ML20080A768

Part 21 Rept Re AFW Pump Turbine Governor Valve Binding Caused by Galvanic & Crevice Corrosion Between Stem & Stem Packaging Components.Turbine Mfg by Terry Steam Turbine Co. Licensee Plans to Periodically Exercise Valve Stems

ML20080A768
Person / Time
Site:	Calvert Cliffs
Issue date:	11/15/1994
From:	Sly C BALTIMORE GAS & ELECTRIC CO.
To:	Huffman W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
REF-PT21-94 NUDOCS 9411210269
Download: ML20080A768 (4)

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NO.U 15 '94 17:06 FROM CCNPP/ NRM NOF-2FLR PAGE.001

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I 10 CFR PART 21 VERBAL NOTIFICATION:

l' AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE

• BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM. PACKING COMPONENTS Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Information

Contact:

Craig Sly, Engmeer-Compliance Unit, (401) 260-4858 On September 21,1994, the No. 22 Auxiliary Fecdwater (AFW) Pump failed a routine surveillance test due to a stuck governor valve. Following the event, the govemor valve bonnet was removed with the valve plug and stem in place, and a root cause analysis was begun ne root cause analysis results were received onsite on November 8,1994 and, after roiew and follow-up with the pump vendor, determmed to be reportable under 10 CFR Part 21 on November 11,1994.

Calvert Cliffs Units 1 and 2 have a total of four essentially identical turbine-driven AFW pumps. The Turbine is manufactured by Terry Steam Turbine Company. Dresser-Rand is the AFW Turbine Driven Pump vendor. In May 1994, the No. 22 pump was noted to be experiencing a problem with a sticking Sovemor valve. In June 1994, the governor valve stem was replaced on the No. 22 pump. Three months later on September 21,1994, the governor valve was sticking again. Prior to this replacement, the original stem had been in the No. 22 pump govemor valve for about 17 years.

He packing gland for the govemer valve stem uses an alternating series of carbon spacers and stamless steel washers. During operation, the carbon spacers expand to tight clearances around the stem as the packing heats up. The stamicss steel wasbers have a slightly larger clearance from the valve stem than the carbon spacers. The valve stem material is 410 stainless steci that has a hard nitrided surface laytr.

Following the govemor vahr sticking event in September, the new 3 months inservice and 17 years inservice valve stems, stainless steel washers, and carbon spacers from the gowrnor valve packing gland 9411210269 941115 PDR ADOCK 05000317 -

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i FROM CCNPP/ NRM NOF-2FLR PAGE.002 NOV, 15 '94 17:06

- 9 10 CFR PART 21 VERBAL NOTIFICATION:

AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM _ PACKING COMPONENTS were sent offsite for analysis. The analysis found that although the manufacturer specified 400 series stainless stect washers for use in the packing gland,15 of the 21 were fabricated from 300 series stainless steel. Additionally, it was noted that the chemical composition of the carbon spacers contained on the order of one percent sulfur. He sulfur in the carbon spacers will leach out as the equipment operates, collect in the clearance space between the wasbers and the valve stem, and form the electrolyte needed for galvanic and crevice corrosion between the stem and washers. The use of 300 series stainless steel versus 400 series stainless steel washers created a higher galvanic corrosion potential since the stem is made from 400 series stainless steel. Both of the above issues were previously reported as Part 21 reports to the h1C by other licensees who have similar equipment in similar applications.

In addition to the above discrepancies, the analysis found the new (replacement) valve stem was metallurgically inferior to the old originally supplied stem. He nitrided layrr on the new stem was essentially non-existent, thus allowing corrosion to initiate and pit the stem deeply in a short period of time.

The old stem, had a thicker well-formed nitridcxl layer that effectively restricted the stem corrosion to shallow areas aloog its surface. The corrosion on the older stem did not penetrate the hard nitrided layer to the base material resulting in a significantly lower corrosion rate and corrosion product buildup.

Tbc analysis concluded that the root cause of the govemor valve binding was galvanic and crevice corrosion of the valve stem brought about by a combination of improper washer material, sulfur contamination in the carbon spacers, and extremely thin nitrided layer on the surface of the new n!w stem.

We are currently trying to determine the net contribution of each of the problems described above to the net corrosion rate of the valve stems We are exercising the No. 22 governor ulve once per four days and all cw-m 2

. NOU 15 '94 17:07- FROM CCNPP/ NRM NOF-2FLR PAGE.003 10 CFR PART 21 VERBAL NOTIFICATION:

AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE

• BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM. PACKING COMPONENTS other Teny Turbin,. governor whts once per seven days to ensure their continued operability. None of the other governor valve sterns have been replaced.

To preclude further events of this type, we are currently denloping corrective measures related to the use of 400 series stainless steel washers and address the sulfur contammants in the carbon spacen. We are also considering purchase specification changes for the valve stem to include a requirement for a specialized surface treatment to enhance its corrosion resistance.

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GENERAL INFORMATION or OTHER EVENT NUMBER: 28032 LICENSEE: CALVERT CLIFFS NUCLEAR POWER PLANT NOTIFICATION DATE: 11/15/94 j CITY: LUSBY REGION: 1 NOTIFICATION TIME: 15:56 [ET)

COUNTY: STATE: MD EVENT DATE: 11/11/94 LICENSE #: AGREEMENT: Y EVENT TIME: 12 : 00 (EST)

DOCKET: LAST UPDATE DATE: 11/15/94 NOTIFICATIONS NRC NOTIFIED BY: CRAIG SLY HQ OPS OFFICER: WILLIAM HUFFMAN EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION:

CDEF 21.21(b) (2) DEFECTS / NONCOMPLIANCE EVENT TEXT STUCK GOVERNOR VALVE ON AUXILIARY FEEDWATER PUMP ( AFW) .

CALVERT CLIFFS REPORTS THAT THEY HAVE RECENTLY EXPERIENCED SEVERAL INSTANCES OF THE GOVERNOR VALVE STICKING ON ONE OF THEIR AFW PUMPS. THE AFW TURBINE UNIT IS-MANUFACTURED BY THE TERRY STEAM TURBINE COMPANY. DRESSER -

RAND IS THE AFW TURBINE DRIVEN PUMP VENDOR.

ROOT CAUSE ANALYSIS OF THE PROBLEM HAS DETERMINED THAT THE BINDING WAS DUE TO GALVANIC AND CREVICE CORROSION ON THE VALVE STEM BROUGHT ABOUT BY A COMBINATION OF SEVERAL IMPROPER MATERIAL CONDITIONS. SPECIFICALLY, THE USE OF 300 SERIES STAINLESS STEEL IN LIEU OF 400 SERIES FOR THE VALVE PACKING GLAND WASHERS. ALSO, SULFUR CONTAMINATION IN THE CARBON SPACERS OF THE VALVE PACKING GLAND. IN ADDITION, A EXTREMELY THIN, ESSENTIALLY NON-EXISTENT, NITRIDED LAYER ON THE SURFACE OF THE VALVE STEM ALLOWED CORROSION TO PENETRATE INTO BASE STEM MATERIAL.

THE LICENSEE HAS FOUR TURBINE DRIVEN AFW PUMPS. THE PUMP WITH THE GOVERNOR VALVE PROBLEMS HAD THE VALVE STEM REPLACED IN 1994. THE VALVE STEMS ON THE OTHER THREE PUMPS ARE THE ORIGINAL STEMS AND HAVE NOT BEEN REPLACED.

TO MITIGATE THE CRANGE OF THE GOVERNOR VALVE STICKING PROBLEMS, THE LICENSEE PLANS TO PERIODICALLY EXERCISE THE VALVE STEMS.

THE LICENSEE NOTES THAT THIS CONDITION RAS BEEN REPORTED BY OTHER LICENSEES

'AND IS DOCUMENTED IN INFORMATION NOTICE 94-66.

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