NRC Generic Letter 1989-08

NRC Generic Letter 1989-008: Erosion/Corrosion Induced Pipe Wall Thinning

ML031470660
Person / Time
Issue date:	05/02/1989
From:	Partlow J G Office of Nuclear Reactor Regulation
To:
References
GL-89-008
Download: ML031470660 (3)

NRC Generic Letter 89-OS: Erosion/Corrosion-Induced Pipe Wall Thinning Index I Site Map FAQ Help Glossary Contact Us Searh AU.S. Nuclear Regulatory Commission Co7Hoe hoWeAr WatW II Nuclear ll Nuclear ll Radioactive ll PublicHoe hoWeAr fWhtWeD Reactors materials Waste involvementHome > Electronic Reading Room > Document Collections > Generic Communications > Generic Letters > 1989 > GL89008May 2, 1989TO: ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FORNUCLEAR POWER PLANTSSUBJECT: EROSION/CORROSION-INDUCED PIPE WALL THINNING(GENERIC LETTER 89 -08)Pursuant to 10 CFR 50.54(f), the U.S. Nuclear Regulatory Commission (NRC) isrequiring information to assess safe operation of reactors when erosion/corrosion significantly degrades piping and components of high-energy carbonsteel piping systems. The principal concern is whether the affected plantscontinue to meet their licensing basis when erosion/corrosion degrades thepressure boundary to below the applicable code design value.Main feedwater systems, as well as other power conversion systems, areimportant to safe operation. Failures in these systems of active componentssuch as valves or pumps or of passive components such as piping can result inundesir-able challenges to plant safety systems required for safe shutdown andaccident mitigation. Failure of high-energy piping, such as feedwater systempiping, can result in complex challenges to operating staff and the plantbecause of potential system interactions of high-energy steam and water withother systems, such as electrical distribution, fire protection, and security.All licensees have committed to adhere to criteria, codes and standards forhigh-energy piping systems described in licensing documents. Such commitmentsare a part of the licensing basis for the facility. An important part of thiscommitment is that piping will be maintained within allowable thicknessvalues.Our concerns regarding this issue were prompted by incidents at Surry Unit 2and the Trojan plant. The Surry incident occurred on December 6, 1986, and itwas caused by catastrophic failure of feedwater piping. The Trojan incidentwas discovered in June 1987, which was the first time that pipe wall thinningled to piping replacement in the safety-related portion of the feedwaterlines. In addition to these two cases, incidents of pipe wall thinning orrupture because of erosion or erosion/corrosion have been reported at manyother nuclear power plants. In many of these cases, the licensees hadinspected the two-phase lines for some years, but it was not until the Surryincident that they started to examine some single-phase lines. Many licenseesdiscovered pipe wall thinning in the single-phase lines. Some of the reportedincidents are listed below:1. A pipe rupture at Haddam Neck occurred in March 1985. The pipe ruptureddownstream of a normal level control valve for a feedwater heater. Theactual rupture was approximately 1/2 inch by 2 1/4 inches, and the failurewas caused by flow impingement. The eroded section of pipe was replaced.In addition, corresponding pipes of similar systems were examined.2. A catastrophic pipe rupture at Surry Unit 2 occurred in December 1986.The break was located in an elbow in the 18-inch line about 1 foot fromthe 24-inch header. A 2- by 4-foot section of the wall of the suction8905040276.Generic Letter 89-08 -2- May 2, 1989line to the A main feedwater pump was blown out. Investigation of theaccident and examination of data by the licensee, NRC, and others led tothe conclusion that failure of the piping was caused by erosion/corrosionof the carbon steel pipe wall.http://www.nrc.gov/reading-rmldoc-collections/gen-comm/gen-letters/1989/gl89008.html 03/13/2003 NRC Generic Letter 89-08: Erosion/Corrosion-Induced Pipe Wall Thinning . During the June 1987 outage at the Trojan Nuclear Plant, it wasdiscovered that at least two areas of the straight sections of the mainfeedwater piping system had experienced wall thinning to an extent thatthe pipe wall thickness would have reached the minimum thickness requiredby the design code (ANSI B31.7, Nuclear Power Piping') during the nextrefueling cycle. These areas are in safety-related portions of the ASMEClass 2 piping inside the containment. In addition, numerous pipingcomponents of the nonsafety-related portions of the feedwater lines werealso found to have suffered extensive wall thinning.4. During the September 1988 outage, the licensee for Surry Unit 2discovered that pipe wall thinning had occurred more rapidly thanexpected. On the suction side of one of the main feedwater pumps, anelbow installed during the 1987 refueling outage lost 20 percent of its0.500-inch wall in 1.2 years. In addition, wall thinning is continuingin safety-related main feedwater piping and in other nonsafety-relatedcondensate piping. The exact cause of the accelerated wall thinning isstill under investigation by both the licensee and the NRC.In light of the above experiences, the NRC issued six information notices(86-106 and Supplements 1, 2, and 3; 87-36, and 88-17) and Bulletin 87-01addressing this problem. The staff review of licensees' responses to thebulletin indicates that the pipe wall thinning problem is widespread forsingle-phase and two-phase high-energy carbon steel systems. The systems andcomponents reported as having experienced pipe wall thinning are listed inSection 6 of the attachment to this letter. The staff review also showed thatwall thinning in single phase feedwater-condensate systems is more prevalentamong pressurized-water reactors (PWRs) but also occurs in boiling-waterreactors BWRs).The staff audited 10 operating plants (7 PWRs and 3 BWRs) in late 1988 toassess implementation of erosion/corrosion monitoring programs by licenseesand to ensure that adequate guidance was provided for corrective actions andother activities regarding repair and replacement of degraded piping andcomponents. Detailed audit findings are described in Section 7 of NUREG-1344,which is enclosed with this letter. In general, all licensees have developedand put in place an erosion/corrosion monitoring program that meets the intentof NUMARC guidelines (Appendix A of NUREG-1344). In addition, all licenseeshave completed their initial examination as recommended by NUMARC. However,the staff found that none of these licensees has implemented formalizedprocedures or adminis-trative controls to ensure continued long-termimplementation of its erosion/ corrosion monitoring program for piping andcomponents within the licensing basis. Therefore, you should provideassurances that a program, consisting of systematic measures to ensure thaterosion/corrosion does not lead to degra-dation of single phase and two phasehigh-energy carbon steel systems has been implemented. The detailedinformation should not be submitted for NRC review..Generic Letter 89-08 -3- May 2, 1989Additional insight into the phenomena related to erosion/corrosion of carbonsteel components is provided in the enclosure to this letter (NUREG-1344).You are required to submit your response, signed under oath or affirmation, asspecified in 10 CFR 50.54(f), within 60 days of receipt of this letter. Yourresponse will be used to determine whether your license should be modified,suspended, or revoked. Your response should include information on whether ornot you have implemented or intend to implement a long term erosion/corrosionmonitoring program that provides assurances that procedures or administrativecontrols are in place to assure that the NUMARC program or another equallyeffective program is implemented and the structural integrity of all high-energy (two phase as well as single phase) carbon steel systems is maintained.If this program is not yet implemented you should include the scheduled imple-mentation date.This request is covered by the Office of Management and Budget Clearance Number3150-0011, which expires December 31, 1989. The estimated average burden is200 man-hours per addressee response, including assessing the actions to betaken, preparing the necessary plans, and preparing the response. Thisestimated average burden pertains only to these identified response-relatedmatters and does not include the time for actual implementation of therecommended actions.http://www.nrc.gov/reading-rm/doc-collections/gen-comrn/gen-letters/1989/gl89008.htmIl 03/13/2003 NRC Generic Letter 89-08: Erosion/Corrosion-Induced Pipe Wall Thinning Send comments regarding this burden estimate or any other aspect of this col-lection of information, including suggestions for reducing this burden, tothe Records and Reports Management Branch, Division of Information SupportServices, Office of Information Resources Management, U.S. Nuclear RegulatoryCommission, Washington, D.C. 20555; and to the Paperwork Reduction Project(3150-0011), Office of Management and Budget, Washington, D.C. 20503.Sincerely,James G. PartlowAssociate Director for ProjectsOffice of Nuclear Reactor RegulationEnclosures:1. NUREG-13442. Listing of Recently IssuedGeneric Lettershttp://www.nrc.gov/reading-rmldoc-collections/gen-comm/gen-letters/I 989/gl89008.html 03/13/2003