Information Notice 1998-45, Cavitation Erosion of Letdown Line Orifices Resulting in Fatigue Cracking of Pipe Welds

Cavitation Erosion of Letdown Line Orifices Resulting in Fatigue Cracking of Pipe Welds

ML031040533
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	12/15/1998
From:	Roe J NRC/NRR/DLPM
To:
References
IN-98-045, NUDOCS 9812100048
Download: ML031040533 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 December 15, 1998 NRC INFORMATION NOTICE 98-45: CAVITATION EROSION OF LETDOWN LINE

ORIFICES RESULTING IN FATIGUE CRACKING OF

PIPE WELDS

Addressees

All holders of operating licenses for nuclear power reactors, except those that have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor.

Purpose

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

addressees to potential problems caused by cavitation erosion of letdown line orifices in the

chemical and volume control system (CVCS). Such erosion has contributed to failures in pipe

welds downstream of the letdown line orifices. 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 September 11, 1996, Surry Power Station, Unit 2, experienced its fourth socket weld failure

in 12 months. The failed welds were located on the low-pressure portion of the CVCS letdown

line, just downstream of the pressure-reducing orifice isolation valves. The licensee determined

that the most likely cause of the weld failure was flow-induced vibration. The licensee

performed a microscopic examination of the Unit 2 letdown line orifices and concluded that two

of the orifices exhibited cone-shaped patterns, wider at the discharge of the orifice and tapering

toward the inlet of the orifice. In addition, the orifice exhibited very rough and irregular surface

profiles. The damage to the letdown line orifices is indicative of cavitation erosion and is

believed to have contributed to flow-induced vibration of the letdown line and to the socket weld

failures.

On March 15, 1997, the licensee performed radiographic examinations on the Surry Unit I

letdown line orifices to check for an erosion condition similar to that previously seen in the Unit

2 letdown line orifices. The licensee concluded that erosion was present in all three orifices and

that the most extensive deterioration was present in the 45-gpm orifice. The licensee's

microscopic examination of this orifice indicated that its nominal diameter of 0.212 inch had

eroded to approximately 1 inch. This erosion occurred over the last 5 inches of the orifice

5-

-j

IN 98-45 December 15,1998 length. One of the 60-gpm orifices exhibited minor erosion, but the second 60-gpm

orifice exhibited deterioration of its 0.242-inch-nominal diameter to approximately 0.5 inch. This

erosion occurred over the last 1.5 inches of the orifice length.

Socket welds have also failed at Diablo Canyon Nuclear Power Plant, Unit 2. From June 1989 through December 1990, four socket welds failed on two of three reactor coolant system (RCS)

pressure letdown lines in the CVCS. All four failed welds were located on the piping

downstream of the RCS letdown orifice isolation valves. On March 19, 1991, Diablo Canyon

Unit 2 experienced the fifth letdown leak since June 1989. During the repair effort, the licensee

determined that the cause of the failures was flow-induced vibration due to a damaged letdown

orifice upstream of the weld failure. The licensee inspected the orifice and found that the

discharge end of the orifice was severely pitted, resulting in a 0.75-inch opening, reducing to

the nominal 0.25-inch diameter at a depth of 1.25 inches.

Discussion

The CVCS letdown orifices control the amount of coolant that is let down (removed) from the

RCS and provide the initial pressure reduction of this high-pressure fluid. The letdown fluid

undergoes purification and filtration to maintain the RCS within its design activity limits.

The letdown orifice is typically a stainless steel cylinder with a 0.25-inch-diameter aperture

through the center. The RCS pressure of 2235 psig is reduced to approximately 350 psig

through the orifice. On the basis of the licensees' examination of the damaged orifices, deterioration was found to have resulted from cavitation erosion.

In the case of Surry's degraded orifices, the licensee's review determined that age and

operating conditions accounted for the varying degrees of degradation among the orifices from

Units 1 and 2. In addition to flow-induced vibrations associated with cavitation erosion of the

letdown orifices, inadequate piping/support configuration, low-cycle operational events, and

weld flaws may also have contributed to the socket weld failures.

The review by the Diablo Canyon licensee concluded that the cavitation erosion was the result

of (1) an out-of-calibration pressure transmitter that reduced the downstream pressure below

that required to prevent cavitation; (2) an incorrectly adjusted blowdown setting of the pressure

relief valve on the downstream line; and (3) once the orifice was damaged, self-induced

cavitation further damaged the orifice. The licensee's root cause determination indicated that

the damaged orifice was causing flow-induced vibrations. The vibrations, in turn, caused

socket welds to fail and also caused some damage to pipe supports.

In summary, cavitation erosion of the letdown orifices can lead to vibration of the letdown line

and, thus, to fatigue failures of letdown line socket welds.

IN 98-45 December 15, 1998 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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Carol Lauron, NRR

301-415-2736 E-mail: cIl@nrc.gov

John R. Tappert, NRR

301-415-1167 E-mail: jrtinrc.gov

Attachment: List of Recently Issued NRC Information Notices

Attachment

IN 98-45 December 15, 1998 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

98-44 Ten-year Inservice InsDection 12110/98 All holder of oDerating licenses

(ISI) Program Update for Licensees for nuclear power reactors, except

that Intend to Implement Risk-informed those that have permanently

ISI of Piping ceased operations and have

certified that fuel has been

permanently removed from the

reactor

98-43 Leaks in the Emergency Diesel 12/04/98 All holder of operating licenses

Generator Lubricating Oil and for nuclear power reactors, except

Jacket Cooling Water Piping those licensees that have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel

98-42 Implementation of 10 CFR 50.55a 12101/98 All holders of operating licenses

(g) Inservice Inspection Requirements for nuclear power reactors

98-41 Spurious Shutdown of Emergency 11/20/98 All holders of operating licenses

Diesel Generators from Design for nuclear power reactors, except

Oversight for those who have ceased

operations and have certified that

fuel has been permanently

removed from the reactor vessel

98-40 Design Deficiencies Can Lead 10/26/98 All holders of operating licenses

Reduced ECCS Pump Net Positive for nuclear power reactors, except

Suction Head During Design-Basis those licensees who have

Accidents permanently ceased operations

and have certified that fuel has

bee permanently removed from

the vessel

OL = Operating License

CP = Construction Permit

IN 98-45 December 15, 1998 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.

[Orig signed by D.B. Matthews]

for Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Carol Lauron, NRR

301-415-2736 E-mail: cllenrc.gov

John R. Tappert, NRR

301-415-1167 E-mail: jrt~nrc.gov

Attachment: List of Recently Issued NRC Information Notices

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DOCUMENT NAME: G:XJRT\MA3272.IN

Reviewed by Tech Editor 11/10 Reviewed by PMs 10/27 To receive a copy of this document, indicate in the box C=Copy w/o attachment/enclosure E=Copy with attachment/enclosur N Ng py

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DATE 10/27 /98 10/27/98 11/19/98 12/01/98 12/3/98 12/9/98 12/ 10°/98 OFFICIAL RECORD COPY

• see previous

IN 98-XX

November xx, 1998 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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Carol Lauron, NRR

301-415-2736 E-mail: cllenrc.gov

John R. Tappert, NRR

301-415-1167 E-mail: jrtenrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\RTUWA3272.IN H' 0

Reviewed by Tech Editor 11/10 Reviewed by PMs 10/27 \i\

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IN 98-XX

November xx, 1998 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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Carol Lauron, NRR

301-415-2736 E-mail: cllinrc.gov

John R. Tappert, NRR

301-415-1167 E-mail: jrtenrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:JRT\MA3272.IN X \\ N:

Reviewed by Tech Editor 11/10 Reviewed by PMs 10/27 To rrceive a rInnv nf this dnuiment indircate in the hbo C=Cnnv w/n attarhment/enninsure E=COnv with attachment/enclosure N = No coDY

OFCc EMCB:Con t act E PECB:Contact E EMCB:(A)BC DE:(A)D I PECB:BC DRPM: (A)D

NAME CLauron * JTappert * ESullivan ;1

, GLainas JStolz JRoe

DATE 10/ 27 /98 10/27/98 1 19/98 10/ /98 IO/ /98 10/ /98 OFFICIAL RECORD COPY

• see previous

IN 98-XX

October xx, 1998 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 Nudear Reactor Regulation (NRR) project manager.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Carol Lauron, NRR

301-415-2736 E-mail: cllinrc.gov

John R. Tappert, NRR

301-415-1167 E-mail: jrtinrc.gov

Attachment: List of Recently Issued NRC Administrative Letters

DOCUMENT NAME: G:\JRT\MA3272.IN Ia/

Reviewed by Tech Editor Io/I ktttbc#JItc l PM$S /, 7 To receive a copy of this document, indicate in the box C=Copy wlo attachmentlenclosure EZopy with attachmentlenclosure N = No copy

OFC EMCB:Contact l1 j -jA

E tEMCB:(A)BC E I PECB:BC I DRPM: (A)D I

NAME CLauron v JTappert ESullivan GLainas JStolz JRoe

DATE 101 'I198 10/ 198 10/ /98 10/ /98 10/ /98 10/ /98 OFFICIAL RECORD COPY