ST-HL-AE-3903, Suppl to Special Rept:On 901126,fuel Oil Leak Noted at Injection Pump 1L of Standby Diesel 23.Caused by Crack on Threaded Portion of Delivery Valve Holder.Injection Pump Delivery Valve & Valve Holder Replaced on 901127

Suppl to Special Rept:On 901126,fuel Oil Leak Noted at Injection Pump 1L of Standby Diesel 23.Caused by Crack on Threaded Portion of Delivery Valve Holder.Injection Pump Delivery Valve & Valve Holder Replaced on 901127

ML20079P162
Person / Time
Site:	South Texas
Issue date:	11/04/1991
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3903, NUDOCS 9111120253
Download: ML20079P162 (7)

Text

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4 The Light c o mp a ny south Tem Projn utenic cenciatingtauonP. a nos m wad.w onli.1 cm 77 m llouston Lighting & Power November 4, 1991 ST ML- AE-3903 File No.. G02 10CFR50 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Vashington, DC 20555 South Texas Project Electric Generating Station Unit 2 Docket No. STN 50-499 Supplement to Special Report Regarding Standby Diesel Generator 23 Valid Failure on Novernber 26. Is Pursuant to the South Texas Project Electric Generating Station (STPECS)

Technical Specifications 4.8.1,1.3 and 6.9.2, llouston Lighting & Power submitted via letter dated December 26, 1990 (ST-1IL AE-3653), a Special Report regarding a Standby Diesel Generator (SDG) valid failure which occurred on November 26, lo90. Please find attached a supplement to that report waich provides additional information concerning investigative findings. Change bars have been added to highlight suppla. ental information.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628 or myself at (512) 9/2 7205.

William J. J'mp T

Manager, Nuclear Licensing AMR/ amp

Attachment:

Supplement to Special Report Regarding a SDC Valid Failure on November 26, 1990 l

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4 W l SREP\91 173.002 A %hsidiary of ! u,'ntof t llidthtries !!)corporated \

9111120253 911104 PDR ADOCK O$000499 S PDR _

ST+HL AE 3903

..llowton Lighting & Power Company File No. : G02 South Texas Project Electric Generating Station - Page 2 l

Cc:

. Regional Administrator, Region.IV Rufus S. Scott Nuclear Regulatory Commission Associate General Cour el .

611 Ryan Plaza Dr ve, Suite 400 Houston Lighting & Powcr Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 Georga bick, Project' Manager U.S. Nuclear Regulatory Commission INPO Vashington, DC .20555 Records Center 1100 circle 75 Parkway J..I..Tapia Atlanta, CA 30339-3064 Senior Resident Inspector c/o U, S. Nuclear Re6ulatory Dr. Joseph M. Hendrie Commission 50 Be11 port Lane P. O. Box 910 Be11 port, NY 11713 Jay City, TX 77414' D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C. = Texas Department of Health 1615LL Street,,N.W. 1100 West-49th Street Washington,-DC1 20036 Austin, TX 78756-3189

-D.-C, Ward /T.- M. Puckett Central-Power and Light Company P. O. Box 2121

-Corpus Christi, TX -78403 J. C. Lanfer/M. B. Lee

. City of Austin l

Electric Utility Department P.O. Box 11088-Austin,- TX 78767f K. J. Fiedler/M. T.-Hardt City Public-Servico Board P. O. Box 1771 San Antonio, TX 78296 Revised 10/11/91 L4/NRC/-

. Attachment ST llL-AE 3903 Page 1 of S South Texas Project Electric Cenerating Statica Unit 2 Docket No. STN 50 499 Supplement to Special Report Regarding Standby Diesel Generator 23 Valid Failure on Novemhgr 26. 1990 DESCRIPTJQF OF EVENT:

On November 26, 1990, Unit 2 was in Mode 5 during a refueling outage.

Ar approximately 0012, during performance of Standby Diesel 23 LOOP ESP Actuation Test,.SDG 23 was found to have a fuel leak at injection pump IL.

The plant operator oticed fuel oil spraying on the hot exhaust header and emergency-stopped SDG 23 at the local control panel. 3 The SDCs are provided with a shield designed to protect the fuel line from falling objects during a seismic event. This shield also protects the SDG exhaust from fuel leaks from the fuel oil lines. In the November 26 event, the plant operator noticed ihat sufficient fuel was spraying through a designed penetration in the shield onro the Fot exhaust header to constitute a fire hazard.

Upon disassembly of the fuel lines, a crack was found across the thrcaded portion of the delivery valve holder. The delivery valve holder,

. located on top of the. fuel injection pump, is the connection point for the high pressure fuel injection pump discharge line (see attached figure,-

Item #3). The delivery valve holder, stop, .nd spring

• were replaced, and

-post maintenance testin5 was satisfactorily completed on November 27, 1990.

SDC 23 was declared operabic on November 27, 1090 at appraximately 1144.

Other similar events have occurred at STPEGS. During initial startup in Unit 1, cracka were found across the threads in the delivery valve holders.

Following that event, a procedure for removal, presetting, and installation of Cooper Bessemer ht;h pressure fuel lines was included in the technical manual.

.Three other events dealing with cracks in che injector s e injection pump fual line threaded connec: ton have occurred in which the root cause was identified as overtorquing of the fuel line nuts. Approved procedures wern-not violated, and manufacturer specifications were not exceeded. When

.procedores for torquing fuel line nuts were first developed, torquing was not well-defined and addressed clearly in the SDC manufacturer's manual. Once cracks were. discovered, proper procedures for torquing fuel line nuts wece approved. Subsequently, the failure mode for .the fuel lines was evaluated, and continued operation with potentially overtorqued connections was determined to be acceptable because it was unlikely that a leak caused by a cracked connection would spray. Non-spraying leaks do not constitute a substantial fire hazard and do not affect overall diesel operability.

• The stop and spring are internal to the delivery valve holder and are not detailed on the attached figure.

' HIP \Q1-273.002

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. Attachment ST-HL-AE-3903 Page 2 of 5 South Texas Project Electric Cenerating Station Unit 2 Dacket No. STN 50-499 Supplement to Special Repcrc Regarding Standby Diesel Generator 23 Valid Failure on November 26. 192Q DESCRIPTION OF EVENT: (cont'd)

A crack across the threads in the delivery valve holder for Unit 2 SDG 21 injection pump 4L-was discovered on October 22, 1990, and injection pump 4L was replaced. The delivery valve holder was sent for failure analysis along with the failed SDG 23 component from the November 26 event. <

An update on the results of the Coopor Bessemer analysis was received in a letter dated February 5,1991. Cooper-Bessemer found from metallurgy lab tests that the material (from'the fallod delivery valve holders) agrees with the manufacturer's specificatlan, but the stress condition produced by tightening the tapared fitting into the holder is aggravated by the sulfide stringers present in the mater.4-1.

In light of the history of failures at five of the seven member utilities, MPR Associates (the Cooper-Bessemer Owncrs Group (CBOG) Project Engineer)'was assigned the task of performing further testing on delivery valve holders to evaluate fuel line assembly methods and their sensitivity to overtightening. A report, " Tests of Crack revelopment in Haynes Corporation Fuel Injection Pump Delivery Valve Holders," was issued on April 30, 1991. A sample of 12 delivery valve holders and 18 feel line fittings was used to determine the effect of tubing-seal (ferrule) presetting methods on the turn of the nut value and the corresponding installation torque required-to cause cracking of the delivery valve holdera.- The principal findings from the tests are as follows: (1) The delivery valve holders are prone to cracking. Cracks were obtained in 11 out of the 12 delivery valve holders at torques ranging frem about 60'to 200 foot-pounds (ft-lb). (2) In terms of aut turning, the failure' torques would range from 1/4 to 3/4 turn. After testing delivery valve holders which used ferrule tubing seal assemblies preset-with a shim, and testing sssemblies which used the Cooper-Bessemer presetting tool (and the Cooper-Bessemer' presetting installation procedure), is was found that the amount of overtightening required-to cause cracking is sensitive to the ferrule presetting method. .(3) Bottoming the fuel line into the delivery

-valve holder before presetting results in lower stresses and therefore greater cracking resistance. (4) Fuel lines purchased from Cooper-Bessemer with Cooper-Bossemer manufactured nuts and factory preset ferrules did not cause cracking inLche delivery valve holders when the nuts were overtightened.

However,-- based on HL&P's experience, these assemblies did not appear likely to be leak-tight in service.

The test results suggesc the likelihood of cracking can be reduced by

' implementing the Cooper-Bessemer Engineering Standard SD-129 installation procedure, except the tubing seal should be preset using the actual delivery valve holder in which the: tubing assembly will be installed rather than the SREP W1-273.002

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.. l Attachment ST-HL-AE 3903 Page 3 of 5 South Texas Project Electric Generating Station Unit 2 Docket No. STN 50-49)

Supplement to Special Report Regarding Standby Diesel Generator 23 Valid Failure on November 26. 1990 DESCRIPTION OF EVENI: (cont'd)

Cooper-Bessemer presetting tool. However, considering the propensity of the delivery valve holders to crack, it appears a design change will be required to completely eliminate the cracking problem.

In a May 1991 meeting, CBOG agreed that MPR would test a new 60 degree taper. seat design being used on TransAmerica Delaval Inc. Enterprise diesel generators and check for its tendency to crack and leak during installation.

In an August 1991 CBOG meeting, the results of the MPR Associates testing of the taper seat design was discussed. The tapered seat design was tested by tightening it from'36 ft-lb to 250 ft-lb with no evidence of cracking or

' leaking. Cooper Bessemer considers the replacement of the current design with the new tapered seat design a pro-active approach to resolving the problem.

The CB00 Technical Committee agteed that the new design was superior and

. recommended that the CBOG promote this design change. Cooper-Besesper and MPR presented this design change at a CBOG Steering Committee meeting on October 24 and 25, 1991. Cooper-Bessemer will prepare ordering and delivery data on the new design and present-it to the utilities.

STPEGS is presently using the equivalent of the Cooper-Bessemer installation procedure provided in the vendor technical manual., In the past, STPEGS was presetting the tubing seal ferrules by using the delivery valve holders as the presetting tool. If the tubing was not properly seated at the bottom of the' delivery valve holder, the-torquing required to seat the ferrule could create a wedging action which would crack the-delivery valve holder.

The current procedure at STPECS' precludes this from happening because the ferrules are preset.using a tool purchased from Cooper-Bessemer and are prepared in the shop pric to seating in the delivery valve holder.

CAUSE OF EVENT:

The cause of the event ic a less than adequate design cf the delivery valve holder which is prone to cracking. Overtorquing of 'he fuel line nuts was identified as a root cause for cracks previously foun2 on delivery valve holders. Failure of the SDG-manufacturer to c1carly address the issues concerning torquing-of fcol line uuts caused inappropriate tarque values oo-be implemented. After maintenance procedtres were changed, however, no wholesale

~ replacement of potentially affected components was performed because non-dastructive-testing did not detect cracks, and the likelihood of oil spraying as a result of the leak is very small.

3 REP)91-273.002

. Attachment ST-HL AE 3903 Page 4 of 5_

South Texas Project Electric Generating Station Unit 2 Docknt No. STN 50 499 Supplement to Special Report Regarding Standbv_piesel Generator 23 Valid Failure on Epvember 26. 1990 ANALYSIS-of EVENI:

Due to the fuel oil spraying on the hot exhaust header, continued operation of SDG 23 would have constituted a fire hazard. SDG 23 would have responded to.a test or emergency start signal, but a fire hazard caused this event _to be classified as a valid failure, In previous everts, fuel Icaks did notz spray (atomize) towards hot surfaces and were judged to not be significant fire hazards. Therefore, they were not classified as valid failurer.

-CORRECTIVE ACTIQH1:

1.. The injection pump IL delivery valve, delivery valve holder, and delivery valve spring were replaced on November 27. 1990.

2. STPEGS will prepare a plan of action for impicmenting the recommendations of _ the CBOG for resolving the delivery val" holder cracking problem. A schedule for the implementation of those actions will be iaeluded in the.

plan of ac. ion once the actions are determined. A supplemantal report outlining the above plan of action will be submitted to the NRC after it is esthblished.

ADDITIOUff.,JJFORMATION:

'he-inj ection pump is a Bendix model_ FDX-22 The delivery valve holder is a caponent ul the injector pump.

-At the time of the event, t.here had been two valid failures in the last 20

-valid tests of SbG 23 and _ the number of valid failures in the last 100 valid Ltests ush'less than f*ur. Therefore, per-STPEGS Technical Specification 34 8.1.2, t ae testing frequency for SDC 23 vaa once 'per 7 days.

5REPi91-273,002

Attachment ST-ilL AE 3903 l' age 5 of 5 3

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i 4A~3Le+ ,.: b .

19. Bolt Y' s

1. Tubing Nut

2. Tubing Seal 20. Cam a ,

3. Delivsry Valve 21. Pla  ; .

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Holder and Flange 22. Roller ,

4 Packing 23. Bushing Collar - - k- /

5. Delivery Vtive 24. Bushing 73 I I '

Assembly 25. rust Drsin $

p

26. g/Ai Fuel Sapply

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6. rush god

7. Fump Housing 27. Snap Ring g ,

8. Control Sleeve 23. Fump Fedestal , b

9. Spring Flate

10. Spring 29.

30.

locknut Fluoger and g .

l h u

^ '

11. F1ungn rollouer Barrel Assembly

12. Spri. Platt 31. Control Rack -* -'-

13. Shia 32. Shis, Indicator

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14. Tuel Drain and Screv 'r' b

from Noa 1e 33. Flowing Yant e I 8

15. 19be oil Inlet Connectica j .

16. Bushing 34. Delivery Yalve I /, <

17. ' Crosshead 35. Screv i  %

18. ' taaring 36 . Fuel Discharge

,ine w .-

rig. 44 Tuel Injection Funp and Pedestal l

l MtEP)91-273.0?2

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