ML20116C600

Final Deficiency Rept CP-92-010 Re Containment Spray Pump Vent Weld Cracks.Initially Reported on 920722.Vent Pipe Replaced & Containment Spray Pump Vibration Being Corrected, Per Steady State Vibration Monitoring Test

ML20116C600
Person / Time
Site:	Comanche Peak
Issue date:	10/30/1992
From:	William Cahill, Woodlan D TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CP-92-010, CP-92-10, TXX-92509, NUDOCS 9211040182
Download: ML20116C600 (2)

Text

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h j Log # TXX 92509 File # 10110 (CP 92 010) '

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October 30. 1992 u mum J. r.a.m. Jr.

Ouwy s ne lura nt U. 5. Nuclear Regulatory Commission Attn Document Control Dest Washington, DC 20555

SUBJECT:

COMAliCHE PEAK STEAM ELECTRIC STATION (CPSES) -

UNIT 2 DOCKET NO. 50 446 C0tlTAINHENT SPRAY PUMP VENT WELD CRACKS SDAR CP-92 010 (FINAL REPORT)

Gentlemen:

On July 22, 1992, via f acsimile,10 Electric notified the NRC of a reportable defect in two welds on 3/4' Containment Spray Pump suction vent piping. An interim report, logged TXX 92380, was submitted on l

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August 21, 1992, and stated that the final report would be submitted by October 30, 1992. TV Electric's investigation into the cause of this defect is now complete.

The welds in question are 3/4" socket welds on Schedule 40 stainless steel vent piping within fourteen pipe-run feet of the Unit 2 Train 'A' Containment Spray Pump suction.

According to a metallurgical analysis, the weld joint failures began at the f usion lines where the tube fitting and weld depo;it met, Stresses (vibrational or other) acted upon the inside surface at the innermost fusion lines. The analysis also identified that pre existing lack of weld penetration, burn throughs, welC porosity and interfacial oxides were present in the subject welds. Under concentrated stress, the crack fronts gradually propagated almost transversely through the weld metal by cyclic loading. Fracture was transgranual and not influenced by the weld microstructure or metallurgy. Eventual failure occurred through-cross-sectional reduction by means of the advancing crack f ronts uninfluenced by corrosion or prior thermal histor;i.

The Containment Spray Pumps experienced vibration problems during their initial runs. This vibration cont ributed to the stresses described in the metallurgical analysis. Vibration induced during flushing may have provided the final loading necessar y' to break the first weld.

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. 9XX 9s509 Page 2 of 2 The second crac6ed weld was discovered four days after the first weld. It was located approximately one foot upstream of the first weld at a fitting connected to the pump suction piping. The same vibration problem contributed to the fatigue cratb initiation. However, during the process of removing the elbow which had the first cracked weld, a hammer was used repeatedly to breat the fitting loose. This could have contributed to or tause,1 the f ailure of the second weld.

The same welder performed both welds. He was onsit e f rom November 1979 through July 1982 and performed 124 welds which were required to be radiographed during the normal construction process. Approximately 21% of the rediographed welds were rejected and subsequently repaired. However, the linear inches reject rate of 1.3% recorded on Class 1 and 2 welds is a more accurate indicttor of the welt',r's perf ormance. This is considered youd in terms of the amount of welo ? pair required per joint.

An additional population of 74 Class 2 and 3 stainless st?el socket weids performed by this welder using the GTAW process on piping from 2' to 3/4' was selected because they were similar in size and t 9 e to those that failed. 1hese welds did not require radiographic inspection during c onstr uct ion. Thirteen were randomly selected f rom this population in ,

accordance with the CPSES statistical sampling plan and radiographically i examined to determine if cracking was present in the root of the weld. All t hirt een welds were acceptable.

The vent pipe has been replaced and the Containment Spray Pump vibration is being corrected in accordance with t he Steady State Vibration Monitoring Test that is performed on all safety-related systems. Based on the analysis of work noted above, no further corrective action is planned.

Sincerely, William J. Cahill, Jr, By:

D. R. Woodlan Docket Licensing Manager CBC/JTC/tg c Mr. J. L. Milhoan. Region IV Mr. D. E. Holian, NRP Resident inspectors, CPSES ( 2 )