NUREG/CR-4302

ORNL-6193

Vol. 2

- Aging- a:rd Service Wear of i

I

Check Valves Used---in Engineered

Safety-Feature Systems of

-Nuclear Power Plants

i.

I

Aging Assessments and Monitoring

Method Evaluations

Prepared by

Prepared by '

H. D. Haynes

Oak Ridge National Laboratory

Prepared for

U.S. Nuclear Regulatory Commission

I
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7

. - . 7.1.
NUREG/CR-4302

ORNL 6193

Vol. 2

RV

Aging and Service Wear of

Check Valves Used in Engineered

Safety-Feature Systems of

Nuclear Power Plants

Aging Assessments and Monitoring

Method Evaluations

Manuscript Completed: September 1990

Date Published: April 1991

Prepared by

H. D. Haynes

Oak Ridge National Laboratory

Operated by Martin Marietta Energy Systems, Inc.

Oak Ridge National Laboratory

Oak Ridge, TN 37831-6285

Prepared for

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

NRC FIN B0828

Under Contract No. DE-ACO5-84OR21400
ABSTRACT

Check valves are used extensively in nuclear power plant safety systems and

balance-of-plant systems. The failures of these valves have resulted in significant

maintenance efforts and, on occasion,haveresulted in water hammer, overpressurization of

low-pressure systems, and damage to flow system components. These failures have largely

been attributed to severe degradation of internal parts (e.g., hinge pins, hinge arms, discs,

and disc nut pins) resulting from instability (flutter) of check valve discs under normal plant

operating conditions. Present surveillance requirements for nuclear power plant check

valves have been inadequate for timely detection and trending of such degradation because

neither the flutter nor the resulting wear can be detected prior to failure. Consequently,

the U.S. Nuclear Regulatory Commission has had a continuing strong interest in resolving

check valve problems.

In support of the Nuclear Plant Aging Research Program, Oak Ridge Nationpi

Laboratory has carried out an evaluation of several developmental and/or commercially

available check valve diagnostic monitoring methods, in particular, those based on

measurements of acoustic emission, ultrasonics, and magnetic flux. In each case, the

evaluations have been focused on the capability of each method to provide diagnostic

information useful in determining check valve aging and service wear effects (degradation),

check valve failures, and undesirable operating modes.

A description of each monitoring method is provided in this report, including

examples of test data acquired under controlled laboratory conditions. In some cases, field

test data acquired in situ are also presented. The methods are compared, and suggested

areas in need of further development are identified.

iii
CONTENTS

LIST OF FIGURES ................. vii

LIST OF TABLES ................. xi

ACKNOWLEDGMENTS ................. 'axiii

SUMMARY ...................... xv

1. INTRODUCTION .... ... 1....

1.1 NUCLEAR PLANT AGING RESEARCH GOALS .............. 1

1.2 NPAR PROGRAM STRATEGY ..... ................ 1

13 NRC INTEREST IN CHECK VALVES ..... .............. 2

1.3.1 Check Valve Function and Types ..................... 4

1.3.2 Selected NRC Notices and Bulletins ................... 5

1.3.3 INPO SOER 86-03 ............................... 6

1.3.4 Generic Letter 89-04 ........... .................... 6

1.3.5 EPRI Application Guidelines ........................ 7

1.4 PHASE I REPORT SUMMARY ........................... 7

1.4.1 General Information .............................. 7

1.4.2 Check Valve Failure Modes and Sites of Degradation ....... 8

1.4.3 Surveillance Requirements and Measurable Parameters ...... 8

1.4.4 Conclusions and Recommendations .................... 9

2. EVALUATION OF CHECK VALVE MONITORING METHODS ........ 11

2.1 GENERAL INFORMATION ............................. 11

2.2 ACOUSTIC EMISSION MONITORING ....................

2.2.1 Basic Principles ...............................

2.2.2 Detection of Valve Disc Movement .................

2.2.3 Qualitative Leak Detection .......................

2.3 ULTRASONIC INSPECTION ...........................

2.3.1 Basic Principles ...............................

2.3.2 Detection of Valve Disc Movement .................

2.4 MAGNE-TlC FLUX MONITORING .......................

2.4.1 Basic Principles ...............................

2.4.2 Detection of Valve Disc Movement ..................

2.4.3 Detection of Worn Hinge Pins .....................

2.5 COMPARISON OF ACOUSTIC, ULTRASONIC, AND MAGNETIC

METHODS ......................................

2.6 OTHER METHODS ..................................

2.6.1 Radiography. .................................

2.6.2 Pressure Noise Monitoring ........................

2.7 CONCLUSIONS-BENEFITS AND WEAKNESSES OF

MONITORING METHODS ..........................

11

11

11

16

17

17

17

19

19

19

21

23

28

28

28

31

v
3. DESCRIPTION OF SELECTED COMMERCIALLY AVAILABLE

CHECK VALVE DIAGNOSTIC SYSTEMS .......... ............ 33

3.1 CHECKMATED II (HENZE-MOVATS, INC.) .... ............ 33

3.2 QUICKCHECKm (LIBERTY TECHNOLOGY CENTER, INC.) .... 33

33 VIP (CANUS CORPORATION) .......................... 35

3.4 AVLD (LEAK DETECTION SERVICES, INC.) .... ........... 36

3.5 MINAC-6 (SCHONBERG RADIATION CORPORATION) ....... 37

3.6 PHYSICAL ACOUSTICS CORPORATION .... .............. 37

4. NUCLEAR INDUSTRY CHECK VALVE GROUP TEST

OF CHECK VALVE DIAGNOSTIC SYSTEMS .... ............... 39

4.1 GENERAL INFORMATION ............................. 39

4.2 SELECTED TEST RESULTS ............................ 39

5. SUMMARY AND RECOMMENDATIONS ........................ 51

REFERENCES . .............................................. 53

Appendix A.- REGULATORY TEST REQUIREMENTS AND CURRENT TEST

METHODS ....................................... 55

vi
LIST OF FIGURES

Figure Page

1.1 NPAR approach . ...................................... 1

1.2 Close-up of the hinge mechanism of a 10-in. swing check valve

that failed to close. 3

1.3 Additional lateral disc movement observed on the same failed

check valve whose severely worn. hinge mechanism

is shown in Fig. 1.2 ..................................... 3

1.4 Typical swing check valve ................................. 4

2.1 Acoustic signal vs time for a 10-in. check valve tested

by Duke Power Company in March 1984 .12

2.2 Acoustic emission equipment (schematic representation) used

by Duke Power Company in 1987 flow loop tests .13

2.3 Acoustic waveform for a check valve during unstable (tapping)

and stable (flow noise only) operations ....................... 14

2.4 Time-of-arrival technique ................................. 14

2.5 Check valve closures with new and artificially worn

hinge pins . ........................................... 15

2.6 Check valve closures with two artificial degradations .......... I .... 16

2.7 Ultrasonic signatures during stable and unstable check valve

operations .18

2.8 Comparison of an ultrasonic signature with that from an RVDT

installed on the hinge pin of a check valve .......... ..... 18

2.9 Magnetic flux signature analysis (MFSA) principle

of operation .20

2.10 Comparison of magnetic field strength and disc angular

position measurements ................................. 21

2.11 Check valve flow loop (photo) .............................. 22

vii
Figure Page

2.12 Check valve flow loop (schematic) .......................... 23

2.13 Use of MFSA to detect disc instability (flutter) ................. 24

2.14 Detecting worn hinge pins using MFSA ....................... 24

2.15 Magnetic flux time waveforms of a 3-in. swing check valve

for three hinge pin conditions: normal (top trace), medium

worn (middle trace), and severely worn (bottom trace).

All signatures were acquired using identical internal

magnet and external gaussmeter locations .25

2.16 Magnetic flux and acoustic signatures for a check valve

under several simulated operational conditions .................. 27

2.17 Pressure probe specifications and points of installation .... ........ 29

2.18 Effect of flow rate on pressure noise spectra ................... 29

2.19 Effect of flow path on pressure noise spectra ................... 30

3.1 A simplified depiction of the CHECKMATETTM II system .... ....... 34

3.2 CHECKMATED and acoustic signatures for a check valve

undergoing backstop tapping .34

3.3 CHECKMATE" and acoustic signatures for a check valve

undergoing seat tapping .................................. 35

3.4 Simplified depiction of the QUICKCHECKTh system .... ......... 36

4.1 QUICKCHECK7' signals for a 12-in. tilting-disc check

valve in "new" condition .41

4.2 QUICKCHECKJ@ signals for a 12-in. tilting-disc check

valve with 30% hinge pin diameter reduction .42

4.3 QUICKCHECK1h signals for a 12-in. tilting-disc check

valve in "new' condition-expanded scale to show

seating transient .43

4.4 QUICKCHECKam signals for a 12-in. tilting-disc check

valve with 30% hinge pin diameter reduction-expanded

scale to show seating transient .44

viii
Figurc Page

4.5 VIP (CANUS Corporation) accelerometer traces from

test 410 (24-in. tilting-disc check valve, full-flow

conditions, induced flow turbulence, worn hinge pin) .... .......... 45

4.6 VIP (CANUS Corporation) accelerometer traces from

test 420 (24-in. tilting-disc check valve, full-flow

conditions, minimal flow turbulence, worn hinge pin) .... ......... 46

4.7 Two ultrasonic signatures, obtained using the CHECKMATEh II

system for the same valve (10-in. Velan swing check) under

different flow conditions: 2251 gal/min (top trace)

and 1295 gal/min (bottom trace) ............................ 47

4.8 A CHECKMATE' II signature for a 12-in. Val-Matic tilting-disc

check valve from the full-open to full-closed positions .... ......... 48

4.9 CHECKMATEV II signature for a 12-in. Val-Matic tilting-disc

check valve having a stuck disc. The top trace was obtained

at no-flow conditions, while the bottom trace was obtained at

2392 gal/min (more than would be sufficient to move the disc) .... ... 49

ix
LIST OF TABLES

Table Page

1.1 Titles of selected NRC/XE Information Notices ..... ............. 5

1.2 Titles of selected NRCAE Bulletins ....... .................. 6

13 Check valve sites susceptible to aging-related degradation .... ...... 8

2.1 Selected diagnostic capabilities and limitations of three

check valve monitoring methods .26

4.1 Check valves tested during the NIC monitoring method

evaluation tests ................................... 40

4.2 Check valve degradations used in the NIC tests ...... ........... 40

4.3 Flow conditions and valve operational modes used in the NIC tests ... 41

)d
ACKNOWLEDGMENTS

The check valve Phase II studies could have been carried out only with the help

of many people, whom the author wishes to acknowledge.

Appreciation is expressed for the advice and guidance provided during this study

by D. M. Eissenberg and W. S. Farmer. The author also wishes to thank D. A. Casada for

his many contributions, including the preparation of a summary of check valve regulatory

test requirements that is included verbatim in this report (Appendix A).

The help provided in the experimental portion of this study by E. L. Biddle, Sr.,

D. E. Hendrix, and B. K Stewart is greatly appreciated.

Much information was obtained from diagnostic system vendors in the form of

product literature and visits to their facilities. In addition, much was learned from

witnessing one day of check valve tests at the Utah Water Research Laboratory. In that

regard, the author would like to thank the following people for their assistance: W. M.

Suslick (Duke Power Company), D. M. Ciesielski and J. N. Nadeau (Henze-Movats, Inc.),

P. Pomaranski (CANUS Corporation), D. Manin (Liberty Technology Center, Inc.), J. W.

McElroy (Philadelphia Electric Company), and M. T. Robinson (Chairman-Nuclear

Industry Check Valve Group).

The assistance of Jeanie Shover and Janice Asher in preparing this report is

gratefully acknowledged.

xiii
SUMMARY

In support of the U.S. Nuclear Regulatory Commission's Nuclear Plant Aging

Research Program, Oak Ridge National Laboratory (ORNL) carried out an evaluation of

several developmental and/or commercially available check valve diagnostic monitoring

methods. Assessments were made of the capability of each method to provide diagnostic

information useful in determining check valve aging and service wear effects (degradation),

check valve failures, and undesirable operating modes. These methods included

* Acoustic emission monitoring.

* Ultrasonic inspection.

* Magnetic flux signature analysis.

* Radiography.

* Pressure noise signature analysis.

The evaluations have been focused on the capability of each method to provide

diagnostic information useful in determining check valve aging and service wear effects

(degradation), check valve failures, and undesirable operating modes. Commercial suppliers

of three check valve monitoring systems recently participated in a comprehensive series of

tests designed to evaluate the capability of each monitoring technology to detect the

position, motion, and wear of check valve internals (e.g., disc, hinge arm, etc.) and valve

seat leakage. These tests, directed by the Nuclear Industry Check Valve Group and carried

out at the Utah Water Research Laboratory, are described in this report.

Of those methods examined by ORNL, acoustic emission monitoring, ultrasonic

inspection, and magnetic flux signature analysis provided the greatest level of diagnostic

information. These three methods were shown to be useful in determining check valve

condition (e.g., disc position, disc motion, and seat leakage), although none of the methods

was, by itself, successful in monitoring all three condition indicators. However, the

combination of acoustic emission with either ultrasonic or magnetic flux monitoring yields

a monitoring system that succeeds in providing the sensitivity to detect all major check valve

operating conditions. When monitoring check valves using either of these combinations,

it is not necessary to apply both methods simultaneously in order to achieve the combined

capabilities of the two methods. Commercial versions of all three methods are still under

development, and all should improve as a result of further testing and evaluation.

xv
1. INTRODUCTION

1.1 NUCLEAR PLANT AGING RESEARCH GOALS

This document describes work performed in support of the U.S. Nuclear Regulatory

Commission's (NRC's) Nuclear Plant Aging Research (NPAR) Program, which was

established primarily as a means to resolve technical safety issues related to the aging of

electrical and mechanical components, safety systems, support systems, and civil structures

used in commercial nuclear power plants.! A comprehensive Phase II aging assessment on

check valves was performed by Oak Ridge National Laboratory (ORNL), the results of

which are' presented in this report.

The goals of the NPAR Program are as follows:

1. To identify and characterize aging effects that, if unchecked, could cause degradation

of components, systems, and civil structures and thereby impair plant safety.

2. To identify methods of inspection, surveillance, and monitoring and of evaluating the

residual life of components, systems, and civil structures that will ensure timely detection

of significant aging effects before loss of safety function.

3. To evaluate the effectiveness of storage, maintenance, repair, and replacement practices

in mitigating the rate and extent of degradation caused by aging.

1.2 NPAR PROGRAM STRATEGY

The methodology employed by the NPAR Program is basically a two-phase

approach, as illustrated by Fig. 1.1. This strategy is applicable for all components, systems,

and structures selected for aging assessments. Research efforts are conducted in accordance

with the objectives associated with each phase.

ORNL-WSC-4060 ETD

Phase I

* Operating Experience Phase It Recommendations for

Select Review and Analysis * VerifIcation of Improved * Evaluation of

Systems C Review of Methods IS&MM* 'Mothballed" Equipment

and and Technology for 0. Tests of Naturally Aged * Modifcation of Codes.

Components IS&MM Components: aendt

for * Screening Type Components. Models, end StendLRds. nd Guides

Assessment Examinalion and Tests - Samples with Simulated * Licn Generic

* Interim Recommendations Degradation

for Engineering Tastse Cost/lenefl tStudy

In Phase ii

*IS&MM - Inspection. surveillance, end monitoring methods

Fig. 1.1. NPAR approach.

l
2

The objectives for an NPAR Phase I aging assessment of a component, system, or

structure are as follows:

1. Identify and characterize aging and wear effects.

2. Identify failure modes and causes attributable to aging.

3. Identify measurable performance parameters, including functional indicators.

Phase I studies result in a determination of whether additional research is needed;

if so, recommendations are developed to identify and guide further studies.

An NPAR Phase II assessment is carried out with the following objectives:

1. Perform in-depth engineering studies and aging assessments based on in situ

measurements.

2. Identify improved methods for inspection, surveillance, and monitoring or for evaluating

residual life.

3. Perform postservice examinations and tests of naturally aged/degraded components.

4. Make recommendations for utilizing research results in the regulatory process.

The results of a Phase II aging assessment are intended to form the basis for

implementing improved inspection, surveillance, maintenance, and monitoring methods;

modifying present codes and standards; developing guidelines and review procedures for

plant life extension; and resolving generic safety issues.

13 NRC INTEREST IN CHECK VALVES

Check valves are used extensively in nuclear plant safety systems and

balance-of-plant (BOP) systems. The failures of these valves have resulted in significant

maintenance efforts and, on occasion, have resulted in water hammer, overpressurization

of low-pressure systems, and damage to flow system components. These failures have

largely been attributed to severe degradation of internal parts (e.g., hinge pins, hinge arms,

discs, and disc nut pins) resulting from instability (flutter) of check valve discs under normal

plant operating conditions. For example, a post-service examination was carried out on a

10-in. swing check valve from a local installation following its failure to close in service.

The cause of failure was determined to be extreme wear in the hinge mechanism, which

permitted the disc to hang up on the valve body before seating occurred. Although service

conditions are not, known, the wear appears to have been a result of disc instability

(oscillation) during service. A close-up of the hinge mechanism for this valve, which shows

the severe wear observed and its effect on disc position, is shown in Figs. 1.2 and 1.3,

respectively. Check valve instability may be a result of misapplication (using oversized

valves) and may be exacerbated by low-flow conditions and/or upstream flow disturbances.2

Present surveillance requirements for nuclear power plant check valves have been

inadequate for timely detection and trending of such degradation because neither the flutter

nor the resulting wear can be detected prior to failure. Consequently, the NRC has had

a continuing strong interest in resolving check valve problems.
I

3

ORNL PHOTO 7382-90

I_ ,I

- i

I

Fig. 12 CQosc-up of the hinge mechanism of a 10-in. swing check valve that failed

to close.

ORNL PHOTO 7998-86 , .. _~~~~~~-

Fig. 1.3. Additional lateral disc movement observed on the same failed check valve

whose severely worn hinge mechanism is shown in Fig. 1.
4

13.1 Check Valve Function and Types

The function of a check valve is simply to open and thus permit flow in only one

direction. When the flow stops or reverses direction, the check valve closes. Check valves

are self-actuating; that is, they require no external mechanical or electrical signal to either

open or close. As a result, most check valves are not capable of being actuated other than

by changing the flow through the valve. Several types of check valves are commonly used,

such as the swing check, piston-lift, ball, stop-check, and duo-check designs. The

descriptions of check valve monitoring methods in this report refer in most cases to their

use on the swing check valve, shown in Fig. 1.4. However, all monitoring methods

described herein have the potential for being applied to other check valve types. A more

comprehensive description of check valve types appears in Ref 3.

ORNL-DWG 884895A ETD

Fg. 1.4. Typical swing check valve.
5

13.2 Selected NRC Notices and Bulletins

Tables 1.1 and 1.2 contain the titles of selected NRC Inspection and Enforcement

(IE) Notices and Bulletins over the last 10 years; these notices and bulletii's are indicative

of the types of check valve problems that have occurred during this period and of the

continued interest that the NRC has had in identifying and solving these problems.

Table 1.1. Titles of selected NRC/HE Information Notices?

Number Title

90-03 Malfunction of Borg-Warner Bolted Bonnet Check Valves Caused by

Failure of the Swing Arm

89-62 Malfunction of Borg-Warner Pressure Seal Bonnet Check Valves Caused

by Vertical Misalignment of Disc

88-85 Broken Retaining Block Studs on Anchor Darling Check Valves

88-70 Check Valve In-Service Testing Program

86-06 Failure of Check and Stop Check Valves Subjected to Low-Flow

Conditions

86-01 Failure of Main Feedwater Check Valves Causes Loss of Feedwater

System Integrity and Water Hammer Damage

84-12 Failure of Soft Seat Valve Seals

84-06 Steam Binding of Auxiliary Feedwater Pumps

83-54 Common Mode Failure of Main Steam Isolation Nonreturn Check Valves

83-06 Nonidentical Replacement Parts

82-35 Failure of Three Check Valves on High-Pressure Injection Lines to Pass

Flow

82-26 Reactor Core Isolation Cooling and High-Pressure Coolant Injection

Turbine Exhaust Check Valve Failures

82-20 Check Valve Problems

82-08 Check Valve Failures on Diesel Generator Engine Cooling System

81-35 Check Valve Failures

81-30 Velan Swing Check Valves

80-41 Failure of Swing Check Valve in the Decay Heat Removal System at

Davis-Besse Unit No. 1 -

aThese information notices are available in the NRC Public Document Room.
6

Table 12. Titles of selected NRCAIE Bulletinsa

Number Title

89-02 Stress corrosion cracking of high-hardness type 410 stainless steel internal

preloaded bolting in Anchor Darling Model S35OW swing check valves or

valves of similar design

85-01 Steam binding of auxiliary feedwater pumps

83-03 Check valve failures in raw water cooling systems of diesel generators

80-01 Operability of automatic depressurization system (ADS) valve pneumatic

supply

aThese bulletins are available in the NRC Public Document Room.

In particular, IE information Notice 86-01 describes an event that occurred at San

Onofre, Unit 1, on November 21, 1985. The most significant aspect of the event was the

failure of five safety-related feedwater system check valves (three main feedwater regulator

check valves and two feedwater pump discharge check valves). The failure of these valves

was the primary cause of a severe water hammer that extensively damaged a portion of

the feedwater system. The details of this event have been described in NUREG-1 190, Loss

of Power and Water Hammer Event at San Onofre, Unit 1, on November 21, 1985.4 This

report presents the findings and conclusions of an NRC Incident Investigation Team sent

to San Onofre by the NRC Executive Director for Operations.

133 INPO SOER 86-03

In 1986, the Institute of Nuclear Power Operations (INPO) issued a significant

operating experience report (SOER), numbered 86-03, which recognized the check valve

problems facing the nuclear industry and recommended that nuclear power plants establish

a preventive maintenance program to ensure check valve reliability. INPO further

recommended that the maintenance program should include periodic testing, surveillance

monitoring, and/or disassembly and inspection.

13.4 Generic Letter 89-04

In April 1989, the NRC issued Generic Letter (GL) 89-04 (Ref. 5) in recognition

of the differences among utilities in the scope of valves included in in-service test (IST)

programs and concerns about methods of fulfilling the requirements of 10 CFR 50.55a(g),

which requires that certain pumps and valves be tested to assess their operational readiness

in accordance with the Sect. XI requirements of the American Society of Mechanical

Engineers (ASME) Boiler and Pressure Vessel Code. GL 89-04 describes potential generic

deficiencies associated with full-flow testing and back-flow testing of valves and an

alternative to full-flow testing (disassembly and inspection). It should be noted that GL

89-04 addresses other aspects of IST programs as well.

At present, the nuclear industry, led by the Nuclear Industry Check Valve Group

(NIC), is preparing guidelines for exemptions to GL 89-04, including methodologies for
7

extending the disassembly and inspection interval defined by GL 89-04 and guidelines for

alternatives to full-flow and back-flow testing of check valves.

135 EPRI Application Guidelines

In January 1988, EPRI issued a set of guidelines for the selection, installation, and

maintenance of check valves in nuclear power plants.2 The stated major objective of this

document is to provide accurate technical information to be used by utilities in assessing

the long-term reliability of their check valve installations and to assist them in responding

to the SOER 86-03. It is noted that this information can also be used in selecting check

valves for new systems and for plant modifications. The document contains considerable

technical information and includes descriptions of several monitoring methods that were

available at the time the guidelines were prepared. The monitoring methods that are

described are as follows:

* Noise/Vibration Monitoring.

* Acoustic Emission Monitoring.

* Ultrasonic Methods.

* Radiography.

* Fiber Optics.

An evaluation of four of these monitoring methods is included in this report. An

assessment of fiber optics inspection methods was not carried out.

1.4 PHASE I REPORT SUMMARY

1.4.1 General Information

ORNL has completed a Phase I aging assessment on check valves.3 Major topics

covered by the study included

1. Check valve design features.

2. Plant operating experiences.

3. Surveillance requirements.

4. Maintenance practices.

5. Failure modes and causes.

6. Parameters to monitor.

Results from this study were based primarily on information from operating

experience records, including the Licensee Event Report (LER) file, the Nuclear Plant

Reliability Data System (NPRDS), and the In-Plant Reliability Data System (IPRDS). In

addition to these data bases, information was gathered from component manufacturers by

reviewing their literature and participating in discussions with their representatives.
8

1.4.2 Check Valve Failure Modes and Sites of Degradation

Five check valve failure modes were identified by the Phase I study:

1.

2.

3.

4.

5.

Failure to open.

Failure to close.

Plugged (limited or no flow through a normally open valve).

Reverse (internal) leakage.

External leakage.

Several check valve sites were identified as being susceptible to aging-related

degradation. These sites and the corresponding aging mechanisms are presented in Table

1.3.

1.43 Surveillance Requirements and Measurable Parameters

Test requirements for nuclear plant check valves were covered briefly in the Phase I

report' and are summarized in this section. A more detailed description of the regulatory

requirements related to check valve testing is presented in Appendix A of this report.

Testing requirements for nuclear plant check valves are contained in the plant

Technical Specifications and are in accordance with Sect. XI of the ASME Boiler and

Table 13. Check valve sites susceptible to agingrelated degradation

Site Aging mechanism

Body assembly Body wear, erosion, corrosion

Fastener loosening, breakage

Internals Hinge pin wear, erosion,

corrosion

Hinge pin fracture

Hinge arm wear, fracture

Disc nut loosening, tightening

Disc nut breakage

Disc wear, erosion, corrosion

Seat wear, erosion, corrosion

Foreign material

Seals Cap gasket deterioration
9

Pressure Vessel Code. Article IWV-3000 of the ASME Code describes in-service inspection

requirements for check valves. This requirement consists primarily of exercising the valve

to verify obturator (e.g., disc) travel to or from the full-open and full-closed positions as

required to fulfill the valve's isolation function. Confirmation of obturator movement may

be by visual observation, a position indicator, observation of relevant pressures in the

system, or other positive means.

Some check valves used for containment isolation are also required to be tested

in accordance with 10 CFR 50, Appendix J. These tests involve pressurizing the check

valve locally in the same direction as when the valve is required to perform its safety

function and comparing leakage rates through the valve with the specified standard.

These tests are intended to demonstrate check valve operability under test conditions

but do not ensure check valve actuation as required under other anticipated operating

conditions. In addition, these tests are inadequate for timely detection and trending of

check valve degradation.

Check valve measurable parameters identified in the Phase I report3 as important

for evaluating operational readiness include force or torque applied to move the obturator;

fluid level, temperature, pressure, pressure differential, and flow rate; reverse leakage rate;

humidity; and noise. Additional parameters identified as being necessary for positive failurecause identification and for enhancement of capabilities for degradation tracking and

incipient failure detection include dimensions, appearance, roughness, cracking, and bolt

torque.

1.4.4 Conclusions and Recommendations

Three major methods that are used for check valve failure-cause identification were

identified in the Phase I report.? These methods are external visual examination, inspection

during normal maintenance, and periodic disassembly and inspection. Potentially useful

measurable parameters for detection of degradation and incipient failure were identified.

The effectiveness and acceptability of these parameters were to be determined by further

study (e.g., the Phase II aging assessment).
11

2. EVALUATION OF CHECK VALVE MONITORING METHODS

2.1 GENERAL INFORMATION

The primary objective of the Phase II check valve aging assessment program is to

identify and recommend methods of inspection, surveillance, and monitoring that would

provide timely detection of check valve degradation and service wear (aging) so that

maintenance or replacement could be performed prior to loss of safety function(s). In that

regard, ORNL has carried out an evaluation of several developmental and/or commercially

available check valve diagnostic monitoring methods, in particular, those based on

measurements of acoustic emission, ultrasonics, and magnetic flux. The evaluations have

been focused on the capability of each method to provide diagnostic information useful in

determining check valve aging and service wear effects (degradation), check valve failures,

and undesirable operating modes.

A description of each monitoring method, including examples of test data acquired

under controlled laboratory conditions, is provided in this report. In some cases, field test

data acquired in situ are also presented. The methods are compared, and suggested areas

in need of further development are identified.

2.2 ACOUSTIC EMISSION MON1TORING

22.1 Basic Principles

Acoustic emissions (pressure waves) can be generated in a variety of ways. Of

particular interest are those generated either when solids contact each other or when liquids

or gases flow through pipes and fittings., Acoustic emissions are detected by sensors, such

as piezoelectric-type accelerometers or microphones, which respond to pressure waves over

a wide range of frequencies. Signal-conditioning electronics can be used to amplify selected

acoustic signals while attenuating others, e.g., unwanted environmental background noise.

Analyses of acoustic emission signals obtained from check valves can be used to monitor

check valve disc position, movement, and mechanical condition, as well as internal

flow/leakage through the valve. Various methods of obtaining and analyzing data are

available. These include filtering, fast Fourier transform (FF1), computer analysis, etc.

22-2 Detection of Valve Disc Movement

Acoustic emission monitoring has been shown to detect check valve disc movement.

As an example, Duke Power Company (DPC) installed an acoustic sensor on top of a 10-in.

cold-leg accumulator discharge check valve.*. A schematic representation of the installation

is given in Fig. 2.1. After initially charging the accumulator to 100 psig, the motor-operated

*W. M. Suslick, DPC, "Proposed Technique for Monitoring Check Valve

Performance," presented at the INPO Check Valve Technical Workshop, October 30-31,

1986.
12

ORNL-DWG 89-5100 ETD

SYSTEM SCHEMATIC

--- COLD LEG ACCUMULATOR C)

CC

Di

MOTOR-OPERATED VALVE BY

r (STROKE TIME -10 SECONDS) IN

v F MONITORED CHECK VALVE

rCLE TEST OF A TEN INCH

)LD LEG ACCUMULATOR

SCHARGE CHECK VALVE

'DUKE POWER COMPANY

MARCH 1984

)M

ACOUSTIC EMISSION SIGNATURE THROTTLING NOISE

TIME 'i I .AC

I (S)

Fig. 2.1. Acoustic signal vs time for a 10-in, check valve tested by Duke Power

Company in March 1984. Source: W. M. Suslick, "Proposed Technique for Monitoring

Check Valve Performance," presented at the INPO Check Valve Technical Workshop,

October 30-31, 1986.

discharge valve was cycled. The acoustic sensor output during this cycling was processed

and displayed on a strip chart recorder. The resulting acoustic signature (Fig. 2.1) shows

that the sensor detected the metal-to-metal contact occurring at the end of both the

opening and closing strokes.

DPC has also carried out check valve acoustic emission testing under controlled

flow loop conditions and with the introduction of various implanted defects that simulated

severe aging and service wear.* Accelerometers were strapped to the bodies of three

check valves in a manner depicted in Fig. 2.2. The following discussion summarizes the

results obtained from those tests.

*W. M. Suslick, H. F. Parker, and B. A. McDermott, DPC, "Acoustic Emission

Monitoring of Check Valve Performance," presented at the EPRI Power Plant Valves

Symposium, October 11-12, 1988, Charlotte, NC.
13

ORNL-DWG 90-3987 ETD

FffC - FFr OSCILLOSCOPE

Qn Q7 -7 CHANNEL TAPE RECORDER

- AUDIO SPEAKER

-PREAMP

- X CHECK VALVE

- ACCELEROMETER

Fig. 2.2 Acoustic emission equipment (schematic reprcsentation) used by Duke

Power Company in 1987 flow loop tests. Source. W. M. Suslick, H. F. Parker, and B. A.

McDermott, "Acoustic Emission Monitoring of Check Valve Performance," presented at the

EPRI Power Plant Valves Symposium, October 11-12, 1988, Charlotte, NC.

Tapping of the valve disc against its backstop was easily detected and distinguished

from background flow noise, as shown in Fig. 2.3. -In addition, by using two (or more)

valve-mounted acoustic sensors, DPC was able to approximately locate the source of the

tapping based on a comparison of the "time of arrival' of the acoustic signals acquired from

the two sensors. An example of this technique is shown in Fig. 2.4.

By using the acoustic emission check valve monitoring method demonstrated by

DPC, it appears likely that the following check valve operational conditions can be

determined:

* Valve rapid opening (backseat impact).

* Valve disc tapping during reduced flow. -

* Hinge arm tapping during reduced flow.

* Valve rapid closing (seat impact).

Although a fully open check valve could be assumed by the existence of flow noise without

the presence of tapping, the absence of detectable tapping noise is itself no guarantee that

the check valve is fully open since the valve disc may be -oscillating without tapping in

midstroke, may have fallen off, or may be stuck in a position that prevents it from

impacting the valve body at any location.

Several tests were carried out by DPC on an 8-in. check valve in new condition

and with simulated degradation. Hinge pin diameters and disc/hinge arm clearances were

both varied during valve cycle tests that generated acoustic emission signatures during

opening and closing.
14

-

-j

z

n

U)

En

8

eORNL-DWG 90-3988 ETD

UNSTABLE OPERATION

= = I __ ISTABLE OPERATION _

. * I I l.T

, -I--- 1__1_ -

TIME

Fig. 2.3. Acoustic waveform for a check valve during unstable (tapping) and stable

(flow noise only) operations. Source: W. M. Suslick, H. F. Parker, and B. A. McDermott,

"Acoustic Emission Monitoring of Check Valve Performance," presented at the EPRI Power

Plant Valves Symposium, October 11-12, 1988, Charlotte, NC.

zC

)cd,-

8

uz S2

-ez

Q

C

-Jc

< 2

< 2

C,

ORNL-DWG 90-3989 ETD

== =E _ =~ II=

_ U~~~I

- -- V 2 t1@-4@40 T T- IIq77

- LME T134 

TAPPING SENSOR RESPONDING

LOCATION TO PRESSURE WAVE FIRST

HINGE PIN

BACKSTOP

THE ONE NEAREST THE HINGE PIN

THE ONE NEAREST THE BACKSTOP

Fig. 2.4. Time-of-arrival technique. Source: W. M. Suslick, H. F. Parker, and B. A.

McDermott, "Acoustic Emission Monitoring of Check Valve Performance," presented at

the EPRI Power Plant Valves Symposium, October 11-12, 1988, Charlotte, NC.
15

Valve closures with new and artificially worn hinge pins are illustrated in Fig. 2.5;

this figure shows that, with the worn hinge pins, an acoustic transient preceded the seat

impact. This transient may result from impact between the hinge pin and hinge arm

surfaces as a result of the increased clearance between these two parts.

A similar transient event occurred as a result of increased clearance between the

disc stud and hinge arm, as illustrated in Fig. 2.6. Also shown is a closure of a check valve

having both a worn hinge pin and a loose disc/hinge arm connection.

In practice, DPC has monitored check valve acoustic emission at three plants for

- 1 year using valve-mounted accelerometers whose outputs are recorded on tape (at the

check valves). Recorded signals are then played back remote from the valve (e.g., in an

office) to both an oscilloscope and a loudspeaker for audio interpretation. Valve instability

is then detected as tapping (clicking) noises heard on the loudspeaker and is quantified by

the oscilloscope.

DPC uses acoustic emission monitoring primarily to identify valves that are operating

in an unstable manner. Those valves are then targeted for close inspection (disassembly)

ORNL-DWG 90-3990 ETD

-j

0

P:

Wn

z

C,)

0

F:

C',

-I

I.-

Cn

NEW

HINGE PIN

0.20-INCH

UNDERSIZED

HINGE PIN

0.40-INCH

UNDERSIZED

HINGE PIN

TIME (20 ms/div)

Fig. 2.5. Check valve closures with new and artificially worn hinge pins. Source:

W. M. Suslick, H. F. Parker, and B. A McDermott, "Acoustic Emission Monitoring of

Check Valve Performance," presented at the EPRI Power Plant Valves Symposium, October

11-12, 1988, Charlotte, NC.
16

ORNL-DWG 90-3991 ETD

ACOUSTIC EMISSION WAVEFORM OF SWING

CHECK VALVE CLOSURE WITH WORN DISC STUD CONNECTION

-J

Z

So

(-

'I,

I I I!,l1je I I = 5if *I1 I

I l lll -tI I I

T I = =

TIME

ACOUSTIC EMISSION WAVEFORM OF SWING CHECK

VALVE CLOSURE WITH WORN HINGE PIN AND DISC ARM CONNECTION

tIic IIII.1 1I11

TnME

Fig. 26. Check valve closures with two artificial degradations. Source: W. M.

Suslick, H. F. Parker, and B. A. McDermott, "Acoustic Emission Monitoring of Check Valve

Performance," presented at the EPRI Power Plant Valves Symposium, October 11-12, 1988,

Charlotte, NC.

at the next convenient time. Roughly 10% of the valves monitored by DPC were

determined to be operating in an unstable mode. After disassembly, roughly 90% of these

valves showed signs of degradation (wear).

223 Qualitative Leak Detection

Acoustic emission techniques have long been used to detect fluid leaking through

a valve. Philadelphia Electric Company (PECO) has been using acoustic techniques to

detect valve leakage in their nuclear power plants since 1974.* Their test procedure

consists of acquiring two sets of valve acoustic emission readings, one while the valve is

unpressurized and one with a pressure difference across the (closed) disc. The noise

associated with a leaking valve is then determined on the basis of the difference in readings.

PECO has had good success with a portable, battery-powered data acquisition unit

for leakage monitoring. The acoustic data collected from baseline (unpressurized) and

pressurized tests are downloaded into a computer for analysis, trending, and archiving.

*J. W. McElroy, PECO, "Light Water Reactor Valve Performance Surveys Utilizing

Acoustic Techniques," presented at the EPRI Power Plant Valves Symposium, August

25-26, 1987, Kansas City, MO.
17

23 ULTRASONIC INSPECTION

2.3.1 Basic Principles

Ultrasonic inspection involves the introduction of high-frequency sound waves into

a part being examined and an analysis of the characteristics of the reflected beam.

Typically, one (pulse-echo) or two (pitch-catch) ultrasonic transducers are used which

provide both transmission and receiving (sensing) capabilities. The ultrasonic signal is

injected from outside the valve by the transmitting transducer and passes through the valve

body, where it is reflected by an internal part (e.g., disc, hinge arm, etc.) back toward the

receiving transducer. (Note: When one transducer is used in a pulse-echo mode, it provides

both transmitting and receiving capabilities.) By knowing the time required for transmission

of the ultrasonic signal from the transmitting transducer and back to the receiving

transducer, the transducer location(s), and other valve geometries, the instantaneous disc

position may be determined.

In general, signal processing circuitry must be used to filter out undesirable

ultrasonic signal reflections present in the raw received signal so that the resultant processed

signal provides a more easily interpreted valve disc position signature. Various methods of

obtaining and analyzing data are available. These include filtering, FFT, computer analysis,

etc.

23.2 Detection of Valve Disc Movement

Ultrasonic inspection techniques can be used to produce a time waveform display

from which disc position and movement may be easily determined. A properly conditioned

ultrasonic signal time waveform can be used to detect the following check valve operational

modes:

Operational Mode Signature Characteristic

Full open or full closed Steady signal

Free flutter Variable signal with rounded peaks

Backstop tapping Similar to free flutter but

with flattened upper* peaks

Seat tapping Similar to free flutter but

with flattened lower* peaks

*Dependent on mounting position of the ultrasonic transducer(s).

Figure 2.7 shows ultrasonic signatures taken from a swing check valve installed in

a laboratory flow loop at two disc positions: full open and partially open. It is noted that

the disc was fluttering (unstable) in the partially open position and that the flutter was

clearly detected using the ultrasonic method. Figure 2.8 illustrates the similarity between

disc motion signatures acquired with an ultrasonic sensor and with a specially installed rotary

variable differential transformer (RVDT) attached directly to the hinge pin to provide a

direct measurement of disc position.
18

ORNL-DWG 89-5103 ETD

0.21

0.00

5 -0.21

-0.41

-0.62 L

CHECKMATE

V2\T6

DISC AT STABLE POSITION

DISC AT lUNSTABLE POSITION

CHECKMATE

* J\ JSVZT5

0.91 r

0.60

B 0.30

0

0.00

-a.: If% . |

Dv I

0.0 0.4 0.8 1.2 1.6 2.0

TIME (s)

2.4 2.8 3.2 3.6 4.0

Fig. 2.7. Ultrasonic signatures during stable and unstable check valve operations.

(Used with the permission of Henze-Movats, Inc.)

ORNL-DWG 90-3999 ETD

0.16 r

o.co

Q)

.0.16

:O

.. I , \~) 1 .,1( \../

CHECKMATE

,A /~ j . (

\J.11 \ ~/ \11

0.3 _-

-0.49 L_

CHECKMATE VS RVDT ON HINGE PIN

0.21 r

ai O.c0

-j

o -0.21

-0.41

RVDT

- N 4 .4 *AJ *tx .j A VZ

"N rw .\y y ,, / rkksd/"N\V ~,

-0.62 _-

0.0

I I I I I I I I I I

0.4 0.8 1.2 1.6 2.0

TIME (s)

2.4 2.8 3.2 3.6 4.0

Fig. 2.8. Comparison of an ultrasonic signature with that from an RVDT installed

on the hinge pin of a check valve. (Used with the permission of Henze-Movats, Inc.)
19

Ultrasonic inspection techniques can be used to detect a missing or stuck disc. For

example, if the disc is missing, no signal will be returned (reflected) from the disc; however,

if the hinge arm remains on the valve, the hinge arm position can be verified by ultrasonic

inspection techniques. Furthermore, under similar flow conditions, a hinge arm without an

attached disc will flutter at higher frequencies than if a disc were attached.*

Disc stud wear can be detected by ultrasonic inspection by monitoring the motion

of both the disc and hinge arm using ultrasonic transducers, one sensing movement of the

disc and the other sensing hinge arm movement. Increased clearance between the disc stud

and the hinge arm can result in increased movement of the disc relative to the hinge arm.

2.4 MAGNETIC FLUX MONITORING

2.4.1 Basic Principles

Research carried out by ORNL as part of the NPAR Phase II study of check valves

has led to the identification of a new check valve diagnostic technique, magnetic flux

signature analysis (MFSA).t MFSA is based on correlating the magnetic field strength

variations monitored on the outside of a check valve with the position of a permanent

magnet placed on a moving part inside the check valve (Fig. 2.9).

In the proof-of-principle tests, a Hall-effect gaussmeter probe was used outside the

check valve to detect the magnitude of the magnetic field produced by a small cylindrical

or rectangular (bar) permanent magnet attached to the hinge arm. The Hall-effect probe

detected both constant and varying magnetic fields and thus continuously monitored both

the instantaneous position and the motion of the check valve disc. Various methods of

obtaining and analyzing data are available. These include filtering, FFT, computer analysis,

etc.

2.4.2 Detection of Valve Disc Movement

MFSA provides the ability to monitor disc position through an entire valve stroke

using one externally mounted sensor. A comparison of disc position measured mechanically

(by'an angular displacement transducer attached to the hinge pin) with that obtained by

MFSA is shown in Fig. 2.10 for a 3-in. swing check valve whose disc was moved manually.

MFSA has been applied to several swing check valves having different body materials and

ranging in size from 2 to 10 in.

MFSA also provides indication of disc flutter. This was demonstrated by' tests

carried out by ORNL on a 2-in. swing check valve that was installed in a water flow loop.

The ORNL check valve flow loop, illustrated photographically in Fig. 2.11 and schematically

in Fig. 2.12, utilized a centrifugal pump that is capable of delivering >300 gal/min through

a 2-in. nominal-diameter line (>30 ft/s).

*R. D. Ryan, CHECKMATE"' Il-A Diagnostic Tool for Check Valves, HenzeMovats, Inc., Technical Resources, May 1990.'

tH. D. Haynes and D. M. Eissenberg, ORNL, "Performance Monitoring of Swing

Check Valves Using Magnetic Flux Signature Analysis," Information Package Containing

Selected MFSA Test Results, May 1989.
20

ORNL-DWG 89-5106 ETD

HALL-EFFECTD

SENSOR

MAGNET7

| I # I~~I

Fig. 2.9. Magnctic flux signature analysis (MFSA) principle of operation.

Flow rate through the tested check valve was controlled by means of three ball

valves located downstream of the check valve and a manually operated gate valve located

in a short, 3-in. nominal-diameter bypass pipe circuit. Low flow rates through the check

valve were achieved by fully opening the bypass gate. If needed, the flow through the

check valve was further throttled by the ball valves. Conversely, higher flow rates through

the check valve were achieved by throttling the gate valve.

The flow loop contains three flowmeters: a 24-gal/min rotameter, a 60-gal/min

rotameter, and a turbine flowmeter. At flow rates less than approximately 20 gal/min

through the check valve (<2 ft/s), the turbine flowmeter does not provide a stable, accurate

measure of flow rate; thus, under these circumstances, the rotameters are relied on for flow

rate measurements. At flow rates exceeding the combined full-scale reading of the

rotameters (24 + 60 = 84 gal/min), the turbine flowmeter provides an accurate means of

monitoring flow rate through the check valve. Bypass flow rate was not measured.

The flow loop also includes a drain and cold water supply, the latter being a tank

located above the ceiling of the room. Under normal flow operations, the loop water

temperature increases because of the energy supplied by the pump. Flow loop water

temperatures were stabilized by adjusting the water supply and drain flow rates so that the

necessary heat removal was achieved.

The acquired magnetic flux signatures (see Fig. 2.13) showed that at a low flow

rate (insufficient to open the valve fully), the disc fluttered considerably in midstroke,

whereas at a higher flow rate, the same valve achieved a fully open and stable condition.
21

ORNL DWG 90-3992 ETD

3-INCH SWING CHECK VALVE -DISC MOVED MANUALLY

z

Q

U,

Z~O

ccw

0

(n

B

aw.

CU,>

dw1

NJ

TIME (s)

I MEASURED MECHANICALLY (ANGULAR DISPLACEMENT TRANSDUCER)

2 GAUSSMETER PROBE INSTALLED ON VALVE CAP

Fig. 2.10.

measurements.

Comparison of magnetic field strength and disc angular position

243 Detection of Worn Hinge Pins

Experiments carried out at ORNL have shown that MFSA techniques can be used

to detect hinge pin wear. Figure 2.14 illustrates a technique for detecting worn hinge pins

that makes use of two Hall-effect gaussmeter probes, mounted so that each probe provides

an independent measurement of instantaneous hinge arm position. When both probes are

mounted on the valve cap at locations equidistant from and perpendicular to the projected

hinge arm travel plane, both gaussmeters should provide identical signatures when the

hinge arm moves in a purely swinging motion as the valve opens and closes.

In addition to swinging, the hinge arm moves in a side-to-side rocking motion as

well, as a result of flow turbulence and the clearances between the hinge pin and hinge

arm. As this clearance increases (e.g., because of hinge pin wear), the propensity to rock

increases. Thus, the increase in hinge arm rocking is detected as increased deviations from

the single line (pure swinging) relationship between the probe output signals, as shown in

Fig. 2.14.
22

ORNL PHOTO 8234-88

~Ii 1i

Fig. 211. Check valve [low loop (photo).

Another technique that appears to be useful for detecting worn hinge pins is based

on an analysis of the magnetic flux time waveform (signature) acquired by a single probe

during a full valve stroke. Figure 2.15 illustrates that, the time waveform changes

appreciably when different hinge pins are installed. This reflects changes in hinge arm

position due to differences in clearance between the hinge arm and hinge pin. During an

opening or closing of the valve, the magnet (which is mounted on the hinge arm) rotates

and translates along a different path that is determined by this clearance.

Figure 2.15 shows that, even when the normal-sized hinge pin was installed, the

magnetic field strength varies with valve position in a nonlinear manner. In fact, when the

valve is near the full-open position, the same magnetic field strength reading is reached at

two distinctly different valve positions. The relationship between the external magnetic field

reading and valve position when the normal-sized hinge pin was installed is different than

that previously discussed (see Figs. 2.10 and 2.13). This relationship was seen to be

approximately linear and without any "humps" in the time waveform that would result in two

valve positions existing for the same magnetic field reading. The differences in these

signatures are simply a result of locating the gaussmeter at a slightly different position.
23

ORNL-DWG 90-3993

WATER SUPPLY

TURBINE

FLOW

METER FLOW

>-

ROTAMETERS BYPASS

GATE

VALVE

24 GPM

BALL

VALVE CHECK VALVE FLOW

TEST SECTION

NEEDLE

VALVE

PUMP

DRAIN

Fig. 2.12. Check valve flow loop (schematic).

During these tests, it was noted that the magnitude of the "hump" could also be

affected by the rate at which the valve opened and closed. For example, the faster the

valve opened, the smaller the hump became even though the full-open signal magnitude

remained the same.

Thus, when using MFSA, the relationship between magnetic field strength readings

and disc position is determined from several factors, including the locations of the internally

installed magnet and the externally attached gaussmeter and the clearance between the

hinge arm and hinge pin.

2.5 COMPARISON OF ACOUSTIC, ULTRASONIC, AND MAGNETIC MELTODS

The preceding three sections of this report have provided descriptions of three

check valve monitoring methods that are useful in determining check valve position, motion,

and leakage. These methods, based on acoustic emission, ultrasonic inspection, and

magnetic flux monitoring, function according to different principles of operation and thus

provide different (and complementary) diagnostic information. The currently estimated

capability of each monitoring method to detect various check valve operational conditions

is given in Table 2.1.

J
24

ORNL-DWG 89.5104 ETD

0.5-- FLUTIER MAGNITUDE

o.4--

< 0 DISC FLUTTERING 0

'O0.2

PUMP STARTED - LOW FLOW RATE

I * (INSUFFICIENT TO OPEN VALVE FULLY)

0

w

0.5.

DISC ON BACKSTOP Ui 0.4-

U0

p0.13

z

(9

< 0.2

0.1

0 _0 PUMP STARTED - HIGH FLOW RATE

0.0 (OPENS VALVE FULLY)

-0.1 I I I

TIME (2 SECONDS/DIVISION)

Fig. 2.13. Usc of MFSA to detcct disc instability (fluttcr).

ORNL-DWG 90-3541 ETD

c

iE 0.40

; 0.30

X GAUSSMETER

Fig. 2.14. Dctccting worn hinge pins using MFSA.
25

ORNL-DWG 90-3394 ETM

Normal Hinge Pin

@2

0

@2

I4)

@2

.2

C..

@2

C#

4)

S.-

C)

@2

ID

4)

4A

S.-

WU

4)

@2

0.40

0.30

0.20

0.10

0.00

-0.10

0.40

0.30

0.20

0.10

0.00

-0.10

0.40

0.30

0.20

0.10

0.00

-0.10

0 10 20 30 40 50 60 70 80 90 100 110. 120

Time (s)

Fig. 2.15. Magnetic flux time waveforms' of a 3-in, swing check valve for three

hinge pin conditions: normal (top trace), medium worn (middle trace), and severely worn

(bottom trace). All signatures were acquired using identical internal magnet and external

gaussmeter locations.
Table 2.1. Sclected diagnostic capabilities and limitations of three check valve monitoring method

Detects Detects Sensitivity Monitors disc

valve Detects fluttering to position throughout Works

internal internal (no ambient the full range with

Method leakage impacts impacts) Nonintrusive conditionsb of disc travel all fluids

Acoustic Yes Yes No Yes Sensitive to No Yes

emission externally

generated

noise/vibration

Ultrasonic No Yes Yes Yes Unknown Not in all No

inspection (indirectly) cases-because of

limited viewing

angle of transducer

MFSA No Yes Yes No-requires Sensitive to Yes Yes

(indirectly) initial nearby

installation of external

permanent magnetic fields

magnet inside (e.g., from

the valve motors)

aRadiography and pressure noise analysis methods are not summarized in this table. This table does not reflect

other attributes such as cost, ease of use, etc. This table reflects the judgment of the author and is based on all

information available at the time this report was prepared.

"Temperature and radiation effects are unknown.

a)

C7%
27

As indicated in Table 2.1, although no single technique has the capability to detect

all check valve operational conditions well, a combination of acoustic emission with either

ultrasonic inspection or MFSA can yield a monitoring system that succeeds in providing

sensitivity to detect all major check valve operating conditions. Both acoustic/ultrasonic and

acoustic/magnetic combinations have been tested.

The combination of acoustic emission and ultrasonic monitoring methods is described

later in this report where commercial systems are discussed. The combination of acoustic

emission and magnetic flux monitoring methods was tested by ORNL on a check valve

whose disc was moved manually to simulate disc'fluttering at different disc positions.

As shown in Fig. 2.16, the acoustic signature did not provide direct indication of

disc'position when the valve's disc was stationary in the fully open and fully closed positions,

nor did it detect the slowly moving disc or disc lutter in midstroke. In all three tapping

modes (seat tapping, backstop tapping, and hinge arm rocking), the acoustic signature

detected the tapping but not its location. The magnetic signature did not unambiguously

detect the tapping but, in conjunction with the'acoustic signature, identified its location.

ORNL-DWG 90-3995 ETD

DISC MOVED MANUALLY

A VALVE OPENED SLOWLY

8 MID-STROKE FLUTTERING

0.8 (HINGE ARM ROTATING

ON HINGE PIN) D E

0.6 C. VALVE CLOSED SLOWLY

D TAPPING ON SEAT

> 0.4 E TAPPING ON BACKSTOP

,J UW F HINGE ARM ROCKING ON I

< 0.2 HINGE PIN I.

~~~~~- 8"fi c II Eo

)>1 0.0

-0.2

-0.6

_ACSTIC SENSOR MOUNTED ON VALVE CAP

-0.8

0.4-

;- TIMEsOPEN

0.3.

CLi W

* . -'., A -.

-~~~~'l 02. 116an11x1n cutc'intrs o hckvleude eea

-J wa

~0.0 CLOSED

-aj10 5 10 Is 20 25 30 35 40

* ~~~~~~~~TIME (s)

Fig.- 2.16. Magnetic flux -and acoustic 'signatures for a check valve under several

simulated operational conditions.
28

2.6 OTHER METHODS

2.6.1 Radiography

The use of conventional and new Thigh-energy" radiographic techniques for

monitoring the condition of check valves is described in Ref. 2. The following is a summary

of the information presented in that reference.

Conventional radiography has been successfully used by several nuclear utilities to

detect certain types of failures and degradation of check valve internals. Examples of swing

check valve failures that were detected with conventional radiography include missing valve

discs, locking devices, and nuts; broken disc studs; discs stuck in full-open position; etc. In

addition, the integrity of discs and guide pins in globe-type stop-check valves has been

verified with this technique. It was pointed out that these cases involved relatively small

(6-in. or smaller) valves and that when applied to larger valve sizes, the interpretation of

the radiographic film becomes more difficult (because of decreased resolution) and thus may

not provide reliable results.

The major drawbacks associated with conventional radiography, identified in Ref. 2,

include

1. Inability to radiographically inspect steel sections in the field that are thicker than

approximately 5 in.

2. Excessive exposure time (and outage time) for field radiography.

3. Inability to acquire good radiography quality in field practice under adverse plant

environmental conditions, particularly those of high temperature and background ionizing

radiation typical of nuclear generating units.

High-energy radiographic equipment has recently been developed which overcomes

the limitations of conventional radiographic techniques, and it has been used by a nuclear

utility to determine the integrity of swing check valve internals. This new technology is

described later in this report where commercial diagnostic systems are discussed.

2.6.2 Pressure Noise Monitoring

Early in the Phase II study, pressure noise (e.g., fluid pressure perturbations) was

identified as a measurable parameter that might be useful in check valve diagnostic

applications. Thus, an evaluation of pressure noise signature analysis was carried out by

ORNL using a 2-in. Stockham swing check valve installed in a cold water flow loop located

in Oak Ridge.

Pressure noise was sensed by two piezoelectric pressure probes, one located

upstream and one located downstream of the check valve. Figure 2.17 illustrates a typical

installation of the two probes and gives a list of selected probe specifications. Throughout

the flow tests, the distance from each probe to the check valve was varied, as well as the

depth of insertion into the flow stream.

Early test results indicated that pressure noise spectral characteristics were noticeably

affected by flow rate. Figure 2.18 illustrates typical noise spectral signatures of both probes

for two flow rates, 20 and 40 gal/min, with both probes located 10 pipe diameters from the

check valve centerline. Among the features seen were relatively sharp frequency peaks

representing pressure perturbations at the pump shaft frequency (motor speed) and at the

pump vane pass frequency.
29

ORNL-DWG 90-3996 ETD

PROBE A CHECK VALVE PROBE B

- I~ I'I I

| k_5D__ 1 10D 1'. 10D

PIEZOELECTRIC PRESSURE PROBES

PCB 102A02

SENSITIVITY 50 MV/PSI

RESOLUTION 0.002 PSI

RESONANCE ,250 KHZ

RISE TIME 2 MICRO SEC

LINEARITY IV

Fig. 2.17. Pressure probe specifications and points o.f installation.

FLOW THRU LARGE ROTAMETER

NB G ODB WTG H A 1.

0,

6

0.

ORNL-DWG 90-3997 ETD

RMS

i PROBE A

)IGP 10D

RMS

GPM PROBE B

-OD

UPSTREAM

0 LIN X HZ 40C

FREQUENCY (HZ)

Fig. 2.1& Effect of flow rate on pressure noise spectra.
30

In addition to these peaks, the pressure noise frequency content of both probe

signals, especially above 200 Hz, varied in amplitude (by up to a factor of 10) as a result

of changes in flow rate. Since the check valve disc position also changed with flow rate,

it seemed likely that certain pressure noise signature features (i.e., those affected by flow

rate) might directly reflect check valve disc position. However, it was soon discovered that

signature reproducibility was not very good because of high sensitivity to many factors,

including

1. Flow path.

2. Water temperature.

3. Tank water level (system pressure).

4. Pressure perturbations induced by pipe vibrations.

5. Air in the system-especially that which collected in the check valve bonnet.

For example, Fig. 2.19 illustrates the effect of flow path on pressure noise spectra. At the

same flow rate (60 gal/min), the pressure noise spectral characteristics changed noticeably

as a result of varying the flow path from (a) through the large rotameter to (b) through

the ball valve.

Pressure noise spectra thus were found to be complex signatures that were greatly

influenced by many system parameters. Consequently, a large effort was made to

understand (and eliminate, if possible) many of these effects. For example, tests were

ORNL-DWG 90-3998 ETD

60 GPM

LOG A NB G 00B WTG H A 1.O V RMS

5 I 01303 1 1 I I

EU _ .__ TI-RU BALL VALVE- 1

tZ DOWNSTREAM

5E--

11-RU BALL VALVEJ

tU

0 LOG B EXPO N 64 9 2.O V RMS

z s

TI- 1RU BALL VALVE - PROBE B

W EU 100

UPSTREAM

SE-3 - e i TH-U ROTAMETER _

00 LIN X HZ 400

FREQUENCY (HZ)

Fig. 2.19. Effect of flow path on pressure noise spectra.
7 l

31

carried out at a constant loop water temperature. Care was taken in establishing

reproducible tank water levels 'and flow paths. Pipe 'vibrations were monitored by

accelerometers, and the spectra were compared with the pressure noise spectra.

In addition, various signal analysis techniques were explored in an attempt to

develop a means of arriving at a diagnostic signature that provided maximum sensitivity to

check valve effects while having minimum sensitivity to other influences. Those techniques

included determining

* the pressure probe signal ratio (PA/PB), where PA is the pressure signal from probe "A"

(downstream from check valve) and PB is the pressure signal from probe "B" (upstream

from check valve);

* the pressure probe signal difference (PA - P8 ); and

* the correlation between pressure probe signals.

These methods, while initially promising, also suffered from nonreproducible results.

In conclusion, pressure noise spectra were complex signatures that were highly

sensitive 'to many system" effects and apparently to other (unidentified) effects as well.

Pressure noise signature analysis thus was judged to be an unattractive monitoring method

for check valve diagnostics and was not considered for further studies, primarily because of

a lack of reproducible results.

2.7 CONCLUSIONS-BENEFrS AND WEABKESSES OFMONITORINGMEITHODS

This chapter has described several check valve monitoring methods and has

identified their strengths and weaknesses. Those methods are acoustic emission, ultrasonic

inspection, magnetic flux monitoring, radiography, and pressure noise monitoring. Of those

methods, the acoustic emission, ultrasonic inspection, and magnetic flux monitoring methods

provide the greatest overall diagnostic capabilities.

Radiography certainly provides unique information in the form of images that can

be very useful in verifying the integrity of check valve internals or in detecting failures or

degradation. Based on information available at the time this report was prepared, its major

drawback is the lack of a high-resolution display that provides quantitative information on

the position of the check valve internals, especially over a short time frame or during a

transient (opening or closing of the valve).

Pressure noise monitoring is intrusive-a transducer must be installed which

penetrates a pressure boundary (e.g., pipe). In addition, pressure noise monitoring was

shown (on a laboratory scale) to be overly sensitive to extraneous inputs (flow rate, flow

path, fluid temperature, pipe vibrations, etc.).

The main limitation of acoustic emission is that the absence of detectable tapping

noise does not by itself guarantee that the check valve is fully open and stable since the

disc may be oscillating in midstroke without tapping, stuck in midstroke, or detached from

the hinge arm and lying still in the bottom of the valve. A minor limitation of this method

is the necessity of using multiple sensors to determine the location of a tapping event.

Ultrasonic inspection, using a single transducer installed at a fixed position, may not

provide valve disc position information over the full travel of the disc because of the limited

viewing angle of the transducer. Furthermore, a low-density fluid, such as steam, may result

in severe attenuation of transmitted and reflected signals and, ultimately, poor transducer

response.
32

It is generally more difficult to apply ultrasonic inspection techniques on stainless

steel valves than on carbon steel valves since ultrasonic signals are attenuated (scattered)

more when passing through stainless steel than when passing through carbon steel. Thickwall stainless steel valves (e.g., 1500-psi service) present the greatest difficulty; however,

additional research needs to be carried out in order to fully explore these limitations.

MFSA requires the installation of a permanent magnet inside the valve; thus, the

method is intrusive. Impacts between the valve disc and valve body may result in time in

a demagnetization of the attached magnet. Furthermore, if the magnet (and/or magnet

assembly) detaches from the check valve, it may present a serious problem. The internal

magnet may attract and hold small metallic particles. The particles can build up and can

affect the magnetic field dispersion pattern, thus possibly changing the strength of the

measured external field. Metallic particles may also accumulate around the internal magnet

in a manner which could affect the operation of the check valve. Finally, the magnet flux

signature features may be difficult to observe under field conditions because of the presence

of nearby ambient magnetic fields.

A check valve methodology that combines acoustic emission monitoring with either

ultrasonic inspection or magnetic flux monitoring provides the following general capabilities:

1. Detecting leakage through a closed valve. (Acoustics)

2. Detecting impacts occurring within the check valve during flow operations. (Any

method)

3. Detecting disc position at all times, whether the valve is experiencing full flow, partial

flow, or no flow. (Ultrasonics or magnetics)

When monitoring check valves using either of these combinations, it is not necessary to

apply both methods simultaneously in order to achieve the combined capabilities of the two

methods. Two check valve diagnostic systems that are based on the combinations described

above are commercially available. These and other commercially available systems are

described in the next chapter of this report.
33

3. DESCRIMPON OF SELECTED COMMERCLALLY AVAILABLE

CHECK VALVE DIAGNOSTIC SYSTEMS

In order to adequately describe the commercially available check valve monitoring

systems, information was requested from several vendors of diagnostic systems, including

those discussed in this chapter. The descriptions provided below are based on the

information provided by the vendors.

3.1 CHECKMATu II (HfNZE-MOVATS, INC)

At present, CHECKMATE7' II is the only commercially available check valve

monitoring system that is based on ultrasonic inspection. The system is available from

Henze-Movats, Inc., of Kennesaw, Georgia. This system represents an upgrade of the

original CHECKMATEV system. According to the vendor, the new system utilizes

improved hardware and software that provide a means of more easily acquiring and

analyzing check valve signatures. Figure 3.1 provides a simplified drawing that illustrates

the basic operation of the CHECKMATE' II system. One ultrasonic transducer is used

(pulse-echo type) which provides both transmission and receiving (sensing) capabilities.*

This system utilizes signal processing circuitry that filters out undesirable ultrasonic

signal reflections present in the raw received signal so that the resultant processed signal

provides a more easily interpreted valve disc position signature. According to HenzeMovats, Inc., since March 1987, approximately 200 valves in 21 power plants have been

tested using CHECKMATET' and CHECKMATEt' II systems.

According to Henze-Movats, Inc., in addition to disc position indication, the

CHECKMATE' II data analysis program can also provide estimates of hinge pin wear

rates and fatigue damage of valve internal parts.

Henze-Movats, Inc., has recently used acoustic emission monitoring with their

ultrasonic inspection system. The result of using the combination of these methods is seen

in Figs. 3.2 and 3.3,t which compare data from the two sensors obtained for a check valve

tapping its backstop and its seat, respectively. In both cases, the acoustic signature detected

the tapping but not its location. The ultrasonic signature did not clearly detect the tapping,

but, in conjunction with the acoustic signature, identified its location.

32 QUICKCHECKu (LIBERTY TECHNOLOGY CENTER, INC.)

Another system that utilizes a combination of monitoring methods is

QUICKCHECK10, a check valve diagnostic system available from Liberty Technology

*Letter from J. N. Nadeau, Henze-Movats, Inc., to H. D. Haynes, ORNL, Subject:

Motor-Operated Valve and Check Valve Systems Information, dated March 1, 1990.

tLetter from D. M. Ciesielski, Henze-Movats, Inc., to H. D. Haynes, ORNL,

Subject: CHECKMATE' System Information, dated July 22, 1989.
34

ORNL-DWG 90-3539 ETD \ULTRASONIC TRANSDUCER

\ W ~ULTRASON11INA COMPUTER-BASED

GENERATOR/ANALYZER SIGNAL ANALYZER

F:g. 31Asmpieddpcc H

% L,

Fig. 3.1. A simplified depiction of the CHECKMA1IV II system.

ORNL-DWG 90.4000 ETD

CHECKIMATE

V2ZT4

-0.71

BACKSTOP TAPPING BACKSTOP TAPPING BACKSTOP TAPPING

14.68

ACOUSTIC

VZT3

0.0 0.4 zo

TIME (s)

2.8 3.6

Fig. 3.2 CHECKMATFV" and acoustic signatures for a check valve undergoing

backstop tapping. (Used with the permission of Henze-Movats, Inc.)
35

ORNL.DWG 90-4001 ETD

0.38

SEAT TAPPING

CHECK MATE

V2ZTS

'PING

ACOUSTIC

V2%T7

12.53

_~ i___

I.-

_J 4.18

0.00

.4.,

0.0 0.4 0.8 1.2 1.6 2.0

TIME (s)

2.4 2.8 3.2 3.6 4.0

Fig. 3.3. CHECKMATED' and acoustic signatures for a check valve undergoing

scat tapping. (Used with the' permission of Henze-Movats, Inc.)

Center, Inc., of Conshohocken, Pennsylvania.* QUICKCHECK"', depicted in simple form

in Fig. 3.4, utilizes a combined acoustic/magnetic dual sensor to monitor simultaneously the

structurally transmitted acoustic noise that results from flow and internal part impacts and

the position and motion of an encapsulated magnet that is permanently installed on a check

valve internal part (e.g., hinge arm, disc, etc.). Data acquisition hardware includes the dual

sensor(s), signal conditioning electronics, and a digital audio tape recorder. Recorded

signals are then processed, displayed, and analyzed with a computer-based system that

provides detailed analysis capabilities for both acoustic and magnetic signals.

3.3 VIP (CANUS CORPORATION)

CANUS Corporation of Laguna Hills, California, has developed a check valve

diagnostic system called Valve Inspection Program (VIP). VIP utilizes accelerometers (from

2 to 12) and associated electronics (charge amplifiers, signal conditioning) to obtain check

valve acoustic emission information that is stored on a digital audio tape recorder for

subsequent manual.and automated analyses.t .,Real-time, .high-resolution displays of the

acoustic waveforms are provided by a digital graphic recorder. In addition, headphones are

used to monitor the signals for qualitative assessments of fow noise, valve tapping, etc.

*Letter' from D. Manin, Liberty Technology Center, to H. D. Haynes, ORNI,

Subject: Motor-Operated Valve, and Check Valve Systems Information, dated March 1,

1990.

tLetter from Peter Pomaranski, CANUS Corporation, to H. D. Haynes, ORNL,

Subject: Valve Inspection Program Information, dated March 1, 1990.
36

ORNL-DWG 90-3540 ETD

DUAL SENSOR

.(ACOUSTICS/MAGNETICS)

Fig. 3.4. Simplified depiction of the QUICKCHECK" system.

According to CANUS, over the last 3 years, they have used this method to test

approximately 150 valves at five plants. Their tests have provided indications of check valve

degradation and check valve operating modes that would lead to degradation.

CANUS is presently developing neural network programs that could provide

automated interpretation of acoustic emission signals.

3.4 AVLD (LEAK DETECTION SERVICES, INC)

Leak Detection Services, Inc., of Annapolis, Maryland, has developed an acoustic

valve leak detector for use aboard U.S. Navy submarines; it has also been used to detect

internal valve leakage at several commercial nuclear and fossil power plants. The device

permits the operator to observe the acoustic emission signals on a meter and to record

them on an x-y plotter. The device provides the capability for acquiring -acoustic signals

from two sensors simultaneously, one sensor mounted on the valve and the other mounted

on the pipe about 10 pipe diameters away from the valve.' The two channel responses are

then adjusted, and the background noise signal (acquired by the pipe-mounted sensor) is

electronically subtracted from the valve-mounted signal. A positive signature is an

indication of valve leakage.
37

35 MINAC-6 (SCHONBERG RADIATION CORPORATION)

The MINAC-6 portable linear accelerator system, available from Schonberg

Radiation Corporation of Santa Clara, California, provides several advantages over

conventional industrial radiography systems.* It is a portable, high-energy (6-MeV,

300-rads/min at 1 m) system that is capable of producing radiographic images through a

12-in. section of steel with a 10-min exposure time and through a 14-in. section in 45 min.

The MINAC system was developed in cooperation with the Electric Power Research

Institute and, since 1981, has been used at approximately 20 nuclear power plants in the

United States for inspection of heavy wall components, including large piping, valves, and

pumps. In particular, the system was used to verify the integrity of internal parts of several

main steam check valves at the Diablo Canyon Power Plant (Unit 2) while the unit was online.

3.6 PHYSICAL ACOUSTICS CORPORATION

Physical Acoustics Corporation (PAC), of Princeton, New Jersey, manufactures

acoustic leak detection instruments as well as provides field test services for leak detection

surveys. PAC has developed a dual-channel acoustic valve leak detector that has been

used by utilities to detect valve leakage for more than 10 years.t The detector uses

acoustic sensors attached to the valve body to determine the acoustic signal levels as well

as frequency content. The output is recorded on an x-y plotter showing signal amplitude

and frequency.

*Product catalogs, "MINAC 1.5, 4/6, Portable Linear Accelerator Systems,"

Schonberg Radiation Corporation, Santa Clara, CA.

tLetter from Sam Ternowchek, Physical Acoustics Corporation, to H. D. Haynes,

ORNL, Subject: PAC Leak Monitors, dated December 14, 1990.
39

4. NUCLEAR INDUSTRY CHECK VALVE GROUP TEST

OF CHECK VALVE DIAGNOSTIC SYSTEMS

4.1 GENERAL INFORMATION

Three commercial suppliers of check valve monitoring equipment recently

participated in a comprehensive series of tests designed to evaluate the capability of each

monitoring technology to detect the position, motion, and wear of check valve internals

(e.g., disc, hinge arm, etc.) and valve seat leakage. Those vendors were Henze-Movats, Inc.

(ultrasonic/acoustic emission); Liberty Technology Center, Inc. (magnetic/acoustic emission);

and CANUS Corporation (acoustic emission). Those tests, which began in late January

1990 and were completed in mid-March 1990, were directed by the Nuclear Industry Check

Valve Group (NIC) and were carried out at the Utah Water Research Laboratory located

on the Utah State University campus.

This chapter presents a brief discussion of these tests, including descriptions of the

check valves used in the tests, the test conditions used, and selected vendor data. It should

be noted that this discussion is based on a limited amount of information that was obtained

primarily from the diagnostic system vendors directly. The results from these tests will be

described in a final report that will be distributed to the NIC utility members that

participated in the funding of the activity. Because of the heavy involvement of vendors

in those tests, a comprehensive review and assessment of the NIC test methodologies,

vendor test data, and NIC conclusions should be carried out by NRC after NIC issues their

final report.

Eleven check valves were used in the tests; Table 4.1 indicates their size,

manufacturer, and type.

These tests were carried out using water as the process fluid. Check valves were

initially tested in "new" condition and then with one or more simulated degradations and/or

operational failures. Several flow conditions (resulting in several check valve operational

modes) were also used. The check valve degradations used in the tests are listed in Table

4.2. Flow conditions and valve operational modes are indicated in Table 4.3.

It is recognized that data analysis and nonintrusive testing technology for check

valves are evolving. After the NIC test results are made available to NRC, the results of

these tests should be reviewed; if necessary, an updated report will be issued.

4.2 SELECTED TEST RESULTS

Figure 4.1 illustrates acoustic and magnetic signatures obtained by the

QUICKCHECK"' system for a 12-in. tilting-disc check valve in 'new" condition.* The

acoustic trace contains a transient (spike) indicative of the impact that occurred when flow

(through the valve) was shut off and the valve closed (seated). The magnetic trace shows

*Letter from D. Manin, Liberty Technology Center, to H. D. Haynes, ORNL,

Subject: Motor-Operated Valve and Check Valve Systems Information, dated March 1,

1990.
40

Table 4.1. Check valves tested during the NIC monitoring method

evaluation tests

Size (in.)

10

12

4

10

10

16

24

24

20

6

6

Manufacturer

Crane

Val-Matic

Velan

Mission

Velan

Rockwell

Val-Matic

Atwood & Morrill

Atwood & Morrill

Powell

Crane

Check valve type

Swing check

Tilting disc

Swing check

Duo-check (split

disc)

Swing check

Tilting disc

Tilting disc

Swing check

Swing check

Swing check

Tilting disc

Body material

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Carbon steel

Stainless steel

Carbon steel

Table 4.1 Check valve degradations

used in the NIC tests

* Induced seat leakage

* 15% and 30% hinge pin diameter reduction

* 15% and 30% disc stud diameter reduction

* Broken spring (for valves having springs)

* Disc stuck open

* Combinations of the above degradations

e Missing disc
41

Table 43. Flow conditions and valve operational

modes used in the NIC tests

0

0

0

0

0

Zero flow

Backstop tapping with and without cavitation

Two mid-stroke flow conditions

Seat tapping

Simulated pump start and trip

Reverse flow

Maximum flow

Minimum flow to open

ORNL-DWG 90-4002 ETD

U)

(Z

C,)

C

-j

z

0

0

0

I -IMPACT WHEN _ Jo~~." VALVE CLOSES

. n~~~~~~~~~~~~~~

d

31 I

I _ .. - ~ ,,> _.. 1 II I I

a6,

75% FLOW, c-

.' .(A NO HINGE

WEAR

z

0

U=

VALVE SEATED

z . LEAVES BIVALVE 

(D - -SEAT

TIME

Fig. 4.1. QUICKCHECKm' signals for a 12-in. tilting-disc check valve in 'new"3

condition. (Used with the permission of Liberty Technology Center, Inc.)
42

direct indication of disc travel in the closing direction prior to the detected impact. The

two signals together thus confirm that the valve closed. When flow was restored through

the valve, the valve opened, as indicated by the magnetic trace. According to Liberty

Technology Center, Inc., the decrease in the magnetic signal magnitude, observed when the

valve initially lifts off its seat, indicates that the valve had been fully seated prior to

opening.

Figure 4.2 shows acoustic and magnetic traces for the same valve, but using a hinge

pin with a 30% reduction in diameter. Changes in features were observed in both signals,

including the absence of a momentary decrease in magnetic signal magnitude as the valve

opened. This, according to Liberty Technology Center, Inc., indicates that the valve's disc

did not fully seat; instead, it hung down past the seat because of the smaller hinge pin. As

the valve opened, acoustic impacts were recorded which were a result of the increased

clearances between the hinge arm and the hinge pin. In addition, when the smaller hinge

pin was used, disc flutter was observed to occur when the valve reached its open position,

as shown by the magnetic trace.

ORNL-DWG 90-4003 ETD

C)I

<

o 0 4 LARGER IMPACT DUE

cD TO 30% HINGE PIN WEAR

,_- __L____-______ C)

a)

C,; A ,l

J [ ~~~~~~LARGER FLUTTER DUE

0

C' _ |___ TO 30% HINGE PIN WEAR

o ~~~~~~~VALVE NEVER SEATS

I- - DISK HANGS DOWN TOO FAR

w

z [/_______ LTHEREFORE, DISK IS NOT

< ABLE TO SEAT

Fig. 4.2. QUICKCHECIC2 signals for a 12-in. tilting-disc check valve with 30%

hinge pin diameter reduction. (Used with the permission of Liberty Technology Center,

Inc.)
43

Figures 4.3 and 4.4 show the differences in the valve seating acoustic signatures that

occurred as a result of the different hinge pin sizes. Figure 4.3 shows that a single acoustic

transient occurred during disc closure when a normal hinge pin was used. Figure 4.4 shows

that, when the smaller hinge pin was installed, multiple impacts (resulting in several acoustic

signal transients) occurred.

These examples further illustrate the complementary information that can be

obtained from using both a disc position (in this case magnetic) monitoring method and an

impact (acoustic emission) monitoring method.

The following two examples also illustrate the benefit of acquiring diagnostic data

simultaneously from multiple sensors of the same type-in this case, accelerometers,

mounted at different locations. CANUS Corporation used several accelerometers installed

on the body of each test valve at several locations, including

* Left and right side of the hinge pin.

* Left and right side of the open stop position (either on the body or the bonnet,

depending on valve type).

* Valve seat.

ORNL-DWG 90-4004 ETD

C.)

* C)_ _ , I

F~~~~~~I I _ ..

CZ

CD,

C:,

, ME' I.1

-.

z

M ~~ ~ ~ ~ TM

Fig. 4.3. QUICKCHECI(" signals for a 12-in. tilting-disc check valve in 'newt

condition-cxpandcd scale to show seating transienL' (Used with the permission of Liberty

Technology Center, Inc.)
44

CD

0)

C

-j

z

0

0

0

'a

0

V)

CD

z

0

z

ORNL-DWG 90-4005 ETD

I

Fig. 4.4. QUICKCIIECK? signals for a 12-in, tilting-disc check valve with 30%

hinge pin diameter reduction-expanded scale to show seating transient (Used with the

permission of Liberty Technology Center, Inc.)

Figure 4.5 shows traces that were obtained from four accelerometers during one test

carried out on a 24-in. tilting-disc check valve.* This test was performed under full-flow

conditions accompanied by induced flow turbulence. As shown in the figure, a hard impact

was detected by the accelerometer mounted on the left side of the hinge pin. A similar

impact was not indicated by the accelerometer mounted on the right side of the hinge pin.

Thus, CANUS' interpretation was that the hinge pin was worn. The hinge pin was, in fact,

degraded 15% during this test, verifying CANUS' prediction.

Figure 4.6 shows traces from the same four accelerometers, mounted on the same

valve, but now operating under full-flow conditions with only a small level of turbulence.

*Peter Pomaranski, CANUS Corporation, "Preliminary Overview of Findings and

Results on Acoustic Emission Nonintrusive Check Valve Testing-Performed at the Utah

Water Research Laboratory, Logan, Utah," presented at the Nuclear Industry Check Valve

Group Spring Meeting, April 24, 1990.
ORNL-DWG 90-4006 ETD

Series No. 7c Test No.410

Trace #2

100% w/Turbulence Expanded @ 10KHZ

Date: 2/27190 Time: DAT 2:07Sampfe: 0.7 sec.

; | i , _ : ! .- ' . .; : i ,| ! . . ! ! * ' !

I ;* . - ! r i STOP i * RIGHT . j ! iOPEN 

.; HINGE , ., . PIN RIGHT I _ .. i . ., S . , i * ; i 

v ! ! . ~~TAP Z..6Ai9

____ _____ ML

;HNGEPINRGHT -T ::z~ -. -___ ,HINGE6PIN RIGHT

- l i, ! I . ! ' I ! ! X tHARD IMPACT ;HINGE PiN LEF .,-

F.g. 45. VIP (CANUS CoNporation) aGeleromeler traces from test 410 (2PNinH

tilting-ic check Vavc, full-flow conditions, induced flo turbulence, worn hingc pin).

Source: Peter Pomaranshi, CANUS Corporation, "Preliminary, Overview of Findings and

Results on Acoustic Emission Nonintrusive Check Valve Testing-Performed at the Utah

Water Research Laboratory, Logan, Utah," presented at the Nuclear Industry Check Valve

Group Spring Meeting, April 24, 1990.
ORNL-DWG904007 ETD

Series No. 7d Test No.420

Tape W2Trace U2

100% w/Small Turbulence Expanded @ 10KHZ

Date: 2/27/90 Time: DAT 8:15:17 Sample: 0.7 sec.

;_i_._!_iii___:_!;_i___i!_Ii_.___j_*_ I - ;!!!i;*j

_______________________ III _=}_____ ; I

--- OPEN STOP RIGHTOPEN STOP LE, I i ? i_? 'N i i LEFI ! _ _ _ _ -, -, - - - !,F ! !;i; ! H I N G E P IN i _ _ _ t _ ! _ ! _

=,.~~~1TiririiT} -r 1,_--~~

1 _

HE PiN LEFTt IHI III " ~ _ HINGE PIN LEFT __ __ _ _ _ _ _ __ _ _ _ _

0o

Fig. 4.6. VIP (CANUS Corporation) accclcrometcr traces from test 420 (24-in.

tilting-disc check valve, full-flow conditions, minimal flow turbulence, wom hingc pin).

Source: Pctcr Pomaranski, CANUS Corporation, "Preliminary Overview of Findings and

Results on Acoustic Emission Nonintrusive Check Valve Testing-Performed at the Utah

Water Research Laboratory, Logan, Utah," presented at the Nuclear Industry Check Valve

Group Spring Meeting, April 24, 1990.
47

The decreased flow turbulence can clearly be seen by comparing the reduced signal noise

level in these traces with the much noisier traces shown in Fig. 4.5. This figure also shows

an impact that was detected by all accelerometers; however, the right-side hinge pin

accelerator detected an erratic ringing pattern rather than the clear ringing pattern indicated

by the left-side hinge pin accelerometer. This feature also led CANUS to predict that the

hinge pin was worn, which, in fact, it was.

Figure 4.7 shows ultrasonic signatures, obtained by the CHECKMATEth II system

during the NIC tests, for the same valve under two different flow conditions. As shown in

the figure, the degree of disc flutter varies with the flow rate, with the largest flutter

occurring at 1295 gal/min. Disc flutter is quantified in both plots as a measure of the disc

angular movement per unit of time (e.g., at 2251 gal/min, the flutter is 2.83 degrees/s,

whereas at 1295 gal/min, the flutter is 3.65 degrees/s. At 2251 gal/min, the

CHECKMATE7' II signal magnitude occasionally reaches its maximum value (of

approximately 14.35 in.), indicating that the valve is tapping its backstop. It is noted that

the restricted movement of the disc (as a result of tapping) results in a lower overall flutter

magnitude. In this case, the ultrasonic transducer was located on the bottom of the valve;

therefore, the largest signal was produced when the disc was at the open position (at the

position furthest from the transducer).

Figure 4.8 illustrates that CHECKMATE7' II can be used to track the motion of

a check valve disc (e.g., in this case, the disc of a 12-in. Val-Matic tilting-disc check valve)

from the full-open to full-closed position. In contrast to Fig. 4.7, the ultrasonic transducer

was located on top of the valve; therefore, the largest signal was produced when the disc

ORNL-DWG 90008 ETD

CHECKMATE Software Signature Plot(s)

14.32- Valve Id

c) \ P \ IGroup Name

c 14.12- MN|254 R 28.4 30 Z KNGE

Trace Name

.U . : ~~~~~~~~2.83 deg/sec .,TW .P o W/7"ruesnm

13.92

0.00 f.17 2.34 3.51 4.68 5.85 7.02 8.19 Secs

12.4a- - .. - . :- -; , . . A ~~Valve Id:

a) Group Name :

c 12.13- F 2 XI HVM

3.65 deg/sec Trace Name :

125. p 3/4 FuLO WrnM echo

11.85.0.00 1.17 2.34 3.51 4.68 5.85 7.02 8.19 Secs

Fig. 4.7. Two ultrasonic signatures, obtained using the CHECKMAT1' II system

for the samc valve (10-in. Vlan swing check) under different flow conditions: 2251 gal/min

(top trace) and 1295 gal/min (bottom trace). (Used with the permission of Henze-Movats,

Inc.)
48

ORNL-DWG90-4009 ETD

CHECKMATE Software Signature Plot(s)

11.309 -

10.803 -

10.300

9.795 -

a,0

U

C

A_.|.. .. . . . . = . ,

FULL CLOSED

-- -I , I .

, :1 ; ' ~~~~~~~~~~~~~~* I \

.-- I FUL OPEN\

Valve Id :

HIC YVAE *2 - W VAL-4TIC

Group Name :

FM 96 BASBINE AUL O1WaE

Trace Name :

WE - MOSE - WM

_-

9.292 .

B.787

8. 284 4

7.778

7.2750 - 0.00 1'. 23 2~.45 3'.68 4'.91 6'.14 7'.36 Secs

Fig. 4.8. A CHECKMATN' H signature for a 12-in. Val-Matic tilting-disc check

valve) from the full-open to full-closed positions. (Used with the permission of HenzeMovats, Inc.)

was at the closed position. It is recognized, however, that a single ultrasonic transducer

(installed at a fixed location) may not provide valve disc position information over the full

travel of the disc of some valves because of valve geometry and the limited viewing angle

of the transducer.

Finally, Fig. 4.9 illustrates that a stuck check valve disc can be detected simply by

comparing the CHECKMATETh II signature obtained at no flow to a CHECKMATEI

II signature obtained at a significant flow rate.
49

ORNL-DWG90-4010 ETD

CHECKMATE Software Signature PlotCs)

7.742 -

On

a)

r 5.161 - U

uI

2.581 -

O0.000 -_

0.00

7.742 -

a)

r 5.161 -

C

I-'

2.581

Valve Id :

VALVE t2 VAL-*ATIC t2 TD.

Group Name :

run 128 stuck open tt hinge

Trace Name :

zero flow stuck open

o gcTfl

1'.23 2.45 3.b8 4.91 6.14 7.36 Secs

; . . . Valve Id:

VALVE 12 VL.-ATIC 12- T.t.

i z ' Group Name

j run 13t stuck cGP" t55 Wlnge

Trace Name

full flow lilneck

* I ' 2392 gpm

0.000 4-

00 1.'23 2'.45 3'.68 4'.91 6'.14 7'.36 Secs

Fig. 4.9. CIECKMATJ"' II signature for a 12-in. Val-Matic tilting-disc check

valve having a stuck disc. The top trace was obtained at no-flow conditions, while the

bottom trace was obtained at 2392 gal/min (more than would be sufficient to move the

disc). (Used with the permission of Henze-Movats, Inc.)
I

51

5. SUMMARY AND RECOMMENDATIONS

The primary objective of the NPAR Program Phase II check valve aging assessment

is to identify and recommend methods of inspection, surveillance, and monitoring that will

provide timely detection of check valve degradation and service wear (aging) so that

maintenance or replacement can be performed prior to loss of safety function(s). In

support of the NPAR Program, ORNL has evaluated several developmental and/or

commercially available check valve diagnostic monitoring methods. In each case, the

evaluations have been focused on the capability of each method to provide diagnostic

information useful in determining check valve aging and service wear effects (degradation),

check valve failures, and undesirable operating modes. Of those methods examined,

acoustic emission monitoring, ultrasonic inspection, and magnetic flux signature analysis

provided the greatest level of diagnostic information. These three methods were shown to

be useful in determining check valve condition (e.g., disc position, disc motion, and seat

leakage), although none of the methods was, by itself, successful in monitoring all three

condition indicators. However, the combination of acoustic emission with either ultrasonic

or magnetic flux monitoring yields a monitoring system that succeeds in providing the

sensitivity to detect all major check valve operating conditions. When monitoring check

valves using either of these combinations, it is not necessary to apply both methods

simultaneously in order to achieve the combined capabilities of the two methods.

Commercial versions of all three methods are still under development, and all should

improve as a result of further testing and evaluation.

The NIC test produced a large volume of useful check valve diagnostic data from

three commercial systems; however, no test data were available (from NIC) for our review

prior to the preparation of this report. Because of the significance of the data obtained

and its impact on determining operational readiness of nuclear plant check valves, it is

recommended that a comprehensive review and assessment of the NIC test

results-including NIC test methodologies, vendor test data, and NIC conclusions-be

carried out by NRC after NIC issues its final report. In addition, any issues not addressed

adequately by the NIC tests and deemed important in regard to safety-related issues should

be considered for further study.
53

REFRENCES

1. U.S. Nuclear Regulatory Commission, Nuclear Plant Aging Research (NPAR) Program

Plan: Components, Systems and Structures, USNRC Report NUREG-1144, Rev. 1,

September 1987. Available for purchase from National Technical Information Service,

Springfield, Virginia 22161.

2. MPR Associates, Inc., and Kalsi Engineering, Inc., Application Guidelines for Check

Valves in Nuclear Power Plants, Electric Power Research Institute, Inc., Report NP-5479,

January 1988. Available for purchase from Research Reports Center (RRC), Box

50490, Palo Alto, California 94303.

3. W. L Greenstreet, G. A. Murphy, R. B. Gallaher, and D. M. Eissenberg, Martin

Marietta Energy Systems, Inc., Oak Ridge Natd. Lab., Aging and Service Wear of Check

Valves Used in Engineered Safety-Feature Systems of Nuclear Power Plants, USNRC

Report NUREG/CR-4302, Vol. 1 (ORNL-6193/V1), December 1985. Available for

purchase from National Technical Information Service, Springfield, Virginia 22161.

4. U.S. Nuclear Regulatory Commission, Loss of Power and Water Hammer Event at San

Onofre, Unit, 1, on November 21, 1985, USNRC Report NUREG-1190, January 1986.

Available from National Technical Information Service, Springfield, Virginia 22161.

5. Letter from Steven A. Varga, NRC, to All Holders of Light Water Reactor Operating

Licenses and Construction Permits, Subject: Guidance on Developing Acceptable

Inservice Testing Programs (Generic Letter No. 89-04), dated April 3, 1989. Available

in NRC Public Document Room for inspection and copying for a fee.

6. J. G. Dimmick and J. M. Cobb, "Ultrasonic Leak Detection Cuts Valve Maintenance

Costs," Power Engineering 9(8), 35 (August 1986). Available in public technical libraries.
55

Appendix A.

REGULATORY TEST REQUIREMESM AND CURRENT TEST METHODS

REGULATORY TEST REQUIREMTM

There are three distinct regulatory requirements related to check valves. These are

the in-service testing (IST) requirements, containment isolation valve leak test requirements,

and reactor coolant pressure boundary isolation valve leak test requirements.

In-Service Testing Requirements

Plant Technical Specifications, which invoke the authority of 10 CFR Part 50.55a,

require that pumps and valves be tested in accordance with Sect. XI of the ASME Code.

The scope of valves to be included in the IST program is defined in Article IWV-1000 of

Sect. XI to include valves", which are required to perform a specific function! in shutting

down a reactor to the cold shutdown condition or in mitigating the consequences of an

accident.".

Valves are categorized by function and functional requirements in Article IWV-2000.

All check valves fit in Category C.-!valves which are self-actuating in 'response to some

system characteristic, such as pressure (relief valves) or flow direction (check valves)." In

addition, some check valves may be defined as Category A valves-valves for which seat

leakage is limited to a specific maximum amount in the closed position of fulfillment of

their function."

Article IWV-3000 of Sect. XI provides test requirements for valves in general, and

Article IWV-3520 specifically identifies those requirements that are particular to check

valves. In essence, check valves are required to be demonstrated to be able to move to

their safety-related position when system conditions so warrant. Testing is required to be

performed quarterly; however, valves that cannot be tested quarterly are to be tested at

cold shutdown. Each plant must submit a test program to the NRC which designates valves

that are to be tested in accordance with the Code and which identifies exceptions to Code

requirements.

Containment Isolation Valve Lcak Tcsting Requirements

Plant Technical Specifications also invoke the authority of 10 CFR 50, Appendix J,

and require that containment isolation valves that are- subject to 'Type C" (not to be

confused with "Category C" valves identified in the ASME Code) tests be leak tested

biennially. The valves that are specified in Appendix J are ". . those that:

1. Provide a direct connection between the inside and outside atmospheres of the primary

reactor containment under normal operation, such as purge and ventilation, vacuum

relief, and instrument valves; -

2. Are required to close automatically upon receipt of a containment isolation signal in

response to controls intended to effect containment isolation;

3. Are required to operate intermittently under postaccident conditions; and
56

4. Are in main steam and feedwater piping and other systems which penetrate containment

of direct-cycle boiling water power reactors."

The specific containment isolation valves that are actually "Type C" leak tested are

normally identified in the individual plant's Final Safety Analysis Report.

Reactor Coolant Pressure Boundary Isolation Valve Testing Requirements

Plant Technical Specifications require that certain valves that provide isolation

between the reactor coolant system (RCS) and connected low-pressure systems (e.g., the

residual heat removal system) be leak tested periodically. The test intervals are variable,

depending upon plant and valve operation conditions, but testing is required at least once

per refueling outage. The maximum allowable leakage rate for each RCS pressure

boundary isolation valve is specifically designated in the Technical Specifications.

There is overlap between these three test requirement sources. For example, since

containment' isolation valves are needed in mitigating the consequences of an accident,

they would fall under the auspices of both the 10 CFR 50, Appendix J, requirements- and

the IST requirements. In general, the IST requirements cover the broad range of check

valves to be tested, while the containment isolation and RCS pressure boundary isolation

valve leak tests apply specific limits to select valves.

CURRENT TEST METHODS

Utilities write and implement procedures to meet the regulatory requirements

associated with check valves. The procedure used to verify a particular valve's operability

may range from a simple test requiring little or no test setup or data analysis, to a complex

test evolution involving system realignment, partial draining, application of special testing

equipment, post-test filling, venting, and realignment, and considerable data analysis.

Depending upon what function is to be demonstrated (e.g., closing or opening on

demand or seat leakage less than allowable), a number of conditions are monitored to

indicate valve functionability. These include, for example,

a. Measuring the seat leak rate.

b. Observing upstream temperature (as is done routinely, for example, in the case of

auxiliary feedwater check valves).

c. Verifying that the required flow rate can be passed through the valve.

d. Observing reverse pressure differential.

e. Listening for the valve'to slam shut on cessation of flow.

f. Observing that the valve is sufficiently closed to ensure that the rate of flow delivered

downstream of the valve to a given target is adequate to meet system demands.

For check valves that are required to transfer from closed to open to satisfy their

safety-related function, testing is conducted by passing the required flow rate through the

valve, when practicable. The NRC has historically accepted full-flow testing as evidence

that the valve has been full-stroked (it is recognized, however, that in some applications,

valves may not fully open, even under maximum system flow). Valves that are required to
57

transfer from open to closed are normally tested by applying a reverse pressure differential

and observing some system parameter for indication of closure.

Typically, a relatively small fraction of the check valves used in safety-related

applications are leak tested to determine a quantitative leak rate. ORNL conducted a

sample review of the IST programs for four units. Included in the review were two

pressurized water reactor units and two boiling water reactor units. There was a total of

466 check valves at the four units. Only 118 of these valves were identified as ASME

Category A valves, that is, "valves for which seat leakage is limited to a specific maximum

amount in the closed position of fulfillment of their function." All 118 valves that were

designated to be seat leak tested are tested under the auspices of either the containment

isolation valve or the RCS pressure boundary isolation valve leak testing programs, with no

additional leak testing specifically for IST purposes. Quantitative seat leakage testing is

conducted by pressurizing the downstream side of the valve with a test pressure source (e.g.,

instrument air or a compatible water source, including, in some cases, the existing

downstream pressure) and observing the leak rate by opening an upstream connection.

It should be noted that the safety-related function of some valves that are not

quantitatively leak tested involves only allowing forward flow; nevertheless, a significant

number of valves for which the safety-related function includes closing in response to

reverse differential pressure are not designated as requiring leak testing. This includes

valves such as safety-related pump discharge check valves.

Seat leakage for valves in applications where quantitative leak rate is not required

to be measured but where the valve must still be demonstrated to close in response to

reverse differential pressure is typically addressed in a qualitative manner. For example, the

pressure differential across a pump discharge check valve may be observed while the pump

is idle and a parallel pump is being run (or the downstream section of the check valve's

piping is otherwise pressurized). Alternatively, the adequate functioning of a valve, in terms

of seating, may be demonstrated by verifying that the required flow rate is delivered through

the demand flow path (thereby proving that the valve in question provided sufficient

isolation).

In the event that the required testing is not practicable during normal operation, the

valve may be partially tested during normal operation (e.g., by passing a flow rate that is

something less than that required to satisfy the safety function) and then tested at the

required flow rate during cold shutdown or refueling. It should be noted that some valves

cannot be even partially tested during normal operation because of the adverse effect that

test conduct would have on the plant.

It is important to note that the current test requirements are not oriented toward

trending or detection of conditions that may lead to valve failure. Disk flutter due to

operation under turbulent conditions with the valve not in a fully open position (pinned

against the backstop, for example) has been recognized as a cause of wear at the hinge

pin pivot area. Substantial hinge pin or pin holder wear can occur without being detected

by current monitoring. Other degradation mechanisms, such as disk pin wear, may also not

be detected. Even catastrophic failure can go undetected for valves in certain applications

(e.g., a check valve that is forward flow tested only may pass its flow test with the disk

having broken off and fallen to the bottom of the valve body or traveled downstream). In

addition to the inability to detect some degradation/failure sources by use of historical

monitoring methods, it is important to recognize that in some system designs/applications,

it is simply not feasible, because of inadequate testability provisions in the system design,

to conduct testing at the required conditions at any time.
58

In recognition of the weaknesses in historical monitoring capabilities and the inability

to test certain valves, utilities have undertaken, at the urging of both the NRC and INPO,

periodic disassembly and inspection. Disassembly and inspection has normally been used

on a sample basis-that is, a representative valve of a group of valves of similar

design/application is disassembled during a refueling outage. During the following outage,

another in the group is inspected, and so on, until the entire group has been inspected.

Typically, group size and sampling rates are such that all valves in a group are inspected

within 4 to 6 years.

While disassembly and inspection provide better information about valve condition

in many respects than can be obtained through any other available method, there are a

number of drawbacks associated with disassembly. These include, for example, scheduling

additional maintenance work during already busy outages, additional radiological burden, as

well as concerns that reassembly errors can go undetected (for valves that cannot be tested

with flow).

The need to improve the knowledge of check valve operating conditions without

requiring disassembly has resulted in the development and improvement of several

nonintrusive diagnostic techniques. It is important to recognize, however, that for those

applications in which the utility has determined that current system configuration does not

permit valve stroking, neither the historical nor the newer techniques are able to confirm

valve operability.
59

NUREG/CR-4302

Volume 2

ORNL-6193/V2

Dist. Category RV

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60

75. H. L. Magleby, Idaho National Engineering Laboratory, MS 2406, P.O. Box 1625, Idaho

Falls, ID 83415

76. Joseph N. Nadeau, HENZE-MOVATS, Inc., 200 Chastain Center Blvd., Kennesaw, GA

30144

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Conshohocken, PA 19428

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{See instructions on the reverse) ORNL-6193/V2

2.TITLE AND SUBTITLE

Aging and Service Wear Of Check Valves 3. DATE REPORT PUBLISHED

Aging Wear and ofService Check Valves ~~MONTH EA

Used in Engineered Safety-Feature Systems April 1991

of Nuclear Power Plants; Aging Assessments 4. FIN OR GRANT NUMBER

and Monitoring Method Evaluations B0828

5. AUTHOR(S) 6. TYPE OF REPORT

Topical

H. D. Haynes

7. PERIOD COVERED lsnclisse Digest

B. PER FORMING ORGAN IZAT ION -NAME AND ADD R ESS aIf NRC. porovr D;vis;on. Office or Region. U.S. Nuclear Regulatory Commission, and maing add'ess: i contractor. pror.i name and mailing adress.J

Oak Ridge National Laboratory

Oak Ridge, TN 37831-6285

9. SPONSOR ING ORGANIZATION -NAME AND ADDRESS WIf NRC. type "Same as abo v,- if conurtcbor provide NRC ODeisson. Office or Region. U.S. Nuclea Regularorv Commission,

and miling address.)

Division of Engineering

Office of Nuclear Regulatory Research

U. S. Nuclear Regulatory Commission

Washington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or kse

Check valves are used extensively in nuclear power plant safety systems and balance-of-plant systems. The

failures of these valves have 'resulted in significant maintenance efforts and, on occasion, have resulted in water hammer,

overpressurization of low-pressure systems, and damage to flow system components. These failures have largely been

attributed to severe degradation of internal parts (e.g., hinge pins, hinge arms, discs, and disc nut pins) resulting from

instability (flutter) or check valve discs under normal plant operating conditions. Present surveillance requirements for

nuclear power plant check valves have been inadequate for timely detection and trending of such degradation because

neither the flutter nor the resulting wear can be detected prior to failure. Consequently, the U.S. Nuclear Regulatory

Commission has had a continuing strong interest in resolving check valve problems.

In support of the Nuclear Plant Aging Research Program, Oak Ridge National Laboratory has carried out an

evaluation of several developmental and/or commercially available check valve diagnostic monitoring methods, in

particular, those based on measurements of acoustic emission, ultrasonics, and magnetic flux. In each case, the

evaluations have been focused on the capability of each method to provide diagnostic information useful in determining

check valve aging and service wear effects (degradation), check valve failures, and undesirable operating modes.

A description of each monitoring method is provided in this report, including examples of test data acquired

under controlled laboratory conditions. In some cases, field test data acquired in situ are also presented. The methods

are compared. and sueeested areas in need of further develonment are identified.

12. KEY WORDS/DESCR !PTORS IListv w'ords Of phrases thatessist researchers In locating the report.) 13. AVAILABILITY STAT EMENT

Unlimited

1<. SECURITY CLASSIFICATION

(This Page)

Valves, aging, service wear, maintenance, degradation, trend Unclassified

measurable parameter, incipient failure, inspection, surveillance, UThisse sflied

monitoring, functional indicators, signature analysis, acoustic emission,

ultrasonic inspection, magnetic flux 15. NUMBER OF PAGES

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