Fundamentalsof CorrosionNov2012

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|Centre for Corrosion Research |Block I |

Lecture 1

………To be a partner of choice in corrosion research.

www.utp.edu.my

ByIr Dr Mokhtar Che Ismail

Copyright reserved

AP Ir Dr Mokhtar Che Ismail B.E(Mechanical Eng) University of

Newcastle, Australia M.Sc ( Materials Science and Eng) National

University of Singapore PhD (Corrosion Engineering) , UMIST,

England

9 years professional industrial experience (INTEL & PETRONAS) and 14 years academic experience.

Course Instructor

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4

Understand the fundamentals of corrosion

COURSE OBJECTIVE

Explain thermodynamics and kinetics of corrosion

Perform corrosion measurement using standard procedures

FUNDAMENTALS of CORROSION : Part 1 -An Introduction to the world of corrosion

|Centre for Corrosion Research |Block I |

Why Metals Corrode?

INTRODUCTION ( what is.. /why..)Corrosion is a natural phenomenon and can be considered as extractive metallurgy in reverse( Fontana).

Earth Mineral Ores Extraction/Refining Metal (Fabrication) Components Corrosion Earth

Several Definitions•Corrodere (Latin) means to chew away or to wear away.

•The degradation of a material that occurs when it reacts with environment.(Fontana)

•Physicochemical interaction between a metal and its environment which results in changes in properties of the metal and which often lead to impairment of the function of the metal, the environment, or the technical system of which these form a part : ISO 8044-1986

•Destruction of a metal by chemical or electrochemical reaction with its environment. Herbert H. Uhlig in Corrosion Handbook

A few more definitions..•The deterioration of a material, usually a metal, that results from a reaction with its environment. (NACE)

•Corrosion is an irreversible interfacial reaction of a material (metal, ceramic, polymer) with its environment which results in consumption of the material or in dissolution into the material of a component of the environment. IUPAC

Examples of Corrosion Phenomena

Offshore 8" Pipeline

Corrosion Pits

due to SRB

LP Riser

Onshore Pipeline Section

Lack of maintenance !!

Smart Flange

Severe corrosion at risers

R4

Lack of maintenance !!

Corrosion Under Insulation

Aboveground storage tank

Lack of maintenance !!

Emulsion line

Sample Background Equip No: Equip Description: Material: Part: Plant: Unit:

Time to Failure: Date of Failure:Photos

Phenomenon

Appearance

Environment

Remedy

4 Years April 2005

Under Deposit Corrosion.

Carbon Steel

Process Fluid: LPG Working Pressure: 15.9 kg/cm2

Working Temperature: 400C

Pipe replacement with in kind material

Thin layer with dry and brown deposit and localized pittingcorrosion.

Consequences/COSTCost in order of 4% of GNP in advanced countries. USA= $100-200 billion.( recent data??)

The effect can be in many ways:

• Appearance/Aesthetic factor: Bad impression – low morale to worker.

•Maintenance and operating cost

•Plant shutdowns

•Contamination of products

•Loss of product

•Effect of safety and reliability

• 1950 H.H. Uhlig – US Study: 2.1% of GNP

• 1970 T.P. Hoar – UK Study: 3.5% of GNP

• 1974 Japan Study: 1.2% of GNP

• 1975 Battelle/NBS – U.S. Study: 4.5% of GNP

Cost of Corrosion – Previous Studies

What are the worries?

Collapse of Sphere

Factors caused the collapse:

o Water caps over the fire-proofing concrete of bad design letting water penetrate between the steel beams and the concrete.

o Vertical cracks on the concrete let water in.

o Repairs had been done to the concrete, but without good workmanship. The new concrete has not adhered to the old concrete, letting water in.

o Deluge system had been tested with salt water, increasing the possibility of corrosion.

Factors

Root cause: bad and lazy maintenance system, added to a bad administration and lack of knowledge in inspection and maintenance services.

A proper maintenance and a suitable inspection plan are major factors on the conditions of the equipment. Inspection should be performed by qualified personnel, to avoid the sad happening which took place after a series of inspections that approved the vessel conditions.

Some actions to be taken to avoid future accidents: • Water caps shall be designed, fabricated and

installed to ensure tightness and avoid infiltration that will cause corrosion.

• Fire protection shall be installed criteriously to reduce the gap between the leg beams and the concrete to a minimum.

• Fire protection shall be of good quality and regularly inspected.

• Peep holes at the top of the legs shall be seal welded before the water cap is installed.

• Legs shall be inspected by qualified companies and inspection reports shall be verified and approved.

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Forms of Corrosion

General Corrosion Localised CorrosionEnvironmentally Induced Corrosion

•Stress Corrosion Cracking

Mechanically Assisted Corrosion

Metallurgical Influenced Corrosion

• Pitting

•Atmospheric corrosion

When Metal Corrodes??1. When there is Anode

2. When there is Cathode

3. When there is electron path connecting anode and cathode

4. When there is ionic path/electrolyte.

metal + oxidizing agent→ oxidized metal + reducing agent

For example, the corrosion of iron in the presence of hydrochloric acid

Fe + 2 HCl (s) (aq) → FeCl 2(aq) + H2(g)

Anode Reaction

•Oxidation occurs – corrodes

•Produces electron (e-)

•Produces cations ( positive-charged species)

Examples: Zn Zn 2+ + 2e-

Fe Fe 2+ + 2e-

All redox reactions consist of two partial reactions, also sometimes called halfcell reactions: the partial oxidation reaction, also referred to as the anodic partial reaction; and the partial reduction reaction or cathodic partial reaction.

Cathodic Reaction

•Reduction occurs.

•Consumes electrons

•Produces lower valency species

2H+ + 2e- H2 Hydrogen evolution

O2 + 2H2O + 4e- 4OH- Oxygen reduction, neutral/basic solution

O2 + 4H+ + 4e- 2H2O Acid solutions

Chemical reactions = elements are added or removed from chemical species. No change in valence

Electrochemical = chemical reactions + change in valence

Example : Precipitation of iron hydroxide (Fe (OH)2)

is pure chemical reaction

Fe 2+ + 2 OH- --- Fe(OH)2

Chemical vs Electrochemical Reactions

Atmospheric corrosion: Brown RustFe2O3·H2O or hydrous ferrous oxide,

• Fe3O4·H2O or hydrated magnetite, also called ferrous ferrite(Fe2O3·FeO), is most often green but can be deep blue in thepresence of organic complexants.

• Fe3O4 or magnetite is black.

White Rust

Gray/black Film

Degradation/Corrosion Failures

Failures come in many different forms!

Corrosion management : different mechanisms for inspection and monitoring

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Method of Corrosion Protection

Corrosion Control

Electrochemical Process

Anodizing

Electrodeposition

Chemical Process

Chemical Conversion Coating

Electroless Deposition

Chemical Vapour Deposition

Physical Vapour Deposition

Surface Coating Inhibitor Material Selection

Cathodic

Anodic

Another Corrosion Cycle

The problems arising from short-sighted corrosion control strategies have been particularly well articulated by Joe C. Bowles (a former president of NACE International) in the so-called corrosion cycle. Four phases were identified in this cycle:Phase 1 - Neglect: Corrosion control is ignored; this may be "tempting" to (poor) management as corrosion problems may not show up immediately. It is easy to be lulled into a false sense of security.

Phase 2 - Panic: The previously hidden corrosion danger becomes apparent, possibly with disastrous financial consequences and safety hazards. It is not easy to combat corrosion rationally and effectively in a state of panic.

Phase 3 - Learning Curve: In dealing with the serious corrosion problems, effective corrosion control measures are eventually introduced and failure rates are reduced to manageable levels. Considerable effort (and time) may be required before effective solutions are found, qualified and implemented.

Phase 4 - Unlearning Curve: Once the initial crisis is over, there is a risk that corrosion control will be neglected again and that hard lessons learnt in the past will be forgotten. This is when the corrosion cycle starts all over again, with the neglect stage re-establishing itself.

General bibliography1. M. Fontana, Corrosion Engineering, 3rd edition, McGraw Hill

International Edition,New York, 1987, 556 pp.

2. H. H. Uhlig, R. W. Revie, Corrosion and Corrosion Control, 3rd edition, JohnWiley, New York, 1985, 441 pp.

3. G. Wranglen, An Introduction to Corrosion and Protection, Chapman and Hall,London, 1985, 288 pp.

4. Jones, Principles and Prevention of Corrosion, Prentice Hall

Thank youThank you