This Special Issue of the AMPTIAC Quarterly is something that

I’ve wanted to do for quite some time. As you may recall from

an earlier Special Issue (Vol. 7, No. 4), corrosion costs our

country an unbelievable amount of money. A few years ago the

US Federal Highway Administration commissioned a study to

quantify corrosion’s toll on the nation’s economy - the result

was a staggering $276B annually across 26 sectors, with

Defense accounting for $20B of this cost. While some may

question the accuracy of these estimates, the scale of the problem is beyond dispute as the amount of funding expended each

year to repair or replace corroded assets is massive.

In response to Congressional direction, the DOD elevated the

fight against corrosion to a department-wide level by establishing the Office of Corrosion Policy and Oversight. This new

office was chartered to integrate the many corrosion activities of

the Services under a unified banner by transcending the traditional organizational stovepipes and cultural boundaries. To

implement its strategies, the Corrosion Office turns to its action

arm, the Corrosion Prevention and Control Integrated Product

Team (CPC IPT). This team is charged with developing and

executing the plans, procedures, and roadmaps to address many

of the larger corrosion issues facing the Department. By directing resources, the CPC IPT is attacking the difficult-to-solve

problems affecting military systems and infrastructure; many of

which have the potential for large returns on investment. Using

guidance developed by the CPC IPT, new acquisition programs

are now beginning to plan for corrosion prevention and control

up-front. This measure will help reduce future life-cycle costs

tremendously, however, more still needs to be done.

Some two decades ago, while working towards my Bachelor’s

degree in mechanical engineering at a major university, I was

one of only three students from the ME department that took

a formal corrosion course as an elective. All the students in 

the department had some exposure to corrosion, which was

covered in a required elementary materials science course.

However, the instruction we received in this class discussed

what corrosion is, and not how to select materials and technologies to prevent its occurrence. Two and a half years ago, when

AMPTIAC first joined the CPC IPT, I began to wonder if my

experience was indicative of how designers are trained today. I

had my staff conduct a study to investigate the state of corrosion education at our top colleges and universities. Using US

News and World Report’s 2004 listing, we identified the ten

top four-year engineering colleges and doctorate-granting universities. We examined their mechanical engineering curricula

and found that my initial observations from twenty years ago

remain true today. The overwhelming majority of colleges and

universities teach designers, as exemplified by mechanical engineers, what corrosion is, not how to prevent it. Since designers

make the vast majority of material selection decisions, I felt it

important that AMPTIAC publish an entire issue of the Quarterly which targets the design community and other interested

parties, and focuses on improving corrosion resistance by

increasing its consideration during material selection.

While conducting research for this issue of the Quarterly, we

may have discovered why corrosion prevention and control,

from a material selection standpoint, isn’t taught to designers.

It’s because material selection that focuses on corrosion prevention and control can follow many different paths. It’s not a single process per se, but is more akin to a discipline, which creates

a quandary: how do you teach an entire discipline to designers

who will only use it sporadically throughout their careers? To

help resolve this plight we developed this Special Issue of the

Quarterly with the intent that it will become a designers’ desk

reference. For this issue, we have taken the major elements of

corrosion analysis independent of path, and assembled a generic process that designers can consider during material selection.

Moreover, we point to sources of data designers can use to

make informed decisions, while also highlighting the major

issues. While this template certainly can’t replace the knowledge acquired through formal training, it does serve to improve

awareness about the need to consider corrosion in design. It

also provides a road map of the necessary considerations to

make during a material selection activity. Taken as a whole, the

body of knowledge within this publication will help designers

reduce the impact of corrosion to future systems.

Dave Rose

AMPTIAC Director

Editorial: 

The Key to Reducing Corrosion Costs Lies in Material Selection

The AMPTIAC Quarterly is published by the Advanced Materials and Processes Technology Information Analysis

Center (AMPTIAC). AMPTIAC is a DOD-sponsored Information Analysis Center, administratively managed by

the Defense Technical Information Center (DTIC). Policy oversight is provided by the Office of the Secretary of

Defense, Director of Defense Research and Engineering (DDR&E). The AMPTIAC Quarterly is distributed to

more than 15,000 materials professionals around the world.

Inquiries about AMPTIAC capabilities, products, and services may be addressed to 

David H. Rose

Director, AMPTIAC

315-339-7023

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URL : http ://amptiac.alionscience.com

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About the Cover: An MV-22 Osprey rising into the salt-laden atmosphere above the Atlantic Ocean illustrates the need to consider

the intended operating environment during system design in order to maximize long-term corrosion prevention. US Navy photo by

Photographer’s Mate Airman Zachary L. Borden.
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 3

THE DESIGN PROCESS: CORROSION STARTS HERE

A serious but often overlooked problem that has enormous cost

and safety implications is corrosion. Each stakeholder in the

design, development, sustainment, and system operation communities likely has a different perspective on the implications

of corrosion. From the standpoint of a system operator, corrosion often results in

excessive maintenance

time and reduced

readiness rates, while a

maintainer views corrosion as an issue that can require substantial financial and personnel resources. A program manager may worry about the cost

of planning for corrosion prevention and control and see it as

an issue that competes for budgetary resources with other technical considerations such as reliability or manufacturing. In

contrast, a manufacturer may experience reduced profits due to

poor reliability and associated warranty problems. A few years

ago Congress commissioned a study to investigate the costs of

fighting corrosion. The results of this study were astounding:

corrosion was estimated to cost the US $276B per year or

3.14% of the US GDP. In the Defense sector alone, corrosion

was estimated to cost approximately $20B per year.[1]

When considering these enormous costs one might ask, can’t

corrosion be eliminated or at least minimized to reduce the

burden that consumes so much of the Government’s budget

and our own paychecks?

From my perspective, one

of the reasons that corrosion

costs are so high is because

of the lack of coordination

between different engineering communities. In particular, poor communication between

materials/corrosion specialists and the design community contributes to the inadequate consideration of corrosion during the

design process. I firmly believe that the overriding factor

responsible for this communication barrier is the fact that

design engineering students (e.g. mechanical engineers) are not

adequately taught corrosion prevention and control (CPAC)

while learning their craft. Upon leaving college and entering

the workforce, many engineers know little about corrosion and

fail to see it as a critical design issue.

Undergraduate studies in mechanical engineering, for example, often offer students little more than a brief introduction to

corrosion. The introductory coursework typically focuses upon

the forms of corrosion themselves, not the process of designing

corrosion resistant components or structures. The result of this

educational deficiency is that practicing designers typically have

some understanding of the galvanic and uniform (traditional

rust) forms of corrosion, but little or no awareness of the multitude of other forms that are far more difficult to detect and

prevent. Many of these other forms are localized and may be

hidden such that they can go undetected until failure occurs.

Design practices that incorporate corrosion prevention and

control during material selection is the most effective way to

develop components and/or systems that possess the desired

attributes to ensure reasonable life-cycle costs and acceptable

readiness rates.

A MULTIDISCIPLINARY CALL TO ACTION

Reducing the cost of corrosion requires engineers, and particularly designers, to break out of their comfort zones and more

fully consider the technology and knowledge resources available

to them from other technical communities. Designers need to

think outside their own discipline and reach out to the materials community; in essence they need to pull the corrosion solutions to them. But in order to do so, they must realize that a

problem exists in the first place. Reaching this level of understanding alone will be a breakthrough.

The United States Government has spent billions of dollars

on research and much of the information generated can be used

by designers to help reduce risk on current projects. Available

are hundreds of thousands of materials-related technical reports

and other information resources that cover a broad range of

subjects including various applications, environments, as well

as system performance under various conditions. Over the

years, the materials community has tried to push this technology and information to users, especially designers, but have had

only limited success. The recent study on the cost of corrosion

should be a wake up call to the entire engineering community.

We must change the way we design new systems, so that the

products we develop are made to be more durable and resistant

to corrosion. This is the one sure way we can strategically

reduce corrosion costs.

Reducing the cost of corrosion is not something that any one

individual or group can do on their own. As mentioned earlier,

the most important aspect is for the design community to recognize the problem and subsequently take steps to rectify it.

One of the steps that must be taken is to update undergraduate engineering curricula to ensure that engineers coming out

of college are armed with the tools and knowledge needed to

fight the corrosion battle during design, rather than having

to mitigate the problem later

when it becomes a costly sustainment issue. Likewise, the

materials community needs to

interact more directly with designers and provide them with the

technology solutions and data needed to produce corrosion

resistant equipment, systems, and structures. By working

Corrosion was estimated to

cost the US $276B per year

or 3.14% of the US GDP

Design engineering students

are not adequately taught

corrosion prevention and

control

The materials and design

communities can convert

the existing technology

push into a technology pull.

David H. Rose

AMPTIAC Director
4 The AMPTIAC Quarterly, Volume 9, Number 3

together, the materials and design communities can convert the

existing technology push into a technology pull, thus streamlining the process of implementing new technologies, which currently takes decades.

Breaking down the institutional and professional barriers

responsible for the inadequate consideration of corrosion prevention and control during design can only occur with the support

of the engineering professional societies. If the design-related

societies, such as ASME, IEEE and SAE, and the societies that

produce material selection type products, such as ASM International and NACE International, would work together in a cooperative enterprise, each of their individual constituencies would

benefit from the activities,

resources, and knowledge available from the others. If this

cooperation were to happen,

then we will have put into place

the processes needed to help

minimize the corrosion problems we currently face. Establishing

the necessary coordination between the participating societies

will not be easy. Furthermore, successful coordination will only

occur if the senior management from each society understands

that it’s in their best interest to cooperatively work together with

the common goal of solving a National problem.

PROPER MATERIAL SELECTION: THE KEY 

TO REDUCING LIFE-CYCLE COSTS

Unlike other design considerations such as fatigue, conducting a

corrosion analysis isn’t a straightforward process and it may be a

costly one since each form of corrosion is essentially a separate

failure mode that needs to be considered individually. The challenge that designers face is balancing the degree of detail put

forth in the analysis against their available resources including

time and budgetary concerns.

One might wonder why a practical, design-based material

selection process that considers corrosion prevention and control

hasn’t already been developed and subsequently taught to new

design engineering students. The following list identifies many

of the factors that contribute to the difficulty in developing a

simplified, readily understood process.

• There are multiple and often competing forms of corrosion

that need to be considered for every design.

• There are a vast number of material/operational environment

combinations, and each can form the basis for potential corrosion problems to occur.

• Corrosion data are overwhelmingly empirical, often widely

scattered, and come in a variety of forms. Since some data are

tabular, other types are graphical, and still others are entirely

qualitative, it makes it somewhat difficult to evaluate and

compare them with each other. 

• Corrosion data are specific to the material and the environment from which it was taken. The corrosion form and rate at

which it occurs varies with slight changes to the material’s

composition/processing history or the environment it’s

exposed to. Thus, corrosion data can be easily misapplied.

• Laboratory test data are not always reflective of how a material will behave in an application.

• Data may not be available for all potential forms of corrosion

that might pertain to a specific application/environment 

combination.

• Corrosion data often cannot be easily used to predict corrosion rates in field applications.

Because of its complexity, corrosion analysis is really more of

a practice or discipline, like reliability engineering, than a

process such as that used when designing fatigue resistance into

a structure. Since designers are routinely pressed for time and

operate under a strict budget,

they don’t often have the luxury of consulting with corrosion

specialists to verify many of the

decisions they make. The

impact of improper consideration of corrosion is exactly the

same as improper consideration of reliability: unanticipated

problems that result in reduced readiness and increased lifecycle costs.

Unanticipated corrosion problems will always occur, and correcting them requires a reactive approach using the services of a

trained specialist to determine the best way to mitigate the problem. Corrosion can be minimized if the design community

proactively considers corrosion resistance early during system

design when material selection has not been ‘locked in’. Improving material selection practices to fully consider corrosion prevention and control will reduce total ownership costs and enable

affordable life extension – two important attributes that DOD

program managers and their prime contractors should consider.

One critical issue to understand when selecting materials is that

you will seldom find

the ‘perfect’ material,

since most materials

will corrode when

exposed to corrosive

conditions. Rather the

goal is to identify the

best material and associated corrosion prevention and control

practices that meet your expected budget for material acquisition

and life-cycle costs.

This issue of the AMPTIAC Quarterly is devoted to the subject of corrosion prevention and control with a special emphasis

on material selection. We are currently writing a book entitled

“Corrosion Prevention and Control: A Program Management

Guide for Selecting Materials.” Included in the book is a chapter on material selection, which the following articles are largely

based upon. The book will be available in the Spring of 2006.

The following article on material selection and the others on

corrosion-related failure modes (MaterialEASE) and corrosion

rules of thumb form the basis for improving consideration of

corrosion during design. By reading all of these articles a designer will gain a better appreciation for the corrosion analysis

process and where they might go to get the data needed to

ensure they develop corrosion resistant designs.

REFERENCE

[1] G.H. Koch, M.P.H. Brongers, N.G. Thompson, Y.P. Virmani, 

and J.H. Payer, Corrosion Costs and Preventative Strategies in the United

States, Federal Highway Administration, FHWA-RD-01-156, September 2001

Corrosion analysis is more

of a practice or discipline

than a process

Improving material 

selection practices to fully

consider corrosion prevention and control will reduce

total ownership costs

Professional Societies need

to work together with the

common goal of solving a

National problem
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 5

INTRODUCTION

In a perfect world, materials engineers and corrosion specialists

would always assist designers with material selection tasks to

ensure that components and systems are designed with longevity in mind. In the real world, however, this not always the

case. Designers typically select the materials of construction

themselves, with these decisions based on meeting critical 

performance requirements. Other factors, such as corrosion

prevention and control, are often given minimal consideration.

A material’s inherent corrosion resistance is largely determined by its elemental composition, but also by its processing

history, surface morphology, geometry, and in some cases its

size. Consequently, two very similar materials may have quite

different resistances to corrosion. Selecting the ‘best’ material,

from a corrosion standpoint, is not a cut-and-dried process.

Numerous factors need to be considered and there is no single

path to making an informed selection. Ultimately, designers

must rely upon their best ‘engineering judgment’ to select the

optimum material, considering corrosion resistance in balance

with other performance requirements, as well as other tangible

factors, including cost, availability, and maintainability.

It is important to realize that one will seldom find the ‘perfect’ choice, since most affordable commercial materials will

corrode under the right set of conditions. Instead, designers

should identify the material and associated corrosion prevention and control practices that meet the program’s budgetary

constraints, while also ensuring acceptable corrosion resistance

over the system’s life-cycle. This strategy will help to ensure that

corrosion-related maintenance requirements are minimized

and predictable, thus reducing overall life-cycle costs and

increasing system readiness rates. Reasonable (and budgeted)

life-cycle costs and high readiness rates (due to reduced maintenance requirements) are two of the most important contributions to lower operating costs, while ensuring long system

service lives and increased safety.

CORROSION PREVENTION AND CONTROL: 

THE RUST STOPS HERE

Most would agree that corrosion is a serious problem, but opinions differ greatly about how to address it. Many mistakenly

believe that corrosion is a maintenance problem – an unavoidable part of doing business. The truth is more sobering: most

corrosion that occurs in military and commercial systems could

have been avoided. While not the intent, many systems were

inadvertently designed to corrode because little or no consideration was given to corrosion prevention and control (CPAC)*

during the material selection phase of the design activity. 

One reason designers pay so little attention to CPAC is that

they have minimal experience in considering corrosion issues.

As mentioned in the previous article, “Designers Take Note!

Improved System Corrosion Resistance Reduces Life-Cycle

Costs,” design engineers typically receive almost no training on

the subject while in college. It is also true that corrosion science

is a complicated matter that doesn’t easily lend itself to the

development of a simplified analysis process. Most material

performance criteria can be expressed numerically, in terms of

a threshold, a range, or even an equation. Choosing material

candidates to meet these requirements is usually a straightforward process. Considering corrosion and CPAC strategies is a

highly qualitative process that requires circumspection. Engineers must not only balance potential benefits against other

performance parameters, but must also consider the longerterm attributes – service life, anticipated maintenance and

repair, and disposal to name a few.

As these issues are complex and not in any way straightforward, it is easy to see why corrosion is overlooked in design,

and is thus passively relegated to the operation and maintenance world. This article provides designers with a rudimentary ‘road map’ covering the major steps needed to assess whether

a new design may be susceptible to corrosion and how potential problems can be effectively mitigated or eliminated. Following these steps during material selection, even without

being an expert in corrosion, should help to reduce the

instances and extent to which corrosion occurs. In critical situations where corrosion can’t be tolerated at all, it’s still best to

involve a professional that has the credentials to ensure that all

aspects of the design are thoroughly investigated.

The other articles published in this issue of the AMPTIAC

Quarterly provide additional detail concerning the forms of corrosion and the approaches that can be used by designers to

reduce future corrosion problems. Bear in mind that the information presented here is not exhaustive. More will be required

before one can confidently conclude that a design will stand the

test of time. For this reason we provide a listing of data sources

that can be consulted to find the additional information needed to complete a corrosion analysis.

David H. Rose

AMPTIAC Director

David J. Brumbaugh

Benjamin D. Craig

Richard A. Lane

AMPTIAC Staff
6 The AMPTIAC Quarterly, Volume 9, Number 3

Identify Initial Slate of Candidate Materials

Figure 1 is a generic process for screening materials in a representative design situation. The body of this article parallels the

steps in the flowchart, from developing a list of candidate materials through final selection. Via a host of traditional means,

designers can readily identify a slate of candidate materials possessing the necessary physical, mechanical, thermal, and/or

electrical properties to meet requirements. The challenge comes

in ensuring that these candidates are scrutinized for their corrosion resistance as well when selecting the best overall candidate

(Figure 2). 

Depending upon the criticality of the application and the

design process being employed, the number of materials chosen

as initial candidates will vary. The advantage of considering more

materials is that it would be more likely that an appropriate candidate could be identified to meet traditional requirements as

well as provide some level of corrosion resistance. The disadvantage is that such an analysis could be more costly. For highly

important decisions with strict deadlines, analyzing multiple

materials simultaneously would be the most efficient approach as

it would minimally impact the project schedule. For less critical

applications it may be more practical to perform a comprehensive corrosion analysis on just a single material instead.

Screen Materials Based on Past Experience

After determining the material(s) to be considered, the next

step is to look at whether there have been corrosion problems

in similar applications to that being designed, and to ascertain

what caused those problems to occur. The cheapest thing to do

(from a life-cycle cost standpoint) is to eliminate from consideration any material that has caused corrosion problems in a

similar application in the past, especially those problems that

couldn’t be controlled using affordable CPAC practices and

associated maintenance procedures. One method to determine

whether ‘legacy’ materials have corroded in a similar application is to analyze the literature to ascertain whether a particular

combination of material and application has been problematic

in the past. Another way is to consult senior personnel, those

‘old-timers’ that may have extensive experience with the design,

production, and sustainment of similar legacy applications.

Figure 1. Generic Process for Selecting Materials to Improve Corrosion Resistance – A Roadmap to Life-Cycle Cost Reduction.

Identify past corrosion failure modes in similar applications

• Gather & analyze literature

• Consult senior personnel

Eliminate the material(s) 

from the candidate list

Conduct environmental assessment

Screen Materials

Based on

Past Experience

Select 

new 

materials

Find 

materials 

that 

perform 

better

Down-select

Final Material

and CPAC Method

Conduct 

Environmental

Assessment

Yes

Yes No

No

Discount unlikely forms of corrosion

No

Identify potential corrosion failure modes

• Perform analysis of literature

• Perform corrosion testing

Eliminate the material(s) 

from the candidate list

Yes No

Yes

Yes

Identify Initial Slate of Candidate Materials

No

No

Evaluate Materials

Based on 

Potential Corrosion

Failure Modes

Select CPACs

Methods

Assess 

Other Factors

Yes

Are there any 

problematic 

materials?

Are there any 

materials left?

Are there any 

problematic 

materials?

Are there any 

materials left?

Are any 

CPAC methods 

needed?

Are these 

results 

acceptable?

Yes Select candidate CPAC method(s)

Evaluate availability and maintainability

Perform cost analysis

No

Use engineering judgment to prioritize, rank, and select optimum material and CPAC method(s)
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 7

Figure 2. Material Property

Needs are Derived from System

Performance Requirements.

Conduct Environmental Assessment

The next step in the process is to immediately discount the

forms of corrosion that are unlikely to occur. As an example,

erosion corrosion occurs when a corrosion prone material is

exposed to a flowing corrosive fluid. If the application being

designed will not be exposed to a flowing fluid, then erosion

corrosion is irrelevant and can be discounted. To determine the

more likely forms that will occur, the analyst should examine

the factors responsible for initiating each corrosion mode and

then determine which ones are present in the application being

designed. Our article, “Corrosion Rules of Thumb: Material

Selection Considerations for Various Forms of Corrosion,” provides examples of this information.

After a candidate material (or materials) has been selected

and the obvious problematic materials have been rejected, the

next step is to analyze the environment in which the application will operate. When considering the operational environment many may automatically consider exposure to

atmospheric, industrial, or marine conditions as the corrosion

inducing factors. While important, such a global or ‘macro’

view may be too restrictive since conditions imposed by the

configuration and operation of the system may result in corrosive microenvironments that need to be considered. For

instance, the build-up of scale within storage tanks and piping

may result in situations where corrosive ions can accumulate

and precipitate hidden corrosion. The same can be said for

structural details used in the construction of a system including

lap joints, gaskets, and enclosed places that cannot be accessed.

These design details and operational conditions are known to

concentrate ions, thus creating a corrosive microenvironment

within certain regions of an application.

Designers should thoroughly analyze the operating conditions the entire system will be subjected to and determine the

potential combinations of design details, temperature, humidity, and chemical exposure that may be present at all points. The

designer should also consider the conditions the system may

experience throughout its life-cycle including maintenance,

storage, and transportation. For example, Army ground vehicles are designed to spend their service lives on dry land, but the

few weeks spent lashed to the deck of a ship while being transported over the ocean can easily initiate corrosive actions that

can rapidly destroy them. When conducting the corrosion

analysis, designers should consider both the micro- and

macroenvironments to determine the specific conditions that

candidate materials will be exposed to during their service. 

A comprehensive analysis of the operating environment can

be an extensive undertaking. Therefore, depending upon the

time and resources available, the extent of the analysis could

range from general to detailed using a tiered approach. It is

most important to first define the general operating conditions

(e.g. atmospheric, immersed in liquid, buried, etc.). From there

more detail can be added on: industrial atmospheric, tropical

seawater, etc. A detailed environmental assessment could

include specifics on pH, pollutants present, temperature, and

other relevant factors. Design details should not be overlooked

since they certainly can initiate the microenvironments responsible for triggering specific corrosion modes.

Evaluate Materials Based 

on Potential Corrosion Failure Modes

Once the candidate materials and the environmental conditions have been determined, the analyst must investigate the

potential for one or more of the many forms of corrosion to

become active. There are several forms of corrosion that should

be considered.

• Uniform corrosion

• Galvanic corrosion

• Crevice corrosion

• Pitting corrosion

• Intergranular corrosion

• Selective leaching 

• Erosion corrosion

• Stress corrosion cracking (SCC)

• Corrosion fatigue

• Fretting corrosion

• Filiform corrosion

The MaterialEASE entitled “A Brief Tutorial on Corrosion

Related Material Failure Modes” found in this issue of the

AMPTIAC Quarterly discusses many of these corrosion forms

and provides a summary of the causative factors responsible for

activating them. There are also some other forms of corrosion

that are less common than those listed above. Additional data

relating to the various forms of corrosion can be found by

reviewing the literature including reference books, handbooks,

and technical reports. Unfortunately, it is seldom the case that

all of the data needed to conduct an analysis can be found in

one reference.

At this point in the process the designer is left with at least

one candidate material and a listing of corrosion modes that

must be considered in the analysis. They also now know the

application’s anticipated environmental conditions. Since the

scope of the analysis has been defined, one can assess whether

any of the potential forms of corrosion may become active

when the candidate material is subjected to the operational

environment. If time allows the best way to investigate both of

these issues is to perform an analysis of the literature.

System 

Performance

Requirements

Required Material

Properties (Traditional)

• Physical

• Mechanical

• Electrical

• Thermal

• Other

Mission 

Objectives

Corrosion

System requirements define what performance levels are needed from constituent materials.

If life-cycle issues are to be addressed as part of a system‘s overall set of requirements, then 

corrosion and other time-dependent material properties must be considered.
8 The AMPTIAC Quarterly, Volume 9, Number 3

The DOD and other Government agencies have invested

considerable funds into researching corrosion modes, and mitigating their effects in existing applications. Much of this work

has been recorded in technical reports that are available from

AMPTIAC and from our sponsor, the Defense Technical Information Center. NASA and DOE also have extensive corrosion

resources. These and other sources for corrosion information

are summarized in Tables 1 and 2. The reports available from

these organizations are excellent sources of relevant data to consult when performing material selection. In many cases they

contain “lessons-learned” information that discusses corrosion

in applications and operational environments that may be similar to the designer’s current interests. Other sources of information include reference books and handbooks. These sources

typically have very good data related to coupon level testing, as

well as discussions on problematic materials. Unlike technical

reports that address very specific issues that may be relevant to

program needs, these resources typically offer more general

information.

The information needed to identify and eliminate problematic materials from consideration can be found in the

technical literature. Literature investigations are also useful

for identifying design details to be avoided and for helping

select the appropriate CPAC practices needed to protect the

chosen material and ensure that it performs as desired. It’s

important to perform these investigations to preclude unacceptable life-cycle costs or catastrophic failure from occurring.

In some situations it might be the case that corrosion susceptibility data concerning a specific material being considered

doesn’t exist. In these situations it may be necessary to perform

corrosion testing to ascertain the candidate material’s behavior

in the intended environment. However, the cost of conducting

the tests, as well as the time needed to get them done, must be

carefully considered since they could affect the development

schedule. There have been many past instances where designers

simply assumed that the needed data didn’t exist, so they either

neglected the analysis completely or they jumped directly into

corrosion testing. This can be a wasteful strategy since the literature is rich with corrosion data.

Following the completion of the literature analysis and/or

testing program one should have adequate information to reject

any problematic materials, thus yielding a listing of candidate

materials that meet performance requirements while simultaneously possessing acceptable corrosion resistance. Please note

that a material with ‘acceptable’ resistance may still corrode

when exposed to the operational environment (but less severely and at a slower rate). CPAC materials and practices might

still be needed to provide the desired overall performance.

Select Corrosion Prevention and Control Methods

Perhaps even more daunting than selecting the actual material

of construction is choosing the corrosion prevention and conTable 1. Listing of Corrosion Information Sources.

Information Sources Source Description Internet Address

DOD Advanced Materials and Processes Technology Technical Library & http://amptiac.alionscience.com/InfoResources/docsearch.html

Information Analysis Center (AMPTIAC)a NAMIS Database http://namis.alionscience.com/

Defense Technical Information Center (DTIC) Public & Private http://stinet.dtic.mil/info/s-stinet.html (public STINET)

STINET Database http://www.dtic.mil/dtic/registration/index.html 

(Private STINET-limited distribution documents)

Department of Energy (DOE) Energy Citations Database http://www.osti.gov/energycitations/index.jsp

National Aeronautics and Space Administration (NASA) Aeronautic & Space Database https://www2.sti.nasa.gov/login/wt/

Technical Reports Server http://ntrs.nasa.gov/

Federal Aviation Administration (FAA) Library Search Engine http://www.faa.gov/library/ 

National Institute of Standards and Technology (NIST) NIST Webspace Keyword http://www.nist.gov/search.htm

Search Engine

NACE International (The Corrosion Society) NACE Store Product http://www.nace.org/nacestore/search.asp

Search Engine

ASM International (The Materials Information Society) ASM Website Search Engine http://www.asm-intl.org/ 

SSPC (The Society for Protective Coatings) SSPC Online Store http://www.sspc.org/books/bookstore.html

Search Engines

SAE International (Society of Automotive Engineers) SAE Website Search Engine http://www.sae.org/jsp/jsps/advancesearch.jsp

SME (The Society of Manufacturing Engineers) SME Website Search engine http://www.sme.org 

ASTM International (source for standards) ASTM Standards Search Engine http://www.astm.org 

ISO (International Organization for Standardization) ISO Store http://www.iso.org/iso/en/prods-services/ISOstore/store.html 

ASCE (American Society of Civil Engineers) ASCE Online Research Library http://www.ascelibrary.org/ 

ECS (Electrochemical Society) ECS Website Search Engine http://www.electrochem.org/search.htm

Swedish Corrosion Institute Webpage with Report Listing http://www.corr-institute.se/english/reports/Rep_list_e.html

a AMPTIAC will soon be merged into a new DOD Information Analysis Center (IAC), the Advanced Materials, Manufacturing, and Testing IAC (AMMTIAC). The Internet address 

will change at that time to reflect the new organization. US Government Data Sources Professional Societies & Other Sources
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 9 US Government Data Sources Professional Societies & Other Sources

Information Type of 

Number of 

Downloadable Free Service Access 

Source Information

Corrosion Available

PDFs? or Fee Based? Restrictions? Related Search

Reports & Engine?

Papers

AMPTIACa Papers, Reports, 22,271b Yes Yes (Limited) Partially free. Fee for subscription Yes, access to limited

Databases to controlled-access databases distribution portion of 

and for ordering hardcopiesc holdings is controlled

DTIC Papers, Reports 38,908b Yes Yes Fee for ordering hardcopies Yes, access to limited 

distribution portion of 

holdings is controlled

DOE Papers, Reports 56,763 Yes Yes Free Service No

NASA Papers, Reports 34,264 Yes Yes Fee for ordering hardcopies Yes, access to limited 

distribution portion of

holdings is controlled

FAA Papers, Reports >500 Yes Yes Free Service No

NIST Papers, Reports >1000 Yes Yes Free Service No

NACE Books, Papers, 74,000 Yes Yes Fee for downloading or No

Reports, Standards, ordering products

Databases, Videos

ASM Books, Papers, 140 Yes Yes Fee for downloading or No

Reports, Standards ordering products

SSPC Books, Papers, >100 Yes Yes Fee for downloading or No

Reports, Standards ordering products

SAE Papers, Reports 2671 Yes Yes Fee for downloading or No

ordering products

SME Papers, Reports 253 Yes Yes Fee for downloading or No

ordering products

ASTM Standards >700 Yes Yes Fee for downloading or No

ordering products

ISO Standards, Papers, 117 Yes Yes Fee for downloading or No

Books ordering products

ASCE Papers, Reports >350 Yes Yes Fee for downloading or No

ordering products

ECS Papers, Reports >1000 Yes Yes Fee for downloading or No

ordering products

Swedish Books, Papers, >150 No Yes Fee for downloading or No

Corrosion Reports ordering products

Institute

a AMPTIAC will soon be merged into a new DOD Information Analysis Center (IAC), the Advanced Materials, Manufacturing, and Testing IAC (AMMTIAC). The Internet address 

will change at that time to reflect the new organization.

b There is some overlap between the document holdings of the AMPTIAC and DTIC libraries.

c AMPTIAC currently has a scanning and database development project underway that will result in over 14,679 corrosion-related electronic documents being available for download from the AMPTIAC/NAMIS websites. Unlimited distribution documents will be free to download.

Table 2. Details Concerning Corrosion Information Sources.

trol technologies that may be needed to protect it. Some materials require no CPAC methods since they possess surface characteristics that make them resistant to corrosion. Stainless steels

are a good example of this. However, most metals (and some

other materials) need some form of additional protection from

the corrosivity of their operating environment. This article

makes no attempt to discuss when, where, and how to employ

CPAC methods in any particular design situation, as that has

already been the subject of many books (which are more comprehensive than anything we could hope to compile within

these pages). Having stated that, there are several strategies that

can be employed to protect a metallic material from corrosion

if and when necessary. A global view of these strategies is presented in Figure 3 and the sidebar on CPAC methods, shown

on pages 12 and 13. One such strategy is to construct a barrier

to prevent the corrosive environment from contacting the surface. Effective barriers include coatings, surface treatments, and

corrosion preventive compounds (CPCs) such as greases.

Another strategy is to modify the environment itself. Now

obviously this won’t work when a structure is exposed to the
10 The AMPTIAC Quarterly, Volume 9, Number 3

elements themselves, but corrosion can also happen inside a

structure or system, especially if it is totally enclosed. A good

example is a heating plant where steam is circulated from the

boiler to heat exchangers. The operational environment within

this type of enclosed system contains water, which certainly will

be laden with minerals and other contaminants that can initiate corrosion reactions. In these situations a chemical substance

known as a corrosion inhibitor can be mixed with the fluid to

reduce the corrosivity of the environment.

Another approach for reducing corrosion is to employ mechanisms that can modify the electrochemical processes that consume materials. Cathodic protection, either through the use of

sacrificial anodes or electronic impressed current devices, can

convert a material that normally will corrode quite readily into

a material that resists corrosion. This approach works very well

for protecting fixed assets, such as steel structures, pipelines,

and buried tanks. A final measure for reducing corrosion

involves maintenance practices. Routine cleaning can significantly reduce the instances of corrosion, but so too can the

reapplication of coatings and corrosion preventive compounds.

Removing the corrosive substances and other debris while also

ensuring the integrity of the protective barrier is one of the

most effective ways to reduce the severity of corrosion.

A complexity with selecting corrosion prevention and control methods is the seemingly infinite number of available

choices, especially coatings. It should be noted that a coating is

rarely a single material but more typically is a system of materials that includes primer and topcoat layers. Specific functional requirements, such as low observability or camouflage, may

dictate even more layers within the system. The important

thing to note is that the coating layers must be compatible with

each other and also with the metal structure or component

being protected.

When selecting coatings an important consideration is that

more durable ones typically come at a higher cost but offer

the promise of a longer life with reduced maintenance. However, in many cases choosing the most expensive technique,

even if it promises the best performance, may be unaffordable. If the component or system being designed can be easily repainted, then a less expensive and poorer performing

coating may suffice. On the other hand, if the component or

system is difficult to repaint, either through difficulty of

access or by operational needs that preclude taking the item

from service, then a better performing coating system is needed. A final consideration is that some classes of materials

might receive additional protection from a surface treatment

or metallic coating that’s applied prior to the primer/topcoat

layers. For example, aluminum structures are often treated

with an AlodineTM[†] conversion coating prior to being

primed and top-coated. Similarly, steel alloys are sometimes

galvanized. The use of surface treatments or metallic coatings

along with the subsequent application of primer and topcoat

layers provides the corrosion resistance needed to protect the

system or component while in service.

Assess Other Factors

Presuming that multiple materials were considered, the time

has now come to downselect the material that will ultimately be

used. Perhaps the most important thing to understand is that

one can seldom select a perfect material, but rather the goal

should be to find the least objectionable one. At this point a

thorough analysis of the initial candidates has been completed,

and most likely, several of the more problematic candidates

have already been rejected. Selecting the best of the remaining

candidates is based not only upon inherent corrosion resistance

and performance, but on a number of other factors including

product availability, maintainability, and cost.

Product Availability and Maintainability Analyses: Prior to

selecting the material and CPAC method that will be

employed, one must first determine whether they are available

as commercial commodities. Selecting the best CPAC method

will be of little value, if it’s too difficult to obtain in the 

quantities required for the production run. Maintainability 

is an equally important issue that relates more to the 

CPAC methods that will be employed. Some of the aspects to

consider include ease of application of coatings and CPCs,

maintenance intervals for reapplication, and ease of access 

to interior spaces for inspection and reapplication. Some 

areas of a structure or system may be difficult and prohibitively costly to access, so all maintainability aspects must be closely determined.

Figure 3. Material Property Needs are Derived from System Performance Requirements.

Initial Slate of Material Candidates

“Design-in“ Resistance

• Corrosion-resistant materials

• “Corrosion-smart“ designs

Higher upfront (acquisition) costs

Less maintenance/repair required

Lower life-cycle costs

Longer service life

Higher reliability

Higher readiness

Lower risk

Extending system life is

 easier to accomplish

A smart approach to corrosion control will provide a proper balance

of all four mitigation strategies in designing, building,

operating, and sustaining systems.

CPAC

Methods

Planned

Corrosion

Maintenance

Repair

or

Replace

Lower upfront (acquisition) costs

More maintenance/repair required

Much higher life-cycle costs

Shorter service life

Lower reliability

Lower readiness

Higher risk

Extending system life is

 more difficult to accomplish

All four strategies are needed for sucess, 

but the leftmost balance possible is best 

for maximizing system life-cycle.
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 11

Cost Analysis: Before conducting the cost analysis one must

first determine the life expectancy of the system or component

being designed. The strategies employed while conducting the

cost analysis differ depending upon whether the system or component will have a short or long life and whether it is a critical

or non-critical item. Corrosion may be tolerated to a greater

extent in short-lived and non-critical applications. In these situations the cheapest remaining material candidate and CPAC

method might be appropriate. Conversely, if the application

being designed is critical and failure cannot be tolerated, or if it

is a component that is expected to remain in-service for a considerable length of time, then far more thought and effort must

be given to selecting both the material and the CPAC method.

When designing critical structures/systems or those that are

expected to be operated for extensive periods of time, it’s

important to consider total ownership costs instead of focusing

solely on acquisition costs. Selecting the lowest priced candidate material and CPAC method may initially provide cost savings but as many programs in the past have learned, an

inadequate consideration of CPAC approaches during design

can ultimately lead to excessive maintenance costs and reduced

readiness rates. These two issues are important considerations

when deciding to employ a system beyond its planned life span.

Life extension of Defense assets has taken greater prominence

lately, and it’s far easier to maintain an aging system for which

corrosion prevention and control were up-front considerations

during design.

Down-select Final Material and CPAC Method

Ensuring the lowest total ownership costs means that the

designer must select both the optimum candidate material as

well as the optimum CPAC method if one is necessary. In this

context ‘optimum’ doesn’t mean the best overall solution since

this may come at an unaffordably high cost. Determining the

optimum solution involves balancing acquisition cost along

with the predicted life and maintenance requirements of the

selected material and CPAC method. For instance, if a metallic

structure were painted to protect it from corrosion, then the

quality of the coating certainly would influence its durability

and expected life. In cases where painted structures are

employed, it may very well be advantageous to select a highquality coating that promises long life, since the time needed to

reapply the coating later during maintenance is a factor that

contributes to life-cycle costs.

The base metal being protected must be selected with adequate consideration given to both its cost and corrosion resistance. It is important to understand that CPAC measures, such

as coatings or other CPCs, will seldom completely protect a

structure or component throughout its life. During the time

when the chosen CPAC method has lost its effectiveness, the

ability of the material to withstand corrosive environments predictably becomes very important, and will help determine

when CPAC methods should be reapplied.

When comparing candidates the best technical solution will

be the material most resistant to the corrosion modes that can

initiate catastrophic failure. The remaining forms of corrosion

might very well be controlled through judicious use of CPAC

methods, especially if they are high quality and long lasting.

But remember, some methods may lose effectiveness over time

so the slight cost increase that may be seen from selecting one

metal over another with lesser corrosion resistance might be

cheaper in the long run. Deciding which material possesses the

best combination of performance and cost can be a difficult

proposition to make, but the return on investment is well

worth the time in doing so.

CONCLUSIONS

For critical applications the best approach for ensuring corrosion resistant designs is to employ the use of trained corrosion

specialists or materials engineers to help select the most appropriate materials and corrosion prevention and control practices.

However, we realize that for many organizations and designs

this may not be feasible. What we present here is an approach

that designers can use to improve their consideration of corrosion prevention and control during material selection. The

approach may seem a bit complicated, but one thing is certain,

using it or a similar process will help reduce corrosion and related life-cycle costs.

The US Government, specifically the Departments of

Defense and Energy, as well as NASA and other Federal agencies, have funded literally tens of thousands of corrosion-related research projects over the past many decades. Much of the

information resulting from this research is available to help

reduce performance risk on new acquisition programs. The

difficulty with using this information is obtaining it in a timely fashion. Much of it currently resides in paper collections or

microfilm, thus restricting the ease at which it can be

obtained. Because of the variety of interests of those who conducted this research, it’s likely that information exists that is

directly relevant to any given application, intended environment, and candidate material. In the absence of using such

data, designers should still endeavor to utilize the more general information contained in reference books and handbooks.

Doing one’s ‘homework’ to the maximum extent possible will

pay dividends later with reduced life-cycle costs and increased

readiness rates.

DOD policy now requires program managers to provide evidence that they have planned for corrosion mitigation when

they present their procurement strategies before acquisition

review panels, such as the Defense Acquisition Board. For those

contractors supporting a DOD-related or other Government

acquisition program, it makes sense to use the best design practices and information to ensure the customer is delivered a

durable system or structure that possesses the lowest life-cycle

costs and highest readiness rates possible, maximizing their

return on investment, and providing the US taxpayer with the

best value for their tax dollar.

This issue of the AMPTIAC Quarterly possesses a good deal

of the kind of information needed to make more informed

material selection decisions that will reduce future corrosion

costs. AMPTIAC is currently developing a handbook entitled

Corrosion Prevention and Control: A Program Management

Guide for Selecting Materials. This new book is nearing completion and will be available in the Spring of 2006. It greatly

expands upon the information we present here and will be

very useful for both program office staff, as well as prime and

subcontractor engineers that are involved in material selection

decisions.
The AMPTIAC Quarterly, Volume 9, Number 3

There are a number of possible approaches to improve the ability of a material, component, or system to withstand the effects of corrosion (see Figure 1). Corrosion prevention and control (CPAC)

methods, however, can be divided up into six main groups including coatings, surface treatments,

corrosion preventive compounds, inhibitors, cathodic and anodic protection, and strategic methods.

Coatings: Coatings may be the easiest, most effective, and least expensive CPAC method available.

Durable metallic, inorganic, and organic coatings are frequently used for providing short- or longterm corrosion protection of metals from various types of corrosive media. There are two main

types of coatings: barrier coatings and sacrificial coatings. A barrier coating acts as a shield, which

isolates the metal being protected from the surrounding corrosive environment. Barrier coatings

are typically unreactive, resistant to corrosion, and also protect against wear. Sacrificial coatings

preferentially corrode, which is an effective mechanism for protecting the cathodic substrate (see

discussion on cathodic protection below).

Surface Treatments: These treatments modify a material’s surface to improve its corrosion resistance. Conversion coating and anodizing techniques employ chemical reactions to create a stable,

corrosion resistant oxide film on the metal’s surface. Shot peening is a mechanical process that

induces compressive residual stresses on the surface, thus improving resistance to stress corrosion

cracking and corrosion fatigue. Laser treatments can modify the surface characteristics of a material including its hardness and morphology. As a result, certain forms of corrosion may be mitigated or prevented. Laser shock peening is a process somewhat analogous to shot peening in that it

too can induce compressive residual stresses within a metal’s surface region to increase its resistance

to stress corrosion cracking and corrosion fatigue.

Corrosion Preventive Compounds (CPCs): CPCs offer temporary protection against corrosion and

as such, are materials that need to be reapplied during scheduled maintenance. They come in four

basic types[1]:

• Water displacing soft films

• Water displacing hard films

• Non-water displacing soft films

• Non-water displacing hard films

Water displacing CPCs penetrate small cracks and crevices, force out any water that may be present, and leave behind a protective film. These films can be oil, grease, solvent, or resin based. They

can be hydrophobic (i.e. they repel water) or they can contain corrosion inhibitors (see below).

Inhibitors: Inhibitors are chemicals that either react with the surface of a material to decrease its

corrosion rate, or modify the operational environment to reduce its corrosivity. Inhibitors may be

dissolved in an aqueous solution or dispersed in a protective film. For instance, they can be injected into a completely aqueous recirculating system (e.g. automobile radiators) to reduce the corrosion rate in that system. They may also be used as additives in coating products, such as surface

treatments, primers, sealants, hard coatings, and CPCs. Furthermore, some inhibitors can be

added to water that is used to wash a component, system, or vehicle. Inhibitors are usually grouped

into five different categories: passivating, cathodic, film forming, precipitation, and vapor phase.

Cathodic and Anodic Protection: Cathodic protection (CP) is a widely used electrochemical method

for protecting a structure or important components of a system from corrosion. There are two

main classes of cathodic protection: active and passive. Active cathodic protection, also called

impressed-current cathodic protection (ICCP), uses an external power supply to provide an electrical current to the surface of a metal. The excess electrons at the surface feed the corrosive medium, thereby protecting the metal from being stripped of its electrons, which would otherwise

result in corrosion of the metal. Passive CP systems are simpler than ICCP systems and involve the

galvanic coupling of the metal being protected to a sacrificial anode, which protects the adjoining

surface by freely giving up electrons and in the process preferentially corroding.

Anodic protection is a more recently developed but less frequently used method of corrosion control. Using an applied electrical current, this method actively creates a passive film on the surface

of the material being protected. For some applications, the current can be sustained during the

material’s service life, in order to maintain the passive film. Passive films are very non-reactive and

consequently materials that possess them are resistant to corrosion. The method is typically

employed to protect materials that are exposed to strongly alkaline or acidic environments. Anodic protection can only be used on metals capable of forming a passive film such as stainless steels.

12

Corrosion Prevention and

Control Methods
◆ Geometry

◆ Material interfaces

◆ Relative sizes

◆ Joints

• Fastened 

• Welded

• Brazed

◆ Applied stresses

◆ Fluid Flow

◆ Cathodic/Anodic 

Protection

◆ Base material

• Metals

• Organics

• Ceramics

• Composites

◆ Heat treatments

◆ Corrosion 

Prevention and 

Control Materials

◆ Surface treatments

• Cleaning

• Conversion 

coatings

• Anodization

• Shot peening

• Laser shock 

peening

◆ Cold working

• Fasteners

◆ Polishing

◆ Coatings

• claddings

◆ Quality control

• Impurities

• Defects

• Surface condition

• Joints

◆ Storage conditions

◆ Cleaning

• Agents

• Abrasives

• Inhibitors

• Biocides

◆ Coating removal

◆ Recoating

◆ Corrosion 

preventive 

compounds

◆ Electrochemical 

sensors

◆ Visual inspection

◆ Weight loss coupons

◆ Bacteria counts/

cultures

◆ NDI

• Thickness

• Cracks

◆ Conversion coatings

• Chromate

• Phosphate

◆ Anodization

◆ Platings/claddings

• Nickel

• Copper

• Chromium

• Gold

• Platinum

• Aluminum

◆ Sacrificial coatings

• Zinc 

• Cadmium

• Aluminum

◆ Paints

• Oil varnishes

• Alkyd resins

• Epoxide resins

• Poyurethanes

◆ Enamels

◆ Powder coatings

• Thermoplastics

◆ High temperature

coatings

• MCrAlY

◆ Passive (anodic)

• Chromates

• Phosphates

• Molybdates

◆ Cathodic

• Poisons

• Precipitates

• Oxygen scavengers

◆ Hydrophobic 

film formers

• Benzoates

• Amines

◆ Precipitation

• Phosphates

• Silicates

◆ Vapor Phase

• Amines

• Morpholine

• Hydrazine

◆ Rubber gaskets

◆ Polymeric gaskets

• Teflon

◆ Metal washers

• Lead

◆ Caulk

• Silicone

◆ Impressed current

anodes

• Precious metals

• Ferrous metals

• Carbonaceous 

materials

◆ Sacrificial anodes

• Zinc

• Magnesium

• Aluminum

◆ Anodic Protection

◆ Hard films

• Plasticized resins

◆ Soft films

• Lanolin

• Petrolatum

◆ Water displacing

grades

◆ Strippable grades

◆ Oil-based films

Corrosion Prevention and Control Materials

Design Material Selection

Coatings/Primers Inhibitors Sealants/Gaskets Cathodic & Anodic

Protection

Corrosion Preventive

Compounds

Preventive 

Maintenance 

Monitoring/

Inspection Processing/Manufacturing

http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 13

NOTES

* Two different acronyms for corrosion prevention and control can be

found in literature: CPAC and CPC. CPAC is used throughout this

issue, however, to avoid confusing it with corrosion preventive compounds which also uses the acronym CPC. Interestingly, corrosion 

preventive compounds are also referred to as corrosion prevention compounds and corrosion preventative compounds throughout literature.

† Alodine is a registered trademark of Amchem Products, Inc.

Strategic Methods: Design, maintenance, and material selection can be strategically used to minimize the extent to which a material, component or system corrodes during its lifetime. Simple elements incorporated into a design can lessen the risk of corrosion. For example, allowing for

drainage of water that otherwise might become trapped can effectively reduce corrosion problems.

Similarly, employing seals to preclude water from entering a component or system will improve its

corrosion resistance. Another effective way to minimize corrosion is to use gaskets to electrically

insulate two dissimilar metals, thus eliminating the possibility of galvanic corrosion. Employing a

maintenance schedule where a vehicle or structure is periodically cleaned will help reduce corrosion. Salt and debris buildup on vehicles or structures, for example, can accelerate corrosion.

Therefore, routinely washing them to remove the contaminants is a sound practice. In addition,

regularly touching up protective coatings or reapplying CPCs will help reduce instances of corrosion. Perhaps the most important way to minimize corrosion from occurring in the first place is to

make appropriate material selection decisions by carefully considering the application, environment, and potential corrosion problems that might occur. Selecting the appropriate materials and

associated corrosion prevention and control practices can reduce maintenance costs and system

downtime over the life-cycle of a system.

REFERENCE

[1] Corrosion Prevention Compounds, Corrosion Doctors’ Website, http://www.corrosion_doctors.

org/Inhibitors/CPCs.htm

Figure 1: Corrosion Prevention and Control Considerations.
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14 The AMPTIAC Quarterly, Volume 9, Number 3
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 15

Material EASE

Material Failure Modes, Part III

A Brief Tutorial on Corrosion Related Material Failure Modes

Benjamin D. Craig

AMPTIAC

Rome, NY

31 AMPTIAC

CORROSION

Corrosion is the deterioration of a metal or alloy and its properties

due to a chemical or electrochemical reaction with the surrounding environment. The most serious consequence of corrosion is a

component or system failure. Failure can occur either by sufficient

material property degradation, such that the component or structure is rendered unable to perform its intended function, or by

fracture that originates from or is propagated by corrosive effects.

While corrosion manifests itself in many different forms and

through various environments and mechanisms, only the most

significant forms are discussed in this article. The following sections contain discussions on failures resulting from uniform,

galvanic, crevice, pitting, intergranular, and erosion corrosion,

selective leaching/dealloying; hydrogen damage; stress corrosion

cracking; and corrosion fatigue.

Uniform/General Corrosion

Uniform corrosion is a generalized corrosive attack that occurs

over a large surface area of a material (Figure 1). The result is a

thinning of the material until failure occurs. Uniform corrosion

can also lead to changes in surface properties such as increased

surface roughness and friction, which may cause component failure especially in the case of moving parts that require lubricity.

In most cases corrosion is inevitable. Therefore, mitigating

its effects or reducing the corrosion rate is essential to ensuring

material longevity. Protecting against uniform corrosion can

often be accomplished through selection of a material that is best

suited for the anticipated environment. The selection of materials for uniform corrosion resistance should simply 

take into consideration the susceptibility of the metal to the type

of environment that will be encountered. Aside from selecting a

This issue of MaterialEASE is the final installment of a three part series on material failure modes. MaterialEASE 29, published in 

Volume 9, Number 1 of the AMPTIAC Quarterly, introduced the concept of material failure modes and covered fracture, ductile 

failure, elastic deformation, creep, and fatigue. MaterialEASE 30, published in Volume 9, Number 2 of the AMPTIAC Quarterly continued the discussion with brief descriptions of impact, spalling, wear, brinelling, thermal shock, and radiation damage. This article 

completes the series on material failure modes, covering uniform, galvanic, crevice, pitting, intergranular, and erosion corrosion;

selective leaching/dealloying; hydrogen damage; stress corrosion cracking; and corrosion fatigue. The three articles taken together

make a valuable desk reference for any professional making material selection and design decisions...and that’s just what we’ve

done! We have combined these three articles into a desktop reference and placed it on our website for download. Type in the following

URL, and download this useful reference guide: http://amptiac.alionscience.com/deskref. - Editor

Figure 1. Uniform Corrosion on Iron Piping in a Fire Sprinkler System Caused by Leaks in the Threaded Joints. (Photos Courtesy of

Corrosion Testing Laboratories, Inc.)[1].
16 The AMPTIAC Quarterly, Volume 9, Number 3

Material EASE

material that is resistant to uniform corrosion, protection

schemes such as barrier coatings can be implemented. Organic or

metallic coatings should be used wherever feasible. There are

also coatings where additional elements, such as chromium, are

incorporated for corrosion resistance. When coatings are not

used, surface treatments that artificially produce the metal oxide

layer prior to exposure to the environment will result in a more

uniform layer with a controlled thickness. A uniform oxide layer

can provide effective corrosion resistance for some materials.

Also, vapor phase inhibitors may be used in such applications as

boilers to adjust the pH level of the environment, thus reducing

the rate of corrosion. Table 1 provides a brief list of guidelines

that can help minimize uniform corrosion.

Galvanic Corrosion

Galvanic corrosion is a form of corrosive attack that occurs when

two dissimilar metals (e.g. stainless steel and magnesium) are

electrically connected, either through physically touching each

other or through an electrically conducting medium, such as an

electrolyte. When this occurs, an electrochemical cell can be

established, resulting in an increased rate of oxidation of the

more anodic material (lower electrical potential). The opposing

metal, the cathode, will consequently receive a boost in its resistance to corrosion. Galvanic corrosion (shown in Figure 2) is usually observed to be greatest near the surface where the two

dissimilar metals are in contact.

There are a number of driving forces that influence the

occurrence of galvanic corrosion and the rate at which it occurs.

Among these influencing factors are the difference in the electrical potentials of the coupled metals, the relative area of each

metal, the system geometry, and the environment to which the

system is exposed.

In most cases, galvanic corrosion can be easily avoided if

proper attention is given to the selection of materials during

design of a system. It is often beneficial for performance and

operational reasons for a system to utilize more than one type of

metal, but this may introduce a potential galvanic corrosion

problem. Therefore, sufficient consideration should be given to

material selection with regard to the electrical potential differences of the metals. Cathodic protection, electrical insulation, or

coatings can also help protect materials from galvanic corrosion.

Table 2 provides a brief list of guidelines that can help minimize

galvanic corrosion.

Crevice Corrosion

Crevice corrosion occurs as a result of water or other liquids getting trapped in localized stagnant areas creating an enclosed corrosive environment. This commonly occurs under fasteners,

gaskets, washers and in joints or in other components with small

gaps. Crevice corrosion can also occur under debris built-up on

surfaces, sometimes referred to as “poultice corrosion.” Poultice

corrosion can be quite severe, due to a gradually increasing acidity in the crevice area.

Several factors including crevice gap width, depth, and the

surface ratios of materials affect the severity or rate of crevice

corrosion. Tighter gaps, for example, have been known to

increase the rate of crevice corrosion of stainless steels in chloride environments. The larger crevice depth and greater surface

area of metals will generally increase the rate of corrosion.

Table 1. Guidelines for Mitigating Uniform Corrosion.

• Select material that has inherent resistance to corrosion in 

anticipated operating environment.

• Use barrier coatings (organic or metallic).

• Apply surface treatment to generate uniform oxide layer on 

surface of metal.

• Use vapor phase inhibitors to deactivate corrosive environment 

in closed systems (e.g. heat exchanger, boiler, etc.).

• Install cathodic protection system (i.e. impressed current, 

sacrificial anodes).

• Design system with proper drainage such that there is 

no standing water.

• Implement routine maintenance schedule to clean/rinse 

material surfaces.

Figure 2. Galvanic Corrosion

between a Stainless Steel

Screw and Aluminum. A

Cathodic Material for Fasteners is Preferred.[2].

Table 2. Guidelines for Mitigating Galvanic Corrosion[3].

• Use one material to fabricate systems or components where 

practical.

• If mixed metal systems are used, select combinations of metals as

close together in the galvanic series as possible, or select metals

that are galvanically compatible.

• Avoid the unfavorable area effect of a small anode and large

cathode. Small parts or critical components such as fasteners

should be the more noble metal.

• Insulate dissimilar metals wherever practical, for example, by 

using a gasket. It is important to insulate completely if possible.

• Apply coatings with caution. Keep coatings in good repair, 

particularly the one used on the anodic member.

• Add inhibitors, if possible, to decrease the aggressiveness 

of the environment.

• Avoid threaded joints for materials far apart in the galvanic series.

• Design for the use of readily replaceable anodic parts 

or make them thicker for longer life.
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 17

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Materials typically susceptible to crevice corrosion include

aluminum alloys and stainless steels. Titanium alloys normally

have good resistance to crevice corrosion. However, they may

become susceptible in elevated temperature and acidic environments containing chlorides. Copper alloys can also experience

crevice corrosion in seawater environments.

To protect against problems with crevice corrosion, systems

should be designed to minimize areas likely to trap moisture, other

liquids, or debris. For example, welded joints can be used instead

of fastened joints to eliminate a possible crevice. Where crevices

are unavoidable, metals with a greater resistance to crevice corrosion in the intended environment should be selected. Avoid the use

of hydrophilic materials (strong affinity for water) in fastening

systems and gaskets. Crevice areas should be sealed to prevent the

ingress of water. Also, a regular cleaning schedule should be

implemented to remove any debris build up. Table 3 provides a

brief list of guidelines that can help minimize crevice corrosion.

Pitting Corrosion

Pitting corrosion, also simply known as pitting, is an extremely localized form of corrosion that occurs when a corrosive medium attacks a

metal at specific points causing small holes or pits to form (Figure 3).

This usually happens when a protective coating or oxide film is perforated, due to mechanical damage or chemical degradation (see

Figure 4). Pitting can be one of

the most dangerous forms of corrosion because it is difficult to

anticipate and prevent, relatively

difficult to detect, occurs very

rapidly, and penetrates a metal

without causing it to lose a significant amount of weight. Failure of a metal due to the effects

of pitting corrosion can occur

very suddenly. Pitting can have side effects too, for example, cracks may

initiate at the edge of a pit due to an increase in the local stress. In addition, pits can coalesce underneath the surface, which can weaken the

material considerably.

Among metals and alloys, stainless steels tend to be the most

susceptible to pitting corrosion. Polishing the surface of stainless

steels can increase the resistance to pitting as opposed to etching or

grinding the surface. Alloying can have a significant impact on the

pitting resistance of stainless steels. Conventional steel has a greater

resistance to pitting than stainless steels, but is still susceptible,

especially when unprotected. Aluminum in an environment containing chlorides and aluminum brass (Cu-20Zn-2Al) in contaminated or polluted water are usually susceptible to pitting. Titanium

is strongly resistant to pitting corrosion.

Proper material selection is very effective in preventing the

occurrence of pitting corrosion. Another option for protecting

against pitting is to mitigate aggressive environments and environmental components (e.g. chloride ions, low pH, etc.).

Inhibitors may sometimes stop pitting corrosion completely.

Further efforts during design of the system can aid in preventing 

pitting corrosion, for example, by eliminating stagnant solutions or by the inclusion of cathodic protection. In some cases,

protective coatings can provide an effective solution to the problem of pitting corrosion. However, they can also accelerate the

corrosion process at locations where the coating has been

breached and the base metal is left exposed to the corrosive environment. Table 4 provides a brief list of guidelines that can help

minimize pitting corrosion.

Table 3. Guidelines for Mitigating Crevice Corrosion.

• Ensure application is designed to have proper drainage and is

absent of areas that can trap moisture and debris.

• Use welded joints instead of mechanical fasteners.

• Select materials that are inherently resistant to corrosion.

• Avoid use of hydrophilic, water absorbing materials.

• Seal gaps and use gap fillers.

• Use and routinely reapply corrosion preventive compounds 

(e.g. greases and oils).

• Implement a routine maintenance schedule to clean/rinse 

material surfaces.

Figure 4. Pitting Corrosion of Copper Radiator Fins under Tin

Coating (200X Magnification – Photo Courtesy of Corrosion 

Testing Laboratories, Inc.)[1].

Figure 3. Corrosion Pit in Grooved

Copper Tube (Photo Courtesy of Corrosion Testing Laboratories, Inc.)[1].

Table 4. Guidelines for Mitigating Pitting Corrosion.

• Select material that is inherently resistant to pitting corrosion.

• Use inhibitors to neutralize corrosive environment in closed 

systems.

• Eliminate potential build-up of stagnant moisture through 

proper design.

• Use cathodic or anodic protection.

• Ensure quality application of protective barrier coatings 

to surface of metal. 

• Use surface treatments, such as anodization and conversion 

coatings, or metal cladding.

• Polish surface to remove surface defects.

• Add alloying elements to metal (e.g. Mo and Cr) for enhanced

pitting resistance.
The AMPTIAC Quarterly, Volume 9, Number 3

Material EASE

18

Intergranular Corrosion

Intergranular corrosion attacks the interior of metals along

grain boundaries. It is associated with impurities, which tend to

deposit at grain boundaries, and/or a difference in crystallographic phase precipitated at grain

boundaries. Heating of some metals

can cause a “sensitization” or an

increase in the level of inhomogeniety

at grain boundaries. Therefore, some

heat treatments and weldments can

result in a propensity for intergranular

corrosion. Some metals may also

become sensitized while in operation if

used at a high enough temperature to cause such changes in

internal crystallographic structure.

Intergranular corrosion can occur in many alloys, but stainless steels, as well as some aluminum and nickel-based alloys, are

predominantly susceptible. Stainless steels, especially ferritic

stainless steels, have been found to become sensitized, particularly after welding. Aluminum alloys also suffer intergranular attack

as a result of precipitates at grain boundaries that are more

active. Exfoliation corrosion (shown in Figure 5) is considered a

type of intergranular corrosion and occurs in materials that have

been mechanically worked to produce elongated grains in one

direction. Precipitation of intermetallic phases at grain boundaries can make certain high nickel alloys susceptible. Methods to

limit intergranular corrosion are listed in Table 5.

Selective Leaching/Dealloying

Dealloying, also called selective leaching, is a less common form

of corrosion where one element is targeted and consequently

extracted from a metal alloy, leaving behind an altered structure

(Figure 6). The most common form of selective leaching is dezincification (shown in Figure 7), where zinc is extracted from

brass or other alloys containing significant zinc content. Left

behind are structures that have experienced little or no dimensional change, but whose parent material is weakened, porous

and brittle. Dealloying is a dangerous form of corrosion because

it can reduce a strong, ductile metal to one that is weak, brittle

and subsequently more susceptible to mechanical failure. Since

there is little change in the metal’s dimensions, dealloying may

go undetected, and failure can occur suddenly. Moreover, the

porous structure is open to the penetration of liquids and gases

deep into the metal, which can result in further degradation.

Selective leaching often occurs in acidic environments.

Reducing the aggressive nature of the atmosphere by removing oxygen and avoiding stagnant solutions and debris buildup

can prevent dezincification. Cathodic protection can also be used

for prevention. However, the best alternative, economically, may

be to use a more resistant material such as red brass, which only

contains 15% Zn. Adding tin to brass also provides an improvement in the resistance to dezincification. Additionally, inhibiting

elements, such as arsenic, antimony, and phosphorous can be

added in small amounts to the metal to provide further improveTable 5. Guidelines for Mitigating Intergranular Corrosion.

• Keep impurity levels to a minimum.

• Properly select heat treatments to reduce precipitation 

at grain boundaries.

• Specifically for stainless steels, reduce the carbon content, 

and add stabilizing elements (Ti, Nb, Ta) which preferentially 

form more stable carbides than chromium carbide.

Figure 5. Exfoliation of an 

Aluminum Alloy in a Marine

Environment[2].

Figure 7. Dezincification

of Commercial Bronze

Wax Actuator from a

Water Supply System

(Photos Courtesy of 

Corrosion Testing 

Laboratories, Inc.)[1].

Figure 6. Dezincification 

of Brass Heat Exchanger

Tube (100X Magnification

– Photo Courtesy of 

Corrosion Testing 

Laboratories, Inc.)[1].

Table 6. Guidelines for Mitigating Selective Leaching.

• Use material that is inherently resistant to selective leaching.

• Some alloying elements for certain metals can improve resistance

to selective leaching.

• Avoid stagnant solution/debris buildup.

• Use inhibitors to neutralize corrosive environment.

• Use cathodic protection.

• Avoid using copper with significant zinc content.
ment. Avoiding the use of a copper metal containing a significant

amount of zinc altogether may be necessary in systems exposed to

severe dezincification environments. Table 6 provides a brief list

of guidelines that can help minimize selective leaching.

Erosion Corrosion

Erosion corrosion is a form of attack resulting from the interaction of an

electrolytic solution in motion relative to a metal surface. It has typically been associated with small solid particles dispersed within a liquid

stream. The fluid motion causes wear and abrasion, increasing rates of

corrosion over uniform (non-motion) corrosion under the same conditions. Erosion corrosion is evident in pipelines, cooling systems, valves,

boiler systems, propellers, impellers, as well as numerous other components. Specialized types of erosion corrosion occur as a result of impingement and cavitation (Figure 8). Impingement refers to a directional

change of the solution, whereby a greater force is exhibited on a surface

such as the outside curve of an elbow joint. Cavitation is the phenomenon of collapsing vapor bubbles, which can cause surface damage if they

repeatedly hit one particular location on a metal.

There are several factors that influence the resistance of a

material to erosion corrosion including hardness, surface

smoothness, fluid velocity, fluid density, angle of impact, and the

general corrosion resistance of the material to the environment.

Materials with higher hardness values typically resist erosion corrosion better than those that have a lower value. There are some

design techniques that can be used to limit erosion corrosion.

These are listed in Table 7.

Hydrogen Damage

There are a number of different ways that hydrogen can damage metallic materials, resulting from the combined factors of

hydrogen and residual or tensile stresses. Hydrogen damage

can result in cracking, embrittlement, loss of ductility, blistering and flaking, and microperforation.

Hydrogen induced cracking (HIC) refers to the cracking of a

ductile alloy when under constant stress and where hydrogen gas

is present. Hydrogen is absorbed into areas of high triaxial stress

producing the observed damage. A related phenomenon, hydrogen embrittlement, is the brittle fracture of a ductile alloy during

plastic deformation in a hydrogen gas containing environment.

In both cases, a loss of tensile ductility occurs with metals

exposed to hydrogen which results in a significant decrease in

elongation and reduction in area. It is most often observed in low

strength alloys, but also occurs in steels, stainless steels, aluminum alloys, nickel alloys, and titanium alloys.

Another form of damage occurs when high pressure hydrogen

attacks carbon and low-alloy steels at high temperatures. The

hydrogen will diffuse into the metal and react with carbon resulting in the formation of methane. This in turn results in decarburization of the alloy and possible crack formation. Metal

plating operations, for example, can cause hydrogen embrittlement. Methods to deter hydrogen damage are listed in Table 8.

Stress Corrosion Cracking

Stress corrosion cracking (SCC) is an environmentally induced cracking

phenomenon (Figure 9) that sometimes occurs when susceptible metals

are subjected to a tensile stress

and a corrosive environment

simultaneously. This is not to

be confused with similar phenomena such as hydrogen

embrittlement, in which the

metal is embrittled by hydrogen, often resulting in the formation of cracks. Moreover,

SCC is not defined as the cause

of cracking that occurs when

the surface of the metal is corroded resulting in the creation

of a nucleating point for a

crack. Rather, it is a synergistic

effort of a corrosive agent and a

modest, static stress. Another

form of corrosion similar to SCC, although with a subtle difference, is

corrosion fatigue. The key difference is that SCC occurs with a static

stress, while corrosion fatigue occurs under a dynamic or cyclic stress.

Stress corrosion cracking is a process that takes place within the

material, where the cracks propagate through the internal structure,

usually leaving the surface unharmed. Aside from an applied

Figure 8. Erosion

(Cavitation) Corrosion

of a Brass Pump

Impeller. Air Bubbles

Eroded the Soft 

Copper Oxide 

Protective Layer

Enabling Corrosion 

of the Base Metal. 

(Photo Courtesy of

Corrosion Testing 

Laboratories, Inc.)[1].

http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 19

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

Figure 9. Stress Corrosion Cracking 

(50X Magnification) in 304L Stainless

Steel Pipeline (Photo Courtesy of 

Corrosion Testing Laboratories, Inc.)[1].

Table 7. Guidelines for Mitigating Erosion Corrosion.

• Avoid turbulent flow.

• Add deflector plates where flow impinges on a wall.

• Add plates to protect welded areas from the fluid stream.

• Increase hardness of surface using surface treatment 

(e.g. shot peening) or hard coating/plating.

Table 8. Guidelines for Mitigating Hydrogen Damage.

• Limit hydrogen introduced into the metal during processing.

• Limit hydrogen in the operating environment.

• Design structures to reduce stresses (below threshold 

for subcritical crack growth in a given environment).

• Use barrier coatings.

• Use low hydrogen welding rods.
The AMPTIAC Quarterly, Volume 9, Number 3

mechanical stress, a residual, thermal, or welding stress along with

the appropriate corrosive agent may also be sufficient to promote

SCC. Pitting corrosion, especially in notch-sensitive metals, has been

found to be one cause for the initiation of SCC. SCC is a dangerous

form of corrosion because it can be difficult to detect, and it can

occur at stress levels which fall within the range that the metal is

designed to handle.

Stress corrosion cracking is dependent on environmental factors

including temperature, solution, and stress, as well as the metallic

structure and composition.[4] However, certain types of alloys are

more susceptible to SCC in particular environments, while other

alloys are more resistant to that same

environment. Increasing the temperature of a system often works to accelerate the rate of SCC. The presence of

chlorides or oxygen in the environment can also significantly influence

the occurrence and rate of SCC. There

are several methods that may be used

to minimize the risk of SCC. Some of

these methods are listed in Table 9.

Corrosion Fatigue

Corrosion fatigue is the environmentally-assisted mechanical degradation of a material due to the

combined effects of corrosion and

fatigue (a direct result of cyclic

stress loading). This corrosion mode

is shown in Figure 10. It is often

considered to be a subset of stress corrosion cracking, but the

fracture mechanics and methods of prevention deviate enough

from those of SCC that it warrants a separate discussion. Furthermore, SCC occurs under static stress while corrosion fatigue

occurs under a cyclic stress (part of which is tensile stress).

Corrosion fatigue is a potential cause for the failure of many

types of metals and alloys in various types of environments. 

Materials that experience corrosion fatigue essentially exhibit a

decrease in fatigue strength due to the effects of electrochemical

degradation (corrosive environment). The stress required for both

crack initiation and propagation is lower in corrosive environments. The crack growth rate can be much higher in a corrosive

environment than it is in a non-corrosive environment. Therefore, the fatigue life of a material is shortened if it is simultaneously exposed to a corrosive environment and fatigue conditions.

Like the general case of fatigue, corrosion fatigue cracking is

often characterized by “beach marks” or striation patterns

(shown in Figure 11), which are perpendicular to the crack propagation direction.

There are a number of factors that affect the onset of corrosion fatigue and the growth rate of cracks caused by this form of

corrosion. For example, corrosion damage, such as pitting,

causes stress raisers in the vicinity of the pit, much like notch

Material EASE

20

Figure 10. Corrosion Fatigue

Crack (60X Magnification) 

Adjacent to a Weld in 316 

Stainless Steel (Photo Courtesy

of Corrosion Testing Laboratories, Inc.)[1].

Figure 11. Fatigue Striations Observed with Scanning Electron

Microscope (1000X Magnification – Photo Courtesy of Corrosion

Testing Laboratories, Inc.)[1].

Table 9. Guidelines for Mitigating Stress Corrosion Cracking.

• Choose a material that is resistant to SCC.

• Employ proper design features for the anticipated forms of corrosion (e.g. avoid crevices or include drainage holes).

• Minimize stresses including thermal stresses.

• Modify environment (neutralize pH, reduce oxygen content).

• Use surface treatments (shot peening, laser shock peening) which

increase the surface resistance to SCC.

• Any barrier coatings will deter SCC as long as it remains intact.

• Reduce exposure of end grains (i.e. end grains can act as initiation sites for cracking because of preferential corrosion and/or a

local stress concentration).

Table 10. Guidelines for Mitigating Corrosion Fatigue.

• Polish surface to make material more resistant to crack initiation.

• Limit operating temperatures.

• Reapply coatings or corrosion preventive compounds in 

damaged areas.

• Employ designs which minimize stresses to the components.

• Choose heat treatments that reduce residual stresses.

• Use surface treatments that enhance corrosion fatigue resistance,

such as shot peening or laser peening.

• Use inhibitors and barrier coatings to block corrosive species 

from the metal.

• Reduce hydrogen contamination during fabrication, heat 

treatment or manufacturing.

• Select materials that are not sensitive to corrosion fatigue.
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 21

effects. This can lead to crack initiation at a stress below that

for a material in a non-corrosive environment. The crack will

then propagate at a faster rate, as corrosive elements enter the

crack. Temperature, metal composition, strength and fracture

toughness are other examples of environmental and material

factors that affect the occurrence and rate of corrosion fatigue.

Similar to preventing stress corrosion cracking, material

selection is very important in corrosion fatigue prevention. Fracture toughness and strength are both important material properties when considering how to protect against corrosion fatigue.

Other methods to deter corrosion fatigue are listed in Table 10.

CONCLUSION

Corrosion is a widespread and costly problem. While some of the

damage it causes is simply cosmetic, several corrosion modes can

cause catastrophic failure before they are even identified as a

problem. Therefore, for critical components and systems, it is

very important to understand the various forms of corrosion failure that were discussed in this article. Material selection during

system or component design is the first step in preventing a catastrophic corrosion problem.

The three-part series of articles on material failure modes

presented in this and the previous two issues of the AMPTIAC

Quarterly has covered the most common and significant failure

mechanisms. However, there is another entire field related to system failure, and that is electronic failure. For many systems,

electronic failure is significant and should be considered during

the design phase of a system or component.

ACKNOWLEDGEMENT

The author would like to thank Corrosion Testing Laboratories,

Inc. for their contribution of photos included in this article.

REFERENCES

[1] Corrosion Testing Laboratories, Inc. (http://www.corrosion

lab.com/)

[2] Corrosion Technology Testbed, NASA Kennedy Space Center,

http://corrosion.ksc.nasa.gov/

[3] E.B. Bieberich and R.O. Hardies, TRIDENT Corrosion Control

Handbook, David W. Taylor Naval Ship Research and Development

Center, Naval Sea Systems Command, DTRC/SME-87-99, February

1988; DTIC Doc.: AD-B120 952

[4] M.G. Fontana, Corrosion Engineering, 3rd Edition, McGraw-Hill,

1986

A DVANCED M A TERIALS AND P ROCESSES T ECHNOLOGY AMPTIAC

This three-part series on 

Material Failure Modes

featured in the AMPTIAC Quarterly

can be downloaded as a Desk Reference

from http://amptiac.alionscience.com/deskref
22 The AMPTIAC Quarterly, Volume 9, Number 3

30th Annual Conference & Exposition

on Advanced Ceramics & Composites

01/22/06 - 01/27/06

Cocoa Beach, FL

Contact: Mark J. Mecklenborg

The American Ceramic Society

Westerville, OH 43081

Phone: 614.794.5829

Fax: 614.794.5882

PACE 2006 (Paint & Coatings Expo)

01/29/06 - 02/01/06

Tampa, FL

Contact: SSPC/The Society 

for Protective Coatings

40 24th St, 6th Floor

Pittsburgh, PA 15222-4656 

Phone: 877.281.7772

Web Link: www.sspc.org

Components for Military & Space 

Electronics Conference & Exhibition

02/06/06 - 02/09/06

Los Angeles, CA

Contact: Leon Hamiter

Components Technology Institute, Inc.

904 Bob Wallace Ave, Ste 117

Huntsville, AL 35801

Phone: 256.536.1304

Fax: 256.539.8477

Email: LHamiter@cti-us.com

Web Link: www.cti-us.com/cmsereg.htm

2006 International Conference on

Tungsten, Refractory & Hardmetals VI

02/07/06 - 02/08/06

Orlando, FL

Contact: Metal Powder Industries Federation

105 College Rd E

Princeton, NJ 08540-6692 

Phone: 609.452.7700 ext 11

Fax: 609.987.8523

Web Link: www.mpif.org/

High Temple Workshop 2006

02/13/06 - 02/16/06

Austin, TX

Contact: Jim Sutter

NASA Glenn Research Center

M/S 49-3, 21000 Brookpark Rd

Cleveland, OH 44135

Phone: 216.433.3226 

Fax: 505.846.8265

Email: james.k.sutter@grc.nasa.gov

Web Link: namis.alionscience.com

Smart Structures and Materials

02/26/06 - 03/02/06

San Diego, CA

Contact: SPIE–The International Society 

for Optical Engineering

PO Box 10

Bellingham, WA 98227-0010

Phone: 360.676.3290

Fax: 360.647.1445

Email: spie@spie.org

Web Link: www.spie.org/Conferences/

calls/06/ss/

Next Generation Materials for Defense

02/27/06 - 03/01/06

Arlington, VA

Contact: Institute for Defense Government

Advancement

555 Rte 1 S

Iselin, NJ 08830 

Phone: 800.882.8684

Fax: 973.256.0205

Web Link: www.idga.org

9th Joint Conference on Aging Aircraft

03/06/06 - 03/09/06

Atlanta, GA

Contact: Galaxy Scientific Corporation

3120 Fire Rd

Egg Harbor Twp, NJ 08234

Phone: 609.645.0900

Fax: 609.645.3316

Email: coordinator@agingaircraftconference

Web Link: www.agingaircraftconference.org/

2006_2/index.php

2006 TMS Annual Meeting & Exhibition

03/12/06 - 03/16/06

San Antonio, TX

Contact: TMS Meeting Services

184 Thorn Hill Road

Warrendale, PA 15086

Phone: 724.776.9000 ext 243

Fax: 724.776.3770

Email: mtgserv@tms.org

Web Link: www.tms.org/Meetings/Annual-06/

AnnMtg06Home.html

Corrosion 2006

03/12/06 - 03/16/06

San Diego, CA

Contact: Cassie Davie, NACE

1440 South Creek Dr

Houston, TX 77084-4906

Phone: 281.228.6217

Fax: 281.228.6300

Email: cassie.davie@nace.org

Web Link: www.nace.org/nace/content/

conferences/c2006/welcome.asp

CARTS USA 2006

04/03/06 – 04/06/06

Orlando, FL

Contact: Components Technology Inst, Inc.

904 Bob Wallace Ave, Ste 117

Huntsville, AL 35801

Phone: 256.536.1304

Fax: 256.539.8477

Web Link: www.cti-us.com/

110th Metalcasting Congress

04/18/06 - 04/21/06

Columbus, OH

Contact: Metalcasting Congress

1695 N Penny Ln

Schaumburg, IL 60173-4555 

Phone: 800.537.4237

Web Link: www.metalcastingcongress.org

IMAPS/ACerS International Conference

& Exhibition

04/25/06 - 04/27/06

Denver, CO

Contact: IMAPS-Intl Microelectronic 

& Packaging Soc

611 2nd St, NE

Washington, DC 20002 

Phone: 202.548.4001

Fax: 202.548.6115

Email: imaps@imaps.org

Web Link: www.imaps.org

SAMPE ‘06 - Where Advanced Materials

Meet the Marketplace

04/30/06 - 05/04/06

Long Beach, CA

Contact: SAMPE

1161 Park View Dr

Corvina, CA 91724-3751

Phone: 626.331.0616

Fax: 626.332.8929

Web Link: www.sampe.org

AISTech 2006 - The Iron & Steel 

Technology Conference & Exposition

05/01/06 - 05/04/06

Cleveland, OH

Contact: Assoc. for Iron & Steel Technology

186 Thorn Hill Rd

Warrendale, PA 15086-7528

Phone: 724.776.6040

Web Link: www.aist.org

2006 National Space & Missile 

Materials Symposium

06/26/06 - 06/30/06

Orlando, FL

Contact: M. Kubal; Anteon Corporation

5100 Springfield St, Ste 509

Dayton, OH 45431

Phone: 937.254.7950 ext 1168

Fax: 937.253.2296

Email: mkubal@anteon.com

Web Link: www.usasymposium.com

Mark Your Calendar
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 23

Richard A. Lane

David J. Brumbaugh

Jeffrey D. Guthrie

Benjamin D. Craig

AMPTIAC

Rome, NY

In order to prevent corrosion related failure modes from occurring they should be considered during the design and material

selection stages of system development. Accounting for many

of the issues that are correlated with corrosion, including test,

design, and metallurgical factors facilitates the development of

an inherently corrosion resistant design. This article addresses

the major considerations for the common forms of corrosion

that factor into design and material selection, and presents

some general ‘rules of thumb’ used in selecting materials for

corrosion resistance.

The ‘rules of thumb’ are contained in the following sections

that address each of the main forms of corrosion. The sections

identify the major failure modes, followed by discussions of the

test, design, and metallurgical considerations. With respect to test

and design considerations, the primary properties used for quantitative measurement, if there are any, are identified. For many

forms of corrosion, there are no quantitative measurement techniques, and thus materials are only rated based upon their relative

susceptibilities. Additional design features that are conducive to

the creation of corrosive microenvironments are highlighted. The

primary metallurgical factors for each form of corrosion are also

identified. Some of the major material classes are discussed as to

their relative susceptibility and resistance to the form of corrosion

under consideration. Together, this information provides a basis

for the down-selection of candidate materials.

The information discussed above has been organized into six

categories for each form of correction including measurement,

design considerations, misapplication of data, metallurgical features, susceptible alloys, and resistant alloys. Each of these categories is explained in some detail below.

Design Considerations: Includes material properties subject to

degradation and the potential for the corrosion form to lead to

catastrophic failure.

Measurement: Refers to the methods used to determine the

extent to which a form of corrosion has affected a material.

Misapplication of Data: Describes principles that are often misunderstood or misused leading to an adverse effect in terms of

corrosion.

Metallurgical Features: Refers to material characteristics that

influence the susceptibility of the material to corrosion or the

rate at which corrosion will occur.

Susceptible Alloys: Alloys that are known to be susceptible to

the form of corrosion under consideration. The list presented is

not comprehensive, but the idea is to convey the types of alloys

that may experience the most severe problems with that particular form of corrosion.

Resistant Alloys: Alloys that are known to be resistant to the form

of corrosion under consideration. The list presented is not comprehensive, but the idea is to convey the types of alloys that may

be the most resistant to that particular form of corrosion.

Although some specific environments are mentioned, they

have been largely left out of this article, because most of the

environmental factors are applicable to all of the forms of corrosion. Such factors include composition, impurities, temperature, pH, degree of aeration, velocity and turbulence of the

environment. The operating environment, including any

applied stresses, must be accurately identified and defined during the selection process. If the environment is not properly

identified, misapplication of data and/or information can

result. Other background information about the various forms

of corrosion is contained in the MaterialEASE in this issue. The

MaterialEASE also contains guidelines for mitigating the forms

of corrosion, which have thus been excluded here.

UNIFORM CORROSION

Failure due to uniform corrosion is a result of the general thinning of material, reducing its load capacity until the material

fails. This kind of failure is extremely rare however, since uniform corrosion is well defined and can be easily mitigated

through the use of coatings or by providing an adequate metal

thickness for a specified design life. Furthermore, it is highly

likely that a different failure mode will precede uniform corrosion failure.

Test and Design Considerations (Uniform)

Design Considerations • Mass loss

• Reduction in load bearing capacity

Measurement

• Thickness loss

• Weight loss

Misapplication of Data • Corrosion rates are averaged values

• Uniform corrosion rates can’t be 

used for localized forms

Extensive uniform corrosion testing has been performed on

both coated and uncoated metals. In the case of uncoated

oxide-film forming metals, the uniform corrosion rate will

decrease once the oxide layer has been established. Eventually
24 The AMPTIAC Quarterly, Volume 9, Number 3

the corrosion rate will reach equilibrium provided the environment remains constant. There is ample uniform corrosion rate

data available in the literature in the form of thickness or

weight loss over time when exposed to a particular environment. Typically, weight loss data are converted to thickness

reduction in mils per year. In this respect, the thickness loss is

an averaged value over the entire surface, where some areas will

have more thickness loss and some less. That is, the corrosion

rate is reported in terms of a mean value with no deviation.

Uniform corrosion rates can be effective for calculating the

thickness loss of bulk structures, although attention must also

be given to the localized forms of corrosion since they may

affect the metal more severely than uniform corrosion. It is

extremely important to note that uniform corrosion rates

should never be used to estimate the extent of localized corrosion forms.

Metallurgical Considerations (Uniform)

Metallurgical Features • Metal composition

• Oxide films

Susceptible Alloys • Magnesium alloys

• Low alloy irons and steels

Resistant Alloys • Stainless steels

• Copper alloys

• Nickel alloys

• Titanium alloys

Uniform corrosion is a process that involves the metal interacting with a particular environment on a macroscopic scale.

Magnesium alloys and low alloy irons and steels are by far the

most susceptible metals to uniform corrosion. They are almost

always coated for protection against uniform corrosion. One

exception is weathering steels, which have small amounts of

chromium, nickel, and copper in their composition. Uncoated

weathering steels have been successfully used for large structural components, such as bridge beams and trusses. In the case of

aluminum, most alloying elements reduce its corrosion resistance. An exception is chromium where small amounts (0.1 –

3.0 wt.%) are beneficial to aluminum-magnesium alloys. The

remaining metal classes are considered to be fairly resistant to

uniform corrosion.

PITTING CORROSION

Pitting corrosion (Figure 1) can lead to the catastrophic failure

of a component, especially in applications that require gas- or

liquid-tight seals, as narrow pits can go undetected and eventually perforate the material. Furthermore, pits are often identified

as the nucleating point of a crack or the initiator of a crack. Corrosion pits can also reduce the integrity of the surface of a material, which can lead to a susceptibility or increase in surface wear.

Test and Design Considerations (Pitting)

Design Considerations • Crack initiator

• Can cause perforation

• Can lead to wear problems

Measurement • Depth

• Diameter

• Density of pits

• Shape

Misapplication of Data • No way of isolating pitting from 

other forms of corrosion

• May be difficult to distinguish 

from uniform corrosion

• Difficult to predict penetration rate

The depth and diameter of a pit are the primary measures for

analyzing the extent of pitting corrosion on a material. A statistical distribution of pits or the density of pits on the surface of

a material can also be used to metric the extent of pitting corrosion on a material.

Since pitting often leads to other forms of corrosion, such

as uniform corrosion, stress corrosion cracking and corrosion

fatigue, it is sometimes difficult to isolate it from other forms.

For example, in some situations pitting may be confused with

uniform corrosion and vice-versa. This is because pits having

a wide diameter and shallow depth may be considered uniform corrosion. Furthermore, a high density of pits on a

material surface may cause them to overlap, resulting in an

appearance similar to uniform corrosion. It is very difficult to

predict the penetration rate of corrosion pits through the

thickness of a metal, even with test data. This is because pits

do not have standard dimensions even under similar environmental conditions.

Metallurgical Considerations (Pitting)

Metallurgical Features • Alloying content

• Alloying contaminants

• Scale formation

Susceptible Alloys • Austenitic stainless steel

• Aluminum brass

• Si, C, Ti, Nb in steel

• All passivated metals

Resistant Alloys • Titanium alloys

• High Ni steels

• Mo and Cr alloying elements

• Steel with high nitrogen content

Pitting may be caused or enhanced by several metallurgical features, including alloying content, defects or contaminants. Alloys that are known to exhibit a particular

susceptibility to pitting corrosion are listed in the table

above. Some alloying elements increase the susceptibility 

of steel to pitting including silicon, carbon, titanium and

niobium. All passivated metals (e.g. stainless steels and 

nickel-based alloys) are to some extent susceptible to pitting

corrosion. Alloys that are known to exhibit a particular

resistance to pitting corrosion are also listed in the table

above. Molybdenum and chromium alloying elements are

known to increase an alloy’s resistance to pitting.

Figure 1. Pitting 

Corrosion of Stainless

Steel Tubing.[1]
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 25

CREVICE CORROSION

Crevice corrosion has been known to lead to failure in fastening systems, electrical contacts, piping systems and storage

tanks. This form of corrosion is of particular concern in aircraft

lap joints, as the build up of corrosion products can cause separation of the two metals, known as pillowing.

Test and Design Considerations (Crevice)

Design Considerations • Strength loss

• Perforation 

• Fastening systems can create crevices

• Loss of electrical continuity 

• Geometries and interfaces conducive 

to electrolyte entrapment

Measurement • Qualitative measure

Misapplication of Data • Difficult to distinguish from other 

forms of corrosion

• Established data not easily transferable 

to other systems due to high dependence 

on environmental conditions

Crevice corrosion is only measured qualitatively by metals’

relative susceptibility to environmental conditions. The crevice

gap width and depth, and the surface ratios of materials can all

affect the extent of crevice corrosion. The larger crevice depth

and greater surface area of metals will generally increase the rate

of crevice corrosion. The degree of attack, however, is highly

dependent upon the environment’s exact constituents and concentration, as well as the humidity and temperature. This

makes quantitative laboratory measurements, such as the area

and depth of attack, in most cases not characteristic of field

experiences. Therefore, crevice corrosion testing is a tool that

can be used to expose the relative susceptibilities of materials

under certain environmental conditions.

Metallurgical Considerations (Crevice)

Metallurgical Features • Passivated metals are susceptible

Susceptible Alloys • Low alloy steels

• Stainless steels

• Aluminum alloys

Resistant Alloys • Copper alloys

• Titanium alloys

In general, passive metals have a greater susceptibility to

crevice corrosion. In particular, these include aluminum alloys

and stainless steels. Most alloying elements for aluminum alloys

reduce crevice corrosion resistance. Silicon, for example, when

used in amounts > 0.1%, can markedly reduce the crevice corrosion resistance of aluminum alloys in seawater.[2] In the case

of stainless steels, the addition of molybdenum and/or manganese will increase resistance. Copper and nickel alloys have

good resistance to crevice corrosion, although some cases of

attack have been experienced under stagnant seawater environments. Titanium alloys normally have good resistance to crevice

corrosion, however, they may become susceptible at elevated

temperature acidic environments containing chlorides. Adding

palladium to titanium alloys increases their resistance to crevice

attack under such conditions. Copper alloys have good resistance to crevice corrosion, although there have been some peculiar instances of corrosion occurring on the outside of the

crevice in seawater environments.

FILIFORM CORROSION

Filiform corrosion can lead to blistering underneath organic

coatings on a metal substrate, and consequently cause the coating to fail. This failure occurs as delamination from the base

metal and chipping, leaving the base metal unprotected from

the surrounding environment. As a result, filiform corrosion

can also lead to other forms of corrosion.

Test and Design Considerations (Filiform)

Design Considerations • Coating failure

• Cause of other forms of corrosion

Measurement • Length and width of filaments

Misapplication of Data • Difficult to tie filiform to property loss

Filiform corrosion often manifests itself in filament-shaped

columns of corrosion stretching across the surface of the material. Thus, the extent of filiform corrosion can be measured by

the length and width of filaments. However, tests for filiform

corrosion are mainly to identify if the material system (base

metal + organic coating) is susceptible to filiform corrosion or

not. It is difficult to tie filiform to property loss or material

degradation beyond surface damage, mainly because it leads to

other forms of corrosion, which can cause more serious damage.

Metallurgical Considerations (Filiform)

Metallurgical Features • Coating thickness

Susceptible Alloys • Alloys with permeable, brittle, 

hydrophilic, organic coatings

Resistant Alloys • Alloys with thick, less permeable 

coatings

• Alloys with non-organic coatings

Coating thickness plays an important role in filiform corrosion, and thickness is a good indication of whether material 

systems will be susceptible or resistant to this form of corrosion.

Any metal that is prone to corrosion in general and has a 

permeable, brittle, or hydrophilic organic coating is susceptible

to filiform corrosion. Metals with thicker, less permeable coatings are generally resistant to filiform corrosion.

EROSION CORROSION

Erosion corrosion results in a thinning of material that can

cause failure under load, as well as perforation and surface

wear leading to reduced efficiency of components such as propellers, impellers, and bearings. Impingement and cavitation

attack are two types of erosion damage and can be accelerated

under corrosive conditions.

Test and Design Considerations (Erosion)

Design Considerations • Strength loss

• Perforation

• Wear

• Thickness

• Impingement 

• Cavitation

Measurement • Qualitative measure

• Thickness loss

Misapplication of Data • Laboratory tests do not correlate 

well with field experience

• Confused with mechanical erosion
26 The AMPTIAC Quarterly, Volume 9, Number 3

All the factors that influence the resistance of a material to

erosion corrosion and their exact relationship are difficult to

define. Some factors include surface smoothness, fluid velocity,

fluid density, angle of impact, and the general corrosion resistance of the material to the environment. Erosion corrosion can

be measured in thickness loss, although laboratory test data

does not always correlate well to field experience. As a result,

materials are often qualitatively rated as to their relative susceptibility to erosion corrosion. Non-corrosive, or mechanical erosion is a common phenomenon, but is governed by a different

mechanism than erosion corrosion. Thus, it is important not to

confuse erosion corrosion with ordinary mechanical erosion.

Metallurgical Considerations (Erosion)

Metallurgical Features • Hardness

Susceptible Alloys • Low alloy steels

• Aluminum alloys

Resistant Alloys • Stainless steels

• Nickel alloys

• Titanium alloys

In general, harder materials are more resistant to erosion corrosion, but there are some exceptions. The metal’s susceptibility to

the environment is also a factor, which in some cases can counter

the effect of material hardness. Low alloy steels, cast irons, and

aluminum alloys are the most susceptible to erosive attack by

impingement. Copper alloys resist impingement attack, but are

susceptible to cavitation damage. Nickel/aluminum and

nickel/copper alloys can be used for applications where cavitation

is likely to occur, although they will suffer material loss under

severe conditions. Nickel/chromium alloys, austenitic and precipitation-hardening stainless steels, and titanium alloys provide the

highest degree of resistance to cavitation attack. Stainless steels

and some nickel alloys are more susceptible to corrosion under

stagnant water conditions, usually by pitting and crevice attack.

Thus, the amount of downtime a system will experience should

also be considered when selecting materials resistant to erosion

corrosion. Figure 2 shows the relative corrosion susceptibility of

some alloys in a flowing water environment.

GALVANIC CORROSION

As with many other forms of corrosion, galvanic corrosion can

cause a reduction in a material’s strength, and thus can lead to

catastrophic failure under load. Galvanic corrosion can also

result in perforation failure by compromising the integrity of

sealed joints. Electronic components, such as electrical contacts

and connectors, are often susceptible to galvanic corrosion.

Test and Design Considerations (Galvanic)

Design Considerations • Loss of strength

• Perforation in applications that are 

required to be sealed (e.g. valves)

• Electronic components

• Fasteners must be cathodic

Measurement • Galvanic series (difference in corrosion 

potentials between metals)

Misapplication of Data • The order of metals on the galvanic 

series chart changes depending 

on electrolyte (seawater versus 

salt water – NaCl)

Since galvanic corrosion can accelerate the rate of corrosion of

a metal, it can lead to the failure of a component much sooner

than expected. Evaluation of galvanic corrosion does not take

into account the amount of corrosion damage (e.g. weight loss),

but rather considers the potential for galvanic corrosion to occur.

Essentially, the corrosion potential, or electronegativity, of a

metal can then be measured in an electrolyte. The electronegativity of a second metal can be measured in the same electrolyte.

When comparing the electronegativity of the two materials, the

potential for galvanic corrosion can be determined.

The tabulated galvanic series commonly displayed in the literature represents the relative electronegativity of various metals and alloys in a single specified electrolyte (usually salt

water). It should be noted that their order on the table could

vary according to the electrolyte used for the test, which is an

important consideration when designing a system to operate in

an environment other than salt water. Therefore, the electrolyte

dependence of the galvanic series must be considered, otherwise the misuse of data will result.

Figure 2. Susceptibility of Metals to Corrosion in a Flowing Water Environment.[3]

Alloy

Alumininum

2024, 2219, 7178, 

7079, 7075, 3003

2014, 6061, 7002,

5052, 5154, 1100

5456, 5086, 5083

90/10 CuNi

70/30 CuNi

Monel (Ni-alloy)

Stainless Steels

Hastelloy C (Ni-alloy)

Flow Condition

Stagnant Quiescent Moderate High Velocity

None Little Moderate Considerable
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 27

Metallurgical Considerations (Galvanic)

Metallurgical Features • Electropotential difference 

between metals is driving force 

for galvanic corrosion

Susceptible Alloys • Aluminum

• Magnesium

• Zinc

• Cadmium

• Dissimilar metals

Resistant Alloys • Similar metals on galvanic series

• Metals that can form 

impermeable scale

The electropotential difference between metals in a bimetallic system is the driving force for galvanic corrosion reactions.

Therefore, there will be a stronger driving force for metals 

with a greater difference in electropotential, and conversely a

weaker driving force for metals with a smaller difference in electropotential. There are several metals and alloys that are typically anodic to all other metals in most environments. These

include zinc, magnesium, cadmium and aluminum. For this

reason these alloys are very prone to galvanic corrosion when

electrically coupled with another metal. In general, metals and

alloys that are far apart on the galvanic series chart are likely to

create a galvanic cell, and the more anodic member will corrode

more rapidly than it would if it were not electrically coupled

with a cathodic metal.

In a bimetallic system, metals and alloys that are close together on the galvanic series chart will be more resistant to 

galvanic corrosion. Furthermore, metals and alloys that are typically cathodic to other metals in most environments will be

resistant to galvanic corrosion. Caution must be taken when

selecting a noble metal, since the introduction of a highly

cathodic material can cause corrosion problems for adjacent

metals in the same system that have traditionally been resistant

to corrosion. Galvanic corrosion can be used to protect a system or component from corrosion. Sacrificial coatings such as

zinc or cadmium are very effective means of protecting a metal.

These materials will preferentially corrode, thus protecting the

more cathodic metal to which they have been applied.

SELECTIVE LEACHING / DEALLOYING

Dealloying (Figure 3) can lead to a dramatic drop in strength

for a material, due to the selective removal of an integral alloying element. This process can leave behind a weakened and

brittle material that is far more susceptible to fracture than its

original form. As a result, in some applications dealloying can

lead a component to catastrophic failure.

Test and Design Considerations (Dealloying)

Design Considerations • Drop in strength

• Loss of ductility

• Catastrophic failure

Measurement • Weight loss

• Presence of dealloyed element 

in corrosive media

Misapplication of Data • Weight loss may be misleading since 

metals can redeposit from solution

• Difficult to separate other corrosion 

modes from weight loss test data

Selective leaching can be measured by weight loss, and by

analyzing the presence of alloying elements dissolved in a corrosive media. Sometimes dealloyed elements can be deposited

back on the surface of the metal after it has been leached from

the metal. This results in the material showing only a very slight

drop in weight. Furthermore, selective leaching may be difficult

to differentiate from other corrosion modes when analyzing

weight loss test data.

Metallurgical Considerations (Dealloying)

Metallurgical Features • Alloy composition

• Heat treatment

• Welding processes

Susceptible Alloys • Cast iron

• Aluminum and silicon bronzes

• High nickel alloys

• Copper alloys, especially 

with high Zn content

• Solders

• Au and Ag in sulfide, nitric acid

• High carbon steel

Resistant Alloys • Red brass (<15% Zn)

• P, Sb, As increase brass resistance

• 2-3% Ni in cast iron in soil

• Austenitic stainless steel 

in brackish water

Metallurgical features possibly affect selective leaching the

most, especially because this form of corrosion is strongly

dependent on alloy composition. Heat treatment and welding

processes can affect selective leaching of a component, but to a

much lesser extent.

Dezincification, denickelification, desulfurization, dealuminumification, desiliconification, destannification (removal

of tin), and decarburization are all types of dealloying that can

decompose materials containing the elements indicated by the

name. Alloys that are typically resistant to selective leaching, as

well as those that are particularly susceptible, are listed in the

table above.

INTERGRANULAR AND EXFOLIATION CORROSION

Intergranular and exfoliation corrosion can be detrimental in

that there may be no apparent weight loss of material even

though there can be a significant reduction in strength. Intergranular corrosion can also effectively produce weakened areas

along grain boundaries that are susceptible to crack formation.

Cracks may then propagate until complete fracture occurs

under an applied stress. Intergranular corrosion in mechanically worked (primarily rolled or extruded alloys) is termed exfoliation corrosion which resembles ‘flaking’ of the material.

Exfoliation corrosion primarily occurs where a corrosive environment can easily attack the endgrains (shown in Figure 4) of

susceptible materials. Exfoliation can also result in a general

strength loss of the material until failure under load occurs.

Figure 3. Dezincification of

Brass Containing a High

Zinc Content.[4]
28 The AMPTIAC Quarterly, Volume 9, Number 3

Figure 4. Mechanically Worked Material Producing Elongated

Grain Structures.

Test and Design Considerations (Intergranular)

Design Considerations • Strength loss 

• Crack initiation

• Adjacent to fasteners (exfoliation)

Measurement • Qualitative measure

• Weight loss

Misapplication of Data • Highly dependent upon heat treatment

Like many forms of corrosion, intergranular and exfoliation

corrosion are measured qualitatively. Tests are highly dependent

upon alloy composition, heat treatment and test technique. In

these tests, materials are typically exposed to an acidic media,

which readily attacks grain boundary precipitates, if present.

Weight loss measurements are used in some cases to identify

susceptible materials. However, this depends on the removal of

grains from the material as a result of the corrosion process.

Microscopic examination may also be used to identify this corrosion mode.

Metallurgical Considerations (Intergranular)

Metallurgical Features • Alloy/heat treatments that produce 

grain boundary precipitates which 

are anodic to the base metal

• Rolled and extruded alloys (exfoliation)

Susceptible Alloys • Welded stainless steels

• Some aluminum alloys

• Some nickel alloys

Resistant Alloys • Quenched aluminum alloys

• Nickel alloys containing Cr and Mo

Intergranular and exfoliation corrosion occur as a result of the

precipitation of intermetallic compounds in grain boundaries,

which are more anodic than the base material. The most predominant susceptibilities have been observed in stainless steels

and some aluminum and nickel-based alloys. Some stainless

steels, especially ferritic stainless steels, have been found to

become sensitized to this form of corrosion, particularly after

welding. Welding can cause the precipitation of chromium carbides at grain boundaries in the heat affected zone often leading

to intergranular corrosion. Aluminum alloys are traditionally

vulnerable to intergranular and exfoliation attack, especially the

2024, 5083, 7030, and 7075 alloys with certain heat treatments.

Quenched aluminum alloys are more resistant to intergranular

corrosion because the fast cooling rate prevents the formation of

grain boundary precipitates. Highly alloyed nickel can be susceptible to intergranular corrosion by the precipitation of intermetallic phases at grain boundaries, while nickel alloys

containing chromium and molybdenum are typically resistant.

STRESS CORROSION CRACKING

The primary concern with stress corrosion cracking (SCC) is

that it can lead to the catastrophic failure of a component.

When stress corrosion cracks form in a component under an

applied load, the material will lose strength until it fails which

can occur instantaneously.

Test and Design Considerations (SCC)

Design Considerations • Drop in strength

• Catastrophic failure

Measurement • Crack propagation rate, da/dt 

(a – crack length; t – time)

• Critical stress intensity factor, KISCC

Misapplication of Data • Pure metals can be susceptible to SCC

• KISCC can be directionally dependent

• KISCC is environmentally dependent

The magnitude of SCC can be measured experimentally based

on a rate of crack propagation. This measure identifies how quickly a material may fail under an applied load in corrosive conditions.

The susceptibility of a material to SCC may also be estimated

based on a critical stress value that will propagate a crack under corrosive conditions. This factor is called the stress corrosion cracking

stress intensity factor, KISCC.

A common misconception regarding this form of corrosion

is that pure metals are always resistant to stress corrosion cracking, when in fact, they can be susceptible. Stress corrosion

cracking differs from many of the other forms of corrosion in

that there exists numerical data, in the form of KISCC, that

quantifies the phenomenon. This data, however, can be directionally dependent, and the designer or engineer needs to be

careful in applying it to the proper direction of the material

under consideration. Furthermore, KISCC is environmentally

dependent, and as a result the environment in which the test

data was produced should be taken into consideration.

Metallurgical Considerations (SCC)

Metallurgical Features • Impurities decrease resistance

• For carbon steel, susceptibility 

increases with increasing C 

content up to 0.12 wt%

• Steels have high susceptibility when 

composition includes Ni up to 9%

• When Ni content is <1% and >40%,

steels have low susceptibility

• Mo, V, and Nb alloying elements 

improve resistance in titanium alloys

• Mechanical working of aluminum alloys

increases directional susceptibility

• Heat Treatment

Susceptible Alloys • Carbon steel

• HSLA steel 

(>1200 MPa strength)

• Austenitic stainless steel

• 2000 and 7000 series aluminum alloys

• Titanium alloys

• Magnesium alloys

• Copper alloys

• Zirconium alloys

• Alloys with highly protective oxides

Resistant Alloys • Aluminum-magnesium alloys 

with <4% Mg

Endgrains
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 29

There are many metallurgical factors that affect the nucleation and/or propagation of a stress corrosion crack or a

material’s susceptibility/resistance to SCC in general. For

instance, impurities in a metal will often decrease its resistance to stress corrosion cracking. Alloying elements can also

affect the susceptibility or resistance to SCC. The presence

of up to 0.12% carbon in carbon steel increases its susceptibility to SCC. Nickel content in steels has a significant

effect on their resistance to SCC. For example, steel with Ni

content up to 9% is highly susceptible to SCC, and when

the Ni content is less than 1% or greater than 40%, steel has

a low susceptibility to SCC. Molybdenum, vanadium and

niobium all improve the resistance of titanium to SCC.

Post-fabrication heat treating, mechanical working, and

joining also have an effect on a material’s susceptibility to

SCC. Mechanical working (e.g. extrusion) of aluminum

alloys, for example, increase the directional susceptibility 

to SCC.

Alloys that are known to have problems with stress corrosion cracking in salt water include those shown in the table.

Aluminum-magnesium alloys with <4% Mg are typically

resistant to SCC.

CORROSION FATIGUE

Corrosion can cause a reduction in the fatigue strength of a

material. As a result, a component designed to withstand a

normal fatigue load can experience catastrophic failure if the

same load is applied under corrosive conditions.

Test and Design Considerations (Corrosion Fatigue)

Design Considerations • Reduced fatigue strength

• Catastrophic failure

Measurement • S/N curves

• Crack growth rate, da/dt

Misapplication of Data • Interacts with other forms 

of corrosion such as pitting

• Difficult to distinguish corrosion 

fatigue from SCC and hydrogen 

damage

Since corrosion fatigue occurs under the conditions of

cyclic stress, data applicable to this form of corrosion are S/N

curves (S – applied stress; N – cycles to failure) for a material

in a particular corrosive medium. In addition, determining

the cycles to failure is a way to measure the durability of a

material in a corrosive medium. The crack growth rate can

also be used to measure the progression of corrosion fatigue

cracking.

Corrosion fatigue may be initiated by or interact with other

forms of corrosion, such as pitting, which can supply crack

initiation points. As a result, using data simply for corrosion

fatigue may lead to underestimating the extent of corrosion

damage to a material. In addition, this form of corrosion is

sometimes difficult to distinguish from stress corrosion cracking and hydrogen damage. This again may lead to a difficulty

in identifying the problem or finding the appropriate solution

to prevent or mitigate further damage.

Metallurgical Considerations (Corrosion Fatigue)

Metallurgical Features • Heat treatment

• Composition

• Increasing tensile strength improves 

normal fatigue properties but is 

detrimental to corrosion fatigue 

properties

• Ferrous alloys do not have an endurance

limit in a corrosive 

environment

Susceptible Alloys • Same as SCC

• Coating processes that produce 

residual tensile stresses or hydrogen 

reduce corrosion fatigue resistance

Resistant Alloys • No metal is immune to corrosion fatigue

• Similar to SCC

Similar to stress corrosion cracking, there are many metallurgical factors that contribute to the nucleation and/or propagation

of a corrosion fatigue crack, or a material’s susceptibility/resistance to corrosion fatigue, in general. For example, heat treatment

and composition are major factors that can influence a material’s

susceptibility to corrosion fatigue. Tensile strength may also be an

indication of susceptibility to corrosion fatigue. Increasing tensile

strength improves normal fatigue properties, but is detrimental

to corrosion fatigue properties. The endurance limit is the lower

bound on the stress required to propagate fatigue cracks in ferrous alloys. However, ferrous alloys do not have an endurance

limit in a corrosive environment.

Stress corrosion cracking is similar to corrosion fatigue in

that many of the same alloys that are susceptible to SCC are

also susceptible to corrosion fatigue. Coating processes that

produce tensile stresses or hydrogen often reduce the corrosion

fatigue resistance of the base material. While there is practically no metal which is immune to corrosion fatigue, those that

are somewhat resistant to stress corrosion cracking are usually

also resistant to corrosion fatigue.

FRETTING CORROSION

Fretting corrosion can result in fatigue strength loss (fretting

fatigue), surface wear, and electrical contact failures. Electrical

contacts have been known to experience fretting corrosion as a

result of thermal cycling and the difference in thermal expansion coefficients of the contacting metals.

Test and Design Considerations (Fretting)

Design Considerations • Strength loss

• Wear

• Loss of electrical continuity 

(in electronics)

Measurement • Qualitative measure

Misapplication of Data • Use of corrosion fatigue data

Fretting corrosion is another form that is measured in 

qualitative terms, and much of the data/information has 

been accumulated from field experience. Fretting can decrease 

the fatigue strength in materials (fretting fatigue), although 

the number of contributing factors including the environ-
answers materials engineering questions

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30 The AMPTIAC Quarterly, Volume 9, Number 3

ment, contacting metal, applied load, and the degree of

motion all make fatigue strength measurements due to fretting

unreliable. Although fretting fatigue may be considered a type

of corrosion fatigue, corrosion fatigue data should never be

used in relation to fretting corrosion.

Metallurgical Considerations (Fretting)

Metallurgical Features • Hard/soft metal combinations

Susceptible Alloys • Steel against steel 

• Nickel against steel

• Aluminum against steel

• Antimony plate against steel

• Tin against steel

• Aluminum against aluminum

• Zinc-plated steel on aluminum

• Iron-plated steel against aluminum

Resistant Alloys • Lead against steel

• Silver plate against steel

• Silver plate against aluminum plate

• Steel with a conversion coating 

against steel

The hardness of the contacting metals is a major factor in the

susceptibility of a material system to fretting corrosion. For

example, a hard metal/soft metal combination provides the 

best fretting corrosion resistance. General susceptible and

resistant alloy combinations are listed in the table above.[5] 

Thermal expansion coefficients should also be considered when

selecting materials, especially for electrical contacts.

SUMMARY

The proper selection of materials should include consideration

of corrosion in the design phase of new systems. Knowledge of

the forms of corrosion and the data used to characterize the

various forms are essential for effective design and material

selection. This article covered some of the key factors that contribute to a material’s susceptibility or resistance to the major

forms of corrosion. It is clear that if corrosion costs are to be

reduced in the future, either a corrosion or materials engineer

needs to be included in the design/material selection processes, or the designers and personnel responsible for material

selection must have a better understanding of the various

forms of corrosion and how they effect system performance

and life-cycle costs.

REFERENCES

[1] Corrosion Technology Testbed, NASA Kennedy Space Center,

http://corrosion.ksc.nasa.gov/

[2] Handbook of Corrosion Data, 2nd Edition, Eds. B.D. Craig and

D.S. Anderson, ASM International, 1995

[3] W.K. Boyd and F.W. Fink, Corrosion of Metals in Marine 

Environments, MCIC-78-37, March 1978; DTIC Doc.: ADA054583

[4] Corrosion on Flood Control Gates, US Army Corps of 

Engineers, http://www.sam.usace.army.mil/en/cp/CORROSION_

EXTRA.ppt

[5] Corrosion in the Aircraft Industry, ASM Handbook, Vol. 13: 

Corrosion, 9th Edition, ASM International, 1987, pp. 1019-1057
http://iac.dtic.mil/amptiac The AMPTIAC Quarterly, Volume 9, Number 3 31

AMPTIAC Directory

Government Personnel

TECHNICAL MANAGER/COTR

Dr. Lewis E. Sloter II

Staff Specialist, Materials & Structures

ODUSD(S&T)/Weapons Systems

1777 North Kent St, Ste 9030

Arlington, VA 22209-2110

(703) 588-7418, Fax: (703) 588-7560

Email: lewis.sloter@osd.mil

ASSOCIATE COTR

ENVIRONMENTAL PROTECTION

& SPECIAL FUNCTION MATERIALS

Dr. James Murday

Naval Research Laboratory

4555 Overlook Ave, S.W. Code 6100

Washington, DC 20375-5320

(202) 767-3026, Fax: (202) 404-7139

Email: murday@nrl.navy.mil

DEFENSE TECHNICAL INFORMATION CENTER

(DTIC) POC

Melinda Rozga, DTIC-AI

8725 John J. Kingman Rd, Ste 0944

Ft. Belvoir, VA 22060-6218

(703) 767-9120, Fax: (703) 767-9119

Email: mrozga@dtic.mil

DIRECTOR, AMPTIAC

David Rose

201 Mill Street

Rome, NY 13440-6916

(315) 339-7023, Fax: (315) 339-7107

Email: drose@alionscience.com

DEPUTY DIRECTOR, AMPTIAC

Christian E. Grethlein, P.E.

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TECHNICAL INQUIRY SERVICES MANAGER

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Alion Science and Technology Personnel

This Year’s Tri-Service Corrosion Conference a Big Draw

Nearly 400 technical and management professionals from government and industry gathered November

14-18 in Orlando, Florida for the 2005 Tri-Service Corrosion Conference. Held on a biennial basis, the

Tri-Service Conference is the preeminent gathering of personnel who address corrosion issues within the

defense community. The conference’s technical program has traditionally been run by corrosion specialists from the three services on a rotating basis. Technical direction for this year’s conference was provided by Drs. John Beatty and Ralph Adler, both from the US Army Research Laboratory. The conference

was chaired by Mr. Daniel J. Dunmire; from the DOD’s Office of Corrosion Policy and Oversight, and

head of its working group - the Corrosion Prevention and Control Integrated Product Team (CPC IPT).

This year’s theme was Transcending and Integrating Corrosion Prevention and Control for the Department

of Defense. In addition to the near-record number of attendees, fifty-seven exhibitors set up displays at

the conference, representing corrosion products and services of companies, government agencies, 

and technical societies. Several pictures from the conference are shown below. The next Tri-Service 

Conference will be held December 4-8, 2007 in Denver, Colorado, where the theme will be Integrating

Corrosion Prevention and Control in Policy, Planning, and Programming. Technical program direction will

be provided by the Air Force.

Representatives of the CPC IPT in front of their booth: pictured left 

to right – Dr. Lewis Sloter (Defense Research & Engineering), 

Mr. Daniel J. Dunmire (Office of Corrosion Policy and Oversight),

and Col. Larry Lee (USAF, ret.).

Conference Attendees Conversing in the Exhibit Hall.
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