ML20195G679
| ML20195G679 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/12/1998 |
| From: | Hartz L VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 98-037A, 98-37A, GL-90-05, GL-90-5, NUDOCS 9811230084 | |
| Download: ML20195G679 (19) | |
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Vii<ciNir EI.ICCTRIC ANil POWI?R Cmil'ANY RICIb10NI), M GINIA U MI November 12, 1998
' United States Nuclear Regulatory Commission Serial No. 98-037A Attention: Document Control Desk NL&OS/ETS Washington, D.C. 20555 Docket Nos. 50-338 50-339 License Nos. NPF-4 N PF-'7
Dear Sir:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 REVISION ,TO SERVICE WATER MIC RELfEF REQUEST NDE-32 in a February 24,1997 letter (Serial No.97-079), as supplemented on August 8,1997 and November 18,1997, Virginia Electric and Power Company requested relief from ASME Section XI paragraph IWA-5250. This relief established a monitoring program l' inat would permit continued Service Water System operation for up to eighteen months from the date of discovery of each minor leak or indication of previous leakage attributed to microbiologicalinfluenced corrosion (MIC). The NRC apprcved this relief request NDE-32, Revision 2, on November 24, 1997. Since that time, we have determined several enhancements that could be made to the program. Therefore, pursuant to 10 CFR 50.55a (a) (3), we are requesting a revision to the previously approved relief from ASME Section XI, paragraph IWA-5250 to permit: 1) performance of a Code repair in fourteen days after discovery in place of structural analysis, and 2) the use of an alternate non-destructive examination technique. Minor program scope changes to correct discrepancies in the listing of the service water lines are also being made.
The current approved MIC monitoring program permits fourteen days after discovery of the leak or indication of previous leakage to perform a structural analysis of the affected line to determine operability. In numerous instances we are able to perform the l appropriate Code repair within the fourteen days and not disrupt plant operations.
Therefore, we are revising the relief request to permit either code repair of the affected )
service water lines or a structural analysis of the affected line to establish operability within fourteen days after discovery. The revised relief (NDE-32, Revision 4) is included as Attachment 1 to this letter.
A detailed engineering evaluation of nondestructive examination (NDE) techniques used to examine the identified MIC locations on the service water piping has been koh completed. The correlation between Radiography (RT) and Ultrasonic (UT) examination is very good as documented in Attachment 2 to this letter. Thus, we are 9811230004 901112 DR ADOCK0500g38
revising the relief request to permit the use of either RT or UT to evaluate the MIC affected locations in the Service Water System.
In our February 24,1998 letter, (NDE-32, Revision 3) a list of the service water lines included in the relief request was provided to the NRC. Since that time, we have identified errors in that listing (transposition error, incorrect line numbers, etc.). A corrected list of the service water lines is provided in the revised relief request, (NDE-32, Revision 4) including one additional service water line which should have been included in the original scope. Additional supporting information has also been incorporated into NDE-32, Revision 4. Therefore, Revision 3 of NDE-32 is superceded by Revision 4.
A bar is included in the right hand margin, which identifies each revision in the attached relief request. Should you have any questions or require additionalinformation, please contact us.
Very truly yours, b k L. N. Hartz Vice President - Nuclear Engineering and Services Commitments made in this letter:
- i. None Attachments cc: U.S. Nuclear Regulatory Commission i Region II Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303 Mr. M. J. Morgan NRC Senior Resident inspector {
North Anna Power Station l
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i Attachment 1 !
Revised Relief Request NDE-32, Revision 4 Service Water MIC Monitoring Program l
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Virginia Electric and Power Company North Anna Power Station l.
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l Virginia Electric & Power Company North Anna Power Station Unit I and Unit 2 Second 10 Year Interval Request for Relief Number NDE-32, Revision 4 I. IDENTIFICATION OF COMPONENTS Drawing #
Service Water System 11715-CBB-40D-2 SHTS. I and 2 !
11715-CBM-78A-2 SHTS. I and 4 i
11715-CBM 78B-2 SHTS.1, and 3 l 11715-CBM-78C-2 SHT. 2 11715-CBM-78G-2 SHTS. I and 2 11715-CBM-78H-2 SHT.1 Components within the scope of this Request for Reliefinclude the welds and associated piping which comprise the moderate energy stainless steel piping of the Service Water l System (SW). This piping system provides cooling water from the Service Water
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Reservoir to safety related equipment and return the Service Water back to the return headers. Normal operating pressure is 100 PSIG. The design pressure is 150 PSIG and the design temperature is 150 F. This is an ASME,Section XI, Class 3 system. I Attachment 2 provides an identification of each piping segment within the scope of this :
Request for Relief. The piping segments are identified by their line number designation, which is a unique identifier. The graphics represented on the associated drawings of each piping segment along with the associated line number designation provide a defining boundary for each pipe segment. The identification of piping segments as '
components is appropriate as both the welds and piping forming the piping segments are subject to developing through wall leaks.
II. IMPRACTICABLE CODE REQUIREMENTS The Service Water System has experienced through-wall leakage caused by Microbiological Influenced Corrosion (MIC). Chemical treatment of the Service Water System has not been effective in eliminating MIC. The Service Water System is being monitored for MIC. Identification of additional through-wall leakage is anticipated.-
Through-wall leakage must be located and evaluated in accordance with the requirements ofIWA-5250 of the 1983 Edition and Summer 1983 Addenda for Unit I and 1986 Edition for Unit 2. The specific Code requirement for which reliefis requested is IWA-5250(a)(2).
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"IWA-5250 Corrective Measures:
(a) The source ofleakage detected during the conduct of a system pressure test shall be located and evaluated by the Owner for corrective measures as follows:.
(2) repairs or replacements of components shall be performed in accordance with IWA-4000 or IWA-7000, respectively."
Articles IWA-4000 and IWD-4000 of ASME Section XI Code repair requirements would require removal of the flaw and subsequent weld repair, Code repairs for through-wall icaks require the line to be isolated and drained. Taking a train of service water out of service in some instances is a major evolution and requires entering a Technical Specification action statement. Welds and piping with through-wall flaws caused by MIC can typically be shown to have adequate structural integrity to !
remain in service. This type of through-wall flaw is unpredictable but not normally i
subject to catastrophic failure. It is impractical to require a Code repair within the time specified by the Technical Specification Limiting Condition for Operation every time a through-wall flaw is identified.
Generic Letter 90-05, " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2, and 3 Piping", provides guidance for submitting relief requests to allow l- continued operation with a through-wall flaw. Submitting a relief request for each L instance of through-wall leakage caused by MIC is an administrative burden and causes additional unnecessary reviews for the NRC. Implementing GL 90-05 each time a through-wall flaw is identified is also impractical.
This relief request (NDE-32, Revision 4) establishes a plan for continued operation with l i through-wall flaws in stainless steel piping in the Service Water System based upon the l
guidance of GL 90-05 to the extent it is believed practical. This relief request will be implemented upon receiving NRC approval. In the interim, relief request NDE-32, Revision 2 will be followed for through-wall flaws in this system.
Ill. ISI BASIS FOR RELIEF REQUEST l
This relief request is submitted in a format laid out in NRC GL 90-05. The following information and justification is provided in accordance with the guidelines of Part B and C of Enclosure i to GL 90-05.
l Scope. Limitations and Specific Considerations Scope The scope consists of welds and stainless steel piping, pipe class 153 A and 163, with evidence of possible through-wallleaks in the Service Water System at North Anna Power Station Units 1 and 2.
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Limitations
' Based on radiographic examinations and laboratory examinations of removed portions of piping from replacements, North Arma Power Station is experiencing MIC in its stainless steel piping. The MIC-caused flaws originate on the inner diameter of the pipe. The Service Water System is conunon to both Units. As long as one Unit is in Mode 1,2,3, or 4 both trains of service water must i'e operable. If both Units are in Mode 5 or 6 then
, one train of Service Water must be oper.tble. The intent of this reliefis to permit l continued operation with the identified 1hrough-wall flaws until repairs are accomplished l
in a scheduled service water outage.
Specific Considerations L
System interactions, i.e. consequences of flooding and spray, will be evaluated. Piping with l
through-wall leakage that could affect plant safety related equipment will be declared inoperable l and the appropriate Technical Specification action statement entered.
l I Welds containing evidence of through wall flaws will be either repaired or assessed for structural L integrity within 14 days of detection. Butt welds and piping remaining in service after leakage is L detected for longer than 14 days and accessible to volumetric examination by Ultrasonic (UT) or Radiographic (RT) examination methods, will be evaluated for structural in+egrity for all design loading conditions, including dead weight, pressure, thermal expansion and seismic (DBE) loads.
The methods used in the structural integrity analysis will consist of area reinforcement, fracture mechanics, and limit load analysis. These methods are detailed in Attachment 1. The welds that are j found to be unacceptable will be declared inoperable and the appropriate Technical Specification action statement entered.
A 3/4" hole will be poetulated for any location with a through-wall flaw that can not be characterized volumetrically by ultrasonics (UT) or radiography (RT), socket welds and welds that are inaccessible for UT or RT. Laboratory examination of cut sections of MIC degraded socket weld samples indicate that flaws are enveloped within the 3/4" size. A leaking socket weld location will be analyzed by treating the cross section as equivalent to the cross section of the attached pipe with a 3/4" hole. The methods used
'in the structural integrity analysis will consist of area reinforcement, fracture mechanics, and limit load analyses. These methods are detailed in Attachment 1. A through-wall flaw size is postulated in ;
order to perfonn a structural analysis. Additional monitoring is perfomied for a period of two (2) months on socket welds to assure the degradation mechanism is behaving in a manner expected for a MlC flaw.
The stmetural integrity for all welds identified with evidence of through-wall leakage will be
! monitored by the following methods:
.- Weekly visual monitoring of through-wall flaws from the time ofidentification until repair of the weld or completion of the structural integrity analysis. Repair of the weld or completion of the structural analysis is required within 14 days of p detecting a through wall flaw. If the welds are determined to be structurally
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I acceptable, then the visual monitoring frequency will be decreased to once every six weeks.
Weekly visual monitodng of through-wall flaws in socket welds and butt welds inaccessible to RT or UT examination for a period of two (2) months. If there is ~no !
significant change in the leakage rate, the monitoring frequency will be decreased to once every sbc weeks until the welds are repaired. A significant change is defmed as a 0.5 gpm increase in the leakage rate from the initial observed leakage condition for each weld. Should any location reach the threshold of a significant change the weld will be reassessed for stmetural integrity and flood / spraying consequences.
, A total leakage rate limit of 1,0 gpm for a single supply or retum line to an individual j component will be established. If this total leakage rate limit is exceeded then an l evaluation will be performed to determine if design service water flow is available to affected components. Inadequate service water supply will cause the associated service water lines and equipment to be declared inoperable and appropriate action will be taken according to Technical Specifications.
l The temporary non-code repair will be to leave the welds as they are found, subject to
! monitoring and meeting the criteria for consequences and for stmetural integrity as described
! above.
Evaluation Flaw Detection During Plant Operation and Imaracticality Determination l
The Service Water System is a common system for both Units at North Anna Power Station. ,
Both trains are required to be operational or the appropriate Technical Specification action statement is entered. The through-wall flaws on Service Water lines in service are anticipated based on the North Anna Power Station history of MIC. Virginia Electric and Poww
! Company requests to evaluate the flaws and leave acceptable through-wall flaws in service in order to perform Code repairs in controlled conditions during scheduled service water outages.
Flaw characterization of MIC has traditionally been performed by radiography and has wide acceptance by the industry as an appropriate technique. Virginia Power has also developed an ultrasonic technique, which is as effective as radiography for detection and length sizing of MIC indications This ultrasonic technique additionally has depth sizing capabilities. The acceptability of ultrasonics as an alternative to radiography is documented in a report titled " Ultrasonic Examination Technique for Detection ofMicrobiologically Induced Corrosion in North Anna Stainless Steel Service Water Piping" dated December 29,1997. Virginia Power proposes to use either radiography or ultrasonics or both to characterize flaws.
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i j Root Cause Determination and Flaw Characterization 3 The Service Water System at North Anna Power Station has previously experienced MIC. Radiograph examinations of service water welds having evidence of through-wall leakage revealed small voids i
surrounded by edoliation, which is typical of MIC. No other type ofinservice defects were identified by
- the radiographs near the areas with through-wall leaks. Additionally, a visual examination performed by j a Virginia Electric and Power Company staff metallurgist of a sample of piping segments removed to j repair the leaking welds confirmed the presence ofMIC.
Flaw Evaluation Flaw evaluation for welds with through-wall leakage will be performed as described in Attachment 1.
The flaws in butt welds that can be characterized by RT or UT examination methods will be evaluated by l l three' types of analyses, area reinforcement, limit load analyses, and fracture mechanics using the 3 guidance from NRC Generic Letter 90-05. The flaws in welds that cannot be characterized by RT or UT examination, i.e., socket welds and inaccessible butt welds, will be evaluated by the same analysis by i j assuming a 3/4" hole for.each point ofleakage within a weld with through-wall leakage. Socket welds
- will be analyzed by treating the cross section at the socket weld as equivalent pipe cross section. I 1
j IV AUGMENTED INSPECTION I
} An augmented inspection program will monitor a sample of ten (10) butt welds in the Service Water ;
l- System using RT or UT examination methods. RT or UT examination methods will be performed every I j three (3) months. The frequency of radiography will be assessed after a year and may be adjusted for
, each location based on the results of the radiographs.
l l V. ALTERNATE PROVISIONS I a \
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[ As an alternative to performing Code repairs in accordance with IWA-5250(a)(2) to through-wall flaws <
- in the Service Water System the through-wall flaws will be left as is. The through-wall flaws will be j monitored for leakage and must meet the criteria for flooding and spraying consequences. Stmetural a integrity must be determined as described herein to remain in service beyond 14 days from detection. If
- structural integrity is determined, operation in this mode will cor.tinue until the subject welds are f
replaced. All welds identified with through-wall flaws will be replaced within 18 months from the time ofdiscovery.
, The structural integrity of the Service Water System will be monitored by the following methods until
[ the repairs required by IWA 5250(a)(2) are completed.
I-Weekly visual monitoring of through-wall flaws from the time of identification until repair or completion' of structural ' integrity analysis. If the welds are determined to be structurally acceptable then the visual monitoring frequency will be decreased to once every six weeks.
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l All welde identified as having through-wall flaws and not repaired within 14 days of detection, will be asossed for stmetural integrity within 14 days of detection. Butt welds will be examined by RT or UT methods, if accessible, to characterize the flaws. Socket welds and butt welds inacassible for RT or UT examinations will be assessed for structural integrity by assuming a cor servative %" diameter hcle. Welds determined to be stmeturally adequate will be included in the above monitoring program. Identification of a structurally inadequate weld will result in the assodated piping to be declared inoperable and the appropriate Teanical Specification action statement to be taken.
. Weekly visual monitoring of through-wall flaws in socket welds and butt welds inaccessible to RT or UT examination for a period of two (2) months. If there is no significant change in the leakage rate, the monitoring frequency will be decreased to once every six weeks until the welds are repaired. A significant change is defined as a 0.5 gpm increase in the leakage rate from the initial l
observed leakage condition for each weld. Should any location reach the threshold of a significant change, the weld will be reassessed for structural integrity and flood / spraying consequences j
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A walkdown of the accessible stainless steel portions of the Service Water System will be ;
performed every six weeks. This inspection frequency is based on a 12 week Maintenance Rule schedule, which reduces the time equipment is out of service for testing and maintenance. Two one week windows, six weeks apart, are available within this schedule to perform service water repairs.
Performing inspections within this schedule will allow repairs to be made in a timely manner and reduce the time safety related equipment is out of service. The frequency of the walkdowns will be j assessed after a year and adjusted based on the results of the inspections. ;
A total leakage rate limit of 1.0 gpm for a single supply or retum line for an individual component will be established. If this total leakage rate limit is exceeded then an evaluation will be performed l to determine if design service water flow is available to affected components. Inadequate service i water supply will cause the associated service water lines and equipment to be declared inoperable and appropriate action will be taken according to Technical Specifications.
- An augmented inspection program will monitor a sample of ten (10) butt welds in the Sersice I Water System using RT or UT examination methods. Examinations will be performed every three
- (3) months. The frequency of radiography will be assessed after a year and may be adjusted for each location based on the results of the radiographs
L The proposed alternative stated above will ensure that the overall level ofplant quality and safety will not be compromised.
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VI IMPLEMENTATION SCHEDULE This alternative to Code requirements will be followed upon receiving NRC approval for the remainder of the second ten-year inspection intervals. The Unit I second ten-year inspection interval will end on April 30,1999 and will be extended, as allowed by Code Case N-535, to April 30,2000 to coincide with a plant outage. The Unit 2 second ten-year interval will end on December.14, 2000 and will be extended, as allowed by Code Case N-535, to April 30,2001 to coincide with a plant outage. The NRC in a letter dated May 29,1998 approved code Case N-535, for both units.
Attachments:
- 1. Flaw Evaluation Methods and Results ,
- 2. Drawing /Line Number Designations l
References:
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- 1. USAS B31.1 Power Piping 1967 Edition
- 2. EPRI Report NP-6301-D, " Ductile Fracture Handbook"
- 3. Nuclear Regulatory Commission Generic Letter 90-05 " Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,2, and 3 Piping" i Page 7 of 7
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l Attachment 1 ReliefRequest NDE-32, Revision 4 Flaw Evaluation Methods and Results l Introduct i on l
Butt welds identified as having possible through-wall leaks will be volumetrically examined by radiographic (RT) or ultrasonic (UT) methods, if accessible. Flaws in butt welds that are inaccessible for examination will be postulated as a 3/4" hole for each area identified with a j through-wall flaw. All butt welds will be analyzed for structural integrity by three methods, l~
area reinforcement, limit load analysis, and linear elastic fracture mechanics evaluation.
Flaw size in socket welds identified as having possible through-wall leaks cannot be i characterized by nondestructive examination. ' A conservatively large hole, 3/4", will be l
- postulated for each area identified with a through-wall flaw. The postulated flaw will be
' analyzed for stmetural integrity by treating the cross section as equivalent to the cross section of the attached pipe.
Area Reinforcement Analysis l
The area reinforcement analysis is used to determine if adequate reinforcing exists such that ductile tearing would not occur. The guidelines of ANSI B31.1 paragraph 104.3.(d) 2 (reference 1) are used to determine the Code required reinforcing area. The actual reinforcing area is calculated and is checked against the required reinforcement area, i
j The Code required reinforcement area in square inches is defined as:
i 1.07(tm)(d1)
Where tm is the code minimum wall, and di is the outside diameter l The Code reinforcement area required is provided by the available material around the flaw in the reinforcing zone.
Limit Load Analysis The stmetural integrity of the piping in the degraded condition will be established by calculating the minimum margin of safety based upon a Limit Load Analysis. These methods are documented in EPRI report NP-6301-D (Ductile Fracture Handbook)
(reference 2).
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The limit load analysis of the postulated flawed sections will be performed with a material flow stress representing the midpoint of the ultimate strength and yield point stress. The flawed sections will be subjected to deadweight, thermal, and seismic DBE loading.
The allowablelimit load is given by,
'l Ma = 2 sf Rm2 t-(2cos(b)-sin (Q)) in-lbf l sf = flow stress = 0.5 (Sy + Su) psi l . Sy = yield stress psi
! Su = ultimate stress psi l Rm = mean radius of the pipe p=6 TI*(R!e + P)+F 2 4
- ayeR.et L Ri = internal radius of the pipe P = pressure psig l
F = axialload in Ibs t = pipe thickness = inches D = Outside diameter inches 0 = half angle of the crack (radians) = crack length 2Rm MR = Resultant Moment -
l MY = Bending Moment MZ = Bending Moment T = Torsion The calculated factor ofsafety is, !
FS = Ma (MR)
The minimum factor of safety of 1.4 is required to be qualified for continued operation.
L Fracture Mechanics Evaluation
. A linear elastic fracture mechanics analysis will be performed for circumferential through-wall crack using the ~ guidance provided in NRC Generic Letter 90-05. The structural integrity of the piping in the degraded condition was established by calculating the minimum margin ofsafety based upon a Fracture Mechanics evaluation. This method is documented in EPRI report NP-6301-D (Ductile Fracture Handbook) (reference 2).
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i l A through-wall circumferential crack will be postulated for every area containing MIC.
l - The cracks will be subjected to a design pressure loading in addition to the deadweight, normal operating thermal and seismic DBE loadings, For the purpose of this evaluation a generic allowable stress intensity factor of KIC = 135 ksi (in.)" will be used for the stainless steel material per NRC GL 90-05.
The applied stress intensity factor for bending, KIB, is found by:
KIB = [sb-(p Rm-Q)0.5] Fb
' The applied stress intensity factor for internal pressure, KIP, is found by:
KIP = sm-(p RnrQ)0.5 Fm The applied stress intensity factor for axial tension, KIT is found by:
KIT = st-(p Rm-Q)0.5 Ft The stress intensity factor for residual stresses, KIR is found by:
KIR = S-(p Rm-Q)0.5 Ft Total applied stress intensity KT includes a 1.4 safety factor and is calculated by:
KT = 1.4-(KIB + KIP + KIT) + KIR The allowable stress intensity factor is taken from Generic Letter 90-05.
KALL = 135 ksiGin Stress Intensity Factor Ratio is defined as:
SR = KT KALL The stress intensity factor ratio shall be less than 1.0 for continued operation.
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l ATTACHMENT 2 l ReliefRequest NDE-32 Revision 4 l List of drawings containing the Service Water System and the associated line number designations for
! pipe class 153A and 163.
l DRAWING 11715-CBB-040D-2, SHEET 1 i
t 1-1/4"-WS-G37-153 A-Q3 4"-WS-G01-163-Q3 l 3/4"-WS-F83-163 4"-WS-F99-163-Q3 l l 3/4"-WS-F82-163-Q3 l l DRAWING 11715-CBB-040D-2, SHEET 2 I
l-1/4"-WS-H78-153 A-Q3 1-1/4"-WF-H81-153 A-Q3 DRAWING 11715-CBM-078A-2, SHEET 1 3/4"-WS-G31-163-Q3 3/4"-WS-F67-163-Q3 3/4"-WS-H77-163-Q3 4"-WS-F64-163-Q3 4"-WS-H76-163-Q3 3/4"-WS-F80-163-Q3 1 3/4"-WS-G30-163-Q3 3/4"-WS-F68-163-Q3 3/4"-WS-339 _163-Q3 4"-WS-F65-163-Q3 u 3/4"-WS-G36-163-Q3 3/4"-WS-F69-163-Q3 3/4"-WS-930-163-Q3 8"-WS- 93-163-Q3 1/2"-WS-F61-163-Q3 8"-WS- 94-163-Q3 2"-WS-D72-163-Q3 4"-WS-F62-163-Q3 3/4"-WS-F78-163-Q3 3/4"-WS-F66-163-Q3 4"-WS-F63-163-Q3 3/4"-WS-F79-163-Q3 4"-WS-G35-163 Q3 %"-WS-F81-163-Q3 l DRAWING 11715-CBM-078A-2, SHEET 4 8"-WS-515-163-Q3 8"-WS-516-163-Q3 8"-WS-513-163-Q3 8"-WS-514-163-Q3 4"-WS-H48-163-Q3 3/4"-WS-F64-163-Q3 3/4"-WS-H52-163-Q3 3/4"-WS-H53-163-Q3 4"-WS-H50-163-Q3 3/4"-WS-H66-163-Q3 3/4"-WS-H54-163-Q3 4"-WS-H51-163-Q3 3/4"-WS-H67-163-Q3 3/4"-WS-H55-163-Q3 3/4"-WS-G32-163-Q3 3/4"-WS-G33-163-Q3 8"-WS-115-163-Q3 8"-WS-116-163-Q3 8"-WS-113-163-Q3 4"-WS- 46-163-Q3 .
l 4"-WS- 47-163-Q3 2"-WS-926-163-Q3 l
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DRAWING 11715-CBM-078A-2, SHEET 4, (Continued) i 3/4"-WS-H60-163-Q3 3/4"-WS-H61-163-Q3 3/4"-WS-H62-163-Q3 3/4"-WS-H63-163-Q3 4"-WS- 56-163-Q3 4"-WS- 57-163-Q3 4"-WS.H49-163-Q3 %"-WS-H65-163-Q3 l 8"-WS-114-163-Q3 DRAWING 11715-CBM-078B-2, SHEET 1 1-1/2"-WS-346-163-Q3 1"-WS-347-163-Q3 1"-WS-G06-163 Q3 1-1/2"-WS-347-163-Q3 1-1/2"-WS-348-163-Q3 1"-WS-349-163-Q3 1"-WS-G05-163-Q3 1-1/2"-WS-349-163-Q3 1-1/2"-WS-350-163-Q3 1"-WS-351-163-Q3 1"-WS-G04-163-Q3 1-1/2"-WS-351-163-Q3 1-1/2"-WS-352-163-Q3 1"-WS-353-163-Q3 1"-WS-G03-163-Q3 1-1/2"-WS-353-163-Q3 l
DRAWING 11715-CBM-078B-2, SHEET 3 1-1/2"-WS-724-163-Q3 1"-WS-725-163-Q3 1"-WS-933-163-Q3 1-1/2"-WS-725-163-Q3 1-1/2"-WS-726-163-Q3 1"-WS-727-163-Q3 1"-WS-934-163-Q3 1-1/2"-WS-728-163-Q3 1"-WS-729-163-Q3 1"-WS-935-163-Q3 1-1/2"-WS-729-163-Q3 1-1/2"-WS-730-163-Q3 1"-WS-731-163-Q3 1"-WS-936-163-Q3 1-1/2"-WS-731-163-Q3 1-1/2"-WS-727-163-Q3 l
DRAWING 11715-CBM-078C-2, SHEET 2 4"-WS- 46-163-Q3 1"-WS- 85-163-Q3 3/4"-WS A47-163-Q3 1"-WS-485-163-Q3 1"-WS- 81-163-Q3 1"-WS-487-163-Q3 1"-WS- 77-163-Q3 1"-WS-489-163-Q3 1"-WS-477-163-Q3 1"-WS-491-163-Q3 1"-WS-481-163-Q3 3"-WS- 75-163-Q3 3"-WS- 73-163-Q3 3"-WS 76-163-Q3 4"-WS- 47-163-Q3 3/4"-WS- 79-163-Q3 3/4"-WS-A49-163-Q3 3/4"-WS-381-163-Q3 1"-WS- 82-163-Q3 2"-WS- 80-163-Q3 1"-WS- 78-163-Q3 3/4"-WS- 83-163-Q3 l 1"-WS-478-163-Q3 3/8"-WS-383-163-Q3 Page 2 of 5
1 11715-CBM-078C-2, SHEET 2 (Cont'd) r l- 1"-WS-482-163-Q3 3/8"-WS-382-163-Q3
) 3"-WS- 74-163-Q3 2"-WS-376-163-Q3 ,
4"-WS- 56-163-Q3 3/8"-WS-397-163-Q3 I l
3/4"-WS-A48-163-Q3 3/8"-WS-398-163-Q3 1"-WS- 90-163-Q3 2"-WS-377-163-Q3 ;
l 3/4"-WS-C06-163-Q3 3/8"-WS-C01-163-Q3 l
l'.'-WS- 92-163-Q3 3/8"-WS-399-163-Q3 ;
1"-WS- 86-163-Q3 3/4"-WS-378-163-Q3 '
3/4"-WS-C01-163-Q3 2"-WS- 84-163-Q3 1"-WS-488-163-Q3 3/4"-WS-379-163-Q3 1 3/4"-WS-913 163-Q3 1"-WS- 88-163-Q3 1"-WS-490-163-Q3 3/4"-WS-380-163-Q3 i 1"-WS- 78-163-Q3 3/4"-WS 83-163-Q3 1"-WS-492-163-Q3 3/8"-WS-383-163-Q3 4"-WS- 57-163-Q3 3/4"-WS-A50-163-Q3 3/4"-WS-773-163-Q3 1"-WS- 89-163-Q3 2"-WS-772-163-Q3 3/4"-WS-400-163-Q3 3/8"-WS-910-163-Q3 3/4"-WS-774-163-Q3 3/8"-WS-914 163-Q3 2"-WS-775-163-Q3 2"-WS-776-163-Q3 3/8"-WS-913-163-Q3 3/8"-WS-916-163-Q3 3/8"-WS-915-163-Q3 2"-WS 777-163-Q3 3/4"-WS-779-163-Q3 1"-WS-486-163-Q3 3/4"-WS-909-163-Q3 3/8"-WS-912-163-Q3 DRAWING 11715-CBM-078G-2, SHEET 1 2"-WS-D46-153A-Q3 2"-WS-C88-153 A-Q3 1"-WS-D50-153 A-Q3 2"-WS-C81-153 A-Q3 l 3/4"-WS-D39-153 A-Q3 2"-WS-C87-153 A-Q3 1"-WS-D30-153 A-Q3 2"-WS- 63-163-Q3 3/4"-WS-D41-153 A-Q3 3/4"-WS-D61-163-Q3 3/4"-WS-D55-163-Q3 2"-WS- 62-163-Q3 1"-WS-D31-153 A-Q3 2"-WS-C80-153 A-Q3 3/4"-WS-D43-153A-Q3 3/4"-WS-C67-153A-Q3 3"-WS- 73-163-Q3 3/4"-WS-C73-153 A-Q3 2"-WS- 54-163-Q3 3/4"-WS-C76-153A-Q3 2"-WS- 52-163-Q3 3/4"-WS-C70-153 A-Q3 3/4"-WS-D67-163-Q3 2"-WS-C86-153 A-Q3 2"-WS- 50-163-Q3 2"-WS- 79-153 A-Q3 3"-WS. 74-163-Q3 2"-WS-C85-153 A-Q3 f- Page 3 of 5 l'
I1715-CBM-078G-2, SHEET 1 (Continued) 2"-WS- 55 163-Q3 3/4"-WS-D62-163-Q3 3/4"-WS-D54-163-Q3 - 2"-WS- 60-163-Q3 2"-WS 53-163-Q3 3"-WS- 75-163-Q3 3/4"-WS-D68-163-Q3 3/4"-WS-D69-163-Q3 ,
2"-WS- 51-163-Q3 2"-WS- 61-163-Q3 )
3/4"-WS-D56-163-Q3 3/4"-WS-D70-163-Q3 2"-WS-C83-153 A-Q3 3"-WS- 76-163-Q3 2"-WS-C89-153A-Q3 2"-WS-C78-153A-Q3 3/4"-WS-D60-163-Q3 3/4"-WS-C66-153A-Q3 2"-WS- 64-163-Q3 3/4"-WS-C72-153A-Q3 l 2"-WS- 65-163-Q3 3/4"-WS-C75-153A-Q3 2"-WS-C82-153A-Q3 3/4"-WS-C69-153A-Q3 l 3/4"-WS-C68-153A-Q3 2"-WS-C84-153A-Q3 l 3/4"-WS-C74-153A-Q3 3/4"-WS-C77-153A-Q3 -
l 3/4"-WS-C71-153A-Q3 l
DRAWING 11715-CBM-078G-2, SHEET 2 l 2"-WS-D46-153 A-Q3 3/4"-WS-D65-163-Q3
. 3/4"-WS-D71-153A-Q3 3/4"-WS-D66-163-Q3 1"-WS-D47-153A-Q3 3/4"-WS-934-153A-Q3 3/4"-WS-D33-153 A-Q3 2"-WS-948-153 A-Q3 J
3/4"-WS-D51-163-Q3 3/4"-WS-940-153 A-Q3 1"-WS-D48-153A-Q3 1-1/2"-WS-976-153 A-Q3 3/4"-WS-D35-153A-Q3 1-1/2"-WS-982-153 A-Q3 3/4"-WS D52-163-Q3 3/4"-WS-943-153 A-Q3 1"-WS-D49-153 A-Q3 - 3/4"-WS-937-153A-Q3 3/4"-WS-D37-153A-Q3 2"-WS-954-153A-Q3 3/4"-WS-D53-163-Q3 2"-WS-947-153 A-Q3 3"-WS- 73-163-Q3 1-1/2"-WS-977-153 A-Q3 3/4"-WS-D63-163-Q3 1-1/2"-WS-963-153 A-Q3 3"-WS- 74-163-Q3 2"-WS-953-153A-Q3 2"-WS-454-163-Q3 3/4"-WS-D58-163-Q3 2"-WS-455-163-Q3 2"-WS-462-163-Q3 2"-WS-452-163-Q3 2"-WS-463-163-Q3 l 2"-WS-453-163-Q3 2"-WS-946-153 A-Q3 2"-WS-450-163-Q3 1-1/2"-WS-979-153 A-Q3 2"-WS-451-163-Q3 1-1/2"-WS-978-153 A-Q3 2"-WS-949-153 A-Q3 2"-WS-952-153 A-Q3 1-1/2"-WS-981-153A-Q3 2"-WS-945-153A-Q3 i- 1-1/2"-WS-965 153 A-Q3 1-1/2"-WS-980-153A-Q3 2"-WS-955-153 A-Q3 1-1/2"-WS-961-153 A-Q3 Page 4 of 5
1 DRAWING 11715-CBM-078G-2, SHEET 2 (Continued) l -
3/4"-WS-D57-163-Q3 2"-WS-460-163-Q3 2"-WS-464-163-Q3 2"-WS-945-153 A-Q3 2"-WS-465-163-Q3 2"-WS-944-153A-Q3 ,
3"-WS- 75-163-Q3 1-1/2"-WS-975-153A-Q3 ;
3"-WS- 76-163-Q3 1-1/2"-WS-971-153 A-Q3 3/4"-WS-D59-163 Q3 2"-WS-950-153A-Q3 '
2".WS-461-163-Q3 2"-WS-951-153A-Q3 1 DRAWING 11715-CBM-078H-2, SHEET 1 1"-WS- 9-163 1"-WS- 10-163 3/4"-WS E03-163 3/4"-WS-F45-163 i 3/4"-WS-F44-163 2"-WS-E64-163 1"-WS-G07-163 1/2"-WS-E68-163 3/4"-WS-E08-163 1"-WS-D97-163 1"-WS-947-163 2"-WS-D91-163 l 1"-WS-G50-163 1"-WS-H48-163 i 1"-WS-G52-163 l
l l
L Page 5 of 5
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Attachment 2 Ultrasonic Examination Technique for Detection of MIC in Stainless Steel Service Water Piping Virginia Electric and Power Company North Anna Power Station
. g.
1 December 29,1997 l I
1 Ultrasonic Examination Technique for Detection of Microbilogically Induced Corrosion in North Anna Stainless Steel Service Water Piping ,
l Prepared By: David R. Dodson Mati's/ISI Engineering Reviewed: M, j TAI 4APS ISl/NDE i
Reviewed: .
Matl'sAngineering i
i.
Reviewed: [/) ~
I,u Supv. Matl's/ISI Engineering V
o' Q y$ s ~ --
v.
en i
Table of Contents S;ction Topic Page ,
l 1.0 Introduction 1 2.0 Program Overview 2 l
3.0 Destructive Examination Results 6 4.0 Comparison of Destructive and 16
! Nondestructive Examination Results l 5.0 Analysis of Examination Results 26 6.0 Conclusions and Recommendations 30 1
1 1
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1.0 Intr duction l
North Anna has been monitoring stainless steel Piping in the service water system for Microbiological l . Induced Corrosion (MIC) since October,1996. To date, monitoring has been accomplished by way of walkdowns looking for visual evidence of leaking components followed by radiography for detection
- and length sizing of MIC indications. Although radiography is believed to be an effective examination m thod, it is not an efficient way to conduct an initial evaluation of MIC. The necessity for radiation l cxposure controls and the inherent slowness of the examination method limits the utility of l radiography for inservice examinations.
l In late 1996, a Service Water Task Team was formed to evaluate the problems associated with MIC in small bore service water piping. In March,1997 the Service Water Task Team issued a report containing short and long term recommendations for management review. Among the long term recommendations made was a suggestion to investigate the use of Ultrasonic testing _(UT) and other l nondestructive examination (NDE) techniques for detection of MIC and to improve our ability to size (estimate the depth) MIC indications. It was felt that an effective UT technique for detection of MIC would allow inservice volumetr;c examination of service water components less intrusively and on a larger scale than with radiography thus improving the effectiveness of our MIC program.
Pursuant to the preceding recommendation, a study was initiated in September 1997 to investigate ths pctential of using UT for detection and sizing of MIC indications in stainless steel service water piping welds. Sections of replaced stainless steel service water piping which had been radiographed wsre obtained for development of a UT technique. Separate sections of piping were selected for examination by UT and these welds were destructively examined.
The results of the study led to the following conclusions:
- 1. The UT technique developed under this program is as effective as RT for detection of MIC but will result in overcalls in some cases. The number of overcalls expected is not significant
- 2. The UT length sizing technique developed under this program is as effective as RT for length sizing of MIC indications when considering the totallength of flawed weld.
- 3. The UT depth sizing technique developed under this program is capable of measuring the depth of MIC indications within 0.60' or about 18% of the average weld thickness.
' It is believed that sizing performance can be improved to about .040" if sizing is limited to indications located on the accessible side when performing sizing on single access
- welds.
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4 l S0 Program Ov rview l
. Objectives 1
l 1. Develop a UT technique for detection and sizing of MIC indications. I 2
- 2. Verify the results of the UT technique by destructive examination.
i - 3. Verify the effectiveness of the UT technique in comparison to radiography Sv relating the results obtained on the same weld samples.
! Sample Selection ,
1
- i. MlC ahack has been experienced in 2",3" and 4" stainless steel service water piping welds at North
! Anna. The 2" service water welds are socket welded and therefore are not suitable for UT. There
. w re no 3" diameter piping available when samples were being selected for this program, however, j UT technique parameters were developed for 3" piping using Virginia Power's Appendix Vill piping i specimens. The majority of the butt welded joints that have been confirmed to contain MIC at North j Anna are on 4" diameter lines.
i l
- j. To the extent practical, the sample set was selected to meet the fabrication conditions specified by
. Appendix Vlli of ASME Section XI for austenitic piping welds. The sample set consisted of ten welds l
~
which were selected from three different service water lines. In order that a blind UT test could be performed on the welds, a separate set of welds was used to develop the UT technique. The sample l I sit included welds with wide weld crowns and welds with pipe fittings that permitted only single side )
- cccess for UT. All welds in the sample set were as-welded which prevented the UT transducer from i - being scanned over the weld. The welds contained areas of root convexity, root concavity, and l various welding defsets. All welds in the sample set were made from 4" diameter standard wall stainless steel piping. Weld metal thickness measurements were made on the specimen set during dsstructive examination which showed the thickness over the sample set to range from .285" to i .375". Five of the ten specimens selected for this program (FW-19W, FW-13, FW-16, FW-61 and FW-
- 64) showed evidence of leakage in the field.
l The weld numbers that were selected for the specimen set are listed on Table 1:
i i Table 1 Drawing Line Number Weld Number WS-16D 4"-WS-57-163-Q3 W-19W WS-16E 4"-WS-57-163-Q3 W 1W WS-19F 4*-WS-46-163-03 FW-94 WS-2D87A 4*-WS-F63-163-03 FW-13 WS-2D87A 4"-WS-F63-163-Q3 FW-14 ki-2D87A 4"-WS-F63-163-03 FW-16 WS-2D87B 4*-WS-F63-163-Q3 FW-61 WS-2D87B 4*-WS-F63-163-03 FW-63 WS-2D87B 4*-WS-F63-163-03 FW-64 WS-2D878 4"-WS-F63-163-Q3 FW-78 L
2 w.m.--- . , ~ - , , - --- , _ , - -y
Rrdiography Eight of the above specimens were radiographed in the field and one additional specimen was radiographed after replacement. A double-wall single viewing radiographic technique was used. FW-14 above was not radiographed.
UT Technique l The morphtalogy of MIC within a weld often presents a challe...ge for detection and sizing when using standard angs beam ultrasonic techniques. MIC often exists within a weld as a group of elongated voids which may enter the ID surface adjacent to the weld root and meander along or through the weld exiting the OD surface at an entirely different location. MIC also tends to occur in clusters which
- results in a network of randomly orientated " worm holes" within a weld. This n7rphology does not
- present an optimum reflecting surface when using standard angle beam techniques. It was felt that a j UT technique that insonified a large percentage of the weld volume would be needed to reliably detect MIC.
Tae UT technique that was developed consists of two examinations. The first examination utilized a 2 Min dua! elen.ent ADEPT tandem (ADEPT-60) search unit. The elements of the search unit are moulted front-to-back with a short sound exit point which allows a closer approach to the weld toe.
l The search unit intrcduces two sound modes (L-Wave and shear) into the specimen. The dual sound modes interrogate both the ID surface and volume of the weld being examined. On very thin material, i such as the specimens in this program, the search unit essentially insonifies the entire volume of the material being inspected. The L-Wave component of the sound beam easily penetrates austenitic weld material resulting in a relatively high sensitivity to MIC. TL ADEPT-60 is used for detection and langth sizing of MIC indications. The second examination utilized a small diameter 45 degree shear wave search unit. The 45 degree shear wave examination is used to further interrogate the
- indications detected with the ADEPT-60 in order to discriminate inherent welding defects, such as
! incomplete fusion, from MIC indications and for through-wall sizing.
Following development of the UT technique, blind examinations (without access to radiographic or 4
other information) were performed on the ten specimens in this program. Radiographic results were reviewed before the specimens were destructively examined.
Destructive Examination J
Following UT examination, the ten specimens were destructively examined. it was first planned to s:ction the specimens into quadrants and remove cross-sectional slices of material by grinding small increments of material, however, this process proved too time consum5g. Only one of the specimens (FW-14) was processed in this manner. FW-14 was chosen as the first specimen to destructively examine because the UT examination revealed no indications in the specimen and it had not been radiographed. This specimen was not dissected completely across, however, it was examined to the extent necessary to determine that there was no evidence of MIC or other indications of significance in the weld.
3
i Tho 9 remaining specimens were fashioned into coupons by cutting through tha base metal perpendicular to the axis of the pipe on each side of the weld. The coupons were then ir,serted into a
- l. lathe and cut in .020" increments perpendicular to the axis of the coupon. Observations were made j after each cut and the results were documented after every three cuts (.060"). The results for each j " Group" of three cuts was labeled on the documentation with the letter "G" followed by a sequential j number (1,2,3 etc.) that relates to the prcgression of cuts through the coupon.
4 The method of processing the final 9 specimens tended to slightly smear the metal on the machined l'
surface of the coupon. The resulting smeared metal resulted in a potential to obscure very tight weld imperfections such as incomplete fusion and shallow conditions at the weld root. However, MIC was
- the primary 'o'm of the destructive examination and it is believed that this method of processing
! effectively re
- w all e' ;ence of MIC that was of any significance.
J A photo of FW-94 mounted in the lathe is shown on Figure 1. The photo clearly shows nodules on the ID of the pipe which are characteristic of MIC attack. Figure 2 shows a close up of a void in the base metal of FW-94 caused by MIC attack. The same void is also visible at approximately 1 o' clock
- on Figure 1.
Figure 1 (FW-94 Mounted in Lathe) l 4 .
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i Figuro 2 (Close Up of MIC Void in FW-94) l l
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3.0 De:tructiva Examin tien Recults l
In order to better show the destructive examination results, cross-sectional sketches were made which graphically depicted the locations of the indications observed. A cross-section view was drawn which represents the results for each group of cuts (i.e., each 0.060" section). Each view shows the circumference of the coupon laid out flat. The views for each group of cuts (G1,G2, G3, etc.) are cligned under one another on the same page to relate the coordinates of each subsequent group to tha preceding group. These views allow one to visualize the progressive circumferential and through-wnli distribution of MIC along the axis of the coupon. A composite cross-section view representing ths cumulative results of all the cuts made on the coupon was developed to serve as the basis for comparing the destructive results to the NDE results.
l The destructive results revealed evidence of MIC as well as other indications such as porosity and !
i wrld inclusions. It is often difficult to differentiate MIC from other indications by visual examination !
j clone, however, it is easy to determine if an indication progresses toward the ID surface by l comparing views from successive cuts. Since MIC always originates at the ID surface, indications which clearly do not progress toward the ID during subsequent cuts are assumed not to be MIC Figures 3 through 11 depict the results of the destructive examinations for all the specin ens listed '
on Table '1 with the exception of FW-14. The results for FW-14 are not shown because no indications of significance were observed in this weld during the destructive examination.
Figures 3 through 11 reveals the following regarding the nature of MIC in the NAPS stainless steel Savice Water piping: j
. 1. in Type 316L SS Welds, MIC appears to be primarily restricted to the weld and the portion of the heat affected zone which is immediately adjacent to the weld. Only One coupon l (FW-94) contained MIC which was located in the base metal outside of the weld.
- 2. MIC appears to form in clusters which should improve the probability of de:ection by i UT. When several clusters exist they tend to be randomly distributed around the weld
! circumference.
- 3. Very deep MIC indications appear to occupy a substantial volume of space uithin the weld which should improve the probability of detecting them with UT.
i 1
6
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O' 14 600' CWGil 00FTowRemoved of# __
O' 14SXP Cd412 020'TotdRemoved1F 7 14 600' 4
12