ML18152A370
ML18152A370 | |
Person / Time | |
---|---|
Site: | Surry, North Anna ![]() |
Issue date: | 05/13/1999 |
From: | Hartz L VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
References | |
99-222, NUDOCS 9905240004 | |
Download: ML18152A370 (18) | |
Text
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VIR~INIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 Mi,;.y 13, 1999 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY Serial No.
NL&OS/GDM Docket Nos; License Nos.
NORTH ANNA AND SURRY POWER STATIONS UNITS 1 AND 2 ASME SECTION XI INSERVICE, INSPECTION PROGRAM REQUEST FOR APPROVAL - CODE CASE N-597 99-222 RO 50-280, 281 50-338, 339 DPR-32, 37 NPF-4, 7 ASME Boiler and Pressure Vessel Code,Section XI, IWA-4000, provides the process for assessing a component for continued service after a defect has been removed. This provision stipulates that where the section thickness has been reduced below the minimum design thickness, the component shall be repaired: As an alternative, the component may be evaluated and accepted in accordance with the design rules of either the construction code or ASME Section Ill.
As an alternative to the requirements of IWA-4000, Virginia Electric and Power Company (Virginia Power) proposes to use the provisions of ASME Section XI Code Case N-597 for the analytical evaluation of Class 1, 2 and 3 carbon and low alloy steel piping components subjected to wall thinning as a result of flow accelerated or other corrosion phenomena.
The ASME Code Committee approved Code Case N-597, "Requirements for Analytical Evaluation of Pipe Wall Thinning,Section XI, Division 1,"
on March 2, 1998. A copy of the Code Case is attached. Code Case N-597 has not yet been approved for use in Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1." However, provisions stated in footnote 6 to 10 CFR 50.55a provide for the use *of other Code Cases upon request, if approved by the Director of the Office of Nuclear Reactor Regulation pursuant to 10 CFR 50.55a(a)(3).
Therefore, in accordance with 10 CFR 50.55a(a)(3)(i), Virginia Power requests NRC approval for the use of ASME Section XI Code Case N-597 as an alternative to the requirements of the ASME Boiler and Pressure Vessel Code,Section XI; IWA-4000 relating to the evaluation of a component where the thickness has been reduced below the minimum design thickness.
The NRC has previously approved a 50.55a(a)(3) request to use Code Case N-597 for Northeast Nuclear Energy Company's Millstone Units 2 and 3 as documented in the safety evaluation report included in a letter dated February 23, 1999. The use of the analytical evaluation criteria specified in Code Case r-9905240004 990513-----~---
PDR ADOCK 05000280 G
'Ii Ll ~l rj0 I
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N-597 to evaluate wall thinning will provide a level of safety and quality consistent with the requirements of Section XI, IWA-4000.
If you have any questions or comments, please contact us.
Very truly yours,
~~ef L. N. Hartz Vice President - Nuclear Engineering and Services Commitments made in this letter: None.
Attachment cc:
U.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. RA. Musser NRC Senior Resident Inspector Surry Power Station Mr. M. J. Morgan NRC Senior Resident Inspector North Anna Power Station
Attachment ASME Code Case N-597, "Requirements for Analytical Evaluation of Pipe Wall Thinning,Section XI, Division 1," dated March 2, 1998 North Anna and Surry Power Stations Units 1 and 2 Virginia Electric and Power Company
.i I_
CASE N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE Approval Date: March 2, 199.8 See Numerical Index for expiration and any reaffirmation dates.
Case N-597 Requirements for Analytical Evaluation of Pipe Wall Thinning Section XI, Division 1 Inquiry: What requirements may be used for analyt-ical evaluation of Class 1, 2, and 3 carbon and low-alloy steel piping items subjected to internal or exter0 nal wall thinning as a result of flow-accelerated or other corrosion phenomena?
Reply: It is the opinion of the Committee that the following rules may be used.
-1000 SCOPE This Subsection provides requirements for analytical evaluation of Class l, 2, and 3 carbon and low-alloy steel piping items (e.g., piping and fittings) with internal or external wall thinning as a result of corrosion phenomena, including flow-accelerated corrosion. These requirements are applicable to nonplanar flaws.
-3000 ACCEPTABLE STANDARDS
-3100 Preservice Examination Piping items examined prior to. commercial service are acceptable for service when the measured wall thickness meets the requirements of the Construction Code.
-3200 INSERVICE EXAMINATION
-3210 General Upon completion of pipe wall thickness examinations, the predicted remaining wall thickness, tp, at the time of the next scheduled examination shall be calculated for piping items under evaluation. The predicted re-maining wall thickness is the spatial distribution of wall thickness remaining throughout the piping item and may have a unique value at any given location on the piping item. Alternatively, the minimum predicted 1175 value, tp*min, may be used in determining acceptability for continued service. Methods of predicting the rate of wall thickness loss and the value of tp shall be the responsibility of the Owner.
-3220 Acceptance
-3221 Acceptance By Examination Piping items whose examination and evaluation re-sults reveal that tp meets the acceptance standards of
-3500 or the Construction Code are acceptable for continued service. When these criteria are not met, the alternatives of. -3222, -3223, and -3224 may be used.
Fig. -3220-1 shows a flow chart of the acceptance alternatives.
-3222 Acceptance by Repair/Replacement Activity Piping items whose thickness is less than that required by -3500, -3223, -3224 shall be corrected by a repair/
replacement activity.
-3223 Acceptance by Engineering Evaluation Piping items whose examination and evaluation re-sults reveal that the criteria of -3221 are not satisfi~d may be accepted for continued service by engineering,
evaluation.
(a) For Class 1 piping items, this evaluation shall be conducted in accordance with evaluation methods and criteria developed by the Owner.
(b) For Class 2 and 3 piping items, an acceptable evaluation method and criteria are provided in -3600.
Alternative evaluation methods and criteria may be specified by the Owner.
-3224 Acceptance by Reduction of Time to Ne.xt Examination Piping items whose examination and evaluation re-sults reveal that the criteria of -3221 are not satisfied, are acceptable for continued service when the time to the next examination for the affected piping. items is reduced such that the acceptance criteria of -3221 or
-3223 are met using the Ip for the reduced examination period.
SUPP. 12-NC
CASE (continued)
~-597 SUPP.12-NC Acceptance standards
-3500 Reduce time to next inspection
-3224 CASES OF ASME BOILER AND PRESSURE VESSEL" CODE No Examination results Predict thickness at next examination, fp
-3210 No Perform engineering evaluation
-3223 Yes Acceptance Yes No FIG. -3220-1 ACCEPTANCE FLOW CHART 1176 Repair/
replacement acitvity
-3222
~
CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL. CODE Req"'ired Thicknen Piping item Reference Straight pipe
-3500(a)(1)
Elbows
-3500(all1 l Reducers1
-3500(a)(2)
Tees1
-3500(a)(3)
Branch
-3500(a)(3) connections 1 Designed item
-3500(a)(4)
Other items
~500(bl 1 Alternate of -3500(a)(5) may be used.
Thickness Limit Code class Reference 1
-3SOO(cl 2
-3500(d) 3
-3500(e)2 2Alternate criteria may be developed in accordance with -3600(f).
Predicted wall thickness, tp No Go to -3222,
-3223, or
-3224 Yes Acceptance FIG. -3500-1 WALL THICKNESS ACCEPTANCE STANDARD FLOW CHART
-3500 WALL TIDCKNESS ACCEPTANCE STANDARDS (2) For the small end of concentric and eccentric re-ducers, tp shall be not less than 0.875 tnom for the pipe size A flow chart for the acceptance standards is shown at the small end. For the large end, the large end transition in Fig. -3500-1.
and the conical portion; tp shall not be less than 0.875 tnom (a) A Class l, 2, or 3 butt welded pipe, elbow, for the pipe size at the large end. For the small end transi-branch connection, or reducer piping item is acceptable - * --,, tion, the required thickness shall be gradually reduced from for continued service without. further evaluation when that required at the large end to that required at the small tp at all locations on the piping item meets the following end (see Fig. -3622-1).
requirements.
( 3) For tees and branch connections, tp shall be (1) For straight pipe and elbows purchased to a not less than 0.875 tnom for the same size pipe for nominal pipe specification with an allowable wall thick-regions outside the limits of reinforcement required by ness undertolerance of 12.5%, tp shall be not less than the Construction Code used in the evaluation. For '
0.875 t00m except that, for Class I short radius elbows, regions within the limits of reinforcement, tp shall be an evaluation shall be conducted to show that the not less than the thickness required to meet the branch..
requirements of NB-3642.2 are met.
reinforcement requirements of. the Construction Code.
- 1177 SUPP. 12-NC
~
CASE (ccmtinued)
N-597*
I CASES OF ASME BOILER~ PRESSURE VESSEI,; CODE
( 4) For regions of piping items designed to specific wall thickness requirements, including designed weld counterbores and regions with integral reinforcement, tp shall be not less than the minimum design thickness, including tolerances and excluding any corrosion allow-ances, specified in the original design analysis for the piping item.
(5) As an alternative to the requirements of
-3500(a)(2) and -~500(a)(3), for reducers, tees, or branch connections purchased to fitting standards allowed in Table NB-3132-1 and for which baseline as-installed thickness measurements exist, tp shall not be less than 0.875 times the as-installed thickness measurements,.
except that the thickness shall not be less than 0.875 tnom*
( b) Acceptance criteria for Class l, 2, and 3 pumps, valves, flanges, reducing elbows, socket weld fittings, and any other piping items not covered by -3500(a) shall be the responsibility of the Owner.
(c) For any Class 1 piping item, when Ip at any location is less than 0.3 tnom, further evaluation is beyond the scope of this Case.
(d) For any Class 2 piping item, when tp at any location is less than 0.2 tnom, further evaluation is beyond the scope of this Case.
(e) Except as provided in (j) below, for any Class 3 piping item, when tp at any location is less than 0.2 tnom or 0.5 tmin* whichever is less, further evaluation is beyond the scope of this Case. The value of tnun shall be determined in accordance with -3600.
(f) As an alternative to -3500(e), decreased wall thickness, including local through-wall leakage in Class 3 piping items whose maximum operating temperature
- does not exceed 200°F and whose maximum operating pressure does not exceed. 275 psi,*m!lY be accepted.
Evaluation methods and acceptance criteria shall be specified by the Owner.
-3600 ANALYTICAL EVALUATION FOR CLASS 2 AND CLASS 3 PIPING ITEMS
-3610
- General Requirements (a) Analytical evaluatjons shall be conducted in ac-cordance with Construction Code. Later Code Editions and Addenda may be used. Use of later Code Editions and Addenda shall be reviewed for acceptability to the regulatory and enforcement authorities having jurisdic-tion at the plant site.
(b) Analytical evaluations shali be conducted using
- the predicted wall thickness, Ip, at the next examination SUPP.12-NC 1178 of the piping item. The methods used to determine tp are the responsibility of the Owner.
(c) A piping item is acceptable for continued service if the minimum pipe wall thickness. branch reinforce-ment requirements, and piping stress criteria of the Construction Code used in the evaluation are met for all specified loading conditions.
(d) As an alternative to -36IO(c). butt welded pipe, elbow, branch connection, and reducer piping items may be evaluated in accordance with -3620.
(e) Alternative evaluation of pumps, valves, flanges, and other piping items are the responsibility of the Owner.
(f) Piping items under evaluation with tp, exceeding the acceptance standards. of -3500 and satisfying -3600 shall be monitored for continued degradation. The fre~
quency and means.of monitoring for degradation are the responsibility of the Owner.
-3620 EVALUATION OF PIPE, ELBOWS, BRANCH CONNECTIONS, AND REDUCERS
-3621 General Requirements (a) The evaluation shall meet the requirements of
-3622 and -3623.
(b) For a branch connection or tee, the region within the limits of reinforcement defined in the Construction Code shall meet the requirements of -3624.
(c) Evaluations shall be conducted using the appro-priate piping equations, loadings, load combinations, allowable material properties, and other acceptance stan-dards from the Construction Code used in the evaluation, except as specifically modified by this Case.
( d) When the ratio Rltp is greater than 50, the potential for buckling of the thinned region shall be evaluated.
Evaluation methods and acceptance criteria shall be specified by the Owner.
-3622 THICKNESS EVALUATION
-3622.1 Evaluation for Minimum Wall Thickness (a) Except as provided in -3622.l(b), the value of tP at any location shall not be less than 90% of the minimum wall thickness of the piping item, tmim required for design pressure, defined in the Construction Code used in the evaluation, exclusive of any additional corrosion allowance.
e CASE (continued)
N-597 CASES OF ASME BOU.ER AND PRESSURE VESSEL-CODE
( 1) For straight pipe, bends, and elbows, tmin shall be detennined by:
PDo tmin=---
2(S + yP)
(2) For concentric and eccentric reducers, tmin at each end shall be equal to tmin of straiglit pipe of the same nominal size as the reducer end. For. the conical portion of the reducer and the transition at the large diameter end, tmm shall be that of the large diameter end. A gradual transition in tmm shall be assumed for the transition at the small end (see Fig. -3622-1).
( 3) For branch connections and tees, except at regions providing reinforcement of the opening required by the Construction Code used in the evaluation, tmin shall be as required for straight pipe.
(b) When tp is less than 0.9 tmin at any location, additional evaluations may be conducted to determine the allowable local thickness, ta1oc, sub)ect to the limita~
tions in (c). The thinned region and the parameters that define the depth and extent of thinning are illustrated in Fig. -3622-2. The allowable local thickness shall be detennined in accordance with any one of the methods in -3622.2, -3622.3, -3622.4, -3622.5, or -3622.6.
( c) Local thinning evaluation shall not be allowed for the following:
( 1) A region adjacent to any branch connection on the run piping, unless the distance between the center of the branch connection and the edge of the thinned area predicted to be less than tmin exceeds D;,
where D; is the nominal inside diameter of the branch connection and L,,, is the maximum dimension of the thinned region less than 'min*
(2) At the small end trimsition of a reducer.
(3) Inner portion of elbows and pipe bends (Fig.
-3622-3), excluding a region within 1.5"'1Rnamtnam of the butt welds, unless the tmin in the evaluation of
-3622.2, -3622.3, or -3622.4 is replaced by t' min* de-fined by:
(
0.5
),.
t' min = 0.5 +
. tmin, pipe cos8 1+--
(Rb!Ro)
-3622.2 Local Thinning -
Limited Transverse Extent (a) The evaluation procedure shall consider the depth and extent of the affected area and require that the 1179 wall thickness exceed tnun for a distance that is the greater of 2.5..JR00mtnam or 2Lm. avg between adjacent thinned regions, where Rnam is the mean radius of the* piping item based on nominal wall thickness and Lm.. avg is the average of the extent of Lm below tmin for the adjacent areas (see Fig. -3622-4). Alternatively,
. the adjacent thinned regions shall be considered a single thinned region in the evaluation.
(b) Provided that the transverse.extent of wall thin-ning predicted to be less than tmin* lmci), is less than or equal to "'1Rmintmin, the allowable local thickness, ta1oc, shall be determined from Table -3622-1, where RDUn is the mean radius of the piping item based on the minimum wall thickness tmin* For straight pipe, Table -3622-1 may be used when Lmct) exceeds
..JRmintmin* except that. an additional thickness tb shall be added to the value determined from Table -3622-1.
( c) This approach shall not be used to'. evaluate a reducer.
-3622.3 Local Thinning -
Limited Axial and Transverse Extent (a) When the maximum extent of wall thinning, L,,,,
- for which thickness is predicted to be less than tmin is less than or equal to 2.65..JRmintmin, and tnam is greater than 1.13 tmin* ta1oc shall be determined by satisfying (b) below and (c) or (d) below. This approach requires that adequate reinforcement be available surrounding the thinned area in accordance with (c) or (d) below.
This evaluation approach is not applicable for the following conditions:
( 1) Thinned areas adjacent to branch connections, when the reinforcement zone, for the thinned area would overlap the required reinforcement of the branch connection.
(2) Thinned areas for which any portion of the reinforcement zone would lie on the conical or small diameter transition zone of a reducer.
( 3) Adjacent thinned areas qualified by this ap-proach when the reinforcement zones associated with each area would overlap.
-* ( b) The-thickness of the.remaining pipe wall at the thinned section is adequate if the following equation is satisfied.
ta1oc 0.353L.n
-~---
'min
""Rmintmio
( c) If there is a surrounding reinforcement zone with predicted thickness of at least loom for a minimum SUPP.12-NC
e CASE (continued)
N-59_7 CASES OF ASME BOILER AND PRESSURE VESSEL CODE dimension of U2 in all directions, reinforcement for the thinned area shall satisfy the following equation.
ta1oc
( 1.5--.JRmintmin ) (tnom
)
-~1-
~-1 tmin L
tmin (d) As an alternative to (c) above, the reinforcement adjacent to the thinned area shall justify the following equation.
ta1oc (0.935Arcin)
-~ 1-tmin L,,,tmin
-3622.4 Local Thinning -
Unlimited Transverse Extent (a) The evaluation shall include consideration of the depth and extent of the.* affected area less than tmin*
The wall thickness shall exceed tnun for an axial distance the greater of 2.5..JRnamtnam or 2 I.ma.max between adjacent thinned regions at each circumferential location on the piping item (see Fig. -3622-5). Alternatively, the adjacent thinned regions shall be considered a single thinned region in the evaluation.
(b) Thickness ta1oc shall be determined from Table
-3622-1.
(c) This approach shall not be used to evaluate a reducer.
-3622.5 Local Thinning -
Elbows and Bent Pipe (a) For locations farther than...)Rmintrrun from welds to adjacent piping items, the predicted thickness on the outer portion of an elbow or bend may be less than rmin for straight pipe. The local allowable thickness at each location shall be determi_ned by:
where 0.5 ta1oc
-- ~ 0.5 + ----
fmin, pipe cos8 L+--
. (~)
Rrrun
_ Rb /Rmin = ratio of elbow bend radius to mean pipe radius, based on tmin for the same size pipe SUPP. 12-NC
-3622.6 Local Thinning -
Central Portions of Concentric Reducers (a) For the conical portion of concentric reducers, the local allowable thickness less than tmin shall satisfy the following equation:
ta1oc do!Di
--~--
tmin, 1 cosa.
( b) For the flared transition at the small end of a concentric reducer, the local allowable thickness shall be gradually reduced from the. value determined at the conical end of the flare to tmin for the small end of the reducer.
(c) This approach shall not be used to evaluate eccentric reducers.
-3623 PIPING STRESS EVALUATION
-3623.1 Evaluation Requirements (a) The effects of piping stresses shall be evaluated in accordance with the equations of the. Construction Code used in the evaluation. If the piping analysis is based on nominal piping thickness, allowable. stresses may be multiplied by 1.143. Consideration shall be given to changes in the pipe metal. area, pipe inside area, section modulus, and stress indices or stress
. intensification factors, as described in -3623.2, -3623.3 and -3623.4. The effects of cyclic operating conditions shall be addressed in accordance with -3625.
(b) The piping stress evaluation, shall be based on the predicted thickness at each cross section of the piping item that exhibits significant thinning or is affected by a change in stress index or stress intensifica-tion factor. Alternatively, the evaluation may be based on the limiting cross section.
- *-3623.2 - Noiriinar Longitudinal
- Pressure Stresses 1180 (a) The pipe metal area and the pipe inside area, for the thinned cross section might result in stresses different from those of the piping stress analysis of record.
(b) For simplified analysis, the piping item may be assumed. to be unifonnly thinned with a thickness of tp, min* For this approach, the nominal longitudinal pressure stress shall be determined by:
e CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE
- When evaluating reducers, the large and small ends shall be evaluated separately. For the large end, tp.min shall be detennined from all locations for the large
- end and conical sectio~. For the small. end, tp.min for the entire reducer shall be used.
( c) Detailed stress analysis may be conducted based on the complete set of measurements around the thinned cross-section of the piping item. The nominal longitudi-nal pressure stress, Sp, shall be determined by:
( J) To evaluate piping at a branch connection beyond the limits of reinforcement, it shall be assumed that the entire region within limits of reinforcement is at thickness tmin for the unreinforced pipe section, with the outside surface at the pipe nominal outside radius.
If excess reinforcement is available within the limits of reinforcement, the excess metal area may be included in Ap.
(2) When evaluating the longitudinal pressure stress in the central cone of a reducer, the stress shall be detennined based on the local radius at the cross section and the local tp at and adjacent to the cross section of interest, except that the resulting stress shall be multiplied by a factor of 1/cosa.
(d) When using Code Editions and Addenda that require use of stress indices, the nominal longitudinal stress determined in accordance with (b) and (c) above shall be doubled.
-3623.3 Nominal Longitudinal Bending Stresses
( a) Thinning of the piping item cross-sectional area the large end, tp. min shall be detennined from all locations for the large end and conical section. For the small end, tp, min for the entire reducer shall be used.
(c) Detailed stress analysis may be conducted based on a complete set of measurements around the thinned cross section of the piping item.
(d) When evaluating thinning at the cross section of a branch connection, the requirements of -3623.2(c)(l) shall be met.
-3623.4 Stress Intensification Factors and Stress Indices The local piping item wall thickness could affect the stress indices or stress intensification factors used in detennination-of the effective piping stress at a branch connection. When reduced wall thickness could increase these factors, the effect shall be considered by using a reduced piping item thickness detennined in accordance with (a), (b), or (c) below.
(a) Except as allowed in (b) or (c) below, stress intensification factors or stress indices for a piping item shall be based on the assumption of uniform wall thickness, using a value of tp. min and an associated mean pipe radius in the formula for these factors.
(b) As an *alternative (a) above, the factors may be based on the average tp of the piping item excluding branch reinforcement zones, except that predicted thick-ness at locations within a distance of twice the pipe nominal wall thickness from butt welds to adjacent components need not be considered. For reducers, the average tp of the small end shall be used with. the small end diameter to determine the factor.
(c) As an alternative to (a) or (b) above, stress analysis of thinned piping items may be conducted to show the effects of wall thinning and the distribution of stresses on an affected piping item.
-3624 EvaluatiQn of Branch Connections might result in bending stresses different from those
-3624.1 The region of branch connections and tees of the piping stress analysis of record. The nominal within limits of reinforcement. of the Construction longitudinal bending stress, Sb, for the various loading Code used in the evaluation shall be evaluated in conditions and *-load**** combinations- -shall
- be.--deter- -** *.. accordance with -3624;2-or -3624.3.
mined by:
(b) For simplified analysis, the piping item section modulus may be based on a uniformly thinned section with thickness tp.min* When evaluating reducers, the large and small ends shall be evaluated separately. For 1181
-3624.2 Branch Connections Not Requiring Reinforcement
( a) The region on the piping run shall be evaluated in accordance with the requirements of -3622 and ~3623, without consideration of the branch connection, except that tp within a region of radius of D; of the branch pipe from the center of the branch connection shall not be less than tmin for the pipe run.
SUPP.12-NC
CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE (b) The. branch piping shall be evaluated in accord-ance with the requirements of -3622 and -3623.
-3624.3 Branch Connections Requiring Reinforcement (a) Branch reinforcement requirements shall be deter-mined in accordance with the Construction Code used in the evaluation.
(b) For the region of the piping run thii,t provides branch reinforcement, the value of tp at any location shall not be less than tnun for the nominal pipe run plus any required reinforcement at that location.
( c) For the region of the branch pipe that provides branch reinforcement, tp shall not be less than tmin for the branch pipe plus any required reinforcement.
-3625 Evaluation for Cyclic Operation (a) For piping items with tp, min not less than 0.75 tnom and subject to no more than.150 equivalent full temperature cycles at the time of the next examination, in accordance with the Construction Code
- used in the evaluation, piping stress equations that include thermal expansion and anchor movement stresses need not be evaluated.
(b) For piping items not meeting the requirements of -3625(a), when the design includes consideration of thermal expansion stresses, the allowable stress range for expansion stress shall be determined in accordance with the Construction Code used in the evaluation, except that the stress intensification factor, i, shall be revised to take into account the geometry of the thinned region. As an alternative to establishing a revised stress intensification factor, the stress range reduction factors of Table -3625-1, which are based on an increase in the stress intensification factor by a factor of 2 over the life of the component, may be used.
( c) The potential for local overstrain in the thinned region for the combination of maximum sustained plus thermal expansion stresses shall be considered. Sus-tained loads include pressure, weight, and other sus-tained mechanical loads. Local overstrain is defined in NC-3672.6{b). Evaluation* methods and*-acceptance criteria shall be specified by the Owner.
-3626 Nomenclature/Definitions A0 = total cross-sectional area of pipe based on
'ITD 2 nominal outside diameter, --
0
, in.2 4
A;=predicted inside cross-sectional area.for a pipe that has experienced wall thinning, in.2 SUPP.12-NC 1182 Am= predicted metal cross-sectional area for a pipe that has experienced wall thinning. in. 2 Ap = predicted metal cross-sectional area of pipe, in.2 Arein =the reinforcement area available in the pipe wall based on the predicted thickness distri-bution in excess of tmin and within the limits of reinforcement of the Construction Code for an opening with diameter Lm at the region of local thinning. in. 2 D0 = nominal outside diameter of piping
- item (e.g., 10.75 for NPS 10 pipe), in.
d0 = maximum outside diameter of a reducer at the thinned location, in.
D1 = outside diameter at the large end of the reducer, in.
D;=nominal inside diameter of a branch connec-tion, in.
f = stress range reduction factor i = stress intensification factor of the Construc-tion Code (not less than 1.0).
lmin = predicted minimum moment of inertia of the thinned pipe about the neutral axis of the pipe section, considering all orientations of the section neutral axis, in.4 L = maximum extent of a local thinned area with wall thickness less than fnom* in.
Lm = maximum extent of a local thinned area with wall thickness less than tmim in.
LmraJ = maximum axial extent of a local thinned area with wall thickness less than tmin* in.
Lma, max= maximum of the axial extents of two. adja-cent local thinned areas with wall thickness less than trrun* in.
Lmro=maximum transverse extent of a local thinned area with wall thickness less than trrun* in.
Lm, avg= average of the extents of thickness less than tmin for two adjacent thinned areas, in.
Mb=resulting bending moment from the design analysis of record for each loading condition under consideration, in-lb
- .P.=design pressure, psi Rb =bend radius of an elbow to the elbow center line, in.
R0 =nominal outside radius (e.g., 2.25 for NPS 4 pipe), in.
Rmax = radius to the nominal outside surface of the pipe plus the nominal distance between the center of the pipe and the neutral axis, in.
Rnun = mean radius of piping item based on the nominal outside radius and the minimum
CASE (continued)
N-597 CASES OF ASME BOU.ER AND PRESSURE VESSEL CODE Large end transition zone ct--- ------
GENERAL NOTE:
Small end transition zone Central conical section Transition zones extend from the point on the ends where the diameter begins to change to the point on the central cone where the cone angle is constant.
FIG. -3622-1 ZONES OF REDUCER wall thickness (e.g., 7.85 for NPS 16 pipe with tniin = 0.30 in.), in.
Rnom = mean radius of piping item based on the nominal radius and thickness (e.g., 6.75 for NPS 14 XS pipe with tnom = 0.5 in.), in.
S = allowable stress for piping item, including joint efficiency factor, E, if applicable, psi.
Sb= maximum nominal bending stress at the thinned section, psi.
SP = nominal longitudinal pressure stress, psi.
ta1oc = allowable local thickness, in.
tb = uniform thickness, of piping item, required by the Construction Code; to withstand sus-tained and occasional bending loadings in the absence of pressure, thermal expansion, and anchor movement loadings, in.
tmm = minimum wall thickness required by the Construction Code to sustain pressure, ex-clusive of tolerances and any allowances for corrosion, in.
tmin. 1 = tmin for large end of a reducer, in.
tmin. pipe= tmm for straight pipe, in.
1183 t' min= adjusted minimum thickness for inner por-tion of an elbow, in.
tnom = nominal thickness of pipe or fitting specified in the applicable industry standard for the piping item. For items designed to specified minimum thickness, the nominal thickness is the design thickness, including corrosion allowance and excluding tolerances, in.
tp = distribution of predicted local thickness of a piping item at the next scheduled examina-tion, in.
tp, min= minimum predicted local thickness of a
- piping item at the next scheduled examina-tion, in.
y = factor required by the Construction Code used in the evaluation Znm = predicted minimum section modulus for the thinned section, including consideration of the shift of the neutral axis of the thinned pipe section, lnur/RIIIJIX, in.3 a= maximum cone angle at the center of a reducer, degree SUPP.12-NC
e CASE (continued)
N-597 tnom SUPP.12-NC CASES OF ASME BOILER AND PRESSURE VESSEL CODE Axial direction
~
1 Transverse
(~oop direction)
FIG. -3622-2 ILLUSTRATION OF FLOW-ACCELERATED-CORROSION WALL THINNING 1184
Extrados I
L e
/
I I
CASES OF ASME BOILER AND PRESSURE VESSEL CODE
/
/
-- -~
Outer portion In er pojion Bend radius FIG. -3622-3 ELBOW AND NOMENCLATURE 1185 CASE (continued)
N-597 SUPP.12-NC
I e
e CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE t ~ tmin in surrounding area Xij = minimum distance between areas i and j Lm,; = maximum extent of thinned area i Lm, avg = 0.5 Lm, i + Lm, j Area 3 tp, 3 < tmin GENERAL NOTE:
Combination-of adjacent-areas into an-equivalent single area shall be.based on dimensions and extents prior to combination.
FIG. -3622-4 SEPARATION REQUIREMENTS FOR ADJACENT THINNED AREAS SUPP. 12-NC 1186
e CASES OF ASME BOU.ER AND PRESSURE VESSEL; CODE Xq ~ minimum distance between areas i and j at any circumferential location on pipe Lm(al, I = maximum extent of thinned area i in axial direction Lmax = maximum of the extents Lmlal,; and Lmlal, j of two adjacent areas NOTES:
CASE (continued)
N-597 Axial Direction t ~ tmin in surrounding area 1
Lmla),4 (1) Areas need not be combined into single areas based on separation in the transverse direction, provided that transverse extents of individual adjacent thinned areas.do not overlap.
(2) Combination of adjacent areas into an equivalent single area shall be based on dimensions and extents prior to any combination of adjacent areas.
FIG. -3622-5 SEPARATION REQUIREMENTS FOR ADJACENT THINNED AREAS 1187 SUPP.12
CASE (continued)
N-597 SUPP. 12-NC e
CASES OF ASME BOILER AND PRESSURE VESSEL CODE TABLE -3622-1 Allowable Local Thickness Lmw taioct.nin
..J Rmint.nin
- 3b22.2
- 3b22.4 0
0.100 0.100 0.20 0.100 0.2bl 0.23 0:100 0.300 0.2b 0.100 0.375 0.32 0.100 0.477 0.38 0.100 0.551 0.45 0.100 O.blb 0.50 0.100 O.b51 O.bO 0.100 0.703 0.70 0.182 0.742 0.83 0.300' 0.778 0.85 0.315 0.782 0.90 0.349 0.794 1.00 0.410 0.813 1.20 0.505 0.841 1.40 0.572 0.8b0 l.bO O.b22 0.873 1.80 O.b59 0.883 2.00 O.b87 0.891 2.25 0.714 0.897 2.50 0.734 0.900 2.75 0.750 0.900 3.00
- 0.7b3 0.900 3.50 0.787 0.900 4.00 0.811 0.900 4.50 0.834 0.900 5.00 0.858 0.900 5.50 0.882 0.900 b.00 0.900 0.900
>c.oo 0.900 0.900 GENERAL NOTE:
Interpolation may be used for intermediate values.
0 = maximum angle from the center of the outer
-one-half of the elbow-to -the location of the thinned area being evaluated, as measured in the pipe cross section, degree B = nominal distance between the center of the pipe and the neutral axis of the thinned piping section, in.
1188
CASES OF ASME BOll.ER AND PRESSURE VESSEL.. CODE TABLE -3625-1 MODIFIED STRESS RANGE REDUCTION FACTORS Number of Equivalent Full Temperature Cycles1, N 650 or less
>650 to 1100
>1100 to 2000
>2000 to 3900
>3900 to 8500
>8500 to 21_,000 over 21,000 NOTES:
Stress Range Reduction Factor2, f 1.0 0.9 0.8 0.7 0.6 0.5 0.4 Cl) Cycles to next scheduled inspection or repair/replacement activity.
(2) The modified stress range reduction factors are based on an Increase In the stress Intensification factor, i, by a factor of 2 over the life of the component.
1189 CASE (continued)
SUPP. 12-NC