Information Notice 1992-07, Rapid Flow-induced Erosion/Corrosion of Feedwater Piping

Rapid Flow-induced Erosion/Corrosion of Feedwater Piping

ML042330670
Person / Time
Issue date:	01/09/1992
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-92-007
Download: ML042330670 (3)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 January 9, 1992 NRC INFORMATION NOTICE 92-07: RAPID FLOW-INDUCED EROSION/CORROSION

OF FEEDWATER PIPING

Addressees

All holders of operating licenses or construction permits for pressurized water

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice

to alert addressees to problems discovered at the Catawba Nuclear Station, Unit

2, involving the rapid flow-induced erosion/corrosion of feedwater piping. The

problem discovered at Catawba affects the piping supplying the upper feedwater

nozzles and may apply to all Westinghouse units employing steam generator

models D-4, D-5, and E, in which a portion of main feedwater is diverted to the

upper feedwater nozzles when the unit is operating. It is expected that

recipients will review the information for applicability to their facilities

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.

Description of Circumstances

On November 4, 1991, while performing ultrasonic testing on a section of 4-inch

feedwater system piping on Catawba's Unit 2 A steam generator, the licensee, Duke Power Company, detected several locations that were at or near minimum

acceptable wall thickness. The licensee detected similar results on the other

three steam generators. The licensee was performing this testing as part of

its prescribed piping erosion/corrosion control program.

The licensee removed sections of the A106B carbon steel piping for analysis or

replacement. This analysis revealed that the piping had undergone significant, symmetric, flow-induced, single phase erosion/corrosion. In some areas, the

4-inch schedule 80 pipe (nominal thickness 0.337 inch) had been thinned to

0.185 inch in only four operating cycles. This implies an erosion/corrosion

rate of approximately 0.040 Inch per cycle. The licensee identified approxi- mately 90 feet of affected pipe for replacement.

It appears that the thinning is directly attributable to the design of the

steam generators (Model D5) on Catawba Unit 2, which requires a split-flow

feedwater delivery system. In this design, typically 10-20 percent of the

total feedwater flow is delivered to the upper feedwater nozzles to prevent

9201090188

IN 92-0i

January 9, 1992 flow-induced vibration damage to the steam generator feedwater preheater

section when full feedwater flow is delivered through the main nozzles.

The original Catawba feedwater system design did not employ split-flow delivery

at power. As a result, the piping was not sized to accommodate the operating

flow rates, resulting in flow velocities of 30-35 feet per second in sections

of 4-inch piping. This high flow rate has led to rapid erosion/corrosion.

In the case of Catawba, Unit 2, if the subject piping in the feedwater preheater

bypass line had ruptured, the break would not have been isolable and would have

resulted in the steam generator fluid being released outside containment.

This problem applies to Westinghouse units employing steam generator models

D-4, D-5, and E if the flow reaches a high velocity when a portion of

normal feedwater is diverted to the upper feedwater nozzles. In numerous

generic communications, the staff has previously stated that high velocity

flows may cause rapid flow-induced erosion/corrosion in carbon steel piping.

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.

hr oss ,frecto

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: William Orders, RII

(803) 831-2963 John Zeiler, RII

(803) 831-2963 Krysztof I. Parczewski, NRR

(301) 504-2705 Attachment: List of Recently Issued NRC Information Notices

~'.'f 'a. cI men t

IN 92-07 January 9, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-06 Reliability of ATWS Mitiga- 01/15/92 All holders of OLs or CPs

tion System and Other NRC for nuclear power reactors.

Required Equipment Not

Controlled by Plant Tech- nical Specifications

92-05 Potential Coil Insulation 01/08/92 All holders of OLs or CPs

Breakdown in ABB RXMH2 Relays for nuclear power reactors.

92-04 Potter & Brumfield Model 01/06/92 All holders of OLs or CPs

MDR Rotary Relay Failures for nuclear power reactors.

92-03 Remote Trip Function 01/06/92 All holders of OLs or CPs

Failures in General Electric for nuclear power reactors.

F-Frame Molded-Case Circuit

Breakers

92-02 Relap5/Mod3 Computer Code 01/03/92 All holders of OLs or CPs

Error Associated with the for nuclear power reactors.

Conservation of Energy

Equation

92-01 Cable Damage Caused by 01/03/92 All holders of OLs or CPs

Inadequate Cable Installa- for nuclear power reactors.

tion Procedures and Controls

91-87 Hydrogen Embrittlement of 12/27/91 All holders of OLs or CPs

Raychem Cryofit Couplings for nuclear power reactors.

91-86 New Reporting Requirements 12/27/91 All licensees authorized

for Contamination Events at to use byproduct materials

Medical Facilities for human use.

(10 CFR 30.50)

91-85 Potential Failures of 12/26/91 All holders of OLs or CPs

Thermostatic Control Valves for nuclear power reactors.

for Diesel Generator Jacket

Cooling Water

OL = Operating License

CP = Construction Permit