Fundamentalsof CorrosionNov2012
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Transcript of Fundamentalsof CorrosionNov2012
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Welcome to Universiti Teknologi PETRONAS
© 2011 INSTITUTE OF TECHNOLOGY PETRONAS SDN BHDAll rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner.
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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
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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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Understand the fundamentals of corrosion
COURSE OBJECTIVE
Explain thermodynamics and kinetics of corrosion
Perform corrosion measurement using standard procedures
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FUNDAMENTALS of CORROSION : Part 1 -An Introduction to the world of corrosion
|Centre for Corrosion Research |Block I |
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Why Metals Corrode?
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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
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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
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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
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Examples of Corrosion Phenomena
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Offshore 8" Pipeline
Corrosion Pits
due to SRB
LP Riser
Onshore Pipeline Section
Lack of maintenance !!
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Smart Flange
Severe corrosion at risers
R4
Lack of maintenance !!
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Corrosion Under Insulation
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Aboveground storage tank
Lack of maintenance !!
Emulsion line
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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.
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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
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• 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
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What are the worries?
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Collapse of Sphere
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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
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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.
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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
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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.
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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)
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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.
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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
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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
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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.
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White Rust
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Gray/black Film
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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
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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.
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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.
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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
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Thank youThank you