ML20147E586

Preliminary Study of Vibration Damping in Electrical Conduit

ML20147E586
Person / Time
Site:	Browns Ferry
Issue date:	03/31/1986
From:	March P TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18032A736	List: ML20147E324 ML20147E392 ML20147E415 ML20147E438 ML20147E546 ML20147E560 ML20147E586 ML20147E653
References
WR28-4-900-140, NUDOCS 8803070105
Download: ML20147E586 (32)

Text

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. QA Recerd

/ B41 '860327 002

- Tennessee Valley Authority Office of Natural Resources and Economic Development Di vi si on of Air and Water Resources Engineering Laboratory i .

A PRELIMINARY STUDY OF VIBRATION DAMPING IN ELECTRICAL CONDUIT f

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!O Report No. . WR28-4-900-140 wd ce n

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Im8 Y. Prepared by J

<& Patrick A. March Q

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G Revised March 1986 N'

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.nDu.TR+.T.......................................................

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~~~"INTRODUCTION...................................................I l

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DESCRIFTION 05' TEi:iT F AG 11 1TY-' AND IN5TRUMENTAT1ON..............

1 1

Test Fac111ty............................................

4 Instrumentation...........................................- ,

t TEST PROCEDURES................................................O .

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R a n d o m E:: c i t a t i o n T e s t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E Sine-Decay Tests.......................................... ,

l 7 l

Snapback Tests...........................................

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DATA ANALYSIS.. ............................................... 7 TEST RESULTS.................................................

10  !

Results f r om Ranc om Ex ci tat i on Test.s. . . . . . . . . . . . . . . . . . . . . !O 1

Results for 1.5" Conouit................................ 10 i Results for 0" Conduit.................................. 02 1

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SUMMARY

, CONCLUSIONS. AND RECOMMEND'.TIONE.................... 23 I

l FEFERENCE5..................... ............................. 0c

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.851 sti4C f That r aport prenant s o mpi ng vol t er- d.+ . -e v.; r iod i r ora snuot.*cr enc wine-onc+y teitt a c.

noucted with 1.5" an; ! ut eirl o'a e c t r i c a l I candust. Under a vae,etv ci c cn c t t i e n s. , is r a . v : ; nq, :.orid u s t diameter, ware looding. i n t i. t a l amplituce, MC Jro wnce or absents of ftre barrter m4t, dempi rig ratt os rirged 1 rom 5*'. to OS*;. Inst 021ation deta.ls and subcecuent c.md.?:c hastery ot the electrical conduit were found to heve e si gni f i c arit influence on its natural +requency and damping. Fire barrta- mat provided increased damping for- hori:ontal onc111stscrs c4 1.5" ccnduat and 3" conduit. Typical first evele camping ra*: or for 1.5" concult with f i r ts b ase r t e r mat r an q,e d f r om 20*'. t c 7. E * . .4 cr i ti cal atmping, and typicel first evcle camping rettos for ! c :r'dui t with fire barrier mat ranged fr oro 5 % t o 21 *,; o f cri ti ce i .,amping. The Jire l barrier ciat u.an more of f ective in prov.ct ng in: essec camping for hori:ontal oscillationc comoered te vertical os:ill ati ons.

Increased d araping wi th increased emp11tude :i e.:c:tatton wos Observed for 0" conduit. For 1.5" conduit, cot:ing was not eu clearly 'eleted to the amplitude of e:tc i t ati on . Recommendaticna are mace f or a comprehensive researen program t: evalu..te c+moing in electrical conduit and small piping systems.

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, @g . * - , , r i .% Fe .:,p er oe d.a gn of onclear power p i , n t s a n c. l i. 7 4,i creal..rtng

. fl . l the response tf nuclear olant ny-stenw andicompensn.s to weism.c ,

i Vjr e n e t t a *,i o n . Th rt dynamic responso of a piping or cot.uuit t. w t. air.

M" 1 will be influenced by tne rerpense of the entt i e pi n.t to the ~

7 selbmic encitetton, b) the location of the wystor within tno 4

plant. and by the chbracte. a ct s cu of t hee system. , j

!. The damping, whicn in related to the smount of energy

discipated per vibretter.aJ cycle s i s a p a r t a c ul u r 'A .- importent ., l

} , paeamoter fur estimat.hg the cynamic t'esponse c' & I votth4. j i Ao di t i on al dan. ping in11rtbation derived f r c t;i enpH amem.Al deth is  :

1 necessary for occurate arc reasonable selsmt-e-quel 1 4 tcations.

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! Tnis report presents damping values ceterminao 4 rom Enesdnch

and sine-decay tests conducted with 1.5" anc 0" strel electrical  ;

1 conduit. Perametarc which were tested include concult d i a 1+ t er ,' '

I wire loading, emplituce of encitat1on, anc prouence er absence cf i

fire barrier mat. l

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DESCRIPTION OF TEST FACILITY AND INSTRUMI.NTATION l i -

1 Test Facilitv t 4 i i

A test facility was constructed to repecduce a mounting configuration typicallt encountered in a plant. An eignt incn by  ;

eignt-inch wide flange beam was mountud hort :ent all y anc welced  ;

j on twenty-foct centers to sin-incn by ten-inch verti:al rto+

j support teams. Four-inch Dy icur-inch bon beam sections were [

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4 welced to the bottom of the hori:ontal beam on ten-4 Lot centers, j and se:tions cf P-1 COO Unistrut were welded to the b a beams.  !

The 1.5" steel el e.c t r i c a l concuit was attached with P-O!55-15  ?

4 .

Unistrut clamps, r,ne-ouarter inch dismoter by one in:h long '

i Unastrut bolts, and one-quarter inch Unistrut spri ng nutt. The  !

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0" steel el ec t ri c al concui t was attaened with F *500-;Q Unistrut . I clamps, three-eighths inch diameter by one and sne cuarter.itich l long Unistrut bolts, and three-ei ghths a nch util strut spring nuts.

For both si:es, four. lengths of conduit, each te. 4ee*'Aong. were '

j Jcined with standarc thresced couplings. Assortec wares for i

leading the conduits, electrical conduit sections, Unistrut,

• Unistrut bol ts, Unistrut spring nute, Unistrut :lanns, and l

.. conduit couplings wera suppliec from the warehouse at the Wattu  !

Dar Nuclear Plant construction site. l i

MOCA fire barrier met, manufa:tured by the On Corporation's

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y@ Techn1chl Cor enu c Reccur ce .Depai t ment , wak Bl su 4:bt M nero i r tai tnc Wat t.u E4ar w +rohous*4. Tho 4 tre h crier .n.it we4 sast#atec in ho 'D 5- ' layerc according t o ;M ' :. I nnt e l 14t i on I n n.t.r w t i m ' it 0-CU , wi th five layern for the 1. ".; " cenduit and tour a+, ors for u n o .*. "

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'-'"' Encitation for the natie-decav tentc wer proviced by an e electromagnetic shaker, power amplaiter,.anc signf1 generatot*, as

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• shown in Figure 1. The shaker was suspended f ro.n cable 6 attached "

N to a strut wnich was mounted to a roof su5porf col umn.' -

Encitation for the snapback tests was,proviced by the tnreadeo j , rod, chain, and turnbuckle snown in Figure 2. -(ne unacceck was initiatec wnen the rod was sevePed w'Ith bolt-cutterc.

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g: t erti c al and hors: ental displacements were measured with 6

9 *: 1 linear displacement transducers. Vertical and hortrontal

, l ' *! accelerations were measured with crystal-type accelerometers. ~~

The transducers are shown in Figure O. Outputs from the displacement transducers and from the accelerometers were scanned, digiti:cd, and stored on magnetic disks for sucsequent

, scaling, plotting , anc analysis. Outputs from tne hort:ontal j -

, displacement transducer and the hori: ental ac:eleremeter were

, also cigiti:ed and stored using a two-channel cynamic signal t

an al y: er . The instrumentation system is shown in the photograpn i in Figure 3 and in the schematic diagram in Figure 4.

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1 1

TEST FROCEDURES

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Random Encitation Tests d

] For the rendom encitation tests, the 1.5" electrical conduit a

was mounted in the test facility, tne electromagnetic shaker was mounted vertically or hori:entally, and the shaker was criven I with a :ero to sinty Jour Hert: "pink" noise signal from the dynamic signal analy:er. The output f rom the ccreesocadi ng -

i accelerometer mounted on the center 'apan was monitored, and

, f requency spectra were .ncasurec and averaged to determine the l,

fundamental natural. frequency for vertical or hort: ental cscillations ci the' center span.

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Si ne-Dec a v Tests i

For the sine-decay tests, the snal er was suspenced from i

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, by the randoni e::ci tati ch test = described above. Wrien a 1' steacy-stete amplitude was acntevec, the snarer cue' rent nom switch <d off. Voltages r et. resenting da upincea ent s e r.c

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cigitt:ed and st ored f or- aucsequent enel ysi c. Sine-dec sy test s _

. were conducted for 1.5" and 0" electrical concult, with enc without fire barrier ciet, and with severa) wire londinge.

a Snaoback Tests e

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At the beganning of eech snapbeCP tect, the displacement trenscucerc were :ercoc. The test condvat wAS moved to 111 initial displatement for the test by using the turnbuckle.

• Digiti:ation of the text data was initiated, anc bolt cuttccc .

were used t'o sever the connecting red, as snown in Figure C.

Voltages representing ci splacements and accelerati ons f or tne ..

transient analysis.

oscillations which resulted were stored for subsequent-Snapback tests were conducted for 1.5" and 0" steel' electrical conduit, with and without fire berrier met, with several wire loadings, and with a range of initial displacements.

DATA ANALYSIS Demping values were cetermined using the logarithmic ce:r en.ent method. Thi s methcc assumes that the dynanite benav1:r of a physical system con be modeled by an expression of the fcr+tt mII + ci: +

kx = F(t) (1) where  :: = Displacement of the stru:ture m = Effective maus e = Effectivo demping i = Effective stii4 ness ~

F(t) = Forcing function. r l

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the freefunction the fcccing vibrettons typical:erot be:omes of unaptack and sine-cucay tests,  !

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• ma y r pp,? 'Acd1tional cefinitions and e el at i on=hi ps aincng vars ebl es see c. e M ;'~ fcllows: .

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w..= wn t l ' - g 2) ** "$ Ww n. .. . (L) c e = 0 (6:m)

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100g = Damping"ratio (*4) (7) w = On4 [9) where w = Rotational frequency ..

(radia ;/second) f = Frequency (Hert:)

. c. = Critical dampirg coefficient.

The " Results from a typical snspback test are shown in Figure 6.

logarithmic cecrement," representing .he natural log of'the ratio of svecessi ve ma::imum ampli tudes, can ce related to the dsmping ratio (Den Hartog, 1056; r1y k l a st ad , 1906):

5 = ( 1/ n > 1 n (:: /::,,,.n >

-(9) 5 x 0xp (10) i j

where 6 = Log decrement t n = Number of cycles i 1

m = D1sp1acement'at cyc1e m

.: .n =

Disolacement n cyc1es after cycle m.

As a convenience in calcule 1nc damping ati ,si the natural logarithm of the displacement values can .a ^

of time, as shown ici Figure c. The campingn ratio otted as a functico is tnen relatec to the slope of the envelope in the following manner:

g (" ) =

100 (1 n:: -1 n::,,,.n ) / Cun) . (11)

Results logarithmic fromplot a typical sine-decs.y test anc tne corresponcing are ptesented in Figure 7.

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Electrical Conduit DampinD Tests y , , , , ,

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Figure 7: Typical S i n e -D.e c a y Test Results L

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Center. span n+tural frequencv values corra.spanding to .hs

_.. .;, ;',' ,', . , v&ricus test condi tionh ' appear below in Table 1:

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Summary of Measured Center Span Nat ur Al Frequencies ,

Diameter Test Ccndi t i on Direction of Meesured Naturel -

Jinches) Encitet)osa l 'r e c u e nc v (Ha t:

1.5 Bare conduit (no Vertical 10.7 wi r e :3 , no mat) 1.5 Wire loading of Vertical 15.7 --

1.14 lbm/ft, no fite barrie mat -

1.5 1.14 lbm/ft, with Vertical 9.9 fire barrier mat 1.5 1.14 lbm/ft,.wi.th . Heri:: en t al 10.5 fire carr.ier_ met, 1.5 1.14 l $/ft, no- Hori:cntal 14.C fire barrier mat 1.5 O.51 1bm/ft, no Hori: ental 17.E fire barrior met 3 1.14 lbm/ft, no Hort:ontal 25.9 fire carrier mat 0 0.27 1bm/ft, no Hori:onta1

- 22.8 fire-barrier ms.t 4

O O.27 lbm/ft, with Hor-i r on t al 20.1

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fire barrier met Duri ng ver-ti cal snapback tests on tne bare 1.5" ccnduit, come rattling of the conduit in its mounting straps was noticed.

Results f rcm random vertical e:< c i t at i o n tests ccnducted before the snapback tests were compared with rancom ver tical e::ci t at i on tests conducted after the snapDeck tests. All conduit couplings were then inspected and t i g h t enrad , all conduit strap bol ts were replaced, and random enci tati on tests wt-re repeated.

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_pd '

inattai installation was 18.0 Harta. end thiv i. ec.:ency dr oppw

', t o 15. 0 Her t: efter the prel i mi te,4 y snapbacl. tehti. When tne

't S r, ,, bol ts were repl aced and the couplings tighteneo, the natural.

i.* , frequency rose to 18.7 Her-t:. An i n c r e a m.e in camping with l~,' loosened clamps and a ' decrease in camptnq w tn ;1gntenec clamps is also apparent from the widths cf tr.e r e sonan:e peM s in Figure .

'$. S.

Results for 1.G" Conduit . .

Displacement versus time plots of typical horizontal snepback tests-for the 1.5" conduit are shown in Figure.9. The influence of' the fire barri er mat in increasing the camping is apparent. Damping ratios f or hori ental e:;ci tati on and me;:imum Wire loacing (9 wires, 1.14 ,1bm/ft), with and without firo barrier mat, are presented'in Figure 10. First. cycle damping ratios for tests conducted without fire barrier mat ranged from.

12% to 17% of critical damping, while first cycle camping ration for tests with fire barrier mat ranged from 20% to 05% of critical damping. Without fire berrier met, oscillations were still present after ten or more cycles, and with fire barrier met, oscillations were damped out witnin three to four cycles.

The reasonable repeatability of the damping test results is indicated by Figure 11, which presents results from six snapback tests conducted under similar conditions. An indication of the influence of initial amplitude of e>:ci t a t i on on tna camping ratio is given by Figures 12 and 13. In Figure 12, results are presented for a series of snepback tests of 1.5" conduit without fire barrier mat, and, in Figure 10, results are presented for a ,

l series of snepback testa of 1.5" conduit witn firc barrier mat.

Witnin this range of i ni ti al amplitudes, the damping rettos are primarily influenced by the presence or absence of the fire barrier met, and the damping ratios are relati vely independent of the i ni ti al emplitudo.

The influence of wite loading on dempirg rati on is incicated in Fi gur 2 14, which presents comping ratio results for 1.5" conduit without fire barrier mat at wire loscings of 1.14 lom/ft ~

(9 wires) and 0.-51 lbm/ft (4 wires). First cycle camping ratios ^

for the wire loading of 1.14 lbm/ft ranged d e am 12% to 17% of critical damping, a,h d first cycle damping retics f or the wite loading of 0.51 l bm/i t ranged from 20% to 2;% of critical demping. The higher damping at the lower wire 1: acing is s

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presumebly wires.

due to increased motion anc interaction emot g the  !

- Figure 15 presents a comoarison of resulty f rom vertical and horizontal snapbsch tests, wi th anc without fire berrier' mat.

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.40 Electrical Conduit Damping Tests

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O Electrical Conduit Damping Tests

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Figure 9: Snapback. Test Results for 1.5" Conduit e

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4 T:.e campi ng r ati os i or the hara;ontel tests w2th and without ftre bare 2er- met were 1arger than the damping rat 2m2 for the vertical teuts. The fir e barrier mst nac little influence :n the damping ratios for the verticel tests, but the iast ptovided s significant increase in campi tig for the hor i::ont al tests.

i Results fer 5" Conduit Di spl acement versus time plots of typical hori: ental snapback tests for the 0" conduit are snown_in Figure Ic. The fire bnrrier mat provides some increase in camping. Damping retics for hori z ont al excitetton and ms:: mum wire loading (06 wires, 0.27 lbm/ft). With and without fire barrier mat, are presented in Figure 17. First cycle c ampi ng r ati os f ot* tests ccnducted without iste barrier nia t ranged from 7% to 10% cf critical demping, while first cycle damping-ratios for tests with f i r e b ari-i er- mat ranged from 5% to-21% of critical damping.

Without fire barrier mat, oscillations were still present after si:: to ten cycles, and with fire barrier mat, oscill ati ons were c a.mp ed out within two to five cycles.

An indication of the influenco ci i ni ti al amplitude of e::Ci tation on the damping ratio for hor t ; ontal e:5 citation is

,given by Figures 18 and'19. In Figure 18, results are presented for a series of snapback tests of 0" concuit without fire barrier mat, and, in Figure 19, results are presented for a seri es of snapback tects of 3" conduit with fire barrier met. Within'this range of i ni ti al amplitudes, the first cycl e damping r etics f or 0" concuit oppear to increGGe with increasing initial emplitude for tests conducted with and without fire barrier- mat.

1 The in41uence of wire loading on camping ratics is indicated in Fi;ure 20, which presents camping ratio results f or 0" conduit without ' ire barr1sr met et wire l oedings of 0.27 lbm/ft (06 wires) and 1.14 lbm/ft (9 wi,ns). First cycle damping ratios for the wire loading of 0.27 lbm/ft range: from 7% ts 10% of critical damping, and +irst cycle damping rati os f or the wire loading of 1.14 lbm/ft rangec trom 10% to 20% o4 critical demoing. The higher damping st the l ower wire loading is presumably due to Mr.

i ncre s.s ed motion and interaction among the wires.

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, 'SUMMAR , CONCLUSIONS, AND RECOMMEND /iTIONS This report presents dsmping values determined ircm Enapbacl l and sine-decay tests c onducted with 1.5" end 0" steel electrica) conduit. Paremeters which were tested incl ude c onovi t dieneter, wir e 1 cading , amplituce of enc 1tation, and presence or absence of fire barrier mat. Imp 3rtent r e su l t i:, eroisummart:ed'below: .

1. Urlder a variety of ccnditions, including conduit ,

diameter, wire ladding, initial amplitude, and presence or absence ci-fire barrier mat, first cycle damping rattos ranged from 5% to OG%. a

2. Installation deteils and subsequent cynamic nistory of the electrical condust c an have a . signi f icent ,

i nf l ue nct> on its natural frequency snd domping.

O. Fire. barrier met provides increased damping for f hori z ont al oscillations of 1.5" conduit and 0"  !

conduit. Typical first cycle damping ratios for 1.5" (

conduit with fire barrier mat ranged from 20% to 06%, j o and typ. cal first cycle damping ratics for 0" conduit l

wi th fire barri er mat ranged from 5% to 21%.

The fire barrier met was more effective in.providing 4.

increasad ( 5maing for hori:ontal oscillations compared ,

to vertical oscillations.

5. Increased damping with increased amplitude of i e:: citation was observec f or 7" conduit. For 1.5" conduit, damping was not as clearly related to the amplitude of encitation. 4 i

These test resul t s provide damping values wh3 ch ere si mi l ar to the values provided by Shibata, et al., (1991) for 0" anc 4" pipe with thermal insulation. However, the results end -t conclusions summari:ed above are based on a limited range of l parameters and only one type of fire barrier mat. Additional testing would provide e broacer st ati stic al base f or estimating the significance of observed cifJerences and trends in the de.mping values. Acd2 51onal laboratory investigations anc surveys _

cf fi el d instellations could also be condu:ted to enamine. the  !

effects of instal l 4ti on end dynamic history on camping and  !

natural frequency. . Investigations could be concuc*.ed'to I determine the mecne,nisms by which the fire barrier mat and otner i similar materials produce increased vi br ati onal damping, with the {

goel of utili:ing these materials for the reduction of vibrations in problem areas.

provi d. .i9 The effectiveness of the fire barrier mat in  !

dam;:ing f or hortcontal e::ci tati on of a vertical concuit j run could al as L- investigated. I

m.

--7 3 29 '

r .:

Th'ese recommendat 1 ons .f or - adct ti creal 2nvestigatIcns should-be discussed, ranied accceding tc relstive ~1mportance. .e d included i n a comprehens,1 ve pr oge t.m to evaluate damping In electrical conduttu and seall .pipi ng systems.

.9 i

FEFERENCES '[ .

Den Hartog,.J. P .; , 1@56, Mecnanical V:brotions. New Yors:: f McGraw-H111 Eoc6: Company. +

t

. . .. I Myklestad, N. O., 195e. .Fundarnent c1 s of Vibration  :

Anal vsi s . New Ycri:: N-Graw-H111 bool: Compsnye j 1

Shibata, H., M. Mal:1guchi. A. Itc. T. Hayashi, T. Chiba.-

. H. Kobayashi, K. Ki temur a , K. . Anco , .and R. Koyanagi,. ,

August 1981, " An E::per i meental Study of' Damping Characteristics With Emphasis on Insul ati on f cr Nuc1 ear - i Power Plant Pi ping. (Sei smi c ' Dampi ng Rati o Evaluati on' Program)", in Transactiens of the 6th International '

. Conference on S t r'.ic t u r a l Meenanics-in Reactor  !

. Technoloov. )

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