PNL-7823

Technical Evaluation Report

Maintenance Practices to

Manage Aging: A Review

of Several Technologies

A. D. Chockie

K. A. Bjorkelo

T. E. Fleming

W. B. Scott

W. 1. Enderlin

October 1991

Prepared for

U.S. Nuclear Regulatory Commission

under Contract DE-AC06-76RLO 1830

NRC FIN B2865

Pacific Northwest Laboratory

Operated for the U.S. Department of Energy

by Battelle Memorial Institute

0OBattelle

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I-4

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PNL-7823

UC-523

MAINTENANCE PRACTICES TO MANAGE AGING:

A REVIEW OF SEVERAL TECHNOLOGIES

A.

K.

T.

W.

W.

D.

A.

E.

B.

I.

Chockie(a)

Bjorkel (a)

Fleming a)

Scott

Enderl in

October 1991

Prepared for

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

under Contract DE-AC06-76RL0 1830

Pacific Northwest Laboratory

Richland, Washington 99352

(a) Battelle Human Affairs Research Center

Seattle, Washington 98105
EXECUTIVE SUMMARY

The quality:of,-a maintenance program directly affects the ability of a-nuclear

power plant to~detect and mitigate theieffects of-age-related degradation.

The Nuclear Plant Aging Research (NPAR) Program, which is sponsored by the NRC

Office of Nuclear Regulatory Research, has contracted with Pacific Northwest

Laboratory and its subcontractor, BattellelHuman-Affairs Research Center, to

analyze effective maintenance activities.used to-manage-the aging of systems

and components. - I . ..- . -. .- - .- -

The maintenance programs:used by two commercial industriesand.-two military

organizations were selected for:this study.'. The.four programs are-as follows:

* the United-States.commercial airline'industry

* g the United States Air Force B-52 bomber -

* the United States Navy-Ballistic-submarine-

* the Japanese nuclear power industry..

'The maintenance programs of-these four.,organizations offersvaluable lessons

-for managing aging.in the;U.S. nuclear.power industry.. Specifically, theyindicate the need-for-an effective maintenance.program.to manage'the

degradation of-critical:systems and.components due to aging; ;An effective

maintenance.program includes.three-basic..elements:.: .

* a systematic approach to the conduct of maintenance tasks

* methods for monitoring and-assessing maintenance activities:.:,

* mechanisms for feedback and corrective actions to improve maintenance

effectiveness.

A systematic approach to maintenance includes a comprehensive maintenance

policy, clear maintenance program objectives and goals, and the physical

conduct of maintenance based on the overall policy, objectives, and goals.

The structure of the maintenance program is important to ensure that aging

issues are addressed. This analysis identified four elements inherent in an

effective maintenance program that are also important to an aging management

program. The elements are as follows:

* the prioritized selection of critical systems and components

* understanding aging through the collection and analysis of equipment

performance information

* mitigating aging with maintenance

* the use of feedback to improve the aging management program.

I iii
.

The first element is the prioritized selection of critical systems and

selected components. Critical systems and components can be selected by

several methods. For example, the aviation industry's reliability centered

maintenance program uses a risk-based approach to identify safety-significant

equipment.

The second element is an understanding of aging processes that affect critical

plant systems and components. This is accomplished by collecting and

analyzing equipment operating characteristics and performance data. The

maintenance program should be designed to detect, identify, and correct

problems caused by aging mechanisms, such as corrosion, wear, and fatigue,

before the safety or reliability of the plant is impaired.

The third element involves the actual conduct of maintenance to mitigate aging

degradation. Once the aging process of critical equipment is understood,

maintenance tasks designed to detect and correct equipment degradation can be

selected and scheduled. Activities to mitigate aging include inspection,

surveillance, equipment monitoring, replacement, and overhaul.

The fourth element is the need for feedback mechanisms to allow for continual

maintenance program refinement and improvement. These mechanisms may consist

of specific maintenance activities that serve as a basis for establishing and

scheduling future inspection and maintenance tasks.- They may also consist of

groups of personnel who evaluate and improve the maintenance programs. The

feedback mechanisms are vital if the maintenance program is to address

changing needs such as the degradation of plant equipment due to aging.

This report examines the approach taken by each of the four organizations to

address these four elements. A summary of the maintenance-related activities

to address system and component aging is presented in Table 1.

iv
'I

TABLE 1. MAINTENANCE ACTIVITIES THAT ADDRESS AGING

ORGANIZATION

AGING ISSUES FOR COUMLEX Air Force Commercial | ERUIP U r P- GL52 P r ogra e Aviation Induxtry Japanese Nuclear Industr y Hi vy B allistic Submarines

Initial Design * Initially designed for 5,666 * Designed for indefinite operation * Designed for indefinite operation * Designed for 33 year life Philosophy flight hours over economic life of aircraft based on successful completion of - no life extension issues - Air Force has repeatedly * Design criteria to ensure periodic inspections extended 8-52 operatIng life aircraft safety includes:

faill-safe

-safe-life

- damage tolerance

Prioritized 

Selection 

* RCU approach * rKU approach * Comprehensive Industry-wide In- * Navy PUS determini stic approach of - 8-52 systems and components - maintenance steering spection requirements determined - continual monitoring of Critical System receive either critical or group (USO) process and specified by MITI operating equipment coN- and Components non-critical classification identifies critical * Phase I of PLEX Program bined with specific pre- quipsent based on risk identified critical plant equip- ventive maintenance tasks

of potential failure ment for life extension

Understanding * Performance data includes: * Performance dat includes: Technical nformation exchange * Performance data includes: Aging lhrough - usage rates of spare parts - failure rates between MITI, utilities, etc. - rate in change of material Collection and - changes in levels of - age-reliability character- * Phase II of PLEX Program tests condition Analysis of corrective maintenance istics equipment to determine and - results in useful life Equipment Infor- - equipment failure rates -simple ranking process provide understanding of the prediction mation - operational readiness rating * FAA, airlines, manufacturers extent of aging degradation * Information analyzed by the Information analyzed by Senior share data and Information on System Maintenance and Moni- Officer Steering Group an industry-wide scale toring Support Operation (SkUSO)

Mitigating Agin * Maintenance activities based on: Maintenance activities based * Periodic/voluntary inspections * Crew performs preventive with - flight hours on: to detect and mitigate aging maintenance during operation Maintenance scheduled in: - flight hours, cycles and degradation * 30-day refit follows 3-month - phase checks every 200 ,age * Phases III and IV of P LEX Program deployments 466, 666 fh's scheduled in: develops and i mplements ainten- * I 8-24 month refueling overhaul * Program depot maintenance - alphabet' checks -a,b,c,d ance activities for life every 12 years - extensive maintenance extension * Trident - hard-time limits in

every 4 Years | some equipment

Feedback to * Aircraft Condition Inspection * Air Worthiness Assurance * Working to reduce duration of * Daily communication between Improve - every 4 years Task Force to: periodic inspection through SUUSO and local repair group Effectiveness - basis for establishing inspec- - evaluate condition of improved technology in main- * Technical feedback reports of 

Managxe 

Aging tion tasks and future schedules aging fleet tenance and inspection techniques are submitted by operating crew ment * Product Improvement Working Group - recommend corrective I H igh level system review It togram convenes to: actions to maintenance meetings to evaluate mainten- - review performance programs ance effectiveness - determine needed improvements * Supplemental Structural

and design modifications Inspection Program specifically . ____ _ _ . I _ - a ddres san s esirc a n i p i rr a L . --_ _ _ _ __ _ _ ____ _ _ _
TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY.............. .. .... .. ... '. *.. '...'............... iii

1.0 INTRODUCTION ............................... 1-1

.-1.1 OBJECTIVE -.--. ............ ;.-.'. 1-1

.1.2 -ORGANIZATION OF.THIS REPORT ... ...... . ........ 1-2

2.0 ELEMENTS-OF-AN EFFECTIVE MAINTENANCE'PROGRAM ...... ' 2-1 .. .. ....... ~~~~~... ................ O.: 2;4::-1-

.2.1 SYSTEMATIC APPROACH TO MAINTENANCE .................. 2-1

.2.1.1 'Maintenance Policy . .... ...................... 2-1

2.1.2 Maintenance Goals and Objectives ....... .... 2-3

.-2.1.3 Conduct of Maintenance'..,. '.. ; . .2-3

2.2 MONITORING AND ASSESSMENTOF EFFECTIVENESS 2-4

-2.3 .FEEDBACK-AND CORRE CTIVEACTIONS.... . ..... 2-4

3.0 DESIGN PHILOSOPHIES AND THE SELECTIONWOF CRITICAL EQUIPMENT .. 3-1

3.1 DESIGNWAND OPERATING PHILOSOPHIES . . .3-1

3.1.1 Aging Criteria in the Aircraft Design Stage . .3-2

3.2 -SELECTION OF.CRITICAL.SYSTEMS AND COMPONENTS ................... 3-3

3.2.1 Reliability Centered Maintenance .... 3-3

.3.2.2 Monitoring and-Inspection -..'...: ....................... 3-5

3.2.2.1 'Japan's-Plant'Life-Extension'Program .3-6

3.2.3 Continuous Monitoring-and Inspections ..... .............. 3-9

4.0 UNDERSTANDING AGING THROUGH THE COLLECTION AND USE OF

PERFOMANCEDATA ................................................... . ;--1

4.1 COMMERCIAL AVIATION-INDUSTRY ........................... *....... 4-1

4.2 JAPANESE NUCLEAR INDUSTRY ..... ............................. 4-2

.4.3 ..U.S..AIRFORCE B-52CBOMBER-FLEET ....... R F. ................... 4-6

4.4 U.S. NAVY BALLISTIC SUBMARINE FLEET ...... .................. 4-6

.- v11
TABLE OF CONTENTS (continued)

Page

5.0 MITIGATING AGING WITH MAINTENANCE .. ............................... 5-1

5.1 COMMERCIAL AVIATION INDUSTRY ................................ 5-1

5.1.1 Types of Maintenance Performed ...................... 5-1

5.1.2 Maintenance Scheduling .............................. 5-2

5.2 JAPANESE NUCLEAR INDUSTRY . ............................... ...... 5-3

5.3 U.S. AIR FORCE B-52 BOMBER FLEET ............ .. .............. 5-3

5.4 U.S. NAVY BALLISTIC SUBMARINE FLEET ......................... 5-7

6.0 FEEDBACK AND CORRECTIVE ACTIONS TO IMPROVE MAINTENANCE .... ....... 6-1

6.1 COMMERCIAL AVIATION INDUSTRY ............................... 6-1

6.1.1 Fatigue and Corrosion: Predominant Dangers

to Aging Aircraft . ................................... 6-1

6.1.2 Supplemental Structural Inspection Program .......... 6-2

6.1.3 Structural Analysis of Aging Aircraft by the

Manufacturer ..... ................................... 6-4

6.1.4 Structural Modifications for High Cycle

Aircraft ............... ............................. 6-4

6.2 JAPANESE NUCLEAR INDUSTRY ......... ......................... 6-5

6.3 U.S. AIR FORCE B-52 BOMBER FLEET .. ......................... 6-7

6.4 U.S. NAVY BALLISTIC SUBMARINE FLEET .. ...................... 6-7

7.0 RESEARCH AND ACTION AREAS ..... ....................................... 7-1

7.1 THE LOGISTICS FOR SPARE PARTS OF AGING COMPONENTS .......... 7-1

7.2 CORROSION CONTROL PROGRAMS ........ ......................... 7-1

7.3 TECHNOLOGICAL DEVELOPMENTS BY THE AIRLINES .. ............... 7-3

7.4 JAPANESE NUCLEAR AGING RESEARCH EFFORTS .......... .......... 7-4

8.0 KEY FINDINGS ...................................................... 8-1

REFERENCES .............................. R-1

BIBLIOGRAPHY .......................................................... B-1

viii
LIST OF FIGURES

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

2.1.

3.1.

3.2.

3.3.

3.4.

4.1.

6.1.

6.2.

7.1.

Elements of an Effective Maintenance Program ..............

RCM Approach to Manage Aging ..............................

Schedule for Plant Life Extension Program (PLEX) - Japan

Study Areas of Phase One of PLEX Program ..................

Key Interactive Elements of Japan's PLEX program ..........

Technical Development Stage of the PLEX Program ...........

Areas of Fatigue and Corrosion Damage on Aging

Aircraft ...................................................

Typical High Cycle Aircraft Modifications .................

Research and Development Areas for Life Extension .........

LIST OF TABLES

Page

2-2

3-7

3-8

3-10

3-11

4-5

6-3

6-6

7-5

Table 1.

Table 4.1

Table 5.1.

Table 5.2.

Maintenance Activities that Address Aging ..................

Approaches to Life Extension for Permanently

Installed Equipment ........................................

Types of Maintenance Performed During Aircraft

Inspections ................................................

Systems Evaluated During Inspections of Pressurized

(PWR) and Boiling (BWR) Water Reactors .....................

Page

y

4-4

5-4

5-5

ix
1.0 INTRODUCTION'

The nuclear industry and the United States Nuclear Regulatory Commission (NRC)

realize that as nuclear power plants age, maintenance program'-effectiveness

plays an increasingly-important role in safe -and economic plant. operation.

Recent events at nuclear power plants have shown that improper or nonexistent

maintenance can significantly contribute to plant incidents.

The Nuclear Plant Aging Research (NPAR) Program, which is sponsored by'the

NRC, is conducting a study to assess maintenance practices to manage nuclear

power plant aging. The NRC Office of Nuclear Regyl~tory Research has

contracted with the Pacific-Northwest Laboratory, operated by Battelle

Memorial Institute for-theDepartment-of-Energy, and its subcontractor,-

Battelle :Human Affairs Research Center, 6to analyze maifitenanrce activities in

government and industrial organizations. Specifically examined'were .- ;

maintenance practices to manage system and component aging.

1.1 OBJECTIVE -.

The objective of this study is-to identify effective maintenance practices

that could be adapted by the U.S. nuclear powerindustry to manage nuclear

power plant aging. This study will help the NRC to understand'the role'6f

maintenance practices in developing and implementing effective aging

management-programs. - ; -

To address this objective,'two commercial industries and two major Department

of Defense programs were analyzed. These organizations were selected.because

they possessed effective maintenance programs,-and because they placed a'high

priority on properly addressing systemand component aging issues. The four

programs are:

* the United States commercial aviation industry

* the United States Air Force B-52 bomber program

* the United States Navy ballistic submarine program

* the Japanese nuclear power industry.

This study examined the current and planned maintenance programs and related

the aging mitigation activities of these four organizations. Interviews were

conducted with the Air Force Logistics Command personnel at the Tinker Air

Force Base and with the Naval Sea Systems Command personnel responsible for

submarine maintenance programs. Also examined were the constraints and

policies under which the organizations have developed and implemented their

maintenance programs. This was particularly important when assessing the

applicability of the programs of the military organizations since they are not

(a) Pacific Northwest Laboratory is operated for the U.S. Department of

Energy under Contract DE-AC06-76RL0 1830.

;1-1
necessarily constrained by the same economic and policy considerations that

affect the commercial industries.

1.2 ORGANIZATION OF THIS REPORT

For a maintenance program to effectively address the aging of systems and

components, it must be developed and implemented in a manner that allows the

plant to identify and respond to changing maintenance requirements (e.g., as

plant age increases). Section 2.0 of this report focuses on characteristics

that have been identified as important elements of effective maintenance

programs.

The subsequent sections are devoted to reviewing the maintenance programs of

the selected organizations. Section 3.0 describes the organizations' design

philosophies and approaches to selecting systems and components critical to

safe equipment operation.

Section 4.0 discusses the types of operating performance data that the

organizations collect and analyze to understand aging and to assess

maintenance program effectiveness. Section 5.0 describes the actual

maintenance activities used by the organizations to mitigate aging, and

Section 6.0 discusses feedback and corrective actions to improve maintenance

practices.

Section 7.0 describes research and action areas from the selected

organizations that are particularly applicable to the U.S. nuclear industry.

Section 8.0 presents key findings of the review to identify aging issues that

are central to a safe and effective maintenance program.

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2.0 ELEMENTS OF AN EFFECTIVE MAINTENANCE PROGRAM

For any maintenance program to be effective, it must be designed to detect and

correct the effects of equipment aging before they impair plant safety or

operation. Thus, the impacts of aging equipment and the maintenance tasks

needed to mitigate them should be inherent to the design of an effective

maintenance program. A systematic maintenance program isneeded to identify

and manage the effects of aging equipment in nuclear power plants.

This section describes the program elements that'have been identified as

necessary for an effective maintenance program. This is intended to build a

foundation that can be used'to discuss specific aspects of maintenance

programs designed~to address issues associated with aging equipment. The

process elements needed for'an effective maintenance program are shown in

Figure 2.1. The rest of this section is devoted to a brief discussion of each

these elements.

2.1 SYSTEMATIC APPROACH TOiMAINTENANCE

The first important elementiof an effective maintenance program is that it be

established and implemented'in a systematic manner. A systematic maintenance

program consists of three components. "The first is the development of an

overall maintenance policy defining the scope of the maintenance program.

Next,"the objectives and goals are defined within the context provided by the

maintenance policy. Only when these'policy objectives and goals have been

established can the methods:and procedures-for the conduct of maintenance be

logically developed. The three'components of a systematic program are shown

in the first pyramid of Figure 2.1.

2.1.1 Maintenance Policy

Sound maintenance policy is the starting point for the development of a

coherent maintenance program. From this'policy stems the objectives and

goals',' the strategies for the conduct of'maintenance, the philosophy for

monitoring and assessment of effectiveness, and the strategies for corrective

action and feedback. Thus,:the purpose of the maintenance policy is to define

the scope, objectives, activities and general responsibilities for all plant

maintenance operations.

A formal maintenance policy represents a statement by top management of the

importance of the maintenance function in achieving-safety and other plant

goals. It emphasizes that maintenance activities-be conducted systematically

and in accordance with objectives and' rules. 'Without such a-policy, the

maintenance program is at risk-of havingiiinsufficient vision and resources to

be successful. In such situations', the maintenance programis prone to

becoming primarily reactive, and the'program will not be structured to most

efficiently respond to changing plant maintenance requirements, such as those

presented by the degradation of plant equipment due to aging. Once the formal

maintenance policy is established, the maintenance management must establish a

set of performance goals and objective's by which the effectiveness of the

maintenance program can be measured.

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Systematic Maintenance

Program

Monitoring & Assessment

of Effectiveness

Corrective Action

& Feedback

FIGURE 2.1. Elements of an Effective Maintenance Program
2.1.2 Maintenance Goals and-Objectives

The maintenance department management is responsible:ffor translating theconditions and requirements set down in the maintenancepolicy into 'effective

maintenance actions. .-This is-accomplished through the development. of clear

program goals -and objectives.-.,The program objectives provide-a means to.focus

the-maintenance activities on the relevant policy-requirements. Quantified

performance goals assist in determining the degree to which.these objectives

are being achieved.

The'primary objective of ,the maintenance-departmentis to.ensure that all.

plant systems and components are available to perform their intended functions

throughout their service lives.:.,.This is:accomplished by developing.effective

maintenance practices according to.the established goals .and objectives of the

program., -The maintenance activities should be.commensurate with:the.safety

and reliability significance of the plant systems and components. By

developing performance goals and monitoring the effectiveness of the

maintenance program with.respect to these goals,- the maintenance management'

can assess how well the objectives are being'met. The develpm'ein't"o'f

maintenance.goals and objectives provides the link between-the overall

maintenance policy and the-actual conduct of maintenance.,,. -

2.1.3, Conduct of Maintenance.

The detailed 'design and physical conduct of maintenance activities is the

third'ma'jo'rcomponent of a systematic maintenance program-. -The conduct of,

imaintenance-'consists of,,activitiesthat prevent, predict,- and restore.failures

or performance degradation of systems andicomponents. -These activities

include: " - -

analysis of performance data

'* 'analysis of operational data

, * predictive mainte'nance based on-operationaldata P -ma -

* preventive maintenance based onfrmanufacturer.'s recommendations,. - operating- experience, good engineering'practice (including aging

* concerns ,-and preventive maintenance feedback

as. corrective maintenance as necessary. :- . -

{ _' .' : ' ' ' " . ; ' ' -' , '- 4 , ' ,, '' - - ' ' _. ' ' !( ;

The'balance and nature of thie'se types of maintenance should be consistent with

meeting the established maintenance program goals and objectives.' For.,

example, corrective maintenance' maybe appropriate for equipment-for which:

degradationfailure willihave no'impact on plant safety or operation.- -On the

other hand,' i'pre'dict'ive' m'aintenance task may.-be desirable for safety - -

significant component's with"-'fa'st-acting failure mechanisms, while,surveillance

or in-service 'test ingriiay be best suited for equipment demonstrating-slowacting failure mechanisms.

..2-3
2.2 MONITORING AND ASSESSMENT OF EFFECTIVENESS

Monitoring and assessment are essential activities in implementing and

sustaining an effective maintenance program. Monitoring and assessment

involve collecting and evaluating the performance data from all levels of a

maintenance organization. This information provides the basis for management

to identify maintenance problems, analyze possible causes, and implement

effective corrective actions.

The specific monitoring points of a maintenance program are determined by the

requirements of both the regulatory agencies and by the policies, objectives,

and goals of the organization's maintenance program. The monitoring and

assessment efforts should provide plant management with the information needed

to identify, diagnose, and correct maintenance problems. This is particularly

important when considering the special problems that apply to aging equipment.

2.3 FEEDBACK AND CORRECTIVE ACTIONS

The third major element of an effective maintenance program is the feedback

and corrective actions needed to continually improve the maintenance program.

This includes the analysis of equipment performance data and the development

of organizational mechanisms for taking corrective actions in response to

maintenance-related problems. With effective feedback, the maintenance

program learns from its own experience and lowers the incidence of repeated

mistakes or errors. Corrective actions may originate in any part of the

maintenance process and may be fed back to which ever portion of the program

will eliminate the cause of the maintenance program's ineffectiveness.

Appropriate corrective actions can be identified by comparing actual

maintenance performance to the plant and maintenance goals and objectives.

Corrective actions result from monitoring and assessing the effectiveness of

the maintenance program, and the feedback process provides information to all

levels of the systematic maintenance program. The corrective actions

resulting from the monitoring and assessment of maintenance performance can

affect the overall maintenance policy, the goals and objectives of a

maintenance program, and the physical conduct of maintenance.

Information from the monitoring and assessment process should be gathered in a

structured and systematic manner. A careful analysis of this information is

necessary to determine the root cause of a problem and to be able to formulate

appropriate corrective actions to feed back into the maintenance program.

The development of a systematic maintenance program ensures that sufficient

attention is directed toward all plant systems and components to ensure safe

operation throughout the life of the plant. The collection and use of

equipment performance data ensures that the maintenance program focuses

attention and resources as necessary to detect and correct equipment aging

problems.

2-4
The following sections describe the manner in which Various organizations have

incorporated these three principal requirements into their maintenance

programs to assist them in addressing the aging degradation of their systems

and components. In general, the findings from this review are that the

programs successfully incorporate these elements into their programs. Also

discussed are the opportunities for the U.S. nuclear power industry to adopt

various aspects of these programs to assist them in managing the aging of

nuclear power plant systems and equipment.

2-5
3.0 :DESIGN PHILOSOPHIES AND-THE' SELECTION OF CRITICAL EQUIPMENT

*, . .. . - , .. - ... . ..

The philosophies that govern.the-operation and maintenance of a system

significantly~influence the approach an organization takes to managing the

aging of the components and systems. :Policies,goals,-:and:objectives for the

maintenance program are all developed-based on:the-underlying design and - operating philosophy. Identifying those components and systems 'critical-for

continued and safe operation is also a related factor that influences the

maintenance approaches to address -equipment-aging .--

This section reviews the design'arid operating-.philosophies of the four ' organizations. Also examined in this.section'are the methods that the four

organizations use to identify.and prioritize those components and systems that

are critical--for-continued'safe.operation.'.

3.1 DESIGN AND OPERATING PHILOSOPHIES -

When comparing the different maintenance programs,.one must understand the:

differences in context and driving forces.that are-inherent in these - industries. The design and operating philosophies of several of the analyzed

organizations are quite different--especially between the commercial and

military organizations. The Japanese nuclear industry and the UiS.--commercial

aviation industry though are similar in their design and operating goals.

Both use equipment that has been designed to operate as long as is

economically feasible,. and both -have-limited resources -available-to'conduct

maintenance activities. - - -

The maintenance of'the Air Force B-52:aircraft-does-not have such resource'

constraints as those of. the commercial organizations. Continued operation is

not based-so.much on economics as-on the strategic requirements that are.

imposed-on the.Air.Force by the Strategic Air Command.' A specified number-of

aircraft-are.required-to.be mission-ready.at'all times, and cost is of :

virtually.no.consideration.in maintaining-the required number of- aircraft.

The.U.S. Air Force.-has-developed a-systematic maintenance program to-support

the operation of its fleet of B-52 bombers. The fleet-consists-of' -

approximately 270 aircraft that are deployed at 24 Air Force bases. The

maintenance-plan is~designed-;to retain the-operational readinesi of the B-52

bomber'fleet-while continuing-to extend the operational life of the. aircraft.

The maintenance program for th -B-521is'mission-driveri, and a specified.:number

of the-aircraft are required to.be operational at any given'time. -- .

Though the B-52-bomber was originally designed for-5,00total flight-hours,

they were redesigned early.in their operational :]ife for.12,000.flight-hours,

and have subsequently received additional modifications to further extend

theirservice lives. .'The -average.-flight-age oftthe-aircraft in the: active

inventory is currently- 13-000:.flight-hours, landait is 'anticipated that-the

flight-age of-these aircraft-will -approach.22,000:.flight-hours by the year'

200.....

: 3-1
Like that of the B-52 bomber, the maintenance program for ballistic submarines

is driven by the requirement to meet an assigned deployment date. The

objective of the maintenance plan is to support the operating schedule and

ensure safe, reliable operations for extended periods between refueling

overhauls. The maintenance program also seeks to maintain 100 percent

operational capability during the submarine deployment period, and to minimize

maintenance cost throughout the submarine's useful economic life, which is

nominally 30 years.

3.1.1 Aging Criteria in the Aircraft Design Stage

The commercial aviation industry has established a record of safety and

reliability by designing maintenance programs that not only keep aircraft

operational, but ensure a minimal impact on safety in the event of failure.

This achievement is the result of close cooperation between regulatory

agencies, aircraft manufacturers, and the airlines in designing the aircraft

and the initial aircraft maintenance programs.

In order to ensure aircraft safety, several concepts are introduced in the

design stage that address aging effects. These are as follows:

* fail-safe

* safe-life

* damage tolerance.

The fail-safe concept is based on the assumption that the failure of any

single component on an aircraft will not cause the catastrophic failure of the

aircraft. Beginning with the Boeing 707, the fail-safe approach was applied

to the design of all U.S. commercial jets. This approach ensures that if a

principal structural component were to fail, a secondary, or fail-safe load

path would have sufficient residual strength to carry the load. The

implications of the fail-safe concept on design requirements, is that parts

must be constructed with a built-in redundancy to allow aircraft to operate

safely with an undetected flaw until the next scheduled maintenance inspection

and correction. For example, if a fatigue crack develops at a fastener hole,

the rate of crack propagation must not reach a critical stage before the next

scheduled inspection.

The safe-life concept was incorporated into aircraft design in the 1950s and

requires the replacement of a part in accordance with the expected life of

that part (e.g., the landing gear of an airplane is replaced after a specified

number of flight cycles). Under this concept, the manufacturer designs

aircraft for a specific life based on economic considerations, and the plane

is retired from service when it becomes economically impractical to replace

structural components such as the fuselage or wings.

Damage tolerance, a third design concept was adopted by the Federal Aviation

Administration (FAA) in 1978. Damage tolerance is the ability of an airframe

to resist failure due to fatigue, corrosion, accidental damage or poor

maintenance practices for a specified period of unrepaired usage. A damaged

structure will continue to carry operational loads until the damage is

detected either by the problem becoming evident, such as a crack, or during a

3-2
scheduled inspection. This approach assumes that damage will occur-to a

component from anyjnumber ;of.-possible.conditions, including poor maintenance

practices or equipment aging. These.components must be designed'tolsafely

accommodate that damage-until-it-is corrected.

The development of aircraft-maintenance programs and-the design of the

aircraft are closely related efforts.-.Maintenance requirements are:structured

so that failures are prevented.or.detected-before.they become critical.

Inspections are scheduled to detect damage from-fatigue-or corrosion"before

the damage reaches a critical stage and affects aircraft safety. The

manufacturer, airlines and FAA work together to.determine.the maintenance

requirements for an aircraft; however, these efforts are not effective unless

they-are'-incorporated into.a-maintenance program that-ensures that.the

inspections.are performed.

3.2 -SELECTION OF-CRITICAL SYSTEMS AND COMPONENTS,

In reviewing the maintenance activities of the four organizations, three

approaches were identified for -the selection oficritical-systems :and

components, and maintenance tasks. Using these approaches, the-organizations

have developed programs for detecting and mitigating equipment aging problems

based primarily.on the safety7significance of. the selected critical systems

and components. The three approaches are as follows:

*~ Reliability Centered Maintenance (RCM), which is used by both the

-commercial aviation industry~and the-U.S..Air.Force-B-52 bomber fleet.

* - The combination of-equipment monitoring.techniques and a-detailed annual

inspection of critical plant systems and-components.used by-the Japanese

nuclear industry. ;- -. . -- -

* The combination of continuous monitoring of operating equipment with

periodic maintenance layovers used by the U.S. Navy ballistic submarine - -program. .

3.2.1 .Reliability Centered Maintenance -

Both the U.S. commercial aviation industry and the U.S. Air Force B-52

maintenance programs are based-on reliability centered maintenance .(RCM). RCM

involves the systematic evaluation -of-system and component failure modes for

the'development of 'scheduled preventive maintenance tasks. An..RCM analysis

identifies the'mainten'ance.-requirements of, systems -and components according to

-the-safety and operational consequences of equipment failure. .

During the development stage of a maintenance program, the systems and

structures of the aircraft are evaluated to determine their failure modes and

safety -significance. Actuarial -analysis is performed to determine the effects

.of age on equipment, and imaintenance-tasks are-chosen that will detect ?'

equipment-and structural degradation before:the safety of the aircraft:is

impacted.-- In order to en's-ure thatfthe maintenance programs are adequate, they

are 'developed 'long before the'aircraft actually goes into service.l-- :..

.3-3
In developing maintenance requirements for the B-52, the Air Force classifies

all aircraft systems and components as either critical or non-critical. The

severity of the component failure consequence determines the classification.

Critical components and systems are limited to a certain number of flight

hours or duty cycles, or until a specified expiration date. Then a critical

item is removed, inspected, repaired if necessary, and tested. It may then be

reinstalled or placed in spares. Non-critical items remain in service until

failure. Normally, when there is a redundancy, the system or component will

be classified as non-critical.

During the commercial aircraft design process, representatives from the

airlines and manufacturer work together in a Maintenance Steering committee.

This committee develops an initial set of aircraft maintenance requirements,

using a logic decision process outlined in the Maintenance Steering Group

handbook. Matteson, McDonald, and Smith (1984) outline four steps used by the

Maintenance Steering Committee in developing an initial maintenance program.

These steps are as follows:

* identification of active and passive items that require preventive

maintenance

* identification of the functional failure associated with each component

* creation of a logic tree to determine applicable maintenance tasks

* review of the aircraft structure to establish an inspection program.

The identification of active and passive maintenance items requires a careful

physical and functional description of each component detailing all of the

functions which it performs. This step also identifies any redundancies that

ensure continuation of function in the event of failure.

The identification of component functional failure addresses the consequences

of degradation failure for each component. Functionally significant systems

and components are identified as part of this activity. These functionally

significant items are analyzed for failure modes and effects to identify the

dominant causes and consequences of failure.

The creation of a logic tree incorporates information from the previous steps

to identify applicable and effective maintenance tasks for the component.

Applicable means that the task works and effective means that it is worth

doing. This process addresses potential multiple failures that affect safety.

If an operator uses a component infrequently, or if its function is unclear,

then the logic tree requires the operator to perform a failure finding task to

prevent multiple failures.

Finally, an aircraft structure review is performed. This review covers the

critical elements of the primary structure that would have a major impact on

structural integrity in the event of a failure. Each element is reviewed to

determine its expected fatigue life, crack propagation rate, and corrosion

susceptibility. These factors are considered in the development of the

inspection program.

3-4
The Maintenance Steering Committee presents a proposed maintenance program for

approval to the FAA Maintenance Review Board (MRB). The.MRB issues a I

Maintenance Review Board Report outlining the,.minimum maintenance requirements

for a new aircraft. This report contains an extensive listing off all,,

maintenance significant items for both the aircraft's structure and its

systems, and includes the following information-for.each item: -

* item location - . .

- failure effect category,-

* specific maintenance task assigned to the item

* frequency of the maintenance task.

This list of.critical components and.,systems is modified over time based on

the analysis of operational performance information.-.These monitoring-and

analysis activities, are reviewed in.Section' 7.of this report. .

Through this method, the.systems andcomponents that are critical to-the

continued safe operation of. the aircraft.are :selected.j Based upon the safety

significance of these systems and components, maintenance tasks that are both

applicable and effective in mitigating aging areselected..

3.2.2 Monitoring and Inspection--v .

The Japanese nuclear-industry combines a required.,annual inspection program

with voluntary programs developed by individual utilities. Annual inspection

requirements include minimum guidelines for the systems 'and components to be

inspected, 'and procedures :to-be followed. :- Voluntary -inspections,-,which a-re

not regulated, are left.,to the:discretion.of each utility.- Figure 3.1

presents a:diagram of how the RCMapproach is used to:refine.the maintenance

program to address aging issues.

One reason for this approach is that, unlike the U.S. nuclear industry, the

Japanese-regulatory strategy does not :specify,a-fixed term -for. -licensing a

nuclear power plant. Rather than granting an operating license for-forty

years, plant re-certification depends upon successful completion'of a periodic

inspection. If~significant degradation of plant components due to aging .is

observed during an inspection, the plant will not be certified for continued

operationuntil. the degradation is repaired.- This consequence encourages

Japanese plants to use voluntary inspections.to enhancethe effectiveness of

their maintenance program and to ensure that their plant is operating safely.

Periodic inspectionsiare conducted according to-standard instructions-that

designate the systems and components subject to inspection, the procedures to

be followed,--andtthe-assessment-criteria used--to.evaluate-the condition of the

equipment. - The following criticalsystems:rand.components tare ,subject to...

inspection: . , - . -

* reactor and reactor coolant systems

* nuclear instrumentationsystem,. a '- - . --- . -

* fuel assembly/handling system

* radiationscontrol system . . - - _- -- _ -

* waste disposal system

-3-5
* reactor containment vessel

* auxiliary boilers

* emergency diesel generator

* steam turbines.

In addition to the periodic inspections, utilities perform voluntary overhauls

and functional tests of equipment not included in the periodic inspections.

This practice confirms that the equipment, and the plant as a whole, will

continue to operate with a high level of safety, reliability and functional

performance.

Each electric utility decides which items are to be inspected and the

inspection frequency, taking into account the safety significance of the

equipment, the availability of equipment spares, the equipment operating

history, and the occurrence and nature of equipment failures. The voluntary

maintenance activities are performed in accordance with standardized work

plans, procedures, and test and inspection instructions. If abnormalities or

evidence of aging degradation are discovered as a result of these inspections

or functional tests,. the equipment is repaired, and efforts are made to

prevent recurrence of the problem.

3.2.2.1 Japan's Plant Life Extension Program

In 1985, the Japanese Government and the Japanese Nuclear Industry began

working together to develop the Plant Life Extension (PLEX) Program. This

eight-year program is managed by the Japan Power Engineering and Inspection

Corporation (JAPEIC), and is directed at researching methods to improve the

level of reliability, economy, and the lifetime of nuclear power plants in

Japan. The program addresses the following issues (Mishima, 1988):

a more precise prediction of nuclear plant life

* a diagnosis of the extent of plant degradation that can be attributed to

aging

* development of methods for monitoring the aging process

* development of new techniques for repairing and replacing components

with short service lives.

The Japanese PLEX program is divided into four separate phases. The

approximate schedule for each phase is outlined in Figure 3.2.

The first phase, PLEX I, was recently been completed. Phase I consisted of a

two-year feasibility study to identify the critical plant systems and

components that need to be considered for plant life extension. This phase

included three parts:

* a survey of current nuclear plant conditions

* plant evaluations to determine the feasibility of life extension

3-6
Maintenance Program

Development and -

Refnement

RCM Approach to

Resolution of

Aging Issues

,FIGURE 3.1. RCM Approach to Manage Aging
l

Io

1985 1986 1987 1988 11989 1990 1991 1992 1993 1994 1995 onward

^ Ai l ^ e _ .', > m i g t .:,;... ..... III ,'. :',:' 

PhaseI1 Phase 11 1V Phase 

|.study) l appci;ica l to, plant) t pn )

| |< -;ldnlikticnar~tsse6m~niiplai~pedlc~: ~iv;teohnpIqueicos| appilcratin~n:.

'Progrm 'Ial. s"I" o'prdainrguaoy Incat n s,

daghosi! and lif p.red.tion

Projet for. service Iffe exten sion oI piant _____

Lcensing impemenatl _______ service lifeof servce lie I ~ ~ ~ ~~~~~~~~~~~~~~~~~~~~-mextenson .. .Identification and assessment of piant specifisexnsn . _ _... _ _.. _. _...... .... .._ _ _ _ _ _ _ _ _ _ _ ra m s :i;

FIGURE 3.2. Schedule for Plant Life Extension Program (PLEX) - Japan
the development of a schedule to determine future technical research

requirements.

A diagram of the study areas included in'Phase I is displayed in Figure 3.3.

Phase II of the PLEX program is aimed at providing aniunderstanding of the

various aging processes that affect critical plant:.equipment. Several

variables are involved in the aging process, including manufacturing

materials, equipment operating environment, aging mechanisms'and degradation

sites. The Japanese nuclear industry is currently addressing these variables

in the second phase' of the' PLEX-pro-gram;'-which-is expected to continue through

1991.

The final two phases of the PLEX program will evaluate the-findifig of-the

Phases!'i and II,-and develop methods-for.mitigating the'effects of aging.

These methods include the use of maintenance and monitoring techniques'to

detectiand correct degradation,'and record keeping and trending to predict

equipment serv'icelife and improve'the program. The development of these two

phases, which areistill in the planning-stage, are expected to continue!

through the inid-1990s. .

The Plant Life'Extension Program is'-an-effort by the Japanese-utilities,

vendors, and regulatory agencies.to improve technology and extend the service

life of existing light water reactors. This will be accomplished by focusing

necessary resources on selected and prioritized systems and components to

ensure the continue safe operation of Japanese.nuclear'power plants.-

A discussion of the current and future activities of the PLEX program is

provided in Section 4 of this 'report.4 A diagram of.the key elements of the

Japanese PLEX program is pr'esented in Figure 3.4.

3.2.3 Continuous Monitoring and Inspections

The U.S. Navy has established a maintena'nce'program for its ballistic'

submarines that uses scheduled maintenance.tasks and extensive monitoring of

the operating condition of'plant systemsand components. The Pr'eventive

Maintenance System (PMS) approach'combines continual monitoring of all;

operating systems and components-with:spetified prevenitiviemaintenanceItasks

designed to detect equipment-degradation. The Navy establishes a detailed

maintenance program-for each-class of submarie.''1''Experience gained from

maintenance'on earlier classes of'submarines is used-in-the development of

maintenance programs for newer classes.'

3-9
1. Survey 2. Evaluation 3. Assessment &

Planning -

.. .. .. .. - - .... ... . .. - -

1, SurveyofLife

Equip- Preliminary Survey at

mentand screening of lile; criteria

structures subject equip- to identify

in power mani life; life, and

plant exposure at feasibility

replacement, of life

* of days and extension

costs of

replacement

11m.~~~~~ q

1, Categorization of equipment by

; riticality

.. P .. . ; .. ... . ....... .... {

Categorization by crilicalily

Life, aging factors, ease to

replace and backlit

4

2. Survey of actual condition of power plant

* Examples of degradation

* Service lie limiting factors

Screening of equipment

* Equipment governing service

lide

* Sublect equipment for

degradation diagnosis and

backilling

Evaluatior by equipment

2. Degradation

diagnosis

techniques

(feasibility)

3. Life evaluation

(applicability,

feasibility)

4. Backfitting life 1

extension measures

to Improve equipment & systems; I

methods to modify I

& replace Y

---

.I II

f i..; Categorization _ bycriticality.] 1

3. Survey of degradation diagnosis.

remaining lie and assessment techniques

Life change- Plant fife >Planl life

Changeable Changeable Durable Chneal equipment equipment

Difficult Permanent

to change __equipment

To Phase 11

_

I 4. Survey of technologies, factors of

backfitting and life extension

r I

I 5. Survey of laws and regulations I S. Evaluation of

^ blaws and i-

. . regulations J

6. Survey of cost assessment techniques

FIGURE 3.3. Study Areas of Phase One of the PLEX Program
/ Pasel I

- Selection of critical plant components\

- Survey of present rife extension technologies\

- Preliminary rife evaluation of critical components

UNDERSTANDING NAGING AGINGA

/Phase 2 /. ET..:\Pases 3 & 4\

- Verification tests on plant equipment - Comprehensiv evaluation studies of

- Collectionoldatatoconductrife ~aging data and rife prediction methodsI - Collection of data to conduct Gfe

prediction - Ufe extension scenarios of nuclear/

\ \ / ~~~~~~~~~~~~~~~~~~power plants/ - Techniques for aging diagnosis and \ /a/

M easurement \ / - Regulation and standards

* Impementlionof results

FIGURE 3.4. Key Interactive Elements of Japan's

PLEX Program
d1

-4.0 -UNDERSTANDING AGING-THROUGH THE'COLLECTION

AND USE OF PERFORMANCE DATA

The second element of-an aging management program is the-set of activities

that monitor and assess.[the effectiveness of the maintenance program. -An

important aspect of efforts :to improve the management of aging equipment.is

,the availability,.completeness, and accuracy of.equipment operational. ;

performance data. Performance-data and.information collected during monitoring activities provides a..basis to identify maintenance problems,

analyze possible causesi'and implement effective corrective actions. It.also

provides the organization with the information needed to understand the

effects of aging on critical systems and components. The four organizations

were found to use-different methods and performance..indicators to evaluate

their maintenance-programs.- ' e , -. -

.4.1- COMMERCIAL AVIATION INDUSTRY.

The-U.S. commercial aviation industry has an extensive system for assessing

the effectiveness of-its maintenance program and.has responded to increased

knowledge -concerning aging with new.programs designed.to incorporate such - knowledge.. During the life of.an aircraft,-.th6 airline, manufacturer, and FAA

continuallylearn more about.-the failure modes and aging mechanisms associated

with aircraft systems and components. This information is used to modify the

aircraft maintenance program to properly address aging issues.

After the initial approval.of the maintenance program, the'-frequency of

performing preventive maintenance is controlled ,by the airline operating the

aircraft, subject to continual surveillance by:the FAA.. To modify its

maintenance program from the initial maintenance requirements described in the

Maintenance.Review Board report,.-2the-airline must -show, based 'on operational

performance records, ,that a change-is warranted.:..

Performance records typically include the following information:

* engine shutdown and removal data

* component removals and verified failures - * system level delays and cancellations

engine performance data. . - .

~Monitoringtechniques.focus -on.failuire rates, age-reliability characteristics,

and the use of: simple ranking-processes to identify:areas needing special

maintenance attention. The'specific methodsused to monitor-reliability-are

generally left to the individual airline's choice. But regardless of the

method employed,-the -information,.is.made available for-airline management and,

as appropriate, FAA analysis'(Matteson, -McDonald, 'and Smith, 1984).-..

The -airline-provides the manufacturer with reliability and maintenance

findings, on:-its aircraft.; When a problem that.has fleet-wide safety,

implications arises (i.e., structural damage is detected that requires.changes

in maintenance procedures), the manufacturer issues a fleet-wide

.. 4-1
-

Service Bulletin. Although not legally required, airlines usually respond to

Service Bulletins.

The Boeing Commercial Airplane Company, for example, began issuing service

bulletins calling for supplemental inspections of aging aircraft structures in

the early 1980s. The service bulletins concern aircraft structures which were

discovered to experience fatigue and corrosion damage not addressed in the

initial maintenance program. These service bulletins have since evolved into

a formal mandated structural inspection program which is one of the aviation

industry's main programs to address the issues of aging aircraft. This

program, entitled the Supplemental Structural Inspection Program, is discussed

in Section 6.1.2.

When a condition has been verified as a safety significant problem, the FAA

develops an Airworthiness Directive (AD) to correct unsafe conditions revealed

by service experience. The AD is the primary vehicle by which the FAA

mandates fleet wide inspection and repairs changes. In general, discussions

among the manufacturer, airline, and the FAA precede the issuance of an

airworthiness directive. Airlines are required to maintain current records of

compliance with ADs for each aircraft in service. In addition, compliance

information is a specific requirement when aircraft custody or ownership is

changed. Most ADs and other design changes are intended to improve the

safety, reliability, maintainability or operating costs of aircraft.

For example, in 1984 the FAA issued an AD requiring operators with aging

aircraft to modify their examinations of structurally significant items by

adjusting their method and frequency of structural fatigue and corrosion

inspection. This AD requires aircraft with over 37,500 flight hours to be

included within the Supplemental Structural Inspection Program.

Though the original aircraft maintenance programs were developed to be

adequate for the full service life of aircraft, the collection and assessment

of equipment performance data has caused the aviation industry to recognize

that special programs are necessary in order to incorporate the results of

recent aging-related research.

4.2 JAPANESE NUCLEAR INDUSTRY

Within the Japanese nuclear industry, extensive technical information is

exchanged among the regulatory agencies, electric utilities, and other nuclear

industry organizations. The power plants use this information to devise and

implement preventive and corrective maintenance procedures, and enhance the

effectiveness of their maintenance programs.

The periodic inspection programs used by the Japanese nuclear industry will

remain in effect as they conduct new research to evaluate current program

effectiveness. In initiating new maintenance programs or supplementing

current ones, the industry considers background information on factors that

affect the service life of nuclear plants. These factors include the

following:

4-2
* Major components have individual service-lives, and-the safety and

reliability of each component-must be individually-'demonstrated. It is

necessary to understand the factors that determine component service

life, such as fatigue,-corrosion, and erosion..

* Preventive-and corrective-,maintenance must take into account aging

factors. Attention should-be given to procuring and replacing parts-to

-ensure continued equipment reliability...

* Reducedperformance mayresult from degradation due to aging factors

that may not affect overall plant reliability.

* ; Even with adequate maintenance,'there may be a point when it is not

economically feasible to repair aged equipment.

Table 4.1 provides examples of data analysis activities that have been

established by the Japanese nuclear power plants to address aging-related

issues for major systems and components.

In 1987, the Japanese nuclear industry implemented the second phase, or

technical development stage,,of the Plant Life Extension (PLEX) Program. -The

focus of Phase II-is to testcritical;plant equipment to better understand'the

equipment aging process. This information will be used to more accurately'

predict service life and will-aid in the development of procedures for the'

repair and replacement of aging equipment.

Results from the first year of Phase II include complete verification tests in

the following areas:

* degradation tests-of low-alloy and stainless steels

* thermal aging in dual-phase stainless steel

* fracture toughness, of stainless steel,:.-

* re-use of surveillance test coupons -

* development of inspection or repair equipment for reactor pressure

vessels. -X, -

Figure 4.1 outlines in detailJthe activities being conducted during 'the

technical development,,stage.- Completion of this phase is expected in,1991.

The final two phases of the Plant Life-Extension (PLEX) programfocus on

developing methods for applying the findings of Phases I and II to Japanese

nuclear power plants. Phase three evaluates the extent these findings were

applied to plants that will compile life prediction data and plant extension

proposals. A plan for plant extension will then be developed, taking into

consideration economic and regulatory requirements. Phase four will implement

the resulting programs.

- 4-3
TABLE 4.1. Apprdaches to Life Extension for Permanently

Installed Equipment

Degradation

System/Component Factor Life Extension Approaches Issues

1. Reactor pressure Fatigue, * Comparison of operating history with

vessel brittle thermal cycle drawing for design

fracture * Review of surveillance program

2. Reactor internal Embrittle- * Study of measures against IASCC

structures ment, corro- * Study of replaceability of equipment

(Shroud, shroud sion, IASCC * Study of repairing technology

support, top guide,

core support, jet

pump, ICM guide

tube, CRD and ICM

housing)

3. Concrete struc- Cracking, * Study of degradation diagnosis

tures, RPV pedes- degradation technology and repairing technology

tal of materials * Installation of degradation monitoring samples

4. Heat exchanger Corrosion, * Review of data of corrosion allow-

(chamber rubber deformation ance

lining, shell, * Installation of degradation monitortube) ing samples - Study of replaceability (making

easier to replace)

5. Cable Insulation * Study of replaceability (making

degradation easier to replace)

6. Turbine low Degradation * Study of repairing technology

pressure casing of materials

7. Piping (those Corrosion * Review of data of corrosion allowance

that cannot be * Study of replaceability (making

replaced such as easier to replace)

buried pipings) * Study of materials

4-4
Categorization of.-

equipment

parts for periodIcal change

_Degrading and

darraged parts

-Durable

equipmenlt ,.

Permanent..'-

equipment

-. t , 

deAnalysis of

deradation factors

Consuming &

we 'aring

Suddenly',

oc6curring

Material

degradation

Property

degradation

Performance

:'degradation

.

I 10

1-1

I I "

- .-1.

I -,l

I _'. ,

Identification of critical

issues for life extension

-*Life extension of replace--.

ment equipment, optimum

replacement interval,

-_Ensuring of supply of

replacement equipment

-_Improving of checking and

Inspection techniques, I '

development of programs

_- EstabIlshing of local

repalring and replacement:

techniques

; ...-.

Life extension

t technology

Improvement and

mitigation of service environment

_Backfitting and

replacement

techniques . Improvement of

durability ,

1,

.1 .

.. . . .

: -

. . _

.* . ...

. , .

.. L _

.

. . .

.. .: ., _

,

. ... ;

. ,

. , . . .

,. . _

, . . .

-.. , .

. . .

. . ...

. . .

-, .

Evaluation of degradailoni

;assessment techniques

-: Technique, to detect

and quantify

de Waldtaon

; 11.+Techniques' to assess. .:_.e iuses't ses

: -faui-ts, . ,' ' ' Advancement of ISI

techniques,

-*Prediction of remaining

life -

.. _Degradaliori of-'

monitoring'programs

Techniques of '. -

In-service Inspection'

-. 4 

t - -

q ;

- 11

I.I

Technologies to diagnose degradation and

to predict extended life

-,Material property

& degradationi

dilagnosis'and,

extended life.

* prediction,

--Degradation

monitoring hhd

* operation:

surveillance

-- Confirmao of

Tcnpermissible levels

and reliability

Assessment of

lfe i* extension

. technologies

, _Safety

. assessment

Economnics

assessment

_0: Exposure"

assessment

Identification

of and planning

measures for . technical

development

:.. ;.,- issues

I - -- r-,! . _. ..1. 1. ,. _. t

.., __ i

. I I

4

.r

:

FIGURE 4.1. Technical Development Stage of the PLEX Program

0
-

4.3 U.S. AIR FORCE B-52 BOMBER FLEET

For both the Air Force and the commercial aviation industry, the use of

Reliability Centered Maintenance requires extensive collection, organization,

and evaluation of equipment performance data. The Air Force Strategic Air

Command (SAC) is responsible for all B-52 operations and must document and

report maintenance problems discovered in the field.

Performance indicators used by the Air Force to assess the effectiveness of

its B-52 maintenance program include the usage rate of spare parts, changes in

the levels of corrective maintenance, failures resulting from inadequate

training, and a low operational readiness rating.

A Senior Officers Steering Group meets regularly to evaluate the maintenance

program. In addition, the Air Force utilizes a Maintenance Data Collection

System (MDCS) to compile a maintenance history of B-52 systems and components

(Summitt, et al., 1983).

Although the U.S. Air Force has good maintenance programs for the B-52

bombers, the MDCS is presently considered unreliable for identifying equipment

aging problems due to limitations of the data base (Summitt et al., 1983).

There is currently no method to test data files for accuracy and completeness,

and data recording practices are inconsistent between air bases.

The Air Force recognizes the current limitations of the quality and ability to

verify the MDCS accuracy and is working to improve the situation. As a

consequence of these difficulties, the Air Force relies mainly on the results

of Aircraft Condition Inspections (ACI) to evaluate the effectiveness of its

maintenance activities. Each year the Air Force selects ten aircraft out of

the B-52 fleet for an ACI inspection. The results of the ACIs are

systematically reviewed to determine the degree of inspection and overhaul to

be performed during the phase inspections. The ACI information is also used

to identify the maintenance activities to be completed during programmed depot

maintenance. If a failure is found during an ACI inspection, thirteen

additional aircraft from the B-52 fleet are inspected. If a repeat is found

during that inspection, an inspection task intended to correct the problem is

considered as an addition to the Programmed Depot Maintenance tasks.

4.4 U.S. NAVY BALLISTIC SUBMARINE FLEET

To date the submarine maintenance plan has proven to be quite effective in

managing aging from an operational standpoint. Originally, the time between

major overhauls was set at five years. A demonstration project involving

three ballistic submarines was undertaken by the System Maintenance and

Monitoring Support Operation (SMMSO) wherein the overhaul period was extended

to seven years, and then to nine years, and finally to twelve years. This

project successfully demonstrated the concept of an extended maintenance cycle

for ballistic submarines.

Data obtained from the logistics database is used as a measure of maintenance

program effectiveness. Indicators examined in this process include spare

parts usage and the failure frequency of a specific system or component.

4-6
Significant failures of systems or components are also evaluated to determine

if improvements to the maintenance program are required.

The Navy presently identifies aging problems by observing a change in

condition over an extended period of time. At each major overhaul, for

example, measurements of equipment operating characteristics are made and data

are recorded on inspection survey sheets, photographs are taken, and the rate

of change in equipment condition over the past performance period is assessed.

Data from the inspection survey sheets is entered into the SMMSO computer

database and subsequently used to analyze the rate of change in condition due

to aging, as well as other factors. This data is used in analysis to

determine the present condition and to project the useful life of the

equipment being surveyed. For the most part, insight on the aging process has

been a learn-as-you-go process. Some accelerated life studies and some

fatigue/cycle to failure studies are also performed; however, this is not

common practice.

4-7
5.0 MITIGATING AGING WITH MAINTENANCE

The identification of appropriate and effective mna'i ntenance processes, to

detect and mitigate aging degradation is an essential part of a maintenance

program of each of the four organizations examined.

The extent to which a maintenance program relies on any particular process.

depends'on many:factors. These include system and comp'onent criticality,,.

operating schedule, maintenance budget', and equipment redundancy. .The success

of-the four maintenance programs.discussed below in managing the aging of

systems and components.is generally credited to their systematic, scheduled

preventive maintenance activities. - . .-

5.1 COMMERCIAL AVIATION INDUSTRY

The maintenance programs used bYthe aviatioin industry are intended to" be'

adequate.for';the,'life 6f. the aircraft.';'This is based on the philosophy rthat

maintenance programs 'are "living",! mweaning that they, are constantly' revised

and improved to take into'account the most'recent 'informa'tion about aging and

the failure modes of aircraft systems and components.

There are some types of failure that cannot be prevented n'o matter how

intensive the maintenance~activities are designed..(Nowlan,<1978).- For.this

reason, .the 'equipment designers donot try to prevent failures~altogether, but

design the aircraft so that such -failures will not a'ffect'safety. - Likewise,

the maintenance programs are designed 'to detect failures before theybecome

critical and affect the safety of the airplane.' '

5.1.1 Types of Maintenance'Performed .

The maintenance program used in the 'aviation industry includes specific

maintenance processes for each piece of equipment. The maintenance processes

are selected based on'.the''safety'significance'of:the equipment 'and on -itsexhibited relationship between age and reliability.' The aviation industry.

uses: - ..

* on-condition equipment monitoring -: .

* hard-time restoration or replacement of equipment

- .conditionmonitoring. . - .

On-condition monitoring is a scheduled inspection or test used to'determine

the functional condition of a system or, component.. This process is restricted

to'those components 'on' which''a'determination", ofjco'n-t'inueed functionality can be

made by visual inspection, measurements, tests, 'or 'otheih 'means without a teardown inspection or overhaul..On-condition monitoring activities~are designed

to 'detect'potential'failures''ca used-byequipnent degradation ad call for

removal 'or 'repair 'of an item"'on 'the condition" that' itdo6es not meet a

required standard.

The'hard-time'pr'ocesses ,laces-'an age limit- on a part, requiring it to be

removed for restoration or repplacement after a specified operating age. For

- .5-1
many, items exhibit wear, and the probability of failure becomes significantly greater after a certain operating age. If no potential failure

condition can be defined for a piece of equipment, on-condition tasks are not

feasible.

Condition monitoring is characterized by the absence of preventive

maintenance. An item is said to be maintained by condition monitoring if it

is permitted to remain in service without preventive maintenance until a

functional failure occurs. This process is oriented to after-the-fact

detection of degradation or failure. Condition monitoring is also used to

detect possible failure of equipment that has hidden functions or are not

readily apparent to the operating crew or maintenance technicians. Condition

monitoring applied to those systems and components where the use of design

redundancies permit failures to occur without affecting operating safety.

Once the appropriate maintenance tasks for the systems and components on an

aircraft have been identified, a schedule for the frequency of preventive

maintenance tasks is established. The initial preventative maintenance

schedule for critical systems and components is specified in the Maintenance

Review Board Report.

5.1.2 Maintenance Scheduling

The most carefully constructed maintenance program would be of little value

without an organized maintenance schedule to keep the program in operation.

An aircraft maintenance schedule requires a series of progressive checks, and

is based on the following factors:

* the number of flight-hours the aircraft has logged

* the number of flight-cycles experienced by the aircraft

* the chronological age of the aircraft.

A typical maintenance schedule for a commercial aircraft is made up of a

series of "alphabet" checks that comply with federal rules. Each check is

progressive, that is a B-check includes everything done in an A-check, plus

more. The five predominant scheduled checks that are performed are:

* Daily: A visual check of the overall condition of the airplane.

* A-Checks: A general inspection performed at least every 125 flighthours.

* B-Checks: An in-depth inspection of control functions at a maximum

interval of 900 flight-hours.

* C-Checks: An in-depth inspection of systems and the structure performed

over four successive B-checks, with a maximum of 3600 flight hours

between checks.

* D-Checks: A complete structural inspection to determine continued

airworthiness after approximately 20,000 flight hours, or about every

four years.

5-2
Table 5.1 presents-.examples jof the types of-maintenance performed during each

scheduled maintenance check.

A-systematic schedule of maintenance-checks is vital to the-aviation--industry

in managing the effects of aging aircraft. Frequent.inspections allow the

industry to identify-and correct problems while they are small, as;well as

providing opportunities to gain a better understanding of component failure

modes-and the aging of-aircraft systems. -- - - - .

The overall objective of the maintenance program developed and used by the:

commercial aviation industry is to ensure the continued airworthiness of an

aircraft over-its-economic life.---The initial maintenance programs -developed

by the-FAA, manufacturer'.s.and.--airlines are thus designed to detect and

correct aging degradation.of aircraft equipment.

5.2. JAPANESE-NUCLEAR INDUSTRY . - .

The Japanese nuclear industry has regularly-scheduled maintenance and

inspection outages in conjunction with plant refueling. The work scheduled

for -these outages is part of-a:10-year inspection -plan, which is submitted to --the.Ministry.of..International.Trade and-Industry (MITI).- MITI, the Japanese

regulatory, authority-for nuclear-power plants, also receives annual updates of

the 10-year plans from the nuclear utilities.---

The periodic inspections-consist-of .nondestructive tests, -overhaul inspections

-and functional tests designed-to determine and alleviate the effects of aging

in nuclear plant systems. The tests and inspections -involve a large number of

preventive maintenance tasks. For-example, all safety valves and selected

pumps and other components are disassembled, overhauled and subjected to

functional --tests. - - - . . -

A list of.systems evaluated during -the periodic inspections -for both -

pressurized and boiling-water reactors is shown on Table 5.2 .(NUREG-1333,

1990)..' Specific components within.the-systems are ialso listed,'as are the

types-of inspectionsfperformed.- .Many~of the inspections are witnessed by MITI

or its designated representative.- Extensive post-maintenance tests are

performed before restarting the plant. '

5.3 U.S. AIR FORCE B-52-BOMBER FLEET- -

The maintenance activities for the B-52;aircraft are scheduled in a series of

maintenance.-inspections that areiconducted-in phases every 200, 400, and 600

flight-hours.' These phase-inspections.:are normally:performed at the

aircraft's home base and consist of a combination of preventive maintenance - and corrective maintenance. - - . -

The Material Management Directorate within the Air Force Logistics Command is

responsible for major inspections of. the B-52;-these inspections''are conducted

at Air.Force.maintenance depots... .Depotfacilities consist of..a set of--

maintenance specialty units where work is performed by a civilian labor force

of skilled specialists.-

5-3
TABLE 5.1. Types of Maintenance Performed During Aircraft Inspections

Equipment

Inspection Category Type of Maintenance

Daily Landing gear Check of tire and brake wear; inspection of landing

gear struts

Structure General inspection of wings

A Landing gear Visual inspection and lubrication, apply brakes and

visually inspect brakes for wear and condition

Structure General visual inspection of external skin condition

with special emphasis on cutouts such as door frames

and windows

Engines Test of standby engine

B Structure Inspection of pressure bulkheads for signs of

corrosion

Engines Inspection of compressor blades for wear

C Landing gear Treatment of wheel wells and main landing gear for

corrosion protection

Structure Inspections of engine pylons and cabin interior

for corrosion

D Cabin Interior removed, seats overhauled and reinstalled.

Modifications made as required including emergency

lighting, installation of fire resistant fabric,

and new equipment

Engines Engines removed, serviced, and remounted. Overhauls performed as required.

Structure Landing gear inspected, new seals installed and

reassembled. Complete internal inspection of wings.

Modifications to prevent fatigue and fix corrosion.

System Navigation equipment repaired, autopilot in tail

system rewired. Worn pivot bushings and metal

sleeves for moving parts replaced. All hydraulic

systems inspected for wear.

5-4
TABLE 5.2.

!

.Systems Evaluated During Inspections.of.Pressurized (PWR)

and Boiling (BWR) Water.Reactors

EJR - PIR-

_ - ~~Contents of ----- Contents of

Electric Facility Name of Facility 'Inspection - 'Name of Facility Inspection

Reactor pressure Inservice inspection Pressure vessel Inservice inspection

vessel (non-destructive (non-destructive

inspection and leak inspection and leak

test) test)

Reactor

Fuel assembly Sippy inspection,- Fuel assembly Sipping inspection,

visual inspection,- visual:inspection,

fuel shuffling , - . fuel shuffling

inspection and 1 inspection and

reactor shutdown-- reactor shutdown

margin inspection margin inspection

gain steam lines . Steam generator heat Eddy current test

Safety valve Disassembling and exchanger tubes

Relief valve inspection, functionIsolating valve al test

Ditto (inclusive --- I

of function of auto- Pressurizer 7-

matic pressure Safety valve Disassembling and

reducing system) inspection, leak test

Leak rate test, functional test

functional test, Ditto

Turbine bypass. Functional test-- Main relief valve Functional test

valve

High pressure core Functional test,a- in steam lines - injection system disassembling in- Safety valve Leak test,

Low pressure core spection (inclusive functional test

injection system of auxiliary steam Relief valve Ditto

Core spray system turbine), main valve Isolating valve Functional test

disassembling and in- Turbine bypass Ditto

Reactor coolant spection valve - -

systems

Reactor isolation High pressure core Functional test, pump

coolant system injection system disassembling and inReactor auxiliary Functional test Low pressure core spection, main valve

coolant system .. injection system disassembling and

Feed water-pump - ; , - inspection

Vessels, pipings, Inservice inspec- Accuaulator Functional'test,~-

pumps and valves tion High pressure, main valve disinjection system assembling and

Reactor upper head - inspection

injection system

Auxiliary feedwater Functional test, pump _ _ _ -; * rsystem - disassembling and

inspection ;- . . ; ,.::-:;.......

Vessel,-piping, Inservice inspection pumps, Valves

.. . I .. - _7 ' !  r - , , - , - , '; ,

O : -1 I .. 1.  I - -1 '.

il r._ . '- . ; :

5-5
TABLE 5.2 (continued)

BIR PIR

Contents of Contents of

Electric Facility Nave of Facility Inspection Name of Facility Inspection

Instrument air system Functional inspection Control rod driving Functional test

Boric acid injection system

systeM Instrument air system

Control rod driving Functional test, Safety protection Calibration test

system overhauling inspec- system

Instrumentation tion of the drive

system mechanism, disassembling and inspection

of the scrum valve

Safety protection Inspection of safety

system protection element

(functional), calibration test

Nuclear reactor Functional test of

protection system plant interlock

Fuel assembly and Fuel handling system Functional test Fuel handling system Functional test

fuel handling

system

Field monitoring Field monitoring

Area-monitoring Functional test Area and process

Process monitoring monitoring

Radiation control Annulus recirculasystem Emergency gas tion exhaust system Functional test

treatment system Functional test, Recirculation system

Recirculation sys- filter performance for main control

tea for main control test room

Gaseous waste treat- Gaseous waste treatment system sent system

Liquid waste treat- Liquid waste treatment system ment system

Waste disposal Leakage detector for Functional test Solid waste treat- Functional test

system liquid radioactive ment system

waste and warning Leakage detector for

device liquid radioactive

waste and warning

device

Solid waste storage Inspection of control Solid waste storage Inspection of control

condition condition

Containment vessel Containment vessel

Leak rate test Leak rate test

Isolation valve Functional test, Isolation valve Functional test,

Disassembling and Disassembling and

inspection Vacuum relief valve inspection

Vacuum breaker Functional test Functional test

Containment vessel Functional test, pump Containment vessel Functional test, pump

Containment Spray system disassembling and in- Spray system disassembling and invessel spection, main valve spection, main valve

disassembling and disassembling and

inspection inspection

Combustible gas Functional test, main Containment vessel Functional test

concentration control valve disassembling hydrogen recombiner

system and inspection

Reactor building Leak test Ice condenser Functional test

5-6
TABLE 5.2 (continued):

Contents of , Contents of

Electric Facility Name of Facility Name of Facility Inspection

Steam turbine V Turbine and aCCes- rhuling inspec- Turbine and acces- Overhaulingjnspecsystem sories (valves, etC.) tion I ories tion . ' ! 

Functional test- Functional test

(valves, etc.) (valves, etc.)

Auxiliary boiler Overhauling inspec- xiliary boiler Functional test

Auxiliary boiler and accessories tion

(Valves, etc.) -

Emergency power Emergency power Functional test Emergency power Functional test

generating system generating set generating set

Others Others Overall plant Others Overall plant

performance test performance test

Programmed-Depot Maintenance (PDM)-is performed every four years,

necessitating that the aircraft be out'of service for about four months.'

Maintenance of critical items is performed at thisltime. The PDM-provides'the

aircraft with four months ofs-extensive-maintenance, refurbishment, upgrade and

overhaul which restores it to new condition. All repaired systems and

components are bench checked before installing them on the aircraft. After

installation, and before'returning the aircraft to operational status, ground

checks of the installed'systems'and components are performed, and-a test-:

flight of the aircraft is conducted.,

AircraftCondition Inspections (ACIs)-are performed concurrently with the-PDM.

An ACI is a special'inspection-over and above the'normal inspection

requirements and'is performed to provide a basis for establishing inspection

tasks and developing future inspection schedules.

5.4 U.S. NAVY BALLISTIC SUBMARINE FLEET

The Navy'sfballistic-submarine-maintenance program identifies the frequency of

maintenance, type of'maintenance,- and organization responsible for the

maintenance for-each system and component on the submarine. The-program also

identifies which items receive condition monitoring'or are allowed-to run to

failure,' and which items~require on-condition monitoring or preventive

maintenance. The maintenance program relies onthe submarine crew'members to

monitor system and.component-operating conditions as'well.as perform selected

preventive. and corrective'-maintenance tasks.. ;More extensive maintenance is

conducted at shipyards. or-submarine tenders. ' -

The maintenance program relies on preventive maintenance much more than on

condition maintenance. Preventive maintenance, based on the performance of

other submarines of the same class, is employed to mitigate the effects of

equipment aging. A maintenance record card (MRC) is prepared and maintained

for each component and system that is designated for monitoring in the

-5-7
maintenance plan. Separate records are maintained for reactor and propulsion

pl.- equipment, and extensive preventive maintenance is performed on both.

The urveillance philosophy for equipment performance monitoring is to use

Non-Destructive Inspection (NDI) where possible. This is to avoid breaking

into systems that have been certified for operational integrity, such as those

exposed to sea-pressure. As a result, commercially available NDI techniques

are relied on extensively to indicate a change in condition.

Monitoring techniques include the use of pyrometers, flow meters, vibration

monitors, ultrasonic measuring devices, and spectroanalysis of oil. These

techniques are used quite effectively to monitor changes in equipment

condition or performance over extended periods of time. Performance data

pertaining to equipment aging on older submarines is used to identify systems

and components on newer submarines where aging could be identified by using

NDI.

Ballistic submarines operate on a three-month deployment schedule followed by

a 30-day refit period at a shipyard or submarine tender. During the refit,

preventive and corrective maintenance that is beyond the capabilities of the

boat's crew is performed, and the submarine is readied for the next

deployment. Approximately once every four years, a 60-day restricted

availability is performed. This is an extended maintenance period intended to

upgrade systems and components.

Over the 30-year life of the submarine, it is scheduled for refueling

approximately every twelve years. During the refueling period, extensive

preventive and corrective maintenance is performed on many of the submarine's

systems, structures, and components (SSCs). The refueling overhaul requires

18 to 24 months. Following a refueling overhaul, each system undergoes

extensive testing while the submarine is still in the shipyard. Subsequently,

the submarine undergoes sea-trials with ship-yard personnel on board. All

items found deficient during sea trials are corrected, a new baseline is

established on the MRC cards, and the boat is returned to the fleet for active

duty.

More recently, the Trident submarine maintenance program has introduced a new

approach into the ballistic submarine maintenance programs. Hard-time

limitations are placed on many components, requiring their removal from the

submarine. A new or refurbished component replaces the original, which is

sent to a maintenance facility for overhaul. The Tridents are designed to

facilitate these activities, and extensive standardization of equipment is

used throughout the Trident submarine class. This approach ensures that when

needed, each submarine is fully operational, and that maintenance activities

have a minimal impact on the submarine's operating schedule.

5-8
. .6.0 FEEDBACK'AND CORRECTIVE ACTIONS TO IMPROVE MAINTENANCE

The performance data gathered-during equipment monitoring provides important

information to address the increased maintenance requirements of aging...:

equipment. An organization's ability to collect and evaluate equipment

performance data is a.critical practice that enables feedback:and corrective

actions to improve the maintenance.program. The ,four organizations take :

different approaches to analyze performance data in-order to'identify and

initiate corrective actionsto their existingmaintenance programs. -

6.1 COMMERCIAL AVIATION INDUSTRY

Time lines for.overhauls and inspections of aircraft systems and components

are established-as part of commercial aviation maintenance programs.. These

time lines are continually modified and-refined,,as.technology advances in

airframe, engine, and equipment design,,and as.knowledge :expands.on preventive

maintenance. Airlines can initiate changes in their maintenance inspection

schedule through negotiations with the -FAA based on specific operating,-

experience data or.engineering studies-., The manufacturer recommends changes

by issuing Service Bulletins-to-the -airlines, .and the FAA issues Airworthiness

Directives..when.mandatory changes to maintenance programs are required.

On April,28, 1988, the -top half of a Boeing 737' fuselage section tore loose on

a flight from Hilo to Honolulu, Hawaii. The National,>Transportation'Safety

Board (NTSB) determined the probable cause of the accident to be the failure

of Aloha Airline's maintenance program todetect ,the presence.ofsignificant

fatigue-damage, which ultimately led;to,,the separation'of the fuselage upper

lobe. This incident has causednew concerns for-the industry.on how to better

ensure the safety and reliability ofaging ,aircraft. -As a result,.,the

aviation industry has formed an Airworthiness Assurance Task:Force to foster a

consistent.approach to aging concerns for each major airplane manufacturer.'

This task force has made several recommendations for industry-wide corrective

actions'.to'airline maintenance programs. , - - -

This section discusses.'the dangersof fatigue and corrosion in aging aircraft.

Special maintenance programs for aging aircraft are also addressed.

6.1.1 Fatigue and Corrosion: Predominant-Danqers to Aqinq'Aircraft

A number of factors other than.chronological-age affect' the~operational and

economic Ilife of a.commercial-jet aircraft. -Perhaps the best indicator *isthe

n'umber of flight cycles,-especially the number of compressions and . decompressions during flight which keep-the air~pressure-in the cabin-at a_

comfortable level. Most planes are designed for a nominal economic lifetime

of_20 years, but for widely varying:numbers of cycles-and flight.hours. :For

example,-the Boeing 747,wasintended-for :long flights.and designed~for.20,000

flights and 60,000 hours. The Boeing 737 was intended for relatively short

flights and so designed for 75,000 flights and 51,000 hours.

Under cyclic loads, imperfections in the aircraft structure can form the

nucleus of tiny cracks that may eventually grow and degrade structural

6-1
capability. This is known as fatigue, and is directly related to the number

of flight cycles an aircraft is subjected to. Any metal part that moves or is

su;ject to stress experiences fatigue. Damage may develop from loads imposed

by repeated cycles of takeoff, flight, pressurization and landings of an

aircraft.

Corrosion occurs when the aircraft structure is exposed to atmospheric salts,

water, or runway contamination. Corrosion is more unpredictable than fatigue,

and is hard to prepare for in the design process. Corrosion will occur at

different rates depending on the surrounding environment, making it especially

difficult to design an aircraft to withstand this type of damage.

The combined effects of fatigue and corrosion can be disastrous. A crack due

to fatigue will normally grow at a predictable and detectable rate. If

corrosion is present, however, the rate of growth may be accelerated by a

factor of ten. Inspection and maintenance programs are the key to managing

the effects of fatigue and corrosion (Murphy, 1989).

Due to the effects of corrosion and fatigue, maintenance programs must change

as aircraft age and accumulate more flight hours. Figure 6.1 illustrates some

of the well known areas of fatigue and corrosion damage. Fatigue usually

starts around the skin rivets and other details such as bolts and fittings.

Corrosion is most often found in the belly of the plane, where water collects.

Maintenance programs are being modified to detect and mitigate these effects

as they are discovered.

Special maintenance activities designed specifically to determine and mitigate

the effects of aging have been implemented by the manufacturers, airlines, and

the FAA. Supplemental Structural Inspection Documents were issued by the

manufacturers as service bulletins, and, with the issuance of airworthiness

directives by the FAA, became mandatory parts of the maintenance programs in

1984. Following the Aloha Airline 737 accident, the Airworthiness Assurance

Task Force on aging aircraft was formed. This task force included members

from the manufacturers, the FAA, and the airline industry's Air Transport

Association (ATA). Several new programs to address the issues of aging

aircraft have been initiated as a result of recommendations from this group.

6.1.2 Supplemental Structural Inspection Program

The Supplemental Structure Inspection Program (SSIP) was developed in the

early 1980s by the FAA and aircraft manufacturers to extend the operational

life of older aircraft and to ensure their safe operation (Fotos, 1988). The

SSIP provides for continuous structural inspection to identify fatigue cracks

and other damage resulting from aging.

This program covers areas of the aircraft structure that were not necessarily

of concern during the original structural analysis and maintenance program

development.

6-2
-Strucral memDers engthise stringers AMd

waCarOunf clnurrwentilaS wnich Snace ana * strengthen mame structure an suletr lague

fromn stress cur"ng ligrt am corrosion torn

tanoed mostre: batn effects are hard to aetect

buse af iilte access to tnese menoerS

WmnqftD tracks: ar ousnrg against Ve

fIlos stresseS them enornroSly. soie

trmes erourn to create lbroue cracs n me nacx that atricnes the noa mednanr

ismns to a wing ceam

, .j;_\

~~~~~~~~~ . 1: '.'."'. . ,' '-.-

-Ve~tical sraojli2. stress here

*- - can Inouce btatzue cracts in

'e tnenterrnl soar Iat strengin ml-Ste slaiurllzet

/

uncmg gear oas anc finrings. hiere arta etsewnere. are

esoecialDaOne to tallguet and

corrosion

Wmig rid tatgue owankS can

result when the sKin 1

stresseda So rnuch at tries

I - Uaway . -

1, ~ ~. .-,: : -, z.~ .

Skin rivers: the stress Of nunerous preSsuriz3110n

C Cycles arten s ans talgue cracxs in the useige - skri. usuilly where it benrts around countersunK

rivets: corrosion irorm water coflecting n the - :I plane5 oely alSo alten begnt5 nere ,-I% -

I... v .I

;: ,r: -, "

q .- :,., '.:': . , I, i

Areas of Fatigue and Corrosion Damage

on Aging Aircraft (Murphy, 1989), ;

FIGURE- 6.1.

I I - . : . - . 1 . . . - I . I -

I - f. 1-

- I- i

6-3
Manufacturers identify and issue a Special Structure Inspection Document for

all structural components of an aircraft that have damage or fatigue

characteristics that could affect the aircraft's structural integrity

(Broderick, 1986). This document establishes a special inspection procedure

for each of those components. Based on the data provided by the manufacturer,

the airlines adjust the frequency and method of structural inspections to

ensure continued airworthiness as aircraft age.

While the program is not a substitute for the operator's existing FAAapproved structural inspection program, the SSIP provides the airlines with

procedures to evaluate and supplement their existing program. Should fatigue

cracking occur, the SSIP allows operators to detect damage before the

aircraft's residual strength falls below the regulatory fail-safe

requirements.

Though the SSIP was initially developed by the manufacturer and distributed to

the airlines as a set of service bulletins, an airworthiness directive was

issued by the FAA in 1984 requiring operators with aging aircraft to

incorporate the inspection requirements of the SSIP into their existing

maintenance programs. The AD requires aircraft that have exceeded 37,500

flight cycles to be included in the SSIP.

6.1.3 Structural Analysis of Aging Aircraft by the Manufacturer

Aircraft manufacturers monitor the structures of high cycle aircraft through

structural tear-downs and fatigue testing. Boeing Commercial Aircraft's aging

aircraft surveillance program includes testing, tear-down, and inspection of

older airframes. In 1987, as a part of this program, Boeing purchased an 18-

year old 737 which had accrued 60,000 flights and 42,000 flight-hours over 18

years of service. The aircraft was subjected to structural load tests to add

another 70,000 simulated flight cycles. The structure was still in good

condition with little corrosion at the end of the test, indicating that a

properly maintained 737 should have a lifetime of at least 130,000 cycles.

Boeing repeated the process with a second 737 airframe, and in 1988 purchased

a high-time short range 747 for similar testing (Ott & O'Lone, 1988). The

fuselage of the 747 is currently being subjected to pressure cycling to

explore extended fleet usage beyond the original economic design life

objectives of 20,000 flights and 60,000 flight hours.

Douglas Aircraft has purchased one of the oldest operating DC-9s and performed

extended service life testing of the equivalent of nearly 70 years of service.

This included 66,500 cycles of original service and 141,500 simulated flight

cycles. After testing, a tear down inspection of 14,000 fastener holes

indicated that their useful life had not been exceeded (AW&ST, 1988).

6.1.4 Structural Modifications for High Cycle Aircraft

A new emphasis on structural requirements has resulted from the Aloha Airline

737 accident. Based on recommendations of the industry's Airworthiness

Assurance Task Force, the FAA has ordered structural modifications to older

aircraft, signaling a change maintenance policy. Previously, the FAA had

required only periodic inspections to detect structural fatigue and corrosion

6-4
damage, and called for replacement only when such conditions were found. In

March 1990, the FAA-issued a series of airworthiness directives calling for

more-than $800 million in'modifications to older Boeing 747, 737, and 727

aircraft. Some-of the required modifications for the aircraft models are

illustrated in Figure 6.2.'

In September 1989, the task force made-recommendations calling for similar

modifications to older McDonnell Douglas aircraft. The FAA is expected to

issue airworthiness directives in the summer of 1990 that will require

mandatory structural modifications ranging from'minor bolt replacements to

landing gear overhauls.

6.2 JAPANESE NUCLEAR INDUSTRY

In addition to the Plant Life Extension Program currently underway, the

Japanese utilities are devoting considerable resources to reduce the duration

of the periodic inspections,' and'to improve'the-quality .of maintenance

activities performed during these inspections. The duration of periodic

inspections has been reduced over'the last.few~years. Several factors

contribute to this trend:

* the reduction in corrective maintenance as initial equipment problems

have been solved - '

* aggressive evaluations and the use of equipment performance information

* increased efficiency in the organization'and administration of periodic

inspections

* long-standing cooperation between utilities, regulatory agencies, and

equipment manufacturers

* overall technical improvements in the performance of maintenance and

repair

* extensive education and training programs.

A periodic inspection currently'takes approximately 100 days. Because of

this,-and the fact-that the maximum-interval between inspections is 13 months,

the maximum operating'capacity'within current regulations is 80%. The

Japanese nuclear^industry is trying to find methods to reduce the time

required to perform an-inspectioniiand to extend the time period between

inspections. The utilities-have proposed-several methods by which to reduce

inspection time: -

* improve detection techniques to'provide more accurate and reliable

inspection results'to minimize inspection and evaluation time

* develop automated inspection tools to minimize radiation exposure and

inspection time '-i l :; - i - ; m

6-5
727 :HIGH TIME AIRPLANE TYPICAL MODIFICATIONS

737 HIGH TIME AIRPLANE TYPICAL MODIFICATIONS

REPLACE LAP

TRAM DOL.TS

747 HIGH TIME AIRPLANE TYPICAL MODIFICATIONS

FIGURE 6.2. Typical High Cycle Aircraft Modifications

(Fotos, 1989b)

6-6
* alleviate "critical paths" in the work performance...

* continually evaluate data collected on equipment performance to identify

inspections -that can be'reasonable be performed less frequently

* develop'computer management systems for processing and evaluating

equipment performance data.

One utility has submitted a request to MITI to extend the amount of time their

facility is allowed to operate between scheduled outages from 13 to 15 months.

MITI is currently investigating the effects of extended inspection intervals

in plants that are performing well and have a 13-month operation and 10-week

inspection cycle. Utilities will also be required to demonstrate that major

components can operate reliably for more than a year to extend their operating

schedule (NUREG-1333, 1990).

6.3 U.S. AIR FORCE 8-52 BOMBER FLEET

The Material Management Directorate communicates daily with the Strategic Air

Command (SAC) maintenance organization at each of the air bases where B-52

aircraft are assigned, and with the maintenance organization at SAC

Headquarters. Each SAC maintenance organization equipped with B-52s has an

extensive maintenance program that ensures the aircraft are mission-ready on a

24-hour basis. Maintenance at this level is conducted using many of the

concepts and techniques of the commercial aviation industry.

The Air Force convenes a Product Improvement Working Group (PIWG) every three

months to review performance, needed improvements, and design modifications on

the B-52. These reviews are based on flight performance data, repair records,

and pilot and crew feedback. The purpose of the PIWG is to resolve major

maintenance problems, such as directing procedural changes and initiating

development programs or authorizing aircraft engineering changes and

modifications. This working group is multi-disciplinary, representing all

parties involved with the aircraft. The Air Force has empowered this group to

make recommendations and generally funds and implements their proposals.

Inspection tasks and schedules can be modified by direction of the SAC air

base Deputy Commander for Maintenance, who is responsible for maintenance at

individual Air Force bases.

6.4 U.S. NAVY BALLISTIC SUBMARINE FLEET

There is daily telephone/computer communication between the repair site team

leader and the System Maintenance Monitoring and Support Operation (SMMSO)

program manager wherein specific highlights are discussed by hull number.

This communication can also include a request for engineering support from

SMMSO. The SMMSO is responsible for determining the need for equipment

condition monitoring, including monitoring for aging and reporting to a

maintenance planning and procurement organization. This organization, in

turn, is responsible for maintenance planning and work procedure development.

In addition to daily communication, a system of Technical Feedback Reports

are initiated at the crew member level and passed up through the chain of

6-7
command to management. Within the SMMSO performance monitoring program, high

level system review meetings are conducted at periods ranging from once per

year to once every three years. Participants at these meetings evaluate the

effectiveness of the maintenance program, identify areas of change, assign new

action items, and evaluate the progress of on-going action items.

6-8
7.0 RESEARCH AND-ACTION AREAS

Each of the four organizations examined have established research programs to

help them understand and mitigate the effects of aging. This section

discusses some of the aging-related research areas which are being considered

bythe four organizations in their aging management programs.

7.1--THE LOGISTICS OF SPARE PARTS FOR AGING COMPONENTSA-factor that will eventually impact the ability of nuclear power plants to

effectivelymanage aging-involves the logistics:of maintaining an adequate

supply of replacement items-for the aging equipment (NRC, 1986). As-equipment

manufacturers discontinue production of older items or abandon nuclear product

lines, it will become increasingly difficult to procure the spare and

replacement parts needed :tovsafely~and efficiently operate the plant. The

-logistics of-maintaining-an adequate supply of replacement items foraging

equipment hastbecome a major problem-in maintaining the operational readiness

of both the, B-52:aircraft and-older Navy ballistic submarines.

Experience has shown that the~cost ofsupporting the-B-52 bomber has increased

dramatically ,as-a result of extending its useful life. This is due in large

part, to the increase in cost caused by-.unavailable:spare parts for many

aircraft components andsubsystems (Capotosti. and Curran, 1981). This - situation, called Diminishing Manufacturing Sources (DMS), has forced .the Air

Force to authorize a "make-in-lieu-of-buy" policy for 'a number of components.

These components are fabricated at a repair depot :by the Air ForceLogistic

Command. .This approach-may be-adopted bythe nuclear industry as maintenance

resourcesjand economics -allow. - , - - -

DMS-is also'recognized bythe Navy as a serious problem,- especially in the

procurement of spare parts -for older submarines. ::In cases where no acceptable

replacement component canzbe-purchased,-the shipyard manufactures-the required

,-component. - - , -

DMS is not a major factor in the airline industry primarily due to its growth.

Currently,,most airlines-have adopted-an-approach where-the-equipment -,

manufacturer guarantees the-availability of spare partsifor the useful,,life of

the aircraft. ,This approach includes maintenance support for most major -

components such'as generators- hydraulic pumps, :avionic systems, and-,

navigation-systems. --Increasingsupport--from-the aircraft and engine

manufacturers has been provided Sinthe form :of, longer product quality

warranties, reliability and maintenance cost guarantees,- and free logistic

support, and'design-changes when inserviceiperformance is less than specified

(EPRI, 1984). , , , -

7.-2 CORROSION CONTROL PROGRAMS <:, < . ; ,

The Supplem)e ntal Stru'ctura Inspection Progriam, which handles the inspection

of aging aircraft-stru'ctures, 'assumes that the operators have kept thei'r' -

aircraft generally free from corrosion. Boeing started an aging fleet

evaluation program in early 1987. By mid-1988, about 60 aircraft had been

7-1
surveyed for the effects of corrosion as part of this program. These aircraft

have shown a wide range of conditions from excellent to "significantly below

expectation," with the primary problem being corrosion. The program also

showed that aircraft without lifelong aggressive corrosion control programs

usually had corrosion problems (Dornheim, 1988).

Airlines must now inspect for corrosion, but the FAA permits the inspections

to be conducted in different ways. The Airworthiness Assurance Task Force was

established to learn whether the airlines should be permitted less discretion

in the way corrosion control is conducted. An important consideration of the

Task Force is the fact that different operational environments argue against

identical procedures. In March 1990, the FAA proposed extensive regulatory

standards for corrosion control of U.S. commercial aircraft as one response to

the midair breakup of the Aloha Airlines 737 in 1988.

The current industry standard states that if corrosion causes a ten percent

loss in fuselage skin thickness, replacement of that portion is required. The

FAA has proposed to further restrict the allowable corrosion loss to five

percent. Measuring equipment calibration errors make it difficult to

accurately measure small amounts of corrosion; therefore, the FAA will require

more frequent and thorough inspections. In addition, the FAA will mandate

"fixes" to problems, referred to as terminating actions by maintenance

personnel. This includes actions such as replacing one metal when dissimilar

metals interact to alleviate the need for further inspections to detect

corrosion (Ott, 1988a).

The commercial aviation industry is also looking to the military for methods

of corrosion control. The Navy has done much research in developing corrosion

control techniques. One of the Navy's several developments is Unicoat paint,

a single coat that serves as primer and topcoat. The single layer improves

protection and saves weight. Several new F-14s treated with the paint are

undergoing operational evaluation. Another development is a water-displacing

compound for internal corrosion coating. One product, called Amiguard, is a

transparent coating that keeps the underlying structure visible and allows for

inspections (DeMeis, 1989).

The Air Force has been conducting research over the last 12 years in the

development of a system to detect corrosion by automatically monitoring

increases in the electrical resistivity between small, metallic sensors

mounted on aircraft components (Battelle, 1989). Output signals from the

individual sensors are transmitted to a centralized computer system mounted on

the aircraft. The computer calculates rates of corrosion occurring on the

surfaces of the airframe structures. The system provides continuous

information, thus enhancing safety and possibly reducing the need to perform

visual inspections. The system is currently being designed for use on Air

Force F-15 fighter aircraft, C-130 transport aircraft, and the MH-60

helicopter. Though still in the development stage, it is envisioned that the

system and the information it generates will be an important tool for use by

maintenance personnel responsible for ensuring the structural integrity of an

aircraft's airframe components.

7-2
7.3 TECHNOLOGICAL DEVELOPMENTS-BY THE AIRLINES

After a commercial-airplane enters service, ongoing inspections and

maintenance of its structure are necessary to ensure a continued :high level of

safety. Experience has shown that-the inherent structural integrity of-- - commercial aircraft has been maintained by operator inspection and maintenance

programs. However, after many years of-service, these aircraft will reach an

age where an increase in fatigue-cracking may be expected.; Non-destructive

inspection (NDI) techniques are being developed and verified for use by.;-

operators to ensure the structural integrity of aircraft (Hagemaier, Bates and

Steinberg, 1988).

Damage tolerance and NDI reliability programs consistently show that eddy

current inspection is superior to other existing non-destructive testing (NDT)

methods for detection of fatigue cracks. Existing eddy current instruments

enable the inspector establish the existence and relative severity of fatigue

cracks and corrosion. CAT Scan techniques from medicine, already used on

engine disks and blades, may improve inspection of material cross sections and

multiple bonds. Infrared thermography can be used to check for composite

debonds and repair integrity. Automation and computer enhanced imagery would

help in detection and record keeping. For example, automated ultrasonic

scanning of a rivet row would contribute an image record forming a comparative

history of the structure over time.

Part of the research conducted by the FAA into developing and evaluating NDI

equipment will address the development of training material on the use of such

equipment for aircraft mechanics, in recognition of the need to ensure their

familiarity with and understanding of new techniques and equipment (Blake,

1988).

Analytical procedures for airframe life prediction have been developed by NASA

and are currently used in the design and assessment of new airframestructures. In future efforts, NASA is expected to assist the FAA in

developing methodology to determine the structural integrity of aging

airframes (Rosen, 1988). They will also help to develop methods of assessing

the effects of multiple crack site behavior in airframe structures, and

determining crack size and distribution parameters that could affect the safe

life of aging aircraft. This information would provide the basis for

determining required inspection techniques and intervals for old airframes and

to provide a rational basis for safe life extension.

NASA has also developed NDI and evaluation methods that can be used for

structural inspections and validation of analytical life prediction methods.

Future NASA efforts will support the FAA in developing improved methods to

assess the integrity of bonded structures, areas of corrosion damage, and

possibly development of automated inspection and evaluation methods. This

would increase the reliability of airframe inspections and enhance the safety

of aging aircraft.

-7-3
7.4 JAPANESE NUCLEAR AGING RESEARCH EFFORTS

The Japanese have established a number of research and development programs to

address nuclear plant aging. These research and development projects,

conducted as joint cooperation efforts between government and private

organizations, are intended to improve the maintenance program currently used

by the Japanese nuclear industry. A list of these research and development

projects is provided in Figure 7.1. Included is information on the scope of

the research and the organization responsible for the project.

7-4
Subject of Example of working Organizations

Research and Subject

Category No. Developeent Contents Equipment Governmental Utilities Suppliers Joint *ork Others Remarks

1. Material 1. Establishment of To collect from literature RPV, SO, 9 (0) -RPV: reactor

basic data bank and-experiments and put-in- RIM, - - - - 1 pressure

for materials order basic data-of mate-' pipings, .r:... vessel

rials (such degradation- valves, . ___-- . SO: steam

phenomena as cracking, fa.! etc. _ _ -- generator

tijue, corrosionasnd (°) RIN: reactor

strength reduction) ssre- internals

quired for the evaluation, -To establish

- of thesfeasibility of s , private seclong-term'continuous'oper- tor dats base

_ . ation of nuclear power -- - .and public

ipant which will be used' dsts bass.

as s'neutral dato'bank for =

'long time.: Obtained data

:' (data of degradation'fac- I

tors such'as corrosion and .. .

fatigue) will be used for;

.' ;;; prediction of life.- - ;;'__

2. Degradation - 1" Establishment of To establish methods to RPVY RIN, M ;(0) -To offiDiagnosis and methods of pre- reasonably predict and de' pipings,. --- L-- cisl

Life Prediction dicting life of . cide'the remaining life of etc. LzL.. J - u -

equipment and major equipment which can _ _ - methods m and

criteria for hardly o be replaced, on the _ _ _- criteria doappropriate basis of checking, degrn- (°). - ; veloped on

maintenance dation'diagnosis and basic - . . the results

;aterials data-and saints- of'studies of

nonce criteria. To isprove the private

existing maintenance cri-' sector.

teris based on the results

-,,' of fracture mechinics, etc.

-I

-I

01M

CODE: (O): Vain responsibility on

:- Supported by .

I . I

FIGURE 7.1. Research and Development Areas for Life Extension
-4

oCb

Subject of Example of lorking Organizations

Research and Subject

Category No. Development Contents Equipment Governmental Utilities Suppliers Joint lork Others Remarks

2. Degradation 2. Establishment of To establish technologies PPV, PCV,

Diagnosis and technologies for for detecting and quantiLife Prediction monitoring criti- fying degradations of (O)

(continued) cal equipment equipment critical to life

extension, taking into account such characteristics _ -

as irradiation and operat- _ - -

ing conditions of a nuclear

power plant. If necessary, (0) --

to make experiments for

demonstration.

3. Establishment of To identify degradation Building, (construction)

method of evalu- mechanism and degradation RPV

ating the sound- diagnosis methods (destruc- pedestal, (0) ness of concrete tion) of concrete structure turbine t

structure and to establish degrada- frane,

tion diagnosis methods, etc.

verification methods of

soundness and life prediction methods.

4. Establishment of To establish system capable General (9) (s)Related to

plant information of conveniently and readily 0 (0) improvement

retrieval system approaching plant informa- of nuclear

tion to be accumulated as power inthe life of plant is ex- formation

tended and to rationalize

jobs for checking, maintenance and management.

FIGURE 7.1 (continued)
-IJ

Subject of Example of Working Organizations

Research and Subject

Category No. Development Contents Equipment Governuental Utilities Suppliers Joint Work Others Remarks

2. Degradation- - 5.- Evaluation by.----- To give fatigue evaluation PRY -RIM,-.()

Diagnosis and actual operating to design thermal cycle priuary

Life Prediction history of de- (low cycle) currently set pressure

(continued) sign thermal with sose allowance using boundaryo

cycle actual operating history,, pipings,

to'predict remaining life etc.

and to improve a method of ; . w. .- z. * onitoring *ctuil ojersttnt _ - 1 s ~~history. ~

6. Study of method to To establish a method to- RPV, etc. 0- (0) 0 Mthod and

take surveillance take test specimen at the. time of tak-.

test specimen - time of service life ei- Ing: Utilltension according to- - ties Alter- - . Notice o1 and JEAC 21 nt ethod:

and an sIternate method. Suppliers.

~~~~ ; , ; ~~~~~~~~~~~~~~~~~~~~~~~~Notice: ; l Oov-- _ - ; - . - .. - -. ernsent

3. Replacement 1. Development of To develop coison basic General i (0) 0 a Method to reand Repairing basic technologies technologies necessary for pair reactor;

for backfitting replacing and repairing ; Internals in

and repairsent rationaily (when a process water is to be

Is shortened) equipment at studied joint- . 3 , the time of life extension ly by BIR

- in the future. As such utilities

, basic technologies,' the (1983 thru . following ire considered: 1988) -- * . - underwater welding - ; - ~ - *. * prearcing , - -

- * undern ter Inspctloe Inspection

remote operability ,,

FIGURE 7.1 (continued)
Subject of Example of Working Organizations

Research and Subject

Category No. Development Contents Equipment Governmental Utilities Suppliers Joint fork Others Remarks

3. Replacement 2. Exposure reduction To reduce exposure at the

and Repairing time of operation and (0) a

(continued) maintenance against the

increase of dose associated with long term operation of plant, by, for instance, improvement of

eater quality decontamination, shielding, remote

automation, etc.

3. Application of To establish, using mock-up SO, RIN,

technologies for equipment, technologies for large

replacement and checking, repairing and re- diameter (0) a a

repairing high placement of major equip- piping,

dosage major expected to require working etc.

equipment under high dose.

4. Application of To shorten plant shutdown Buried

technologies for time at the time of life pipings,

replacing and re- extension1 by establishing turbine,

pairing plant chnog for rationally etc.

equipment replacing and repairing

(including handling, bringin and removing-out technologies) major equipment

within plant.

FIGURE 7.1 (continued)
Subject of Example of Working Organizations

Research and Subject

Category No. Development Contents Equipment Governmental Utilities Suppliers Joint Work Others Remarks

4. Economics 1. Study of necessity To study necessities of General (a)

of life extension constructing, decommisbased on long-term sioning and life extending

power supply pro- nuclear power plants based

grai on the projected economic

growth, energy demands,

etc.

2. Development of Plant life extension re- General (0) 0 Uaintenanc.

long-tere plant quires well-planned check- of relisbilmaintenance ing, maintenance and re- ity up to lIfe

program placement, taking into extension.

account degradation of

equipment and life cycle

costs. To develop longterm program for the ma intenance of plant for that

purpose.

NOTE: Nanes of specific equipment and technologies wilI be

reviewed by utilities in their joint research activities

in the future.

-4

'.0

I G U R 7 . ( _ o t i n u e .d )

.IUR-7 (conti nued )
8.0 KEY FINDINGS

Safe' and reliable'powerplant operation depends on a mainternance.program'that

incorporates-well-planned-maintenance, assessment activities', and corrective

action. The'iss'ue of age-related degradation s'pans every element of a

maintenance program. A safety-related aging incident 'could.be traced to

poorly designed equipment, to-an ill-planned'maintenance schedule,'or-toantiquated maintenance~techniques.. As. industries learn more about aging.

systems, structures, and.components,'their commitment .to an'effective.',;

maintenance program becomes increasingly important.. 'Most important at this

stage are methods for indust'ry -to apply aging issues to existing or developing

maintenance programs. Bas'ed on~our-revi'ew'of industrial and governmental

organizations, four'aging-issues are central to a'safe'and effective''-

maintenance program: ,X

* the prioritized selection of critical 'systems'and components

* understanding aging through the collection and analysis of equipment

performance information

* mitigating aging with maintenance

* the use of feedback to improve the aging management program.

First, maintenance activities for systems and components must be prioritized.

Section 3.0 discussed the importance of prioritizing systems and components

according to safety significance. It also presented methods by which to

determine safety significance. Several design concepts, when applied to

systems and components, make such systems less safety-significant and thus

reduce maintenance requirements. The fail-safe concept assumes that the

failure of any single component will not cause a catastrophic failure of the

equipment. Safe-life refers to the replacement of a part in accordance with

its expected life, regardless of condition. Damage tolerance assumes that a

damaged structure will continue to operate safely until the damage is

detected.

Determining initial maintenance requirements is not enough to ensure proper

maintenance. An effective maintenance program must conduct activities to

collect and analyze equipment performance data. Such analyses allow one to

better understand the effects of aging degradation on equipment. This

information can be used to alter maintenance activities, upgrade schedules, or

replace equipment. Section 4.0 discusses several examples of analysis

activities. For example, the Japanese nuclear industry has implemented the

Plant Life Extension Program to test critical equipment for age-related

degradation.

Once maintenance requirements are determined, it is also important to select

and perform the appropriate types of maintenance activities. Section 5.0

discusses three maintenance processes that are particularly applicable to

aging. On-condition monitoring is a scheduled inspection to determine

. 8-1
condition. This test is designed to detect potential failures caused by aging

degradation. Hard-time restoration places an age limit on each part after

which it is replaced, regardless of condition. Age limits are determined

through equipment performance analysis programs such as those described in

section 4.0. Condition monitoring is used only for redundant systems and

components. In this case, the equipment is allowed to operate until a failure

occurs, since this failure will not affect system safety.

Finally, an effective maintenance program must include a system of feedback

and corrective actions. Such a system helps to ensure that maintenance

programs incorporate the most current information on aging and other safety

issues. These systems vary among industries. The aviation industry, for

example, has recently created an Airworthiness Assurance Task Force which

studies aging-related safety incidents and recommends corrective actions to

airline maintenance programs. Section 6.0 provides initiatives from other

industries that have also worked to improve maintenance programs.

8-2
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DeMeis, R. 1989. Aging aircraft. Aerospace America, July, pp. 38-42.

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