ML20058A454
| ML20058A454 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 10/26/1993 |
| From: | Joseph Willis DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML20058A447 | List: |
| References | |
| CNC-1201.04-01, CNC-1201.04-01-0001, CNC-1201.04-1, CNC-1201.04-1-1, NUDOCS 9312010091 | |
| Download: ML20058A454 (14) | |
Text
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HEWSiON 14 Form 01077 (R7 92) l rvfict 4-.
CERTIFICATION OF ENGINEERING CALCULATION bcdTAniba ( ) AIh 2-STATION AND UNIT NUMBER TITLE OF CALCULATION 006fa b i f ihu nh (/uc ka b)plh on KC Q ggy-
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CALCULATION NUMBER CAdC-l2OI.04-DI-D00/
ORIGINALLY CONSISTING OF:
/
PAGES THROUGH bf4 TOTAL ATTACHMENTS I
TOTAL MICROFICHE ATTACHMENTS TOTAL VOLUMES I
TYPEICALCULATION/ ANALYSIS YESO NO F TYPE I REVIEW FREQUENCY b, A THESE ENGINEERING CALCULATIONS COVER OA CONDITION ITEMS. IN ACCORDANCE WITH -
ESTABLISHED PROCEDURES, THE QUALITY HAS BEEN ASSURED AND l CERTIFY THAT THE ABOVE CALCULATION HAS BEEN ORIGINATED, CHECKED OR APPROVED AS NOTED BELOW:
ORIGINATED BY DATE
/0 'N ~ O 3
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CHECKED BY 2 M Il /
DATE
/D -/ 4 - 73 i
/O-/Y-APPROVED BY DATE ISSUED TO DOCUMENT CONTROL DATE RECEIVED BY DOCUMENT CONTROL C.".T MICROFICHE ATTACHMENT LIST: O Yes 91[o SEE FORM 101.4 RE CALCULATION PAGES(VOL)
ATTACHMENTS (VOL)
VOLUMES ORG CHKD APPR g
TE R
REVISED DELETED ADDED REVISED DELETED ADDED DELETED ADDED DATE DATE DATE E
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tJlA N/A 9)A tJlA dlA (vol.r)
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9312010091 931115 PDR ADDCK 05000414 P
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Operability of Cracked Weld on KC Hx. 2B Statement of Problem / Purpose The cracked weld is located near the bottom center of the 2B KC Hx..
This weld is a circumferential butt weld between two cylinders, h crack consists of 4 distinct, parallel, discontinuous, overlaping cracks.
The cracks run perpendicular across 'the weld.
The approximate combined length of the crack is 1.0".
Per attachment A the crack is due to an existing flaw in the weld and not due to fatigue. The crack will be repaired during the next Unit 2 refueling outage. The purpose of this calculation is to determine if the crack will remain stable until the next Unit 2 outage for its design loading conditions.
Quality Assurance Condition This calculation is QA condition 1 becane it serves as the basis for the qualification of a QA condition I stmeture, system or component.
Analysis Methods Used
)
Method 1 l
The above condition will be evaluated using hand calculation employing Linear Elastic Fracture i
Mechanics (LEFM) methodology (see pages 1-5).
1 Method 2 (See attachment B, pages land 2)
This condition will also be evaluated using Generic Letter 91-18 sectiot 6.14 (Flaw Evaluation).
Paragraph's 3 and 4 state that moderate energy Class 3 piping (maximum operating operating temperature less than 200 degrees F and a maximum operating pressure less than 275 psig) may be evaluated using Generic letter 90-05. The component in question is however not a pipe but the shell side of a heat exchanger with a 64" diameter. Both of the components are long cylindrical vessel with thin walls. The crack is located at a distance of 4.5" from the only discontinuity in the region, which is a support saddle.
I Catawba Nuclear Station Unit 2 Page:
Operability of Cracked Weld on KC Hx. 2B File No.: CNC-1201.04-01-0001 Rev. I g
By:fM Date: /0/25/'73 Check:
N3 Date:
/0hdC
.4
Amlysis Methods Used (cut.)
This distanc: is greater than the square mot of Rt (R = 64.125/2 = 32.06" and t = 0.5625" see ref.
3 page 2.3, (Rt)" = 4.25"). This would locate the crack in a region of low discontinuity stress.
Based on the above sinularities the accepted method of thmugh wall flaw evaluation given in Generic Letter 90-05 will also be used to evaluate this condition.
References
- 1. Elementary Engineering Fracture Mechanics, By David Bmek 2.1992 ASME Code Section XI Appendix A and E
- 3. KC Hx. Stress report CNM-1201.06-0081 rev.1
- 4. Flow Diagram CN-2573-1.0 rev.14
- 5. Attachment A
- 6. NRC GenericLetters 9005 and 91-18 Assumptions Listed as used in body of calculation Evaluation
'Ibe crack will be evaluated using linear clastic fracture mechanics. 'Ihe crack is known to be thm wall because the vessei is leakmg. The leak consists of about 15 drips per minute which is not considered a significant amount. Based on a review of the stress report (See reference 3) the only significant loading normal to the crack is boop stress. 'Ibe center of the crack is also Imated at a distance of 4.5" from the closest discontinuity, this is greater than the square root of Rt (R =
64.125/2 = 32.06" and t = 0.5625" see ref. 3 page 2.3, (Rt)u = 4.25"), which would put the crack in a region of low discontinuity stress. 'Ihe only signi& ant cyclic loading will be that of pressurmng and depres9 Wag the vessel. 'Ibe 4 cracks will be considered as one continuous crack 1.0" long. The stress intensity factor KI will be calculated using reference 1, page 76, table 3.1. The model assumes a crack of length 2a in a flat plate of width W. Since the vessel is a cylinder with a 5' diameter the width W was assumed to be inf' mite. ' Ibis would make the equation for KI as follows.
Catawba Nuclear Station Unit 2 Page:
2-Operability of Cracked Weld on KC Hx. 2B
' File No.: CNC-1201.04-01-0001 Rev.1 By: ON Date: / 0 / 25 /4 3 Check:
kO Date:
/o/2 (,/ 93 i
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s.
Evel=tism (cet.).
KI = (stress normal to the crack) * (3.14 ? a)*8 atese Normel to Cred i
1l il ll il iI y
w n n o o n
. y C*ntata Stresses Normal to the Crack Hoop stress = Pd/2t where: P = 135 psig (see ref.4) 1 d = 64.125" (see ref. 3) t = 0.5625" (see ref. 3) -
= (135
- 64.125) /( 2
- 0.5625)= 7700 pai or 7.7 kai Residual stresses due to fabrication - Per reference 2 appaadh E table E-2 residual stresses due to fabrication may be assumed to be +/- 10 ksi. Based on the thin wall of this vessel and the direction of the crack a residual stress of 5 kai should be sufficient.
Total stress normal to the crack = 7.7 + 5.0 = 12.7 kai Catawba Nuclear Station Unit 2 Page:_ 3 Operabdity of Cracked Weld on KC Hx. 2B Fde No.: CNC-1201.04 010001 Rev.1 c h ek-
/k Date:
Ik* 6 bT
'O,,M Date: 10/25./9 i By:
4 sp g
Evaluation (cont.)
Calculate KImax. and KI min.
K1 max = 12.7 * (3.14
- 0.5)" = 15.9 ksi (in.)"
K1 min = 5.0 * (3.14
- 0.5)" = 6.3 ksi (in.)"
Determine delta KI delta KI = KI max. - KI min. = 15.9 - 6.3 = 9.6 ksi (in.)"
Detemune R R = Kmm. / K max. = 6.3 /15.9 = 0.4 Per reference 3 the tank material is carbon steel SA-515-70. Per reference 2 appendix A article A-4200(b) and A 4300(b-1) the lower bound curves contained in the appendix can be used if actual data is not available. Since this flaw is thru-wall, and is exposed to water, section A-4300(b-2) of reference 2 will be used. Using A-4300, equations 1,3, and 4 of reference 2, with a delta KI of 9.6 and R = 0.4 calculate the crack gmwth (a) per cyc';.
Max. delta KI for low delta KI values = 17.74[(3.75 x R + 0.06) / (26.9 x R - 5.725)]*
where: R = 0.4
= 17.74[(3.75 x 0.4 + 0.06) / (26.9 x 0.4 - 5.725)]"
= 13.24 ksi(in )" > 9.6 use low curves da / dN = C, x (delta KI )* Where: Co = 1.02 x 1042 xS I
S = 2.6.9 x 0.4 - 5.725 = 5.035 n = 5.95
= 1.02 x 1042 x 5.035 x ( 9.6 )"$ = 3.59 x 10" in / cycle 3
Ca:awba Nuclear Station Unit 2 Page: h Operability of Cracked Weld on KC Hx. 2B File No.: CNC-1201.04-01-0001 Rev.1
'/!A By: Cl M Date: /0/25/f3 Check:
Date:
/ o/2 & /N j
Evaluation (coat.)
To conservatively estimate the crack growth without, gmwing the crack and recalculating delta KI for each cycle, the da / dN value will be multiplied by a factor of amund 25, which would yield a value of 0.0001 in/ cycle, which equals 0.0002 total crack growth per cycle (2a = 2 x.0001 =
.0002). The above delta KI is based on a full pressure cycle, which is conservative, since while the unit is in operation the heat exchanger would remain pressurized even when not in service.
Since this crack is going to be repatred during the next refueling outage the total crack growth will be conservatively estimated by assuming 100 full pressure cycles. ' Ibis would make the crack growth equal 0.02" ( 0.0002
- 100 = 0.02) at the time of repair. 'Ibe final crack length would be approximately 1.02". 'Ibe critical crack length will be determmed using KIc from Fig. A-42001 of reference 2. The value of (T-RTNDT) was conservatively assumed to be -100 degrees F, this yields a KIc of about 35 ksi (in.)"'. Using the previous equation for KI and solving for (a), with KI = 35, the critical crack length would be as follows. It should be noted that the total crack length is equal to 2a.
2ac = ((KIc)2 / ((total stress normal to the crack)2
- 3.14)
- 2)
= ((35):/ ((12.7)2
- 3.14)
- 2)
= 4.84" using a factor of safety 2, 2ac = 4.84/2 = 2.42" or ac Since the crack length at the time of repatr is less than the critical crack length the crack is acceptable (2.42" > 1.02").
Conclusion Based on the above, the crack in the weld on the KC Hx. 2B, as dommen'~3 in PIP 2C93-0824 will remain stable until the end of the next Unit 2 refueling outage.
Catawba Nuclear Station Unit 2 Page:
6 Operability of Cracked Weld on KC Hx. 2B File No. CNC-1201.04-01-0001 Rev.1 Check:
/kb Da*.e:
I'2/ZGhL.
/n,/X,/4.R By:
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Date:
1 ATTACHMENT A PAGE 1 OF 3.
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CALCULATION CNC-1201.04-01-0001 DESCRIPTION OF FLAW The flaw is located in the circumferential weld adjacent to the smaller middle support of the 2B KC Heat Exchanger. -Specifically, the flaw is located in the circumferential vessel weld 4 1/2" from the vessel support weld and approximately 5 degrees from the bottom center of the vessel or 25 inches from the upper edge of the support.
The flaw was first identified by a drip of water.
The paint was removed from the vessel surface and an inspection was performed by Engineering Personnel (TL Mauldin, HD Mason, and SS Lefler) and also by Personnel from the Metallurgy Lab (Sue Anderson and David Bartlett). These inspections revealed two pinhole indications that resembled porosity in the weld and possibly a
crack.
UT examination was performed and these results indicated there was a crack approximately_one inch in length.
UT examinations on either' side of the crack found the actual thickness met or exceeded the nominal vessel wall thickness of 9/16".
Grinding of the surface of the weld was then performed to aid in examining and evaluating the defect.
This further surface preparation found the defect to consist of four discontinuous cracks spaced closely together.
Surface examination found the cracks to be limited entirely to the weld bead and approximately 3/4" in length.
One of the original pinhole indications was still visible in the middle of one of the cracks.
All of the cracks are located in a longitudinal orientation with respect to the vessel centerline or transverse to the ciremferential weld.
EVALUATION 1
Visual inspection of the defect concluded that this is a defect in i
the manufacturer's weld.
The cracks resulted from the pinholes or porosity that were observed.
The vessel welds were spot radiographed by the manufacturer. (Reference drawing CNM 1201.06-0051)
As a result, this defect would not have been found in one of i
the areas of the vessel that did not receive' radiography.
It appears that this weld was made by the vendor using a submerged arc welding process.
This is a common welding process used for fabricating pipe and vessel sections in the shop.
Discussions with Brian Kruse and Clyde Freeman revealed that some defects have been found in ' vendor submerged arc welds in other vessels.
CONCLUSIONS This defect was present in the weld when the vessel was fabricated.
The spot radiography performed'in accordance with ASME Section III I
-l
l ATTACHMENT A PAGE 2 OF 3 CALCULATION CNC-1201.04-01-0001 did not find this defect.
The nominal wall thickness measured by UT on either side of the defect is nominal wall thickness or greater indicating that the defect is not the result of corrosion.
,(
The small amount of water loss from the drip through the crack in the vessel wall'does not cause a problem with system inventory and operability.
Reference attached 10/13/93 summary of field examination from Sue Anderson.
II A, Date: O'/4~73 Summary By:
'n l
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Fromi SXA3347 --PRDC.
Date and time 10/13/93 08:42:19 To: HDM9312 --PRDC H. Dennis Mason SSL1401 --PRDC Samuel S. Lefler, TMM937$ --PRDC Tony M. Mauldin JFW8363 --PRDC BJK1331 --PRDC Brian Kruse I
From:
Sue Anderson 875-5326/5275 SXA3347 6:30-5 M-Th Anilytical & Predictive Technologies - Metallurgy Lab Generation Services Department
Subject:
. Leaking weld in 2B KCHX The Metallurgy Lab examined the leaking weld near the bottom center of the 2B KCHX at Catawba on 10/11 and 10/12.
First, the observations:
- Leak as!found was a weeping pinhole.
Difficult to see anything else due to heavy grinding marks.
- Station personnel ground weld flat and did some buffing - axial crack became visible.
Leak rate increased.
Met lab did some fine polishing in area and examined crack w/5X magnifier:
o crack was actually 4 distinct, discontinuous cracks o cracking confined entirely to weld bead o weld 1-1/4" wide; crack tip visible 5/16" from edge of weld, ran axially for 3/4" original pinhole leak visible as wide part of one of the cracks' o
From these observations, some thoughts:
- Fatigue cracking is virtually ruled out, as fatigue cracks do not form step wise on parallel planes.
However, must consider possibility that if parallel cracks existed as flaws, each could have grown independently.
- Most likely explanation is that cracks existed for some time as weld flaws.
The nature of the flaw is not obvious; the cracks are not in the direction in which hot cracking might occur, and hot cracking is not common in plain carbon steel. Due to the size of the structure, stresses generated during fabrication could have been significant.
The pinhole (original leak) at one crack is further evidence of weld flaws; pinhole leaks can sometimes result from interconnected porosity.
In this case, the pinhole may instead be a spot of localized corrosion:
flaws /
cracks open to the KC water would have acted as a crevice.
Although the KC water contains corrosion inhibitors, the environment in a crevice is different from the bulk water and is usually more hostile.
i If you have any questions concerning these thoughts or would like to discuss further,.please call.
~
l Thanks - Sue l
l l
Evaluation of Train B KC Heat Exchancer Leakace Since KC has redundant independent trains which are each capable of bringing the plant to a complete shutdown, and since KC trains automatically isolate upon lo-lo surge tank level in either tank, assured uakeup from nuclear service water (RN) is not needed to mitigate an accident.
Per the Standard Review Plan (NUREG-0800),
an assured makeup source must still be provided, however.
If a most limiting pipe rupture occurs (the assumed single failure) on 2B, then that train is unavailable.
RN makeup will not suffice, but may help mitigate a less severe break.
Per CNC-1223.24 0013, about 346 gpm can be delivered to each train of the KC system.
In this scenario, a leak on the order of drops per minute will not make any difference in the ability to achieve train separation before depleting the surge tanks during a pipe rupture.
Also, since for this case it is being assumed that the pipe rupture has occurred on train B, this leakage will not matter, since the train is assumed to be rendered ineffective anyway.
If the pipe-i break occurs on train A, there is still 346 gpm of makeup on train B with very little demand, since train B is assumed to be intact.
Compared to the ability to make up, the train B heat exchanger leak can be considered inconsequential.
l r
90-05 Evaluation of Cracked Weld (Attachment B) l 1
Evaluation i
Per section C, part 3, of generic letter 90-05, the stmetural integrity of a through wall crack like flaw may be evaluated using, part 3.a ("'Ihrough-Wall Flaw" Approach). The following is an
)
evaluatim using this method.
Determine t,,,, (Ref. ASME Code Section III Division I - Subsection ND, ND-3324.3) t,,,, = P
- R / (S
- E - 0.6
- P)
Where: P = Design Pressure (135 psig, see ref. 4)_
R = Inside radius before corrosion allow.
(31.5", see ref. 3 page 2.3)
S = Allowable Stress (17500 psi, see ref. 3)
E = Joint efficiency (A=nmM to be 0.8 per ND-3352 and Dwg. CNM-1201.06 51)
- t. = 135
- 31.5 / (17500
- 0.8 - 0.6
- 135) 1
= 0.306" l
Flaw relation to t,,,, as shown in figure 2b of 9045 - The maximum flaw length was conservatively assumed to exist at t,,,,.
i The length 2a for the flaw in question is 1.0" which is less than 3.0". _ 'Ibe crack is less than 15%
of the circumference byinW Stress at the flawed location - Based on a review of the stress report (See reference 3) the tangential stress prndirM by intemal pressure is greater than the longinulinal stress prndied by the combination of all other loadings, this stress equal 7.7 kai (see page 3).-
l Catawba Nuclear Station Unit 2 Page:
l 90-05 Evaluation of Cracked Weld File No.. CNC-1201.04-01-0001 Rev.1, Attachment B
/kb Date:
/0/24/N By: O Date: /C/IA/9Y Check:
,}
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Evaluation (cont.)
Determine Stress Intensity Factor K K = 1.4
- S
- F * (3.1416
- a)"
Where: F = 1 + A
- c + B cu + C c
c = a / (3.1416
- R) = 0.5 / (3.1416
- 31.78) = 0.005 I
R = mean radius ((64.125 - 0.5625)/2 = 31.78")
r = R / t,,, = 31.78 / 0.306 = 103.86 2
A = -3 26543 + 1.52784
- r- 0.072698
- r + 0.0016011
- r' 2
B = 11.36322 - 3.91412
- r + 0.18619
- r - 0.004099
- r' 2
C = -3.18609 + 3.84763
- r - 0.18304
- r + 0.00403
- r' a = flaw length / 2 = 1.0 / 2 = 0.5" A = -3.26543 + 1.52784
- 103.86 - 0.072698
- 103.862 + 0.0016011
- 103.86' = 1165.0 B = 11.36322 - 3.91412
- 103.86 + 0.18619
- 103.862 - 0.004099
- 103.862 = -2979.0 C = -3.18609 + 3.84763
- 103.86 - 0.18304
- 103.862 + 0.00403
- 103.86' = 2936.9 l
F = 1 + 1165.0
- 0.005- 2979
- 0.0052' + 2936.9
- 0.005 = 1.407 K = 1.4
- 7.7
- 1.407 * (3.1416
- 0.5)" = 19.01 ksi(in)"
Conclusion l
l Since the vessel is made of carbon steel, which is a ferritic steel, the critical stress intensity factor K will be 35.0 ksi(in)". Since the above calentata3 stress intensity factor is less than the critical value the requirements of generic letter 9005 have been met (K = 19.01 < 35.0
> OK).
l Catawba Nuclear Station Unit 2 Page:
2-90-05 Evaluation of Cracked Weld File No.: CNC-1201.04-01-0001 Rev.1. Attachment B Check:
M Date:
/ M, Z /./D
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ATTACHMENT 2 LEAKAGE EVALUATION a
5 m