201 d document

201D Script

Corrosion Management

Methodology

IInnttrroodduuccttiioonn

This segment discusses decisive questions that must be answered to define the

corrosion problems being addressed; links these questions to a corrosion risk

management approach; describes the corrosion prevention and mitigation design

process; and covers the role of corrosion planning and actions during the

acquisition of new systems and facilities.

RReessoollvviinngg CCoorrrroossiioonn PPrroobblleemmss

Sound management decisions and effective courses of action are important to

resolve specific corrosion problems.

First, you need to communicate an awareness of corrosion risks and

consequences to everyone involved in the acquisition, operation, and

maintenance of systems vulnerable to corrosion.

Second, you need a sound strategy backed up by an effective corrosion

prevention and control plan to assure better corrosion management and

mitigation throughout the systems life cycle. That means taking action to

avoid or mitigate high risks during system design; specifying practices to

avoid detrimental effects during manufacturing and assembly; defining tools

and techniques to identify high risk conditions and poor quality maintenance

during inspection and repair; and specifying the relevant processes to guide

failure analysis and corrective action when corrosion-causedfailures occur.

201D Ch1 Practice of Risk-Based Management for Corrosion

Section 1: Introduction

DDeecciissiivvee CCoorrrroossiioonn QQuueessttiioonnss

Developing effective courses of action to thwart or minimize the incidence and

effects of corrosion depends on the answers to decisive corrosion questions.

These questions are focused around: types of equipment and facilities, materials

from which they are manufactured or constructed, and of environments to which

they are exposed.

For example, results of exposure to seawater, harsh environments, temperature,

and stress will vary in in

tensity, depending on the specific operating or storage environment and the

exposure time.

CCoorrrroossiioonn QQuueessttiioonnss:: GGuuiiddee ttoo IIddeennttiiffyy RRiisskkss

A risk based approach to corrosion management and mitigation refers to these

decisive questions as a guide to identifying corrosion risks, and to determining

potential barriers you can employ to control those risks.

Although the objective is to prevent corrosion when possible, that is not always

technologically or financially practical.

In those cases, you determine allowable corrosion and develop a corrosion

management plan for acceptable life performance. Then implement and follow up the

plan.


Section 2: Problem Definition

CCoorrrroossiioonn RRiisskk VVaarriiaabblleess

Corrosion risk is a function of vulnerability, probability, and consequence. If

any of the variables equal zero, there is no risk.

As each variable increases, the risk also increases and you must assess the

compound effect in terms of allowable corrosion and acceptable performance.

CCoorrrroossiioonn:: RRiisskk,, UUttiilliittyy,, aanndd RReelliiaabbiilliittyy

The relationship between risk, utility, and reliability can also be quantified.

When expressed in terms of risk, utility is the product of frequency, consequence

and a utility function, such as cost of equipment failure, summed over the

individual corrosion scenarios.

Utility is often used to assess business or enterprise risk, where financial risk

needs to be evaluated and related to non-technical risk.

Reliability is the probability that a system will perform its specified function

over a given time period. Mathematically, reliability is the inverse of failure

probability.


Section 3: Risk Management Perspective

RRiisskk MMaannaaggeemmeenntt:: BBooww--TTiiee AApppprrooaacchh

The Bow-Tie Approach to Risk Management is shown in this diagram.

Threats listed on the left side can lead to critical adverse events, such as an

explosion, a crash, or the failure of a critical component. Consequences of those

failures are listed on the right.

You need to define multiple barriers that can isolate the event from the threat,

and also define barriers that can prevent the consequences of the event. The

barriers should be chosen such that the probability of all barriers failing is

virtually zero.

CCoorrrroossiioonn BBaarrrriieerrss

This illustration of the application of barriers to prevent unacceptable events

or consequences shows the compound effects of multiple barriers in reducing the

occurrence of adverse events or the incidence of damage.

CCoorrrroossiioonn BBaarrrriieerrss:: SSwwiissss CChheeeessee MMooddeell

One method of creating barriers for corrosion threat management is the Swiss

Cheese Model shown here, where a series of barriers with unavoidable holes allow

threats to advance until they encounter a solid section of one of the barriers.



Only if a threat avoids all solid barrier sections can it cause a critical event

or subsequent damage. Thus the more barriers and fewer small unavoidable holes,

the lower the risk of corrosion.

RRiisskk--BBaasseedd IInnssppeeccttiioonn

Risk Based Inspection (RBI) links potential risks with appropriate inspection

methods and techniques. RBI assesses and manages safety, health, environmental

and economic risks at the equipment level.

RRiisskk aanndd IInnssppeeccttiioonn AAccttiivviittyy

This graph shows risk versus inspection activity. The upper curve reflects risk

using typical inspection programs. Note that risk eventually increases even with

more inspection because damage is accumulating and evolving. The risk based

inspection program lowers overall risk by reducing probability of failure, but it

never reduces risk to zero.



There is usually some residual risk that must be accepted or dealt with.

CCoonnddiittiioonn--BBaasseedd MMaaiinntteennaannccee

Well, condition-based maintenance allows us the opportunity to identify the

condition of the equipment so we know the requirements and the repair

requirements on an asset prior to going in and if you will induct it into a

facility that may not be needed. So our baseline means a lot to us in the Marine

Corps to know the condition of that asset so thats what we refer to as

condition-based maintenance:

What is the need?

What is the requirement?

What skill sets are required to repair that asset?

By identifying all of our assets by a corrosion category code and those category

codes go from a category code 1 being a best condition asset to a category code 5

being the worst condition asset.

And we identify our repairs and our levels of maintenance requirements by those

category codes so our condition-based maintenance is what we use every day on how

we repair our assets.

RReelliiaabbiilliittyy--CCeenntteerreedd MMaaiinntteennaannccee

Reliability-Centered Maintenance (RCM) takes Condition-Based Maintenance (CBM)

to the next level and condition-based maintenance is more of a reactive mode -

you see a failure and youre going to correct that.



With reliability-centered maintenance, youre taking a look at the actual parts

and trying to do and find methods and processes to increase the reliability so

you do not have these failures again in the future. Its a process that started

back in the 60s and it takes a more in-depth look to try to find the methods and

processes to increase the reliability which has impacts, again, on the

availability and the over-all system performance.

The AAV now has to last for another 15 years so were looking at all the

different components that have been failing over the years and trying to figure

out ways to increase the reliability since were starting to get a lot of higher

failures. So theyre gonna be looking heavily at reliability-centered maintenance

in order to increase the availability, the system performance and over-all total

ownership cost of the system.

MMaaiinntteennaannccee AApppprrooaacchh VVaarriiaabblleess

Each of the above approaches to managing corrosion risk depends on quality

information, design, plans, people, and judgment. No approach can compensate for

shortfalls in information, design, planning execution, qualified personnel and

teams, or poor engineering or operational judgment.



CCoorrrroossiioonn MMiittiiggaattiioonn aanndd DDeeffeennssee AAccqquuiissiittiioonn PPrroocceessss

Reducing the incidence, frequency, and impact of corrosion is best accomplished

during the design and development of a system or facility. The defense

acquisition process provides a model within which to insert plans, decisions, and

actions to prevent or mitigate corrosion and its effects early in the design

process.

Corrosion planning should be introduced very early during concept refinement, and

a corrosion prevention action team established before milestone A (indicated by

A in the triangle). The corrosion prevention and control plan should be

included in the request for proposal process during technology development.

Other important actions are indicated on the model shown here. The sooner that

corrosion planning and decision-making is integrated with the entire development,

the more likely that corrosion risks will be avoided or controlled. Waiting until

a system or facility is operational to correct a faulty design or configuration

is many times more expensive than addressing potential problems up front.


Section 4: Corrosion Prevention and Mitigation Design

Process

SSyysstteemm DDeessiiggnn aanndd PPeerrffoorrmmaannccee

While designing to the specified form, fit and function is the essence of

engineering work, the best performance measure is the degree to which a system

conforms to its specified objectives.

Unfortunately, many engineers consider that performance is defined by how well

the system operated the day it leaves the factory.

The traditional design flaw is the failure to focus on how a system will perform

in the years after deployment.

SSyysstteemm PPeerrffoorrmmaannccee TThhrroouugghhoouutt LLiiffeessppaann

Fortunately, a new engineering paradigm focuses on system performance throughout

its useful lifespan. Engineers can analyze the likely environmental conditions,

predict how and when certain components are likely to fail, and plan to avoid or

mitigate such potential failures.

The key questions engineers must answer are:

1. How well will the system perform its mission requirements at a given point in its life cycle?

2. What is the probability of mission success when a system is required to perform?

3. For how many years can the system be expected to exhibit cost effective performance?

PPeerrffoorrmmaannccee--BBaasseedd AAccqquuiissiittiioonn

Since the year 2000, many new systems have been acquired by the federal

government using Performance-Based Acquisition (PBA), a technique that structures

all aspects of a systems acquisition around its purpose and desired outcomes, as

opposed to the process by which the work is to be performed.



Process

Since the advent of performance-based acquisition, most military system

specifications are articulated in terms of operational performance of the

finished product. Decisions regarding material selection and detailed designs to

meet those performance specifications are left to the manufacturers and their

subcontractors.

While the objectives of PBA are to reduce cost and accelerate acquisition, it

shifts additional risk (including corrosion risk) to the government for increased

sustainment costs over the life cycle of the system.

Still, the goal is to reduce total operating cost.

DDooDD SSttrraatteeggiicc PPeerrffoorrmmaannccee RReeqquuiirreemmeennttss

This figure shows the flow of performance requirements from DoD strategic

objectives through specific technical objectives to a prime contractors system

definition for manufacturing. Once performance specifications establish technical

objectives such as range, payload, size, weight, human factors, and corrosion

prevention and control, it is up to the prime contractor to define major systems

and develop top-level technical requirements and designs.

These requirements and designs establish a baseline for specifying and designing

assemblies, subassemblies, components, and materials that comprise the major

systems and will be manufactured and assembled by the prime contractor,

subcontractors, and suppliers.



Process

While performance-based acquisitions are supposed to contain measurable

performance standards and a performance assessment plan, effective implementation

of these standards and plans depend on sufficient government oversight to assure

performance quality and reliability.

PPeerrffoorrmmaannccee RReelliiaabbiilliittyy aanndd EExxppeecctteedd SSeerrvviiccee LLiiffee

Performance reliability is the measure of how well a system can be expected to

perform specified functions, when it is employed, throughout its service life.

Reliability can be quantified either intuitively or mathematically. Service life

is the period of system use from initial operational employment until it can no

longer be usefully employed.

Service life might be ended by system loss, major failure, obsolescence and

replacement, or planned retirement and disposal. Expected service life is usually

expressed in calendar years or total operating hours and is often determined by

reliability prediction or accelerated life testing to failure.

Systems for which loss or failure have no health or safety consequences may be



Process

operated until failure. Other systems may be refurbished or retired based on CBM

or RCM conditions that dictate intervention before failure.

SSyysstteemm DDeevveellooppmmeenntt:: PPaarraaddiiggmm SShhiifftt

The old paradigm of developing systems based almost exclusively on initial

performance and unit cost is being replaced by the concept of affordable system

operation throughout its life cycle.

This means evaluating performance, availability, and life cycle cost over the

projected life of the system. This emphasizes the need to understand corrosion

processes, to know how corrosion mitigation systems behave, and to establish a

sound technical basis to support performance, availability, cost calculations,

and judgments.

AAffffoorrddaabbllee SSyysstteemm LLiiffee

This diagram shows the elements of Affordable Systems Operational Effectiveness.

System performance and availability provide technical effectiveness.

Process effectiveness means cost effective production and support, which



Process

translates technical effectiveness into system effectiveness.

With reasonable controlled life-cycle cost, this system effectiveness yields an

affordable system throughout its useful life.

DDoowwnnssttrreeaamm LLiiffee CCyyccllee CCoossttss

This diagram illustrates the impact of downstream life cycle costs, which

typically account for between 65% and 80 % of total life cycle costs.

What this diagram does not show is the leverage up-front expenditures can have on

downstream costs.

UUpp--FFrroonntt CCoorrrroossiioonn IInnvveessttmmeennttss

Typically, each up-front dollar spent to reduce downstream costs leverages five

to ten dollars in cost avoidance. This is particularly true of corrosion

prevention investments R&D dollars spent upfront to design corrosion prevention

or resistance into the system can significantly reduce corrosion procurement

funds, and avoid huge expenditures of operation and maintenance funds to repair

or replace corroded facilities and equipment.



Process

CCoorrrroossiioonn MMiittiiggaattiioonn:: AAccqquuiissiittiioonn CCyyccllee

The time to prevent or mitigate corrosion and reduce total ownership costs is

early in the acquisition cycle.

BBaatthh TTuubb CCuurrvvee ((LLiiffee CCyyccllee CCoossttss))

The bathtub curve shown here illustrates the typical trend in life cycle costs

for systems and facilities. Early costs are attributed to birth defects, and

these costs bottom out early in the life cycle. Normal operating costs gradually

increase until near the end of the life cycle where age and wear cause ever-

increasing failures.

Early investment in corrosion prevention and mitigation can reduce failures and

costs along the entire bathtub curve, and also extend the life of the system,

leading to a better performance, availability, and an overall increase in

affordability.

MMaatteerriiaall SSeelleeccttiioonn aanndd EEnnvviirroonnmmeenntt CCoonnddiittiioonnss

In order to select the best material for corrosion resistance, you need to

thoroughly understand the operational environment, including corrosive

environments during transportation and storage.

Even after effective material selection, certain environmental conditions can

accelerate corrosion.

Finally, there are several design considerations that, if overlooked, can have

serious if not catastrophic results.



Process

IInnttrroodduuccttiioonn:: DDiiaaggnnoossttiiccss aanndd PPrrooggnnoossttiiccss

This segment discusses diagnostics and prognostics, accelerated testing, and

application of prognostics to system health management.

CCoorrrroossiioonn RRiisskk:: CCuurrrreenntt ttoo FFuuttuurree SSttaattee

Where there is a risk of corrosion, we need to determine the current state of

corroding materials and the attendant causes of that corrosion.

We also need to forecast the expected future state and behavior of corroded or

vulnerable materials, including their predicted reliability and length of service

life.

Such determinations and predictions are undertaken by using diagnostic and

prognostic technologies and methods; by applying accelerated test techniques; and

by performing system health monitoring, performance assessment and integrity

management during a systems service life.

CCoorrrroossiioonn DDiiaaggnnoossttiiccss

Corrosion diagnostics consists of an analysis and assessment of corrosion damage

and its causes. The corroded material is inspected along with the environment to

which it has been exposed to establish the current status of the material and the

type of corrosion that was initiated.

Analysis and assessment is based on these observations along with knowledge of

the material characteristics, design, construction, and associated manufacturing

and repair processes.

CCoorrrroossiioonn DDiiaaggnnoossttiiccss:: PPuurrppoossee

Corrosion diagnostics are used to determine if a component or system conforms to

its design and operational requirements, and is safe for continued use.

Results can be used to evaluate the effectiveness of current corrosion prevention

and control strategies, and if needed, to develop alternative strategies and

methods.

Diagnostics also provide early warning of corrosion-induced failures, such as

metal cracking and embrittlement that can trigger catastrophic results.

201D Ch2 Systems Health Management Section 1: Diagnostics and Prognostics

CCoorrrroossiioonn DDiiaaggnnoossttiiccss:: SSyysstteemm iinn OOppeerraattiinngg PPaarraammeetteerrss

Diagnostics will reveal if a system is still being maintained within specified

corrosion allowances or operating parameters. Corrosion damage increases as time

passes, so periodic inspections, and reassessment are necessary.

Risk based corrosion management, covered in segment one, is needed to establish

appropriate inspection methods and intervals, based on the observed corrosion

process and damage evolution.

Non-destructive inspection methods, covered later in the course, are often used

to detect, measure, and evaluate the form and extent of corrosion damage.

CCoorrrroossiioonn PPrrooggnnoossttiiccss

Corrosion prognostics is the technical process of analyzing and predicting the

likelihood and extent of future corrosion damage. The baseline for this

prediction is the existing state determined by the corrosion diagnostics.

Results of diagnostic monitoring and analysis is used in predictive models to

forecast corrosion growth rates, damage potential, and impact on system

performance and service life. Monitoring methods include direct measurement;

electrical, electrochemical, and inductive resistance sensors; hydrogen probes;

and non-destructive inspection.

CCoorrrroossiioonn PPrrooggnnoossttiiccss:: PPuurrppoossee

Prognostics can guide future corrosion prevention and control strategy. It

provides a good foundation for maintenance and material decisions regarding

inspection intervals and schedules; actions to reduce life-cycle costs and

increase reliability; and feasibility of replacement, repair, or retirement of

equipment or facilities.

CCoorrrroossiioonn PPrrooggnnoossttiiccss

Predictive models process corrosion diagnostics and prognostics data, corrosion

database information, and multiple physics models. These models analyze and

correlate physical, chemical, mechanical, and electrochemical effects integrating

associated materials, environmental and mechanical data.


Predictive models also use data from laboratory or field tests that evaluate

material performance under operating conditions. A simple example of a predictive

model computation is the prediction of remaining service life by dividing the

remaining corrosion allowance found in the corrosion database by the observed

diagnostic corrosion rate.


AAcccceelleerraatteedd CCoorrrroossiioonn TTeessttiinngg

Accelerated testing is a method of environmental stress testing at increased

operational rates to more quickly improve product reliability during system

development.

It can reveal design weaknesses early in development and allows engineers to

change design parameters on a system still in development, thus reducing the

probability of in-service failures.

It also identifies safe operating limits and design margins, such as corrosion

allowances. Accelerated tests may be performed on materials, components, or

complete systems to evaluate competitive designs and to increase confidence in

effective, long-term performance of the selected alternative.

TTyyppeess ooff AAcccceelleerraatteedd CCoorrrroossiioonn TTeessttiinngg

Accelerated testing falls into two categories - qualitative testing and

quantitative testing. Qualitative tests stress components to accelerate failures

that can affect reliability.

The object is to identify failure modes and define the best material for an

application. However, qualitative testing does not indicate overall reliability

or expected service life. Quantitative tests are used to characterize the effects

of given failure modes on component performance and to determine a systems time

to failure.

To determine time-to-failure, Quantitative tests are used to characterize the

effects of given failure modes on component performance and to determine a

systems time to failure. To determine time-to-failure, that will be used

continuously or at a very high rate. Usage rate acceleration is used on

components that are not operated continuously.

201D Ch2 Systems Health Management Section 2: Accelerated Corrosion Testing

SSyysstteemm FFaaiilluurreess

Catastrophic failure occurs when a system or component stops working and is

beyond repair. This table depicts catastrophic failure modes for common products

that you use frequently.

PPeerrffoorrmmaannccee TThhrreesshhoolldd VVaalluuee

To prevent a catastrophic failure of a system or component, we assign a

performance threshold value. This value is below which a system or component is

defined to have failed, and at which point we remove it from service. This

process is referred to as defined failure.


AAcccceelleerraatteedd TTeessttiinngg PPuurrppoosseess

Accelerated testing is used for many purposes related to material selection,

component design, quality, performance, and reliability.

This is a list of 12 uses of accelerated testing. Click here for a full

description of each.


AAcccceelleerraatteedd TTeessttiinngg MMooddeellss

Accelerated testing is one approach to performing quantitative analysis. Models

and analytic representations provide tools with which to describe mechanisms

governing the process being investigated.

Selecting the proper model to analyze test data is vital since most accelerated

testing involves fitting test data to the model and extrapolating the results.

SSttaattiissttiiccaall MMooddeell

Statistical Modeling is a quantitative analysis technique used to predict the

success or failure of a component or system. This mathematical model is developed

or selected to address a well-defined problem. Once a model is developed or

selected, the frequencies of occurrence of various stresses may be fed into that

model.

For the exposure of the component or system being analyzed so you can have things

like both the level and occurrence of things like mechanical stresses, thermal

stresses, or chemical stresses.

Once you feed those into the model, then you would have a fairly accurate

prediction if you have the correct model of the success or failure of that system

or component.


AAcccceelleerraatteedd TTeessttiinngg:: PPiittffaallllss aanndd LLiimmiittaattiioonnss

Accelerated testing is not without its limitations and pitfalls. Test failures

might be induced by failure modes not experienced during normal operation and

lead to false conclusions.

Likewise, failure to properly identify operating or environmental conditions can

produce inaccurate accelerated test results. If operating conditions are not

properly recorded or qualitatively tested, unexpected failure modes might occur.

If an accelerated test fails to identify a relevant, realistic failure mode, that

failure mode will not be evaluated. For example, testing for uniform corrosion

without accounting for the possibility of localized pitting corrosion can cause

unexpected failure during subsequent operational use.

Selecting the wrong model will often produce unrealistic results. Finally,

failure to account for coupled or sequential corrosion reactions, such as stress

corrosion cracking following pitting corrosion, can generate false analytic

conclusions and downstream fatigue or material failures.


PPrrooggnnoossttiiccss aanndd HHeeaalltthh MMaannaaggeemmeenntt SSyysstteemm

The integration of diagnostics, prognostics and quantitative and qualitative

testing and analysis provides the foundation for a modern Prognostics and Health

Management System.

The objective is a system capable of using the inputs described in this slide to

estimate the likelihood and time of a future system failure, so appropriate

preventive actions can be taken now.

PPrrooggnnoossttiiccss aanndd HHeeaalltthh SSyysstteemm AArrcchhiitteeccttuurree

This diagram illustrates the Prognostics and Health System architecture under

development at the Sandia National Laboratory.

Although the technology may not yet be sufficiently mature for use with many

weapon systems, this integrated approach continues to be developed and should be

considered and employed by decision-makers at all levels.

201D Ch2 Systems Health Management Section 3: Applications

CCoorrrroossiioonn DDeetteeccttiioonn aanndd IInnssppeeccttiioonn IInnttrroodduuccttiioonn

This segment of Course 201D addresses both corrosion detection and inspection

methods, as well as corrosion monitoring and sensors.

CCoorrrroossiioonn PPrreevveennttiioonn aanndd CCoonnttrrooll GGuuiiddee

The AMMTIAC Corrosion Prevention and Control Guide is the source of much

information in this segment, and provides an excellent reference for further

information.

NNoonn--DDeessttrruuccttiivvee EEvvaalluuaattiioonn aanndd IInnssppeeccttiioonn

Non-destructive evaluation (NDE) and non-destructive inspection (NDI) methods

provide the capability to detect, characterize, and quantify corrosion damage.

Non-destructive inspection employs visual techniques, as well as eddy current,

ultrasonic, acoustic emission, thermographic and electromagnetic radiation

technologies.

VViissuuaall IInnssppeeccttiioonn

Visual inspection is the easiest method to detect corrosion. The type of

corrosion often is described and classified based on the appearance of its

visible surface, and in some cases it can be measured. In other cases, it is

documented using sketches, photography, or video.

VViissuuaall IInnssppeeccttiioonn:: CCoorrrroossiioonn PPrroodduucctt AAppppeeaarraanncceess

These types of corrosion are frequently associated with specific alloys and the

appearance of resulting corrosion products. Aluminum is susceptible to pitting,

intergranular and exfoliation corrosion.

The corrosion products tend to be white or a gray powder. Magnesium alloys tend

to pit, and corrosion produces mounds of snow-like powder.

Low alloy steels are susceptible to surface oxidation, pitting, and intergranular

corrosion. The corrosion products are reddish brown oxides - which you would call

'rust'.

201D Ch3 Corrosion Detection and Monitoring Section 1: Non-destructive Evaluation and Inspection

VViissuuaall IInnssppeeccttiioonn:: CCoorrrroossiioonn PPrroodduucctt AAppppeeaarraanncceess

Copper-based alloys suffer from pitting and intergranular corrosion, and

corrosion products are usually dark oxides on a rough surface.

It is important to collect samples of these products in order to characterize the

corrosion and analyze its mechanisms.

To learn more, click here to a downloadable table that details the appearance of

corrosion in various alloys.


VViissuuaall IInnssppeeccttiioonn DDeevviicceess

Visual inspection often depends on devices to enhance observation. These devices

include microscopes, magnifying glasses, boroscopes, fiberscopes and odoscopes.

Boroscopes and fiberscopes are designed to inspect hidden surfaces and feature

lighting and lenses to enhance visibility.

BBoorroossccooppee VVSS.. FFiibbeerrssccooppee

Boroscopes tend to be fairly rigid, while fiberscopes are flexible and can be

used in more difficult-to-access locations.

LLiiqquuiidd PPeenneettrraanntt IInnssppeeccttiioonn

In liquid penetrant inspection, a colored dye is spread on the material and

allowed to penetrate cracks and other openings. After removing excess penetrant

from the surface, a powdery substance is applied to highlight patterns of surface

cracks or other corrosion-related surface damage, such as pitting.


MMaaggnneettiicc PPaarrttiiccllee IInnssppeeccttiioonn

Magnetic particle inspection detects surface imperfections, cracks, pits, or

breaks when magnetic particles deposited on the surface are exposed to a magnetic

field.

The magnetic field induces flux lines that are distorted by the imperfections and

cause the magnetic particles to form patterns that reveal those imperfections.

EEddddyy CCuurrrreenntt IInnssppeeccttiioonn

The portable eddy current instrument shown here can detect cracks in fastener

holes due to crevice corrosion or stress corrosion cracking.

Eddy current inspection uses electromagnetic induction to produce eddy currents

in the material being inspected. Surface or subsurface defects are detected by


induction coils or probes that measure eddy currents throughout the material.

These coils or probes locate where cracks, pits, or other defects disturb the

eddy currents.

UUllttrraassoonniicc IInnssppeeccttiioonn

Ultrasonic inspection is used to detect surface and subsurface flaws, cracks and

delamination. An ultrasonic transducer transmits high frequency sound waves

through the material being tested.

Sound waves reflected by inclusions, defects and delaminations in the material

are processed and analyzed.

This technique is particularly useful for detecting and examining subsurface

corrosion and resulting damage.

EElleeccttrroommaaggnneettiicc RRaaddiiaattiioonn

Electromagnetic radiation is used on materials to determine structural conditions

and detect corrosion related defects and associated characteristics.


Electromagnetic radiation employs microwaves, thermal rays, x-rays and gamma rays

or neurons. This diagram depicts the electromagnetic radiation spectrum.

MMiiccrroowwaavvee IInnssppeeccttiioonn

This picture shows a portable microwave tester consisting of a laptop computer,

transducer, scanning device and instrumentation. Microwave inspection is a

technology that can reliably detect defects such as poor adhesion, incomplete

bonding or structural defects in non-metallic materials. The transducer produces

microwaves that penetrate the material being tested.


When discontinuities are encountered, they reflect and refract the microwave

energy back to a probe that detects differences in microwave voltage amplitude at

different positions on the material.

The data are processed and produce digital images of amplitude at these positions

for analysis and interpretation by experts.

RRaaddiiooggrraapphhiicc IInnssppeeccttiioonn

As shown in this illustration, radiographic inspection devices transmit x-rays,

gamma rays or neurons through the material being tested and onto a sensing medium

that records the results.


Since material radiation absorption characteristics differ with changes in

material composition and configuration, flaws and other anomalies are depicted in

the recorded result.

TThheerrmmooggrraapphhiicc IInnssppeeccttiioonn

Thermographic inspection uses heat-sensing devices to detect infrared radiation

emitted from heat conductive materials.

Measurement of temperature variations are used to map accurate, two-dimensional

thermal patterns that indicate defects such as subsurface flaws, voids, cracking,

corrosion, debonding, and water absorption.


Thermographic inspection is particularly useful for inspecting components with

complex shapes.

NNoonn--DDeessttrruuccttiivvee IInnssppeeccttiioonn MMeetthhooddss

Heres the table of the non-destructive inspection methods, listing the

technology, advantages, disadvantages, and types of defects detected by each

technology.


TTooppiicc 1188:: NNoonn--DDeessttrruuccttiivvee EEvvaalluuaattiioonn AApppprrooaacchheess

To summarize non-destructive evaluation approaches, visual inspection is simple

but cannot detect or evaluate corrosion below the surface.

Electromagnetic detection techniques such as electrical, acoustic, radiographic,

or thermographic technologies can detect and analyze subsurface defects as well

as surface corrosion.

All of these methods depend on trained, experienced operators capable of using

these technologies to identify and analyze corrosion and its effects.


CCoorrrroossiioonn MMoonniittoorriinngg

Corrosion monitoring is a technique to develop and evaluate corrosion control

methods.

Corrosion monitoring can detect material status or environmental conditions that

could cause corrosion and subsequent damage, and indicate needed prevention and

control requirements and methods.

Such methods might include inspection, changes in process control, revised

maintenance schedules, treatments, or repairs.

Corrosion monitoring also can be valuable in predicting useful life of materials

or components and assessing remaining service life.

CCoorrrroossiioonn MMoonniittoorriinngg MMeetthhooddss

Corrosion is monitored by various analytic methods including direct observation

and measurement, as well as electrical and electrochemical techniques.

Electrical monitoring techniques measure resistance, electrical potential

(voltage) and current. Electrochemical methods sense various electrochemical

phenomena such as polarization, passivation and impedance.

CCoorrrroossiioonn MMoonniittoorriinngg AAnnaallyyttiiccaall MMeetthhooddss

Analytical methods are based on measuring the presence and concentration of

chemical and biological elements and ions as well as corrosion products and

inhibitors. Direct measurement of ion, bacteria, and corrosion products reveal

the amount of corrosion. Indirect methods measure pH, conductivity, reaction

products, and amount of inhibitors.

LLiinneeaarr PPoollaarriizzaattiioonn RReessiissttaannccee TTeecchhnniiqquuee

Linear polarization resistance is a non-destructive electrochemical measurement

technique that makes real-time measurements.

201D Ch3 Corrosion Detection and Monitoring Section 2: Corrosion Monitoring

EElleeccttrroocchheemmiiccaall IImmppeeddaannccee SSppeeccttrroossccooppyy

Electrochemical impedance spectroscopy or EIS is a highly specialized technique

to measure the quality of organic coatings, as well as changes in the state of

the material that can be related to corrosion damage.

EElleeccttrroocchheemmiiccaall NNooiissee MMeetthhoodd

The electrochemical noise (EN) method measures surface potential compared to a

reference electrode, where fluctuations in potential predict the onset of pitting

or other forms of localized corrosion.

EElleeccttrroocchheemmiiccaall RReessiissttaannccee SSeennssoorrss

Electrical resistance sensors are metal probes inserted into the corrosive

environment.

Corrosion causes probes to lose cross sectional area. Measuring increasing

electrical resistance of the cross section indicates the corrosion rate.


IInndduuccttiivvee RReessiissttaannccee PPrroobbeess

Inductive resistance probes contain a coil in the sensing element that measures

changes in reductive resistance, and thus corrosion, as the sensing element

thickness changes.

TTooppiicc 99:: HHyyddrrooggeenn PPrroobbeess

Hydrogen probes are used to measure corrosion rate and penetration of materials

in acidic environments, where hydrogen is a byproduct of the corrosion reaction.

The rate at which hydrogen is generated and material is consumed indicates how

much corrosion is being generated. Even in high strength materials, where

corrosion may not cause structural problems,atomic hydrogen can generate on the

surface, be absorbed by the material, and cause delayed hydrogen embrittlement or

hydrogen stress cracking.

CCoorrrroossiioonn MMoonniittoorriinngg MMeetthhooddss aanndd SSeennssoorrss

Corrosion monitoring methods and sensors are powerful tools available to help

prevent or control corrosion.

They sense current material and environmental conditions and track trends useful

in evaluating corrosion prevention and control programs and in predicting future

problems and useful service life.


CCoorrrroossiioonn TTeessttiinngg ffoorr PPeerrffoorrmmaannccee EEvvaalluuaattiioonn:: IInnttrroodduuccttiioonn

This segment of Course 201D discusses corrosion testing for evaluation and

performance. It concludes Course 201D by briefly discussing Department of Defense

Corrosion policy, specifications, and standards.

CCoorrrroossiioonn TTeesstt MMeetthhooddss CCllaassssiiffiiccaattiioonn

Corrosion testing and evaluation test methods can be classified as non-

electrochemical type tests and electrochemical type tests.

TTooppiicc 33:: NNoonn--EElleeccttrroocchheemmiiccaall TTeesstt MMeetthhooddss

Non-electrochemical test methods include several forms of coupon testing, salt

spray testing, atmospheric corrosion testing, and environmental and chemical

analysis.

CCoorrrroossiioonn CCoouuppoonn TTeessttiinngg

Corrosion coupon testing exposes metal specimens to a corrosive environment.

Coupons are cut to specific dimensions, measured, weighed, and cleaned prior to

exposure to a controlled corrosion environment.

The coupons are periodically removed from the corrosion environment, cleaned,

weighed, and measured to determine weight-loss and the extent of corrosion.

These tests provide information on the general corrosion resistance of materials

in a given environment, or the corrosive effects of different environments on a

specific material.

There are standard test procedures on specimen preparation and cleaning after

test exposure to ensure accurate measurement of material loss due to corrosion.

SSaalltt FFrroogg TTeessttiinngg

Salt Fog testing is a commonly specified commercial practice, where samples are

exposed to a salt spray in an enclosed chamber at an elevated temperature.

Bare or coated specimens are exposed for specific time periods, then removed and

evaluated for corrosion and coating losses.

201D Ch4 Corrosion Detection and Monitoring Section 1: Non-electrochemical Test Methods

SSaalltt SSpprraayy CChhaammbbeerr

This salt spray chamber shows coupons exposed to a continual spray of warm moist

salt solution.

This aggressive test is not very reliable for predicting material lifetime and

life performance, but is an excellent test of coating, plating, or surface

preparation quality.

SSaalltt SSpprraayy TTeessttiinngg CCaauuttiioonn

Salt spray testing should be used with caution since test environment conditions

often are not the same as operational environment, temperature, moisture content,

acidity, and wet-dry cycles.

AAttmmoosspphheerriicc CCoorrrroossiioonn TTeessttiinngg

Atmospheric corrosion testing is conducted at various locations in the United

States and around the world in rural, marine, and industrial environments.

Moderate-sized rectangular metal panels are placed on exposure racks under

controlled conditions, and corrosion rates are measured over varying periods of

exposure time.

CCoorrrroossiioonn TTeessttiinngg RRaacckkss aanndd PPaanneellss

This picture shows atmospheric corrosion testing racks, where the metal panels

are held by ceramic insulating fixtures to eliminate galvanic action.

Panels with coatings applied may have scribes in the coating to expose the

underlying metal to the atmosphere and thus to corrosion.

Sample sets may be removed at different times to evaluate corrosion rates as a

function of exposure time.


SSttrreessss CCoorrrroossiioonn CCrraacckkiinngg:: UU--BBeenndd SSppeecciimmeenn

This shows a U-bend specimen being tested for susceptibility to stress corrosion

cracking in an atmospheric environment. The specimen is held in a non-metallic

fixture to avoid galvanic action.

The outer fibers of the specimen at the u-bend are in tension from the

deformation. If this material is susceptible to atmospheric corrosion, stress

corrosion cracks would initiate at the outer surface and move toward the inner

surface.

EEnnvviirroonnmmeenntt aanndd MMaatteerriiaall CChheemmiiccaall AAnnaallyyssiiss

Environment and material chemical analysis evaluates corrosion as a function of

exposure time with respect to both the environment and corrosion products. It is

very useful for determining corrosion causes and mechanisms.

MMaatteerriiaall QQuuaannttiittaattiivvee AAnnaallyyssiiss:: SSppeecciiaalliizzeedd TTeecchhnniiqquueess

Metalsmaterial quantitative analysis uses atomic absorption spectrometry, ion

chromatography, plasma-atomic-emission spectroscopy, and scanning electron

microscope analysis for inspecting specimens after they've corroded. These

specialized techniques characterize the corrosive environment, analyze corrosion

products, and inspect metal corrosion morphology to evaluate the extent of

corrosion and the composition of corrosion products.


NNoonn--MMeettaalllliicc MMaatteerriiaall CChheemmiiccaall AAnnaallyyssiiss

Non-metallic material chemical analysis is used to gather element spectroscopy

and morphology information from plastics, polymers, ceramics, glasses, and

composites that are used in corrosion applications.

CChheemmiiccaall AAnnaallyyssiiss:: AAddvvaannttaaggeess aanndd DDiissaaddvvaannttaaggeess

This table summarizes advantages and disadvantages of chemical analysis

techniques. The primary disadvantage is the inability to measure material

corrosion rates.


EElleeccttrroocchheemmiiccaall TTeesstt MMeetthhooddss

Electrochemical Test Methods are used to evaluate corrosion control alternatives,

monitor the effectiveness of corrosion control programs, and monitor corrosion

rates.

Analysis of corrosion rates indicates movement toward end-of-life failures and

enables optimization of maintenance, repair, replacement and retirement schedules

for better life cycle cost effectiveness.

Electrochemical methods are also used to evaluate alternative materials during

material selection.

LLiinneeaarr PPoollaarriizzaattiioonn TTeecchhnniiqquuee

Linear polarization uses a power supply to impose a very small voltage on a metal

structure and to monitor the direct current response.

The slope of the resulting voltage versus current line is related to the

corrosion rate of the metal.

EElleeccttrroocchheemmiiccaall NNooiissee TTeecchhnniiqquuee

Electrochemical noise is the fluctuation of voltage and current between freely

corroding electrodes. Observing the frequency and the distribution of that noise

provides some indication of the onset of localized corrosion such as pitting, or

the condition of the corroding material.

201D Ch4 Corrosion Detection and Monitoring Section 2: Electrochemical Test Methods

CCoorrrroossiioonn PPootteennttiiaall MMeeaassuurreemmeennttss

Corrosion potential measurements use reference electrodes to measure the

potential of a metal compared to the potential of the reference electrode. For

example, the breakdown of a materials passivity can be recognized by a

significantly negative potential.

Other changes indicated by potential measurements include the oxygen level in a

solution and the effectiveness of specific corrosion protection methods.

PPootteennttiioossttaattiicc PPoollaarriizzaattiioonn

Potentiostatic polarization uses an external power source to polarize the

material. The potential of the surface of the metal is measured with respect to a

reference electrode.

When the surface is polarized, the resulting potential as a function of current

density scans provide information regarding corrosion rates and corrosion

mechanisms and behavior.

PPootteennttiioossttaattiicc PPoollaarriizzaattiioonn:: PPoollaarriizzaattiioonn CCuurrvveess

Polarization curves developed from potentiostatic polarization scans can be used

to measure the corrosion rate of materials.

This is particularly useful in analyzing active-passive metal behavior, where

passivity is an extremely important property of the material.


This graphic shows the polarization curve for an active-passive metal. Such

graphics indicate how well the passive film protects the metal, and if the metal

will repassivate quickly or continue to corrode locally.

PPootteennttiioossttaattiicc PPoollaarriizzaattiioonn:: CCyycclliicc PPootteennttiiooddyynnaammiicc PPoollaarriizzaattiioonn

A form of potentiostatic polarization

called cyclic potentiodynamic

polarization increases the potential at

a constant rate until the current

begins to increase, then decreases the

potential, which results in cyclic

polarization. As shown here, this can

produce a very large hysteresis loop.

Within the entire hysteresis range, the

material could either be passive or

active, and if it is active, very

serious crevice corrosion could occur.

Thus, cyclic polarization provides

valuable information regarding the

relative corrosion resistance of

passive metals.


CCyycclliicc PPoollaarriizzaattiioonn CCuurrvveess

This shows the use of cyclic polarization to compare localized corrosion

resistance of two Iron-Chromium-Nickel-Molybdenum alloys, where one alloy

contains much more chromium and molybdenum.

The alloy with added chromium and molybdenum shows little or no hysteresis, while

the other alloy is characterized by a large hysteresis loop, indicating it is

less corrosion resistant.


DDooDD PPoolliicciieess,, SSppeecciiffiiccaattiioonnss aanndd GGuuiiddaannccee

DoD Policies, Specifications, and Guidance mandate corrosion testing.

CCoorrrroossiioonn PPrreevveennttiioonn aanndd CCoonnttrrooll SSppeecciiffiiccaattiioonn aanndd SSttaannddaarrddss

There are scores of specifications and standards applicable to corrosion

prevention and control. These include structural specifications, material

specifications, test methods, and standards.

TThhee CCoorrrrDDeeffeennssee WWeebbssiittee

The CorrDefense website at www.corrdefense.org maintains up-to-date versions of

the various corrosion policy guides, standard procedures, specifications and

standards, or links to such documents.

201D Ch4 Corrosion Detection and Monitoring Section 3: DoD Policy Scpecifications and Guidance

for Corrosion Testing

201 d document

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