Why Study Corrosion 1 Sheldon W. Dean 12/7/02. What is Corrosion? What does it look like? How do you...

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?