Information Notice 1994-79, Microbiologically Influenced Corrosion of Emergency Diesel Generator Service Water Piping

Microbiologically Influenced Corrosion of Emergency Diesel Generator Service Water Piping

ML031060426
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, 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, Crane
Issue date:	11/23/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-079, NUDOCS 9411170039
Download: ML031060426 (9)

I

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

November 23, 1994

NRC INFORMATION NOTICE 94-79:

MICROBIOLOGICALLY INFLUENCED CORROSION OF

EMERGENCY DIESEL GENERATOR SERVICE WATER PIPING

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

PurDose

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

notice to alert addressees to degradation resulting from microbiologically

influenced corrosion in carbon steel piping systems that supply service water

to emergency diesel generators.

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

Haddam Neck Plant

On February 12, 1994, a through-wall leak developed in the service water

system supply piping to the "A" emergency diesel generator. The leak occurred

in a weld in an area of low flow, where the licensee was doing light surface

grinding to prepare for ultrasonic test (UT) inspection.

Previously, in March

1993, the licensee had found a similar leak associated with the "B" emergency

diesel generator. After removing the leaking section and examining the pipe, the licensee determined that the leak was caused by poor initial weld quality

and microbiologically influenced corrosion. Lack of penetration of some welds

created a crevice condition.

Radiographic tests (RT) of additional emergency

diesel generator service water system piping revealed three additional welds

that could form similar leaks.

It was during preparation of one of these

welds for UT examination that the through-wall leak associated with the "A"

emergency diesel generator was found.

The licensee had previously performed a structural integrity determination in

1993 by radiography. Though based on a uniform wall loss instead of a sharp

,disruption, the licensee had at that time concluded that the worst-case

degraded cross-section of the as-found pipe welds, located in the unisolable

portions of the emergency diesel generator supply piping, met the Generic

Letter 90-05 acceptance criteria for structural integrity and that the

degraded piping would have sufficient mechanical and structural integrity to

remain operable.

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IN 94-79 November 23, 1994 Beaver Valley Power Station. Unit I

On May 6, 1994, the licensee found a through-wall leak (an 8 mm [5/16 inch]

diameter hole) on the "Al train reactor plant river water system header to the

emergency diesel generators. The leak developed on the below-grade portion of

the 15-cm [6-inch] diameter A106 Grade B carbon steel piping.

The licensee

excavated the "A" and 'B" train headers, ultrasonically examined them using

the "autoscan" area mapping technique, and found localized pitting to less

than minimum required wall thickness in three additional locations along the

"A" train piping.

The pits were not clustered or closely spaced, but were

located along the pipe length between the five and seven o'clock positions.

For reference, the nominal pipe wall thickness is 6.4 mm [0.25 inch] and

minimum code wall thickness is 1.5 mm [0.06 inch].

The licensee evaluated the pitting in accordance with the American Society of

Mechanical Engineers (ASME) Code of record.

The basis for the localized

thinning evaluation was conducted in accordance with industry guidance, EPRI

NP-59IISP, "Acceptance Criteria for Structural Evaluation of Erosion-Corrosion

Thinning in Carbon Steel Piping." This evaluation was reviewed by personnel

in NRR and deemed as an acceptable conservative means of demonstrating ASME

Code conformance. The licensee determined microbiologically influenced

corrosion to be the cause of the pitting and through-wall leak. The licensee

removed a 0.61 m [24 inch] long section of piping to culture and characterize

the microbial activity and perform additional ultrasonic testing.

The general inside surface of the piping was moderately corroded, with

localized pits and tubercles. Cultures from the pits contained sulfur- reducing bacteria and the anaerobic bacteria Clostridium. The tubercle

formation was the result of the growth of the iron-oxidizing bacteria

Gallionella. Ultrasonic examinations of a heat-affected zone indicated that

the weld examined was not subject to preferential microbiologically influenced

corrosion attack.

Discussion

Stagnant or intermittent-flow conditions, as in the case of emergency diesel

service water supply headers, are conducive to the growth of microorganisms

that can accelerate corrosion rates. Service water supply lines to emergency

diesel generators are stagnant because motor-operated isolation valves are

normally maintained shut (except during monthly surveillance testing).

Crevices such as those in piping welds that lack penetration can enhance

microbiologically influenced corrosion attack by giving a place for deposits

and, therefore, for the bacteria to collect. Microbial films form when

aerobic species, such as iron-oxidizing bacteria, create anaerobic conditions

underneath them for microorganisms, such as sulfate-reducing bacteria, to

accumulate at the metal surface.

Sulfate-reducing bacteria attack the metal

surface, produce corrosive chemicals, and cause deep pitting.

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IN 94-79 November 23, 1994 Microbiologically influenced corrosion on carbon steel will increase general

corrosion, through-wall pitting, and the formation of tubercles. Tubercles

consist of corrosion products, microbes, and debris. Tubercle growth could

restrict cooling water flow to equipment.

Stainless steel piping is not immune to microbiologically influenced corrosion

because microbes can attack at the weld heat affected zone (HAZ) in stainless

steels when this zone becomes sensitized. Microbiologically influenced

corrosion can also damage metals lined with polymeric materials, typically at

coating imperfections.

Once microbial films are established on metal surfaces, they are extremely

difficult to eliminate because of the resiliency of the individual

microorganisms. Biocides are applied by some licensees in areas where

continuous flow conditions cannot be maintained. However, biocide treatments

are not always effective against established microorganism colonies because

the biocide cannot penetrate through the tubercles or aerobic biofilms.

Treatment against established colonies involves a combination of mechanical or

chemical pipe cleaning, continued water treatment and regular maintenance.

Continuous flow conditions have been found to prevent the attachment and

growth of microbial films.

It may be necessary to replace materials if microbiologically influenced

corrosion severely damages them or where mitigation measures cannot bring the

system condition under control.

Possible alternatives include replacing

carbon steel with stainless steel or replacing stainless steel with more

resistant materials, such as 6-percent molybdenum stainless steels, nickel

base alloys, titanium, or nonmetallic materials.

The licensee did not regularly treat the Beaver Valley River water supply

lines to the diesel with biocide or corrosion inhibitors. The chlorination

injection point for the main river water headers is downstream of the branch

lines to the emergency diesel generators. It also appears that the existing

program at Haddam Neck of hypochlorite injection was not successful in

mitigating the microbiologically influenced corrosion problems in stagnant

dead-end lines at such locations as the emergency diesel generator supply.

IN 94-79 November 23, 1994 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.

Vv BaD

D ision f Project Support

Office of Nuclear Reactor Regulation

Technical contacts: Michael Modes, RI

James A. Davis, NRR

(215) 337-5198

(301) 504-2713 Peter P. Sena, RI

Vern Hodge, NRR

(412) 643-2000

(301) 504-1861 Attachment:

List of Recently ssued NRC Information Notices

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Attachment

IN 94-79

November 23, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

94-78

94-77

94-76

93-60,

Supp. 1

94-75

94-74

94-73

94-72

94-71

Electrical Component

Failure due to Degrada- tion of Polyvinyl Chloride

Wire Insulation

Malfunction in Main Gen- erator Voltage Regulator

Causing Overvoltage at

Safety-Related Electrical

Equipment

Recent Failures of Charging/

Safety Injection Pump Shafts

Reporting Fuel Cycle

and Materials Events to

the NRC Operations Center

Minimum Temperature

for Criticality

Facility Management

Responsibilities for

Purchased or Contracted

Services for Radiation

Therapy Programs

Clarification of Critical- ity Reporting Criteria

Increased Control Rod

Drop Time from Crud

Buildup

Degradation of Scram

Solenoid Pilot Valve

Pressure and Exhaust

Diaphragms

11/21/94

11/17/94

10/26/94

10/20/94

10/14/94

10/13/94

10/12/94

10/05/94

10/04/94

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for pressurized water

reactors.

All 10 CFR Part 70

fuel cycle licensees.

All holders of OLs or CPs

pressurized-water reactors

(PWRs).

All U.S. Nuclear Regulatory

Commission Medical

Licensees.

All fuel fabrication

facilities.

All holders of OLs or CPs

for pressurized water

reactors.

All holders of OLs or CPs

for boiling water reactors

(BWRs).

OL - Operating License

CP = Construction Permit

-

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IN 94-79 November 23, 1994 The licensee did not regularly treat the Beaver Valley River water supply

lines to the diesel with biocide or corrosion inhibitors. The chlorination

injection point for the main river water headers is downstream of the branch

lines to the emergency diesel generators.

It also appears that the existing

program at Haddam Neck of hypochlorite injection was not successful in

mitigating the microbiologically influenced corrosion problems in stagnant

dead-end lines at such locations as the emergency diesel generator supply.

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.

Original signed by B.D. Liaw for

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

Michael Modes,

(215) 337-5198 RI

James A. Davis, NRR

(301) 504-2713

Peter P. Sena, RI

(412) 643-2000

Vern Hodge, NRR

(301) 504-1861 Attachment:

List of Recently Issued NRC Information Notices

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The chlorination injection point for the main river

water headers is downstream of the branch lines to the emergency

diesel generators.

It also appears that the existing program at

Haddam Neck of hypochlorite injection was not successful in

mitigating the microbiologically influenced corrosion problems in

stagnant dead-end lines to such locations as the emergency diesel

generator supply.

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.

Brian K. Grimes, Director

Division of Operating Reactor

Support

Office of Nuclear Reactor

Regulation

Technical contacts:

Michael Modes, Region I

(215) 337-5198

Peter P. Sena, Region I

(412) 643-2000

James A.Davis, NRR

(301) 504-2713 Attachment:

List of Recently Issued NRC Information Notices

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This information notice requires no specific action or written

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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.

Brian K. Grimes, Director

Division of Operating Reactor

Support

Office of Nuclear Reactor

Regulation

Technical contacts:

Michael Modes, Region I

(215) 337-5198

Peter P. Sena, Region I

(412) 643-2000

James A. Davis, NRR

(301) 504-2713 Attachment:

List of Recently Issued NRC Information Notices

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this notice, please contact one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation

(NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor

Support

Office of Nuclear Reactor

Regulation

Technical contacts:

Michael Modes, Region I

(215) 337-5198

Peter P. Sena, Region I

(412) 643-2000

James A. Davis, NRR

(301) 504-2713 Attachment:

List of Recently Issued NRC Information Notices

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