NUREG/CR-48 19

Volume 1

ORNL/Sub/83-28915/4/Vl

OAK RIDGE

NATIONAL

LABORATORY

Y,:,&,d - -

Aging and Service Wear

of Solenoid-Operated Valves

Used in Safety Systems

of Nuclear Power Plants

Volume 1. Operating Experience

and Failure Identification

V. P. Bacanskas

G. C. Roberts

G. J. Toman

Work Performed for

U.S. Nuclear Regulatory Commission

under

DOE Interagency Agreement 40-551-75

NRC FIN No. B0828

OPERATED BY

MARTIN MARIETTA ENERGY SYSTEMS, INC.

FOR THE UNITED STATES

DEPARTMENT OF ENERGY
NUREG/CR-4819

Volume 1

ORNL/Sub/83-28915/4/Vl

Dist. Category RV

AGING AND SERVICE WEAR OF SOLENOID-OPERATED VALVES

USED IN SAFETY SYSTEMS OF NUCLEAR POWER PLANTS

Volume 1. Operating Experience and

Failure Identification

V. P. Bacanskas G. C. Roberts

G. J. Toman

In Support of

Nuclear Plant Aging Research

U.S. Nuclear Regulatory Commission

Manuscript Completed - February 6, 1987

Date Published -March 1987

Report Prepared by

Franklin Research Center

Division of Arvin/Calspan

20th & Race Streets

Philadelphia, Pennsylvania 19103

under

Subcontract No. BOA 41B-28915C

Letter Release 41Y-12

for Oak Ridge National Laboratory

Work Performed for

U.S. Nuclear Regulatory Commission

under

DOE Interagency Agreement No. 40-551-75

NRC FIN No. B0828

OAK RIDGE NATIONAL LABORATORY

Oak Ridge, Tennessee 37831

operated by

MARTIN MARIETTA ENERGY SYSTEMS, INC.

for the

U.S. DEPARTMENT OF ENERGY

under contract No. DE-AC05-840R21400
iii

CONTENTS

Page

LIST OF FIGURES . ............... ................ . ....... ............ v

LIST OF TABLES ................................................ vii

EXECUTIVE SUMMARY ......... ................................... ................. . ix

ACKNOWLEDGMENTS ..................................................... xi

ABSTRACT .................................................................... 1

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

2. PRINCIPAL TYPES AND APPLICATIONS OF SOLENOID-OPERATED VALVES

IN SAFETY-RELATED SYSTEMS OF NUCLEAR POWER PLANTS ............ . 4

3. IDENTIFICATION OF SOLENOID-OPERATED VALVE MANUFACTURERS ....... 8

4. DESCRIPTION OF OPERATION ...................................... 9

4.1 Automatic Switch Company Solenoid-Operated Valves ........ 9

4.1.1 ASCO direct-acting, three-way solenoid valve,

normally closed construction ...................... 9

4.1.2 ASCO pilot-controlled, three-way solenoid valve ... 11

4.2 Valcor Engineering Corporation Solenoid-Operated Valves .. 14

4.2.1 Valcor direct-acting, three-way solenoid valve .... 14

4.2.2 Valcor direct-acting, two-way solenoid valve ...... 16

4.2.3 Valcor pilot-assisted, two-way solenoid valve ..... 19

4.3 Target Rock Corporation Solenoid-Operated Valves ......... 21

4.3.1 Description of valve ...... .................. .. ........ . 21

4.3.2 Valve operation ..... .................. ............ ... 21

4.3.3 Materials of construction .... ..................... 23

5. STRESSORS AND AGING MECHANISMS ..... .................... ... ... 24

5.1 Identification of Stressors and Aging Mechanisms ......... 24

5.2 Expected Stressors .............. ......................... 24

5.3 Abnormal Stressors ....... . . ............................... . 27

6. EVALUATION OF SOLENOID-OPERATED VALVE FAILURE DATA ..... ....... 29

6.1 Sources of Failure Data .................................. 29

6.2 Summary of Failure Data . ....................... ... *..... . 29

6.3 Analysis of Failure Data .................................... 33

7. FAILURE MODE AND CAUSE ANALYSIS ............. ................. 34

7.1 Information Sources . ................. ... ................. 34

7.2 SOV Failure Modes ........... ............................ 34

7.3 Valve Failure Cause Analysis ....................... * 34
iv

Page

8. TESTING AND MAINTENANCE REQUIREMENTS .......................... 41

9. AGING AND SERVICE WEAR MONITORING AND ASSESSMENT .............. 42

9.1 Failure Mode and Cause Determination ..................... 42

9.2 Measurable Parameters for Establishing Degradation

Trends ................ *..*.*............................ 46

9.3 Potential Monitoring Techniques .......................... 46

10. CONCLUSIONS . ... ... .. ....................... . . ................* ..... . 53

11. RECOMMENDATIONS ...................................... .............. 54

REFERENCES .............................................................. 55
v

LIST OF FIGURES

Figure Page

1 NPAR Program Strategy .......... . . ..................................... . 2

2 Schematic diagram of three-way SOV (refer to Fig. 8

for sectional view) used to control a pneumatically

actuated valve .............. 0......... 5

3 Schematic diagram of four-way SOV used to control

a piston-actuated valve ......... . .. . ................................... . 6

4 Pneumatically actuated valve with appurtenances ........... 7

5 Exploded view of ASCO direct-acting, three-way valve ...... 10

6 View of the ASCO Model NP831665E solenoid valve ...... *.... 12

7 Exploded view of ASCO pilot-controlled, three-way valve ... 13

8 Section drawing of Valcor direct-acting, three-way valve .. 15

9 Electrical schematic of Valcor ac-powered valve ...... O.... 16

10 View of Valcor Model No. V52610-5292-3 solenoid valve ..... 17

11 Diagram showing functioning of a Valcor direct-acting,

two-way, normally closed valve ....... ... ... 18

12 Diagram showing functioning of a Valcor pilot-assisted,

two-way, normally closed valve ........................ 20

13 Component parts of a TRC pilot-assisted, two-way,

normally closed valve ...... .. ........... . ....... . 22
vii

LIST OF TABLES

Table Page

1 Breakdown of NPRDS-documented failures of SOVs,

September 5, 1978-July 11, 1984 30

2 NPRDS failures not documented in LERs ..................... 31

3 ASCO direct-acting, three-way solenoid valve .............. 35

4 ASCO pilot-controlled, three-way solenoid valve ........... 36

5 Valcor direct-acting, two-way solenoid valve .............. 37

6 Valcor pilot-operated direct-lift, two-way

solenoid valve ................................... * ........ 38

7 TRC pilot-operated, two-way solenoid valve ................ 39

8 Method for identifying failure causes - ASCO

direct-acting, three-way solenoid valve ................... 43

9 Method for identifying failure causes - ASCO

pilot-controlled, three-way solenoid valve . .44

10 Method for identifying failure causes - TRC

pilot-operated, two-way solenoid valve .................... 45

11 Measurable parameters - ASCO direct-acting,

three-way solenoid valve .. ...................... 47

12 Measurable parameters - ASCO pilot-controlled,

three-way solenoid valve ..... .. ........ ...... 48

13 Measurable parameters - TRC pilot-operated,

two-way solenoid valve ........... * ........................ 49

14 Summary of valve part failure assessment .................. 50
ix

EXECUTIVE SUMMARY

The purpose of this report is to provide an assessment that characterizes the aging mechanisms of solenoid-operated valves (SOVs) and the

nuclear power plant experience with failures of SOVs in service. The

goal is to identify the specific degradation mechanisms present in SOVs

and to correlate these mechanisms to the potential for detection utilizing current inspection, surveillance, and maintenance techniques. The

ultimate goal of the program is to identify methods of inspection and

surveillance of components that are effective in detecting significant

aging and service wear effects prior to loss of safety function, so that

maintenance can be performed in a timely manner to restore the component's functional capabilities.

Chapter 2 describes the principal types and uses of SOVs in safetyrelated systems of nuclear power plants. Chapter 3 provides the basis

for inclusion of the manufacturers and models used in the assessment.

Chapter 4 provides a detailed description of the components, materials

of construction, and operation of each of the SOVs included in the

assessment. Chapter 5 provides a description of the stressors and aging

mechanisms for SOVs, and Chapter 6 provides an analysis of failure data

from the Nuclear Plant Reliability Data System (NPRDS) and the Licensee

Event Reporting (LER) system.

It is worth noting that 50% of the reported failures occurred as a

result of worn or degraded component parts, contamination by foreign

materials, or from solenoid coil failures. Methods for detection of

these three failure causes are discussed, including the inherent limitations in using the degradation monitoring techniques. While this report

does show that the frequency of SOV failure is relatively low, reduction

of the failure frequency is indeed possible if adequate degradation

monitoring techniques are developed. Recommendations for refinement of

existing monitoring techniques as well as for development of new techniques are provided.
xi

ACKNOWLEDGMENTS

The authors wish to thank Dr. S. P. Carfagno of the Franklin

Research Center for his technical direction and thoughtful comments on

the drafts of this document. We would like to express our appreciation

to the following individuals and organizations who provided pictures,

drawings, and information contained in the report.

Mr. John Shank - Automatic Switch Company, Florham Park, N.J.

Mr. William Brown - Automatic Switch Company, Florham Park, N.J.

Mr. Joseph B. Borge - Hammel Dahl & Jamesbury Control Corporation,

Warwick, R.I.

Mr. George Murphy - Oak Ridge National Laboratory, Oak Ridge, Tenn.

Mr. Fred N. Ferri - Target Rock Corporation, East Farmingdale, N.Y.

Mr. Richard Heilman - Valcor Engineering Corporation, Springfield,

N.J.


3

information pertaining to the types and uses of SOVs, identification of

significant stressors and aging mechanics, and review of pertinent failure data and operating experience. It concludes with an interim assessment of potential condition monitoring techniques. This report results

from a study conducted under a subcontract with Martin Marietta Energy

Systems, Inc., operator of Oak Ridge National Laboratory (ORNL), as part

of an NPAR task entitled, "Detection of Defects and Deterioration Monitoring of Nuclear Power Plant Safety Equipment."

Note that there are numerous manufacturers of SOVs; however, for the

purposes of this program, SOVs from three manufacturers were chosen for

evaluation as being representative of the types with the greatest populations in safety-related service in nuclear power plants. The manufacturers were Automatic Switch Company (ASCO), Valcor Engineering Corporation,

and Target Rock Corporation (TRC).
4

2. PRINCIPAL TYPES AND APPLICATIONS OF SOLENOID-OPERATED VALVES

IN SAFETY-RELATED SYSTEMS OF NUCLEAR POWER PLANTS

An SOV is a valve that is opened and closed by means of an electrically actuated solenoid coil that, in most designs, lifts a plunger to

open or close the valve *port. The process ports of SOVs range in size

from 1/4- to 6-in. NPT. SOVs may be direct-acting (i.e., the solenoid

coil provides the motive force for opening and closing of the valve) or

may be pilot-assisted (i.e., the solenoid coil causes the opening of the

pilot orifice, allowing the process fluid to force the main orifice

open).

Two-, three-, or four-way SOVs are available. The two-way SOV is

normally used directly in a process line (either liquid or gas) to stop

or allow passage of the process fluid. The three-way SOV is normally

used as a control device that operates a pneumatic (air-operated) or

hydraulic valve actuator. This type of application is illustrated in

Fig. 2, which depicts a three-way SOV that is used to supply and vent the

control air source to and from the diaphragm operator of the pneumatically

actuated valve. Upon energization of the solenoid coil (for a normally

closed SOV), the air supply or process port (marked P) is connected to

the cylinder port (marked C) of the SOV. The air pressure applied to the

diaphragm cavity through the SOV provides sufficient force to overcome

the actuator spring force and close the pneumatically actuated valve.

Upon deenergization of the SOV, the air supply port (P) is closed and the

cylinder port (C) is connected to the exhaust port (E) and the air in the

diaphragm cavity of the pneumatically actuated valve is exhausted, allowing the operator spring to open the valve.

The four-way SOV, although not frequently used in nuclear power

plants, is used primarily with piston-type valve actuators as shown schematically in Fig. 3. With the SOV energized, the air supply port (P) is

connected to cylinder B, and cylinder A is connected to the exhaust port

(E). The air above the piston is exhausted, and the process pressure

applied under the piston lifts the piston to open the valve. Deenergizing

the solenoid coil reverses the cylinder connections and exhausts the air

pressure under the diaphragm while using the air pressure over the piston

to close the valve. The four-way SOV will not be addressed further in

this assessment because of its limited use in nuclear applications.

The populations of SOVs in nuclear power plant safety systems vary

substantially depending upon the plant design and vintage, but they

usually number from 1000 to 3000. In the boiling water reactor (BWR),

the control rod drive system uses more SOVs than any other plant system.

Over 300 SOVs are used to control the position of the control rods and

for scramming the control rods. Although some questions exist with

regard to the exact safety classifications of these SOVs, the BWR plant

accident analyses assume proper operation of the SOVs used to scram the

control rods, and hence, they are definitely safety related. Elsewhere

in the plant, the SOVs are used to control isolation valves, containment

gas sampling valves, and ventilation system dampers, as well as many

*American National Standard Taper Pipe Thread.
5

f- ELECTRICAL

POWER

ORNL-DWG 86-5313 ETD

PNEUMATIC

- OPERATOR

SOLENOID HOUSING

CYLINDER PORT

EXHAUST A

E

AIR SUPPLY

(PROCESS)

C

P

SOLENOID OPERATED VALVE

-- ENERGIZED

- - DEENERGIZED

VALVE DISC

VALVE BODY

Fig. 2. Schematic diagram of three-way SOV (refer to Fig. 8 for

sectional view) used to control a pneumatically actuated valve.
6

ORNL-DWG 86-5314 ETD

PISTON

A E

EXHAUST

AIR SUPPLY

(PROCESS)

SOLENOID OPERATED

VALVE

VALVE DISC

1 - VALVE BODY

I I

PISTON OPERATED VALVE

Fig. 3. Schematic diagram of four-way SOV used to control a

piston-actuated valve.

other applications. One of the more important applications of SOVs in

BWRs is their use to control the main steam isolation valves. In pressurized water reactor (PWR) plants, the number of SOVs is lower than in

the BWR because the PWR control rod drives are electromechanical and do

not use SOVs. In many plants, SOVs are used to control the safety relief

valves. The PWR plant does have SOVs for isolation, sampling, ventilation system dampers, and an abundance of control applications on pneumatically actuated valves in the various process systems. Figure 4 shows

a pneumatically operated valve configured as it would be used for a containment isolation function.
7

ORNL PHOTO 6812-86

X - PNEUMATIC OPERATOR

AIR -

BOTTLE

VALVE BODY

Fig. 4. Pneumatically actuated valve with appurtenances. Photo

supplied by Hammel Dahl & Jamesbury Control Corp., Warwick, R.I.
8

3. IDENTIFICATION OF SOLENOID-OPERATED VALVE MANUFACTURERS

SOVs from three manufacturers were selected for detailed evaluation

for this aging assessment. The three manufacturers were selected based

upon the frequency of use of their SOV in the safety systems of nuclear

power plants and the similarity of other SOV designs to the three

selected. While SOVs manufactured by other suppliers may have slight

differences in the coil or shaft seals, the basic operations are similar

to those addressed herein.

The manufacturers and the types of SOVs selected for this assessment

include:

1. ASCO: three-way direct acting and three-way pilot controlled;

2. Valcor Engineering Corporation: three-way direct acting, two-way

direct acting, and two-way pilot assisted;

3. TRC: two-way pilot assisted.

4
9

4. DESCRIPTION OF OPERATION

4.1 Automatic Switch Company Solenoid-Operated Valves

4.1.1 ASCO direct-acting, three-way solenoid valve,

normally closed construction

The ASCO three-way, direct-acting SOV is so named because it has

three process ports that are opened and closed through the direct action

of the solenoid. The ASCO three-way, direct-acting SOV is used mainly to

control pneumatically actuated valves, as shown in Fig. 2.

The ASCO valve is of normally closed construction, which means that

the cylinder of the valve being controlled is isolated from the supply

pressure when the electrical power supply to the solenoid is off. The

SOV is designed to operate with either a 120-V ac, 60-Hz solenoid coil,

or a 125-V dc solenoid coil and is housed in a National Electrical Manufacturer's Association (NEMA) Type 4 en losure. The valve has ethylene

propylene diene monomer (EPDM) or Viton seating surfaces. The discholder disc and all 0-rings and seals are also made of EPDM or Viton.

The normal ambient service temperature limit of the SOV is 140'F (60'C).

4.1.1.1 Valve operation.2 Figure 5 provides an exploded view of

the ASCO three-way valve. When the coil is not energized, the core

spring forces the core assembly (with valve seat) down onto the process

pilot orifice, sealing the supply air from the supply port (P) as shown

in Fig. 2. At the same time, the core assembly pushes the disc-holder

subassembly away from the exhaust pilot orifice connecting the cylinder

port (C) to the exhaust port (E). As a result of this action, the cylinder of the air-operated valve (AOV) being controlled is connected to the

exhaust port (E) of the SOV. This connection allows pressurized air

within the cylinder of the AOV to be vented to the atmosphere, causing

the AOV to return to its normal position. Upon energizing the solenoid

coil, the magnetic force of the coil pulls the core assembly with its

seat away from the process pilot orifice, allowing supply air to pass to

the cylinder port (C). The three prongs of the disc-holder subassembly,

which press against the seat of the core assembly, also apply force from

the disc-holder spring that aids in unseating the core. The disc-holder

spring then pushes the disc-holder subassembly against the exhaust pilot

orifice and seals supply air from the exhaust path. Therefore, a flow

path is created between the diaphragm cavity of the AOV, which is connected to the cylinder port (C) of the SOV (see Fig. 2), and the air

pressure source. This path allows air to enter the cylinder of the actuator, causing the diaphragm to move.

4.1.1.2 Materials of construction. The materials of construction

of the major components of the ASCO Model NP 8320 three-way, direct-

*Viton is a registered trademark of the E. I. Dupont DeNemours

Company.
10

ORNL-DWG 86-5315 ETD

R WITH SCREWS (3) AND

'LATE ATTACHED.

t GASKET

P -NSPRING WASHER

RETAINING CLII

YOKI

-INSULATING WASHER

(OMITTED WHEN MOLDED

COIL IS USED)

HOUSINGRETAINER Gi

SPRING

HOLDER SPRING

F-NEND CAP

Exploded view of ASCO direct-acting, three-way valve.

BuUetin 8320, Automatic Switch Co., Florham Park, N.J.,

Fig. 5.

Source: ASCO

1978.
11

acting SOVs are as follows:

Component Material of construction

Cover EPDM

Cover gasket EPDM

Coil Class H insulation

Solenoid base subassembly Stainless steel

Electrical housing Steel

Core seat EPDM or Viton

Core spring Stainless steel

Valve body Brass

Disc-holder subassembly EPDM or Viton

Disc-holder spring Steel

4.1.2 ASC0 pilot-controlled, three-way solenoid valve

4.1.2.1 Description of valve. The ASCO three-way, pilot-controlled

SOV has three external ports. The main orifice of the valve is opened

and closed.through the opening and closing of a smaller pilot orifice.

The main use of the SOY is to control pneumatically actuated valves that

require large-volume air flow. The SOV can be obtained as a normally

closed valve in which the cylinder port (C) of the SOV (see Fig. 2) is

blocked from the supply air pressure when no power is supplied to the

solenoid. In this case, the actuator of the air-operated device being

controlled is simultaneously connected to the exhaust (E) of the SOV.

The ASCO three-way, pilot-controlled valve can also be obtained as

a normally open valve with the cylinder port (C) connected to the air

supply (S) when the power supply to the solenoid is off. The result is

that the actuator of the device being controlled is connected to the

supply pressure when the solenoid is deenergized.

The valve can be obtained with either 125-V dc or 120-V ac, 60-Hz

solenoid coils. Both coils are housed within a NEMA Type 4 enclosure.

A NEMA Type 4 construction code specifies a watertight and dusttight

design that is used indoors to protect the enclosed equipment against

splashing water, seepage of water, hose-directed water, and severe

external condensation. The pressure and exhaust diaphragms of the valve

are EPDM on Nomex fabric. The disc-holder subassembly disc and all

O-rings and seals are also made of EPDM or Viton. The normal ambient

service temperature limit of the SOV is 140'F (60%C). Figure 6 is a

photograph of an ASCO Model NP831665E.

4.1.2.2 Valve operation.2 Figure 7 provides an exploded view of

the ASCO pilot-controlled, three-way valve when the coil is not energized.

With the coil deenergized, the core assembly and seat are held

against the process pilot orifice by the core spring. The core assembly

pushes down on the tripod of the disc-holder assembly, forcing the assembly away from the exhaust pilot orifice and thus allowing the air seating

the exhaust diaphragm assembly to pass through the exhaust body passage,

through the insert, and to the exhaust port (E) shown in Fig. 2. The

cylinder pressure then unseats the exhaust diaphragm, which causes the
12

ORNL PHOTO 6813-86

0,

Fig. 6. View of the ASCO Model NP831665E solenoid valve.

supplied by Automatic Switch Co., Florham Park, N.J.

Photo

pressure in the cylinder to vent through the exhaust port (E). While

deenergized, air from the air supply (P) passes through the small hole in

the pressure diaphragm assembly into the pressure body passage and maintains pressure on the larger area on the outside of the pressure diaphragm assembly (see Fig. 7), which seats and holds the diaphragm in

place. Upon energizing the coil, the core assembly is lifted from the

process pilot orifice, and the disc spring forces the disc-holder subassembly against the exhaust pilot orifice. The air pressure held in the

process body passage and behind the pressure diaphragm assembly is vented

through the insert, through the exhaust body passage, to the back of the

exhaust diaphragm assembly; it forces the exhaust diaphragm assembly

against its seat, thereby sealing the exhaust port (E). Releasing the
13

ORNL-DWG 86-5316 ETD

I WITH SCREWS

:R GASKET

RETAINING

!WASHER

COIL IS USEDI

-COIL

LPPER SOLENOID -INSULATING WASHER

(OMITTED WHEN MOLDED

COIL IS USED)

UPPER INSERT GASKET

i BONNET

Fig. 7. Exploded view of ASCO pilot-controlled, three-way valve.

Source: ASCO Butletin 8316, Automatic Switch Co., Florham Park, N.J.
14

pressure on the back of the pressure diaphragm assembly allows the process air to unseat the pressure diaphragm assembly and pressurize the

process cylinder.

4.1.2.3 Materials of construction. The materials of construction

of the major components of the ASCO Model NP831665E SOV are as follows:

Component Material of construction

Cover Steel

Cover gasket EPDM

0-rings EPDM

Electrical housing Steel

Solenoid base subassembly Stainless steel

Core seat EPDM

Disc-holder subassembly seat EPDM

Disc-holder spring Stainless steel

Valve body Brass

Diaphragm EPDM on Nomex fabric

Core spring Stainless steel

4.2 Valcor Engineering Corporation Solenoid-Operated Valves

4.2.1 Valcor direct-acting, three-way solenoid valve

4.2.1.1 Description of valve. The Valcor direct-acting, three-way

SOV can be powered by either dc or 60-Hz ac and has an operating voltage

range of 90 to 140 V. The operator enclosure is of NERA Type 4 (watertight and dusttight) construction. The Valcor three-way SOV is used

primarily to control pneumatic-actuated valves. The Valcor valve has a

normal service temperature limit of 150 'F (660 C) (Ref. 3).

4.2.1.2 Valve operation.3 Figure 8 provides a section view of a

Valcor direct-acting, three-way SOV. Energizing the solenoid coil produces a magnetic force that lifts the plunger against the reaction of the

spring with the aid of the process pressure. The seal assembly, which is

pinned to the plunger, is in turn lifted from A and transferred to the

seat at port C, causing port C to be sealed off and likewise connecting

ports A and B.

Deenergizing the solenoid coil results in loss of the magnetic

holding force, which allows the spring to push the plunger and the seal

assembly onto its seat at port A against the lift of the process supply

pressure. Port B is then connected to port C, and port A is isolated

from the other two ports, as shown in Fig. 8. The valve may be configured as normally open or normally closed, depending upon which port is

connected to the pressure source, as shown in Fig. 8.

In the "normally open" configuration, port C is the air supply port

shown in Fig. 2. Energizing the solenoid coil causes ports A and B to be

isolated from the supply pressure, as shown in Fig. 8. Deenergizing the

solenoid connects the supply pressure port C to port B and isolates port

A from the other two ports.
15

CGo

ORNL-DWG 86-5317 ETD

COIL ASSEMBLY

_-SPRING

-PLUNGER

PORT C

-SEAL ASSEMBLY

PORT A

BeC B C BeC B C

A A A A

DE-ENERG IED ENERGIZED DE-ENtERGI2ED ENtRGIZED

(DR ~L1tE POQ A} (PRE55URE 'OP.T C-)

NORMALLY CLO5ED NORMALLY OPEN .

Fig. 8. Section drawing of

(Ref. 3).

Valcor direct acting, three-way valve

In the "normally closed" configuration, port A is the air-supply

port. Energizing the solenoid coil causes port A to be connected to port

B and also isolates port C from the port B. Deenergizing the solenoid

coil connects port B to port C and isolates port B from the supply pressure at port A.
i

16

Dc-powered valves operate with power applied directly to the solenoid coil. Ac-powered valves contain two diode assemblies, one a full

wave bridge rectifier and the other a zener diode assembly, as shown in

Fig. 9. The rectifier converts the ac input power into dc power to

energize the solenoid coil. The zener assembly is connected across the

input power leads to protect the solenoid assembly from transient highvoltage surges and to minimize inductive voltage spikes when the coil is

deenergized.

ORNL-DWG 86-5318 ETD

,-

ZENER DIODE

ASSEMBLY

COIL

ASSEMBLY.

.i

AC INPUT

POWE R

Fig. 9. Electrical schematic of Valcor ac-powered valve.

4.2.1.3 Materials of

of the major components of

three-way SOV are as follow

Component

construction. The materials of construction

the Valcor Model V70900-21-1 direct-acting,

s:

Material of construction

0-rings

Valve body

Plunger

Disc

Disc seal

Coil

EPDM

Brass

Stainless steel

Stainless steel

EPDM

Class H insulation

4.2.2 Valcor direct-acting, two-way solenoid valve

4.2.2.1 Description of valve. The Valcor direct-acting, two-way

valve is closed when deenergized; that is, the outlet is internally

blocked from the inlet. This SOV is available with either a 120-V ac

coil or 125-V dc coil and a watertight, dusttight NEMA Type 4 solenoid

-d
17

operator enclosure. The valve disc is of stainless steel and seals

against a metal seat in the stainless steel valve body. The disc seal

and valve 0-rings are of EPDM. The normal service temperature limit of

the SOV is 150'F (660C). Figure 10 shows the Valcor Model V52610-5292-3

SOV.

4.2.2.2 Valve operation.4 Figure 11 provides a simplified view of

the functioning of Valcor direct-acting, two-way SOVs.

Energizing the solenoid coil causes a current to flow through the

coil, thus creating an axial magnetic field within the coil. The resulting force lifts the plunger against the force of the main spring. The

plunger, in turn, lifts the disc assembly away from its seat in the valve

body with the aid of the process pressure, allowing the valve inlet to be

connected to the outlet.

Deenergizing the solenoid coil causes the main spring to force the

plunger downward against the process pressure, returning the disc assembly to its normally closed position and thereby isolating the inlet from

the outlet.

ORNL PHOTO 6814-86

Fig. 10. View of Valcor Model V52610-5292-3 solenoid valve. Photo

supplied by Valcor Engineering Corp., Springfield, N.J.
18

ORNL-DWG 86-5319 ETD

T

0.-ZNrQRGiZD rENRG12ED

E.453PLllN PRMSSURE

Fig. 11. Diagram showing functioning of a Valcor direct-acting,

two-way, normally closed valve. Source: Operation and Maintenance

Manual, OMM 20010 BSC, Issue F, Valcor Engineering Corp., Springfield,

N.J., October 1984.

4.2.2.3 Materials of construction. The materials of construction

of the Valcor Model V52610-5292-3 direct-acting, two-way SOV are as

follows:

Component

O-ring

Coil

Stop

Plunger spring

Plunger

Disc

Valve body

Valve seat

Material of construction

EPDM

Class H insulation

Stainless steel

Stainless steel

Stainless steel

Stainless steel

Stainless steel

EPDM
19

4.2.3 Valcor pilot-assisted, two-way solenoid valve

4.2.3.1 Description of valve. The Valcor pilot-assisted, two-way

SOV is closed when deenergized and is available with either a 120-V ac or

125-V dc coil and an NEMA Type 4 (watertight and dusttight) operator

enclosure. The stainless steel main disc seals against a metal seat in

the valve body, isolating the outlet port from the inlet port. The poppet seal is made of stellite 63 and the 0-rings are of EPDM. The SOV has

a normal service temperature limit of 150'F (660C).

4.2.3.2 Valve operation.5 Figure 12 provides a simplified view of

the functioning of a Valcor pilot-assisted, normally closed two-way SOV.

Energizing the solenoid coil creates a magnetic force that lifts the

plunger against the force of the plunger spring. The pilot poppet is

consequently lifted from its seat in the piston, allowing process pressure behind the seal piston to be vented through a pilot discharge orifice, as shown in Detail 11 of Fig. 12. The decrease in pressure behind

the piston, coupled with the process medium pressure, develops an unbalanced force. This unbalance is sufficient to overcome the spring load of

the piston spring that holds the piston against the main seat, causing

the piston to move off the main seat, thus opening the valve.

Deenergizing the solenoid coil allows the plunger spring to push the

plunger onto the pilot seat, thus preventing any venting of process fluid

through the pilot discharge orifice. With the pilot poppet on the pilot

seat, the differential pressure between the front and back of the piston

is equalized. The piston spring force is sufficient to initiate movement

of the piston to its closed position on the seat. The piston spring is

aided in closing by the process medium supply pressure that is being bled

into the back piston cavity behind the poppet seal through a piston inlet

orifice. As the piston begins to move, process fluid in the back piston

cavity is vented into the space behind the piston, assisting the closing

of the valve.

4.2.3.3 Materials of construction. The materials of construction

of the major components of the Valcor Model V526-5631-18 pilot-assisted,

two-way SOV are as follows:

Component Material of construction

Main seat Stainless steel

Pilot seat EPDM

Pilot poppet Stainless steel

Piston Stainless steel

Plunger Stainless steel

Plunger spring Stainless steel

Valve body Stainless steel

0-rings EPDM
20

ORNL-DWG 86-5320 ETD

P1LUI4PrzR

SPAII414

PILUP"O.UR

Pi*aT w4 .,

PoLOar

6SAT

MAIN

fi^t

AwTLWy

I

Im"'T

OnJtIoT OUTLET

m

W- LIKE PRESSUR.E

eza- Pqrissjos as, t vp

Fig. 12. Diagram showing functioning of a Valcor pilot-assisted,

two-way, normally closed valve. Source: Operation and Maintenance

Manual, OMM 6500 BSC, Valcor Engineering Corp., Springfield, N.J.
21

4.3 Target Rock Corporation Solenoid-Operated Valves

4.3.1 Description of valve

Figure 13 provides a view of the components of a TRC pilot-assisted,

two-way, normally closed SOV. The TRC pilot-assisted, two-way valve is

closed when deenergized and can be obtained with either a 125-V dc or

125-V ac coil.

The basic valve construction (Fig. 13) consists of a stainless steel

bonnet assembly that houses a magnet assembly, fixed core, and two

plungers. The bonnet assembly is threaded into the valve body and then

seal welded to prevent stem leakage. The valve body contains the main

disc and the pilot disc.

The solenoid assembly is mounted around the midsection of the bonnet.

The reed switch assembly consists of electrical circuits containing two

reed switches that indicate the position of the valve. When the valve is

open, one of the two reed switches is open and the other is closed. On

closing the valve, the switches reverse position. The main disc and

pilot disc are connected to a disc rod by a loosely fitting pin, thereby

providing a controlled amount of play between the pilot and main discs.

The disc rod is threaded into the lower plunger, which is connected to

the magnet assembly by a second rod. This rod moves the upper plunger

between the lower plunger and the fixed core.

4.3.2 Valve operation6

Energizing the solenoid coil generates a magnetic field that

attracts the upper plunger to the fixed core. Toward the end of its

travel, the upper plunger engages the rod, lifting the lower plunger and

the pilot disc. With the pilot disc raised, fluid is vented through the

vent port in the main disc, decreasing the differential pressure across

the main disc, and allowing the lower plunger to fully raise the main

disc. The magnet assembly lifts in unison with the main disc and the

lower plunger, and the movement of the magnet assembly activates the reed

switches, signaling that the valve is open.

Deenergizing the solenoid coil causes the magnetic field to dissipate. A return spring initiates the closing of the pilot disc, resulting

in an increase in differential pressure of the process medium across the

main disc, which drives it closed. As the main disc, the lower plunger,

and the magnet assembly move away from the fixed core, the magnetically

actuated reed switches are activated, signaling that the valve is closed.

In the absence of a differential pressure from the process medium

across the valve, the solenoid coil develops sufficient magnetic force to

fully open the valve; the return spring has enough force to completely

close the valve.
22

INLET PRESSURE

CONTROL PRESSURE

VENTED CONTROL

PRESSURE

INL-DWG 86-5321 ETD

MN

-REED SWITCH ASSEMBLY

_-MAGNET ASSEMBLY

ROD

FIXED CORE

UPPER PLUNGER

LOWER PLUNGER

BONNET ASSEMBLY

\// ,OSPR ICG

'PILOT DISC

SOLENOID ASSEMBLY

DISC RODBODY

INLET - OUTLET

Fig. 13. Component parts of a TRC pilot-assisted, two-way,

normally closed valve. Source: Technical Manual - Solenoid-Operated

Valve, PN 1041120-3, Target Rock Corp., Farmingdale, N.Y., October 1984.
23

4.3.3 Materials of construction

The materials of construction of the major components of the TRC PN

1041120-3 pilot-assisted, two-way SOV are as follows:

Component

Valve body

Disc spring

Plunger spring

Main disc

Pilot disc

Upper plunger

Lower plunger

Disc rod

Coil

0-rings

Seats

Material of construction

Stainless steel

Stainless steel

Stainless steel

Stainless steel

Haynes alloy

Stainless steel

Stainless steel

Stainless steel

Class H insulation

EPDM

Stainless steel
24

5. STRESSORS AND AGING MECHANISMS

5.1 Identification of Stressors and Aging Mechanisms

The SOVs installed in nuclear power plant systems experience degradation over their in-service lifetime because of the actions of multiple

stressors and aging mechanisms. Many of the stressors and aging mechanisms that act to shorten the operational life of the nuclear plant SOVs

are common to all SOV types. A few of the aging mechanisms, however, are

specific to particular SOV designs.

Stressors that have a significant adverse effect on the reliability

of SOVs can be divided into two distinct categories, that is, those

stressors that are expected to occur during operation and those that are

abnormal and should be controlled or eliminated.

Expected stressors

1. elevated temperature because of:

- heat generated by continuously energized coil,

- heat conducted and convected from process lines, and

- heat conducted and radiated from a high-temperature

environment;

2. inductive surge following current interruption in dc energized

coils;

3. erosion because of fluid flow;

4. friction between contacting surfaces;

5. vibration of piping; and

6. low dose-rate radiation exposure.

Abnormal stressors

1. high dose-rate radiation exposures,

2. high transient line voltages,

3. elevated dc voltage during station battery float charging,

4. frequent cycling,

5. corrosion products and other contaminants in the process fluid,

and

6. pressure transients.

These stressors and the resulting aging mechanisms are discussed in the

following sections.

5.2 Expected Stressors

One of the major stressors, which is common to all types of SOVs, is

the elevated temperature because of the ohmic heating effect of the coil

current during continuous or long-term energization. Various tests, both

completed2 and ongoing, have shown that a 40'C (72°F) or more temperature
25

rise above ambient in the area of the solenoid coil is usual for SOVs as

is a 20'C (360F) or more rise at the SOV elastomers. A temperature rise

of this magnitude, when coupled with high ambient temperatures [e.g.,

60'C (140'F) containment operating temperatures], causes rapid deterioration of the elastomeric parts in the valve. Seats and 0-rings may

experience hardening, cracking, or a compressive set that can result in

leakage past the seat of a closed valve or through the spaces between

valve body parts.

It must be recognized that the SOVs used in nuclear power plants

were originally designed for industrial applications where an energizeto-operate philosophy is prevalent. In the industrial applications, the

SOV is normally maintained in the deenergized state, resulting in the

coil and elastomers being maintained at room ambient or process fluid

temperature. The nuclear safety philosophy of returning to a fail safe

condition on loss of air or electrical power can result in a valve being

maintained in an energized state throughout most of its installed life.

The consequence of the continuously energized SOV is more rapid degradation of the elastomers and solenoid coils because of the long periods

at elevated temperatures. Although SOV manufacturers have considered the

continuous energization in design changes and material changes of their

products, the continuously energized SOV will generally undergo more

rapid degradation than an SOV used mostly in a deenergized state.

The temperature rise of the body of an SOV may also result from the

conduction and convection of heat from high-temperature process lines or

from a high-temperature environment. In some applications, the SOV is

installed in close proximity to or is mounted directly on the AOV being

controlled by the SOV. The conduction of heat from a high-temperature

process line through the body and casing of the AOV and the transfer of

heat by convective ambient air currents combines to raise the temperature

within the SOV. Heat may also be transferred to the internal cavity of

the SOV from the environment by conduction through the valve body and by

radiant heat transfer. An example of ambient conditions contributing to

more rapid degradation of an SOV would be an SOV located in close

proximity to a high-temperature process or steam line. Small leakages

from the high-temperature process or steam line can dramatically change

the environment in which the SOV is located. If these temperature rises

are not considered and controlled properly, premature aging of the

elastomers within the SOV will occur.

An elevated temperature in the SOV coil housing can lead to coil

damage if an incompatibility exists between the magnet wire's varnish

coating and the wire's insulation. The NRC Inspection and Enforcement

Bulletin, IE Bulletin 80-23 (Ref. 7), documents such a failure of a

Valcor SOV operating in a high-temperature environment, as a result of a

dielectric breakdown leading to turn-to-turn shorts within the coil.

Another significant stressor on the insulation of solenoid coils

occurs during interruption of the current flowing in dc coils. Interruption of the supply current to the coil results in a large voltage

(inductive surge) being developed across the coil as a result of rapid

collapse of the solenoid's magnetic field. The surge will be the

greatest at the moment of interruption. As reported in Ref. 8, voltages

of >10 kV can be generated across 125-V dc coils, although 2.5 kV is a

more typical value. This transient voltage may be dissipated by arcing
26

across the contacts that interrupt the coil current or through the coil

insulation system. The inductive surge, generic to all coils, has been

known to damage and destroy relay coils when the cyclic operation

occurred too frequently. The overvoltage surges cause breakdown of turnto-turn and layer-to-layer coil insulation, which eventually leads to

short circuits within the coil. Eventually the ohmic heating caused by

these internal coil shorts causes the conductor of the coil to burn

open. To combat the stress of the inductive surge, many solenoid coil

circuits are equipped with surge suppression diodes that are connected

directly across the coil. These diodes are not conductive at normal

system voltage, but are good conductors when the voltage increases occur

at the time of coil deenergization. Because the coil current has a path

through the diode, the voltage buildup is limited to a level that the

coil insulation can withstand. However, the operational speed of the SOV

is adversely affected by the surge suppression diode. When the coil is

deenergized, the current continues to flow through the diode for some

time rather than ceasing instantaneously. Therefore, the magnetic field

of the coil collapses more slowly. Testing has shown that the operation

of a relay actuated by a coil with surge suppression usually takes twice

as long as one without this protective feature.8 Generally, this time

delay is small enough not to be a practical concern in control circuits.

For two-way valves, erosion due to the effects of fluid flow, contaminants, and high temperature is a perennial concern. The turbulence

generated by sharp edges and corners in the flow path within the SOV can

cause a high-frequency stress cycling of the valve seat material, resulting in cracking or pitting of the seat. Contaminants, such as corrosion

products, in the airflow can cut the valve seat and may also cause pitting. The wear caused by these mechanisms is aggravated by high temperatures, which tend to make elastomeric seats less resilient.

Wear of surfaces that may be in contact, such as the interface between the core assembly and core guide, can cause misalignment that may

result in faulty SOV operation. In some designs, for example, the core

assembly is supposed to "float" concentrically within the core guide

whenever the core assembly is moved by either the energizing or deenergizing of the solenoid. Ideally, there should be no contact between the

core guide and the core. However, pumping vibrations or water hammer can

cause the core assembly to be pushed off center and to drag along the

surface of the guide as the core assembly moves. The friction between

the core assembly and the core guide could result in binding or sticking

of the core assembly.

Normal vibration in piping and other forms of mechanical excitation

(e.g., water hammer) may lead to failure of an SOV over a period of time.

IE Notice No. 85-47 (Ref. 9) cites a case where certain models of TRC

SOVs failed during environmental testing as a result of line vibrations

which caused the loosening of the solenoid holddown nut that, in turn,

caused wear of the solenoid coil lead wires, resulting in shorting of the

coil.
27

5.3 Abnormal Stressors

Exposure to high levels of radiation has damaging effects on elastomeric seats and O-rings similar to the effects of heat. Tests2 have

shown that radiation can cause seats and 0-rings to harden, crack, or to

take a compressive set that may lead to leakage. Testing performed by

Robert Barbarin1 o showed that for ethylene propylene compound 0-ring

materials, a mild-to-moderate compressive set (28 to 46%) was found after

exposure to 107 rads of gamma radiation with severe compressive set (90

to 96%) after exposure to 108 rads gamma. Fluorosilicones and fluorocarbon materials (e.g., Viton) showed a much higher susceptibility to

radiation-induced damage with -70% compressive set noted after exposure

to 107 rads gamma. Work performed under a joint U.S./French research

program and documented by Sandia National Laboratoryll showed similar

results, with a 78% compressive set noted for ethylene propylene rubber

after exposure to -2.4 x 107 rads of gamma radiation, and an 80% compressive set for Viton after a similar exposure. Radiation can also cause

hardening and warping of environmental seals such as the coil housing

cover gasket in some designs, allowing steam in-leakage under design

basis accident (DBA) environments or penetration of dampness during normal service.

High transient voltages can also cause an extra motive force on the

valve core, thereby adversely affecting the valve's mechanical life.1 2

The additional force imparts excessive velocity to the core assembly or

valve stem when it moves. On closing, this extra momentum can cause the

core or stem to literally crash against the seat, causing damage or

accelerating wear.

SOVs with a dc coil may experience additional stress when the station batteries are charged at "float" voltage. When a station battery is

found to have a low charge on one or more of its cells, the usual procedure is to raise the battery voltage about 15% above nominal voltage

(142-V dc for a 125-V dc battery) for a period of a few days to a few

weeks. Although this occurs fairly frequently at nuclear power plants,

the effect on other devices such as SOVs may not be considered. Raising

the supply voltage to the SOV increases the current drawn by the coil and

hence the heating effect because heating is proportional to the square of

the current. Coil failure or failure of power lead insulation has

occurred as a result of the effects of heating from elevated operating

voltage.

Another mechanism of concern in the aging of SOVs is wear of elastomeric seats caused by frequent cycling of the valve. The closing of an

SOV is usually achieved by the core assembly or valve stem pressing

against a seat in the valve body. For SOVs with metallic discs and

organic seats, this action applies a compressive stress to the seat that

is relieved when the valve is opened. The cycling of the stresses in an

elastomeric seat can lead to cracks as a result of fatigue failure. Frequent cycling of the SOV can also accelerate wear of the organic seat

because the metallic core is driven forcefully into the seat on closing.

Over a period of time, the seat becomes deformed as it is indented with

an impression of the end of the core, leading to severe leakage or possibly sticking of the valve.
28

Valve failure or loss of some degree of valve function may be due to

the effects of contaminants in the air system over a period of time.

Particulate matter such as corrosion products and waste material from

machining and assembly processes can accumulate in an SOV over time, preventing its proper operation. Corrosion products may also damage elastomeric seats and 0-rings and thus create leaks. One major concern is

leakage or contamination of the instrument air (IA) system with oil or

lubricants. While the IA systems at most nuclear power plants are supplied by oil-free compressors, several plants have the capability to

cross over to the service air (SA) compressors to provide air pressure on

loss of the instrument air compressors. While the crossover to the SA

compressors is done only on an emergency basis, the SA compressors are

generally not oil-free. Although it may appear that for short-term use

little oil is likely to enter the IA system, unless the IA system is

purged of any resulting contamination, the contaminants will be spread

throughout the IA system. Oil from air compressors or from oil-based

lubricants used on threaded connections in the air system can cause

damage to elastomeric materials used in SOVs.13 In particular, some

valves use an ethylene propylene elastomer that swells when contaminated

by oil. Degraded elastomers can cause the SOV to fail by sticking,

swelling that restricts flow paths, or rupturing that causes leakage

across the seat or to the atmosphere. In addition, airborne contaminants

could become embedded in elastomeric materials, providing an uneven seating surface and resulting in seat leakage.

Corrosion from certain process fluids and contamination in process

fluids have also been identified as having caused failure of metallic

components within the SOV. A recent example of this type of failure is

discussed in IE Information Notice 86-72.14 The information notice

reports failures of Valcor SOVs because of hydrogen embrittlement of the

stainless steel core spring. The manufacturer has identified the failure

mechanism as a complex function of high temperature, water chemistry,

water flow conditions, and length of exposure to these conditions.

Pressure transients in a process line may create stresses in an SOV

leading to fatigue. For example, a fast-closing, two-way valve installed

in a water line may experience the overpressure conditions of water hammer that if it occurs frequently, might cause fatigue failure at valve

body weld joints or at normally high-stress areas, such as sharp corners

and edges of the valve body.

A,
29

6. EVALUATION OF SOLENOID-OPERATED VALVE FAILURE DATA

6.1 Sources of Failure Data

The failure data analyzed included the Nuclear Plant Reliability

Data System (NPRDS) records of the Institute of Nuclear Power Operations

(INPO) for SOVs, covering September 5, 1978-July 11, 1984, and the NRC

Licensee Event Reporting (LER) system records for January 26, 1981-July

11, 1984. Entries in the LER data base are determined by the NRC reporting requirements provided in 10 CFR 50.72 and 10 CFR 50.73 and do not

necessarily include all SOV failures; however, the failures reported

under the LER system are deemed to be of safety significance. NPRDS is

a voluntary reporting system that includes failures that may or may not

have safety significance and, thus, provides a more complete data base

for data analysis.

Comparison of the failures reported in each of the data bases revealed that all of the failures reported in the LERs were also contained

in the NPRDS. As a result, the NPRDS was then chosen to be the principal

data base for analysis.

6.2 Summary of Failure Data

The NPRDS data base contained 206 records of SOV failures from

September 1978 through July 1984. Four principal failure modes dominated

the data:

1. failure to operate - 136 failures (66%),

2. failure to operate as required - 48 failures (23%),

3. internal and external leakage - 20 failures (10%), and

4. miscellaneous failures - 2 failures (1%).

Table 1 provides a breakdown of the NPRDS failure data by failure

mode, as well as by the failure cause identified in the data base. Table 2

provides the failure data for those failures reported in the NPRDS but

not included in the LERs.

For each of the four failure types, the SOV failures listed in Table 1

were evaluated to identify the causes. The following are summaries of

failure causes and failure mechanisms:

1. Failure to operate (136 failure records)

Ninety-one of the 136 failure records listed a probable cause.

Cause: Coil open circuit

Eighteen records attributed the failure to an open-circuited coil.

An open coil usually follows a turn-to-turn or layer-to-layer short

in the coil that eventually burns through the coil conductor. These

shorts result from insulation breakdown because of voltage surges

during deenergization or excessive localized heating that causes
Table 1. Breakdown of NPRDS-documented failures of SOVs, September 5, 1978-July 11, 1984a

Number of failures in each failure type

Listed cause Failure to Failure to Miscellaneous Total by

operate operate as Leakage failures cause required

Incorrectly rebuilt or assembled 1 1

Worn, degraded, or broken part 14 2 5 1 22

Corroded part 1 1

Excessive continuous cycling 2 2

Foreign materials, including corrosion 17 10 5 1 33

products, dirt, lubricants, scale,

crud, and moisture

Improper installation 3 3

Loose parts or misalignment 2 2

Zener/rectifier short or open circuit 3 3

Coil burnout or short in coil 30 30

Coil open circuit 18 18

Unspecified causes 45 36 10 91

Total 136 (66%) 48 (23%) 20 (10%) 2 (1%) 206 (100%)

aThe NPRDS data include all failures reported by the LER system.

W

.,
Table 2. NPRDS failures not documented in LERsa

Number of failures in each failure type

Listed cause Failure to Failure to Miscellaneous Total by

operate operate as Leakage failures cause required

Incorrectly rebuilt or assembled 1 1.

Worn, degraded, or broken part 6 1 1 8

Corroded part 0

Excessive continuous cycling 1 1

Foreign materials, including corrosion 12 6 4 22

products, dirt, lubricants, scale,

crud, and moisture

Improper installation 0

Loose parts or misalignment 1 1 2

Zener/rectifier short or open circuit 2 2

Coil burnout or short in coil 11 11

Coil open circuit 0

Unspecified causes 24 15 5 44

Total 58 21 11 1 91

aThe NPRDS source data also cover the period September 5, 1978-January 25, 1981, which

the LERs did not cover.

WJ
32

current cascade breakdown. (The insulation resistance decreases with

temperature, allowing higher current to flow. Higher currents result

in higher temperatures, resulting in a cascading effect.)

Cause: Coil short circuit

There were 30 failure records that identified a short circuit in the

SOV coil as the root cause. These 30 failures may have been induced

by aging mechanisms or by contaminants, such as moisture intrusion,

or may have resulted from elevated temperatures or voltage surges, as

previously described. Nine of the 30 failures resulted in a blown

fuse or shorted component in the SOV control circuit.

Cause: Foreign material

Seventeen failures to operate were related to contamination by foreign materials. Contaminants, such as corrosion products and dirt,

can interfere with the SOV components and cause the moving parts to

bind.

Cause: Worn or degraded parts

Another 14 SOVs failed to operate because of worn or degraded parts,

such as ruptured or perforated diaphragms, broken seat discs, and

worn inserts. These failures may have resulted from either aging

mechanisms, such as frequent cyclic operation, or external influences, such as contaminants or system pressure surges.

Cause: Miscellaneous

The remaining of the 12 records identified failure causes such as

rectifier diode failures, improper or incorrect maintenance, and

excessive cycling.

2. Failure to operate as required (48 records)

Cause: Sticking, binding, or seizing.

With no further indication of cause, 36 records indicated sticking,

binding, seizing, or slow response as the type of failure.

Cause: Foreign material

Seven records indicated that sticking, binding, or seizing were

caused by foreign materials. Three more records indicated that

foreign materials caused slow response to the SOV.

Cause: Worn or degraded parts

Two records indicated that slow response was caused by worn or

degraded parts.

3. Leakage (20 failure records)

Only 10 of the 20 failure records listing leakage as the failure type

identified a probable cause of failure. Five of the failures were

attributed to worn, degraded, or broken parts; the other five cited

contamination by foreign materials as the root cause.
33

4. Miscellaneous failures (two failure records)

The two failure records included under the miscellaneous-failure

category had probable causes identified. One failure was attributed

to worn or degraded parts, and the other failure resulted from contamination by foreign materials.

6.3 Analysis of Failure Data

With no failure cause provided for 91 (44%) of the 206 failure

records, conclusions with respect to predominant failure causes and failure mechanisms must be drawn with care. Note that 50% of the failures

(103) can be attributed to 4 specific failure causes: worn or degraded

parts, contamination by foreign materials, short circuit in the SOV coil,

and open circuits in the SOV coils. Forty-eight failures were coil related and accounted for -50% of the failures with specific reported failure causes. Degraded parts and short-circuited or open-circuited coils

may be the result of aging influences and, therefore, are not readily

controllable; the contamination by foreign materials, however, is the

result of external influences that can be controlled during system setup

and operation.

Review of the failure data from a probabilistic viewpoint sheds further light on the failures of SOVs in plant service. Assuming a population of roughly 1000 SOVs per operating power plant and 63 nuclear power

plants in commercial operation before January 1, 1979* (and in operation

during the period covered by the NPRDS and LER failure data), a failure

probability of 7 x 10-8 failures per plant hour can be calculated.

Because it is known that all SOV failures are not reported under the LER

system, a higher failure rate is expected. Although the failure rate

does not appear to be high, a potential for improvement is evident by

analysis of the specific failure causes identified previously.

The periodic maintenance required by the environmental qualification

programs for SOVs also plays a role in limiting the potential for failures as a result of long-term aging effects because the service life for

coils and elastomeric components is generally limited to <10 years (often

5 years or less) before replacement. In general, failure of a single SOV

will not cause an immediate safety problem. For example, containment

isolation systems have two valves in series on each penetration. Failure

of one valve's control SOV will not prevent isolation. However, the

failure could cause an immediate operational problem, resulting in an

automatic shutdown. For example, failure of the coil of a normally energized SOV could cause a process line used during operation to be isolated

(the valve is driven to the fail-safe state). Such operational upsets,

although not causing immediate safety concerns, are undesirable and could

cause unwanted reactor protection system challenges and unwanted reactor

thermal cycles.

*Nuclear News "World List of Nuclear Power Plants," 28(10), 193-212

American Nuclear Society, LaGrange Park, Ill., August 1985.
34

7. FAILURE MODES AND CAUSE ANALYSES

For this study, the SOV boundary was defined to include the valve

body, solenoid enclosure and internals, and seals. Electrical leads

supplying power to the SOV were considered to be outside the boundary;

however, where terminal blocks and ac-to-dc power-conversion diodes were

located within the solenoid enclosure, they were considered to be within

the boundary.

7.1 Information Sources

The analysis of the SOV failure modes and causes was conducted by

Franklin Research Center (FRC) by using various sources. Failure data

were compiled by review of the NPRDS and LER data bases and compared with

probable failure causes. The probable failure causes were determined by

a review of SOV manufacturer technical literature on SOV construction and

by review of instruction and maintenance bulletins. FRC's experience

with performing failure analyses of SOVs and extensive experience in

equipment qualification testing of SOVs were also considered.

7.2 SOV Failure Modes

From information sources, it was found that the failure modes for

SOVs could be grouped into four generic classifications: (1) failure to

operate (i.e., upon application or removal of a control signal, the SOV

provided no response), (2) failure to operate as required (i.e., upon

application or removal of a control signal, the SOV responded improperly,

such as failing to completely change state, continuous chattering of the

SOV, or simultaneous opening of all SOV ports), (3) seat leakage (i.e.,

the process medium flows through the SOV even though the process port

should be isolated), and (4) body leakage (i.e., leakage of the process

medium past valve body seals to the environment).

7.3 Valve Failure Cause Analysis

Each of the major SOV constructions discussed earlier in the report

was analyzed on a component-by-component basis to identify any potential

failure cause, the failure mechanism responsible for the resulting

failure, and the net result of the failure on operation of the SOV. The

results of this analysis are provided in Tables 3-7, which show that all

potential failure causes have been addressed regardless of the probability of occurrence. To place the failure cause analysis in a more realistic perspective, the postulated failure causes may be compared with the

actual failure data reported in the NPRDS and LER data bases.
Table 3. ASCO direct-acting, three-way solenoid valve

Failure mode Component Failure cause Failure mechanism Effects on device

Failure to Coila Coil conductor Conductor burnout Solenoid armature travels

operate fails open to, or remains in, the

deenergized position

Coil short Insulation failure Open circuit will eventually

result, or protective fuse

of interrupter will open

Core Binding of core Contaminants between core Partial or complete inability

guide tube and guide tube to change position

Disc holder b Valve disc adheres Degradation of elastomers Inability to change state

assembly seat to orifice because of temperature (valve seat remains in

or contaminants energized position)

Failure to Disc holder Spring relaxation Defect in spring material All three valve ports open

operate as spring or failure or corrosion from simultaneously when

required contaminants energized

Seat leakage Core spring Spring failure Defect in spring material Inability to close upperor corrosion from valve orifice when valve

contaminants is deenergized

Disc holder Seat degradation Aging of elastomers or Valve operable but leakage

assembly seatb damage caused by contami- present

nants' overtemperature

aUnder accident conditions, the coil deterioration rate may increase because of higher ambient

temperatures, and water and contaminants may enter if coil-housing seal failure occurs.

bAdditional seals and gaskets of organic materials are used on ASCO solenoid valves; however, they

are used as static seals, and failure would result in external leakage only.

en
Table 4. ASCO pilot-controlled, three-way solenoid valvea

Failure mode Componentb

Failure to CoilC

operate

Failure to

operate as

required

Seat leakage

Core

Disc holder

assembly seatb

Disc holder spring

Pressure diaphragm

bleed hole

Exhaust diaphragm

bleed hole

Core spring

Disc holder

assembly seat

Pressure diaphragm

seat

Pressure diaphragm

Failure cause

Coil conductor

fails open

Coil short

Binding of core in

guide tube

Valve disc adheres

to orifice

Spring relaxation

or failure

Foreign material

Foreign material

Spring failure

Seat degradation

Leakage through

exhaust port

Continuous exhaust

Failure mechanism

Conductor burnout

Insulation failure

Contaminants between core

and guide tube

Degradation of elastomers because

of temperature or contaminants

Defect in spring material or

corrosion from contaminants

Blocked bleed hole

Blocked bleed hole

Defect in spring material or

corrosion from contaminants

Aging of elastomers or damage caused

by contaminants' overtemperature

Irregularity or degradation of seat

elastomers because of temperature

or contaminants

Diaphragm failure (puncture or

degradation)

Diaphragm failure (puncture or

degradation

Effects on device

Solenoid armature travels to, or remains

in, the deenergized position

Open circuit will eventually result, or

protective fuse of interrupter will open

Partial or complete inability to change

position

Inability to change state (valve seat

remains in energized position)

All three valve ports open simultaneously

when energized

Device operable but exhibits slow

response

Device will be inoperable

Inability to close upper-valve oritice

when valve is deenergized

Valve operable but leakage present

Device is operable, but leakage rate

is high

Diaphragm seat will not close on

application of pilot pressure

Device will not change process flow path

when electrical state of coil changes

I..

ON

Exhaust diaphragm Leakage through

exhaust port

aThis type of valve uses a direct-operating SOV body to provide pilot pressure to diaphragm-operated valves.

bAdditional seals and gaskets of organic materials are used on ASCO solenoid valves; however, they are used as static seals,

and failure would result in external leakage only.

CUnder accident conditions, the coil degradation rate may increase because of higher ambient temperatures, and water and

contaminants may enter if coil-housing seal failure occurs.

.- V!I
Table 5. Valcor direct-acting, two-way solenoid valve

Failure mode Component Failure cause Failure mechanism Effects on device

Failure to

operate

Coil Coil conductor

fails open

Conductor burnout Solenoid armature travels

to, or remains in, the

deenergized position

Coil short Insulation failure Open circuit will

eventually result, or

protective fuse or

interrupter will open

Plunger spring Binding of plunger

in guide tube

Contaminants between

plunger and guide tube

No operation

W4D

Spring breakage Defect in material or

corrosion from

contaminants

May not close when

deenergized process may

lift plunger

Failure to

operate as

required

Plunger Binding of plunger

in guide tube

Contaminants between

plunger and guide tube

Sluggish or no operation

Seat leakage Poppet seat

material

Elastomer poppet

seat deteriorates

Aging, erosion, or

damage from contaminants or temperature

of elastomeric seat

material

Process through leakage or

loss of tight shutoff
Table 6. Valcor pilot-operated direct-lift, two-way solenoid valve

Failure mode Component Failure cause Failure mechanism Effects on device

Failure to Coil Coil conductor Conductor burnout Solenoid armature travels to, or

operate fails open remains in, the deenergized

position

Coil short Insulation failure Open circuit will eventually

result, or protective fuse or

interrupter will open

Plunger spring Binding of plunger Contaminants between No operation

in guide tube plunger and guide tube

Spring breakage Defect in material or corro- May not close when deenergized

sion from contaminants process may lift plunger

Pilot spring Spring failure Material defect or corrosion Pilot port does not close

from contamination or deenergize

Failure to Plunger Binding of plunger Contaminants between Sluggish or no operation

operate as in guide tube plunger and guide tube

required

Pilot spring Spring failure Material defect or corrosion Slow closure of pilot port

from contaminants

Position reed Contact wearout Contact failure No position indication for

one valve position

Contact failure Arcing or insulation failure Constant position indication

Seat leakage Poppet seat Elastomer poppet Aging, erosion, or damage Process through leakage or

material seat degradation from contaminants or loss of tight shutoff

temperature of elastomeric

seat material

Pilot seat seal Elastomeric pilot Aging of elastomers, erosion, Process medium through

seat degradation or damage from contaminants leakage or loss of tight

or temperature shutoff

,,
I

Failure mode

Failure to

operate

Failure to

operate as

required

Component

Coil

Coil diode

Movable core

Pilot disc

seats

Main disc

Position switch

Table 7.

Failure cause

Coil conductor

fails open

Coil short

Diode failure

(open circuit)

Binding of core

core tube

Seat damage

Jammed disc

Reed failure

TRC pilot-operated, two-way solenoid val

Failure mechanism

Overheating of insulation or

voltage surges

Insulation failure

Conductor burnout

in Contaminants between core and

guide tube

Degradation of elastomers because

of aging or damage from contaminants or overtemperature

Contaminants between disc and

valve body

Contact wearout

Effects on device

Valve fails closed

Open circuit in coil will eventually

result if protective fuse or

interrupter does not open

Valve fails closed

Valve inoperable

Pilot will not fully close

Valve inoperable

Loss of position indication

Position relay

Seat leakage Return spring

Internal Main disc seat

Contact failure

Coil conductor

fails open

Coil short

Spring breakage

Seat degradation

Arcing or insulation failure

Conductor burnout

Insulation failure

Defect in spring material or corrosion from contaminants

Aging and extrusion of seat edges

Loss of position indication

Failure to change position

indication

Failure to change position

indication

Pilot disc will not close main disc;

remains open when deenergized

Loss of tight shutoff
40

With respect to the actual failure data reported in Chap. 6 and in

Tables 3-7, four failure causes have the highest probability of occurrence and the greatest impact on operability of an SOV: (1) coil open

circuit, (2) coil short circuit, (3) worn or degraded parts, and

(4) foreign material contamination.

The first two failure causes (coil open circuit and coil short

circuit) can result from aging mechanisms (discussed in Chap. 4) and have

the greatest impact on operability because these failure causes normally

render an SOV inoperable. Worn, degraded, or broken parts may also render an SOV inoperable although the net result on operation may be limited

either to hesitation in operating or to leakage. Foreign material contamination may affect operation of the SOV in many different forms and

could include anything from hesitation of the SOV to inability to return

to its fail-safe position.
41

8. TESTING AND MAINTENANCE REQUIREMENTS

The ASCO, Valcor, and TRC operations and maintenance instructions

were reviewed for testing, maintenance, and surveillance requirements.

Although each of the manufacturers recommends periodic inspection and

operability checks of the SOVs, no specific maintenance or testing is

required. However, each of the manufacturers requires periodic replacement of certain components for SOVs used in safety-related applications.

The replacement period is based on lifetime limits from the environmental

qualification programs. In conversations with maintenance personnel

during the last few years, the authors have found that, in most instances,

the entire SOV is replaced at the end of its qualified life because of

the cost and difficulty in replacing subcomponents. Because SOVs are not

high-cost items, the cost of stocking and replacing parts and subcomponents, coupled with strict quality and control requirements, can easily

exceed the cost of replacing the entire unit.

A review of the Standard Technical Specifications for light-water

reactors1 5 '18 did not reveal any specific requirements for periodic surveillance or testing of SOVs. Most SOVs are used as control devices on

larger pneumatically or hydraulically actuated valves and dampers, some

governed by surveillance requirements. Therefore, the SOVs are operated

periodically during the tests of main valves and dampers. However, in

general, only gross failure of the SOV would be detected because these

tests are aimed at the performance of the large valve, not the SOV

control.

Surveillance requirements for the BWR control rod drive system17 do

state that the insertion times of the control rods are to be timed using

deenergization of scram pilot valve solenoids as time zero. Performance

of this type of surveillance test may identify slow operation of the SOVs

if they operate significantly slower than normal.

SOVs operating in a degraded condition may sometimes be detected by

observation. High seat leakage, humming of the solenoid coil, or chattering of the solenoid core can often be noticed by personnel in close

proximity.
42

9. AGING AND SERVICE WEAR MONITORING AND ASSESSMENT

Several techniques and methods have potential for providing a means

for monitoring the aging and service wear of SOVs. These methods are

based on current maintenance practices, plant experience, manufacturers'

product information, and material obtained during this study.

9.1 Failure Mode and Cause Determination

Failure detection methods do not appear to be in use. Current

technical specifications do not require periodic testing of SOVs but do

specifically require exercising of devices actuated by SOVs. Testing of

SOV-actuated equipment normally entails cycling of the equipment by

application or removal of control power to the SOV. The actuated equipment may be monitored for position changes locally or remotely through

visual status indications or variations in process parameters (e.g.,

flow). Although no direct indication of the SOV operability is provided,

performance of the SOV is indirectly monitored through observation of the

actuated device. Because only indirect monitoring methods are in use,

other methods for evaluation of measurable parameters directly related to

SOV function and operability are described even though they are not presently used. The measurable parameters have also been chosen to specifically address the predominant failure causes identified in Chaps. 6 and 7

of this study.

Tables &-10 address general means for identification of failure

causes during inspection of SOVs and general design features for most

SOVs in service.

Review of the LER failure data for SOVs indicated that failure to

operate is the most predominant failure mode for an SOV. Causes for this

mode may include open-circuited or short-circuited coils, as well as

binding from contamination by foreign or internally generated materials.

As evidenced by the high number of failures having unspecified

causes (44% NPRDS, 48% LER), a reliable procedure for identifying failure

causes is required. Tables 8-10 identify some methods for isolating SOV

failure causes. Despite these methods, postservice examination through

teardown is the principal means for identification of failure causes.

The inaccessibility of many SOVs in service and difficulties with transportability of required test equipment may contribute to the postservice

examination's being the most practical means of identifying failure

causes.

Visual inspection of SOV components during teardown and refurbishment can provide useful data if the findings of the inspections are

documented and applied to other SOVs in similar service conditions at a

plant. In addition, periodic inspection of SOVs on a sampling basis can

provide information for degradation trending.
Table 8. Method for identifying failure causes - ASCO

direct-acting, three-way solenoid valve

Failure mode Component Failure cause Methods for identification

Failure to Coil Coil conductor Measurement of hot and cold coil resistance

operate fails open

Coil short Measurement of hot and cold coil resistance,

measurement of inrush and holding current

Core Binding of core in Measurement of coil inrush current,

guide tube measurement of exhaust time, inspection

during maintenance

Disc holder Valve disc adheres Measurement of flows through valve, visual

assembly seat to orifice examination, inspection during maintenance

Failure to Disc holder Spring relaxation Measurement of flows through valve,

operate as spring or failure inspection during maintenance

required

Seat leakage Core spring Spring failure Measurement of flows through valve,

inspection during maintenance

Disc holder Seat degradation Measurement of valve-flow coefficient,

assembly seat inspection during maintenance

w.)
46

9.2 Measurable Parameters for Establishing Degradation Trends

Several measurable parameters identified as being of potential value

in a degradation-trending and predictive-failure program are considered

in this section. In particular, the parameters of coil resistance, coil

inrush current, stroke or exhaust time, and leakage rate can be significant in the development of capabilities in the aging and service-wear

assessment of SOVs. Tables 11-13 summarize the measurable parameters and

the related failure causes. Although appearance is a qualitative parameter, the information obtained through a visual examination of SOV components can provide data for rough degradation trending and for determining

aging and service-related wear. By correlating component condition with

SOV performance, a criterion for acceptance and rejection can be developed to enhance preventive maintenance procedures.

A summary of SOV component failure mechanisms is presented in Table

14. The table documents basic relationships among component, materials,

stressors, failure mechanisms, and measurable parameters.

9.3 Potential Monitoring Techniques

A computerized data search was conducted to identify publications

pertinent to this program. The National Technical Information Center

(NTIC) engineering data base and the Dialog Information Services, Inc.,

data bases were searched. Of the articles and publications reviewed from

these data bases, no information was found relating to condition monitoring methods or techniques for SOVs. Reference 19 does, however, provide

information on SOV design parameters and was considered during identification of potential monitoring techniques.

Several methods potentially useful for condition monitoring have

been identified by FRC for consideration and are briefly discussed here:

1. Measurement of seat leakage

Seat leakage measurements are limited in value for condition monitoring purposes because they only provide information relative to the

condition of the SOV seats. A simple method of evaluating seat leakage would appear most practical for nuclear power plant use. This

method employs a short piece of flexible tubing, a graduated cylinder,

and a bucket of water. The tube is connected to the exhaust port of

an SOV, the graduated cylinder is filled with water and inverted in

the bucket of water, and the free end of the flexible tubing is

inserted in the graduated cylinder. By recording the displacement of

water in the graduated cylinder over a fixed period, a leakage rate

may be calculated for the SOV. This method may be undesirable because of the inaccessibility of many SOVs and the limitations and

restrictions on transporting water through controlled access or contaminated areas.
Table 11. Measurable parameters - ASCO direct-acting, three-way solenoid valve

Failure mode Component Failure cause Measurable parameters

Failure to Coil Coil conductor Coil resistance

operate fails open

Coil short Coil resistance, measurement of current

Core Binding of core Inrush current, exhaust time, appearance

in guide tube

Disc holder Valve disc adheres Flow, appearance X

assembly seat to orifice

Failure to Disc holder Spring relaxation Flow, leakage rate, appearance

operate as spring or failure

required

Seat leakage Core spring Spring failure Flow, leakage rate, appearance

Disc holder Seat degradation Leakage rate, appearance

assembly seat
Table 12. Measurable parameters - ASCO pilot-controlled, three-way solenoid valve

Failure mode

Failure to

operate

Failure to

operate as

required

Seat leakage

Component

Coil

Core

Disc holder

assembly seat

Disc holder

spring

Pressure diaphragm

bleed hole

Exhaust diaphragm

bleed hole

Core spring

Disc holder

assembly seat

Pressure diaphragm

seat

Pressure diaphragm

Exhaust diaphragm

Failure cause

Coil conductor fails open

Coil short

Binding of core in guide tube

Valve disc adheres to

orifice

Spring relaxation or failure

Foreign material

Foreign material

Spring failure

Seat degradation

Leakage through exhaust port

Continuous exhaust

Leakage through exhaust port

Measurable parameters

Coil resistance

Coil resistance, measurement of current

Coil current, exhaust time, appearance

Flow, appearance

Flow, leakage rate, appearance

Stroke time, appearance

Appearance

Flow, leakage

Leakage rate,

rate, appearance

appearance

Leakage rate, appearance, stroke time

Leakage rate,

Leakage rate,

dimensions, appearance

dimensions, appearance

.. ..
Table 13. Measurable parameters - TRC pilot-operated, two-way solenoid valve

Failure mode

Fail to

operate

Component

Coil assembly

Failure cause

Coil conductor fails open

Measurable parameters

Coil resistance

Coil short

Coil diode bridge

Movable core

Pilot disc seats

Main disc

Position switch

Diode failure (open circuit)

Diode short

Binding of core in core tube

Seat damage

Jammed disc

Reed failure

Coil resistance, measurement of coil

current

Diode resistance

Diode resistance, measurement of current

Inrush current, stroke, or exhaust time

Stroke time, appearance, leakage rate

Stroke time, appearance, leakage rate

Failure to Appearance, resistance

operate as

required

Position relay

Seat leakage Return spring

Internal Main disc seat

leakage

Contact failure

Coil conductor fails open

Coil short

Spring breakage

Seat degradation

Appearance, resistance

Coil resistance

Coil resistance, measurement of coil

current

Leakage rate, appearance, dimensions

Leakage rate, appearance, dimensions
Table 14. Summary of valve part failure assessment

Component Material Significant stresses and failure mechanisms Measurable parameters

Coil Copper (conductor) Electrical: arcing Coil resistance

Varnish (insulator) Thermal : insulation deterioration

Seat Elastomer Mechanical: compression set, wear, aging Leakage rate, dimensions

distortion

Chemical : erosion

Thermal : softening

Spring Stainless steel Mechanical: loosening, breakage Leakage rate, appearance

Chemical : corrosion

Core Mechanical: wear Stroke time, dimensions,

appearance

Diaphragm Elastomer Mechanical: rupture, wear, aging Leakage rate, stroke

Chemical : erosion time, dimension,

Thermal : softening appearance

Position Copper Mechanical: wear, fracture Appearance, resistance

switch Electrical: arcing

(reed) Chemical : corrosion

U, (-

i
51

2. SOV flow coefficient, CV, measurement

Measurement of the differential pressure across the seat of an SOV

and the flow downstream can provide information on the seat condition

by calculation of Cv obtainable at system operating conditions vs the

manufacturer's specified value. The Cv of the valve is calculated

from Cv = Q/(Ap)1I2, where Q = flow rate in gallons per minute and Ap

is equal to the differential pressure across the valve.20 The Cv

should be constant. This technique is of limited use in evaluating

the overall condition of the SOV because it only provides information

on the condition of the valve seat. Although trends of results from

this measurement over time may provide information with a predictive

value, a single fragment of material (contamination) lodging in or

damaging the seat could change the Cv sharply.

From a practical standpoint, the SOV Cv measurement is difficult to

perform because process connections must be disconnected to allow

installation of test equipment. As an example, the SOVs shown in

Fig. 4 would be most difficult to subject to this type of testing.

As with the seat leakage tests, accessibility would limit use of this

test method.

3. Hot and cold coil resistance tests

Measurement of the solenoid coil resistance at hot and cold temperatures may provide useful information with respect to the condition

of the coil. These tests can show turn-to-turn shorting through

decreases in measured values or weakening of the conductor that will

lead to an open circuit when the measured value increases.

Resistance value trends may indicate substantial changes in the

resistance over time, demonstrating gradual coil breakdown. Coil

resistance measurements must be compensated for the temperature of

the coil because the coil resistance is proportional to temperature.

Limitations of coil resistance testing include accessibility of the

solenoid coil leads. Most safety-related SOV coil leads are spliced

and covered by heat-shrink tubing for applications inside containment. Removal of the splices and reconnection of the leads and other

coil sealing devices are undesirable from an equipment qualification

standpoint. Lifting of solenoid coil leads at a termination cabinet

outside of containment would require inclusion of the control cable

in the resistance measurements and would, thus, introduce a greater

margin for error. The resistance measurements provide partial information that relates only to the solenoid coil.

4. Inrush current and holding current measurements

Measurement of the inrush current on ac coils can provide information

on both the solenoid coil and on the valve transfer mechanism (when

combined with other tests). Increasing levels of inrush current over

time could be indicative of coil shorts or binding of the solenoid

plunger. Measured values of holding currents in both ac and dc

solenoid coils can be used to provide indications of the condition of

the coil insulation system. In addition, Idaho National Engineering

Laboratory (INEL) has performed some preliminary studies with time-
52

domain frequency analysis to determine whether the inrush current

changed over the life of the SOV. INEL found that the SOV degradation may be indicated through this test method. Although no

published information has been identified describing these tests,

further development of this methodology may provide a means for monitoring SOV degradation.

5. Infrared temperature detection

Infrared temperature monitoring of SOV coils is a promising means of

detecting solenoid coil degradation over time. By placing an infrared probe within a few inches of the solenoid coil, the temperature

of the coil can be measured. Because the operating temperature of

the coil is directly proportional to the electrical parameters of the

coil, this measurement (when compensated for ambient temperature)

gives an indication of the degradation of the solenoid coil insulation through evidence of higher operating temperatures. Higher

operating temperatures would be indicative of turn-to-turn or layerto-layer shorts in the coil winding because these conditions would

result in additional current being drawn by the coil and, thus, in

higher operating temperatures. The principal limitation to this

method is the present lack of data correlating coil operating

temperature to condition of the coil. The data necessary could be

developed empirically through long-term testing of several coil

types. All valves connected to the same dc voltage source found to

be operating at higher than normal would be the result of higher

battery voltage during special charging conditions.

6. Exhaust timing tests

SOV exhaust timing tests can be used to provide an indication of the

condition of many of the SOV components (excluding the SOV coil).

Data trends from these tests can be used to detect degradation of the

elastomeric seats and buildup of friction forces in the solenoid

plunger. The apparatus required for exhaust timing tests can be

relatively simple and portable (such as a dual trace oscilloscope),

and the test can be performed quickly. Baseline data before service

would generally be required, but some SOV manufacturers do have

specifications on exhaust timing.

The present state of the art does not offer any one methodology for

complete condition monitoring of SOVs. Guidelines for interpretation of

the test results, as well as baseline data, need to be developed for

proper use of the methods described. Presently, it appears that multiplecondition monitoring techniques would be required to assess the condition

of the solenoid coil and the other components of the SOV. Additional

research is required to develop the methods and the corrective action

criteria for condition monitoring of SOVs. Presently, failure evaluation

results may be the most significant source of information regarding agerelated deterioration with respect to the overall population of SOVs of a

particular type in a particular application.
53

10. CONCLUSIONS

Performance of this study has led to several conclusions regarding

detection of defects and deterioration monitoring for SOVs used in

nuclear power plant safety-related applications:

1. The reported incidence of SOV failure in safety-related applications

has been reasonably low (Sect. 6.3).

2. The most prevalent causes of SOV failure have been open-circuited

coils, short-circuited coils, worn or degraded mechanical parts, and

foreign material contamination.

3. Review of technical literature did not reveal any degradationmonitoring techniques, either in use or under development, that are

oriented specifically to SOVs. However, several potentially useful

methods were identified in this study.

4. SOV failures caused by air system contamination and high dc voltages

result from stressors that need to be addressed at the system level

rather than at the component (SOV) level.

5. Emphasis should be placed on development of degradation-monitoring

techniques for the solenoid coil.

6. Considering the large number of SOVs used in nuclear power plants and

the low incidence of failure, degradation monitoring on a sampling

basis should be considered.

7. The periodic replacement of elastomers and solenoid coils to maintain

environmental qualification of safety-related SOVs aids in minimizing

the incidence of SOV failure.

8. Because of the importance of SOVs in controlling equipment - such as

control rod drives (BWR) and isolation valves (BWR and PWR) - SOV

failures can initiate unwanted challenges to plant safety systems and

be responsible for unanticipated transients. Development of a

methodology for detection of incipient failures will reduce the frequency of these challenges and enhance plant safety and operability.
54

11. RECOMMENDATIONS

Review of the present deterioration-monitoring technology, the

failure records from SOVs in service, and potential monitoring techniques

indicates that the development of acceptable monitoring techniques would

provide advance notice of SOV failures. Specific efforts should be

directed to the following areas:

1. research and development to devise test methods suitable for evaluation of the electrical and mechanical portions of SOVs;

2. testing of the proposed monitoring techniques with new and used SOVs

to evaluate the suitability, cost effectiveness, and practicality of

the techniques;

3. testing with new and used SOVs to determine baseline monitoring data

and correlation of data to develop predictive models and acceptance

criteria;

4. site visits to operating nuclear power plants to gain further insights

into utility operating experience, testing capabilities, and general

accessibility and in situ maintainability of SOVs; and

5. evaluation of SOV failures for basic causes at operating power plants

to ensure that pertinent failure causes and mechanisms are not overlooked.

I
55

REFERENCES

1. Nuclear Plant Aging Research (NPAR) Program Plan, U.S. Nuclear

Regulatory Commission, July 1985.

2. D. V. Paulson, T. A. Shook, V. P. Bacanskas, and S. P. Carfagno,

Test Program and Failure Analysis of Class lE Solenoid Valves,

NUREG-CR-3424, U.S. Nuclear Regulatory Commission, Franklin Research

Center, November 1983.

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Solenoid Valves, Series V70900-21, OMM 70900-21, rev. B, Valcor

Engineering Corp., Springfield, N.J., February 1982.

4. Operation and Maintenance Manual for Solenoid Valves, OMM 20010 BSC,

issue F, Valcor Engineering Corp., Springfield, N.J., October 1984.

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Pilot Assisted, issue B, Valcor Engineering Corp., Springfield,

N.J., April 1983.

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Corp., Farmingdale, N.Y., October 1984.

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Corporation, IE Bul. No. 80-23, U.S. Nuclear Regulatory Commission,

November 1980

8. Applied Protective Relaying, Westinghouse Electric Corp., 1976.

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Nuclear Regulatory Commission, June 1985.

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Engineering, December 1977.

11. The Effect of Thermal and Irradiation Aging Simulation Procedure on

Polymer Properties, NUREG/CR-3629, Sandia National Laboratories,

U.S. Nuclear Regulatory Commission, April 1984.

12. L. Schrader, Troubleshooting Pneumatic Directional-Control Valves,

Vol. 34, No. 5, Plant Engineering, March 6, 1980.

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Fire Protection Systems, IE Information Notice No. 80-11, U.S.

Nuclear Regulatory Commission, March 1980.

14. Failure 17-7 PH Stainless Steel Springs in Valcor Valves Due to

Hydrogen Embrittlement, IE Information Notice 86-72, U.S. Nuclear

Regulatory Commission, August 19, 1986.
56

15. Standard Technical Specifications for Westinghouse Pressurized Water

Reactors, NUREG-0452, rev. 4, U.S. Nuclear Regulatory Commission,

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16. Standard Technical Specifications for Babcock and WiZcox Pressurized

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No. 410, Crane Company, Chicago, Ill., 1957.
57

NUREG/CR-4819

Volume 1

ORNL/Sub/83-28915/4/Vl

Dist. Category RV

Internal Distribution

1. W. G. Craddick 19. A. P. Malinauskas

2-8. D. M. Eissenberg 20. G. A. Murphy

9. J. A. Getsi 21. H. E. Trammell

10-14. W. L. Greenstreet 22. ORNL Patent Office

15. H. D. Haynes 23. Central Research Library

16. D. E. Hendrix 24. Document Reference Section

17. A. D. Kimmins 25-26. Laboratory Records Department

18. R. C. Kryter 27. Laboratory Records (RC)

External Distribution

28. V. P. Bacanskas, Franklin Research Center, 20th & Race Streets,

Philadelphia, PA 19103

29. T. Campbell, Institute for Nuclear Power Operations, 1100 Circle

75 Parkway, Suite 1500, Atlanta, GA 30339

30-34. S. P. Carfagno, Franklin Research Center, 20th & Race Streets,

Philadelphia, PA 19103

35. W. S. Farmer, Division of Engineering Technology, Office of

Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission,

5650 Nicholson Lane, Rockville, MD 20852

36. A. B. Johnson, Pacific Northwest Laboratory, P.O. Box 999,

Richland, WA 99352

37. P. McDonald, EG&G Idaho, Inc., P.O. Box 1625, WCB-3, Idaho

Falls, ID 83415

38. C. Michelson, ACRS, 20 Argonne Plaza, Suite 365, Oak Ridge, TN

37830

39. J. E. Rhoads, Washington Public Power System, 3000 George

Washington Way, PO Box 968, Richland, WA 99352

40. J. E. Richardson, Division of Engineering Technology, Office of

Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission,

5650 Nicholson Lane, Rockville, MD 20852

41. G. C. Roberts, Franklin Research Center, 20th & Race Streets,

Philadelphia, PA 19103

42. G. Sliter, Electric Power Research Institute, 3412 Hill View

Ave., P.O. Box 10412, Palo Alto, CA 94303

43. D. F. Sullivan, Division of Engineering Technology, Office of

Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission,

5650 Nicholson Lane, Rockville, MD 20852

44. J. H. Taylor, Engineering and Risk Assessment Division, Department of Nuclear Energy, Brookhaven National Laboratory, Upton,

NY 11973
58

45-46. G. J. Toman, Franklin Research Center, 20th & Race Streets,

Philadelphia, PA 19103

47. J. P. Vora, Division of Engineering Technology, Office of

Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission,

5650 Nicholson Lane, Rockville, MD 20852

48. Office of Assistant Manager for Energy Research and Development,

Department of Energy, Oak Ridge Operations Office, Oak Ridge, TN

37831

49-50. Technical Information Center, Department of Energy, Oak Ridge,

TN 37831

51-380. Given distribution as shown in NRC category RV (10-NTIS)

F.
NRC FORM 332 U.S. NUCLEAR REGULATORY COMMISSION I REPORT NUMBER (Assrod bv rODC. add Vol NO. ir anJ

121841 NUREG/CR-4819 320M 1202. BIBLIOGRAPHIC DATA SHEET Volume 1

SEE INSTRUCTIONS ON THE REVERSE ORNL/Sub/83-28915/4/Vl

2. TITLE AND SUBTITLE 3 LEAVE BLANK

Aging and Service Wear of Solenoid Operated Valves

Used in Safety Systems of Nuclear Power Plants.

Vol. 1. Operating Experience and Failure Identification 4 DATE REPORT COMPLETED

MONTH YEAR

5 AUTHOR(S) February 1987

6 DATE REPORT ISSUED

V. P. Bacanskas, G. C. Roberts, and G. J. Toman MONTH YEAR

March 1987

a PERFORMING ORGANIZATION NAME AND MAILING ADDRESS lciudeZro Code) S. PROJECTITASKNVORK UNIT NUMBER

Franklin Research Center

Division of Arvin/Calspan 9 FIN OR GRANT NUMBER

20th and Race Streets

Philadelphia, PA 19103

10. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS fMc1.de Zp Code) 11.. TYPE OF REPORT

Division of Engineering Technology, Office of Nuclear

Regulatory Research, U.S. Nuclear Regulatory Commission,

Washington, DC 20555 - and - b. PERIOD COVERED fI,,cus.- do Ies

Oak Ridge National Laboratory, Nuclear Plant Aging

Program, Oak Ridge, TN 37831 12 SUPPLEMENTARY NOTES

*3 ABSTRACT 1200 ,or, o, !*fl/

An assessment of the types and uses of solenoid operated valves (SOV) in nuclear power

plant safety-related service is provided. Through a description of each SOV's operation, combined with knowledge of nuclear power plant applications and operational

occurrences, the significant stressors responsible for degradation of SOV performance

are identified. A review of actual operating experience (failure data) leads to

identification of potential nondestructive in-situ testing which, if properly developed,

could provide the methodology for deterioration monitoring of SOVs. Recommendations are

provided for continuation of the study into the test methodology development phase.

14 DOCUMENT ANALYSIS - . KEYWORDS.DESCRIPTORS

Aging, degradation, environmental qualification, failure cause, failure

mechanism, failure mode, inspection, maintenance, monitoring, operational

life, operating experience, preventive maintenance, solenoid-operated

valves, stressors, surveillance, testing, trend.

0 IDENTIFIERS OPEN ENOED TERMS

15 AVAILABILITY

STATEMENT

Unlimited

16 SECURITYCLASSIFICATION

Art, oage!

Unclassified

ArT,, 'coorJ

Unclassified

I? NUMBER OF PAGES

id PRICE

*tU.S. GOVERNMENT PRINTING OFFICE 1987-748-168/40117