Information Notice 1991-18, High-Energy Piping Failures Caused by Wall Thinning

High-Energy Piping Failures Caused by Wall Thinning

ML042380261
Person / Time
Issue date:	12/18/1991
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-91-018, Suppl 1
Download: ML042380261 (5)

UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555December 18, 1991NRC INFORMATION NOTICE 91-18, SUPPLEMENT 1: HIGH-ENERGY PIPING FAILURES CAUSEDBY WALL THINNING

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

Purpose

The U. S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to continuing erosion/corrosion problems affectingthe integrity of high energy piping systems and to alert addressees toapparently inadequate erosion/corrosion monitoring programs. It is expectedthat recipients will review the information for applicability to their facili-ties and consider actions, as appropriate, to avoid similar problems. However,suggestions contained in this information notice are not NRC requirements;therefore, no specific action or written response is required.BackgroundOn March 12, 1991, the NRC issued Information Notice (IN) 91-18, "High EnergyPiping Failures Caused by Wall Thinning," to describe ruptures and leaks insecondary systems carrying high energy fluids at the Millstone Nuclear PowerStation, Unit 3, the San Onofre Nuclear Generating Station, Unit 2, and aforeign plant.Following the pipe rupture at the Surry Power Station in 1986, the NRC issuedBulletin 87-01, "Thinning of Pipe Walls in Nuclear Power Plants," July 9, 1987.In this bulletin, the staff requested licensees and applicants to inform theNRC about their programs for monitoring the wall thickness of carbon steelpiping in both safety-related and nonsafety-related high energy fluid systems.IN 91-18 included references related to this bulletin. IN 82-22, "Failures ofTurbine Exhaust Lines," July 9, 1982, also provides relevant informationregarding pipe wall thinning in steam lines.In 1989, following an audit of the erosion/corrosion programs at ten plants,the NRC issued Generic Letter (GL) 89-08, "Erosion/Corrosion-Induced Pipe WallThinning," May 2, 1989. In this generic letter, the staff requested licenseesand applicants to implement long term erosion/corrosion monitoring programs.The staff made this request to obtain assurances that procedures or administra-tive controls were in place to maintain the structural integrity of all carbonsteel systems carrying high energy fluids.9121720218ATTACHMENT 14 IN 91-18, Supplement 1December 18, 1991 The Electric Power Research Institute (EPRI) released computer codes CHEC andCHECMATE in June 1987 and April 1989, respectively, to assist in selecting fortesting those areas of the piping systems with highest probabilities for wallthinning. The CHEC calculation applies to pipes containing a single liquidphase and the CHECMATE calculation applies to pipes containing both liquid andvapor phases.On June 11, 1987, the Technical Subcommittee Working Group on PipingErosion/Corrosion of the Nuclear Management and Resources Council (NUMARC)issued a summary report describing a method using the CHECMATE computer code formonitoring carbon steel components exposed to the conditions conducive toerosion/corrosion.

Description of Circumstances

At Millstone Unit 2, on November 6, 1991, while the licensee, the NortheastNuclear Energy Company (NNECO), was operating the plant at 100 percent of fullpower, a rupture occurred in train B of the moisture separator reheater (MSR)system. An 8-inch elbow, located between the first stage MSR drain tank andthe feedwater heater, ruptured at its extrados (Figure 1). The elbow waslocated downstream from a 4-inch flow control valve and a 4- to 8-inchexpander. The high energy water in the pipe (approximately 463 F, 470 psig)flashed to steam, actuating portions of the turbine fire protection delugesystem. The water level in the steam generator decreased slightly. The licen-see had not selected the ruptured elbow for ultrasonic testing (UT) in itserosion/corrosion monitoring program.The ruptured elbow was made of carbon steel with nominal wall thickness of0.322 inch. Wall thickness at the failed area was eroded to 95 percent of theinitial nominal value. Other areas, away from the failed area, showed a lossof 22 percent of the wall thickness. The identical elbow in the A train had amaximum wall loss of 34 percent of the initial nominal value.DiscussionThe licensee has had a program for monitoring high energy fluid piping since1981. The criteria for choosing components to be inspected include componentlocation and service conditions as determined by the engineering judgement ofthe plant personnel. In contrast, more relevant parameters that could indicateerosion or corrosion wastage include piping material and geometry,'fluid prop-erties (flow, temperature, and acidity), and fluid contents (the acidity-controlling agent and the concentration of dissolved oxygen).In its response to GL 89-08, NNECo indicated that its Engineering ProcedureEN-21153, "Thickness Testing of Secondary Piping," describes its monitoringprogram, established in accordance with EPRI guidelines and using the CHEC pro-gram to select for testing those areas of the pipi ng systems with highest prob-abilities for wall thinning. The licensee also selects areas on the basis ofplant experience. However, although the pipe wall thickness testing programvlas included in the licensee's procedures, the licensee had not implemented themethodology using the EPRI computer codes at Unit 2. This omission may accountfor the licensee not having tested previously the piping that ruptured onNovember 6, 1991.

.i~ 5X*-13, Supp Li st IDecember 18, 1991 The licensee did use an earlier version of the CHEC computer code in limitedanalyses at its other nuclear units. The licensee's program did not reflectthe use of current versions of EPRI codes (either CHEC or CHECMATE). .TheUnit 3 rupture described in the March 12, 1991, issuance of this informationnotice prompted NNECo to commit to perform CHEC or CHECMATE analyses at all itsunits by December 31, 1991. However, at the time of the second rupture onNovember 6, 1991, the licensee was implementing this program at its corporateengineering office and not at Unit 2. The Unit 2 personnel were consequentlyrelying on inspection procedures that did not possess the benefit of the EPRI'smethodology for selecting areas of piping for UT inspection. AfterNovember 6, 1991, NNECo performed a CHECMATE analysis that did identify thisportion of the MSR system as highly susceptible to erosion or corrosion andthus as a candidate for UT inspection.This information notice requiresyou have any questions about theof .the technical contacts listedReactor Regulation (NRR) projectno specific action or written response. Ifinformation in this notice, please contact onebelow or the appropriate Office of Nuclearmanager.(Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:K. 1. Parczewski, NRR(301) 504-2705Vern Hodge, NRR(301) 504-1861Attachments:1. Figure 1, "Rupture of Elbow in Secondary System atMillstone Unit 2 on November 6, 1991"2. List of Recently Issued NRC Information Notices

6"xl2" FISH-ItIOUTHBREAK AT EXTRADOSFLOW4 in. dia.4 in. dia.8 in. dia.Motes:Vo. 1 B First Stage Moisture SeparatorReheater Drain Tank Drain LinePipe: Carbon SteelNo Chromium ContentFluid: H2O @ 470 psig, 4630FpH: 8.2-*8.702: <2ppbCD (D .ra' r i 'Figure 1. Rupture of Elbow in Secondary System at Millstone Unit 2 on November 6, 199, CD-

A-ttzac~:.^,IN 91-18, Supplem~nt 1December 18, 3991Page 1 of iLIST OF RECENTLY ISSUEDNRC INFORMATiON NOTICESInformation Date ofNotice No. Subject Issuance Issued to91-8291-8191-8091-7988-92,Supp. 191-7890-57,Supp. 191-7791-76Problems with Diaphragmsin Safety-Related TanksSwitchyard Problems thatContribute to Loss ofOffsite PowerFailure of AnchorHead Threads on Post-Tensioning System DuringSurveillance InspectionDeficiencies in theProcedures for Instal-ling Thermo-Lag FireBarrier MaterialsPotential for SpentFuel Pool DraindownStatus Indication ofControl Power forCircuit Breakers Usedin Safety-Related Appli-cationsSubstandard, Refur-bished Potter & Brum-field Relays Repre-sented as NewShift Staffing atNuclear Power Plants10 CFR Parts 21 and50.55(e) Final Rules12/18/9112/16/91 All holders of OLs or CPsfor nuclear power reactors.12/11/91 All holders of OLs or CPsfor nuclear power reactors.12/06/91 All holders of OLs or CPsfor nuclear power reactors.11/29/91 All holders of OLs or CPsfor nuclear power reactors.11/28/91 All holders of OLs or CPsfor nuclear power reactors.11/27/91 All holders of OLs or CPsfor nuclear power reactors.11/26/91 All holders of OLs or CPsfor nuclear power reactors.11/26/91 All holders of OLs or CPsand vendors for nuclearpower reactors.All holders of OLs or CPsfor nuclear power reactors.f1OL = Operating LicenseCP = Construction Permit