ML18036A165

Guidelines for Demonstration of Operability of Deep Draft Pumps

ML18036A165
Person / Time
Site:	Comanche Peak
Issue date:	08/24/1981
From:	NRC
To:
Shared Package
ML18036A167	List: ML18036A165 ML20005B782
References
IEB-79-15, NUDOCS 8109020183
Download: ML18036A165 (19)

Text

ENCLOSURE

~

GUIDELINES FOR DEYiOMSTRATIOM OF OPERABILITY OF DEEP DRAFT PUHPS DISCUSSIOH I.E.Bulletin 79-15 dated July 1979, identified problems associated with deep-draft pumps found at operating facilities and near term operating licensee facilities.

Deep draft pumps, which are also called "vertical turbine pumps," are usually 30 to 60 feet in length with impellers located in casing bowels at the lowest elevation.of the pump.

The motor tdriver) is located at the highest pump elevation with the discharge nozzle just below the motor.

Bulletin 79-15 was initiated because several nuclear power plant facilities could not demonstrate operability of their pumps.

The pumps were experiencing excessive vibration and bearing wear.

The rapid bearing wear suggested that these pumps could not perform their required functions during or following an accident.

As a result of the staff's initial revie~ of the responses to IEB 79-15,.

several plants were identified as having potential problems with their deep draft pumps.

These guidelines are provided for these plants'so that the licensee or applicant involved may" have a method acceptable to the staff for demonstrating the operability of deep-draft pumps.

GUIDELINES FOR DEHOMSTRATION OF OPERABILITY OF DEEP DRAFT PUHPS DISCUSSION I.E.Bulletin 79-15 dated July 1979, identified problems associated with deep-draft pumps found at operating facilities and near term operating licensee facilities.

Deep draft pumps, which are also called "vertical turbine pumps," are usually 30 to 60 feet in length with impellers located in casing bowls at the lowest elevation of the pump.

The motor (driver) is located at the, highest pump elevation with the discharge nozzle fust below the motor.

Bulletin 79-15 was initiated because several nuclear power plant facilities could not demonstrate operability of their pumps.

The pumps were experiencing excessive vibration and bearing wear.

The rapid bearing wear suggested that these pumps could not perform their required functions during or following an accident.

As a result of the staff's initial review of the responses to IEB 79-15,.

several plants were identified as having potential problems with their deep draft pumps.

These guidelines are provided for these plants so that the licensee or applicant involved may have a method r

acceptable to the staff for demonstrating the operability of deep-draft pumps.

DEEP DRAFT PUMP OPERATING CHARACTERISTICS In order to better understand the operating characteristics of 1

these pumps, a rotor Qnamics analyses was performed to ascertain the response of the pump rotor under steady state operation.

The analyses considered journal'earing to shaft Qnamic response at various eccentricities and fluid viscosities.

The model for the analysis depicted a typical deep draft pump utilized by the nuclear industry.

The analysis resulted in recomnendations for improving the stability of the pump rotor from externally applied inputs and by self-generated inputs; The conclusions which were derived from the analysis and staff evaluations of North Anna, Beaver Yalley and Surry facilities with similar pumps include:

1.)

Pumps with this type of configuration are prone to bearing whirl vibration problems due to the flexibilityof the rotor and casing structure.

This phenomenon is accentuated as journal bearing clearance becomes large.

This phenomenon leads to bearing wear (Journal bearings).

1 "Low Head Safety Injection Pump Rotor Dynamic Ahalyses",

by Franklin Research

Center, Report

FC4982, dated May 1980.

lt

/

3 2.)

There may be natural frequencies associated with the pump assembly which occur near the operating speed of the pump.

Pump operation will drive these frequencies and can cause 4

bearing wear.

The severity of this condition is dependent on bearing diametral clearance, rotor unbalance conditions and housing flexibility.

As an example, if the wear in column Journal bearings becomes sufficiently large

( twice the original diametral clearance) so that these bearings are no longer active and the undamped critical frequency near the operating speed of the pump

~is allowed to expand, the additional uncontrol-led bearing wear will occur.

This wear can continue until the shaft rubs against the support structure of the bearing and can potentially sever the shaft.

3.)

One acceptable method for correcting instabilities in the pump shaft is to utilize a )ournal bearing design which exhibits stable characteristics.

One such design is the Taper land bearing'.

This design is more stable than tbe plain journal bearing, is less susceptible to wear because of the taper and will cause the bearing to form a hydro-Qnamic film quickly during startup.

4.)

Stiffening of the column sections of the pump is advantageous if there is a column frequency near the operating speed of the pump.

The shifting of the column frequency to a higher level will eliminate any coupling between the pump operating speed and the

. column frequency.

5.)

Flow inlet conditfons to the pumps and sump designs can be important to pump operability.

Certain installations have demonstrated flow characteristics which produced vortexing at the bellmouth of the pump.

This vortexing is due to sump design or sump supply line entrance con-ditions.

This condition can contribute to additional pump vibration and wear.

Flow straightener devic'es, reduction of bellmouth diameters, and bottom clearance reductions have proven to be effective in eliminating this problem.

6.)

This type of pump has exhibited operational problems due to design and installation deficiencies.

The high flexibilityof the shaft and column make this design rather forgiving when it comes to installation deficien-cies such as misalignment between the shaft and column,

low-precision coupling assemblies, and non-perpendfcular mounting flanges.

This fact however, can lead to excessive bearing wear without sfgnfficant noticeable change in pump operating characteristics.

To ensure proper pump operation, proper alignment should be established between all mating surfaces and measures should be emphasized which prevent column and shaft-eccentrfcftfes.

These measures can fnclude optical alignment of the column segments, use of high precision couplings and use of.accurate techniques to establish that the sump plumb line is perpendicular to the pump mounting flange.

The above findings and conclusions have contributed significantly'o the development of these guidelines.

The guidelines listed below are divided into installation and test areas.

The subjects to be addressed in these areas are considered to be of prime

'I importance when establishing a

pump operability assurance program.

The extent to which each of the two areas are implemented at z specific facflity fs dependent on specific symptoms which have been identified with these pumps while in operation and during service periods.

~

~

Impleme'ntfng the measures outlfned below, at North Anna 1

8 2 in total, has been shown to provfde reasonable assurance that the pumps will be operable when required for their'afety function.

These guidelines are not intended to replace the requirements of Standard Review Plan 3.9.3, Regulatory Gufde ).68 or any other requirements presently enforced by the staff.

Rather, the guidelines are to be used as supplementary materfal for establishing deep-draft pump operability.

r GUIDELINES FOR OPERABILITY INSTALLATION 1.0 IHSTALLATIOH PROCEDURES Experfence has shown that'hese pumps are prone to having operabflfty problems as a result of poor installation procedures.

The guidelines emphasize those areas of the installation procedure, which ff implemented, could sfgnfffcantly improve the likelihood of an operable pump.

The procedures utilized should be submitted to the staff for review.

1.1 PUMP INSTALLATION a.

Determine by measurement that all shaft segments are straight wfthfn tolerances specfffed by the manufacturer.

b.

Determine by measurement or provide cert)ffcation that all couplings (for shaft segments 5 pump to motor coupling) are of high precision as specfffed by the manufacturer.

c.

Determine by measurement that all pump segment flanges are perpendicular to the centerline of the segment, that the segments are straight and that any mating surfaces are concentrfc to an established datum.

Mhere )ournal

bearing guides (SPIDERS) are used, establish con-centricity between this assembly and its mating surface.

d.

Align full pump casing assembly optically to assure maximum straightness and concentricity of the assembly.

Any equivalent method is acceptable, as long as the I

procedure stresses column straightness and concentricity.

e.

Assure pump to motor flange perpendicularity and that proper coupling installation is perforrred.

f.

Assure that all mating surface bolting is properly attached and that manufacturer torquing sequences are adhered to.

1.2 SUMP INSTALLATION a.

Assure (where used) that sump/pump mating flange is perpendicular to the sump pump line.

b.

Assure that sump design prevents fluid anomalies such as vortexing or turbulence near the intake to the pump bellmouth and that incoming piping is not so designed as to allow fluid conditions favorable to these anomalies (i.e., sharp bends in piping prior to entrance. into sump).

c.

Assure that interference does not exist between the sump and any pump appendage such as a seismic restraint.

The installation procedures are essential in establishing pump operability.

In addition to careful installation, testing nay be required which will verify proper operation of these pumps.

After corrpletion of the installation checks, licensees or appli-cants should evaluate the need for further testing and report the. results of this evaluation together with the details of any test plans to the staff.

Should tests be required, an acceptable test procedure should include the items listed.tallow.

The staff recognizes that the instrumentation and procedures outlined below may be difficult to implement at a'll facilities and, therefore, the staff is emphasizing good installation practices which lead to operable components-If tests demonstrating operability cannot encompass all the items listed below, then alternative procedures should be proposed for evaluation by the staff.

The tests should emphasize measurement of pump dynamic characteristics and wear data at different stages of testing, culminating with an extrapolation of the data to the desired life goal for the pump.

2.1 Test Instrumentation The following instrumentation should be incorporated into the test procedure aside from normal floe measurement, pressure and Yibration instrumentati on:

a;)

X, Y proximity probes at three axial locations on the pump column, for measuring and recording radial positions of shaft with respect to the column.

b.)

X, Y, accelerometers (at proximity probe locations) for measuring and recording radial accelerations of the column.

c.)

Dynamic pressure transducers for measuring fluid pressure at the following locations:

1.

Bottom of Column (suction) 2.

Mid-Column 3.

Top of Column.

d.)

Shaft Rotational speed and dynamic variation instrument.

2 2 PRE-TEST DATA Mith the pump disassembled, measure all journal bearing O.D.'s, bearing I.D.'s and calculate bearing diametral clearances.

1n addition with pumps fully assembled and.using the proximity probes, obtain the "clearance circle" at each of the three axial stations by rolling the shaft section within the clearance volume of its bearings and in this way, establish proper operation of the probes.

~

~

r 3.l

~PHASE I T tf (6 t pl pl 2 This phase of testing should be comprised of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> of testing tBreak-in) followed by start-stop testing.

Test conditions should simulate as nearly as possible normal and accident conditions.

Parameters to be considered are flow, temperature,

debris, and chemical composition of fluid being pumped.

Static torque tests should be performed before and after the test (i.e. measure amount of torque required to turn shaft by hand).

Data should be taken during the six'hour test at 1/2 hour intervals.

A total of 12 start-stop tests will be performed con-sisting of a start up from zero speed up to full-speed, 10-minute dwell at full-speed and a shutdown from full speed to zero speed, with recording of all instrumentation during full cycle of start-stop.

Upon completion of Phase 1 testing, the following data should be obtained and recorded:

1.)

Obtain the 'clearance circles" using the'three sets of proximity probes.

'ests at North Anna 1

E 2 and tanufacturers input indicates that 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is an adequate time interval for bear'ing "break in" period.

/

2.)

Heasure and record the following dimension for each bearing:

a.)

Journal O.D.

b. )

Bearing I-D.

c.)

Bearing to Journal diametral clearance d.)

Establish Phase 1 test bearing wear.

THE ACCEPTANCE CRITERIA IS AS FOLLOMS:

1.) If wear is) 5 mils for any bearing, wear is unacceptable

'3

~

and test-should be terminated.

2.) If wear is/5 mils for all bearings a.)

Reassemble the pump b.)

Obtain "clearance circles" c.)

Reinsta11 pump in test. loop.-

2.4

~Ph 2T i

t48h Phase 2 testing is to be performed at full system pressure and temperature and fluid conditions simulating those expected during accident and normal operation.

Before start and at cooqletion of Phase 2 test, obtain measurement of static torque.

Data should be recorded continuously during the start-vp period, r

~This acceptable wear value may be tmdified based on manufacturers recomre ndat ion.

and during the shutdown period.

Data should also be recorded at 1-hour time intervals during the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> test.

The following measurements should he made at the completion of Phase 2 of the test:

1.)

Obtain the "clearance circles" using the three sets of proximity probes.

2.)

Heasure and record the following dimensions for each beari ng:

a.)

Journal O.D.

b.)

Bearing I.D.

c.)

Bearing to Journal diametral clearance.

d.)

Establish accuaulated bearing wear.

THE ACCEPTANCE CRITERIA IS AS FOLt OMS:

1.) If accunulated bearing wear on any bearing is 3

P7 mils, wear is unacceptable and test should be termi nated.

2.) If accumulated wear on all bearings is47 mils for all bearings'.

a. )

Reassemble pump b.)

Obtain "clearance circles" I

c-)

Reinstall pump in test loop.

5)

~Ph 3T f

(95t Phase 3 testing fs to be performed at full system pressure and temperature and fluid conditions simulating those expected during accident and normal operation.

The same procedures should be followed as in Phase 2 testing except that data may be taken with less frequency..

The same measurements should be taken at the completion of this phase as wiCh the other phases with the following acceptance criteria:

1.) If accumulated bearing wear is p 8 mils for any bearin r any ear ng, wear is unacceptable and test should be terminated.

2.) If accumulated wear is C 8 mils for all bearings, a

decision needs to be made to establish:

I a.)

the need for additional testing or b.)

whether or not the bearing wear will be acceptably low.

The recommended decision process is outlined below.

Plot the values of accumulated. wear versus time (H) for each bearing after Phase 2 and Phase 3 tests, namely.

Wear at H2 54 hour6.25e-4 days <br />0.015 hours <br />8.928571e-5 weeks <br />2.0547e-5 months <br /> Wear at H3 150 hours0.00174 days <br />0.0417 hours <br />2.480159e-4 weeks <br />5.7075e-5 months <br /> Straight lines are then drawn through the plotted values of wear and extended to the right (See example Figure I). If the extension intercepts the maximum acceptable value of wear (B mils) at a value H less than the life goal for this. pump, additional testing should be performed. If the intercept of the line with wear of 8 mils exceeds the life goal for this pump, no additional testing is required and bearing wear is acceptable.

If additional testing is deemed necessary it should be done in a similar manner to that performed during Phase 3 with similar acceptance criteria and decision process.

It is expected that such additional testing will either show a stable pump operation with no increase

$ n bearing wear or increased bearing wear with unacceptable results.

2.6 Evaluation of Pump Acceptability If bearing wear (after all testing phases) is acceptably low (as per decision process) and if vibration levels over the frequency spectrum of 3 cps to 5000 cps are acceptably low and show no unfavorable trend of increasing magnitude during the testing, the pump may be judged acceptable for its intended use.

~ I

4 V

1e M

A Lu u

S O

ya VeeV>>0

~t Je Vl 00 Ot Vt>>

~

0

~

~

~ ~

~ O

~

~

0

~

~

J

~ O ~

00 ~

~ ~ 0 ~

~ ~

~

~

~

~ ~

~ ~

~ 0

~

I 0

~ ~

O. ~.

~

~

~

~

~ 0 1

~

~ [0

~ g

~\\

~

~ ~

~ ~ ~

~

~

>> 0

~

~ ~t 0 ~ 00

~ ~ ~ ~ >> 0 ~

~ ~ ~

~ ~ ~ ~

~

000 OO

~ 0 0

tt

~ ~I ~

I

~I

~ ~

~ ~

~ ~ ~

I I

I

. ~ I.0

~tt

~ ~

\\ ~ 0

~

I 0

Qp'

~ ~

~

I

~

~ ~

~ 0 ~ t

~ I':

~ ~ ~ 0

"'I("

~

~

~

~

~.'Il

~ 0 0 ~

~ ~ ~

~ \\ ~

~

~

00

~

0 ~

~

~ 0

~ ~ WI

~

~

~

1

,'s I

'.j'l I

~

it.i u lf

~

~

~ ~

I ~

~

~ ~

~ tt

~ I

~ ~

~

0 I

~

~

I

~

I'"

I

~

~ 0 I ~

~

>>0

~ ~

~ ~

~

~

~ ~

~

~ g 0

~

~ '

I

~ 0 I '

~

~ ~

~~g~J

~

0 ~

~

~

~ >>

~

~ I

~

~

I

~ >>

~

~ ~

~ 0

~ ~ ~

~ ~

~

~

~

Q

~

lt<<

~>>

0 N ~ ~

..V t

~ ~

~

0 ~

~ ~

>> ~ 0>>

~ ~

~ ~ 0

~

~

~

~ ~ ~

~ 0 I

~ ~ 1.>>0 I I 0>>OO

~>>

I

~ >>0 ~ ~ 0 ~ I

~

~

0

~ t ~ 0

'I ~

~ ~

~

~ ~ ~

~ ~ ett

~

~

~ ~

~

~

~

~ 0

~

I JJ

~

~

~

~

1

~

~

~

0 ~

~Q

~

~

~

~ ~

~ ~

I 0

~ ~

1'

~

P'

~

I' I

,. I.

0 ~t I

~fO

~

~

~ 0 ~

~ ~ ~

~ ~ 0

~ >> ~ ~ J

~ ~ ~

~ ~ ~

~ ~

~ ~ ~

~

I

~ ~

~

~

00

~

~ ~

~ ~ ~

~

~

~ ~

~

~

~

I

~

~

~

AhSQ'.

Ti sO..

-.<<.l-e

~

I

~

~

I

~

~

~

~ ~ I

~

~ 0

~ ~

~

~ ~

..1...

~ ~ ~

~

~

~ ~ ~

\\

~ ~ ~ ~

~

~ 0

~ ~

~ ~

~

~ 1.

~

~

~

~

0 <<0

~

~ ~ ~

~ 0

~

~

~

I

~

~

~

~

~ \\

\\ ~

~

~

I l.

l I

~0

~ l C

L t

I

~

~

~

I I

~

~ ~

I

~ t

~

I ~

04

~

~ ~

h)g'

~

~

~

~ ~

~ <<

~

~ -

l-.

I;.

I

~ -

I I ~

~

~

~t

-1

'I

~ I yb 3I gtIq I

C

~

~

~

~

~

~

~

.g>

~ 0

~ >>

~ ~ ~ 0

~

~

~

~

~

~

~

QOO.

~ ~

~

~

~ ~

~ >>00

~

~

~

~

it

-iIt

~l I 0 <<00 00 <<>> ~

~ 0

~

I I

~

I I

I m I N>> ~

~ >>I>>

~ ~

~

~ ~ 0

~ ~

~

I 00 0

~

O>>t ~

0

~

~ ~

0 ~ ~

~ 0

~ t<<

~ ~

-1 ~

I

>>0 I ~

~

~ ~

~ ~

0 ~ I

~ ~~,

0 ~

Qt

~

~

~

~ ~

~

~ ~

~

0 j)Pu OI~)g pi'<~

i J

i I

I O.I Ppatp

~>>00 0 ~ 0000<<

Pp~'r PJLO V)JtjJ"

~

~

~

~

~

~

~

~

~

~

~

~

0 0'

~

~

~ I 1 I::

1>>

~ I I

~

~

i l 1:! I;l I

~

~

0

~

~