ULNRC-04942, Revision of Request for Relief from ASME Section XI Requirements in Order to Temporarily Restore Wall Thickness of ASME Class 2 Carbon Steel Main Feedwater Piping by Weld Overlay Reinforcement

Revision of Request for Relief from ASME Section XI Requirements in Order to Temporarily Restore Wall Thickness of ASME Class 2 Carbon Steel Main Feedwater Piping by Weld Overlay Reinforcement

ML040480389
Person / Time
Site:	Callaway
Issue date:	01/22/2004
From:	Keith Young AmerenUE
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-04942
Download: ML040480389 (10)

Text

AmerenUE PO Box 620 Callaway Plant Fulton, MO 65251 January 22, 2004 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P I - 137 Washington, DC 20555-0001 ULNRC-04942

='Ameren Ladies and Gentlemen:

10 CFR 50.55a UE CALLA WAY PLANT UNION ELECTRIC CO.

DOCKET NUMBER 50-483 REVISION OF REQUEST FOR RELIEF FROM ASME SECTION XI REQUIREMENTS IN ORDER TO TEMPORARILY RESTORE WVALL THICKNESS OF ASME CLASS 2 CARBON STEEL MAIN FEEDNWATER PIPING BY WELD OVERLAY REINFORCEMENT Pursuant to 10CFR50.55a(a)(3)(i), and by letter ULNRC-04875 dated July 22, 2003, Union Electric Company (AmerenUE) submitted for NRC approval a request for relief from ASME Section XI requirements in order to permit temporary weld overlay reinforcement of affected ASME Class 2 carbon steel piping sections associated with the main feedwater system at Callaway.

As noted in the July 22, 2003 submittal, the scope of the request is limited to particular areas where, due to wall thinning monitored under Callaway's Flow-Accelerated Corrosion (FAC) program, the projected pipe wall thickness may be slightly less than desired when inspections are completed during the next refueling outage at Callaway, i.e., RF-13. As explained in the July 22, 2003 submittal, the affected piping sections are already scheduled to be replaced during RF-14 due to planned replacement of the steam generators at Callaway. Application of the weld overlay in RF-1 3 would restore pipe wall thickness to ensure more than adequate margin for the period of plant operation between RF-13 and RF-14, and would therefore obviate consecutive replacement of the same piping sections (i.e., once in RF-13 and then again in RF-14). The service life of the weld overlay(s) permitted by the relief request (if approved) would thus be limited to one operating cycle.

qWA) a subsidiary of Ameren Corporation

ULNRC-04942 January 22, 2004 Page 2 AmerenUE's relief request is currently under review by the NRC staff. The request was discussed in detail during a telephone conference between NRC and AmerenUE personnel on November 20, 2003 and then again on December 23, 2003.

From those discussions, several additions to the relief request were agreed upon, including clarifying that the weld overlays are to be applied over the complete circumference (360 0) of the affected area. It was also agreed that additional data would be provided, including pipe wall thickness measurements obtained over at least the last two operating cycles at Callaway, as well as pipe wall thicknesses projected for RF-13 and RF-14, for the applicable pipe sections.

The relief request has been revised to incorporate the agreed-upon changes and/or additional information, and is hereby provided as an attachment to this letter.

Please contact Dave Shafer at 314-554-3104 for any additional questions you may regarding the relief request.

Very truly yours, Young Manager, Regulatory Affairs KDY/TBE/mlo Attachment

ULNRC-04942 January 22, 2004 Page 3 cc:

U. S. Nuclear Regulatory Commission (Original and 1 copy)

Attn: Document Control Desk Mail Stop PI-137 Washington, DC 20555-0001 Mr. Bruce S. Mallett Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 7E1 Washington, DC 20555-2738 Manager, Electric Department Missouri Public Service Commission PO Box 360 Jefferson City, MO 65102

ULNRC-04942, Attachment Page I of 7 Request to Restore Wall Thickness of ASME Class 2 Carbon Steel Main Feedwater Piping by Weld Overlay Reinforcement

Background

As an alternative to piping replacement in accordance with ASME Section XI IWC-4000, and pursuant to the provisions of 10FR 50.55a(a)(3)(i), Callaway Plant requests permission to restore the wall thickness of high energy ASME Class 2 feedwater piping by weld overlay.

Requested service life of the weld overlay reinforcement is one operating cycle from Refuel 13 to Refuel 14. Piping reinforced by weld overlay will be cut out and replaced during installation of new steam generators in Refuel 14.

The 1989 Edition with no Addenda of ASME Section Xl currently governs repair/replacement activities at the Callaway Nuclear Plant. Callaway Plant is currently in the second 10-year inservice inspection interval, which began on August 1, 1995. The 1974 Edition with Summer 1975 Addenda of ASME Section III is the Construction Code for the main feedwater piping system.

Areas Identified that May Require Weld Overlay Reinforcement The Callaway Flow Accelerated Corrosion (FAC) program is used to monitor and evaluate the remaining life of ASME Class 2 feedwater piping at the Callaway plant. Evaluation and ultrasonic wall thickness examinations have revealed a small number of locations where repair and/or piping replacement will be necessary in the future. Table 1 lists feedwater piping areas where repair by overlay reinforcement is requested. The piping/part description, Callaway location identifier, nominal pipe size, pipe schedule, and base material type are listed for each location.

Table 2 provides wall thickness data for these locations. The design minimum wall thickness, measured wall thickness, projected wall thickness, and expected margin are provided for each location. The maximum projected axial length requiring overlay reinforcement (L dimension in Figure 1) is expected to be 8 inches or less.

Justification for Weld Overlay Reinforcement Projections based on calculated wear rates and ultrasonic examination data obtained during Refuel 11 and Refuel 12 Indicate weld overlay reinforcement may be necessary to maintain the required structural integrity until Refuel 14 when new steam generators will be Installed. Piping reinforced by weld overlay will be cut out and replaced during installation of the new steam generators.

The piping areas that may require weld overlay reinforcement are relatively small localized areas.

Adjacent areas have been Inspected and verified to have wall thickness that meets design requirements. Weld overlay reinforcement will restore wall thickness of the piping to a value greater than or equal to design minimum wall thickness with adequate margin, considering predicted wear rates, to provide a service life of one operating cycle. In addition, the weld overlay material is not predicted to become exposed to feedwater during the cycle. The weld overlay will have a uniform width and extend 360 degrees circumferentially around the piping. The proposed overlay reinforcement will ensure a sufficient level of safety and provide adequate structural integrity for one operating cycle.

The weld overlay reinforcement alternative will result in a significant reduction in personnel radiation exposure during refueling outage maintenance work. In addition, by avoiding replacement of the piping during Refuel 13 and again in Refuel 14, outage duration and costs are reduced by decreasing the overall scope of work.

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ULNRC-04942 Attachment Page 2 of 7 Requirements for Restoration of Internal Wall Thinning by Weld Overlay Weld overlay reinforcement on the outside surface of the piping shall be installed in accordance with the following requirements and rules:

1. General Requirements 1.1. The weld overlay(s) installed to restore wall thickness shall be performed in accordance with the Callaway Repair/Replacement Program a.

1.2. The wall thickness restoration shall meet all requirements of the Callaway Repair/Replacement Program except as permitted in this relief request.

2. Initial Evaluation 2.1. The piping base material where the weld overlay is to be installed shall be evaluated to establish the existing average wall thickness and the extent and configuration of degradation to be reinforced by the weld overlay.

2.2. Areas of piping, parts, or components, adjacent to the identified overlay area shall be examined to verify that the entire defect area will be encompassed as necessary by the weld overlay and to validate any design assumptions relative to the structural integrity of the piping.

3. Weld Overlay Design 3.1. The thickness of the weld overlay reinforcement shall not exceed 1/4 inch. See thickness dimension Win Figure 1.

3.2. Evaluation of areas that require restoration by weld overlay shall consider the design life of the piping, future internal wall thinning in the weld overlay area, and shall be based on the design thickness as prescribed by ASME Section 1I1 2.

3.3. The weld overlay shall have a uniform width and extend 360 degrees circumferentially around the piping.

3.4. Unless otherwise established by design analysis, the weld overlay shall extend axially a distance of at least s in each direction beyond the area that requires restoration, where s is defined as:

R = average outer radius of the component

= nominal wall thickness of the component 3.5. Edges of the weld overlay shall be tapered to the existing piping surface to a maximum angle of 45°. See angle a shown in Figure 1.

3.6. Final configuration of the weld overlay reinforcement shall permit nondestructive examination as required in 5.1 and 5.2.

3.7. Except for the tapered edges, the weld overlay reinforcement shall have a uniform thickness.

3.8. Tensile strength of the weld filler metal used for the overlay shall be at least that specified for the piping base material.

The Callaway Repair/Replacement Program Is in accordance with the 1989 Edition of ASME Section Xi.

2 ASME Section 111, 1974 with Summer 1975 Addenda Is the Construction Code for the feedwater system.

ULNRC-04942 Atachmcnt Page 3 of 7 3.9. Design shall be in accordance with ASME Section III 3 and shall consider the weld overlay as afi integral portion of the piping upon which it is applied (not as a weld).

3.10. The allowable stress values of the base metal shall apply to the design of the deposited weld metal.

3.11. The following factors shall be considered In design of the weld overlay reinforcement:

3.11.1. The effects on the piping system of radial and longitudinal shrinkage caused by application of the overlay; 3.11.2. The effects on flexibility, stress concentration, and section properties of the added section thickness; 3.11.3. Stress concentrations resulting from existing and predicted piping internal surface configuration; 3.11.4. The effects of different coefficients of thermal expansion between the weld overlay filler metal and the base metal.

3.12. The effect of the weld overlay shall be reconciled with the original flexibility analysis required by ASME Section 1I1 3. Unless a lower stress intensification factor (SIF or l) is established, an SIF(i) of 2.1 shall be applied for overlays on straight pipe and adjacent welds; a stress multiplier of 1.7 shall be applied to the SIF(i) for standard elbows; and an SIF(i) of 2.1 shall be applied for tees and branch connections when the toe of the overlay is not less than 2.54Z.

from any branch reinforcement.

4. Installation 4.1. The entire surface area to which the weld overlay is to be installed shall be examined using either the liquid penetrant (PT) or magnetic particle (MT) test method. Acceptance criteria shall be in accordance with NC-250015300 3 for the specific product form that was examined (e.g., base material or weld metal).

4.2. The weld overlay reinforcement shall be installed in accordance with the Callaway Repair/Replacement Program.

4.3. The overlay weld metal shall be installed using a groove weld procedure qualified in accordance with ASME Section IX and Section lIlI.

4.4. The surface of the final overlay reinforcement shall be prepared by machining or grinding as necessary to permit performance of surface and wall thickness examination.

5. Examination 5.1. The completed weld overlay reinforcement shall be examined using liquid penetrant (PT) or magnetic particle (MT) test method. The acceptance criteria shall be in accordance with ASME Section III, NC-5300 3.

5.2. The weld overlay reinforcement and the base material below the reinforcement shall be examined by ultrasonic examination to verify acceptable wall thickness.

6. Documentation Use of this relief request shall be documented as specified in the Callaway RepairlReplacement Program.

3 ASME Section Ill, 1974 with Summer 1975 Addenda ho.

ULNRC.04942 Attachmcnt Pagc 4 of 7 Table 1: Feedwater Piping Areas That May Require Weld Overlay Reinforcement Area Description FAC ID No.1 &

2 NPS 3 Sch.

Mat.

Downstream area of A SIG 14" by 16" expander AE04-DE7E 16 80 CS Downstream area of C SIG 14" by 16" expander AE05-135E 1.6 80 Cs Downstream area of D SIG 14" by 16" expander AE05-CD7E 16 80 CS Upstream area of 45D elbow upstream of AEV0122 AE05-E645 14 80 CS Upstream area of 940 elbow downstream of AEV0123 AE05-AB590 14 80 CS Midspan area of A SIG sD bend AE04-E890 14 80 CS Midspan area of B SIG 5D bend AE04-C4590 14 80 CS Midspan area of C SIG 5D bend AE05-3590 14 80 CS Midspan area of D SIG 5D bend AE05-D890 14 80 CS Notes:

1. Usted FAC ID Numbers are those currently Identified in the Callaway FAC Program.

2. Figures 2 and 3 show location of areas by FAC ID No.

3. NPS is pipe size of area for weld overlay reinforcement.

Table 2: Feedwater Piping Wall Thickness Data 1 Design 2 Wear Rate RF1 1 3 RF12 3 RF13 4 RF14 4 FAC ID No.

Location Min (m ls/yr) measured measured projected margin projected margin AE04-DE7E Upstream 0.489 8.203 0.549 0.514 0.502 0.013 0.490 0.001 AE04-DE7E Downstream 0.680 7.590 0.687 0.687 0.676 o0.004 0.665

-0.015 AED4-E890 General 0.614 11.122 0.700 0.676 0.659 0.045 0.642 0.028 AE04-C4590 General 0.643 8.347 0.671 0.684 0.671 0.028 0.658 0.015 AE05-B5E Upstream 0.489 9:421 0.544 0.519 0.505 0.016 0.491 0.002 AE05-B5E Downstream 0.559 8.513 0.649 0.644 0.631 0.072 0.618 0.059 AE05-8590 General 0.643 12.603 0.650 0.663 0.644 0.001 0.625

-0.018 AE05-AB590 General 0.489 12.522 0.535 0.510 0.491 0.002 0.472

-0.017 AE05-CD7E Upstream 0.489 8.185 0.609 0.603 0.591 0.102 0.579 0.090 AE05-CD7E Downstream 0.680 7A34 0.693 0.685 0.674

• 0.006 0.663

.0.017 AE05-D890 General 0.614 10.950 0.655 0.649 0.633 0.019 0.617 0.003 AE05-E645 General 0.489 9.776 0.535 0.516 0.501 0.012 0.486

• 0.003 Notes:

1. Wal thickness values are in inches.

2. General design minimum wall was determined by analysis at each location. Structural integrity was verified by additional detailed analysis at specific locations where the measured wal thickness encroached on general design minimum wall thickness.

3. Anomalous UT readings are attributed to changes in inspection personnel and test equipment and are considered within acceptable tolerances. These variances do not adversely Impact the model for calculating projected wear.

4. Projected wall thickness is based on average wear rates determined by the Callaway FAC program. Wall thickness margin is the difference between the projected thickness and the design minimum.

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