ML20202F688
| ML20202F688 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 09/29/1997 |
| From: | Doyle J, Kocunik D, Komanduri G SARGENT & LUNDY, INC. |
| To: | |
| Shared Package | |
| ML20202F670 | List: |
| References | |
| NUDOCS 9802190275 | |
| Download: ML20202F688 (18) | |
Text
- 2 in
?
S Evaluation of Underground
- Essential Service Water Pipeline Leak
.)-
o Prepared for Wolf Creek Nuclear Operating Corporation Wolf Creek Station Prepared by
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QWA ser gerW& Luncty
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Prepared by: bL G. V. Komanduri hY C: '$<dC D. C. Kocunik
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Reviewed by:
Richard J. Netze September 29,1997 P C O O O 82 P PDR _.
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\ TABLE OF CONTENTS b
U East Purpose 2 Industry Experience with Buried Pipe Leakage 2
- Oyrter Creek 2
- Beaver Valley 3 -
e Farley 3 ESW Pipe Alignment 3 Geotechnical Considerations 4
. Excavation 4
- BuMH 5 Lcakage Scenarios 5 e Scenario 1: Leakage Through the Hedding of the Pipe 6
- Scenario 2: Seepage to the Ground Surface 7 StructuralIntegrity of the Pipe 7 Summary and Conclusions 8 References 10 Attachments Exhibits
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j Underground Essential Service Water Pipeline leak t
y S Purpose a3 Sargent and Lundy was requested by 'Volf Creek Nuclear Operating Corporatior.
(WCNOC) to address the potential problem ofleakage nom the underground ponion of the Essential Service Water (ESW) Pipes (both intake and discharge), The purpose of this evaluation is to determine if the pipes with a small leak would continue to be operable until repairs can be planned and implemented. Further, it was stipulated that the maximum leak should not be more than 140 gpm as determined by Wolf Creek Systems Engineering.
This leakage rate ensures adequate availability of cooling water during ESW operation (USAR, section 9.2.5, Ref.1). Two scenarios ofleakage flow propagation (seepage) and surrounding matedal transport are discussed and_the possible resulting conditions-are investigated hom the viewpoint of pipe fhilure.
Industry Experience with Buried Pipe Leakage Several industry related organizations were contacted - for reference material and experience repons. These organizations included the Bureau of Reclamation, American Water Works Assodation (AWWA), Ductile Iron Pipe Research Association (DIPRA),
Iowa Institute of Hydraulic Research, Geotechnical Research Centre, The University of Western Ontario, and the Water Distribution Department, City of Chicago. None of these organizations could provide any reference material relevant to the issue of addressing sustained pipe leakage. Their ext wience was to locate the leak, isolate and repair the lak.
Sargent and Lundy was refened by WCNOC to three nuclear stations where leakage from buried pipes have occurred: Oyster Creek, Beaver Valley and Farley Nuclear Generating Stations. These stations were contacted to describe.the type of pipe failures they experienced and the subsequent effects of leakage in the buried pipes. The telephone conversations are documented in Attachment 1. The following is a summary of the information obtained kom each station regarding their experience.
Oyster C>sek Naclear Generseing Staalon:
The leakages occurred in non-safety related wvice water pipe. The water transpoited by c the 20" diameter pipe was brackish water from the Barnegat Bay on the east coast and the leakage occurred due to failure of the coal tar coating and resulting corrosion of the steel pipe. The pipe had a nomal operating pressum of 50 to 70 psi. The pipe was buried approximately 14 feet below ground _ level. The backfill material around the pipe was (ossuitwomentapeness)
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' I a i locally availab!e sandy soil. The leakage was noticed at the pipe penetrations in the l s Turbine Building and also on the ground surface as bubbling water. In both cases the '
9 leakage rate was small. The leak was found by visual observation of bubbling water at the J
ground surfhce. Therefore, the high pressure in the pipe was dissipated by the time it passed through the leak opening and seeped through the backfill.
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Beaver Valley }%werStation:
The leakages occurred in the circulating water pipe and also in the fire protection lines.
The leakage in the 108 inch diameter circulating water pipe occuned at the joints. The pipe was buried 8 feet below the ground surface and had a water pressure of approximately 5 psi to 10 psi. The leakage appeared on the ground and the rate ofleakage was very small. The leakages were repaired by grouting the joints.
The fire protection lines were under pressure and were buried 12 feet to 15 feet below ground level. All the pipes were 6" to 12" carbon steel pipes. The leakage was detected by noting the pressure changes in the lines and were reptdred. There was some erosion along
- the pipes but only small cavities were observed.
FedeyNuclearStation:
The pipes where leakages occurred were 4" to 10" size fire protection lines and a 4" supply line to the chlorination building. The leakages occurred due to local exterior corroslou of the pipes. The circumstances leading to the leak and the duails of the surrounding bedding and backfill material were not known.
From the foregoing discussion ofleakages in buried pipes at nuclear stations, it it clear that none of the leakages occurred in any safety related pipes. The faihires were mostly due to corrosion of the pipes over a period of time or failure of joints. In addition, the soepage pathway for the leakage water was either along the pipe and bedding interface or vertically up to the ground surface. In all these cases the leakage rates were small and the failures were not due to large scale erosion of the material around the pipe or by a large blowout of the backfill. No substantial erosion of the bedding and/or backfill material was reported. It also appears that the leakage was noticed at the pipe penetrations inside a building or by water bubbling through the ground surface. The 6tructural integrity of the pipe was not a concem and repairs were undertaken to fix the leakage.
ESW Pipe Alignment There are two trains of supply (intake) and return (discharge) buried ESW pipes between the powerblock and the ESW pumphouse and the Ultimate Heat Sink (UHS). The plan and a typical cross section showing the location of these pipes are shown in Exhibits 1 and
- 2. The supply pipes are all 30" in diameter and the return pipes are 30" in diameter for ThiE wampmw
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part of the length and 42" in diameter for the remainder. Both the supply and return pipes !
- \ are steel pipes with weldedjoints.
4 j The supply and return pipes are placed in the same trench, with the centerline of the return 3
pipes 6 feet above the centeriine of the supply pipes. The two trains of pipes are
$ horizontally spaced at '20 feet center to center. The proAles of the ESW pipes were reviewed (Wolf Creek Design Drawings Ref. 2). The centerline elevations of the ESW
- pipes vary. The maximum and minimum depths from ground level to centerline of the l pipes vary from 21.65 A. to 17.5 A. for the supply pipes and 15.65 A. to 7.5 A. for the l return lines.
Each of the 42" dia noter return lines splits into two, with one 30" diameter line going to i
the ESW pumphouse as a warm water line and the other 42" diameter line going to the UHS as a discharge line. The length of each of the supply pipes is more than 3000 A. and l the length of each of the return pipes is more than 5000 A.
The general grade elevation for this evaluation is taken as 1999.0 A. (All elevatlons are referred to SNUPPS datum.) The design pressures in the supply and return pipes are 200 psig and 50 psig, respectively, (USAR, section 9.2.1, Ref.1 ) and the operating pressure is approximstely 150 pdg for the supply pipes.
- Geotechnical Considerations Ereamsdon
4 The geologic proAle along the ESW pipelines from the powerblock towards the pumphouse and the UHS is shown in USAR Figure 2.5-47, Sheets 1 and 2. This figure, in conjunction with the USAP, description and the Dames & Moore report (Ref. 3), state that ;
the excavation for the pipeline was extenkt down to the hard residual clay or into the Heumader Shale (Section 2.5.4.10.3.1, Ui. A, Ref.1 ).
The subgrade along the pipeline is either hard residual clay or shale. The permeability of i
both of those materials is very low, as shown on USAR Tables 2.5 34 and 2.5 35. The maximum value of the is.dility listed was 3x104cm/sec.
- The side slopes of the excavation were I horizontal to i vertical. The elevation of the bottom of the excavation varied, but was generally at elevation 1982 A. Extensive y dewatering was not required during pipoline installation cince there was no standing ground. vater reported in the excavation, with the exception of rainfall.
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9 Figure 2.5105w of the USAR (Exhibit 2) shows the typical backall section along the o ESW pipelines. The bedding beneath the pipes was a granular matarial 12" thick when the .
w subgrade was hard shale and 6" thick whan the subgrade was soAer or weathered shale.
There wm 12" of the same grar.ular material above the crest of the pipe. There was generally 12" of the granular material between the pipe and other pipes or electrical ducts t~
in the same excavation. Similarly, there was a minimum of 12" of granular 611 between the edge of the ripe and the side of the excavation. This granular material was compacted to ;
a minimum relative density of 80% per ASTM D2049.
The remainder of the excavation above the uppermost pipes was backfilled with cohesive material Aom the pipeline excavation. This material was compacted to a minimum of 95%
of ASTM D698.
Most m the granular material used around the pipes has the gradation requirements of Altemate 2 which was 95 - 100% passing the %" sieve,0 20% passing the #4 sieve, and 0 - 8% passing the #8 sieve. This is a coarse sand gradation with a Da size of-approximately the #4 sieve (0.48 cm). The data indicates that most of the material had 1 -
5% passing the #8 sieve.
'the estimated permeability of the bedding matenal is approximately I cm/sec. Based on ,
the information fbm the Dames & Moore report (Ref. 3) for the pipeline installation, '.
some of the bedding material could have a Sner gradation equivalent to Alternate 4. This l material had a maximum size of #4 material with 0 15% pasring the #100 sieve _ <
Leakage Scenarios For the evaluation of the potential consequences ofleakage it is assumed that the water in the supply pipe is under a maximum pressure of 150 psi and the maximum pressure in the return line is 50 psi. A maamm allowable leakage flow rate of 140 gpm is determmed for '
either pipe based on the maximum water loss that can occur and still maintain the cooling fhnellon of the ESW System. ,
Two scenarios for leakage and possible erosion of the material surrounding the pipe were considered. These~ modes ofleakage propagation and erosion were' identified based on discussions with personnel at other nuclear stations as discussed in the section on Industry Experience with Buried Pipe Leakage.
It la estimated that with a pressure of 150 psi in the pipe, a leakage opening size of
_approximately 3/4' diameter would be required to pass a flow of 140 gpm considering the ,
opening as an orifice discharging into the atmosphere.
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- enanto 1: Leahnwe Along and nrough the Bedding ofthe PIfpe:
i9 lT In this scenario, the Waka6e fkom the pipe exits as a jet of water and locally compacts the ;
!j surroundir.g soil, and then soaps klong the exterior of the pipe and through the adjacent l bedding material. The backell gets saturated and, as the water contim.os to flow out of the opening, a hydraulic connection is made and the outside submerged granular backfill material will be under pressure. As water continues to leak from the pipe, the leakage rate would be restricted by the seepage rate through the bedding material and hence the _
differeraial pressure .4om inside to outside of the pipe would decrease as the outside pressure in the water n the submerged material increases.
The permeability of the granular bedding material is several orders of magnitude more r
than the permeshility of the surrounding in situ clay and shale. Therefore, the pipe leakage would seep alons the exterior of the pipe and thrmagh the beddins, but would not permeate out through the natural soils and rock, The seepage through the bedding material could cany the fines in the bedding, w15ch are a very small percentage of the bedding (less than 10%).
The curra.nding soil is shale and residual clay, and therefore no large pathways for
! r.gsge to escape and carry the surrounding material are expected. The clay and shale wculd potentially swell due to the presence ofwater and self-heal any cracks. Therefore, it is anticipated that the seepage through the bedding would not carry any significant i
amount of Ane material from the surrounding cohesive soil. Hence, the creation of a cavity
- in the pipe bedding that would be a detriment to the pipe is not possible.
If a small cavity could form, the following is an analytical approach to estimate the <
maximum extent of an erosion cavity. Wimi a free jet fhlis vertically into a pool in a riverbed, a plunge pool will be scoured as a result of the abrading action of the churning water and sediment in the pool. The scour will reach a limiting depth as the energy of the jet is no longer able to remove bed material from the scour hole. A simple empi.ical approximation for the ultimate scour depth using the flow rate and the pressure head is l given in the book ' Design of Small Dams' by U.S. Bureau of Reclamation (Ref. 4, Chapter 9, page 402). Using this empirical relation, the maximum scour hole is estimated to be 2.6 ft. into the surrounding material from the periphery of the pipe at the leakage opening It should be emphaai-i that this scour hole is estimated for an rpen jet impinging on a natural soil surface. For the case of a leaking jet in a confined environment 4 with compacted bedding and ha-Will. the extent of the scour hoie or erosion cavity would be much smaller. Therefore, even if this cavity could form, its small size it would not effect j the structural integrity of the pipe.
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, It should be noted that the erosion and transport of the fines in the bedding material would .
i \ be possible if an exit for the seepage water and the eroded matel exists. Considering the i long length and variation in the elevation of the pipes, this is porsible only if the leakage j( location is very close to the power block, or near the ESW pumphouse and the UHS. If i
- , the leakage Ands its exit pathway to the powerblock buildings, the leakage at the pipe j a penetrations in the walls would be detected and immediate repair could be done. If the i 4
leakage pathway is to the ESW pumphouse or the UHS, the leakage would not be a loss l l of water u it returns to the UHS and replenishes the ESW system. However, in either i
- case the size of the cavity would be small as discussed earlier, i
1 Seasonio h Sepage to the GroundSurface:
! In this scenario, leakage water under some residual pressure would seep upwards towards ;
l the ground surke through the tedding and the cohesive backftll. Since there is a i hydraulic connection between the water in the pipe and the water along the seepage path, there would be seepage pressure acting on the water. -
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This seepage pressure would be much less than the pressure in the pipe due to energy loss
- in the leakage water when it passes through the opening, due to. severe turbulence in the
- cavity around the pipe, and due to Siction losses during its travel vertically through the bedding and the cohesive soil hacMil. When the residual neepage pressure exceeds the i
overburden pressure, the water would come bubbling out of the ground. This would be
- . noticed and proper repairs could be performed in a timely manner, hem- of the small leakage flow rate, the flow momentum is not high enough for the l water to cause a blowout and the Bow will not be able to move a large amount of backfill.
! It is highly unlikely that a very large hole would open up from the ground surface all the 4 way down to the lower pipe with a flow of 140 gpm, because of the energy dissipation of the water jet and the cohesive nature of the backfill. In order to open up a large hole from the ground to the buried pipe, several thousand cubic feet of material would have to be washed out, which is not expected.
4 Leakage fiom the supply pipe, u it soeps upwards, would tend to saturate the granular backfill around the return pipe, which is 6 fee: above the supply pipe. This saturated soil condition does not affect the structural capability of the return pipe.
4 StructuralIntegrity of the Pipe
]
In consideration of the structural capacity of the pipes, subject to. changed loading configurations caused by the changes in backfill condition that are postulated in the two L scenarios presented, two modes of behavior are considered. That is, the ring capacity of r ;
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a the section, in case lateral support of the soil surrounding the pipe is lost and the buckling g capacity of the pipe, assuming the groundwater table is at the ground surface.
M N Regarding the Scenario I loads, the loss oflateral support is not critical because of the
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D ring capacity of the intake pipes and the fact that the total length oflost support is less
- than two pipe diameters. The capacity of the 30" diamotu pipe to support vertical loads, without lateral support, assuming dmhys.mt of plastic hinges at the spring line, invert ,
and crown of the pipe, is 1.4 times the overburden load on the intake lines. For the 42" '
j diameter discharge line, the ratio of pipe capacity to applied load is 1.08. In addition, the short length oflaterally unsupported pipe would be prevented from excessive deflection by 4
restraint of the pipe in the adjacent area of undisturbed backfill which remains circular.
The maximum deflection in the unsupported zone, cansidering that the ends remain circular, is esumated to be only a small fraction of the deflection cf an unrestrained ring
- subject to verticalload.
In Scenario 2, the soil amund the discharge lines we ' become saturated. In order to nsness the capacity of those lines to suppoit the impo J lowis, the buckling capacity is determined according to Equation (6-7) of AWWA ManuJ Mi1 (Ref. 5). Based on two conservative assumptions: first, that the water table extends to the ground surface, and second, that the modulus of soil reaction, E', is equal to 1000 psi, the ratio of applied load :
to allowable buckling load is approximately 0.30. Therefore, the strength of the discharge linen is adequate to support the imposed loads.
Summary and Conclusions An evaluation was performed to determine the consequences ofleakage propagation and erosion of the b3dding and backfill matW on the ESW underground pipes. Based upon the in situ soil conditions, two scenan iere deemed realistic to address the seepage ;
e froin the postulated pipe leak.
The following summarizes the conclusions reached in the evaluation ofleakage from the
- e. In Scenario 1, a maximum leakage flow rate of 140 gpm was assumed. This corresponds to an opening of ap >roximately 3/4" diameter when the pipe is running at a pressure of 150 psi. The leakage flow would exit like a jet and would compact the material around the pipe and erode the fine material in the bedding and carry it along the outside of the pipe along the bedding. Therefore, a cavity could form arounci the leakage opening. Since most of the material is coarse and would remain in place, the
- cavity would be very small.
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3 It sould be emphasized that this cavity formatior. could only be possible due to :
s seepage flow along the pipe and progressive movement of soil to a hoe exit surfbee. (
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Considering the long length and variation in the elevation of.the pipes, this la only V
possible where the pipe enters a powerblock building or near the ESW pumphouse and
-; UHS. In either case, the leakage would be noticed at the pipe penetrations in the a buildings or the leakage would not causs any potential loss of emergency cooling water by Sowing back to the UHS.
e Structural investigation of the strength of the pipes due to a very small cavity formation shows that the structural integr;ty of the ESW pipes is not impaired.
- In Scenario 2, the leakage Sow would soep upwards and the water would come bubbling out of the ground. Though the pressure inside the pipes is high, the energy of water coming out of the ground would be small because of the losses due to ori8ce ,
flow, turbulence of flow around the pipe, and fHetion loss due to seepage through the ,
cohesive backs 11 soil. The momentum due to the 140 spm flow rate coming out of the soil cannot erode a large_ volume of material. Hence, a large hole at the leakage location extending &om the bottom pipe to the surface is not possible.
e Due to a leak in the supply pipe, as the leakage water seeps upwards a portion of the return pipe (which is 6 feet above the supply pipe) could be surrounded by saturated granular baMil. This is not a concern since the buckling capacity of the ESW pipes, for this saturated soil condition is approximately three times the applied load.
In summary it can be concluded that the stu 4 integrity of the ESW pipes will not be i impaired due to a postulated leak. The scenario; - Nated clearly show that the leakage j would be identified by seeping water in the plant buildings at the pipe penetrations, bulgea and depressions in the ground surface along the pipe line alignment, or by bubtling water out of the ground. The repairs could then be performed in a timely manner.
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REFERENCES s
4 1. Wolf Creek , Updated Safety Analysis Report (USAR) 10
.'; 2. WCNOC Design Drawings:
n e C-K201 Rev 8
- C K202 Rev 9 e C K204(Q)Rev 7
- C-K205 Rev 11
- C-K211 Rev 6
- 3. " Final Report, Surveillance of Earthwork Essential Service Water System, WCGS" by Dames & Moore, dated May 26,1982.
- 4. " Design of Small Dams," U.S. Bureau of Reclamation, 'Ihird Edition 1987.
- 5. " Steel Pipe - A Guide for Design and Installation," American Water Works Association Manual Ml l, 3rd. Edition,1989.
(owmwdsskep 29. p doc)
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$ Telephone Conversation:
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?J Oyster Creek Nuclear Generstles Station M Mr. John Caesari Tel 60)- 971 - 4111
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j ew ofdiscussion:
- 1. Leakage: occurred in non nuclear pipes - in conventional service water pipes.
- 2. Water used is brackish water - sea water mixed with river water, near Barnegat Bay.
- 3. Failure and Leakage due to corrosion of the pipe.
Pipe was protected with bituminous coal tar coating (inside and outside) coating is past its life.
- 4. Pipe - carbon steel 20" dia.
Pressure rated for 150 pai.
Normal ops '. ting pressure = 50 psi 70 psi
- 5. Leakage occurred close to Turbine Building ( ~ 300 ft. from intake)
- 6. Pipe buried 14' below ground level.
- 7. General grade slopes away to sea.
- 8. Saly soil backfill
- 9. Leaks:
- Water leaked along the pipe and into the building at the pipe penetrations
- In some cases Water bubbled through the ground surface .
Nojet of water coming out of the ground even at 50 - 70 psi pipe pressure.
Appears pressure dissipated in the soil and bedding surrounding the pipe.
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] Telephone Conversaties:
l) Beaver VaBey Power Station -
Mr. Chas McFeeten Tel: 412 393-4730
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o Summary ofdiscussion:
0 Had Leakage failures in Circulating Water and Fire Protection pipes.
Cir=1**iam Water Pine:
- 1. Typically 5 10 psi pressure Leakage atjoints.
108" diameter Buried 8' below ground level.
Bedding and packed soil on top.
Leakage volumes small.
- 2. Leakage water appeared on the ground surfhce.
in one location water came through the asphalt road pavement.
Water bubbled through the ground surfhce.
- 3. Leakage appeared quickly on the surfhee.
- 4. Repairs done by ir$ecting grout at joints.
- 5. Root cause analysis is not completed, so no reports available.
Fire Protection pipes:
(Mr. McFeeters was not directly involved in these failures)
- 1. Pipes are under pressure.
6 - 12" carbon steel pipe lines Approx.12' to 15' below ground level
- 2. Leakage did not appear on the ground surface.
They could know that leakage was present by noticing pressure changes and by observing that the pipes were not able to get enough water.
Mostly water and part of soil moved along the pipe.
Erosion occurred along the pipes but no large cavity around the Pipes.
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D' %... Attachements ri , Pap 3 ef 4 m
. i 3 Telephome Conversation:
)4 Fadey Nuclear Station Ms. Pat Evans Tel: 334 - 899 - 5156 Est. 3517
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D Summary ofData:
o The following is a summary ofinformation received from Farley Station.
Ufc Proemlan Pine Report by Southern Company Services, Inc.
December 5,1996
- 1. Types ofPipes 10 - inch Cement Lined Ductile Cast Iron Pipe, Bell & spigot 4 -inch Steel Pipe
- 2. 10 -inch Cast Iron Pipe Failure due to pressure excursion at bruised or injured portion of pipe.
No discussion of bedding material provided.
No mention of circumstances when failure was noticed.
3, 4 -inch Steel Pipe Failure due to localized exterior corrosion.
No discussion of bedding material provided.
No mention of circumstances when failure was noticed.
4 - Inch Supply Iinn to Chlorination BujidiBS Report by Southern Company Services, Inc.
February 3,1993
- 1. Low carbon steel service water pipe
- 2. Design Criteria - 150 PSIG at 200'F
- 3. Actual working conditions - 125 PSIG at 95'F
- 4. Failure due to extenor corrosion - perforation lead to loss of coating - pitting
- 5. Hole was 1 %" by %"
- 6. No disci.ssion of bedding material provided.
- 7. No mention of circumstances when failure was noticed.
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12 -Inch Service Water Return Pine i -
4j L ,3 Root Cause Analysis T eport l s February 28,1991 D
=0 1. SA106, Grade B m:'eriel.
- 2. Failure caused by rock rubbing a hole in coating and then through the 5;n '
- 3. Circular hole 3/8" diametre (inside diameter) and %" diameter (outs'.
- 4. Vibration from the construction of access facility (PAP) accelerated -
.g.
- 5. Estimated leak was 15 GPM.
- 6. Backfdl was clay with rocks.
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