Lance Taylor Jessi Hartman

Adam Flournoy

ENGR 45, SRJC, Fall 2013

Richmond Refinery Fire August 2012

The destruction of a material by a chemical or electrochemical process through interaction with its environment.

Typically this is a transfer of electrons from one metal to another which is an oxidation-reduction reaction.

The corrosion of a metal is a chemical process by which the metal is oxidized.

Normal rain water has a slightly acidic pH of 5.6.

Acid rain has a typical value of 4.3.

Acid rain not only affects the health of the environment but also the health of materials and alloys.

There are 8 common forms of corrosion: Uniform (rust) Galvanic Crevice Pitting Intergranular Selective Leaching Erosion-Corrosion Stress Corrosion

Most common form of corrosion

Oxidation-Reduction reactions occur randomly over entire exposed surface

Occurs when two metals or alloys with dissimilar compositions are electrically coupled while exposed to the same electrolyte.

Typically in marine environments. The more inert metal is protected from

corrosion while the more reactive metal will degrade.

Magnesium Shell

Steel Core Galvanic Corrosion

Both are forms of localized corrosion. Occur from concentration differences of ions

forming a concentration cell. Oxidation occurs within the pit or space between

two metals. Insidious form of corrosion because it can go

undetected with little material loss until failure occurs.

Crevice

Pitting

Corrosion occurs preferentially along grain boundaries for some alloys in specific environments.

Also known as weld decay. Specific to stainless steels

where heat treatment allows the formation of small precipitate particles that form along grain boundaries.

This leaves a chromium depleted zone that is highly susceptible to corrosion.

• Occurs when one element is preferentially removed from an alloy during the corrosion process. • This leaves behind a porous and weak material susceptible to failure. • Example: The dezincification of Brass. Zinc is selectively leached from the alloy and leaves behind the reddish copper in the region bereft of Zinc.

Occurs because of chemical reactions combined with mechanical wear from abrasive fluids in motion.

Commonly found in pipes and especially around bends and elbows or where there are changes in pipe diameter.

Increased fluid velocity = increased corrosion rate.

Erosion

Example: Richmond Refinery!

Cracks grow perpendicular to grain boundaries because of applied tensile stresses combined with a corrosive environment.

Stress Crack

Our goal was to simulate the effect of acid rain, a uniform corrosion, on various metals and alloys commonly used for building and tool materials.

The experiment was conducted within a temperature range of 50 to 70 degrees degrees Fahrenheit.

A plastic non-reactive tank was used for the control environment.

0.01 M Sulfuric Acid was used to simulate the corrosive environment; about 100x stronger than normal acid rain.

Zinc

Brass

Monel Steel Aluminum Copper

Stainless Steel

Failure during cold working

Samples used for Acid Rain simulation

Stainless Steel touching Monel Steel Annealed Stainless Steel

Stainless Steel touching Monel Steel Annealed Stainless Steel

Annealed Stainless Steel Stainless Steel touching Monel Steel

Annealed Stainless Steel Stainless Steel touching Monel Steel

-60

-40

-20

0

20

40

60

80

100

120

1 2 3 4 5 6

Roc

kwel

l Har

dnes

s B

Effects of CW on Hardness

Cold Worked

Not Cold Worked

1 – Copper 2 – Aluminum 3 – Stainless Steel 4 – Brass 5 – Monel Steel 6 – Zinc

“Effect of cold-work on corrosion of metals in general is greatest when a second phase precipitates to form active galvanic cells, whereas the increase in internal energy of a disarrayed metal lattice has little if any effect. Preferred grain orientation of surface metal sometimes resulting from cold-work may either increase or decrease corrosion.”(3)

No measurable difference in loss of mass. Scales used were not able to measure difference in pre and post weights of metal samples.

No difference in hardness after 3 weeks corrosion testing. Samples did not have enough time to sufficiently degrade.

Corrosion of unannealed stainless steel possibly through galvanic corrosion.

Corrosion of aluminum not cold worked possibly from crevice corrosion. Sample was laid flat on the bottom of the tank.

No effect of corrosion on hardness before and after corrosion testing.

Several measures may be taken to prevent, or at least reduce, corrosion. These include material selection, environmental alteration, the use of inhibitors, design changes, application of coatings, and cathodic protection.

Sacrificial Anode

Surface coatings can also be used to prevent corrosion Painting, plating and anondizing metals can limit the

amount of surface area susceptible to corrosion. Some materials such as aluminum and stainless steel

form oxide barriers that prevent oxidation at the surface

Oxidation-Reduction reaction without an oxide barrier or surface coating

Choose corrosion resistant materials Prevent accumulation of water, salts, gasses within

structures Inspect C.C.P. (Critical Control Points) regularly with

non-destructive techniques.

Don’t let this happen to you!

1 - Callister, Jr., William D. and David G. Rethwisch Materials Science and Engineering: An Introduction. Eighth ed. USA: Wiley, 2010. Print.

2 - Serway, Raymond A., and John W. Jewett, Jr. Physics for Scientists and Engineers. Eigth ed. Belmont: Brooks/Cole, 2010. Print.

3 – Journal of the Electrochemical Society http://jes.ecsdl.org/content/111/5/522.abstract

Certain images used courtesy of open internet domain