ML20195G491
| ML20195G491 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 11/09/1998 |
| From: | Tulon T COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9811230012 | |
| Download: ML20195G491 (9) | |
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Commonwealth Edison Company Braidwood Generating Station
- a' Route al, Ikix 84 Braceville, IL 60io73X>19 Tel HI545&2801 November 9,1998 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington. D. C. 20555 - 0001 Braidwood Station, Unit 1 Facility Operating Licenses NPF-72 NRC Docket Nos. STN 50-456 i
Subject:
ASME Section XI Flaw Evaluation i
The purpose of this letter is t', transmit a flaw evaluation performed on an indication in the base metal of a Breldwood Station, Unit 1, Main Steam piping system elbow. The indication was identified during the ultrasonic examination of weld number IMS 01.01, a Main Steam elbow to safe-end weld. This weld was being examined as part of the preservice, baseline examination program conducted on welds which were newly installed during the ongoing Braidwood Station, Unit 1, steam generator replacement outage.
Weld IMS-07-01.01 is a new weld installed between the existing Main Steam elbow fitting and the new, replacement steam generator nozzle safe-end. As stated above, the indication in question is in the base metal of the elbow and was detected during the ultrasonic inspection of base material conducted prior to, and as preparation for, the ASME Section XI ultrasonic, angle beam, examination of the required volume of this weld.
l The elbow containing the laminar indication has been determined to be acceptable by evaluation. The evaluation conducted in accordance with ASME Section XI, subsection IWC-3122.4 is attached.
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I November 9,1998 U.S. Nuclear Regulatory Commission Page 2 1
Please address any comments or questions regarding this matter to Mr. T. W. Simpkin at 1
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.(815) 458-2801 extension 2980.
Respectfully, t y J.Tulo%n T-
' e Vice President raidwood Nuclear Generating Staticn i
Attachment:
Evaluation of Laminar Indications in IMS-07-01.01
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cc:
Regional Administrator-USNRC,RegionIII NRC Senior Resident Inspector-Braidwood Station NRC Senior Resident Inspector-Byron Station j
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Byron Project Mainager-NRR Braidwood Project Manager-NRR Office of Nuclear Safety-IDNS Nicholas Reynolds - Winston & Strawn i
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EVALUATION OF LAMINAll INDICATIONS IlEPOllTED FOlt P-MSC-453 FW2 (ISI NO. IMS-07-01.01) 1.0 BACKGitOUND During the preservice ultrasonic examination of"C" Steam Generator weld number FW 2, existing main steam elbow to new main steam generator safe end, an area ofintermittent laminar renectors was discosered. These reflectors were identified during the 0 base material inspection looking for laminar reDectors that would interfere with the required code angle beam inspection. These examinations were performed to support the ASME Section XI repair / replacement activities resulting from the Braidwood Unit 1 Steam Generator replacement project. The examination category for this Main Steam Piping weld is C-F-2, with Code Case N-408-2. The area encompassing these indications has been sized by 0 ultrasonic technique, and is located adjacent to the longitudinal and circumferential weld seams at the intrados area of the elbow (see Attachments 1 & 2). The elbow has been in service since 1988 and the indication is outside the Section XI required examination volume for a Category C-F-2 full penetration weld. The indication is likely to be the result of the steelmaking process where such indications are caused by impurities from the ingot which are trapped in the center of the plate as it is progressively rolled. In accordance with the laminar Haw sizing criteria ofIWA-3360, the area of a laminar Oaw is defined as 0.75 times the area of the square or rectangle that contains the detected flaw (s)(in this case, the area is 0.75 x 6.6 in. x 4.25 in. = 21.03 in2 ),
Because the laminar indication is located outside of the required preservice examination volume and in an existing component, the indication is subject to the rules ofIWC-3120,
" Inservice Volumetric and Surface Examinations" According to ASME Section XI (Reference 5.1) paragraph IWB-3514.6 and Table IWB-3514-3, the maximum allowable area oflaminar Daws for the thickness of the main steam piping is 2.9 in.2. Thus, by the code paragraphs applicable to the examination and its acceptance criteria, the indication is considered unacceptable. Those Daws considered to be unacceptable are allowed to be corrected by Repair (IWC-3122.2), Replacement (IWC-3122.3), or analytical evaluation (IWC-3122.4). The analytical evaluation provision ofIWC-3122.4 is used for the disposition of this laminar indication.
Although previous preservice and inservice examinations did not report any indications in the area, this Haw is considered to have existed since original construction. And, although the Code requirement (IWB-3514.6) for laminar indications states: "The area of allowable laminar Daws, as defined by IWA-3360, within the boundary of the examination zones shown in Figs. IWB-2500-8 through IWB-2500-11, shall not exceed the limits specified in Table IWB-3514-3", it has been decided that an evaluation is warranted even though the Oaw exists entirely outside the boundary of the examination zone.
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2.0 FLAW EVALUATION APPROACil
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l The NDE report attached to this evaluation indicates that the laminar reflectors are located in a plane whose depth ranges from 0 68in. to 0.78in., near the center of the elbow wall.
j The elbow has a minimum measured wall thickness of 1.44 inches.
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The piping examination category for the main steam piping is C-F-2. Code paragraph number IWC-3514 is reserved to address this category, but the rules are still in course of preparation. Until such time that the standards for Class 2 piping are prepared and incorporated into the code, the standards for Class I piping in IWB-3514 are used.
l Paragraph IWB-3514.6 contains the rules for allowable laminar flaws, and in turn l
references Table IWB-3514-3. Although the reflectors are aligned in a laminar plane, the l
indication was conservatively characterized as projected flaws with radial depth in the axial and circumferential planes as well as a laminar flaw. This is because the laminar plane's position throughwall changes from 0.68" to 0.78",
The indication was conservatively evaluated relative to four different criteria. First, the ductile failure limits of the original code of construction (Section 111) were considered, and I
then, as stated above, treated as a planar flaw, in three orientations. The first orientation is a planar flaw projected on to a radial and circumferential plane, the second is projected on to a radial and axial plane, and the third is laminar.
2.1 Eraluation ofIWB-3514 For this evaluation, the criteria oflWA-3340 was used to characterize the condition. Due to the varying depth of the laminar reflectors, (0.68 in. to 0.78 in.) the projections of the indication onto planes normal to the principal stresses were defined as two planar flaws in the circumferential radial and axial radial direction as shown below. The dimensions of projected flaws are as defined in IWA-3300.
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The circumferential radial and axial radial projections of the Daw were be evaluated against the criteria in IWB-3514.2, and for the purpose of this evaluation, should the evaluation of the flaw meet the limits in Table IWB-3514-1, the flaw is considered acceptable.
3.0 FRACTURE MECilANICS EVALUATION 3.1 Ductile Failure Evaluation The elbow is made of SA-234 WPB which has an allowable stress of 15 ksi at 600 F. The outside diameter of the Otting is 32 inches and the design pressure is 1185 psi (Reference 5.3). The lamination is parallel to the longitudinal pressure stresses, hoop stresses, and pipe bending stresses, and as such will not tend to propagate. The radial pressure stresses will be compressive on the Daw plane. For the design of the main steam piping, the hoop stress is the predominant stress (Reference 5.4). Based on the ASME Section 111 code pressure calculations (NC-3641.1), the minimum thickness, based on hoop stress, is 1.23 inches.
Since the depth of the indication varies from 0.68 to 0.78 inches, it can be conservatively assigned a through wall thickness of 0.10 inches. Deducting this thickness from the minimum thickness reported in Reference 5.5, leaves a 1.34 in. pipe wall thickness which is greater than the minimum wall thickness required by the pressure calculation. Therefore the indication meets the ductile failure limits of Section 111.
3.2 CircumferentialRadialFlaw Evaluation The aspect ratio (a/l) of the circumferential radial Daw is 0.05/4.25 = 0.012. Per Table IWB-3514-1, the allowable Daw as a percentage of pipe thickness for inservice examination for a subsurface flaw is interpolated for a pipe thickness of 1.44 in, and an aspect ratio of 0.012. Since S/a (depth from the surface divided by the Daw thickness)is greater than one by inspection, Y=1 per note 4 of Table IWB-3514-1.
For 1 in. thickness at 0.012, the interpolated value is 12.7 For 2 in thickness at 0.012, the interpolated value is 10.9 Interpolating for 1.44 in., the resulting allowable is 11.9 Therefore, since 0.119 = alt, the allowable a = 0.17. The actual a of the circumferential radial Daw is 0.05 in. Since 0.05 < 0.17, the circumferential projection is acceptable per Table IWB-3514-1.
3.3 AxialRadial Flaw Evaluation l
l The aspect ratio (a/l) of the axial radial Daw is 0.05/6.6 = 0.008. Per Table IWB-3514-1, l
the allowable Daw as a percentage of pipe thickness for inservice examination for a l
subsurface flaw is interpolated for a pipe thickness of 1.44 in. and an aspect ratio of 0.008.
l Since S/a (depth from the surface divided by the Daw thickness) is greater than one by inspection, Y=1 per note 4 oflable IWB-3514-1.
For 1 in. thickness at 0.008, the interpolated value is 12.6 For 2 in. thickness at 0.008, the interpolated value is 10.8 3
Interpolating for 1.44 in., the resulting allowable is 11.8 Therefore, since 0.118 = a/t, the allowable a = 0.17. The actual a of the circumferential flaw is 0.05 in. Since 0.05 < 0.17, the circumferential radial projection is acceptable per Table IWB-3514-1.
3.4 Laminar Flaw Evaluation The lamination is parallel to the longitudinal pressure stress, hoop stress and pipe membrane and bending stress fields, and as such will not tend to propagate. The radial j
stresses resulting from internal pressure would tend to compress the lamination. Structural and pressure integrity is assured because there are no tensile loads to open the lamination.
The effect on the pipe structural integrity is therefore minimal.
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4.0 CONCLUSION
S The indication has been evaluated relative to all applicable criteria, and found to be acceptable to the requirements ofIWB-3600. In addition, the lamination is parallel to the longitudinal pressure stress, hoop stress, and pipe membrane and bending stress, and as J
such will not tend to open up or propagate.. The lamination will not affect the radial stresses resulting from internal pressure, since these would tend to close the lamination. The structural integrity of the piping is not affected. Therefore, the recommended disposition is to leave the flaw as is.
5.0 REFERENCES
5.1 ASME Section XI,1983 Winter Addenda.
5.2 Comed Ultrasonic Examination Procedure NDT-C-2, Rev. 24 5.3 Drawing IC-MS-18, Rev. E, Main Steam System Piping Isometric Drawing 5.4 Main Steam Pipe Stress Calculation EMD 055269, Rev. 8, Addendum E 5.5 Preservice Inspection Report for FW 2; P-MSC-453 FW2 (ISI NO. IMS-07-01.01) l I
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