RA-11-087, Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-789, Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate Energy Carbon Steel Piping for Raw Water Service, Section XI, Divisi
| ML113180232 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Peach Bottom, Oyster Creek, Byron, Braidwood, Limerick, Clinton, Quad Cities, LaSalle, Crane (DPR-016, DPR-019, DPR-025, DPR-029, DPR-030, DPR-044, DPR-050, DPR-056, NPF-011, NPF-018, NPF-037, NPF-039, NPF-062, NPF-066, NPF-072, NPF-077, NPF-085) |
| Issue date: | 11/10/2011 |
| From: | Jesse M Exelon Generation Co, Exelon Nuclear |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-11-087, RS-11-182, TAC ME7303, TAC ME7304, TAC ME7305, TAC ME7306, TAC ME7307, TAC ME7308, TAC ME7309, TAC ME7310, TAC ME7311, TAC ME7312, TAC ME7313, TAC ME7314, TAC ME7315, TAC ME7316, TAC ME7317, TAC ME7318, TAC ME7319, TMI-11-160 | |
| Download: ML113180232 (14) | |
Text
10 CFR 50.55a RS-11-182 RA-11-087 TMI-11-160 November 10, 2011 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249 LaSalle County Station, Units 1 and 2 Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374 Limerick Generating Station, Units 1 and 2 Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353 Oyster Creek Nuclear Generating Station Renewed Facility Operating License No. DPR-16 NRC Docket No. 50-219 Peach Bottom Atomic Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-44 and DPR-56 NRC Docket Nos. 50-277 and 50-278
Proposed Alternative to Utilize Code Case N-789 November 10, 2011 Page 2 Quad Cities Nuclear Power Station, Units 1 and 2 Renewed Facility Operating License Nos. DPR-29 and DPR-30 NRC Docket Nos. 50-254 and 50-265 Three Mile Island Nuclear Generating Station, Unit 1 Renewed Facility Operating License No. DPR-50 NRC Docket No. 50-289
Subject:
Response to Request for Additional Information - Proposed Alternative to Utilize Code Case N-789, "Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1"
References:
1)
Letter from M. D. Jesse (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "Proposed Alternative to Utilize Code Case N-789,
'Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1,' "
dated October 7,2011 2)
E-mail from J. Wiebe (U.S. Nuclear Regulatory Commission) to T. R. Loomis (Exelon Generation Company, LLC), "Exelon Fleet - Non-acceptance with Opportunity to Supplement (Modified) RE: Proposed Alternative to Utilize Code Case N-789 (TAC Nos. ME7303 - ME7319)," dated November 1, 2011 In the Reference 1 letter, Exelon Generation Company, LLC (Exelon) submitted in accordance with 10 CFR 50.55a(a)(3)(i), a proposed alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to use Code Case N-789 for Class 2 and 3 moderate-energy raw water piping system repairs resulting from degradation mechanisms such as erosion, corrosion, cavitation, or pitting. In the Reference 2 letter, the U.S. Nuclear Regulatory Commission requested additional information. Attachment 1 is our response.
There are no regulatory commitments contained in this letter.
If you have any questions, please contact Tom Loomis (610) 765-5510.
Respectfully, Michael D. Jesse Director - Licensingpnd R ulatory Affairs Exelon Generation*
pany, LLC Attachments: 1) Response to Request for Additional Information
- 2) Revised Proposed Alternative to Utilize Code Case N-789
Proposed Alternative to Utilize Code N*789 November 10, 2011 Page 3 cc:
Regional Administrator* NRC Region I Regional Administrator* NRC Region III NRC Senior Resident Inspector* Braidwood Station NRC Senior Resident Inspector* Byron Station NRC Senior Resident Inspector - Clinton Power Station NRC Senior Resident Inspector* Dresden Nuclear Power Station NRC Senior Resident Inspector - LaSalle County Station NRC Senior Resident Inspector - Limerick Generating Station NRC Senior Resident Inspector* Oyster Creek Nuclear Generating Station NRC Senior Resident Inspector* Peach Bottom Atomic Power Station NRC Senior Resident Inspector - Quad Cities Nuclear Power Station NRC Senior Resident Inspector - Three Mile Island Nuclear Generating Station, Unit 1 NRC Project Manager - Braidwood and Byron Stations NRC Project Manager - Clinton Power Station NRC Project Manager* Dresden Nuclear Power Station NRC Project Manager - LaSalle County Station NRC Project Manager - Limerick Generating Station NRC Project Manager* Oyster Creek Nuclear Generating Station NRC Project Manager - Peach Bottom Atomic Power Station NRC Project Manager - Quad Cities Nuclear Power Station NRC Project Manager - Three Mile Island Nuclear Generating Station, Unit 1 Response to Request for Additional Information
Response to Request for Additional Information Proposed Alternative to Use Code Case N-789 Page 1 of 1 Question:
1.
Include in the relief request Code Case N-789. This code case has not been approved by the NRC; therefore, all the wording in Code Case N-789 must be included as part of the submittal.
Response
The relief request has been revised to include a copy of Code Case N-789. See Attachment 2.
Question:
2.
Clarify that the "raw water piping systems" referred to in the ASME Code Component(s)
Affected section in the relief request is applicable to those plants that use other nomenclatures such as "service water system" and "emergency service water systems".
Response
Section 1.0 ("ASME Code Component(s) Affected") of the relief request has been revised to include the definition of raw water as provided in the code case.
Additionally, the specific operating conditions for the raw water piping have been added to Section 1.0. See Attachment 2.
We note that as an additional change to this relief request, the relief has been expanded to include the Oyster Creek Nuclear Generating Station fifth Inservice Inspection (lSI) interval.
Revised Proposed Alternative to Utilize Code Case N-789
Attachment Proposed Alternative to Utilize Code Case N*789 Page 1 of 3 1.
ASME Code Component's) Affected:
All ASME Class 2 and 3 moderate energy carbon steel raw water piping systems. Raw water is defined as water such as from a river, lake, or well or brackish/salt water* used in plant equipment, area coolers, and heat exchangers. In many plants it is referred to as "Service Water." This Code Case applies to Class 2 and 3 moderate energy (Le., less than or equal to 200"F (93"C) and less than or equal to 275 psig (1.9 MPa) maximum operating conditions) carbon steel raw water piping.
===2.
Applicable Code Edition and Addenda===
PLANT INTERVAL EDITION START END Braidwood Station, Units Third 2001 Edition, through 2003 July 29, 2008 JUly 28, 2018 1 and 2 Addenda October 17, 2008 October 16, 2018 Byron Station, Units 1 and Third 2001 Edition, through 2003 January 16, 2006 July 15, 2016 2
Addenda Clinton Power Station Third 2004 Edition July 1,2010 June 30, 2020 Dresden Nuclear Power Fourth 1995 Edition, through 1996 January 20,2003 January 19, 2013 Station, Units 2 and 3 Addenda LaSalle County Stations, Third 2001 Edition, through 2003 October 1, 2007 September 30,2017 Units 1 and 2 Addenda Limerick Generating Third 2001 Edition, through 2003 February 1, 2007 January 31, 2017 Station, Units 1 and 2 Addenda Oyster Creek Nuclear Fourth 1995 Edition, through 1996 October 15, 2002 October 14, 2012 Generating Station Addenda Oyster Creek Nuclear Fifth 2007 Edition, 2008 October 15, 2012 October 14, 2022 Generating Station Addenda Peach Bottom Atomic Fourth 2001 Edition, through 2003 November 5, 2008 November 4, 2018 Power Station, Units 2 Addenda and 3 Quad Cities Nuclear Fourth 1995 Edition, through 1996 March 10, 2003 April 1, 2013 Power Station, Units 1 Addenda and 2 Three Mile Island Nuclear Fourth 2004 Edition April 20, 2011 April 19, 2022 Station, Unit 1
Attachment Proposed Alternative to Utilize Code N-789 Page 2 of 3
===3.
Applicable Code Requirement===
ASME Code,Section XI, IWA-4400 of the 1995 Edition through 1996 Addenda, 2001 Edition through 2003 Addenda, 2004 Edition, and 2007 Edition though 2008 Addenda provides requirements for welding, brazing, metal removal, and installation of repair/replacement activities.
===4.
Reason for Request===
In accordance with 10 CFR 50.55a(a)(3)(i), Exelon Generation Company, LLC (Exelon) is requesting a proposed alternative from the requirement for replacement or internal weld repair of wall thinning conditions resulting from degradation in Class 2 and 3 moderate energy carbon steel raw water piping systems in accordance with IWA-4000. Such degradation may be the result of mechanisms such as erosion, corrosion, cavitation, and pitting - but excluded are conditions involving flow-accelerated corrosion (FAC), corrosion-assisted cracking, or any other form of cracking. IWA-4000 requires repair or replacement in accordance with the Owner's Requirements and the original or later Construction Code. Other alternative repair or evaluation methods are not always practicable because of wall thinness and/or moisture issues.
The primary reason for this request is to permit installation of a technically sound temporary repair to provide adequate time for evaluation, design, material procurement, planning and scheduling of appropriate permanent repair or replacement of the defective piping, considering the impact on system availability, maintenance rule applicability, and availability of replacement materials.
===5.
Proposed Alternative and Basis for Use===
In accordance with 10 CFR 50.55a(a)(3)(i), Exelon proposes to implement the requirements of ASME Code Case N-789 ("Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1") as a temporary repair of degradation in Class 2 and 3 moderate energy raw water piping systems resulting from mechanisms such as erosion, corrosion, cavitation, or pitting, but excluding conditions involving flow-accelerated corrosion (FAC), corrosion-assisted cracking, or any other form of cracking. These types of defects are typically identified by small leaks in the piping system or by pre-emptive non-code required examinations performed to monitor the degradation mechanisms.
Code Case N-789, which is included as part of this relief request, is attached.
The alternative repair technique described in Code Case N-789 involves the application of a metal reinforcing pad welded to the exterior of the piping system, which reinforces the weakened area and restores pressure integrity. This repair technique will be utilized when it is determined that this temporary repair method is suitable for the particular defect or degradation being resolved.
The Code Case requires that the cause of the degradation be determined, and that the extent and rate of degradation in the piping be evaluated to ensure that there are no other unacceptable locations within the surrounding area that could affect the integrity of the repaired piping. The area of evaluation will be dependent on the degradation mechanism present. A
Attachment Proposed Alternative to Utilize Code Case N-789 Page 3 of 3 baseline thickness examination will be performed for a completed structural pad, attachment welds, and surrounding area, followed by monthly thickness monitoring for the first three months, with SUbsequent frequency based on the results of this monitoring, but at a minimum of quarterly. In the case of the pressure pads, in lieu of inservice monitoring, the design of pressure pads conservatively assumes 2 times the actual measured corrosion rate, or 4 times if using an estimated rate; therefore, no inservice monitoring will be performed. The repair will be considered to have a maximum service life of the time until the next refueling outage, when a permanent repair or replacement must be performed. Additional requirements for design of reinforcement pads, installation, examination, pressure testing, and inservice monitoring are provided in Code Case N-789.
Based on the above justification, the use of Code Case N-789 as a proposed alternative to the requirements of ASME Section XI will provide an acceptable level of quality and safety.
All other ASME Section XI requirements for which relief was not specifically requested and authorized by the NRC staff will remain applicable including third party review by the Authorized Nuclear Inservice Inspector.
Code Case N-789 was approved by the ASME Board on Nuclear Codes and Standards on June 25, 2011; however, it has not been incorporated into NRC Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI Division 1," and thus is not available for application at nuclear power plants without specific NRC approval. Therefore, Exelon requests use of this alternative repair technique described in the Code Case via this relief request.
===6.
Duration of Proposed Alternative===
The proposed altemative is for use of the Code Case for the remainder of each plant's ten (10) year inspection interval as specified in Section 2.
===7.
Precedents===
A similar repair relief request (RR-3-43) was approved for Indian Point Nuclear Generating Unit No.3 on February 22, 2008.
CASES Of' ASME BOIU2R AND PRESSURf2 VESSEL CODE Approval Date: June 25, 2011 Code Cases will remain available for use until annulled by the applicable Standards Committee.
CASE N-789 Case N-789 Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service Section XI, Division I InquirF As an alternative to replacement or internal weld repair in accordance with IWA-4400, what require-ments may be applied for wall reinforcement of Class 2 and 3 carbon steel raw water! piping systems that have experienced internal wall thinning from localized erosion, corrosion, and cavitation or pitting?
Reply: It is the opinion of the Committee that, in lieu of IWA-4400, areas of Class 2 and 3 moderate-energy [i.e., less than or equal to 200°F (93°C) and less than or equal to 275 psig (1.9 MPa) maximum operating conditions] carbon steel raw water piping experiencing internal wall thinning from localized erosion, corrosion, and cavitation or pitting may have the wall reinforced by applying reinforcing pads to the outside surface of the piping in accordance with the following requirements.
Excluded from these provisions are conditions involving flow-accelerated corrosion (FAC), corrosion-assisted cracking, or any other form of cracking.
GENERAL REQUIREMENTS (a) Application of the reinforcing pad shall be per-formed in accordance with a Repair/Replacement Plan sat-isfying the requirements of IWA-4l50.
(b) The design, materials, and installation shall meet the requirements ofthe Construction Code and IWA-4000, except as stated in this Case.
If the minimum required thickness of reinforcing pad necessary to satisfy the requirements of 3 is greater than the nominal thickness for the size and schedule of the piping, this Case shall not be used.
I Raw water is defined as water such as from a river. lake, or well or brackish/salt water; used in plant equipment, area coolers, and heat exchangers. In many plants it is referred to as "Service Water."
Additional reinforcement or repair is not permitted on top of an reinforcing pad.
Reinforcing pads, including those installed during a refueling outage, shall not remain in service beyond the end of the next refueling outage.
(I) This Case may only be applied to piping not required to be ultrasonically examined for inservice inspection.
2 INITIAL EVALUATION (a) The material beneath the surface to which the rein-forcing pad is to be applied and the adjacent area shall be ultrasonically measured to establish the existing wall thickness and the extent and configuration of degradation to be corrected by the reinforcing pad.
(b) The cause and rate of degradation shall be deter-mined. If the cause is determined to be flow-accelerated corrosion (FAC), corrosion-assisted cracking, or any other form ofcracking, this Case shall not apply. The extent and rate of degradation in the piping shall be evaluated to ensure that there are no other unacceptable locations within the surrounding area that could affect the integrity of the repaired piping. The dimensions of the surrounding area to be evaluated shall be determined by the Owner, considering the type of degradation present.
(c) The effects of the repair on the piping and any remaining degradation shall be evaluated in accordance with IWA-4311.
3 DESIGN 3.1 Types of Reinforcing Pads (a) Reinforcing pads may be used for pressure only or for pressure plus structural reinforcement of thinned areas including areas that do, or are expected to, penetrate the piping walL (I) Pressure pads are designed to retain pressure, and may be used only where the piping is predicted to retain full structural integrity until the next refueling outage assuming a corrosion rate of either 2 times the actual mea-sured corrosion rate in that location, or 4 times the esti-mated maximum corrosion rate for the system.
(2) Structural pads are designed for pressure plus structural reinforcement and may be used where the piping The Committee's function is to establish rules of safety, relating only to pressure integrity, governing the construction of boilers, pressure vessels, transport tanks and nuclear components, and inservice inspection for pressure integrity of nuclear components and transport tanks, and to interpret these rules when questions arise regarding their intent. This Code does not address other safety issues relating to the construction of boilers, pressure vessels, transport tanks and nuclear components, and the inservice inspection of nuclear components and transport tanks. The user of the Code should refer to other pertinent codes, standards, laws, regulations or other relevant documents.
PDF RELEASE I (N-789)
NC - SUPP. 6
CASE (continued)
N-789 is not to retain full structural mtegJrity until the next refueling outage.
3.2 General Design Requirements ~ Pressure and Structural Pads The of pads shall be in accor-dance with the applicable ofthe Construction Code or Section III 100. ND-3100 and NC-3600, ND-3600 including Appendix 11).
(b) The reint()rcing pad shall be sized to encompass the unacceptable area with the attachment welds located on ad.iacent base material of sufficient thickness to accommo-date the stresses.
The plate tor the reinforcing pad shall be rolled or otherwise tormed to fit the contour of the piping to achieve proper weld fit-up.
(ei) The thickness of the reintorcing pad shall be suffi-cient to maintain required thickness until the next retheling outage.
The tensile strengths of the plate and weld tiller metal for the reintorcing pad shall be at least that specified tor the base metal to which it is applied.
(/) The predicted maximum degradation of the rein-forced piping until the next refueling outage shall be included in the design. The predicted degradation of the piping shall be based on in-situ inspection of, and estab-lished data tor, similar base metals in similar environments.
If the reintorcing pad is predicted to become exposed to the raw water, the predicted degradation of the reintorcing pad shall be based upon established data for base metals or weld metals with similar chemical composition to that used for the reintorcing pad.
(g) Material tor reinforcing pads shall be ferritic, with welds of compatible weld filler metaL (11) The tollowing factors shall be included, as applica-ble, in the design and application of the pad:
(I) shrinkage effects, if any, on the piping (2) stress concentrations caused by installation of the reintorcing pad or resulting tram existing and predicted piping internal surface configuration (3) effects of welding on any interior coating (4) added weight ofthe pad with respect to any design analyses that could be affected (i) If flexibility analysis was required by the original Construction Code, the etfect of the reinforcing pad shall be reconciled with the original analysis. For rectangular-shaped reintorcing pads on piping designed to NC-2650, ND-3650 and aligned parallel or perpendicular to the axis of the piping, unless a lower stress intensification factor
[SIF or (i)] is established, an SIF (i) of2.1 shall be applied tor reinforcing pads on straight pipe and adjacent welds.
Also, a stress multiplier of 1.7 shall be applied to the SIF (i) for standard elbows, and an SIF 0) of 2.1 shall be applied for tees and branch connections when the toe of the attachment weld is not less than 2.5 from any branch reintorcement in I.
Comers of pad plates shall be rounded with radii not less than the pad thickness, and the toes of attachment welds at the comers shall have I in.
(25 mm) minimum radius.
(k) The distance between toes of attachment welds and other attachments or branch reinforcement (Figs. I and 2) shall not be less than the following equation:
d 2.5 where ei = minimum distance between toes of fillet welds of adjacent fillet welded attachments R
the outer radius of the piping (nom nominal thickness of the piping
(/) When permitted by the design, suitable gasket mate-rial may be applied inside the pad to prevent moisture during welding (see Figs. I and 2).
3.3 Specific Design Requirements ~ Pressure Pads Pressure pads shall meet the requirements of 3.2, Fig. 2, and the tollowing:
(a) Fillet-welded pressure pads shall be designed to withstand the membrane strain of the piping in accordance with the requirements of the Code specified in 3.2(a) such that the following criteria are satisfied:
(1) The allowable membrane stress is not exceeded in the piping or the pad.
(2) The strain in the pad does not result in fillet weld stresses exceeding allowable stresses tor such welds.
(b) Design as a reinforced opening in accordance with the Construction Code shall satisfy 3.3(a).
(c) As an alternative to 3.3(a), pressure pads may be designed as structural pads in accordance with 3.4 or as prequalified designs in accordance with 3.5.
3.4 Specific Design Requirements ~ Structural Pads Structural pads shall meet the requirements of3.2, Fig. I, and the following:
(a) Unless otherwise established by analysis in accor-dance with the requirements on.2(a), structural pads shall be attached by partial penetration attachment welds (see Fig. I) that extend for a distance of at least s in each direction beyond the area predicted, by the next refueling outage, to infringe upon the required thickness. 2 2 Design thickness as prescribed by the Construction Code.
NC - SUPP. 6 2 (N-789)
PDF RELEASE
CASES OF ASME BOIl.ER AND PRESSURE VESSEl. CODE CASE (continued)
N-789 FIG. 1 STRUCTURAL PAD d
Appropriate gasket material C =predicted circumferential growth of degradation L = predicted axial growth Limit of branch reinforcement Required thickness
~--- d --
..~I I........f---L, C--.....
t bevel optional Partial penetration attachment weld~
Ref. 3.4(a)
~
tnom I
S I
._-r--------._--...
Minimum dimensions of plate
= predicted maximum dimensions of degradation below minimum required thickness d:2: 2.5 ~ Rtnom s ;:: O.75JR/nom where R = outer radius of the component s = I in. (25 mm) minimum
'nom = nominal wall thickness of the component (h) The thickness of the partial penetration attachment welds shall equal the thickness of the pad and the edges of the welds shall be tapered to the piping surface at a maximum angle ("a" in Fig. I) of 45 deg.
(e) Final configuration of the structural pad including attachment welds shall pennit the examinations and evalua-tions required herein, including any required preservice or inservice examinations of encompassed or adjacent welds.
(d) Except for the tapered edges, the structural pad plate and attachment welds shall have a unifonn thickness.
3.5 Prequalified Design Application of structural pads on straight pipe, standard elbows, and associated welds shall be exempt from the requirements of 3.2(a), provided all of the following conditions are satisfied.
(a) All other requirements of 3.1, 3.2, and 3.4 are satisfied.
(b) The axial length of structural pad plus width of partial penetration attachment welds shall not exceed the greater of 6 in. (150 mm) or the outside diameter of the plpmg.
(e) The finished structural pad shall be circular, oval, or rectangular in shape.
(1) The maximum dimension compensated by a circular structural pad shall not exceed two-thirds of the nominal outside diameter of the piping.
PDF RELEASE 3 (N-789)
NC - SUPP. 6 Copyright Q 2011 by the Americnn &xiety of Mechanical Engineers.
No reproduction may be made of this material without written consent of ASME. ~
CASE (continued)
N-789 CASES OF ASME BOJU:R AND PRESSURE V~:SSEL CODE FIG.2 PRESSURE PAD Required thickness d '2: 2.5 ~ Rtnom Predicted growth of degradation below minimum required thickness Appropriate gasket material I
~L,C-~.I Minimum dimensions of plate -..J
= 2 x predicted maximum dimensions of degradation below minimum required thickness ( 4 x if rate based on estimate is measured) o LJ 2 x or 4 x predicted growth of degradation below minimum required thickness
~~-----/
(2) Rectangular structural pads shall be aligned parallel with or perpendicular to the axis of the piping.
(3) For oval structural pads, the end radii shall not be less than 0.75jRtnom, and the axis of the structural pad shall be aligned parallel with or perpendicular to the axis of the piping.
4 WATER-BACKED APPLICATIONS (c) Provisions for venting during the final closure weld, or for pressurizing for leak-testing, shall be included, if necessary.
(d) The surface of the attachment weld shall be pre-pared, if necessary, by machining or grinding to permit performance of surface and volumetric examinations required by 6. For ultrasonic examination, a surface finish of 250 RMS or better is required.
(a) Attachment welds on water backed piping shall be applied using the SMAW process with low-hydrogen electrodes.
(b) For piping materials other than P-No. I, Group I, the surface examination required in 6 shall be performed no sooner than 48 hr after completion of welding.
5 INSTALLATION (a) The base material in the area to be welded shall be cleaned to bare metal.
(b) Weld metal shall be deposited using a groove -
welding procedure qualified in accordance with Section IX and the Construction Code.
6 EXAMINATION (a) The completed attachment weld shall be examined using the liquid penetrant or magnetic particle method and shall satisfY the surface examination acceptance criteria for welds of the Construction Code or Section III (NC-5300, ND-5300).
(b) Except for the tapered edges, partial penetration attachment welds, including the piping base metal upon which they are applied, shall be ultrasonically measured to verifY acceptable wall thickness.
(c) Partial penetration attachment welds shall be volu-metrically examined when full penetration girth welds in the piping are required by the Construction Code to be NC - SUPP. 6 4 (N-789)
PDF RELEASE
CASES OF ASME BOILER AND PRESSURE VESSEL CODE CASE (continued)
N-789 volumetrieallv examined. Where configuration does not pemlit meani~gful volumetric examination, the first layer, each in. (13 mm) thickness ofweld deposit, and the final surface shall be examined in accordance with 6(a) in lieu of volumetric examination.
(d) If volumetric examination is required, the full vol-ume of the attachment weld, excluding the tapered edges, but including the volume of base metal required for the intended life of the reinforcing pad, shall be examined in accordance with the Construction Code or Section III, using either the ultrasonic or radiographic method, and shall, to the depth at the surface ofthe piping, satisfy the acceptance criteria for weldments of the Construction Code or Section III (NC-5320, ND-5320 or NC-5330, ND-5330).
Any volume of the piping beneath the reinforcing pad that is credited in the design shall satisfy the volumetnc acceptance criteria of Section III (NC-5320, ND-5320 or NC-5330, ND-5330), as applicable.
7 PRESSURE TESTING In lieu ofIWA-4540, a system leakage test ofthe repair/
replacement activity shall be performed in accordance with IWA-5000 prior to, or as part of, returning to service.
8 INSERVICE MONITORING (a) Upon completion of the repair, inspections shall be performed for structural pads, using ultrasonic or direct thickness measurement, to record the thickness ofthe plate, the thickness at the attachment welds, including the under-Iving base metal, and to the extent examinable in a 3 in.
(75 mm) wide band, surrounding the repair, as a baseline tor subsequent monitoring of the repair.
(b) The Owner shall prepare a plan for additional thick-ness monitoring tor structural pads using ultrasonic or direct thickness measurement to verify that minimum design thicknesses, as required by the Construction Code or Section III, are maintained until the next refueling out-age. The monitoring shall be monthly for the first quarter and the subsequent frequency shall be based on the results of the monitoring activities, but at least quarterly.
(c) If the results of the monitoring program identify leakage or indicate that the structural margins required by 3 will not be maintained until the next refueling outage, additional repair/replacement activities not prohibited by I(d) shall be performed prior to encroaching upon the design limits.
(:1; Reinforcing pads shall not remain in service beyond the end of the next refueling outage.
PDF RELEASE 5 (N-789)
NC - SUPP. 6