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 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.

Li I st

.i~5X*-13, Supp

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 no specific action or written response. If

you have any questions about the information in this notice, please contact one

of .the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project 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

a' (Dr i.r '

CD

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 Problems with Diaphragms 12/18/91 All holders of OLs or CPs

in Safety-Related Tanks for nuclear power reactors.

91-81 Switchyard Problems that 12/16/91 All holders of OLs or CPs

Contribute to Loss of for nuclear power reactors.

Offsite Power

91-80 Failure of Anchor 12/11/91 All holders of OLs or CPs

Head Threads on Post- for nuclear power reactors.

Tensioning System During

Surveillance Inspection

91-79 Deficiencies in the 12/06/91 All holders of OLs or CPs

Procedures for Instal- for nuclear power reactors.

ling Thermo-Lag Fire

Barrier Materials

88-92, Potential for Spent 11/29/91 All holders of OLs or CPs

Supp. 1 Fuel Pool Draindown for nuclear power reactors.

91-78 Status Indication of 11/28/91 All holders of OLs or CPs

Control Power for for nuclear power reactors.

Circuit Breakers Used

in Safety-Related Appli- cations

90-57, Substandard, Refur- 11/27/91 All holders of OLs or CPs

Supp. 1 bished Potter & Brum- for nuclear power reactors.

field Relays Repre- sented as New

91-77 Shift Staffing at 11/26/91 All holders of OLs or CPs

Nuclear Power Plants for nuclear power reactors.

91-76 10 CFR Parts 21 and 11/26/91 All holders of OLs or CPs

50.55(e) Final Rules and vendors for nuclear

f1 power reactors.

OL = Operating License

CP = Construction Permit