Information Notice 1994-79, Microbiologically Influenced Corrosion of Emergency Diesel Generator Service Water Piping
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
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.
K>J 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
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 hi It6 J'4 K>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
-1/4<> A~-' 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*err DDrFlVT) rnCUriRFNrEN
OFFICE *OGCB/DORS
- TECH ED *REGION I *REGION I NAME CVHodge JDMain MCModes PPSena DATE J 09/08/94 09/09/94 09/01/94 10/03/94__ _ _ _ _ _ _ _ _ -EI I __ If_*Ann-nfEDrIOTAN
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G& I _J1 10/06/94 10/20/94 10/25/94 1 1 ff_/_ 4 Lj DOCUMENT NAME: 94-79.IN
IN 94-XX October xx, 1994 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 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*SEE PREVIOUS CONCURRENCE
OFFICE *OGCB/DORS
- TECH ED *REGION I *REGION I NAME CVHodge JDMain MCModes PPSena DATE 09/08/94 j09/09/94
09/01/94 10/03/94._ -11*Ann:DRA/RFCION
I I *EMCB/DE I *S:EMCB/DE
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ARBlough JADavis RAHermann
JRStrosnider
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I IWS/NRR BWSheron RLW A af e B j jes 10/06/94 10/9 1,/94 10/ /94 _________DOCUMENT NAME: NECK-MIC.
INY
-IN 94-XX September
xx, 1994 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.-- "tf A R'lena-*QVV DPRVUSTnT1 CONCURRENCE
--.:L: -a V -__s_ ___ -r- -m --OFFICE *OGCB/DORS
- TECH ED *REGION I REGION I A NAME CVHodge I JDMain MCModes PPSena DATE j09/08/94
09/09/94 09/01/94 ff /o3/94_ I ., ._II annlnPq/RFnTON
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BKGrimes__/__ /94 09/ /94 09/ /94 DOCUMgNT NAME: NECK-MIC.1fir
A-- 016 I IN 94-XX September
xx, 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.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*SEE PREVIOUS CONCURRENCE
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6 2 OFFICE OGCB/DORS
TECH ED A REGION I REGION I NAME CVHodge k ^JDMain MCModes PPSena DATE 1 O9/08/94 09/09/94 09/01/94 09/ /94 ADD:DRS/REGION
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09/ /94 09/0O/94 09/7v/94 09/ /94 D: DE AC:OGCB/DORS
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BKGrimes 09/ /94 09/ /94 09/ /94 DOCU;MENT
NAME: NECK-MIC.INF