
TRANSCRIPT
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?
• 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
• 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
• 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 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
Careers in CorrosionTechnician-Work• Lab technician
- Chemistry laboratory
- Materials laboratory
- Materials or chemical company
• Field technician – civil engineering
- Pipeline monitoring
- Bridges, tunnels etc.
Careers in CorrosionCivil Engineer - Education
• Civil, mechanical or electrical SB
• MBA or MS (not required but often helpful)
• PE license
• NACE Certification
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
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
• Short courses, some with certification
• Annual meeting and show
• Standards development
• Local sections
• Symposia
• Books, videos and computer products
NACE InternationalThe Corrosion Society
• Address: P.O.Box218340, Houston,TX77218-8340
• Phone: 281-228-6200
• Website: www.nace.org
ASTM International
• 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
• 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 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
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
• 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 TestMaterials
• 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 testProcedure
• 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 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?
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 281-228-6210
• 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?
top related