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) | |
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e e VIR~INIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 Mi,;.y 13, 1999 United States Nuclear Regulatory Commission Serial No.99-222 Attention: Document Control Desk NL&OS/GDM RO Washington, D.C. 20555 Docket Nos; 50-280, 281 50-338, 339 License Nos. DPR-32, 37 NPF-4, 7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA AND SURRY POWER STATIONS UNITS 1 AND 2 ASME SECTION XI INSERVICE, INSPECTION PROGRAM REQUEST FOR APPROVAL - CODE CASE N-597 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
'Ii Ll 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 rj0~l I
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-----~---
e e 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 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 value, tp*min, may be used in determining acceptability Requirements for Analytical Evaluation of Pipe for continued service. Methods of predicting the rate Wall Thinning of wall thickness loss and the value of tp shall be the Section XI, Division 1 responsibility of the Owner.
Inquiry: What requirements may be used for analyt- -3220 Acceptance ical evaluation of Class 1, 2, and 3 carbon and low-alloy steel piping items subjected to internal or exter 0
-3221 Acceptance By Examination nal wall thinning as a result of flow-accelerated or Piping items whose examination and evaluation re-other corrosion phenomena? sults reveal that tp meets the acceptance standards of
-3500 or the Construction Code are acceptable for Reply: It is the opinion of the Committee that the continued service. When these criteria are not met, the following rules may be used. alternatives of. -3222, -3223, and -3224 may be used.
Fig. -3220-1 shows a flow chart of the acceptance alternatives.
-1000 SCOPE
-3222 Acceptance by Repair/Replacement This Subsection provides requirements for analytical Activity evaluation of Class l, 2, and 3 carbon and low-alloy steel piping items (e.g., piping and fittings) with internal Piping items whose thickness is less than that required or external wall thinning as a result of corrosion by -3500, -3223, -3224 shall be corrected by a repair/
phenomena, including flow-accelerated corrosion. These replacement activity.
requirements are applicable to nonplanar flaws.
-3223 Acceptance by Engineering Evaluation Piping items whose examination and evaluation re-
-3000 ACCEPTABLE STANDARDS sults reveal that the criteria of -3221 are not satisfi~d may be accepted for continued service by engineering ,
-3100 Preservice Examination ... evaluation .
Piping items examined prior to .commercial service (a) For Class 1 piping items, this evaluation shall are acceptable for service when the measured wall be conducted in accordance with evaluation methods thickness meets the requirements of the Construction and criteria developed by the Owner.
Code. (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.
-3200 INSERVICE EXAMINATION
-3210 General -3224 Acceptance by Reduction of Time to Ne.xt Examination Upon completion of pipe wall thickness examinations, the predicted remaining wall thickness, tp, at the time Piping items whose examination and evaluation re-of the next scheduled examination shall be calculated sults reveal that the criteria of -3221 are not satisfied, for piping items under evaluation. The predicted re- are acceptable for continued service when the time to maining wall thickness is the spatial distribution of the next examination for the affected piping. items is wall thickness remaining throughout the piping item reduced such that the acceptance criteria of -3221 or and may have a unique value at any given location -3223 are met using the Ip for the reduced examination on the piping item. Alternatively, the minimum predicted period.
1175 SUPP. 12-NC
CASE (continued)
~-597 CASES OF ASME BOILER AND PRESSURE VESSEL" CODE Examination results Predict thickness at next examination, fp
-3210 Acceptance Yes standards
-3500 No Repair/
Reduce time to Perform engineering replacement next inspection evaluation acitvity
-3224 -3223 -3222 No No Yes Acceptance FIG. -3220-1 ACCEPTANCE FLOW CHART SUPP.12-NC 1176
CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL. CODE Req"'ired Thicknen Piping item Reference Straight pipe -3500(a)(1)
Predicted wall Elbows -3500(all1 l thickness, tp Reducers 1 -3500(a)(2)
Tees1 -3500(a)(3)
Branch -3500(a)(3) connections1 Yes Acceptance Designed item -3500(a)(4)
Other items ~500(bl No 1Alternate of -3500(a)(5) may be used.
Go to -3222,
-3223, or Thickness Limit -3224 Code class Reference 1 -3SOO(cl 2 -3500(d) 3 -3500(e)2 2Alternate criteria may be developed in accordance with -3600(f).
FIG. -3500-1 WALL THICKNESS ACCEPTANCE STANDARD FLOW CHART
-3500 WALL TIDCKNESS ACCEPTANCE (2) For the small end of concentric and eccentric re-STANDARDS 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 of the piping item. The methods used to determine tp wall thickness requirements, including designed weld are the responsibility of the Owner.
counterbores and regions with integral reinforcement, (c) A piping item is acceptable for continued service tp shall be not less than the minimum design thickness, if the minimum pipe wall thickness. branch reinforce-including tolerances and excluding any corrosion allow- ment requirements, and piping stress criteria of the ances, specified in the original design analysis for the Construction Code used in the evaluation are met for piping item. ** ' all specified loading conditions.
(5) As an alternative to the requirements of (d) As an alternative to -36IO(c). butt welded pipe,
-3500(a)(2) and -~500(a)(3), for reducers, tees, or branch elbow, branch connection, and reducer piping items connections purchased to fitting standards allowed in may be evaluated in accordance with -3620.
Table NB-3132-1 and for which baseline as-installed (e) Alternative evaluation of pumps, valves, flanges, thickness measurements exist, tp shall not be less than and other piping items are the responsibility of the 0.875 times the as-installed thickness measurements, . Owner.
except that the thickness shall not be less than 0.875 tnom* (f) Piping items under evaluation with tp, exceeding
( b) Acceptance criteria for Class l, 2, and 3 pumps, the acceptance standards. of -3500 and satisfying -3600 valves, flanges, reducing elbows, socket weld fittings, shall be monitored for continued degradation. The fre~
and any other piping items not covered by -3500(a) quency and means .of monitoring for degradation are shall be the responsibility of the Owner. 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.
-3620 EVALUATION OF PIPE, ELBOWS, (d) For any Class 2 piping item, when tp at any BRANCH CONNECTIONS, AND location is less than 0.2 tnom, further evaluation is REDUCERS beyond the scope of this Case.
(e) Except as provided in (j) below, for any Class -3621 General Requirements 3 piping item, when tp at any location is less than 0.2 (a) The evaluation shall meet the requirements of tnom or 0.5 tmin* whichever is less, further evaluation
-3622 and -3623.
is beyond the scope of this Case. The value of tnun (b) For a branch connection or tee, the region within shall be determined in accordance with -3600.
the limits of reinforcement defined in the Construction (f) As an alternative to -3500(e), decreased wall Code shall meet the requirements of -3624.
thickness, including local through-wall leakage in Class (c) Evaluations shall be conducted using the appro-3 piping items whose maximum operating temperature priate piping equations, loadings, load combinations,
- does not exceed 200°F and whose maximum operating allowable material properties, and other acceptance stan-pressure does not exceed .275 psi ,*m!lY be accepted.
dards from the Construction Code used in the evaluation, Evaluation methods and acceptance criteria shall be except as specifically modified by this Case.
specified by the Owner.
(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.
-3600 ANALYTICAL EVALUATION FOR CLASS 2 AND CLASS 3 PIPING ITEMS
-3610
- General Requirements
-3622 THICKNESS EVALUATION (a) Analytical evaluatjons shall be conducted in ac-
-3622.1 Evaluation for Minimum Wall Thickness cordance with Construction Code. Later Code Editions and Addenda may be used. Use of later Code Editions (a) Except as provided in -3622.l(b), the value of and Addenda shall be reviewed for acceptability to the tP at any location shall not be less than 90% of the regulatory and enforcement authorities having jurisdic- minimum wall thickness of the piping item, tmim required tion at the plant site. for design pressure, defined in the Construction Code (b) Analytical evaluations shali be conducted using used in the evaluation, exclusive of any additional
- the predicted wall thickness, Ip, at the next examination corrosion allowance.
SUPP.12-NC 1178
~
e CASE (continued)
N-597 CASES OF ASME BOU.ER AND PRESSURE VESSEL-CODE (1) For straight pipe, bends, and elbows, tmin shall wall thickness exceed tnun for a distance that is the be detennined by: greater of 2.5..JR00mtnam or 2Lm. avg between adjacent thinned regions, where Rnam is the mean radius of PDo the* piping item based on nominal wall thickness and tmin=---
2(S + yP) Lm.. avg is the average of the extent of Lm below tmin for the adjacent areas (see Fig. -3622-4). Alternatively, (2) For concentric and eccentric reducers, tmin at .the adjacent thinned regions shall be considered a single each end shall be equal to tmin of straiglit pipe of the thinned region in the evaluation.
same nominal size as the reducer end. For .the conical (b) Provided that the transverse .extent of wall thin-portion of the reducer and the transition at the large ning predicted to be less than tmin* lmci), is less than diameter end, tmm shall be that of the large diameter or equal to "'1Rmintmin, the allowable local thickness, end. A gradual transition in tmm shall be assumed for ta1oc, shall be determined from Table -3622-1, where the transition at the small end (see Fig. -3622-1). RDUn is the mean radius of the piping item based on
( 3) For branch connections and tees, except at the minimum wall thickness tmin* For straight pipe, regions providing reinforcement of the opening required Table -3622-1 may be used when Lmct) exceeds by the Construction Code used in the evaluation, tmin ..JRmintmin* except that. an additional thickness tb shall shall be as required for straight pipe. be added to the value determined from Table -3622-1.
(b) When tp is less than 0.9 tmin at any location, ( c) This approach shall not be used to'. evaluate a additional evaluations may be conducted to determine reducer.
the allowable local thickness, ta1oc, sub)ect to the limita~
-3622.3 Local Thinning - Limited Axial and tions in (c). The thinned region and the parameters Transverse Extent that define the depth and extent of thinning are illustrated in Fig. -3622-2. The allowable local thickness shall be (a) When the maximum extent of wall thinning, L,,,,
- detennined in accordance with any one of the methods for which thickness is predicted to be less than tmin is in -3622.2, -3622.3, -3622.4, -3622.5, or -3622.6. less than or equal to 2.65..JRmintmin, and tnam is greater
( c) Local thinning evaluation shall not be allowed than 1.13 tmin* ta1oc shall be determined by satisfying for the following: (b) below and (c) or (d) below. This approach requires
( 1) A region adjacent to any branch connection that adequate reinforcement be available surrounding on the run piping, unless the distance between the the thinned area in accordance with (c) or (d) below.
center of the branch connection and the edge of the This evaluation approach is not applicable for the thinned area predicted to be less than tmin exceeds D;, following conditions:
where D; is the nominal inside diameter of the branch ( 1) Thinned areas adjacent to branch connections, connection and L,,, is the maximum dimension of the when the reinforcement zone , for the thinned area thinned region less than 'min* would overlap the required reinforcement of the branch (2) At the small end trimsition of a reducer. connection.
(3) Inner portion of elbows and pipe bends (Fig. (2) Thinned areas for which any portion of the
-3622-3), excluding a region within 1.5"'1Rnamtnam of reinforcement zone would lie on the conical or small the butt welds, unless the tmin in the evaluation of diameter transition zone of a reducer.
-3622.2, -3622.3, or -3622.4 is replaced by t'min* de- (3) Adjacent thinned areas qualified by this ap-fined by: proach when the reinforcement zones associated with each area would overlap.
., - 0.5 ) ,. ,, -* ( b) The- thickness of the .remaining pipe wall at the t'min = 0.5 + . tmin, pipe thinned section is adequate if the following equation
( cos8 1+-- is satisfied.
(Rb!Ro) ta1oc 0.353L.n
-3622.2 Local Thinning - Limited Transverse -~---
'min ""Rmintmio Extent (a) The evaluation procedure shall consider the depth ( c) If there is a surrounding reinforcement zone with and extent of the affected area and require that the predicted thickness of at least loom for a minimum 1179 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 -3622.6 Local Thinning - Central Portions of the thinned area shall satisfy the following equation. Concentric Reducers (a) For the conical portion of concentric reducers, the local allowable thickness less than tmin shall satisfy ta1oc ( 1.5--.JRmintmin ) (tnom )
-~1- ~-1 the following equation:
tmin L tmin ta1oc do!Di (d) As an alternative to (c) above, the reinforcement --~--
tmin, cosa.
adjacent to the thinned area shall justify the following 1 equation.
( b) For the flared transition at the small end of a ta1oc (0.935Arcin) concentric reducer, the local allowable thickness shall
- ~ 1- be gradually reduced from the. value determined at the tmin L,,,tmin conical end of the flare to tmin for the small end of the reducer.
(c) This approach shall not be used to evaluate
-3622.4 Local Thinning - Unlimited Transverse eccentric reducers.
Extent (a) The evaluation shall include consideration of the depth and extent of the.* affected area less than tmin* -3623 PIPING STRESS EVALUATION The wall thickness shall exceed tnun for an axial distance the greater of 2.5..JRnamtnam or 2 I.ma.max between -3623.1 Evaluation Requirements adjacent thinned regions at each circumferential location (a) The effects of piping stresses shall be evaluated on the piping item (see Fig. -3622-5). Alternatively, in accordance with the equations of the .Construction the adjacent thinned regions shall be considered a single Code used in the evaluation. If the piping analysis is thinned region in the evaluation. based on nominal piping thickness, allowable .stresses (b) Thickness ta1oc shall be determined from Table may be multiplied by 1.143. Consideration shall be
-3622-1. given to changes in the pipe metal. area, pipe inside (c) This approach shall not be used to evaluate a area, section modulus, and stress indices or stress reducer. . intensification factors, as described in -3623.2, -3623.3 and -3623.4. The effects of cyclic operating conditions
-3622.5 Local Thinning - Elbows and Bent Pipe shall be addressed in accordance with -3625.
(a) For locations farther than ...)Rmintrrun from welds (b) The piping stress evaluation, shall be based on to adjacent piping items, the predicted thickness on the predicted thickness at each cross section of the the outer portion of an elbow or bend may be less piping item that exhibits significant thinning or is than rmin for straight pipe. The local allowable thickness affected by a change in stress index or stress intensifica-at each location shall be determi_ned by: tion factor. Alternatively, the evaluation may be based on the limiting cross section.
ta1oc 0.5 * *-3623.2 - Noiriinar Longitudinal
- Pressure Stresses
- - ~ 0.5 + - - - -
fmin, pipe cos8 L+-- (a) The pipe metal area and the pipe inside area,
. (~)
Rrrun 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 where assumed. to be unifonnly thinned with a thickness of
_Rb /Rmin =ratio of elbow bend radius to mean pipe tp, min* For this approach, the nominal longitudinal radius, based on tmin for the same size pipe pressure stress shall be determined by:
SUPP. 12-NC 1180
e CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE 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.
- When evaluating reducers, the large and small ends (c) Detailed stress analysis may be conducted based shall be evaluated separately. For the large end, tp.min on a complete set of measurements around the thinned shall be detennined from all locations for the large cross section of the piping item. .
- end and conical sectio~. For the small. end, tp.min for (d) When evaluating thinning at the cross section of the entire reducer shall be used. a branch connection, the requirements of -3623.2(c)(l)
( c) Detailed stress analysis may be conducted based shall be met.
on the complete set of measurements around the thinned -3623.4 Stress Intensification Factors and Stress cross-section of the piping item. The nominal longitudi- Indices nal pressure stress, Sp, shall be determined by:
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
( J) To evaluate piping at a branch connection by using a reduced piping item thickness detennined beyond the limits of reinforcement, it shall be assumed in accordance with (a), (b), or (c) below.
that the entire region within limits of reinforcement is (a) Except as allowed in (b) or (c) below, stress at thickness tmin for the unreinforced pipe section, with intensification factors or stress indices for a piping item the outside surface at the pipe nominal outside radius. shall be based on the assumption of uniform wall If excess reinforcement is available within the limits thickness, using a value of tp. min and an associated of reinforcement, the excess metal area may be included mean pipe radius in the formula for these factors.
in Ap. (b) As an *alternative (a) above, the factors may be (2) When evaluating the longitudinal pressure based on the average tp of the piping item excluding stress in the central cone of a reducer, the stress shall branch reinforcement zones, except that predicted thick-be detennined based on the local radius at the cross ness at locations within a distance of twice the pipe section and the local tp at and adjacent to the cross nominal wall thickness from butt welds to adjacent section of interest, except that the resulting stress shall components need not be considered. For reducers, the be multiplied by a factor of 1/cosa. average tp of the small end shall be used with .the (d) When using Code Editions and Addenda that small end diameter to determine the factor.
require use of stress indices, the nominal longitudinal (c) As an alternative to (a) or (b) above, stress stress determined in accordance with (b) and (c) above analysis of thinned piping items may be conducted to shall be doubled. show the effects of wall thinning and the distribution
-3623.3 Nominal Longitudinal Bending Stresses of stresses on an affected piping item.
(a) Thinning of the piping item cross-sectional area -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:
-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, (b) For simplified analysis, the piping item section without consideration of the branch connection, except modulus may be based on a uniformly thinned section that tp within a region of radius of D; of the branch with thickness tp.min* When evaluating reducers, the pipe from the center of the branch connection shall large and small ends shall be evaluated separately. For not be less than tmin for the pipe run.
1181 SUPP.12-NC
CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE (b) The. branch piping shall be evaluated in accord- Am= predicted metal cross-sectional area for a ance with the requirements of -3622 and -3623. pipe that has experienced wall thinning. in. 2 Ap = predicted metal cross-sectional area of
-3624.3 Branch Connections Requiring pipe, in. 2 Reinforcement Arein =the reinforcement area available in the pipe wall based on the predicted thickness distri-(a) Branch reinforcement requirements shall be deter-bution in excess of tmin and within the limits mined in accordance with the Construction Code used of reinforcement of the Construction Code in the evaluation.
for an opening with diameter Lm at the (b) For the region of the piping run thii,t provides region of local thinning. in. 2 branch reinforcement, the value of tp at any location D0 = nominal outside diameter of piping
- item shall not be less than tnun for the nominal pipe run (e.g., 10.75 for NPS 10 pipe), in.
plus any required reinforcement at that location.
d0 = maximum outside diameter of a reducer at
( c) For the region of the branch pipe that provides the thinned location, in.
branch reinforcement, tp shall not be less than tmin for D1= outside diameter at the large end of the the branch pipe plus any required reinforcement.
reducer, in.
D;=nominal inside diameter of a branch connec-
-3625 Evaluation for Cyclic Operation tion, in.
(a) For piping items with tp, min not less than 0.75 f = stress range reduction factor tnom and subject to no more than .150 equivalent full i = stress intensification factor of the Construc-temperature cycles at the time of the next examination, tion Code (not less than 1.0) .
in accordance with the Construction Code *used in the lmin = predicted minimum moment of inertia of evaluation, piping stress equations that include thermal the thinned pipe about the neutral axis of expansion and anchor movement stresses need not be the pipe section, considering all orientations evaluated. of the section neutral axis, in.4 (b) For piping items not meeting the requirements L = maximum extent of a local thinned area of -3625(a), when the design includes consideration of with wall thickness less than fnom* in.
thermal expansion stresses, the allowable stress range Lm = maximum extent of a local thinned area for expansion stress shall be determined in accordance with wall thickness less than tmim in.
with the Construction Code used in the evaluation, LmraJ = maximum axial extent of a local thinned except that the stress intensification factor, i, shall be area with wall thickness less than tmin* in.
revised to take into account the geometry of the thinned Lma, max= maximum of the axial extents of two. adja-region. As an alternative to establishing a revised stress cent local thinned areas with wall thickness intensification factor, the stress range reduction factors less than trrun* in.
of Table -3625-1, which are based on an increase in Lmro=maximum transverse extent of a local the stress intensification factor by a factor of 2 over thinned area with wall thickness less than the life of the component, may be used. trrun* in.
( c) The potential for local overstrain in the thinned Lm, avg= average of the extents of thickness less than region for the combination of maximum sustained plus tmin for two adjacent thinned areas, in.
thermal expansion stresses shall be considered. Sus- Mb=resulting bending moment from the design tained loads include pressure, weight, and other sus- analysis of record for each loading condition tained mechanical loads. Local overstrain is defined under consideration, in-lb in NC-3672.6{b). Evaluation* methods and*-acceptance *.P.=design pressure, psi criteria shall be specified by the Owner. Rb =bend radius of an elbow to the elbow center line, in.
-3626 Nomenclature/Definitions R0 =nominal outside radius (e.g., 2.25 for NPS 4 pipe), in.
A 0 = total cross-sectional area of pipe based on
'ITD 0 2 .
Rmax = radius to the nominal outside surface of the nominal outside diameter, - -, in. 2 pipe plus the nominal distance between the 4 center of the pipe and the neutral axis, in.
A;=predicted inside cross-sectional area .for a Rnun = mean radius of piping item based on the pipe that has experienced wall thinning, in. 2 nominal outside radius and the minimum SUPP.12-NC 1182
- CASE (continued)
N-597 CASES OF ASME BOU.ER AND PRESSURE VESSEL CODE Large end transition zone Central conical section Small end transition zone ct-- - ------
GENERAL NOTE:
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 t'min= adjusted minimum thickness for inner por-with tniin = 0.30 in.), in. tion of an elbow, in.
Rnom =mean radius of piping item based on the tnom =nominal thickness of pipe or fitting specified nominal radius and thickness (e.g., 6.75 for in the applicable industry standard for the NPS 14 XS pipe with tnom = 0.5 in.), in. piping item. For items designed to specified S = allowable stress for piping item, including minimum thickness, the nominal thickness joint efficiency factor, E, if applicable, psi. is the design thickness, including corrosion Sb= maximum nominal bending stress at the allowance and excluding tolerances, in.
thinned section, psi. =
tp distribution of predicted local thickness of
=
SP nominal longitudinal pressure stress, psi. a piping item at the next scheduled examina-
=
ta1oc allowable local thickness, in. tion, in.
=
tb uniform thickness, of piping item, required tp, min= minimum predicted local thickness of a by the Construction Code; to withstand sus- **piping item at the next scheduled examina-tained and occasional bending loadings in tion, in.
the absence of pressure, thermal expansion, y =factor required by the Construction Code and anchor movement loadings, in. used in the evaluation tmm =minimum wall thickness required by the =
Znm predicted minimum section modulus for the Construction Code to sustain pressure, ex-
- thinned section, including consideration of clusive of tolerances and any allowances the shift of the neutral axis of the thinned for corrosion, in. pipe section, lnur/RIIIJIX, in.3
=
tmin. 1 tmin for large end of a reducer, in. a= maximum cone angle at the center of a tmin. pipe= tmm for straight pipe, in. reducer, degree 1183 SUPP.12-NC
e CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE tnom Axial direction
~
1 Transverse
(~oop direction)
FIG. -3622-2 ILLUSTRATION OF FLOW-ACCELERATED-CORROSION WALL THINNING SUPP.12-NC 1184
e CASE (continued)
N-597 CASES OF ASME BOILER AND PRESSURE VESSEL CODE Extrados
-- -~ Outer portion In er pojion I
/ I
/
/ Bend radius I
FIG. -3622-3 ELBOW AND NOMENCLATURE 1185 SUPP.12-NC
e e CASE (continued)
N-597
' - CASES OF ASME BOILER AND PRESSURE VESSEL CODE t ~ tmin in surrounding area Area 3 tp, 3 < tmin Xij = minimum distance between areas i and j Lm,; = maximum extent of thinned area i Lm, avg = 0.5 Lm, i + Lm, j 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 I_
e CASE (continued)
N-597 CASES OF ASME BOU.ER AND PRESSURE VESSEL; CODE
! Axial Direction t ~ tmin in surrounding area 1
Lmla),4 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:
(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
e CASE (continued)
N-597 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.
SUPP. 12-NC 1188
CASE (continued)
CASES OF ASME BOll.ER AND PRESSURE VESSEL.. CODE TABLE -3625-1 MODIFIED STRESS RANGE REDUCTION FACTORS Number of Equivalent Full Stress Range Temperature Cycles1, N Reduction Factor2, f 650 or less 1.0
>650 to 1100 0.9
>1100 to 2000 0.8
>2000 to 3900 0.7
>3900 to 8500 0.6
>8500 to 21_,000 0.5 over 21,000 0.4 NOTES:
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 SUPP. 12-NC
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