Text

10 CFR 50.55a Request to Use ASME Code Cade N-789-2 for the Fourth Inservice Inspection Program Interval
	ML16069A029
Person / Time
Site:	Wolf Creek
Issue date:	03/02/2016
From:	Mccoy J; Wolf Creek
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	ET 16-0006
	Download: ML16069A029 (13)
	v • d • e

W0LF CREEK -'NUCLEAR OPERATING CORPORATION Jaime H. McCoy Vice President Engineering March 2, 2016 ET 16-0006 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Docket No. 50-482: 10 CFR 50.55a Request to Use ASME Code Case N-789-2 for the Fourth Inservice Inspection Program Interval Gentlemen:

Pursuant to 10 CFR 50.55a(z)(1), Wolf Creek Nuclear Operating Corporation (WCNOC) hereby requests Nuclear Regulatory Commission (NRC) approval of the attached 10 CFR 50.55a Request for the fourth 10-year inspection interval of WCNOC's Inservice Inspection (I51)

Program. This 10 CFR 50.55a Request seeks approval to use American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Case N-789-2, "Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service, Section Xl, Division 1,"' as an alternative to ASME Code Section XI, Paragraph IWA-4000. The attachment provides the details of this 10 CFR 50.55a request.

WCNOC requests approval of the proposed alternative by February 28, 2017. A copy of ASME Code Case N-789-2 is provided as the enclosure for information.

This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4156, or Cynthia R. Hafenstine (620) 364-4204.

Sincerely, Jaime H. McCoy JHM/rlt

Attachment:

10 CFR 50.55a Request for Approval to Use ASME Code Case N-789-2

Enclosure:

ASME Code Case N-789-2 cc: M. L. Dapas (NRC), w/a, w/e C. F. Lyon (NRC), w/a, w/e N. H. Taylor (NRC), w/a, w/e Senior Resident Inspector (NRC), w/a, w/e '

P.0. Box 411 / Burlington, KS 66639 / Phone: (620) 364-8831 * '*

An Equal Opportunity Employer M/F/HC/NET

Attachment to ET 16-0006 Page 1 of 5 Wolf Creek Nuclear Operating Corporation 10 CFR 50.55a Request for Approval to Use ASME Code Case N-789-2

Attachment to ET 16-0006 Page 2 of 5 10 CFR 50.55a Request for Approval to Use ASME Code Case N-789-2 Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1)

Alternative Provides Acceptable Level of Quality and Safety

1. ASME Code Component(s) Affected American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section III, Class 2 and 3, moderate energy carbon steel raw water piping systems.

2. Applicable Code Edition and Addenda

ASME B&PV Code Section Xl, 2007 Edition with 2008 Addenda.

3. Applicable Code Requirement

ASME B&PV Code, Section Xl, IWA-4400 provides the requirements for welding, brazing, metal removal, and installation of Repair/Replacement activities.

4. Reason for Request

In accordance with 10 CFR 50.55a(z)(1), Wolf Creek Nuclear Operating Station (WCNOC) is requesting the proposed alternatives to replacement or weld repair of pipe wall degradation (wall thinning conditions) in Class 2 and 3 moderate energy carbon steel raw water piping systems, in accordance with IWA-4000. The degradation may be the result of erosion, corrosion, cavitation, and pitting mechanisms; but excluded is degradation resulting from flow-accelerated corrosion (FAC), corrosion-assisted cracking, or any other form of cracking. The repairs or replacements shall be 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 reason for this request is to permit installation of technically sound alternative repairs in accordance with code Case N-789-2. This will allow adequate time for evaluation, design, material procurement, planning and scheduling of appropriate permanent repair or replacement of the item in accordance with the Owner's Requirements and the original or later Construction Code, considering the impact on system availability, maintenance rule applicability, and availability of replacement materials.

5. Proposed Alternative and Basis for Use Proposed Alternative In accordance with 10 CFR 50.55a(z)(1), WCNOC proposes to implement the requirements of ASME Code Case N-789-2, 'Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1" as an

Attachment to ET 16-0006 Page 3 of 5 alternative 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 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. ASME Code Case N-789-2 is provided as the enclosure to this letter.

ASME Code Case N-789-2 was approved on June 23, 2015, by the ASME Board on Nuclear Codes and Standards; however, this Code Case has not been incorporated into Nuclear Regulatory Commission (NRC) Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability, ASME Code Section XI Division 1." As such, ASME Code Case N-789-2 is not available for application at nuclear power plants without specific NRC approval. Therefore, WCNOC requests NRC approval of the proposed alternative to implement this repair technique.

Basis for Use ASME Code Case N-789-2 applies to Class 2 and 3 moderate energy (that is, systems less than or equal to 200 degrees Fahrenheit and less than or equal to 275 pounds per square inch gauge pressure maximum operating conditions) carbon steel raw water piping. ASME Code Case N-789-2, footnote 1, states that:

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."

The alternative repair described in ASME Code Case N-789-2 involves the application of a metal reinforcing pad welded to the surface of the piping system that either restores pressure integrity or reinforces the weakened area and retain the system pressure. ASME Code Case N-789-2 requires the design and examinations to Comply with the Construction Code or ASME Code Section II1. Reconciliation and use of editions and addenda of ASME Code Section III will be in accordance with ASME Code Section Xl, Paragraph IWA-4220. If an edition of ASME Code Section III other than the Construction Code is applied, it will have been accepted by the NRC in accordance with 10 CFR 50.55a. The edition of ASME Code Section Xl applicable to the WCNOC current 10-year inservice inspection (ISI) interval, as defined in Section 2, applies to the repair.

The reinforcing pad may be used for leak prevention only (pressure pad), or for leak prevention plus structural reinforcement of thinned areas including areas that do, or are expected to, penetrate the piping wall (structural pad). 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 measured corrosion rate in that location, or four (4) times the estimated maximum corrosion rate for the same degradation mechanism in that system or similar system at the same plant site. Structural pads are designed for pressure plus structural reinforcement and may be used where the piping is predicted not to retain full structural integrity until the next refueling outage. In this context, "full structural integrity" means the piping maintains full capability to withstand structural (mechanical) loading for which it is designed without need for additional support or reinforcement. The appropriate repair technique will be determined based on the characterization of the degradation.

Reinforcing pads may be applied on the outside of pipe or fittings for mitigation of internal or external corrosion, except that pressure pads applied externally may not be used to mitigate

Attachment to ET 16-0006 Page 4 of 5 externally corroded areas that are subject to bulging due to wall thinning. Reinforcing pads may also be applied on the inside of pipe or fittings for mitigation of internal or external corrosion.

Following discovery of a through-wall flaw, the flaw will be characterized to determine the cause of the degradation. Additionally, the surrounding areas will be examined to bound the degraded area and ensure no other unacceptable locations exist which could affect the integrity of the repaired piping. The area of the reinforcing pad will be determined based on the identified degraded area. Corrosion rates will be established based on the estimated maximum corrosion rate for the same degradation mechanism in that system or similar system at the same plant site. If the development of a corrosion rate based on actual thickness measurements of the degraded area is not feasible due to the time constraints associated with an emergent repair or replacement, then the established corrosion rate will be conservatively multiplied by the safety factor of four established in ASME Code Case N-789-2 to ensure the design of the reinforcing pad (for example, thickness and weld size) will provide a structural or pressure boundary, as appropriate, until the next refueling outage. If the established corrosion rates are less than the actual corrosion, the short duration of the repair, along with the applicable corrosion rate safety factor and inservice monitoring defined in ASME Code Case N-789-2, provide reasonable assurance that the structural integrity and leakage integrity will be maintained during the one-cycle of application.

When a reinforcing pad is installed to a leaking area, precautions will be taken as necessary, such as installation of a gasket or sealant beneath the pad, to prevent welding on wet surfaces.

Externally applied reinforcing pads attached to piping that has not been breached shall be equipped with pressure taps for performance of pressure testing.

Baseline thickness examinations will be performed for completed structural pads, attachment welds (except for the tapered edges), and the surrounding areas, followed by monthly thickness monitoring for the first three months, with subsequent monitoring frequency based on the results of this monitoring, but at a minimum frequency of quarterly.

For structural pads on buried piping, provisions will be made for access during plant operation in order to perform these examinations.

In order to verify the leak tightness of the pressure pad, areas containing pressure pads and internally applied structural pads shall be monitored monthly for evidence of leakage. If the areas containing such pads are not accessible for direct observation, then monitoring will be accomplished by visual assessment of surrounding areas or ground surface areas above the pads on buried piping, or monitoring of leakage collection systems, if available.

For all reinforcing pads, regardless of when during an operating cycle they are installed, the repair will be considered to have a maximum service life of the time until the end of the next refueling outage, and by that time a permanent repair or replacement must be performed.

Detailed requirements for design of reinforcement pads, installation, examination, pressure testing and inservice monitoring are provided in ASME Code Case N-789-2.

Based on the above, the use of ASME Code Case N-789-2 for temporary repairs is justified, since utilizing ASME Code Case N-789-2 would result in an acceptable level of quality and safety. All other ASME Code Section Xl 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.

Attachment to ET 16-0006 Page 5 of 5

6. Duration of Proposed Alternative The duration of the proposed request extends to the end of the first refueling outage following the end of WCNOC's Fourth 10-Year ISI Interval, which began on September 3, 2015 and ends on September 2, 2025.

ASME Code Case N-789-2 reinforcing pads (structural or pressure) installed before the end of the 10-year ISI interval are removed before the end of the refueling outage following their installation, even if that refueling outage occurs after the end of the 10-year inspection interval.

7. Precedents

1) NRC Safety Evaluation for Exelon Generation Co. LLC,

Subject:

[Associated plant names listed below] - Request to Use American Society of Mechanical Engineers Boiler and Pressure Vessel 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" [Associated TAC Numbers listed below], dated May 10, 2012 (ADAMS Accession No. ML12121A637).

Plant Names: Braidwood Station, Units 1 and 2; Byron Station, Units 1 and 2; Clinton Power Station, Unit 1; Dresden Nuclear Power Station, Units 2 and 3; LaSalle County Station, Units 1 and 2; Limerick Generating Station, Units I and 2; Oyster Creek Nuclear Generating Station; Peach Bottom Atomic Power Station, Units 2 and 3; Quad Cities Nuclear Power Station, Units 1 and 2; and Three Mile Island Nuclear Station, Unit 1 TAC Nos.: ME7303, ME7304, ME7305, ME7306, ME7307, ME7308, ME7309, ME7310, ME7311, ME7312, ME7313, ME7314, ME7315, ME7316, ME7317, ME7318, and ME7319

2) NRC Safety Evaluation for FirstEnergy Nuclear Operating Company,

Subject:

Beaver Valley Power Station, Unit Nos. 1 and 2 - Relief Request No. BV3-N-789 Regarding Carbon Steel Piping for Raw Water Service (TAC Nos. M4563 and MF4566), dated June 19, 2015 (ADAMS Accession No. ML15163A147).

3) NRC Safety Evaluation for Northern States Power Company-Minnesota,

Subject:

Prairie Island Nuclear Generating Plant, Units I and 2 - Relief Requests (1-RR-5-5 and 2 RR-5-5) for the Fifth 10-Year Interval for the Inservice Inspection Program (TAC Nos. MF4839 and MF4840), dated May 4, 2015 (ADAMS Accession No. ML15079A003).

Note: WCNOC is submitting this 10 CFR 50.55a request to use ASME Code Case N-789-2, whereas the precedents cited above requested the use of earlier revisions to this Code Case.

ENCLOSURE ASME Code Case N-789-2, "Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1" (6 pages)

CASE ASME BPVC.CC.NC.S2-2015 N-789-2 Approval Date: June 23, 2015 Code Cases will remain availablefar use until annulled by the applicable Standards Committee.

Case N-789-2 (d) Additional reinforcement or repair is not permitted Atternative Requirements for Pad Reinforcement of on top of an existing reinforcing pad.

Crass 2 and 3 Moderate-Energy Carbon Steel Piping for (e) Reinforcing pads, including those installed during a Raw Water Service refueling outage, shall not remain in service beyond the Section XI, Division 1 end of the next refueling outage.

(f) This Case may only be applied to piping not re-Inquiry: As an alternative to replacement or weld repair quired to be ultrasonically examined for inservice in accordance with IWA-4400, what requirements may be inspection.

applied for wall reinforcement of Class 2 and 3 moderate-energy carbon steel raw water' piping systems that have experienced wall thinning from localized ero- 2 INITIAL EVALUATION sion, corrosion, and cavitation or pitting?

(a) The material beneath the surface to which the rein-forcing pad is to be applied and the adjacent area shall be Reply: It is the opinion of the Committee that, in lieu of ultrasonically measured to establish the existing wall meeting IWA-4400, areas of Class 2 and 3 moderate- thickness and the extent and configuration of degradation energy [i.e., less than or equal to 200°F (930 C) and less to be corrected by the reinforcing pad.

than or equal to 275 psig (1.9 MPa) maximum operating (h) The cause and rate of degradation shall be deter-conditions) carbon steel raw water piping experiencing mined. If the cause is determined to be flow-accelerated wall thinning from localized erosion, corrosion, and cavi- corrosion (FAC), corrosion-assisted cracking, or any other tation or pitting (collectively referred to herein as "corro- form of cracking, this Case shall not apply. The extent and sion") may have the wall reinforced by applying rate of degradation in the piping shall be evaluated to en-reinforcing pads to the surface of the piping in accordance sure that there are no other unacceptable locations within with the following requirements. Excluded from these the surrounding area that could affect the integrity of the provisions are conditions involving flow-accelerated cor- repaired piping. The dimensions of the surrounding area rosion (FAC), corrosion-assisted cracking, or any other to be evaluated shall be determined by the Owner, consid-form of cracking. ering the type of degradation present.

(c) The effects of the repair on the piping and any re-maining degradation shall be evaluated in accordance 1 GENERAL REQUIREMENTS with IWA-4311.

(a) Application of the reinforcing pad shall be per-formed in accordance with a Repair/Replacement Plan satisfying the requirements of IWA-415 0.2 3 DESIGN (b) The design, materials, and installation shall meet 3.1 TYPES OF REINFORCING PADS the requirements of the Construction Code and IWA-4000, except as stated in this Case. (a) Reinforcing pads may be used for leak prevention (c) If the minimum required thickness of reinforcing only (pressure pad), or for leak prevention plus structural pad necessary to satisfy the requirements of 3 is greater reinforcement of thinned areas including areas that do, or than the nominal thickness for the size and schedule of are expected to, penetrate the piping wall (structural the piping, this Case shall not he used. pad).

1 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."

2 The references to Section Xl in this Case refer to the 2015 Edition. For use of this Case with other Editions and Addenda, refer to the Guide-line for Cross-Referencing Section Xl Cases, Table 1.

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.

1 (N-789-2) NC - SUPP. 2

[( Cepyrishit *) 2515 by the American Society ol Mechanical Engiece...

No eprducionmaybe made of this material 'ithrout wrtenconett of ASME. ' /

CASE (continued)

N-789-2ASME BPVCCC.NCS2-2015 (1) Pressure pads are designed to retain pressure, (2) stress concentrations caused by installation of and may be used only where the piping is predicted to re- the reinforcing pad or resulting from existing and pre-tain full structural integrity until the next refueling outage dicted piping surface configuration assuming a corrosion rate of either 2 times the actual (3) effects of welding on any coating measured corrosion rate in that location, or 4 times the (4) added weight of the pad with respect to any de-estimated maximum corrosion rate for the same degrada- sign analyses that could be affected tion mechanism in that system or similar system at the (5) for internally applied pads, impact on flow and same plant site. need for protective coating (2) Structural pads are designed for pressure plus (i) If flexibility analysis was required by the original structural reinforcement and may be used where the pip- Construction Code, the effect of the reinforcing pad shall ing is predicted not to retain full structural integrity until be reconciled with the original analysis. For rectangular-the next refueling outage. shaped reinforcing pads on piping designed to NC-3650 (b) Reinforcing pads may be applied as follows: or ND-3650 and aligned parallel or perpendicular to the (1) On the outside of pipe or fittings for mitigation of axis of the piping, unless a lower stress intensification fac-internal or external corrosion, except that pressure pads tor [SIF or (i)] is established, an SIF (i) of 2.1 shall be ap-applied externally may not be used to mitigate externally plied for reinforcing pads on straight pipe and adjacent corroded areas that are subject to bulging due to wall welds. Also, a stress multiplier of 1.7 shall be applied to thinning. the SIF (i) for standard elbows, and an SIF (i) of 2.1 shall (2) On the inside of pipe or fittings for mitigation of be applied for tees and branch connections when the toe internal or external corrosion. of the attachment weld is not less than 2.5 Rno from any branch reinforcement in Figure 1.

3.2 GENERAL DESIGN REQUIREMENTS-(I) Corners of reinforcing pad plates shall be rounded PRESSURE AND STRUCTURAL PADS with radii not less than the reinforcing pad thickness, (a) The design of reinforcing pads shall be in accor- and the toes of attachment welds at the corners shall have dance with the applicable requirements of the Construc- 1 in. (25 mam) minimum radius.

tion Code or Section III (NC-3100 and NC-3600 or (k) The distance between toes of attachment welds and ND-3 100 and ND-3600, including Mandatory Appendix other attachments or branch reinforcement (Figure 1 and II). 2) shall not be less than the following equation:

(b) The reinforcing pad shall be sized to encompass the unacceptable area with the attachment welds located on d = 2.5 Rno adjacent base material of sufficient thickness to accom-modate the design stresses. where (c) The plate for the reinforcing pad shall be rolled or otherwise formed to fit the contour of the piping to d = minimum distance between toes of fillet welds of achieve proper weld fit-up. adjacent fillet welded attachments (d) The thickness of the reinforcing pad shall be suffi- R = the outer radius of the piping tnom = nominal thickness of the piping cient to maintain required thickness until the next refuel-ing outage. (1) If permitted by the design, suitable gasket material (e) The tensile strengths of the plate and weld filler me- or sealant may be applied between the pad and the piping tal for the reinforcing pad shall be at least that specified surface to prevent moisture during welding (see Figures for the base metal to which it is applied. 1 and 2). Any residual moisture shall then be removed (9fThe predicted maximum degradation of the rein- by heating prior to welding.

forced piping until the next refueling outage shall be in-cluded in the design. The predicted degradation of the 3.3 SPECIFIC DESIGN REQUIREMENTS -

piping shall be based on in-situ inspection of, and estab- PRESSURE PADS lished data for, similar base metals in similar environ-ments. If the reinforcing pad will be, or is predicted to Pressure pads shall meet the requirements of 3.2, become, exposed to the raw water, the predicted degrada- Figure 2, and the following:

tion of the reinforcing pad shall be based upon estab- (a) Fillet-welded pressure pads shall be designed to lished data for base metals or weld metals with similar withstand the membrane strain of the piping in accor-chemical composition to that used for the reinforcing pad. dance with the requirements of the Code specified in

(,q) Material for reinforcing pads shall be ferritic, with 3.2(a) such that the following criteria are satisfied:

welds of compatible weld filler metal. (1) The allowable membrane stress is not exceeded (h) The following factors shall be included, as applic- in the piping or the pad.

able, in the design and application of the pad: (2) The strain in the pad does not result in fillet weld (1) shrinkage effects, if any, on the piping stresses exceeding allowable stresses for such welds.

NC -SUPP. 2 2 (N-789-2)

No ~maeocio y be m~ade of tbis material weithout written consent of ASME.'(S

CASE (continued)

ASME BPVC.CC.NC.S2-201S N-789-2 Figure 1 Structurat Pad C= predicted circumferential growth of degradation 1 L = predicted axial growth Partial penetration attachment weld Ref. 3.4(a) Required Minimum dimensions of plate--

= predicted maximum dimensions of degradation below minimum required thickness d ->2.5 Rtnom (b) Design as a reinforced opening in accordance with requirements of 3.2(a), extend for a distance of at least the Construction Code shall satisfy (a). s in each direction beyond the area predicted, by the next (c) As an alternative to (a), pressure pads may be de- refueling outage, to infringe upon the required thickness, 3 signed as structural pads in accordance with 3.4 or as pre- where qualified designs in accordance with 3.5.

s Ž_ 0.75 RtnR-om and s Ž 1in.(25 mam) 3.4 SPECIFIC DESIGN REQUIREMENTS -- where STRUCTURAL PADS R = D/2 = outer radius of the piping Structural pads shall meet the requirements of 3.2, tnom = nominal wall thickness of the piping Figure 1, and the following:

(a) Structural pads shall be attached by partial-penetration welds (see Figure 1) that, unless otherwise established by analysis in accordance with the 3 Design thickness as prescribed by the Construction Code.

3 (N-789-2) NC - SUPP. 2 by tho An~ic~ S~xiotyof Mech~nc~IEngoeors ASME'~

CASE (continued)

N-789-2 ASME BPVC.CC.NC.SZ-2015 Figure 2 Pressure Pad

.* ..... Predicted growth of

.- ," degradation below minimum

~wall thickness based on 2 x(

i I or 4 X estimated corrosion rate.

priate gasket material / *

L *-

if req~luired tnom Ireq Required

+4 thickness Minimum dimensions of plate--

= predicted extent of degradation below minimum wall thickness based on 2 X the measured corrosion rate at the location or 4 x the maximum estimated corrosion rate for the system.

(b) The thickness of the partial penetration attachment 3.5 PREQUALIFIED DESIGN welds shall equal the thickness of the pad and the edges of Application of structural pads on the outside surface of the welds shall be tapered to the piping surface at a max- straight pipe, standard elbows, and associated welds for imum angle ("ax" in Figure 1) of 45 deg. the mitigation of internal corrosion shall be exempt from (c) Final configuration of the structural pad including the requirements of 3.2(a), provided all of the following attachment welds shall permit the examinations and eva- conditions are satisfied. 4 luations required herein, including any required preser- (a) All other requirements of 3.1, 3.2, and 3.4 are vice or inservice examinations of encompassed or satisfied.

adjacent welds. (b) The axial length of structural pad plus width of par-(d) Except for the tapered edges, the structural pad tial penetration attachment welds shall not exceed the plate and attachment welds shall have a uniform greater of 6 in. (150 mm) or the outside diameter of the thickness. piping.

(e) Where structural pads are applied on the outside of (c) The finished structural pad shall be circular, oval, or piping to mitigate externally corroded areas with poten-rectangular in shape.

tial for bulging, the corrosion cavity shall be filled to the (1) The maximum dimension compensated by a cir-original contour of the pipe with hardenable fill to mini-cular structural pad shall not exceed two-thirds of the mize the gap beneath the reinforcing pad. [See Figure 1 nominal outside diameter of the piping.

sketch (b).] (2) Rectangular structural pads shall be aligned par-allel with or perpendicular to the axis of the piping.

SPrequalified configurations are based on experimental analysis and burst testing reported in EPRI Report TR 108142.

NC -SUPP. 2 4 (N-789-2)

CASE (continued)

~N-789-2 ASME BPVC.CC.

intended life of the reinforcing pad, shall be examined (3) For oval structural pads, the end radii shall not be less than 0.75 Rtnom, and the axis of the structural pad in accordance with the Construction Code or Section Ill, using either the ultrasonic or radiographic method, and shall be aligned parallel with or perpendicular to the axis shall, to the depth at the surface of the piping, satisfy of the piping.

the acceptance criteria for weidments of the Construction Code or Section III (NC-5320, ND-5320 or NC-5330, 4 WATER-BACKED APPLICATIONS ND-5330). Any volume of the piping beneath the reinfor-cing pad that is credited in the design shall satisfy the vo-(a) Attachment welds on water backed piping shall be lumetric acceptance criteria of Section III (NC-5320, applied using the SMAW process with low-hydrogen ND-5320 or NC-5330, ND-5330), as applicable.

electrodes.

(b) When welding a reinforcing pad to a leaking area, precautions, such as installation of a gasket or sealant be- 7 PRESSURE TESTING neath the pad, shall be taken to prevent welding on wet surfaces. In lieu of IWA-4540, a system leakage test of the repair/

(c) For piping materials other than P-No. 1, Group 1, replacement activity shall be performed in accordance the surface examination required in 6 shall be performed with IWA-5000 prior to, or as part of, returning to service.

no sooner than 48 hr after completion of welding. Externally applied reinforcing pads attached to piping that has not been breached shall be equipped with pres-sure taps for performance of pressure testing.

5 INSTALLATION (a) The base material in the area to be welded shall be 8 INSERVICE MONITORING cleaned to bare metal.

(b) Weld metal shall be deposited using a groove - (a) Upon completion of the repair, inspections shall be welding procedure qualified in accordance with Section performed for structural pads, using ultrasonic or direct IX and the Construction Code. thickness measurement, to record the thickness of the (c) Provisions for venting during the final closure weld, plate, the thickness at the attachment welds, including or for pressurizing for leak-testing, shall be included, if the underlying base metal, and to the extent examinable necessary. in a 3 in. (75 mm) wide band, surrounding the repair, (d) The surface of the attachment weld shall be pre- as a baseline for subsequent monitoring of the repair.

pared, if necessary, by machining or grinding to permit (b) The Owner shall prepare a plan requiring additional performance of surface and volumetric examinations re- thickness monitoring for externally applied structural quired by 6. For ultrasonic examination, a surface finish pads using ultrasonic or direct thickness measurement of 250 RMS or better is required. to verify that minimum design thicknesses, as required by the Construction Code or Section III, are maintained until the next refueling outage. Initial monitoring shall 6 EXAMINATION be monthly for the first quarter and the subsequent fre-(a) The completed attachment weld shall be examined quency shall be based on corrosion rates calculated using using the liquid penetrant or magnetic particle method reductions in thicknesses since the previous monitoring and shall satisfy the surface examination acceptance cri- inspections, but at least quarterly.

teria for welds of the Construction Code or Section III Provisions shall be made for access to structural pads (NC-5300, ND-5300). on buried piping during operation to accomplish these (b) Except for the tapered edges, partial penetration at- examinations.

tachment welds, including the piping base metal upon (c) Areas containing pressure pads and internally ap-which they are applied, shall be ultrasonically measured plied structural pads shall be monitored monthly for evi-to verify acceptable wall thickness. dence of leakage. If the areas containing such pads are not (c) Partial penetration attachment welds shall be volu- accessible for direct observation, monitoring shall be ac-metrically examined when full penetration girth welds in complished by observation of surrounding areas or the piping are required by the Construction Code to be vo- ground surface areas above the pads on buried piping; lumetrically examined. Where configuration does not per- or leakage collection systems, if available, shall be mit meaningful volumetric examination, the first layer, monitored.

each '/2 in. (13 mm) thickness of weld deposit, and the fi- (Cd)If the results of the monitoring program identify nal surface shall be examined in accordance with (a) in leakage or indicate that the structural margins required lieu of volumetric examination. by 3 will not be maintained until the next refueling out-(d) If volumetric examination is required, the full vol- age, additional repair/replacement activities not prohib-ume of the attachment weld, excluding the tapered edges, ited by 1(d) shall be performed prior to encroaching but including the volume of base metal required for the upon the design limits.

5 (N-789-2) NC -SUPP. 2 by the Aoencoo Sodety of Mechon~c~l Engoeers No ,epeodootioo n~oyho m~doofthis ,ootehol without wrtten cooseot of ASME'~

CASE (continued)

N-789-2 ASME BPVC.CC.NC.S2-2015 (e) All reinforcing pads, regardless of when installed, shall be removed no later than the end of the next refuel-ing outage.

NC -SU PP. 2 6 (N-789-2)