BMFB 4212
CORROSION & DEGRADATION
FIRST LECTURE
INTRODUCTION TO THE CORROSION &
DEGRADATION OF ENGINEERING
MATERIALS
• The student will learn about…
• The effect of environmental conditions on
the mechanical and physical properties of
materials
• The student will be able to…
• Describe the conditions that cause the
physical, chemical and biological
degradation of materials.
• Describe how materials degrade in certain
conditions and how materials are altered
by degradation.
Definition of Corrosion
Destruction or deterioration of a material
(metal or nonmetals) because of reaction or
chemical attack by its environment.
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Examples
Corrosion of metal: reverse extractive metallurgy.
Degradation of ceramic refractory: chemically attacked at high temp. by molten
salts.
Degradation of organic polymer: chemical attack of organic solvents,
dimensions or property changes by water absorption, oxygen and ultraviolet
radiation.
Corrosion Engineering: Application of science and
art to prevent or control corrosion damage
economically and safely
Although the term is usually applied
to metals, all materials, including
wood, ceramics (in extreme
conditions) and plastics, deteriorate
at the surface to varying degrees
when they are exposed to certain
combinations of sunshine (UV light),
liquids, gases or contact with other
solids.
Finishing of Materials
• Wood
• The environmental factors that affect
degradation in wood are;
• Biological organisms – fungi and insects
• Risk of wetting or permanent contact with
water
• Wood is susceptible to attack when the
moisture content exceeds 20%
Dry Rot
Furniture Beetle
(Woodworm)
Degradation of Materials
• Physical and Mechanical effects of degradation in
wood
• Change in cross-sectional dimensions, swelling
and shrinkage
• Strength and stiffness decrease as moisture
content increases
• Durability is affected
• Coatings can be compromised
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Degradation of Materials
• Plastics
• It is widely accepted that plastics do not corrode
however micro organisms which can decompose low
density polyethylene do exist
Degradation of Materials
• Plastics
• Elastomers can cause other plastics to corrode or melt
due to prolonged contact e.g. rubber left on a setsquare
Degradation of Materials
• Plastics
• UV light will weaken certain plastics and produce a
chalky faded appearance on the exposed surface
Degradation of Materials
• Plastics
• Heat will weaken or melt certain plastics even at
relatively low temperatures
Degradation of Materials
• Plastics
• Cold can cause some plastics to become brittle and
fracture under pressure
Degradation of Materials
• Plastics
• Mould can grow on plastics in moist humid conditions
Degradation of Materials
• Plastics
• Bio-degradation – the chemical breakdown in the body of
synthetic solid phase polymers
Degradation of Materials
• Metals
• Most metals corrode because they react with oxygen in
the atmosphere, particularly under moist conditions –
this is called oxidation
Degradation of Materials
• Metals
• Ferrous metals such as steel are particularly susceptible
to oxidation and require ongoing maintenance or they
will suffer inevitable structural failure
• Choice of metal, environmental location and design
features must all be considered carefully
Degradation of Materials
• Metals
• Some non-ferrous metals are particularly resistant to
corrosion, e.g. Copper and Zinc
Copper Cladding
Zinc Cladding
• They form strong oxides on their surfaces (as do aluminium
and lead) and these protect the metal from further oxidation.
Shown as cladding on the buildings above
Figure 1: Metallurgy in reverse.
Notes:
1. In nature most metals exist in combined state (oxides, sulfides, carbonates,
or silicates – lower energy !! ).
2. Metallic state – higher energy (spontaneous tendency to react chemically to
form compounds.
3. Example: Iron oxides to iron (higher energy state) to rusting (iron oxides –
lower energy state).
*** rusting refer to steel and iron corrosion (many metals form oxides due to
corrosion)
Since corrosion is caused by chemical reaction, the
rate at which the corrosion takes place will depend
to some extent on the temperature and the
concentration of the reactants and products.
Corrosion can be fast or slow (environment).
Higher temperature and pressures usually involve
more severe corrosion conditions.
Many of the present-day industrial manufacturing
operations would not have been possible or
economical without the use of corrosion-resistant
materials.
Environments of Corrosion
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Aircraft corrosion
Car corrosion
Electronics
Highway bridges
Pipelines
Process Industries
Refineries
Classification of Corrosion
• First approach: high temp and low temp
corrosion.
• Second approach: oxidation and
electrochemical corrosion.
• Preferred classification: wet and dry corrosion.
Wet corrosion:
(i) occurs when liquid present
(ii) involves aqueous solution or
electrolytes
(iii) Accounts greater amount of
corrosion.
(iv) eg: corrosion of steel by water
Dry corrosion:
(i) absence of liquid phase or above
dew point of the envi.
(ii) vapors and gases are usually the
corrodents.
(iii) often associated with high temp.
(iv) eg: attack on steel by furnace
gases.
Corrosion Damage
• Appearance: rusted surfaces of automobile,
rusted equipment in plant, building
appearance
• Maintenance and operating costs: cost on
changing corroded bolt in some equipment,
higher repair cost due to corrosion, (close
cooperation between materials, process and
design engineer before a plant is built can
eliminate or reduce maintenance cost in many
cases.
Cont..
• Plant shutdowns: due to unexpected
corrosion failures eg. SCC of the vessels –
production delayed for some time =
manufacturing loss. (periodic inspection of
equipment solve the problem – corrosion
probe).
• Contamination of product: very small
amount of corrosion introduce certain metal
ions into the solution may cause catalytic
decomposition of a product, eg: manufacture
and transporting of concentrated H2O2 or
hydrazine.
Cont..
• Loss of valuable products: leakage due to
corrosion, eg. slight losses of uranium compound or
solutions are hazardous and can be very costly.
• Effects on safety and reliability: (i) handling of
hazardous and toxic materials at high temp. and
pressure requires construction materials that
minimize corrosion failures. SCC corrosion type:
corroding equip. can cause explosion due to SCC.
(ii) Corrosion products could make sanitizing of
equipment more difficult, eg. milk and dairy product
plant. (iii) medicals metals used for hip joints,
screws, heart valves, etc – high reliability is of
paramount importance.
Cont..
• Product liability: manufacturer of a product
must make sure that it is made a proper
materials, under good quality control, to a
design that is as safe as possible, and the
inspection must be critical. The corrosion
engineer must be doubly sure that failure will
not occur in actual envi. and should be aware
of the legal liability aspects.
Cost of Corrosion
• No specific & realistic figure (estimation, prediction or
may be assumption.
• USA – annual cost vary between $ 8 bil to $ 126 bil.
• Corrosion cost for oil and gas industries – nearly $ 2
bil (resource from Wall Street Journal).
• Another example: (i) Sulfuric acid plant company
spent more than $ 400, 000 per year for corrosion
maintenance. (ii)$ 2 million per year is spent for
painting steel to prevent rusting by a marine
atmosphere
• Etc.
Future Outlook
• Demand on corrosion engineers increased (career
prospect and salary) – great future!! (eg- any
manufacturing plant, oil and gas refinery, engineering
consultation, etc.).
• R&D on new advanced materials that could reduced
corrosion – in searching for low cost materials with
amazing props.
• New research tools to aid in the study and
understanding of corrosion and its prevention.
• Great national awareness on corrosion cost and
failure.
• Understanding on the role of materials engineer as
corrosion engineer in developing / setup the
manufacturing plant.
EXAMPLES OF CASE STUDY
CASE I: CORROSION OF STEEL PILES IN
SEAWATER ENVIRONMENT
• Seawater contains about 3.4% salt, mostly chloride salts and
it is slightly alkaline (pH=±8). It is an aggressive electrolyte
and can cause uniform and localized corrosion. Corrosion of
metals such as steels is affected by dissolved oxygen content,
velocity, temperature and biological organisms.
• Greatest attack occurs in the splash zone because of
alternate wetting and drying and also aeration.
• Most of wharfs are supported by steel piles. As services life of
unprotected piles will be very limited, several attempts have
been made to control the corrosion of steel piles especially in
splash, submerged and mud/soil zones.
• Basically coating and cathodic protection are applied to
control corrosion in submerged and mud/soil zones while
wrapping are applied to control corrosion in splash and tidal
zones.
A combination of galvanic and
atmospheric corrosion can occur
where pilings connect to the structural
framework of a pier
The lifejacket, installed above on bridge
Piers, uses sacrificial anode technology
to protect against corrosion. Coastal
structures suffer corrosion at a much
greater Rate than those inland –
chloride ions from seawater migrate
into the porous concrete by diffusion
and eventually reach the steel
reinforcement.
One can ask many question, e.g.
• Why does the greatest corrosion attack
occur in splash zone?
• Why the protection method for submerged
and mud/soil zones differs than that for
splash and tidal zones?
• How effectives does the cathodic
protection?
• How to design a cathodic protection?
• Etc?
To know the answer we have to had
knowledge and skills of:
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Mechanism of electrochemical corrosion
Behavior of marine environment
Corrosion resistance of steel in seawater
Forms of corrosion that can occur on steel
Methods for corrosion protection and their
limitation
• Methods for corrosion inspection
• How to repair the damage structures
• Etc
CASE II:
Aloha Airline Boeing 737 lost a major portion of its upper
fuselage while in flight at 24,000 feet
Case II
• The fuselage panels that are joined together along lap
joints using rivets were corroded resulting in cracking
and debonding over the life of the air-craft.
• Structural failure of the fuselage occurred in mid-flight
due to corrosion-accelerated fatigue.
• The two aluminum alloys used most often in fuselage
skin, 2024-T3 and 7075-T6, possess excellent static
and fatigue strengths. Unfortunately, they are also
more prone to corrosion damage such as pitting and
exfoliation (MATERIALS SELECTION PROBLEM !!!!)
For those we need to have following basic
engineering sciences:
Electrochemical
Physical Chemical
Corrosion
Resistance
Thermodynamic
Metallurgical
PCB damage due to corrosion
Photograph showing corrosion damage
of a fuel tank system due to bacteriological
infestation. The damage was caused in just
six months.
Damage due to saltwater exposure
Thanks for Your Attention !!!
Any Question ???