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 STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 December 18, 1991 NRC INFORMATION

NOTICE 91-18, SUPPLEMENT

1: HIGH-ENERGY

PIPING FAILURES CAUSED BY WALL THINNING

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

The U. S. Nuclear Regulatory

Commission (NRC) is issuing this information

notice to alert addressees

to continuing

erosion/corrosion

problems affecting the integrity

of high energy piping systems and to alert addressees

to apparently

inadequate

erosion/corrosion

monitoring

programs.

It is expected that 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.Background

On March 12, 1991, the NRC issued Information

Notice (IN) 91-18, "High Energy Piping Failures Caused by Wall Thinning," to describe ruptures and leaks in secondary

systems carrying high energy fluids at the Millstone

Nuclear Power Station, Unit 3, the San Onofre Nuclear Generating

Station, Unit 2, and a foreign plant.Following

the pipe rupture at the Surry Power Station in 1986, the NRC issued Bulletin 87-01, "Thinning

of Pipe Walls in Nuclear Power Plants," July 9, 1987.In this bulletin, the staff requested

licensees

and applicants

to inform the NRC about their programs for monitoring

the wall thickness

of carbon steel piping in both safety-related

and nonsafety-related

high energy fluid systems.IN 91-18 included references

related to this bulletin.

IN 82-22, "Failures

of Turbine Exhaust Lines," July 9, 1982, also provides relevant information

regarding

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 Wall Thinning," May 2, 1989. In this generic letter, the staff requested

licensees and 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 carbon steel systems carrying high energy fluids.9121720218 ATTACHMENT

14 IN 91-18, Supplement

1 December 18, 1991 The Electric Power Research Institute (EPRI) released computer codes CHEC and CHECMATE in June 1987 and April 1989, respectively, to assist in selecting

for testing those areas of the piping systems with highest probabilities

for wall thinning.

The CHEC calculation

applies to pipes containing

a single liquid phase and the CHECMATE calculation

applies to pipes containing

both liquid and vapor phases.On June 11, 1987, the Technical

Subcommittee

Working Group on Piping Erosion/Corrosion

of the Nuclear Management

and Resources

Council (NUMARC)issued a summary report describing

a method using the CHECMATE computer code for monitoring

carbon steel components

exposed to the conditions

conducive

to erosion/corrosion.

Description

of Circumstances

At Millstone

Unit 2, on November 6, 1991, while the licensee, the Northeast Nuclear Energy Company (NNECO), was operating

the plant at 100 percent of full power, 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 and the feedwater

heater, ruptured at its extrados (Figure 1). The elbow was located downstream

from a 4-inch flow control valve and a 4- to 8-inch expander.

The high energy water in the pipe (approximately

463 F, 470 psig)flashed to steam, actuating

portions of the turbine fire protection

deluge system. The water level in the steam generator

decreased

slightly.

The licen-see had not selected the ruptured elbow for ultrasonic

testing (UT) in its erosion/corrosion

monitoring

program.The ruptured elbow was made of carbon steel with nominal wall thickness

of 0.322 inch. Wall thickness

at the failed area was eroded to 95 percent of the initial nominal value. Other areas, away from the failed area, showed a loss of 22 percent of the wall thickness.

The identical

elbow in the A train had a maximum wall loss of 34 percent of the initial nominal value.Discussion

The licensee has had a program for monitoring

high energy fluid piping since 1981. The criteria for choosing components

to be inspected

include component location and service conditions

as determined

by the engineering

judgement

of the plant personnel.

In contrast, more relevant parameters

that could indicate erosion 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

Procedure EN-21153, "Thickness

Testing of Secondary

Piping," describes

its monitoring

program, 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 of plant experience.

However, although the pipe wall thickness

testing program vlas included in the licensee's

procedures, the licensee had not implemented

the methodology

using the EPRI computer codes at Unit 2. This omission may account for the licensee not having tested previously

the piping that ruptured on November 6, 1991.

.i~ 5X*-13, Supp Li st I December 18, 1991 The licensee did use an earlier version of the CHEC computer code in limited analyses at its other nuclear units. The licensee's

program did not reflect the use of current versions of EPRI codes (either CHEC or CHECMATE). .The Unit 3 rupture described

in the March 12, 1991, issuance of this information

notice prompted NNECo to commit to perform CHEC or CHECMATE analyses at all its units by December 31, 1991. However, at the time of the second rupture on November 6, 1991, the licensee was implementing

this program at its corporate engineering

office and not at Unit 2. The Unit 2 personnel

were consequently

relying on inspection

procedures

that did not possess the benefit of the EPRI's methodology

for selecting

areas of piping for UT inspection.

After November 6, 1991, NNECo performed

a CHECMATE analysis that did identify this portion of the MSR system as highly susceptible

to erosion or corrosion

and thus as a candidate

for UT inspection.

This information

notice requires you have any questions

about the of .the technical

contacts listed Reactor Regulation (NRR) project no specific action or written response.

If information

in this notice, please contact one below or the appropriate

Office of Nuclear manager.(Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts: K. 1. Parczewski, NRR (301) 504-2705 Vern Hodge, NRR (301) 504-1861 Attachments:

1. Figure 1, "Rupture of Elbow in Secondary

System at Millstone

Unit 2 on November 6, 1991" 2. List of Recently Issued NRC Information

Notices

6"xl2" FISH-ItIOUTH

BREAK AT EXTRADOS FLOW 4 in. dia.4 in. dia.8 in. dia.Motes: Vo. 1 B First Stage Moisture Separator Reheater Drain Tank Drain Line Pipe: Carbon Steel No Chromium Content Fluid: H2O @ 470 psig, 4630F pH: 8.2-*8.7 02: <2ppb CD (D .r a' 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

1 December 18, 3991 Page 1 of i LIST OF RECENTLY ISSUED NRC INFORMATiON

NOTICES Information

Date of Notice No. Subject Issuance Issued to 91-82 91-81 91-80 91-79 88-92, Supp. 1 91-78 90-57, Supp. 1 91-77 91-76 Problems with Diaphragms

in Safety-Related

Tanks Switchyard

Problems that Contribute

to Loss of Offsite Power Failure of Anchor Head Threads on Post-Tensioning

System During Surveillance

Inspection

Deficiencies

in the Procedures

for Instal-ling Thermo-Lag

Fire Barrier Materials Potential

for Spent Fuel Pool Draindown Status Indication

of Control Power for Circuit Breakers Used in Safety-Related

Appli-cations Substandard, Refur-bished Potter & Brum-field Relays Repre-sented as New Shift Staffing at Nuclear Power Plants 10 CFR Parts 21 and 50.55(e) Final Rules 12/18/91 12/16/91 All holders of OLs or CPs for nuclear power reactors.12/11/91 All holders of OLs or CPs for nuclear power reactors.12/06/91 All holders of OLs or CPs for nuclear power reactors.11/29/91 All holders of OLs or CPs for nuclear power reactors.11/28/91 All holders of OLs or CPs for nuclear power reactors.11/27/91 All holders of OLs or CPs for nuclear power reactors.11/26/91 All holders of OLs or CPs for nuclear power reactors.11/26/91 All holders of OLs or CPs and vendors for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.f1 OL = Operating

License CP = Construction

Permit