BMFB 4212 CORROSION & DEGRADATION FIRST LECTURE INTRODUCTION TO THE CORROSION & DEGRADATION OF ENGINEERING MATERIALS.

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.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

•

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

• 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

and Zinc

Copper Cladding Zinc Cladding

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

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.

• 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.

Cont..

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 technologyto protect against corrosion. Coastalstructures 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:

• 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:

Physical Chemical

Electrochemical

Thermodynamic

MetallurgicalCorrosion Resistance

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 ???