ML19346A241

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Updated LER 81-041/03L-1:on 810304,failure Rate of 20% Was Observed on Snubbers Located Outside Drywell.Caused by Worn Snubber Poppets Due to Poppet Low Resistance to Pipe Vibrations.Snubbers Rebuilt.Unit 1 Snubbers to Be Replaced
ML19346A241
Person / Time
Site: Brunswick Duke Energy icon.png
Issue date: 06/01/1981
From: Pastva M
CAROLINA POWER & LIGHT CO.
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19346A239 List:
References
LER-81-041-03L, LER-81-41-3L, NUDOCS 8106050456
Download: ML19346A241 (15)
v • d • e


Text

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. LICENSEE EVENT REPORT Updnte Riport Proviru3 R p3rt Data 3-18 s t l l (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATIONF CONTROL BLOCK: l i

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CON'T M 8 3oyR$ [dl 0 l 5 l 0 l - l 0 l 3 l 2 l 4 @l 0 l 310 l 4 l 8 l 1 @l 0 l 6 l 0 l 1 l A l1 68 14 75 REPORT DATE 80 lh 7 60 St DOCKET NUM8ER 63 EVENT DATE EVENT OESCRIPT10N AND PROBAB,LE CONSEQUENCES h ,

l o 121 l While performing Periodic Test 19.6.1. Function Test nf Saforv Re19ead acco==4hla I

,o,3, gSnubbers, a failure rate of approximately 20% was observed on snubbers located outsidel

o,,,;the drywell. After evaluating the modes of failure and the high failure percentage l l c I s 1 [ rate, it was decided to shut down Unit No. 2. The snubber inspection continued and l l o is- 1h l as now been completed. Of the 640 snubbers tested, 130 failed the functional test. l l0l7ll l IoIe I i Technical Specifications 3.7.5, 6.9.1.81 l

'NI'E *^$E CO sis 8Ciot COMPONENT CODE SL8C O'E S E

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_ SEQUENTI AL OtCURAENCT REPORT R EVISION L EVENT YEAR R EPORT NO. CODE TYPE N O.

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33 3 [36Al@ 37 40 di 42 o. 43 44 47 CAUSE OESCRIPTION AND CORRECTIVE ACTIONS li j o i {The majority of the snubber failures were caused by worn snubber poepets which occurred g gdue to poppets' low resistance to pipe vibrations. The failed snubbers were rebufle. I ii121 1 retested satisfactorily and reinstalled. A 100% snubber reolacement has been l l g,;3; jscheduled for Unit No. 1 during its current maintenance outage. The Unit No. 2 snubbed i

1 g l valve bodies will be replaced during a future outage. I

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$ $ $*CWER OTHER STATUS i O RY DISCOVERY DESCRIPTION Ii l 5 l l E ]@ l 0l 9 l 5 l@l NA l lBl@l Routine Surveillance l ACTIVITY CO TENr RELEASED OPRELEASE AMOUNT OF ACTIVITY LOCATION OP RELE ASE li l6 dl 9l Z j @ l Zlgl 10 NA l 44 l'

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is u @ia t ,0N ttuij lWg[8l NA l ll ll llllll llljI i 4 'J tu 68 0 -) 50* 3 M. J. Pastva, Jr. 919-457-9521 2 PHONE. _,_

s 3 o s o sAif g & Asen "

1981 UNIT NO. 2 CHOCK SUPPRESSOR TESTING REPORT INTRODUCTION In March 1981, Carolina Power & Light's Brunswick Unit No. 2 began , testing hydraulic shock suppressors - snubbers - according to technical specifications.

A total of 640 snubbers were removed from service and functionally tested. Of this number, 130 failed the tests. An additional 80 snubbers were rebuilt for preventative maintenance, raising the total rebuilt to 210. A program was established to inspect and evaluate each snubber that was rebuilt. A large percentage of the rebuilt snubbers were found to be degraded with worn poppets, and deformed poppet retaining springs.

DESCRIPTION Each snubber pulled was functionally tested at least once. If a snubber failed the acceptance criteria, it was categorized as a " failure" and rebuilt, retested satisfactorily, and reinstalled. Those snubbers which passed with low margin were rebuilt, ratested satisfactorily, and reinstalled. These are classified as preventive maintenance rebuilds.

During disassembly all parts were inspected by an engineer or technician. Stan-dard inspection sheets were used for consistent inspections. The snubbers were then rebuilt using ncy parts as necessary and retested. After reinstallation all snubbers were inspected by plant QA personnel for proper installation. -

All test data and inspection sheets were forwarded from the inspection group to the evaluation group to determine from the information available the. reason for the test rejection and the cause of the degradations found during the part inspections. Included in this analysis was a determination if the system's operation had an effect on the function of the snubber to the extent it would cause failure; that is, determine if the snubber is " service sensitive."

An information file was established for each snubber received by the evaluation group. Each snubber was researched to determine which system and line it was from, and the function of the line. The location of the snubber was inspected for evidence of either snubber or pipe movement. The testing and maintenance history of the snubber was examined for past or recurring problems. Comments

! were also obtained from Operations personnel as to whether the line vibrated during service or had a history of water / steam hammer.

I From the information compiled in the folder, each snubber was first evaluated individually. The results of the part inspections were compared to the reason for test rejection to identify the rejection mode. Next, a determination of service censitivity was made. For this determination, all the information in the folder was weighed together. The determination that a snubber is service sensitive was not made unless the majority of the information substantiated such an evaluation. In cases where the snubber appeared to have experienced a l

water / steam hammer situation, the same snubber and adjacent piping on Unit No. I was visually inspected for signs of water hammer. Had a similar situction been identified, the line would have been declared inoperative and the applicable LCO initiated.

l

8 RESULTS_

The results of the evaluation program described above are shown in Tables 1 through 3. .

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DISCUSSION l

Comparing the test data for each snubber and the test criteria, the reason for test rejection for each snubber was identified. See Table 1. Test rejections include both snubbers rebuilt due to failure of the acceptance criteria and g

those rebuilt due to low margin. TI% most prevalent reason was ' low bleed. ' Of ,

the snubbers rebuilt for failure and preventive maintenance, 45*. were rebuilt )

because of low Lleed velocities. The second highest reason for test rejection .i was 'high lockup' which accounted for 17*. of the snubbers rebuilt.

Review of the inspection sheets for each snubber identified ' the degraded-condition of its co=ponents. Snubbers were frequently found degraded in more than one way. For example, a snubber could have worn poppets, and deterioriated  !

3 seals. The percentages shown in Table 2, therefore, represents the number of snubbers in which the type of degradation appeared.  !

Varying degrees of poppet wear were found in 62*. of all the snubbers evaluated.

This was predictable since the majority of the snubbers were rejected because of

  • low bleed velocities. The worn poppet grooves restrict nuid f1ow thus causing j lower velocities. ,

Evidence of spring capture was found in 367. of the snubbers rebuilt. Spring -f capture was identified either by spring imprints on both the poppet head and valve body seat or damaged poppet retaining springs. The' spring imprints i identified ranged from " slight marks" to " deep gouges. g Worn poppets, spring capture, and piston / cylinder wear (uniform wear of the h piston or cylinder wall) comprise the three major categories in Table 2. These I categories are the possible consequences of service related conditions. Pipe i vibrations cycle the snubber to the extent that the grooves on the poppet head i begin to wear, and the piston wears on the cylinder walls. Continued cycling g causes the retaining springs to fail and/or deform such that the spring can be ,

' captured.' l t

Deteriorated seals, grease in the fluia, and side loading (localized l piston / cylinder wear) account for the three remaining major categories. These categories are possible cmsequences of improper installation. [

l i By comparing the degradations found for an individual snubber with the reason for test rejection, the rejection mode was establistl ed. This was not always an ,

easy or clear cut task since more than one degradation could be present. The .

degradations were reviewed and a category was chosen as the primary rejection l mode. For instance, worn poppets can lead to low bleed velocities, spring g' capture can lead to no lockup, piston / cylinder wear or deteriorated seals can lead to either high bleed or high lockup velocities, and side loading can lead I

to binding. Worn poppets and spring capture were the rejection mode of 27*. and -!

16* of the snubbers rebuilt respectively; which, as stated above, may be attributable to pipe vibrations.

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9 As seen in Table 3, 41% had inconclusive evidence to determine the rejection mode. Included in this c'ategory would be the 8% that had no visible degradations. The rejections with no apparent degradation could be attributable '

to improper installation of 0-rings, etc., which was not evident after disassembly. ..

The 41% with inconclusive rejection modes are snubbers with degradations' which c.e seemingly unrelated to the reason for test rejection. A worn compression poppet does not contribute to' low bleed velocities found during the extension test. Worn poppets don't contribute to high bleed rates. Evidence of spring capture doesn't lead to low bleed rates. The 41% were reviewed, and no trends were observed. There were many different reasons for test rejection, and many different degradations found. However, worn poppets were evident in most of these snubbers.

Piston / cylinder wear, found in 31% of the snubbers rebuilt, appears to be a less sensitive degradation since it was the rejection mode of only'3% of the snubbers rebuilt.

Reviewing the inspection sheets for each snubber with the other information in the file, an evaluation of service sensitivity was made. Individual maintenance histories, line histories , field inspections, and operational comments were taken into account. Of the snubbers rebuilt, 37% were determined to be service sensitive. That is, the operating conditions of the line and/or snubber were found to have signs of vibration or water hammer and the type of degradation -

fot.nd could be caused by these conditions. 3e majority of the service sensitive snubbers were attributed to vibration, with a nominal number due to water hammer.

In addition to physical inspection of the snubbers, fluid samples were obtained and analyzed. The result of this indicated that nominal fluid viscosity for the GESF1154 fluid varied about + 10% from the typical published range of 175-195 anti-stokes at 77*F. An evaluation of the affect of this variation indicated a maximum impact of less than 5 ipm on lockup and fluid velocities. Also, since the functional test actually measures the lockup and bleed velocities, the viscosity affect is included in the test evaluation. Samples analyzed outside the nominal range indicated that foreign materiel such as grease accounted for exceptionally high viscosity readings. Enhanced maintenance instructions will preclude future problems in this area.

CONCLUSIONS In our review of the evaluations, the primary degradation and rejection mode was worn poppets. This is attributable to the poppets' low resistance to pipe vibrations. Replacing the valve bodies with a new, more vibration resistant one should lessen this anomaly. The secondary category of spring capture will also be lessened by replacing the valve bodies. A 100% replacement is scheduled for Unit No. I during the current outage. The valve body replacement is scheduled at a future outage for Unit No. 2.

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The remaining degradations are attributable to improper installation practices.

To prevent this occurrence in the future, the maintenance procedures have been revised with additional emphasis in areas found to be deficient suel, as increasing the torque value on the jam nut. Each snubber will be rebuilt and inspected during the service life of the snubber. Sufficient QA surveillance-to ensure proper installation quality will also be mainta'ined.

Snubbers - failing the functional tests -in the future will be rebuilt and the parts inspected. Particular emphasis will be given to identifying degradations; namely poppet wear, spring capture, and piston / cylinder wear; and noticing new trends. Engineering evaluations will be made as necessary.

In addition, the information below is provided in response to specific questions which have been asked by NRC Region II personnel.

Lockup Criteria The maximum lockup velocity criteria of 55 ipm was reviewed for all snubbers on both unirs. Vertical snubbers were uniquely analyzed to assure that this criteria was acceptable. Final results on both units found that no supports ,

would fail under this criteria; however, three supports per unit require upgrading to stay within code allowable stresses. These support modifications have been completed on Unit No. 2 and will be completed prior to startup of Unit

  • No. I which is presently in a maintenance outage.

Test History Of the 13 Unit No. 2 snubbers that failed in 1979, five failed in 1981.

Additionally, five'of the eight that passed were rebuilt for preventative maintenance.

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% of Total Rebuilt No Lockup 13 ,

High Lockup 17 , ,

Low Bleed 45 High Bleed 13 Other 12

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Reason for Test Rejection TABLE 1 .

% of Total Rebuilt Worn Poppets 62 Spring Capture 36 ,

Piston / Cylinder Wear 31 Deteriorated Seals 28 Grease in Fluid 7 Side Loading 7 None -8 Degradations Found TABLE 2 4

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% of Total Rebuilt Worn Poppets 27 Spring Capture 16 Piston / Cylinder Wear 3 Deteriorated Seals 3 .

Grease in Fluid <1 Side Loading i Inconclusive Evidence 41 Miscellaneous 8 .

Rejection Mode i

TABLE 3 I

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SNUBBER NO. SIZE TYPE OF FAILURE SYSTEM LOCATION 2B21-44SS129 3 High L/U (ext) Nuclear steam vent line 2" Nuclear steam vent line 2B21-701SS177 3 High L/U & bleed (ext)

- 2B21-51SS105 3 No bleed locked up in ret HSL condensate drain 2" 2B21-19sS194 10 High L/U (ext) SRV discha: ge line 6" j

i 2B21-6SS240 10 High L/U (ext) B feedwater line 2B21-18SS213 3 Low Bleed (ret) SRV discharge line 2B21-51SS113 3 High bleed (ext) MSL condensate discharge 2"

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2B21-7SS56 3 High L/U (ext) B feedwater line i 2B21-11SS220 10 Low bleed (ret) SRV discharge line 2B21-3SS12 3 No bleed locked up in ret A feedwater line 2B21-12SS312 10 Lc', bleed (ret) SRV discharge 2B21-11SS223 10 Low bleed (ret / ext) SRV discharge

~

2B21-11SS224 10 Low bleed '(ret) SRV discharge 2B21-2SS4 10 High L/U (ext) A feedwater line 2B21-34SS296 10 Low bleed (ret) SRV discharge i 2B21-6SS20 10 H!gh biced (ext) high L/U (ext / ret) B feedwater line 2B21-33SS251 20 Low bleed (ret) SRV discharge 2B21-19sS193 10 Low bleed (ext) SRV discharge i

L/U - Lockup ret - retracted i ext - extended 4

SNUBBER NO. SIZE TYPE OF FAILURE SYSTEM LOCATION 2B21-27SS270 10 Low bleed (ret) SRV discharge 2B21-59SS330 10 Low bleed (ret / ext) SRV discharge 10" 2B21-5SS17 - 10 Low bleed (ext) B feedwater line 2B21-58SS276 10 Low bleed (ret) SRV discharge 10" 2B21-12SS308 3 Low bleed (ret / ext) SRV discharge 2B21-33SS335 10 Low bleed (ret / ext) SRV discharge 2B21-11SS221 , 10 Low bleed (ret) SRV discharge 2821-33SS333 10 Low bleed (ret) SRV discharge 2B21-34SS299 20 Low bleed (ret / ext) SRV discharge 2B21-47SS155 3 High L/U & bleed (ext) Nuclear steam vent line 1"

. 2B21-27SS269 3 Low biced (ret) SRV_ discharge

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2B21-59sS329 10 Low bleed (ret) SRV discharge 10" 2 Ell-90SS277 3 No bleed (ret) RHR head spray 3/4" 2B21-58SS279 10 Low bleed (ret) SRV discharge 10" 2B21-44SS142 3 Low bleed (ret) Nuclear steam vent line 2" 2B21-20SS757 3 Lo'w bleed (ret) SRV discharge 2B21-27SS267 3 Low bleed (ext / ret) SRV discharge 2B21-llSS222 10 Low bleed (ret) SRV discharge 2B21-58SS305 10 Low bleed (ret) SRV disch+.3e 10" L/U - Lockup ret - retracted ext - extended -

SNUBBER NO. SIZE TYPE OF PAILURE SYSTEM LOCATION 2B21-26SS201 . 10 Low bleed (ret) SRV discharge 2B21-20SS261 10 Low bleed (ext) SRV discharge

~

2B21-2S53 3 Lou bleed (ret) A feedwater 2B21-58SS275 20 Low bleed (ext) SRV discharge 10" i

2B21-58SS277 20 1.ow bleed (ret)

! 2 Ell-90SS391 3 liigh L/U (ext / ret) RHR head spray 3/4" 2821-12SS310 3 Low bleed (ret) SRV discharge

' 2PSN-A2SS30 3 Low bleed (ret) Main steam line A 10" r

2B21-12SS312 10 Low bleed (ext / ret) SRV discharge 1

2PSN-B3SS47 20 High bleed (ext) Main steam line B 10" 2B21-llSS314 10 Low bleed (ret) SRV discharge 4

L/U - Lockup ret - retracted ext - extended l

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' SNUBBER NO. SIZE TYPE OF FAILURE SYSTEH LOCATION

,1

'2B21-12SS287 30 liigh L/U (ret) high L/U & bleed (ext) SRV discharge i .

. 'Sil-87SS318 30 liigh L/U (ret) B RilR return 2012-16SS11 - 3 liigh bleed (ret) high L/U (ext) CRD return line 1.

2C12-16SS8 3 liigh L/U & hieed (ext) CRD return line 2012-16SS10 3 liigh bleed (ext) CRD return line 2C41-9sS8 3 liigh L/U & bleed (ext) SLC pump discharge 1 1/2" 2C41-9sS11 , 3 liigh bleed ext high L/U (ret) SLC pump discharge 1 1/2" 2C41-9SS13 3 No bleed (ext) SLC pump discharge 1 1/2" i '

2C41-9SS5 3 tilgh L/U (ret) high bleed (ext) SLC pump discharge 1 1/2" 2B21-26SS207 30 Binding (ext) high L/U (ret) ,

SRV discharge No bleed (ret) i E41-4SS51 10 liigh L/U & (ext) IIPCI steam supply 2B41-4SS49 10 liigh L/U & bleed (ext) HPCI steam supply i

2C12-16SSI 3 liigh biced (ext) CRD return line ,

2PSN-B5SS51 3 Low Bleed (ret) Main steam line B 10" i

2B51-4SS66 3 liigh bleed (ext) RCIC steam supply

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4 2B51-4SS101 3 No biced (ext / ret) RCIC steam supply 2B32-SSB12B 5" No L/U or bleed (ext) '2B reactor rectre, pump L/U - Lockup i ret - retracted ext - extended l

SNUBBER NO. SIZE TYPE OF FAILURE SYSTEM LOCATION 2RCC-65SS129 3 No bleed (ext) 2A RCR pump cooling Nuclear steam vent line 2B21-44SS131 3 Low bleed (ret) 2RCC-71SS139 3 No bleed (ext) RBCCW to BRCR pump 2RCC-73SS145 3 No bleed (ext) RBCCW to 2C floor drain HX 2B21-26SS208 10 Low biced (ret) SRV discharge 2B21-3SS231 10 Leaking fluid A feedwater line 2B32-B9B 3 1/4" High bleed (ret) 2B reactor recirc pump i 2B32SSB6 3 1/4" Binding (ext / ret) 2B reactor recirc oump 2E41-2SS106 10 No L/U HPCI pump disch 2E41-2SS104 10 No L/U HPCI pump die:h 2 Ell-91SS575 3 No L/U RHR head spray

'2E21-2SS32 3 Low bleed Core spray pump 2A disch valve bypaas 2SW-103SS121 10 No L/U' SW supply to RHR booster pumps 2E51-42SS82 3 Broken shaft RCIC steam supply 2E51-40SS83 3 No L/U RCIC pump supply 2E41-61SS100 3 No L/U HPCI steam supply 2E41-2SSS 3 No L/U HPCI pump disch 2E41-6SS38 3 No bleed (ret) HPCI steam exhaust-L/U - Lockup ret - retracted ext - extended

SNUBBER NO. SIZE . TYPE OF FAILURE SYSTEM LOCATION 2E51-40SS85 3 Binding RCIC pump supply I' 2E11-18SS470 10 No L/U RllR LPCI injection a

2SW-173SSil4 3 Binding SW return line 2E41-6SS32 3 No L/U llPCI steam exhaust 2E41-6SS33 3 Pio L/U IIPCI steam exhaust 2E51-42SS80 3 No L/U RCIC steam supply

2E51-19SSil3 3 No L/U RCIC turbine inlet drain 2 Ell-46SS9 3 ~No bleed RilR pump discharge 2E51-40SS84 3 -No L/U RCIC pump supply a

2E41-12SS98 3 No L/U Fuel' pool cooling from RilR 2SW-106SS156 3 No bleed Supply i

2SW-153SS176 3 No L/U SW return line 2 Ell-58SS36 10 No L/U RilR pump B&D discharge 2SW-106SS151 3 Binding Supply to'RBCCW llX 2E41-6SS30 3 Binding IIPCI steam exhaust 2RCC-39SS80 3 No L/U RBCCW pump discharge 2E51-19SSil4 3 No L/U RCIC turbine inlet drain f

L/U - Lockup ret - retracted ext - extended v

SNUBBER NO. SIZE TYPE OF FAILURE SYSTEM LOCATION 2E41-44SS86 3 No L/U llPCI vacuua pump to vent 2E51-42SS79' 3 No bleed RCIC steam supply 2E51-41SS95 3 Binding RCIC pump discharge 2SW-174Ss70 3 No L/U SW return line

.2SW-139SS172 3 No L/U SW RBCCW llX outlet 2E21-6SS42 3 No L/U CS pump di,scharge 2E51-42S377' 3 Binding RCIC steam supply

]

2SW-142SS82 3 Shaft internally disconnected SW pump 2C discharge 2SW-106SS213 3 No bleed SW RBCCW llX outlet q

2E11-56SS13 3 No bleed RilR pump A&C discharge 2 Ell-58SS33 No biced RilR pump B&D discharge

) 3 47 2PS-3423 3 No L/U A0G 2PS-3417 3 No L/U AOC 2PS-3418A 3 No L/U A0G 2PS-3417B 3 No bleed A0G 2 Ell-53SS195 3 No L/U RilR heat exchange relief line 2E11-46SS510 3 No bleed RilR pump discharge 2 Ell-71SS174 3 Low bleed RilR drain to.radwaste

'i 4

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I SNUBBER NO. SIZE TYPE OF FAILURE SYSTEM LOCATION 2 Ell-47SS328 3 Binding RilR connection & IIPCI steam supply I 2 Ell-128bS355 3 No L/U Cooling for RilR liX 2A 2 Ell-71SS393 3 No L/U RilR drain to radwaste 1 2PS-3418B 3 No L/U A0G i'

2 Ell-68SS448 3 Relief valve lifting RilR return & test line j- 2E11-56SS517 3 No L/U RilR pump A6C discharge

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, 2 Ell-127SS435 3 No L/U Cooling for RilR llX 2A ,

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