Why Study Corr

8/12/2019 Why Study Corr

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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 DamageAutomotive 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 corrosionoccurs


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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+++ O2Fe2O3+ 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) DiagramVery 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


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Characteristics of Corrosion

ProductsVery 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.


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There are many ways to prevent or minimize corrosiondamage


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Alloying to Resist Corrosion - SteelAdd >13% Cr (stainless steel)

Add >2% Mo to stainless (to resist pitting)

Add Si, P, Cu, Cr ( and others) to obtain weatheringsteel


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Alloying to Resist Corrosion -

CopperAdd Ni and Fe (cupronickel) sea water

Add As, Sb, or P to prevent dealloying of brass (Cu + 10to 35% Zn)

Add Al or Si to resist erosion


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Metallic CoatingsWidely 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 seawater

Anodic protection increase potential to produce aless soluble corrosion product used in some chemicalplants


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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 becomethinner 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, andfailure of components

What is your answer?


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Break Time


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Careers in Corrosion

Technician - Education High school diploma + interest in chemistry or

technology

Associates degree possible night school - notrequired at entry level

- Chemistry

- Electrical technology

- Materials science


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Technician-Work Lab technician

- Chemistry laboratory

- Materials laboratory- Materials or chemical company

Field technician civil engineering

- Pipeline monitoring

- Bridges, tunnels etc.


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Civil Engineer - Education Civil, mechanical or electrical SB

MBA or MS (not required but often helpful)

PE license NACE Certification


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Civil Engineer - Work Engineering firm or consultant

- Cathodic protection design

- System monitoring and evaluation State or local government

- Specify protection systems for bridges, tunnels, otherfacilities

- Inspection and monitoring


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Mat., Chem., Chem. Eng.

Education High School Diploma

College SB, Major: Mat. Eng., Chem., Chem. Eng., orMech.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 International

The Corrosion SocietyAddress: P.O.Box218340, Houston,TX77218-8340

Phone: 281-228-6200

Website: www.nace.org


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ASTM International Standards development, Vol.03.02

Training courses

SymposiaAddress:100 Barr Harbor Drive, West Conshocken,

PA 19428-2959

Website: www.astm.org

Corrosion committee: G-1
http://www.astm.org/http://www.astm.org/


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Corrosion Testing Used for a variety of purposes

Standard test methods available

Some tests are simple and easy to runASTM corrosion tests are in Volume 03.02 of the

Annual Book of ASTM Standards


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Corrosion Testing-PurposesAccelerated tests to demonstrate products durability

Acceptance tests to show that a material meetsstandard

Monitoring tests to show changes in a systemcorrosivity

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 toreproduce Standardization helps reproducibility

Consensus standard tests: ASTM and NACE


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Accelerated Test ExampleASTM G48 Pitting and Crevice Corrosion Resistance

Ferric chloride, 6%solution

72Hrs at 22o

C (room temperature) Report pitting or crevice corrosion

Simulates sea water attack of stainless steels


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Acceptance Test - Al AlloysASTM 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 + 2.7%H2O2, 22

oC

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/ldetergent solution

Record potential at several points on the surface


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Analyze DataArrange values in ascending order and number the

values sequentially

Determine plotting position,f

f = r/(n +1) where r is the measurement number, andn is the total number of values

Plot on probability paper


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ASTM C876 Report Potential > -0.20 V, rebar is not corroding

Potential


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Demonstration of CorrosionA simple test to show local cathodes and anodes with a

corroding specimen

Uses indicators to show where reactions occur

Phenolphthalein turns red at cathode (OHiongenerated there)

K3Fe(CN)6turns blue at anode


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Demonstration Test

MaterialsAgar agar

Salt (NaCl)

5%K3Fe(CN)

6solution

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 test

Procedure Prepare 250 ml of 3%salt (7.5g) and 2% agar agar

solution

Boil to dissolve agar agar

Add 5ml K3Fe(CN)6solution and 1ml ofphenolphthalein solution

Pour into 2 dishes, one with bright nail, one withbright nail wired to galvanized nail


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Demonstration Test

Procedure ContinuedAllow 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 thebright nail wired to the galvanized nail?


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Follow-up NACE Foundation NACE Foundation wants to help high schools withprograms 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


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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 experiencefor students

Many opportunities for careers in corrosion prevention


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Thank You!Questions please?

Why Study Corr

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