ML20210T532
| ML20210T532 | |
| Person / Time | |
|---|---|
| Site: | Fermi, 05000000 |
| Issue date: | 01/14/1987 |
| From: | Lainas G Office of Nuclear Reactor Regulation |
| To: | Adensam E Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20210T193 | List: |
| References | |
| FOIA-87-50 TAC-63376, NUDOCS 8702180212 | |
| Download: ML20210T532 (49) | |
Text
_ _ _ - _ _ . __ _
[== aeg'o UNITED STATES
. 8 n NUCLEAR REGULATORY COMMISSION WASMNGTON. D. C. 30506 y g i M I A spf Docket No.: 50-341 MEMORANDUM FOR: Elinor G. Adensam, Director Project Directorate No. 3 Division of BWR Licensing FROM: Gus C. Lainas, Assistant Director Division of BWR Licensing
SUBJECT:
FERMI UNIT 2: MAIN STEAM BYPASS LINE FAILURE (TAC #63376)
Introduction In September 1985, Detroit Edison (DECO) discovered through-wall cracks in two main steam bypass lines at Fermi Unit 2. Subsequently, DECO replaced both lines with a thicker wall pipe, redesigned some of the pipe supports, and analyzed the piping vibration. DECO has identified the root cause of the problem to be acoustically induced flutter of the pipe wall. On December 11, 1986 a meeting was held in Betbesda, Maryland for DECO to present their assess-ment of the problem and corrective actions that they have taken to resolve the issue. The Engineering Branch and Region III staff have evaluated this issue from the viewpoint of sound engineering practices rather than from assessment of meeting license requirements since the lines in question are a part of balance of plant. The assessment by the staff is to critique DECO on the basis of performance for this issue as an indicator of how they might address a similar problem in the " safety-related" part of the plant.
Both bypass lines (the West line and East line) are made of 30 inch diameter carbon steel pipe (API 5L Grade B) and are reduced to 24 inch diameter at the inlet to condenser. The cracks were found at various locations on the pipe surface including, pipe support lug attachments, small test connections, and flow seasurement orifices. Deco replaced the original 0.375 inch thick pipe with a 1.0 inch thick pipe for the 30-inch diameter section and 1.25 inch thick pipe for the 24-inch diameter section. Deco also eliminated all pipe j
i weld attachments. As a part of the modification, Deco conducted a test program to obtain as-built stresses and strains at various locations of the lines and contracted Hopper and Associates and Stone and Webster to predict the service life of the pipe using the test data. After resolutions of disagreements
Contact:
J. Tsao '
x29408 1
8702180212 e70209 PDR I d 587 TE 7-50
Elinor G. Adensam /
rega Ning the fatigue life of the pipe predicted by the two contractors, Deco concluded that the west line is acceptable if cumulative operation with bypass valve position between 30% and 45% opened for a period not to exceed 100 days, and that the east line can be operated indefinitely.
Discussion and Evaluation The staff believes the licensee has properly identified the root cause of this vibration as acoustically induced pipe wall fluttering resulting from high l pressure drop across the bypass dump valve seat. The dump valve opening is about 9 inches whereas the pipe opening is 28 inches. The supersonic steam entering the pipe is choked at the valve exit. When the steam is expanded into the larger pipe, the flow becomes turbulent and generates the acoustic vibrations.
The modification that has been performed by the licensee has not been success-ful in elminating the acoustically induced vibration from the piping system.
The arguments presented by the licensee on alternative designs and why they could not be implemented at the facility appear plausible. However, in the design of the modification, it does not appear that sufficient considerations were given to this system with its inherent vibration problem. For instance, several supports on the system have cracked and nuts on clamps have fallen off. We understand that fillet welds rather than full penetration welds were used in the support design. Although this practice would meet the usual code requirements for supports of this type for power pipings, we believe that the fillet welds, with their inherent stress raisers, were not appropriate for this application. Further, no special care appears to have been taken by the I licensee to preclude loosening of bolting in the system. As with the supports,
. no special considerations were taken with regard to the circumferential weldments in the piping. Weldments were made using backing rings. This type of joint is 1ess desirable than an full penetration weldment made without a backing ring.
l A joint made without a backing ring would not only have been more readily inspectable but also would have been less likely to provide a site for potential fatigue crack initiation. With regard to inspection, volumetric examinations of the girth weld following fabrication could have provided added assurance that discontinuities from fabrication would not be present to serve the fatigue crack initiation sites. Also, no volumetric inservice inspection has been proposed to monitor if service-induced degradation has occurred.
CONCLUSION The staff concludes that the licensee has been thorough and effective in identifying the root cause of the pipe vibration. However, the modification which is admittedly a compromise because of physical limitations and cost appear to have been done without going significantly beyond what the applicable ASME Codes would require. The licensee has attempted to reduce some stress raisers but has neglected quite a few others. Further, non-destructive inspections per-formed in past and those proposed by the licensee for the future are minimal.
v Elinor G. Adensam Nad this problem occurred in the " safety-related" part of the facility, the staff would have expected the licensee to have been more attentive to design, fabrication and inspection factors discussed above.
This completes our action on this TAC.
,,.:ed BT-G .ames Gus C. Lainas, Assistant Director Division of BWR Licensing cc: R. Bernero W. Houston G. Lainas J. Stefano E. Adensam '
B. D. Liaw ,
R. Hermann J. Jacobson, R III D. Danielson, R III J. Harrison, R III J. Tsao
Contact:
J. Tsao X-29408 Distribution Docket File BWR/EB Rdg File BWR/EB Plant File
(
,( ) _
0FC : DBL:EB : DBL:EB :DB : .AD : : :
NAME :JTsao: :R.He ann :B. :G/ Lainas : : :
7.............................................
. . :01/
. . . . .9. /87 . . . . . . :01/
. . . . .0.\ ./87
. . . . :E
. . . .p/V /8 7 : : :
DATE:01/3P /87 0FFICIAL RECORD COPY (5520 document name: Tsao-6)
- v s
Detroit Edison / Region III !"eeting January 21, 1987 ct 9:00 a.m.
799 Roosevelt, Glen Ullyn, ILL tit!E TOPIC SPEAKER 9:00 Introduction D. R. Sylvia 9:15 Long Term bypces J. Contoni line monitoring 9:45 Failure of weldc in C. Gelletly 3/4 in. instrument lines attached to main stean lines.
10:30 Questions open 10:45 Conclusion B. R. Sylvia
)
DPJF2 U. S. IMclecr negulatory Cariscion Attn: Docuraent Control Desk I:cshington, D. C. 20555
Reference:
- 1) Ferti 2 12C Docket Co. 50-341 ICC License !!o. I!PF-43
Subject:
Long Tem I:onitoring of the I:cin Stoc=
EvTcc Lines On Decerber 14,19C5 'a raeeting, ucs held in Ecthesda to discuss the repairs Detroit Edison made to the !!ain Steam Bypass Lines. DurinA that Decting, Detroit Edison stcted that c icng tenton;toring program uould be it.plemented. Thc ~
l'onitoring of the;$pecified'of the Femi 2 Long Term 12 tin St$akBypass Lines is
\ , ;.\ f ' F
- 1) 11aintcin n'dtt1ulative
\ running total of the time spent eith the vest bypass line operr. ting with the bypacs valve position between 30% and 45%. Annual totcir to be reported to the C C Region III inspectors. 'Ihis vill be accar.plished with a control roaa panel mounted recorder.
- 2) Utili::ing an ultrasonic test device calibrated to the ra::imtra cllcuable f1cu cize cf .0625" survey the longitudinal pipe team ucld on the vest bypccc line from the bypass valve to the first orifice picte. Inere any significant indication is noted, radioloaical examine the pipe at that location.
Vicually examine all girth velds in this cair piping section for linear crcel;ing approaching
.0525" in vidth. 7 hic progra: to be performed during each of the first five (5) refueling outages cnd eval c:h:;r refuc_ing outcge there cfter so long ac the accumulated c:: pended life remains less than 80 dayc.
- 3) Inspect cl1 cnubber and hcnger locc:.:,cnc cn the
- 2in Steam Dypacc Linen for loorening hardware end uclament dictrecc ct the f1rct tuo (2) refueling outagec. Infortcl undocu:. tented incpectionc cay be carried out on cn er needed bacic. Tae rer. ult cf cny cuch infornc1 inumction are not c::nected to cftec: 4.c: ,2ci..cn cJ e.:... e.. ...
A 4
\- i\ - %q /
t s ra i l .
! l l!
! !! . 8 I ) I! i! I! !1
, N ir ll
' i! ; !
, ;i i J / ., 2
- I i N 7 3
\ -
E N
, .i 5
j.
ii:=
t N
A ef {O
\
E N !
- i h ,. / ..
II It
. I I !!-
'=
n -
0 's ,
er BI
- *t IE
- i s 8 s
.. . \ !
ii i :
i! i.i i ti : I
2 ,
StJf4RY
- 1. INSRftNT LIES - CR4XS FOUt0 IN F0lR VEDS MERE SOKE V/M
% OCMECTED TO 3/4" PIR NIPPLE. JNUH(2,1987
- 2. FLUSHING 0[NECTION - CPKK F010 IN VED kERE 1 1/2" NIPPLE E ATT/OED TO TLFBIE STP VALE CASING.
- 3. StlBERS - SOE Q#P BCLTS FOUt0 LOOSE. TVD LUG RETAINERS CRKKED AT VED.
- 4. fGITmlNG PROGVM -
STRAIN CAES PWET ISI OUTKE INTECTIONS
3 O
e O
D Q
$N \
f\
ow g
N
/
{o >
E d N" 4 cm( l u - hh I b u a i;
- e. ..
w g
mm
'v ..* g 1
- of
$ /
- ~l@
)
~
p:J'R i if; 2.-
^
- i isj/ * #j4.,9, .
as y ,
'M vil o
- P.,
.b y O
,9 , b 3 N f- Ge..r.s ** ) g c, .
i i, . i j 5JL 9 o
s
\
a -
7
-,.....<>.o Y \ ;"' _ _
Qs ii.\
{'l\ !'% e.b I . .
i' 3. .'.-
- ht Q
>l M i
gg a ._.5 j W r
\
o
. sn.
, l-y, s-4 d) j,i M Y. i s
J .
! . 4, N
\_- . O+ ;
g #
- i. .1
1 f~A/ LED ACTIVE INSTRLIMENT TAP MEAR TUR8/ME f *~ '
CASIMG
/
' ') m:,,m=. =w:
I / Osnotasesomel0 l 3 RD Floor '- Y _y ~\
g ,)
i y
M
& 70R8mE tevet ~~, -'
g \
@/
! 5 A-sTor rmeoTTE
- Y IYh '
i i 'lI y,zygs y) f /,R '
\,\ s. g 1 . i ft . 1
\, q" ' , ggt /
b ,
Y'"k ig g #
.) 1. VFAKED \ FLOSll E T j
=
h
& CopHE C7/OA/ $ 3 y
,0 t \' , AT 3 TOP VALVE ; g ,,,,gg $ppgg 2 FAILEO SPARE \ Vm. INSTRUMENT TAP
/NSTRUMENT TAPS ,
EL E VA T/ON Look/NG SOUTH g
a INSTfDENT LIE SQRE QMECrimS LOCATION -
ON iMIN STEAM TmBIE LDCP PIPING #O TWBIE STP #0 TROTTLE VALES. (LOT PIPING - 27" 0.D. ,1 1/8" l@LL, 21/4% m)
INSTRUENT ONECTIONS 3/4" N10ED, IN USE - 38 (1 DVCED KLD) 3/4" N1DED, CAPPED - 4 (3 OVCKED N1DS) 3/4" N10ED, PLUGED - 6
~
IID M .-
- ALL UNECTIONS FRm 52" 6%NIF01) TO TWBIE
- E)' 11RD
- ALL ROOT WlDS PASSED VT #D PT EXAMINATION CAUSE 0 GA0(S AT VALE -
DISSIMILM WlD #0 ACCUSTICALLY ltOU2D VIERATION F0FCES, Him CYQE FATIGE 00RRETIE ACTION -
- SKRTEMD ALL UNECTimS, b%CE EAVIER (SCH 160 REPLACED Sm 80 NIPFLES) bONITORING FROG @M -
STRAIN CAE DATA PVEET ISI QJTNE INSPECTIONS REVIEW OTER SYSTB6 i
fo
- V4' SOCKET WELDED 5.S. GLOBE VALVE 24' DTA. MAIN STEAM LINE . , , , .
U-j VISSIMILAR" ME.TAL WELO I ---
-1 /4 DIA -~
3/4"c.s.'WIPPLE ,
Awp u n n y i i, a u t.
N i
gyj N N q ~""""d 4 C.S. NIPPLE
, j,-
/
A106 CARBON STEEL }
r b* r I APP ROX.12"I I
l FAILED WELD 7
3/4 C.S. dlPPLE ~3/4~ socket l
l \N WELDED S.S.
GLolR VALVE 1///q / ///) .
1 t l l
\
('
s 3 SSIM _AR ME A _ ~W E _.)
'7 S/4" SOCKET WEL DED S.S. GLOBE VALVE 24" DlA. MAIN STEAM LINE m, , .
, ,p ttSSIMILAR METAL WELD s', k -l%" DIA. --
. \ ud y a // if :s a p mmw g3dRup/
, ' ' ,' A106 CARBON STEEL 4" C.S. NIMES
.-
APP ROX. 12" AS FOUND
. ,7,,.
//- is/, oia - % 's X!.
g//, , ,
QG %"D/A MUG l _ _
'kV/ $,W %~narr wao .
/. . l l,= s- ,
AS LEFT l
S ?AR E INS ~~RU M E N ~ ~~A o I
T
-V4 SOCKET WELDED
, 5.5. GLOBE VALVE
, 24' DlA. MAIN STEAM LINE . , . , _
y/u ,, VISSIMILAR METAL WELD
/ gg.pgg, 5/e" 5.5. TUBIN G
- A W\ F // // /> , / // // // ri JA
~
}
~
l
)} -} // // //3[ // // // // H \
lw M j. L~
T- A106 CARBON STEEL C.S. NIPPLES
_ b- _
APPROX. 12" AS FOUND V4' SOCKET WELDED
.5. GLOBE VALVE 74 DI A. MAIN STE:AM LINE: W f
is
- e G
3 r,
_g/iDIA. ,i 5/e" 5.5. TUBIN G
/
/* \\\\\\\\\\\\WW I D S ,,/ ,, mZh gp e xxxxx w g p d
~e- -
,T{ Alo(o CAESOW STEEL #/i r "C. 5.N/P/4E ,
c W :
APPROX.12' _
AS LEFT AC"lVE INS-~RUMED "AD l
9 ELUSBlNG CCMECTION LOCATim -
TLFBIE STCP VALE CASING (21/4 CR CASTING) ON LPSlREM SIDE QFNTITY -
FOR DESGIPTION -
1 1/2" PIE NIPRf (1.9" 0.D.),14"LDE, CAPRD, S0XT VELDED TO CASTING GKX F0lf0 IN FILLET VELD T DE NIPR.E. STEAM IIA VAS SSLL.
CAUSE -
MoRTENSITIC VELD, SI-RIN(AE GACK. (10I CYO_IC FATlaE)
QRRECTIE ACTION -
SCREW PLUG WITri SE/L VELD. OlWR TFREE - VT & PT, SHORTEN TO 3" i
1 i
1 4
T//READED Pl.UGm
(
VALVE SONNET = '
VALVE BODY = s g. s K
e
//z
/
,/
APPROX.14'
\ s
! - //
/ p / /p
____c- //A C.S CAP <
Y\ il \
. / , ,2 \
s 's l'
\ '
, ~ . ,, _
i d' ' ' '\' "; '
,K N, !! I
~
y J .-[ l
- t" '
N
/
s N wao
~
VALVE BODY AS f"OUND AS LEFT l -
l l
4 MAIN STEAM STOP VALVE FLUSH CONNECTION 4
//
9 SNLBEERS #D l@NERS NO HWER HENRE VAS FQ10 LOOSE SOE SNEEER Cl#P Ba.TS VERE FMO LOOSE SitBEER Cl#PS WITH LLE - 6 LLE - TOTA. CF 48 RLM OE LLE DlE TO LM11NAT10N - ATT/O+ENT VELDS A_L SATISFACTOR(
LLE ETAIM RS - 24 2 LLE RETAIMRS F010 BROEN AT FABRICATION VELD. OE VAS CRAND RERECllE ACTION -
REPlKED - 3 PIECE RETAINERS 6 RERKED - IVD TO RBGE FOR Cl#P RBO/AL 12 SATISFACTOR( AS IS 3 TOTA. 24 f0NITORING FROG?#1 -
STRAIN CKE [RTA PMET ISI OUTNE INSPECTIONS REVIEW OTER SETBS
/Z t 27'A" # PIPE i
?$f 7-LUG .RETAlW ERS
_M n rn Fri
,y g ,
.i' .
., g
$ @ l l l @ y@- -
- ~- .
I I l l
- 5MUBBER suuseER---
U E
- 1
% \, -
'\
\ \
. , /
b N~ ,' p, G' ,
\
\ .
]
S \ J33 E R W _JGS A\ E~A \ E RS
r jy LUG RETA:NER tu e
o.
LUG =TT f- I = LUG
{ $_ __
U ;
K CLAMP /A
)-(TYP. ,
STANDARD RETAINER SPECIAL ._/
LUG /
K RETAINER -
u LUG =I .
< E y:
~ ~
SPECIAL RETAINER LUG e RETAINER S_
1 .
= LUG ~ g ,
t 1 -
\#
4[ \ CLAMP SPECIAL RETAINER I
~~Y J CA _ _UG RE~~A NERS @ FERV 2
H 9
4 l
8 J
Q
, =. : 5 W
~jN g '
?'
cA LUG R E~Al bj E R -
l
[
MAIN STEAM S70f/
\ THRO TTLE VALVES H.P.
\ e- TURB/NE r M
< x \
r M \ .
, x \-
h -52 ~ MANIFOLD t
L -
aA %
u_p >
REA C TOR a \xy , .
W \ * '
N; ,1
! s MA/M STEAN /SQLATION VALVES l
- DR YWELL
/VA/N STEAM L/NES - REACTOR TO HP TUA'B/NE s
I/s
LINES CONTINUE TO MAIM STEAM \ p
@)
MANIFOLD 9 . Y
>~>
g/ ,
KEY 'D' F0 CE SENSING PIN ACCELEROMETER A
- [ M
@ STRAIM GAGE A X P
P mg
- ^
$$ITI[NMENT PEMETRA110NS FROM REACTOR FERMI PVDET MAIN STEAM
y . .
i To TURaiue j sToP/CouTRot VALVES (TYPICAL oF Foug) l 4 +
- o94 A F D F
i 1 F i A '
l F O
O D
~
l BYPASS LIMES 57. MAMIFoto MAIN STEAM LINES I
TO CONDENSOR THROUGH STEAM TlJMMEL I
i ,
52' MAIN S~EAM M ANI COLJ AklD RELA-'ED 31 DIN G i xev FER MI DVDET MAlhi S"EAM Lvor FoecE SEN51M4 Plu ACCELEROMETER.
I STRAlM QAGE Ni
'Tunstur
)
po nLEs _ gg j Y i MKJ cow'Ro L i mv ad an.v as l 7 cofygi-y o M *%
!. B o o o
L M AI N STE AM LOO D S ~O ~U R BINE l
l i
FERM:: DVDE" MAIN 5 EAM i KEY
@ 'VM l . @ roece seusui Piu
@ ACCELEli!0 METER i @ STRAIN GAQE g i
w
, l. ,
STEAN BYPASS SYSTEN STUDY for Enrico Fe mi Unit 2 Detroit Edison Company by E. R. Floyd M. Fortini T. L. Wang Y. S. Sun l
l l
/
Prepared by a & /_ -
Approved by ./ . ,h . A
\
1047-1568011-NC4
&- l
se TABLE OF CONTENTS
', Title Pag.e
1.0 INTRODUCTION
1 "I t
2.0 M VIEW OF 30FFR AIID ASSOCIATES REPORT 1-3.0 VIRRATION ANALYSIS OF TURBINE STEAM BYFASS SYSTEM 2 4.0 FEASIBILITY STUDY OF MODIFYING INTERNALS OF MAIN 10 STEAM BYFASS BtBIP VALVES 5.0 FEASIBILITY STUDY OF INDEFEMDENT PRESSURE- 12 REGULATING SYSTEM 6.0 FURCHASE SPECIFICATION FOR A REPLACEMENT TURBINE 18 STEAM BYPASS CONTROL VALVE
7.0 CONCLUSION
S AND RECOMMENDATIONS 19 Attaciument A - Pipins ArranSements for Independent Pressure-Regulatins Systes 4
eo P
O 1047-1568011-NC4 4
1.0 INTRODUCTION
During startup testing of Enrico Fermi Unit 2, through-wall cracking was discovered sa main turbine bypass lines downstream of both ste,am dump valves. Cracking on both bypass lines was observed at severa$ welded attachments where lugs were affixed by full penetration welds.
{
After review of test data taken on the bypass lines during operation, it was concluded that the tracking was due to high cyclic fatigue feilare resulting from pipe vibration induced by acoustic energy in the line.
The most likely source of this acoustic energy was determined to be the two steam dump valves manufactured by English Electric Company.
To partially resolve this condition, DECO rebuilt the bypass lines in- '
stalling new 30-in.-diameter carbon steel pipe with a 1-in well in place of the existing 30-in. Schedule 40 pipe, in accordance with EDP-4410. In addition to the pipe replacement, a majority of the pipe supports were redesigned.
As a further action, MCO contracted Hopper and Associates of California to review systes strain and vibration data to estimate the life espectan-cy of the system.
DECO also, through Edison Task No. SCP-86-019, requested SWEC to perform the following: ,
- 1. Analyze the conclusions of the Hopper and Associates Report dated March 28, 1986, to determine the validity and content within which this report should be used. This analysis is dis-cussed in Sections 2.0 and 3.0 of this report.
- 2. Determine the feasibility of sodifying the existing turbine steam bypass valves to accept noise-reducing tria. This is discussed in Section 4.0 of this report.
- 3. Determite the feasibility of providing an independent pressure-regulating system to operate in conjunction with the existing l
steam dump valves. This is discussed in Section 5.0 of this I report.
l I 4. Provide a purchase specification for a replacement turbine steam bypass control valve. This is discussed in Section 6.0 of this report.
2.0 REVIEW OF NOPiER AND ASSOCIATES REPORT l
I SWEC reviewed that portion of the Hopper and Associates analysis included in Mano No. NE-PJ-86-0103 which was forwarded with the DEC0's scoge docu-l ment for this task. As this meno did not provide either the analytical
> basis for the conclusions of the report or copies of the celeslations l performed, SWEC contacted Ropper and Associates and requested a full copy of its analysis as well as any support calculations. Although Hopper and Associates agreed on two occasions to supply these documents, they have l still not been received as of the date of this report.
l, 1047-1568011-NC4 1 1
~ . - _ . - . _ _ , _ , _ _ _ _
Coas:guently, SWEC has r: viewed th2 conclusions sf the Eopper report based on our experience with fracture mechanics analysis and determined j .
that the fracture mechanics modeling technique used for the analysis ap-pears to be appropriate for this application. We would note, however, that a more comprehensive review would require additional details from Bopper and Associates. Specifically, we believe the following peacerns
! seed to be addressed: -
- 1. The governing forcing functions based on the test data of dam-aged piping, which is essential to estimate the dynamic re-sponses. Alternating stresses and crack growth rate should be considered.
- 2. The difference between the structural models of damaged and
! modified piping should be considered. For example, the damaged i
pipe failure occurred at asymmetric discontinuities, such as lugs and clamp retainers. These discontinuities have been re-moved from the modified bypass piping.
j 3. The assumption that mean and alternating stresses are Ainearly i proportional to the mass flow rate is overly conservative. The assumed mean stress value of 7.1 kai at full opening needs I
clarification, especially since test data shows approximately
- sero mean forced vibration displacement responses.
! 4. The assumed stress concentration factor of 2.78 needs clarifi-l cation in its relevance to the damaged and modified piping.
! The high-stress concentration locations are at the welded at-l tachment junctions to the damaged piping and at the short-i radius elbow node for the modified piping, which has a stress t
index of 6.60. A detailed fracture analysis of the modified
' bypass piping will be beneficial to supplement this calcula-tion. Considering the above clarifications, this technique has been widely adopted by the industry for both nuclear and power piping to supplement the ANSI /ASME stress analysis technique.
I 3.0 VIBRATION ANALYSIS OF THE TURBINE STEAM BYPASS SYSTEM 3.1 OBJECTIVES In order to estimate the potential for low-frequency, vibration-induced fatigue damage to the main steam bypass lines, as modified by EDP-4410, and to independently estimate fatigue life of those lines, SWEC has pre-pared a calculation entitled Flow / Acoustic Induced Vibration Analysis -
Turbine Steam Dypass System.
The specific objectives of this analysis were as follows:
- 1. Determine the cause of acoustic-induced vibration.
i
- 2. Identify the locations of high stress / fatigue in the dodified
, bypass line.
1047-1568011-HC4 2
g,
- 3. Establish cimuistad farcing functitas ct 31 peresat and ic11 i apening of the duny valve.
l 4. Estimate the life espectancy of the modified steam bypass lines based on the methods specified for ASE Section III cod 6 ANSI /
ASME OM3 criteria for steady-state vibrations (Refer ce 1),
and field experience (Reference 2).
! 3.2 ASSUNPTIONS
. The analysis made use of the following assumptions:
l 1. The asial restraint function provided by the superstiff clasps l i installed by EDP-4410 are assumed to be maintained under the '
dynamic loading conditions imposed on the piping. It is recem-mended that those clamps be periodically inspected for evidence of alippage during testing.
- 2. Fatigue analysis is based on the endarance syess limit derived
! from the alternating stress intensity at 10' cycles taken from the ASE/ ANSI CH3 code. Since the ASE fatigue curve has l
built-in safety margin, a realistic assessment of life expec-tancy is based on the field experiences reported in Reference 2.
I 3.3 E THOD AND CRITERIA l Severe flow / acoustic-induced vibration in a piping system usually in-
- volves some amount of resonance of the piping system with the fluid flow l and/or the acoustic emission. To properly evaluate the potential for j severe vibration in a piping system, both the forcing function and the piping frequency spectrum need to be determined. The forcing function for this analysis is determined for two flow conditions: a 31 percent bypass dump valve opening and a full valve opening. .
The criteria used in determining forcing function frequencies require checking the flow acoustic frequencies against the piping vibration data (Reference 3). This is necessary, because no acoustic source measurement has been made to date. Since the piping vibration is a forced vibration, the driver signal will be reflected in the structure responses. The acoustic frequencies checked are as follows:
- 1. Acoustic standing wave frequencies
- 2. Eelmholtz resonator frequency of the valve cavity
- 3. Frequency of the large-scale coherent turbulent structure and the asyneetric spiral mode generated by the shear layer
- instability.
i The piping frequency is calculated using the computer program
- NUPIPE (Reference 4); it considers the following:
- 1. Masses of the pipe and the insulation 1047-1568011-EC4 3
- 2. Pipe support type, orientation, and stiffness
- 3. Piping configuration, fleafbility, material, and pipe wall thickness. -
g Criteria for NUPIPE modeling adequacy are: (
- 1. Nodal span shall be smaller than the length scale of the coher-eat turbulent structures.
- 2. Cutoff frequency shall exceed the forcing function frequencies.
The synthesized forcing function is then applied to the NUPIPE model to determine the locations of potential high-stress regions with the appro-priate stress indeses, i
Since the bypass piping is nonsafety related, a code check on both the damaged and the modified piping was performed in accordance with the ANSI-B31.1 Power Piping Code.
] The acceptability of vibration levels is based upon a comparison of vibration-induced stresses to the endurance limit stress derived from the alternating stress intensity at 10 cycles, which is the basis of the ANSI /ASE OM3 standard.
The life expectancy of the modified bypass piping was then estimated by I comparing the calculated safety factor with the reported field experi-ences (Reference 2).
Computer Proaram Identification
- 1. STENAM - Steauhammer Analysis for Piping System t
E167 V02LO3 (Reference 5)
- 2. NUPIPE - Computer Code for Stress Analysis of Nuclear Piping
- i Ello V05L00 (Reference 4)
- 3. PILUG - Computer Code for Local Stress due to Integral Attachments on Pipe (Lugs)
E095 V03LO3 (Reference 6) 3.4 ANALYTICAL PROCEDURE Fiuce the piping configuration of the original 1) designed and modified turbine bypass piping remains essentially unchanged, only one fluid model is needed to analyze the steam bypass system. This model is coded into the SWEC computer code STEMAM to calculate the steam flow velocity and I
pressure in the bypass line. The pressure at the dump valve azit is then used in the valve model to calculate the steam jet velocity at tpe valve exit. The calculation is done at two valve positions, 31 percent. opening and full opening, for the west loop.
1047-1568011-EC4 4
Th2 farci 3 functics far th2 flow /cetustic-indue::d vibratica is thea cyn-thesized from the acoustic standing wave and the aspeetric mode of the l
shear layer instability. Magnitudes are determined from the instability wave and the measured piping response. , .,,
i i
The forcing function is then applied to the piping model. Peaks)ressis calculated from the deadweight, thermal, pressure, and monest stresses.
Dynamic alternating stress consists of the moment stress and boop stress i resulting from the piping flexural vibration. giace NUPIpg does not com-pute the piping flezural response, the latter is manually added to the NUPIPE-calculated moment stress.
The calculated steam line pressure, pipe stress, and acceleration for the originally designed piping are compared and beachnerked with measured
! data to establish the validity of the forcing function. The validated forcing is then applied to the modified piping for stress evaluation.
j The resultant dynamic alternating stress is checked against the endurance
- stress limit specified by the ANSI /ASME ON3 standard for steady-state vibration. The life expectancy of the modified bypass piping is estab-lished through a comparison with field experience.
3.5 DESIGN INPUT 3.5.1 Fluid Model *
(
Two STEHAM models were set up to determine the steam flow characteristics in the west loop of the turbine bypass line. In one model (Model 1), the dump valve is modeled as an SVALVE (Reference 5); in Model 2, the dump
- valve is as a CHESTV (Reference 5) to simulate the large cavity above the valve steam. ,
( Both Models 1 and 2 were executed for one-third valve opening and full l valve opening.
l 3.5.2 Piping Model Two piping dynamic models were developed to determine piping frequency spectrum and to calculate the flow-induced vibration responses. The first model is based on the original bypass design. The second model ,
simulates the modified system.
3.6 RESULT
SUMMARY
3.6.1 Canae of the Flow / Acoustic Vibration Because of the sudden expansion at the dump valve emit, where the short 9-in.-diameter discharge neck is immediately expanded to 30-in.-diameter pipe, the stema jet discharged from the dump valve behaves as if 'it were a free jet. The unstable shear layer formed between the steam det and the relatively stagnant surrounding steam rolls up to form a large-scale coherent wortez pair at about six jet diameters downstream. This axisyn-metric wave mode is a very effective excessive noise generator. The large-diameter bypass piping then serves as an effective organ pipe type 1047-1568011-EC4 5 l
- - , - . . . . . _ - - - - - _ _ _ ~ _.- - , . - -
i sf rsoenater thrsugh ut the catira dischar32 piping run. This escassive jet noise excites the pipe wall vibration in the kBa range. It should be mentioned that this excessive jet moise is characterized by specific spectrum peaks at the suisymmetric wave frequency, which is superimposed on top of the ordinary wide band jet mixing noise that is generat.ed from the smaller scale Reynold stresses. l To further complicate the phenomena, spiral modes with asimmthal wave numbers +1 and -1 continue to be amplified on the bell shape sort of pro- ,
file further downstream, more than eight jet diameters downstream of the i
valve exit. This is augmented by the elbow which happens to be located right in this region. This spiral wave is then rolled and carried down-stream throughout the discharge pipe and acts as a steady-state treas-verse load on the piping system. This transverse load eacites strongly the piping system along with a higher mode (the fourth mode) acoustic j standing wave. The latter is an asial load, similar to the ordinary i steam hammer type of load.
The Belmholtz frequency does not seem to play a direct role in the piping vibration, except to possibly assist in triggering the shear layer instability.
3.6.2 Forcing Function
} The forcing function on the piping system is derived from the jet veloci-
) ty, the steam velocity, and the acoustic speed in the discharge piping.
1 Calculation of the jet velocity at the valve exit shows that at one-third dump valve opening, the emitting jet is an underexpanded supersonic jet,
- whereas at full opening, an oblique shock wave would develop at the valve
- exit. At some intermediate position between one-third and full valve
- opening, the jet would change both its characteristics and its structure.
Although this initial jet velocity affects primarily the piping flexural vibration, it does not control the piping system movement. The flexural l vibration forcing function is not specified on the NUPIPE model, but the
! effect of the pipe wall flexural vibration is accounted for in the piping l analysis section.
1 The steam velocity in pipe after complete mixing is calculated by the computer code STEHAM, which shows that the steam velocity and the acous-tic speed remain practically unchanged. The flow rate increase corre-sponding to the larger opening area is accomplished through a three-fold steam density increase.
i l The forcing function for the piping system consists of an asial and a j lateral load component. The axial load is constructed from the acoustic l frequency. The first four harmonics have frequencies of 3, 6, 9, and 12 Rz. The 3 , 9 , and 12-Ez components were observed in the data, with a predominant 12-Ez component. The 12-Es signal is an effective asial l load driver for the west loop configuration; therefore, only the 12-Rz component is input into the simplified axial load forcing function. The l lateral load is determined by the spiral mode, which escites the*1ateral jet oscillation; the 120-Ez frequency is calculated from the dominant Strouhal amber. The magnitudes of these loads are estimated from the turbulent fluctuation.
l 1047-1568011-EC4 6 1
l l
i The synth:sicsd farcias function has the fire )
,. Y=7000* SIN (2n*12*t)a+11000* SIN (2n*120*t)t 1
where g
! 4 = mait vector along the run pipe (
i = unit vector transwerse to the run pipe
! Since both the steam velocity and the acoustic speed remain unchanged at
! the two-dump valve spesias positions, 31 percent and full eyesias, the
- forcing function frequency would not be modified. The three-fold ta-
! crease in the steam density could increase the forcing function ampli-tude, but this increase would be offset by the reduction in the i instability wave strength, which is proportional to the jet velocity, j Thus, the same forcing function is specified for both the one-third and the full valve opening positions. Bowever, the forcing function at some
- intermediate valve opening position will increase. This also is evi-j desced from the strain gauge measurement.
l 3.5.3 Fiping Analysis t
l Based on a study of steam flow operating data, and test results, the me-
- jor forcing function that caused damage on main steam bypass piping was l determined to be composed of two components: a low-frequency longitudi-mal component at 12 Ez and a high-frequency,120-Ez, transversal steady-state force component. The simulated forcing function for the piping i model input was then developed, and NUPIPE computer coding of the damaged j piping model of the turbine steam bypass lines was constructed.
l A comparison between test data and computer run results revealed that the analytical responses of the piping model from the simulated forcing func- 3
- tion closely approximated the test data both in shape as well as in au- [
t merical value, thus they validate the analytical model and input.
l j Subsequently, both the east and west loops of the modified main steam bypass piping models were coded into the NUFIFE program. Dynamic analys-es using the same simulated forcing function showed that critical re-sponses from the west loop are higher than the east loop. Therefore, failure analysis of the west loop was considered to be representative and response governing.
Both the old and new pipe systems were checked in accordance with ANSI-331.1 requirements. The modified pipe meets those code requirements. -
, 3.6.4 Fatigue Evaluation ,
From the BUPIPE computer run, results provided dynamic and styic re- I
! sponses of the maximum stress and stress indexes (eg hg ) at ese6 mode.
- Additionally, the pressure flemural pipe well vibration stress is esti- l ested to be 1500 psi from test data, which will be added to the total ;
l
! stress. i 1047-1563011-NC4 7 !
e
It was dat:rmined that o poltt lecat:d ct th) first c1 bow from the dump j valve has a maximum stress of 10,700 psi. The peak peak (p-p) equivalent
. stress is 21,400 psi, which exceeds the ANSI /ASE ON3 suggested
- 20,000-psi p-p allowable. The safety factor is less than 1.0 (actaal
- calculated value is 0.93). Even based os 31-percent valve 'sepenias, eventual feilare on the main steam bypass lines would be g'apeeted.
Therefore, the life espectancy of the modified main steam bypahs lines needs to be estimated.
3.6.5 Estimate of Life Espectancy 1
{ From a realistic point of view, considering the built-in commervatism of i the ANSI /ASE OM3 allowable and the N-curve of the age Section 11 Code, several receded piping vibration field case histories are used to esti-mate the life espectancy range of modified bypass piping and were cem-i pared with five receded histories of failed piping.
- The fatigue cycles determined from the ASE Section III N-curve showed that the modified piping system can be espected to operate coatinuously for at least 2 days (48 hr) at one-third valve opening, based on the ASE Section 11 fatigue cycles N-curve. It is known that the N-Curve was con-structed with a built-in commervatism of life expectancy stress cycles between 20 to 30.
j A comparison with reported field experiences reveals that the realistic i fatigue life of piping in steady-state vibration is 45 to 250 times long-i er than that calculated from the N-curve. Therefore, it is assessed that I the life espectancy of the bypass piping can be estimated to be between f ?40 deps,jgj00,daypAsppagamous jperst(so.d~4biYd W'9811 volve -
opening I This analysis is only applicable to gypass valve opening up to one-third or at full opening of dump valves. R' sore' severe cese of forced vibra-pa gyggsJtsegma Angg. But this was not covered l
3.7 CONC 1,USION Jt Asaresultoftheforegoinganalysis,gs.hasbeenfoundthatthehighest alternating stress of the modified pi I 'st111 EsoF hSEJp6st h ysesr-
- bactC3bgest-1984t@ttN5st.W.MMM. standard for steady-J state vibration. However, the modified piping gMp 6 in its ability to withstand steady-state vibration; the esti-i mated life espectancy is 40 days to over a year ,sf continuous operation at up to 31-percent sustained dump valve opening or at the full valve f
i opening position. For intermittent operation, the fatigue life will be significantly longer.
! Physically, this can be conceived to be the results of replac'ing the thia-walled pipe with a thick d the elimination of lugs at $he sup-
. Newever, the 6-W 1047-1568011-NC4 8 t
l'
The addition of two orifices, the effectiven:cs cf which is s bjset to operational verification, @ Megpas ehe mgpeastammt s
The small holes of the orifices may racilitate to break Qad the_oytficop.
down the coherent large-scale eddies into smaller-scale turbulence, thus reducing the system forcing function. Bowe, Their instal-For the interim basis, the present study covers only the case when the valve o ens up to either 31 percent or 100 percent.
E ' D' a . .
- .980'9Et8EDI!4MP.2El
\
M e study be eaten to include It is recommen this case. A detailed failure analysis using the fracture mechanics technique, which incorporates the parameters from the piping and fluid model, will be beneficial and confirmatory.
Over the long tern, modification of the piping system through additional l
supports may also help to reduce piping stress. '
IWl3EEs. Some suggestions are given below:
- 1. Attenuate the acoustic excitation source. Since the instabil-ity has to be triggered by upstream acoustic sources, a silenc-er valve that attenuates the upstream noise or inhibits the formation of shear layer would help the situation.
- 2. Revise the piping system to incorporate multistage expansion l
that limits the diameter expansion ratio to less than 2 at any stage. When the pipe diameter is less than the instability wave scale, it would interfere and damp out the vortex formation.
- 3. Relocate the first elbow away from a point 8 jet diameter downstream.
3.8 RITERENCES
- 1. Requirements for Preoperational and Initial Startup Vibration Testing of Nuclear Power Plant Piping System, ANSI /ASME OH3, Rev. 1 (proposed), May 1985
- 2. J. C. Wachel, Vibration-Induced Piping Stress, ASME FVP Confer-ence, Pressure Safety and Reliability, Orlando, Florida, June 27 through July 2, 1982
- 3. Investigation of the Damage on the Main Steam By-Pass system, September 30, 1985, trip report to Enrico Fermi 2 site by T. L. Wang j
- 4. Computer Code for Stress Analysis of Nuclear Piping - NUPIPE, Computer Program. Version 05, Level 00, Stone & Webster July 1974, revised February 1986 1047-1568011-HC4 9
__ _ - . _ ~ _ _ _ _ - __. - ._ - _ - - - _ - _ . -
l... .
i 5. Steanbaumer Analysis fr Piping System - STEEAN, Stone &
Webster Computer Program, Version 02, Ievel 03, July 1977, re-vised February 1936
- 6. Computer Code for local Stress Calculation - FILtk Stone
- & Webster Computer Program, Versies 03, Inval 03 (
4.0 FEASIBILITT STUDT OF MODIFTING INTEREALS OF MAIN STEAM ETPASS IRBIP VALVES .
i i
4.1 OBJECTIVE
. Perform a feasibility study for modifying the laternals of the esisting meia steam bypass dump valves to reduce acoustic energy and vibration. ,
4 4.2 DISCUSSION l As part of this study, English Electric, the designer and manufacturer of I the esisting steam dump valves, was contacted at their Rugby, England facility by M. Fortini of SWEC's Boston Office. English Electric stated that they do not believe there is or was any problem with their main steam bypass dump valves as supplied, and further esplaimed that they i would not recommend modifying the valve laternals. They also stated that j they do not have any experience with modifying valves internals in other
- applications. SWEC requested that English Electric supply names of the j utilities that have similar main steam bypass dump valves. English Elec-l tric responded that they do not have any similar valves installed in a j power plaats or other facilities la the United States.
i j In addition to the discussion with English Electric, detailed discussions regarding the feasibility of modifying the esisting valve internals were l
held with other valve manufacturers who have entensive esperience in sup-i plying valves to the power generation industry.
l i ..
These manufacturers include the Fisher and Masoneilan companies. Repre-sestatives from these valve manufacturers were shown available valve ar-rangement drawings, piping drawings, and were provided with performance requirements, noise limitations, and sising data for the suisting valve l
to aid them in assessing the feasibility of modifying the valve internals to accommodate high-pressure drop tria or other acceptable alternatives to lower the acoustic energy and vibration levels.
l
4.3 CONCLUSION
S ,
Based on the evaluation of the taformation supplied by the valve meaufac- '
turers and our own engineering judgment, modification of the esisting asia steam bypass dump valves would present the following problems:
4.3.1 Vendors would not be willing to guarantee the fast stroke time (0.22 sec) because of uncertainties involved la modifiing the esisting electrobydraulic operator to accept a tria case assen-bly with a stroke approximately 10 times as long as the stroke ,
in the esisting valve. This also is complicated by the lack of precise design data on the esisting operator.
i 1047-1568011-EC4 10 l
4.3.2 Vendors would not be tilling ta guaraatco the Cv versus per:ent opening or the moise level versua percent openias due to uncer-tainties in valve performance. Valve performance is not only based on the tria characteristics but on the internal profile of the valve body. Normally, performance esta is developed by estensive research and testing programs. Inthiscasejinthe absence of detailed shop fabrication drawings and rec 43 nising that the esisting valve physically cannot be removed to support testing, performance guarantees could only be estiastes at best.
The cost of modifying the esisting valve bodies would be pro-4.3.3 hibitively high. Although no detailed estimates were solicited from other manufacturers, preliminary information indicates a total cost on the order of that required to procure a new valve. The reason for this high cost is as follows.
Manufacturers have standard case, tria, and shaft designs.
giace detailed shop fabrication drawings are not presently available from Eaglish Electric, the valves would have to be disassembled in place and fully dimensioned. The vendors would then have to produce new shop fabrication drawings, incorporat-ing their internals, in order to develop machining directions.
This would require a much greater design effort than manufac-turers usually make in providing valves. Finally, ,an implace operation would be needed to complete the modification.
4.3.4 The sound attenuation requirements will require a large in-crease in valve travel. The contacted vendors all proposed a similar arrangement to handle the range of flows while limiting the noise generated by the valve. Basically, the trim would reduce acoustic energy by progressively uncovering a series of small ports. The longer the valve stroke, the more ports are uscovered and therefore, output flow is proportional to valve travel. To handle the range of flows, the esisting 1.553-in.
valve travel would have to be increased to approximately 14 in.
Comaequently, the new tria case would take up a significantly larger volume inside the valve. Preliminary indications are that adequately sized internals would not fit inside the esist-i las casing.
4.3.5 As noted above, the large increase in valve stroke would neces-sitate either modifying or replacing the esisting electrohy-draulic operator. Presently, there is insufficient data available to determine whether it would be feasible to modify the existing operator. What could be seen during a site walk-down, however, indicates that the required modifications would '
be extensive.
i*
4.4 REC 000ENDATIONS In sum ry, the valve manufacturers contacted are unwilling to accept either the contractual or the technical lisbility for modifying valve 1047-1568011-EC4 11
intoraals bas:d on th2 cbov2 stotcd r:asms. We, thersfare, woz1d not recommend attempting to modify the esisting steam dump valves.
5.0 FEASIBILITY STUDY - INDEPENDENT PRESSL5tE REGUIATING STSTEM 5.1 OBJECTIVE Perform a stady to determine the feasibility of providing a separate and independest pressure regulation system to operate in conjunction with the esisting main steam dump valves. The new system would operate to regu-late steam pressure during operational transients and plant disturbances such as partial load rejections or losses of one feedwater or recircula-tion pump, or as directed by the TG pressure control system, and would drive the valves full open following a full generator load rejection or turbine trip.
I
)
The existing steam dump valves would remain in service to manually con-trol pressure during startup and shutdown but, as discussed in Sec-tion 3.0 of this report, would be limited to 30 percent of their design flows to minimize the potential for acoustically induced vibration j damage.
i 5.2 TECENICAL REQUIREMENYS The independent steam pressure regulating assembly must be sized to l throttle saturated steam between 750,000 lb/hr and 3,716,000 tb/hr with
! an inlet pressure of 997 psia. Under all operating conditions, genera-i tion of acoustic energy should be kept as l w as possible. Based on pre-i liminary valve data, 105 dBA should be an achievable maximum level. .
(Note that ASME Paper No. 82-WA/PVP-8 defines maintaining 170 dBA as a design limit for 12-in. pipe to avoid acoustically induced pipe vibration j problems.)
To maintain controlability throughout the operating range, an array of I four control valves mounted on a common steam header and controlled in a l -
cascading arrangement was chosen. (See Figure 1. All figures for this section are found in Attachment A.) Each valve would discharge to the condenser via separate 12-in. discharge lines. Finally, each discharge l
line would be provided with a flow element and transmitter and restric-tion orifices.
This configuration was chosen for the following reasons:
- 1. Sas11er lines appear to be more resistent to fatigue failure.
ASME paper 82-WA/PVP-8, Acoustically Induced Piping Vibration in Eigh Capacity Pressure Reducing Systems, found some indica-tion that fatigue failure was more prevalent in thin-wall, large-diameter pipe. The authors recommended mains minimum-i diameter piping consistent with process requirements add maxi-j mum line velocities. j
~
1
- 2. Individual orifices in each line, each sized for 25 percent of total flow, will provide better pressure control over the oper-
- sting range.
i l
1047-1568011-EC4 12
_ - _ . __ ____ _ _. . _ _ - . . ~
- 3. A cir:10 manifold will permit Eco af hydraulic cetustars on each valve and a remotely located hydraulic power skid.
5.3 INSTALIATION REQUIREMENTS
, 'c The following criteria were used to determine the feasibility ofj design-ing and installing the conceptual system: .
i
- 1. The new valve assembly shall be designed to perform the follow-
- ing functions
'; a. Throttling 997 psia saturated steam in the operating range 750,000 lb/br to 3,716,000 lb/br as directed by j the turbine steam pressure control system.
- b. Opening fully in less than 0.22 see in the event of a turbine / generator trip or severe load reduction.
- c. Maintain acoustic noise levels below 105 dBA under all operating conditions.
i'
- 2. The plant location for the new valve assembly with its connect-ing piping must have a minimum size of 12 ft long by 6 ft wide by 12 ft high and must be usable without redesign of existing i piping and equipment. There also must be space avai}able for a hydraulic power supply, size not yet determined, close enough 4
to the valve assembly to minimize hydraulic tubing runs which j could affect valve response times.
1 l 3. Access to the proposed areas must be sufficiently clear of ob-structions to permit the carrying of piping, tools, and equip-ment, either fully assembled or, if access is limited, in the largest feasible sizes.
i l 4. Space for four 12-in. lines and required supports must be available between the valve assembly and the main condenser.
This space must either be free of interferences or minimize the redesign of existing large bore pipe, supports, cable tray, or ventilation duct.
- 5. Four additional 12-in. condenser nozzles are required. These may be either existing spare nozzles or new connections to be installed in the condenser wall.
5.3.1 Valve Requirements heo types of control valves were investigated for use in the pressure
- control system
- angle valves mounted vertically on a 24-in. head and globe valves mounted horizontally. For angle valves, an additional com-son valve chest and common operator arrangement (similar to the arrange-ment used or current BWR plants designed by GE-NERG) were also considered.
l
\
1047-1568011-EC4 13
Figures 2 cod 3 cra ekstch2s af o system using mais valvas. This cr-rangement has a minimum overall dimension of 12 ft long by 11 ft high by 6 ft deep. A design using globe valves sculd be espected to require less vertical space but more horizontal depth. -
g The common valve chest arrangement would be similar in height hd depth to Figure 2 but overall length would be closer to 15 ft. This is because it is presently designed to be fed steam from both ends.
To handle the full 3,716,000 lb/hr, each of the four valves should be sized to pass 930,000 lb/hr, which requires approximately 550 cv. Using i a Fisher Company catalog as a reference yields a valve, either globe or angle, with an 8-in. inlet and a 12-in. outlet. Valves of this size and capacity are available from several manufacturers and can be provided with noise reducing tria capable of reducing acoustic emissions below i 105 dBA.
i
- 5.3.2 space Availability l
In the course of this study two areas were identified as potential loca-tions for a pressure reduction manifold.
Area A is located on el 628 ft at the west end of the main steam tunnel, up against the south wall adjacent to the 52-in. mixing manifold. This
! area has approximately 12 ft by 6 ft by 12 ft available for installation.
Area B is located on el 613 ft at the north end of the condenser area near columns M x 11, directly below the existing east steam dump valve.
This area also has 12 ft by 6 ft by 12 ft available.
Figures 2 and 3 show a possible steam valve header located in Area A.
The basic equipment and piping can be made to fit; however, there is only minimal area for pipe and equipment supports and there is very little margin available for pipe expansion provisions if required by the stress j analysis.
l There is also no room for installation of a hydraulic power supply skid in I,ocation A; however, the valve operator area directly above the main steam valves on el 646 ft 6 in, appears to have room available, depending on the actual size of the hydraulic power supply required.
On this basis, it appears feasible to install the valve header in Location A. ,
The area of Location B, while physically large enough to acconnodate the valve header, would require relocation of several large bore piping runs.
The valve header itself would extend outward, partially blocking area access. The walkdown identified no available space in and around Loca-tion B for a hydraulic power skid. Therefore, it would be infes ible to install the valve header in Location B.
1047-1568011-BC4 14
5.3.3 Accessibility s .
Based on a walkd(wn of the affected tareas, accessibility to both Locations A and B is\autremely limited. ,,
t In I,ocation A any material would have to be rigged over the mshn steam piping. Similarly, in Location B, material would have to be carried in through the tight labyrinth access passage.
In recognition of the above, although access to the two potential areas is limited, it does appear feasible.
5.3.4 Pipe Routing ,
Should the valve header be installed in I,oestion A, the four individual discharge lines must drop down to el 613 ft, parallel to the existing i steam dump lines. This area is filled with large bore piping and valves ]
and, based on a field walkdown, it appears virtually impossible to. route .
additional piping through this area.
To reach a valve header at Location B,,it would be necessary to route a 24-in. line from the 52-in. manifold down to el 613 ft. ' As noted above, this area is extremely congested with large bore pipe. It does not ap-pear feasible to route an additional 24-in. line through this area with- ,
out major redesigr/ of existing piping.
Piping between Ideation B and the condenser would sbe similar for both locations. There are a number of interferenc'es on el 613 ft and pipe support locations will also be difficult to find. Beyond this, the floor cutout to el 581 ft 6 in. has adequate room for the horizontal run to the condenser on el 583 ft 6 in.
5.3.5 Condens'er Connectiona-Based on the results of a field walkdown and subsequent review of Condenser - General Arrangement Drawing No. T2-57, there does not appear l
to be four spare 12-in. or larger condenser penetrations to terminate the four new return lines. Additionally, the design of the concrete condens-er shield wall precludes the installation of any additional nozzles.
5.4 CONCLUSION
S i
Based upon a review of the above criteria it would be infeasible to pro-vide an independent steam pressure regulating system to operate in paral-1el with the existing steam dump valves. This conclusion is based on the following:
- 1. Extreme congestion in the pipe chase between the steam, the
! 52-in. manifold, and el 613 ft.
i*
- 2. Absence of spare condenser penetrations.
Additionally, although the following items would not make the change in-feasible, they will greatly increase the difficulty of any work:
1047-1568011-EC4 15
)
- 1. Large bore pipe, conduit, and instrument tubing interferences in Locations A and B.
- 2. Limited access for materials. ..
- 3. Difficulty of locating the hydraulic power skid, pardicularly for Location B.
5.5 ALTERNATIVE SCHEffES 5.5.1 Alternative 1 Preliminary analysis of steam velocities existing in the 30-in. dump lines indicates that these lines are substantially oversized for the ap-plication even at full dump flow of 1,858,000 lb/hr. Furthermore, limit-ing the existing steam dump valves to 30 percent flow would equate to a maximum flow rate of 557,400 lb/hr on each line.
Assuming an average downstream velocity of 8,000 ft/ min, (standard prac-tice for saturated steam flow is to size piping for velocities between 6,000 and 10,000 ft per minute), a flow of 557,400 lb/hr could be handled by a 10-in. line. Such a change would have the following advantages:
- 1. Provide additional space for running four new 12-in. lines to the condenser. -
- 2. Provide the opportunity to use the existing 24-in. steam dump condenser connections for the new lines.
Unfortunately, this alternative would not alleviate the extreme conges-tion between the 52-in. manifold and el 613 ft. Therefore, there would still be no feasible way to run the four 12-in. lines down to el 613 ft.
5.5.2 Alternative 2 The range of operating flows associated with startup pressure control and decay heat removal would be well within the capability of the independent pressure regulating valves if these valves were switched to manual con-l trol. Since the independent system would have to be designed for both throttling and fast open operation, these capabilities would also encom-pass the requirements for startup pressure control and decay heat removal and could be handled by the new valves if the existing steam dump valves were deleted from the system.
a There now appears to be no technical reason why the steam dump valves would be additionally required for an independent pressure regulating system. Actually, deleting the steam dump valves would offer several advantages: ,
- 1. Space now occupied by the 30-in. steam lines and valvds could be reused for routing the four new 12-in. lines.
- 2. The four existing 24-in. condenser nozzles could be reused.
1047-1568011-EC4 16
It sh uld be osted that I,ocaticas A ced B ore otill v2ry tight ced so action should be taken until a stress analysis verifies that the header,
'- as sketched in Figure 4, can be physically constructed and adequately supported. ,,
t 5.5.3 Alternative 3 Using the same four angle valves proposed above, it would also be possi-ble to split the header into two sets of valves located in the volumes originally occupied by the two steam dump valves (see Figure 5).
This alternative would have the following advantages:
- 1. Simplified pipe routing of discharge piping.
- 2. I.ess pipe flexibility problems.
- 3. Space allocation advantages.
- 4. Incation of hydraulic power skids above valves at el 643 it 6 in.
This alternative would have the following disadvantages:
- 1. More complicated control cable routing. .
- 2. Need for two hydraulic power supplies.
5.5.4 Alternative 4 The final alternative considered was prepared in accordance with Item 4 of DECO Scope Document No. SCP-86-019, and involves providing a purchase specification fer a replacement bypass valve.
^
This alternative would provide a single replacement valve for each of the existing steam dump valves to be installed in the same locations.
Bydraulic power supplies for the actuators would be located above the valves at el 643 ft. The valves would either be fit into the existing 30-in. lines or, if required to reduce vibrations, be installed with smaller diameter discharge lines. Smaller lines would reduce the noise generated by the severe expansion between the valve port and the adjacent 30-in. pipe.
The valves will each generate a noise level of less than 100 dBa at the most severe control point for acoustic energy and vibration.
The valves will be able to pass 1,858,000 lb/hr with an inlet pressure of 997 psia and an outlet pressure of 527 psia during the maximum flow con-dition and be capable of maintaining 375,000 lb/hr with an inlet pressure of 997 psia and an - outlet pressure of 104 psia during startup mode.
They will have an approximate inlet diameter of 16 in. and outlet diane-ter of between 20 in. and 24 in. with a Cv of approximately 1,175.
1047-1568011-EC4 17 i
- - .---.--_.u.. . ,- _~..,_-_._,_.m, , . , , - - - - - - - , m,.-
Th2 downstrsam brsakdown crifica plates will smarcts o subst:ntici dBA level. This could be partially alleviated by removing the orifice plates and replacing them with a diffuser which would act as an orifice plate but would contribute substantially to noise attenuation.
t 5.6 REcot9ENDATION As a result of this feasibility study, Alternative 4, the installation of a replacement steam dump valve, is the most feasible and provides the best chance of resolving potential problems with the redesigned system.
6.0 PURCHASE SPECIFICATION FOR A REPIJCEMENT TURBINE STEAM BYPASS CONTROL VALVE 6.1 GENERAL CRITERIA Specification No. 3071-012-TUR-132 has been prepared to cover the pro-curement of replacement valves with new electrohydraulic operators.
These valves have been specified to throttle over the full range of re-guired flows, between 375,000 to 1,858,000 lb/hr of saturated steam per valve. Two replacement valves would be required.
These valves have aise been specified to have a fast-open capability of 0.22 see to full open, which is equivalent to the existing English Elec-tric valves.
6.2 NOISE CRITERIA The vendors contacted during preparation of this specification, Fisher .
I Valves and Masoneilan, both stated that the use of appropriate noise-reducing tria would reduce acoustic levels below 100 dBA; therefore, we have used 100 dBA as a specified limit (reference Section 3.6 of Specifi-ration No. 3071-012-TUR-132).
6.3 PHYSICAL SIZE LIMITATIONS Both Fisher and Masoneilan concluded that an 18-in. m 24-in. angle valve would be appropriate for this application. In this case, the replacement valves would be physically smaller than the existing English Electric valves. Consideration should be , given to verifying from the bidders' proposal package that this smaller size is being provided.
~
An additional limitation is imposed by the 60-in.-diameter circular cut-out directly above the existing valves. Since ,the new valves must be installed down through these holes, this also must be considered in re-viewing the proposals.
6.4 CONTROLS INTERFACE At the time this specification was prepared, the detailed interface be-tween English Electric's turbine steam control system and a new electro-hydraulic control unit was not defined. It is anticipated that additional control devices may be necessary to complete this interface.
1047-1568011-EC4 18 m
. , - - - , ,- - ,w 9 ,,.--m-- --,,wyiw=-piw=rr ,-v-- '- - en,-v-------+---T P-* =***-w- - - ' - - - " ' -
Th2 dateilo sf th2 es= trol cystem interface chsuld be addrssssd during the EDP preparatica for installctica cf th2 gew valvas.
7.0 CONCLUSION
S AND REC 0f0ENDATIONS As a result of the analysis performed in Section 3.0, it is decluded that the modifications performed under EDP-4410 are not adequatef to pro-vide a long-term solution of vibration-induced fatigue failure.
Based on this analysis and our review of the other conclusions described in Sections 4.0, 5.0, and 6.0, SWEC reconnends replacement of the steam dump valves as the most effective long-term solution by valves designed specifically to handle the expected range of flows and to keep noise lev-als below 100 dBA.
SWEC believes that the driving force for the excessive vibrations experi-enced in this system is the English Electric valves. Installation of noise-reducing valves will reduce the magnitude of the forcing function, i which will in turn significantly reduce the pipe fatigue.
For the short-term period until the bypass valves can be replaced, SWEC recommends that the following actions be taken:
- 1. Any strain and vibration data taken during system restart should be forwarded to SWEC for review. This additional data will permit SWEC to revise its fatigue life estimates.
- 2. The satisfactory operation of the superstiff clamps installed by EDP-4410 was an assumption used in the analysis. SWEC has no experience with this type of device and did not review the clamps' design bases. We would recommend that the clamps be monitored during operation for evidence of slippage and/or pipe crimping.
O 1
1 1047-1568011-EC4 19 b
E. Farmi 2 -
Attechnent A St >as Byp :ss system Study Pas; 1 cf 5 J.O. Ms. 15680.11
- i. '
I T k 52' Mswirotb .
3,. T h* 30' c *~. g- -EDey Tg g
-o
'7h M L i
, ,. g,r, s-A s
N i
'l 13 ~ G u sts.sc e ,s*
U D';
9/
QHn; ,,.. $\ '
f i
tl' _s qlt !
I
/2- l \
-)
....'"'%.._, . . _ ^. J l
b T'T d
[/6&8E / SCALE:
JNDEPENDeMr .5 11?* 4 PRc:uge~ ante; RC&uLAT1HG 6ysWH nPenovco suricM NUMBER s;rvisioNs h h h ,
h;
. ~ _ . . . - . . . _ _ _ _ _ _ . . - . _ _
E. Fntai 2 .
l1. Attachment A *
, Steam Bypr.m Synten Study p. : 793, 2 cf.5 .. .
- J.O. No. 15600.11 ,.
l -
1 ,
1 -
i
. 1 .
i ,
i ,
\
1
.._..u. . , _ . _ _ _ . . .
g ,,,
- F~lCuRE 2 Locenen A .. _ . . _ _ _ _ _ _
I.ii
@ . Mto. --
'@;'l ,
\ N ,
,&^f_ , %, y 4r 3
n' t'G 7
n O . / c.wwe J
( - --
/ \
(k .
{
Tr<,-,~ &~<
a.< a j .,
ws s f Gs i...
-b' '
,e - ,i .3. vu s '
'h' 4~ x,' i ,
- e
.o '
}
' *xx hrW l '
l
) ' /
' -eru m M a s .r*e-
,. m , ,. n..,n.a
?
..~ _ i> .
r -
m.. aw r r .
y.( A- '- Y~.," -~~- -
)
'~-.(.:4:-y 9. . 4 - x ; n
- s.- i b.' s.~
- ,ic .
- ,' i Hee .' -
~
\ f
( M,,
, - , <t ,
j, u i .s e I I
j %,j'.," ' .
8 M' A[ ,
j,.g Q.().{ .;
dI% Y
< 4 y?l.r m ..eae..new-
,,l,
,,ig
.,, 4
-_e.e. -w- .
4 1
il
, , , e , . , , e
'"'*. Orldrs -h we JE'
.?
. 4 ., .s7 .
_gtg fs- f.s* fs' We* ^
AEM_MWr..lfut_
. ,.2
- t. % :. . ,.4 *t!.e, _
);., a g8 L
'k .g dI ESP >-#// _
g a. g __
1 ,3 iV .
4 .
. s.
- i _. _ _ _ _
~ ~
,.t. .. . . s.i . t. . u r ' .W r * \ < . - .s n '$N. k .
- n ,sf ? as a1. w or '
E. Fenni 2 Attactment A Steam Bypass dysteen Study
- Page 3.of 5 J.D. No. 15680.11
, s,
. + . . ), . '
i.-. .
.r. . ~
- i .
i -t i
l i :4~,@.
.Ficu. e..r._3 _ .L ocnn__sw A I .
t
', l'i'y _
- a. l .:.Q.
s T
/..taeana ()-()-
~
3
(_ C, .
l h, . ./% */%..
s% .s (i
~ - -
. .- 4
.; .)
~
H .;;'.:o
~~
H Sh'H v
' ~
~S\' V
~
Nl/ /J~ 4 e se'.s' nv
., / hx _ e i g
.gp_g- , .',
- K u__ >' -- ~94 )c)c ).4 < == =&*'
. J _ _ _ _ :-
.. -r .
m e v n n e n ,s
.. .: .: - . m.
. . t .." % ,,.,. --- ~
u o,
) ~
e.
L L l . . . . . . - - . -
e #1" /*/ , ,
s e
g su-g ...
4 .
. l
E. F.rai 2 Attcchment A
' Stcan Bypros System Study Fas2 4 cf 5 J.0. No. 15680.11 5
6 2** M M Ifot D WTE)
-~
.. s grm g)La,,,:;
'E Ap g H ,,. M ,
( I t I !I_ . %
Ft i #2a 'l \ }
- c. w' W }ur_ _ _ _ _ gg; g
i! 12a j
g I ADD l
l e
o 5
6 TITA.E f/6uRE + cut:
CHECKED DATE:
CORRECT ~'
APPROVED SKETCH NUMBER C"EvtSIONS h h h I l
' ~~
e ernrtznnna ammowm svarvamim
, . e'
'
- Attcchment A
~' E. F rmi 2 Pcg2 5 ef 5 Steam Bro si system study J.o. Ms.15680.11 Y
I' i es- r '8 " ;
m $ 2 *e M (4/ V / F O L O i ga ge
.a -
k y24 6--
, =
I 3. r r , mO .
l Ts ' ' FK t
P 1 P 1 I
/s & /-
To CDNMA/.sER e
1 i
/6DMb SCALE.
CHECKED CCRRECT DATE :
APPROVED SKETCH NUMBER l
CEvtS80NE h! h -
h hl t -- , - - - , , ---- . . - , . . . . . _ , . . . . . . . ,. - - _ . _ - _ _ _ _ . _ _ , . , - . _ , . - - . - - . . - - - - - , . . . ,