ML20078R272

Part 21 Rept Re Auxiliary Feedwater Pump Turbine Governor Valve Binding.Caused by Galvanic & Crevice Corrosion Between Stem & Stem Packing Components.Licensees Replaced Stem & Packing Gland Matls

ML20078R272
Person / Time
Site:	Calvert Cliffs
Issue date:	12/14/1994
From:	Denton R BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-94 NUDOCS 9412230282
Download: ML20078R272 (5)

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Roar.mT E. Dr.NTON Baltimore Oas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant Nuclear Energy 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 586-2200 Ext.4455 local 410 260-4455 Baltimore l

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! December 14,1994 )

l U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Cahert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 10 CFR Part 21 Report; Auxiliary Feedwater Pump Turbine Governor Valve Binding Caused by Galvanic and Crevice Corrosion Between Stem and Stem Packina Components We have recently identified a design inadequacy that is allowing accelerated ev..osion rates between the new stem and stem packing material in a governor valve to one of our Auxiliary Feedwater Purr:p Turbines.

The accelerated corrosion rate resulted in the binding of this governor valve after a relatively short period of standby service. This design inadequacy potentially presented a substantial safety hazard at our facility and is reportable in accordance with 10 CFR Part 21 requirements.

This letter provides the information required to be reported pursuant to 10 CFR Part 21. A verbal notification and written summary were submitted to the Nuclear Regulatory Commission Operations Center via facsimile on November 15,1994.

Should you have any questions regarding this matter, we will be pleased to discuss them with you.

Very truly yours,

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RED /CDS/bjd Attachment 9412230282 941214

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. D:-:s-:e Control Desk December 14,1994 Page 2 l.

cc: D. A. Brune, Esquire J. E. Silberg, Esquire L. B. Marsh, NRC D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC R. I. McLean, DNR J. H. Walter, PSC

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. ATTACHMENT (1) 10 CFR PART 21 REPORT CONCERNING AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM PACKING COMPONENTS Calvert Cliffs Nuclear Power Plant, Units 1 and 2 Docket Nos. 50-317 and 50-318 (i) Name and address ofindividual making notification:

R. E. Denton, Vice-President, Nuclear Energy Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657-4702 (ii) Basic Component Affected:

Auxiliary Feedwater Pump Turbine Governor Valve (iii) Firms Supplying Component:

Supplier of Auxiliary Feedwater Pumpfrurbine: Dresser Rand Fabricator of Turbinc: Terry Steam Turbine  ;

I (iv) Nature of Defect: i i

Calvert Cliffs Units 1 and 2 have a total of four essentially identical turbine-driven auxiliary feedwater (AFW) pumps. He Turbine is manufactured by Terry Steam Turbine Company. Dresser-Rand is the AFW Turbinc-Driven Pump vendor. In May 1994, the No. 22 turbine was noted to be experiencing a problem with a sticking governor valve. In June 1994, the No. 22 turbine governor valve stem was replaced. On September 21,1994, during a routine surveillance test the No. 22 turbine govemor valve was  ;

found to be bound Prior to the valve stem replacement, in June 1994, the original stem had been in the No. 22 turbine govemor valve for about 17 years.

The turbine governor valve stem material is 410 stainless steel that has a hard nitrided surface layer. The packing for the govemor valve . stem utilizes an alternating series of carbon spacers and stainless steel washers. During operation, the clearances between the stem and the carbon spacers become tighter as the packing and stem heat up. %c clearances between stainless steel washers and the stem remain approximately cons?wt.

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, ATTACIIMENT n) l 10 CFR PART 21 REPORT CONCERNING AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM PACKING COMPONENTS Following the AFW turbine governor valve sticking event in September, the new (3 months in senice) and old (17 years in service) valve stems, stainless steel washers, and carbon spacers from the No. 22 turbine governor valve packing gland were sent offsite for analysis. The analysis found that although the in.facturer specified 400 series stainless steel washers for use in the packing gland,15 of the 21 were t.: aicated from 300 series stainless steel. Additionally, it was noted that the chemical composition of the carbon spacers contained approximately one percent sulfur. It is suspected that the sulfur in the carbon spacers car leach out as the equipment operates, collect in the clearance space between the stainless steel washers and the valve stem, and form the electrolyte needed for galvanic and cresice corrosion between the stem and stainless steel washers. He use of 300 series stainless steel versus 400 series stainless steel  ;

washers created a higher galvanic coirosion 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 NRC by other licensees who have similar equipment in similar applications.

In addition to the above discrepancies, the analysis found the newer (replacement) valve stem was metallurgically inferior m the old originally supplied stem. The nitrided layer used to harden the surface of the new valve stem was very thin, thus allowing corrosion to initiate and pit the stem deeply in a short i period of time. The old stem, had a thicker well-formed nitrided layer that effectively restricted the stem corrosion to shallow areas along its surface. The corrosion on the older stem did not penetrate the hard nitrided layer to the base matcrial resulting in a significantly lower corrosion rate and corrosion product buildup. A review of the fabrication specifications for the newer governor valve stem found the thickness of the nitrided layer satisfied the specification requirements. Additionally, it was discovered that the specified thickness of the nitrided layer had been reduced several times since the original stem was manufactured over 17 years ago.

he analysis concluded that the root cause of the governor valve binding was galvanic and cresice corrosion of the vahe stem brought about by a combination of improper washer material, sulfur contamination in the carbon spacers, and an extremely thin nitrided layer on the surface of the new valve stem.

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(v) Date on Which Defect was Identifkd .

1 On September 21,1994, the No. 22 AFW Pump failed a routine surveillance test due to a stuck governor l valve. Following the event, tb governor valve bonnet was removed with the valve packing plug and stem l in place. The vahe washers, stem and carbon rings were sent offsite for a root cause analysis. he root l cause analysis results were received onsite on November 8,1994 and, after review and follow-up with the l pump vendor, determined to be reportaW ader 10 CFR Part 21 on November 11,1994. 1 (vi) Number and Location of Components:

Cahert Cliffs has two Turbine-Driven AFW Pumps at each Unit for a total of four. Both AFW pumps for each unit are located in their own room on the 12 foot level of their respective Turbine Building.

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,- ATTACHMENT (1) 10 CFR PART 21 REPORT CONCERNING AUXILIARY FEEDWATER PUMP TURBINE GOVERNOR VALVE BINDING CAUSED BY GALVANIC AND CREVICE CORROSION BETWEEN STEM AND STEM PACKING COMPONENTS (vii) Corrective Actions Taken:

We have communicated this problem to the vendor.

On November 18, 1994, INPO notified the industry via NE'IVORK that problems with the sticking of these gove. nor valves has been experienced at several nuclear power plants. Based on the industry trend, INPO has classified this issue as significant and is in the process of preparing a SEE-IN document to summarize the industry failure experience caused by governor valve stem binding and identify causes and corrective actions.

We are currently in the process of determining the net contribution of each of the three problems discovered during the root cause analysis to the overall net corrosion rate of the valve stems.

We are currently developing corrective measures to ensure the use of 400 series stainless steel washers and address the sulfur contaminants in the carbon spacers. We are also considering purchase specification changes for the valve stem to enhance its corrosion resistance.

Upon discovery of the bound No. 22 AFW turbine gove.nor valve on September 21,1994 we replaced its stem and packing gland materials. To ensure the binding did not recur, we started exercising tlw govemor valves for all of our AFW turbines once every four days. Based on the root cause analysis results and the results of the exercising program we have decreased this frequency to once per seven days. We plan to continue exercising the governor valves according to the current frequency until preventative actions are complete.

(viii) Other Advice Related to Purchasers or Licensees:

We advise all licensees who have reccotly replaced the valve stem and/or stem packing of similar AFW turbine governor valves to exercise them more frequently to ensure no corrosion related binding is occurring, especially if the turbine is in standby ser5 ice.

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