Aging aircraft fleets are experiencing increased structural failures, excessive maintenance costs, and increasing down time due to corrosion. The effects of undetected and untreated corrosion can lead to catastrophic consequences, and this is especially true of older aircraft which may suffer from cumulative corrosion and fatigue damage.
This course presents both fundamental principles and practical instruction in corrosion theory and control as it applies to aircraft airframe corrosion. The subject of high-temperature corrosion of components is introduced and the lectures emphasize corrosion events viewed from time-dependent, time-related, and time-independent mechanisms. The specific types of corrosion are noted for their severity, frequency, and cycle dependency. Time-dependent corrosion, such as pitting, exfoliation, and crevice corrosion, will—if not prevented or controlled—accumulate to unsafe limits. With time, corrosion may cause the degradation of airframe structures and engine components to unacceptable levels. The effects of corrosion, however, are not just time-dependent but can affect airworthiness at any age. The events of environmental embrittlement, including stress corrosion cracking, can occur anytime, producing failure without warning.
The course covers prevention of corrosion failures based on proper design, materials and processes selection, and the use of corrosion preventive compounds (CPCs). It begins with a lecture on elementary electrochemistry as applied to corrosion and an introduction to fracture mechanics. Subsequent lectures define and discuss types of aircraft corrosion, identification of corrosion and corrosion-prone areas, and corrosion prevention and control. The important topic of combined effects of corrosion and stress, monotonic, sustained, and cyclic stresses are given special emphasis. The course also examines state-of-the-art products, procedures, and techniques for aircraft corrosion control used by both the military and civilian sectors.
The text, Corrosion Engineering: Principles and Practice, Pierre R. Roberge (McGraw Hill, 2008), and lecture notes are distributed on the first day of the course. The notes are for participants only and are not for sale.
Coordinator and Lecturer
Paul N. Clark, Ph.D., Principal Engineer, Southwest Research Institute, San Antonio, Texas – Hill Air Force Base Extension and Adjunct Professor, Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah.
Dr. Clark is considered a subject matter expert in the areas of fatigue and corrosion of aging aircraft, crack growth mechanisms, damage tolerance and fracture mechanics. Life prediction, risk analysis, failure evaluation, failure prevention, experimental protocol development and test planning are other areas of expertise. He works in concert with United States Air Force ASIP (Aircraft Structural Integrity Program) managers to provide engineering services and continuity to continually evolving programs. Fleet-wide trending and risk projections as well as failure investigations pave the way for new structural inspections as well as repair designs, modifications, redesigns and analyses.
Additionally, Dr. Clark serves as an Adjunct Professor for the Department of Mechanical Engineering at the University of Utah in Salt Lake City where he has mentored dozens of graduate students and engineers through challenging programs geared toward developing solutions for today’s structural integrity and aging aircraft challenges.
Pierre R. Roberge, PhD, PE, Professor, Department of Chemistry and Chemical Engineering, and Associate Dean of Continuing Studies, Royal Military College of Canada, Kingston, Ontario. Dr. Roberge’s research activities cover a wide spectrum of topics, from the development of accelerated tests for the characterization of the corrosion resistance of metallic materials to the design and development of information systems. Specific areas of interest include life prediction and reliability analysis; failure mode characterization and corrosion modeling for materials performance; analysis of causes and remedial actions for preventing future failures; corrosion monitoring, system design, implementation, and analysis; and information and knowledge-based systems.
Dr. Roberge has worked as a research scientist, engineer, or advisor on different Canadian Defense projects and for various industries on subjects related to the performance of materials in service, corrosion engineering, and the production of energy with electrochemical power sources (fuel cells, batteries). His recent consulting clients include Alcan International (Ontario), American Bureau of Shipping (ABS), American Water Works Association (AWWA), Detra Builders (Ontario), Electric Power Research Institute (EPRI), EnviroTower (Toronto), Fenclo Ltée (Québec), Hydro Quebec (LTEE) (Québec), Lauralco (Québec), Magna Powertrain (Ontario), NACE Foundation, Nickel Institute (NI), Peacock Engineering (Montreal), and Trojan Technologies Inc. (Ontario). He has also recently served as an expert witness for Chevron v. Amercoat (Canada), North York v. Toronto Transit Commission (TTC) (Toronto), Norton v. Ultramar Ltd. (Ontario), and Sun Pac Foods v. Domtar Ltd. (Ontario).
Dr. Roberge is the author or co-author of more than 100 scientific publications in journals and book chapters, as well as nearly 200 papers in conference proceedings. He also is the author of Handbook of Corrosion Engineering (McGraw-Hill, 2000), now also published in Chinese; the last of NACE Corrosion Testing Made Easy books entitled Erosion-Corrosion ; the second edition of Corrosion Basics: An Introduction (NACE International, 2006), a landmark textbook in corrosion science and engineering; and is the webmaster of the popular Corrosion Doctors website.
Dr. Roberge is a member of the American Society for Metals (ASM), American Society for Testing of Materials (ASTM), International Standard Organization (ISO), NACE International (NACE), and Professional Engineers Ontario (PEO).
Introductions and Course Overview
Fundamentals of Electrochemistry
Course overview and objectives; elementary electrochemistry as it applies to corrosion theory; polarization and polarization plots to determine corrosion potentials and currents. Aspects of thermodynamics of corrosion and kinetics of corrosion. Corrosion Doctors website. Handbook on corrosion.
(Clark) A brief history of aircraft structural fatigue and structural integrity experience and requirements from early aircraft to current aircraft. Basic fatigue mechanisms and fracture mechanics background.
Types and Mechanisms of Corrosion
Descriptive mechanisms and discussion of general attack: pitting, intergranular corrosion, exfoliation, crevice corrosion, galvanic corrosion, filiform corrosion, and microbiological corrosion. Examples for aircraft
Aspects of fatigue related to environmental effects on fatigue and structural integrity. Fundamentals of fracture mechanics with emphasis on environmental effects on fatigue and structural integrity. The introduction of linear elastic fracture mechanics and its simplifications for course use. The effects of the corrosive environment on the basic fatigue behavior and threshold stress intensities and crack growth rates in both sustained load environmental effects (stress corrosion) and cyclic load environmental effects (corrosion fatigue).
Stress Corrosion and Embrittlement Mechanisms, High-Temperature Corrosion
Electrochemical and metallurgical aspects of stress corrosion cracking, hydrogen embrittlement, and liquid metal embrittlement as it applies to aircraft alloys subjected to the effects of stress and environment simultaneously. The introduction of high-temperature corrosion mechanisms, including oxidation, sulfidation, and hot corrosion as it affects aircraft engines and components. Examples.
Design Criteria for Structural Integrity Control, including Corrosion Effects on Structural Integrity
The application of fracture mechanics design criteria and the damage tolerance Continuation of structural integrity design criteria with emphasis on modeling the damage process. Holistic structural integrity concepts.
Design Criteria for Structural Integrity Control with Emphasis on Corrosion
Continuation of structural integrity design criteria with emphasis on modeling the damage process. Holistic structural integrity concepts.
Aircraft Corrosion Control/NDI
The use of state-of-the-art products, procedures, and techniques for aircraft corrosion prevention and control, including dehumidification, corrosion prevention compounds, and coatings. “On-the-horizon” products and inspection tools.
Summary and Wrap-Up
(Roberge and Clark)
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