ML13311A400
| ML13311A400 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/31/1985 |
| From: | Southern California Edison Co |
| To: | |
| Shared Package | |
| ML13311A399 | List: |
| References | |
| NUDOCS 8506060493 | |
| Download: ML13311A400 (46) | |
Text
SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1 Long Term Service Seismic Reevaluation Program Technical Basis for Piping Strain Limits and Development of Linear, Elastic Analysis Methodology Prepared for:
NUCLEAR REGULATORY COMMISS10N Prepared by:
SOUTHERN CALIFORNIA EDISON COMPANY 8506060493 850604 May 31, 1985 PDR ADOCK 05000206 P
TABLE OF CONTENTS Section Page TABLE OF CONTENTS
1.0 INTRODUCTION
1-1 1.1 Purpose 1.2 Background -
SEP and SONGS1 1.3 SONGS-1 Proposed Criteria and Methodology 2.0 BASIS FOR STRAIN LIMITS 2-1 2.1 ASME Code Criteria 2.2 Code Case N-47 2.3 Component Testing Programs 2.4 Stress-Strain Curves 2.5 Summary 3.0 DEVELOPMENT OF LINEAR, ELASTIC ANALYSIS METHODOLOGY 3-1 3.1 Correlation of Strains to Elastic Analysis Method 3.2 Piping System Testing Programs 3.3 Summary 4.0 CONSERVATISMS AND MARGINS 4-1 4.1 Categorization of Seismic Loadings 4.2 Dynamic Versus Static Loadings 4.3 Operating Plant Experience
5.0 REFERENCES
5-1 APPENDIX A:
List of Piping Materials and Allowable A-1 Stresses 1
1.0 INTRODUCTION
1.1 Purpose This document presents the criteria and methodology proposed for the qualification of large bore (greater than 2 inch NPS) piping at San Onofre Nuclear Generating Station Unit 1 (SONGS-1) under the Long Term Service (LTS) Seismic Reevaluation Program. The purpose of this document is to present and justify the proposed criteria and methodology and to demonstrate that adequate margins of safety exist for the proposed criteria and methodology.
1.2 Background - SEP and SONGS-1 The seismic reevaluation of SONGS-1 is being performed under the NRC's Systematic Evaluation Program (SEP).
This program was developed to compare the older nuclear plants against current regulatory criteria and access the safety impact of any discrepancies.
In the case of severe seismic events, new information and techniques for evaluating the effects of these events has resulted in a re-review of the SONGS-1 seismic capabilities.
In order to facilitate their review of the seismic capabilities of the older nuclear plants, the.NRC developed "guidelines" for seismic review of large-bore piping.
These guidelines can be modified on a plant specific basis as warranted by circumstances.
The SEP guidelines for large bore piping are specified as:
For Class 1 piping:
PDo + 0.75iM
(_
1.8 Sh 4t Z
For Class 2/3 piping:
PDo + 0.75iM <
2.4 Sh 4t Z
For most SEP plants, these criteria provide an appropriate level of seismic consideration and do not impose a significant impact on the existing plant. Most of the SEP plants are located in the eastern United States and were evaluated to a seismic event in the range of 0.2-0.3g.
However, the SONGS-1 design basis is a 0.67g Modified Housner Earthquake, and the SEP guidelines are overly conservative relative to the treatment of seismic stresses, based on current knowledge. This excessive conservatism will result in installation of piping supports which provide additional restraints to normal movement of systems, expose construction personnel to high radiation levels, and which are not necessary to accomplish the seismic objectives of the SEP. With respect to the 0.67g Modified Housner Earthquake Event, the objective is the preservation of piping integrity with sufficient margin to insure that safe shutdown conditions can be achieved and maintained following the earthquake. To achieve this objective, an approach is proposed for SONGS-1 which is site 1 -1
specific and includes a more rigorous application of strain-based criteria to insure pipe integrity. This is consistent with the SEP guidelines which provide for alternate criteria to be reviewed on a case-by-case basis by the NRC. Such an approach is also consistent with current industry studies which are in progress to provide higher dynamic allowables for piping or to allow seismic -stresses to be treated as secondary stresses.
1.3 SONGS-1 Proposed Criteria and Methodology The development of the site-specific approach for the SONGS-1 large bore piping evaluation requires the definition of two items:
Design Criteria Evaluation Methodology 1.3.1 Design Criteria The design criteria proposed for the SONGS-1 LTS are based on the criteria presented in the ASME Code for faulted conditions.
The large bore qualification criteria are based on limiting piping strain levels to ensure that the piping remains structurally integral under the earthquake loadings. The basis of the ASME Code,Section III, Appendix F for faulted conditions is that the piping will remain structurally integral and that the pressure boundary will remain intact. The Code recognizes that the Appendix F rules allow for large deformations of the piping system. The SONGS-1 criteria will be more stringent than the ASME Code, Appendix F, criteria because the SONGS-1 limits will ensure piping integrity.
"Piping integrity" is defined herein as piping which maintains structural integrity and shows no significant decrease in rated flow capacity.
Piping integrity can be defined by establishment of limits on material strains to ensure limitation of deformation and provide suitable margin to rupture. The strain limits established for the LTS large bore piping evaluation are:
e = 1% for Carbon Steel e = 2% for Stainless Steel These strain limits are selected in order to ensure the "integrity" of the piping system. They are selected by considering the acceptable strain limits specified in the ASME Code for faulted conditions for structural integrity; by reviewing test data on elbows and piping systems to ensure that the system can pass its rated flow; and by reviewing the strain limits in Code Case N-47 for normal and upset conditions.
A detailed description and basis for the strain limits and a discussion of the margin are included in Section 2.0.
1-2
1.3.2 Evaluation Methodology The strain limits specified in the above section are based on inelastic system and inelastic component analyses.
Several methods are available for calculating piping strains.
however, the performance of nonlinear analysis is very expensive and time-consuming. Therefore, an approach which allows the use of standard linear analysis techniques is desirable.
Such a method allows use of standard piping analysis codes to be used as a screening methodology to ensure that strain limitations are satisfied.
The evaluation methodology to be used for LTS will provide for standard piping evaluation, but will correlate conservatively with the specified strain limits.
The approach selected for LTS is based on the ASME stress intensification method. The stress-based screening criterion which satisfies the proposed strain limits, is:
PDo + 0.75iM K 2.0 S The 2 0 S value is determined by correlation with the specified strain li its for carbon and stainless steel.
The determination of the 2 0 S limit is presented in Figure 1-1.
The above equation was seleced because it is consistent with previous piping analyses at SONGS-1. The use of a different equation (such as the stress index approach) could have been selected, although the stress limit would be different.
The primary goal of determining strain-correlated allowable stresses was to provide a measure of piping system acceptability for systems analyzed by practical, less costly linear elastic analysis methods, as opposed to requiring piping evaluations by nonlinear analysis methods. A detailed discussion of the development of the linear elastic piping methodology and a presentation of the margin are presented in Section 3.0. A comparison of 2.0 Sy and 2.4 Sh for typical piping materials at SONGS-1 is presented in Appendix A.
1-3
ASME Code, App F Acceptable Strain limits:
= 1% CS Elbow Tests
=2% SS Piping System Tests Determined seismic event which produces strain limits Performed nonlinear dynamic analysis (typical seismic event)
Performed response spectrum elastic analysis Determined stresses by:
PD/4t + 0.75iM/z Specify elastic stress limit:
2.0 Sy Figure 1-1 SONGS-1 LTS STRAIN/ELASTIC ANALYSIS CORRELATION 1-4
2.0 BASIS FOR STRAIN LIMITS This discussion defines the bases for selecting the proposed strain criteria for carbon and stainless steels. The correlation of the stress based screening criterion with these strain limits and the determination of margins are presented in the following sections. The strain limits are determined by reviewing the ASME Code faulted condition limits and by then reviewing test data on piping integrity.
The strain limits selected for LTS are:
e = 1% for carbon steeel e = 2% for stainless steel 2.1 ASME Code Criteria The ASME Code provides stress limits for Level D service loading when piping analysis is performed using elastic analysis methods.
However, the Code recognizes that alternate methods may be used to perform the piping qualification and additional criteria are specified which depend on analysis methodology.
The specification of these alternate limits for faulted (Level D) conditions is provided in Appendix F of Section III, ASME B&PV Code (1980 Edition, Winter 1980 Addenda).
Appendix F presents criteria which are intended to ensure structural integrity of the piping (the ability to maintain the pressure boundary).
Appendix F provides for inelastic analysis to determine loads which result in a particular strain within the component (F-1321.1 (f)).
The use of inelastic system analysis and component strain limit load analysis (F-1324.5) provides a means of specifying strain limits for Level D conditions.
By reviewing the Level D criteria, an approximation of the strains allowed by the Code for structural integrity can be determined. For inelastic system and inelastic component analyses, Appendix F states that the primary stress limits of NB-3221 can be satisfied using a value of Sm equal to the greater of [0.7 Sul or [Sy + 1/3(Su-Sy)].
The acceptance limits thus become:
Pm J 1.0 Sm 0.7Sy or Sy +1/3(Su-Sy)
PL +b E 1.5SM 1.05 u or 1.5Sy + 1/2(Su-Sy) where Pm is the primary membrane stress intensity and PL +b is the primary membrane plus primary bending stress intensity. For piping systems, P is associated with pressure loadings only and the governing conwition is normally the PL + Pb limit.
Sample determinations of acceptable piping strain limits are shown in Figure 2-1, using a typical stainless steel stress-strain curve, and in Figure 2-2, using a typical carbon steel curve.
2-1
As shown in Figure 2-1, the strains associated with each primary stress check are:
e = 12% for Pm e = 60% for PL +b Based on this sample evaluation, it is shown that the Code accepts large strain limits in piping to demonstrate structural integrity.
However, for use in SONGS-1 LTS, more restrictive strain limits will be selected in order to ensure that the piping system will pass sufficient flow to allow the plant to be brought to safe shutdown conditions and maintained in these conditions following the earthquake. It is apparent from this evaluation that the LTS stainless steel strain limit or 2% has a large margin against the Code allowable limits. The margin based on strains for the PL +
Pb limit is approximately 30, and the margin considering strain energy is considerably larger.
As shown in Figure 2-2, the strains associated with each primary stress check for carbon steel are:
e = 11% for P.
e = 20%.for PL +b Based on this review, the 1% carbon steel strain limit proposed for LTS shows a margin of 20 for strain and a much higher limit for strain energy.
Therefore, based on the ASME criteria for faulted condition limits specified in Appendix F, the LTS strain criteria has a very large margin against structural integrity failure of the material.
2.2 Code Case N-47 Code Case N-47 [2-2] addresses the design and analysis of Class 1 components at elevated temperatures.
Elevated temperatures are defined as temperatures exceeding those covered by the rules and stress limits of ASME Subsection NB and the tables in Appendix I.
At these high temperatures, creep effects may become significant and the stress criteria are not appropriate. The rules of the Code Case guard against deformation-related failures, such as:
o Creep rupture from long term loadings o
Creep fatigue failure o
Loss of function due to excessive deformation o
Gross distortion due to incremental collapse and racheting.
Appendix T of Code Case N-47, "Rules for Strain, Deformation, and Fatigue Limits at Elevated Temperatures" provides the following strain limits for Service Levels A, B and C loadings (corresponding to Normal, Upset and Emergency conditions, respectively):
2-2
1 percent Averaged through thickness (membrane) 2 percent Surface strain due to a linearized distribution through the thickness (membrane plus bending) 5 percent Local strain at any point.
The strain limits which are developed in the Code Case are directly applicable to the seismic evaluation for SONGS-1.
Although the strain criteria in the Code Case were developed for use at elevated temperatures, where stress criteria cannot be applied, the strain criteria can also be applied to the dynamic analysis of components at lower temperatures. The strain limits established by the Code Case consider all strains - plastic strains as well as creep strains
- and are intended to define acceptable piping performance in terms of total strain, regardless of the mechanism producing that strain.
The Code Case criteria address the absolute strains calculated by inelastic analysis methods due to all types of loadings. The strain limits are selected for the Code Case to ensure that small deformation theory is applicable. The basis for the low temperature rules (Section III) is small deformation theory. In addition, the strain limits are specified for Levels A, B and C service conditions. The use of these strain limits, therefore, must allow for operation under these strains with no significant piping integrity impact. [Normal ASME Code philosophy is based on limits for Level A conditions which are 50% of limits for Level D conditions; limits for Level B conditions which are 60% of limits for Level D conditions; and limits for Level C conditions which are 75% of limits for Level D conditions]. Therefore, the use of the above strain limits for use in the 0.67g Modified Housner Design Spectrum evaluation provides a conservative limit on the piping system strains. In NUREG 1061, Rodabaugh [2-3] refers to the applicability of Code Case N-47 strain limits in his discussion of Code limits and inelastic analysis criteria for dynamic loads.
The strain limits presented provide assurance of the structural integrity of the piping and limit gross distortion (which is the phenomenon addressed in the seismic evaluation).
The limits presented in the Code Case were developed for inelastic analysis methods, since elevated temperature conditions often result in stresses above the elastic range.
However, the strain limits which are developed in the Code Case are applicable for use in the seismic evaluation for SONGS-1, and provide a conservative criteria for Level D type loadings.
The classification of stress intensities, and therefore the classification of strains, is given in Tables 2-1 and 2-2 which are taken from Table-3217-2 of Code Case N-47 and Table NB-3217-2 of Section III, Subsection NB, respectively. A review of the tables shows that only internal pressure causes general membrane (P )
stresses and strains. Thus, the 1 percent limit is only applied to the portion of the strain caused by internal pressure. Stresses and 2-3
strains due to mechanical loads, including gravity and seismic loading, are classified as local membrane (PL) plus bending (Pb).
Therefore, the 2 percent strain limit for local membrane plus bending is applicable to seismic loading. It should be noted that this strain limit is equally applicable to both carbon and stainless steel, although the criteria proposed for SONGS-1 provide for a reduced strain limit for carbon steel based on lower elongation capability.
2.3 Component Testing Programs Numerous experimental studies have been carried out to investigate the behavior of critical components of piping systems.
Results of three studies are described below in detail.
The first study by Imazu [2-4] evaluated five stainless steel elbows under static loads.
In the second study, Greenstreet [2-5] tested four stainless steel elbows statically.
In the third study, Teidoguchi [2-6]
performed static and dynamic tests on stainless steel elbows.
Elbow tests are considered here because the piping integrity of the elbow will govern the integrity of the piping system.
Imazu Test Results Imazu performed plastic instability and buckling tests on five thin-walled stainless steel elbows.
The elbows were 12-inch Schedule 10S and 20S long radius elbows made from Type 304 stainless steel.
The elbows were loaded statically in both in-plane and out-of-plane directions to, and past, the plastic instability point using displacement-controlled techniques.
The results from these tests demonstrate that strains of up to 2 percent resulted in an ovality of the cross-section which corresponds to a flow area reduction of no more than five percent.
This five percent flow area reduction occurs only at a local point in the piping system and would have an insignificant overall effect on pipe rated flow.
It should be noted that these tests were performed on thin-walled, non-pressurized elbows at elevated temperatures (600*C).
For SONGS-1, stainless steel elbows are thicker, are pressurized, and are at much lower temperatures than those tested by Imazu.
Therefore, the Imazu elbow test results represent a conservative bounding case for SONGS-1 application.
Greenstreet Test Results Greenstreet determined the plastic deflection responses of four 6-inch Schedule 40S and bUS commercial stainless steel (SA312-304L) elbows subjected to external static in-plane bending moment without the application of internal pressure. Tests were carried out to the maximum capacity of the testing apparatus which provided the limitations to the test's recorded response. In all the cases, 2-4
there was no indication of failure or gross structural instability.
Ibrahim and Kitz [2-7] demonstrated that these results correspond to elastically calculated piping stresses 2 to 5 times the Code Level D limits.
Teidoguchi Test Results The experimental study by Teidoguchi included extensive testing to justify the functional capability of Class 1 stainless steel elbows. Static and dynamic tests were performed at room temperature. The static tests were performed with an external force large enough to produce a predominantly plastic response. The load deflection curves reported from the study indicated that the tests were conducted up to a strain.level of 2 percent (which corresponds to ten times the proportional limit).
At these strain levels, geometric and structural stability of the components were maintained. These results also showed that internal pressure improves the integrity and stability of the designed elbows under dynamic loading.
The dynamic tests reported for elbow piping components were for a 3-inch long radius light-wall elbow welded to a 3-inch Schedule 40 pipe. The material of these elbows was SUS27TP, which is equivalent to the ASME stainless steel TP-304. The piping system was supported on a shaker table and subjected to harmonic excitation.
Corresponding piping stresses were calculated, ranging from a maximum value of 6.2 to a minimum value of 2.9 times the ASME Class 1 Level D limits. These ratios were derived by applying the Class 1 stress index approach and the 3.0 Sm allowable, which is approximately equal to 2.0 Sy.
2.4 Stress-Strain Curves Stainless steel piping materials are significantly more ductile than carbon steel materials and thus have a significantly greater inherent reserve capacity. This can be shown from the comparison of typical mechanical properties at room temperature as follows [2-8j.
Tensile Yield Ultimate Reduction Brinell Strength Strength Elongation of Area No.
Ksi Ksi Mild Carbon Steel 50-65 30-40 25-40 Min 30 120 Stainless Steel 85-95 30-35 55-70 65-75 145-160 18 Cr -
8 Ni (Type 304)
Figures 2-2 and 2-1 are engineering stress-strain curves for mild carbon steel (0.25 carbon) and stainless steel (Type 304),
respectively, from [2-9] and [2-10J. At the tensile (or ultimate) 2-5
strength, carbon steel exhibits approximately 20% strain while stainless steel exhibits approximately 60% strain.
All of the above results support the acceptability of a strain limit of 2 percent for stainless steel materials. This allowable limit will ensure structural integrity as well as no loss of integrity due to significant flow area reduction.
2.5 Summary The discussion presented in this section provides background for the strain criteria selected for the SONGS-1 LTS program.
The strain limits bases are:
Stainless steel: 2% selected based on Code Case N47 and material stress-strain curves.
Carbon steel:
1% selected based on material stress-strain curves.
The test data on elbows, which will be the limiting components, indicates that the components maintain integrity at strains above 2%.
Additionally, the test data include a high degree of conservative since they-are performed on thin-walled components much more flexible than the components at SONGS-1 and without internal pressure.
The strain limits selected for LTS ensure than an adequate margin exists against loss of piping integrity.
'2-6
0 Boo Oc 000 soo a
C QS I
- a.
I I
C c
w 200 0
1 0.2 0.3 0.4 0.5 0.6 0.7 03 SI Engineering Stroin Figure A-2.
Effect of strain rate on stress-strain curve of tension specimens machined from 0.33-inch (8.4-nm) thick Type 304 stainless steel plate.
Fig 2-1:
Engineering Stress-Strain Curve for Type 304 Stainless Steel 2-7
Cam!1. sitruM, i. Per i 2 a n
0 00000 00 V:
To-
-CM
-Uttifficle strenqth I Severe mockin S30,d
£L
]a, Pmporfi I Iiimit F
/
FV I 2-8
CASES OF ASME BOILER AND PRFSSURE VESSEL CODE Tae -3217*2 Clamification of Sr Ineniti in Pping, Typica Cmm Discomntiuitis Consied P
Companent LicationsOrigin tof Strmes Classification' Grom Local Pipe or tube, elbows. and Any, except crotch regions Internal pressure P0 No No reducers. Intersections of Intersections PLadQ Yes No and branch connections F
yes Yes except in the crotch Sustained mechanical loads A
No No regions including weight PL and Q Yes NO F
Yes Yes Expansion P.,.?6 and Q*
Yea No F
Yes Yes Axial thermal gradient Q1 Yes No F
Yes Yes Interseedons.
In the crotch region Internal pressure, sustained PL and Q3 Yes No including tees mechanical loads and F
Yes Yes and branch expansion cennedons Axial thermal gadient Yes No F
Yes Yes Dolts and Any Internal presse, gasket Pr No No anges compression, bolt load Q
Yes No F
Yes Yea Thermal gradient Q1 Yes No F
Yes Yes Expansion
?., Pb and Q'-*
Yes No F
Yes Yes Any Any Nonlinear radial thermal F
Yes Yes gradient Linear radial thermal gradient Q1 Yes No
' Thes classifications may be modified for purposes of certain criteria in Appendix T.
sSee -3138 and -3213.8.
$Analysis is not required when reinforced in accordance with -343.
Table 2 Stress Classifications, Excerpted from ASME Code Case N-47 2-9
TABLE NB-3217-2 CLASSIFICATION OF STRESS INTENSITY IN PIPING, TYPICAL CASES Discontinuities Consider Piping Component Locaons Origin of Sress Classification Gross Local Pipe or ue, elbows, and Any, except crotch regions Intnal pressure P.
No No reducem. Intersections of Intersections P, and Q Yes No and branch coMectom F
Yes Yes ecept incch ad regions Sustained mechanical loads, P&
No No Including weight P, aid Q Yes No F
Yes Yes Expansion P,
Yes No F
Yes Yes Axial drmal gradient 0
Yes No F
Yes Yes Intersections, In croth region Internal pressure, sustained P, and 0 (Note (1)]
Yes No including tees mechanical loads, and F
Yes Yes and branch expmion connuctions Axial thermal gradient 0
Yes No F
Yes Yes sots and Any Internal pressure, gasket P
No No flanges compression, and bolt load 0
Yes No F
Yes Yes Thernal gradient Q
Yes No F
Yes Yes Expansion p,
Yes No F
Yes Yes Any Any Nontinear radial thermal F
Yes Yes gradient Linear radial thermal gradient F
Yes No Anchor point motions, including Q
Yes No dose resulting fron earthqake NOTE:
(1) Analysis is not reauired when reinforced in accordance with NB-3643.
Table 2 Stress Classifications, Excerpted from Subsection NB 2-10
3.0 DEVELOPMENT OF LINEAR, ELASTIC ANALYSIS METHODOLOGY This section discusses the correlation analysis to develop an elastic analysis method which corresponds to the specified strain criteria. The development of the methodology is described in this section and piping system test data is presented which demonstrates the margin in the SONGS-1 approach. Subsection 3.1 presents the results of a nonlinear analysis which establishes that a 2.0 Sy stress limit will effectively ensure that systems meeting this screening criterion will experience less than the proposed strain limits. Subsection 3.2 provides test results which clearly establish the conservatism of the 2.0 Sy stress limits.
3.1 Correlation of Strains to Elastic Analysis Method The strain criteria established for LTS are based on inelastic analysis methods.
There are several approaches for determining the strains by inelastic analysis.
However, nonlinear analysis is very costly and time consuming.
A standard linear, elastic piping approach is a desirable means to evaluate the piping.
To be effective, this method and its associated limits should meet the following requirements:
- 1.
The method should be based on standard linear methods to allow use of benchmarked computer programs and standardized methodologies.
- 2.
Stress limits must be high enough to approximate the nonlinear limits or their use as screening limits will be substantially diminished.
- 3.
Because of approximations involved, correlation must be established between these limits and the strain criteria to assure that the strain criteria are never exceeded.
A correlation study was performed to develop an elastic stress approach which corresponds to the strain criteria.
The correlation study consisted of a comparison of nonlinear analysis results with elastic analysis results.
Physical test data were also used.
The purpose of the nonlinear analyses performed for SONGS-1 [2-1]
was to show that typical piping systems maintain their piping integrity (i.e., below the 1% and 2% strain limits) at an elastically calculated stress limit of 2.0 S.
The load combination considered in the analysis was pessure, gravity and seismic inertia.
Numerous hot safe-shutdown piping systems were reviewed and two representative piping systems (AC-19 and MW-01) were selected for the study. The two systems provided a good representation of the various piping components, materials, and system types represented in the plant. Both carbon and stainless steel materials were considered, as well as piping components of different sizes and 3-1
flexibilities. Both systems have typical configurations incorporating a mix of various component types. Although the design response spectra did not produce seismic stress levels in the system at the functionality stress limit of 2 0 S input motions were increased to produce the desired maximum eXastic stress in the most highly stressed portion of the system. The elastic stresses are calculated based on the ASME stress intensification factor approach.
Elastic analyses were performed for gravity and seismic inertia to provide results for comparison with the results from nonlinear analyses. This ensures proper development and accuracy of the nonlinear analysis model.
To maintain piping integrity (i.e., to deliver the rated flow), the elbow, tee and straight pipe components must not distort excessively (ovalization). The ANSYS computer program was used for the nonlinear analyses. Models were developed with elbow and tee components which closely matched experimentally verified behavior (see attached nonlinear analysis models, Figures 3-1 and 3-2).
The time history loading used to develop the elastically calculated stress of 2.0 S (the study used limits of 2 0 S for carbon steel and 2.2 for stainless steel) at critical components (elbow for both'systems) was input for the nonlinear analysis. The strains calculated from the nonlinear analysis were correlated with the stresses calculated from the elastic analyses with the same input. As shown in the attached Tables, 3-1 and 3-2, the strains were less than 1 percent for carbon steel and less than or equal to 2 percent for stainless steel.
These strain levels were used to compute maximum ovalization.
At these strain levels, maximum ovalization and flow rate reductions were considered to be acceptable (less.than 5 percent flow area reduction).
A major conservatism in the nonlinear analyses was the material law assumed for the ANSYS model.
The moment-deflection curves used on the ANSYS model match closely with experimental data; thus, the proper global response was assured. Additionally, by matching the moment-deflection curves, a conservative moment-strain relationship was produced. This can be seen by reviewing the attached Figures, 3-3 and 3-4. For example, a moment of 200 in-kips produces deflections of approximately 0.35 inches in both the ANSYS and experimental studies (Figure 3-3).
However, this same moment produced experimental strains of 0.16 percent while the ANSYS model predicted 0.45 percent (Figure 3-4).
Thus, the ANSYS-calculated strains are greater than those reported in experimental studies.
The moment-strain curve is more conservative as the strain increases from 0.2% to 2.0% strain. At values of 2%, the analytical moment-strain curves overpredict actual strain by a factor greater than 2.0 versus the experimental curves.
Thus, the value of 2%
strain in Table 3.2 in fact would be less than 1 percent strain, if a more realistic moment-strain relationship were used.
3-2
Other conservatisms in the analysis are as follows:
o Code-specified minimum material strengths were used in the analyses.
Actual material strengths are greater than.
Code-specified minimums.
Based on material properties used for supports, a 20-30% material overstrength is available.
o Nominal component thicknesses were used on the analysis.
Component thicknesses are normally significantly greater than nominal values. This increases the strength and moment-carrying capacity of the components.
o Strain rate effects which enhance yield strength are neglected.
o Pressure effects increase collapse moments of components.
These effects were neglected in the analysis.
In summary, this study conclusively demonstrates that an elastic piping stress limit of 2.0 Sy for carbon and stainless steel piping systems provides assurance that the piping systems will still remain integral.
This criterion allows local yielding in components such that load redistribution reduces maximum moments and stresses, yet provides limits on the extent of yielding such that functionality of the system is maintained.
Similar nonlinear analyses have also been performed at Commonwealth Edison's Dresden and Quad Cities plants to successfully license the 2.0 S as an elastically calculated stress limit of their IE Bullein 79-14 program [3-1]. The load combination considered in the analysis was pressure, gravity and seismic inertia in accordance with ASME Code Class 2/3 Equation 9.
3.2 Piping System Testing Programs The relationship between elastically calculated stresses and piping strains has also been evaluated from available test data. These data confirm the results from the nonlinear analysis and show that strains associated with an elastically determined stress of 2.0 Sy is clearly below a 2 percent strain limit. Additionally, they show that piping systems can retain integrity when subjected to loadings well in excess of these levels. The first such test examined was a jointly sponsored piping research program by the U.S. Nuclear Regulatory Commission and the Electric Power Research Institute which involved the design, analysis, fabrication, erection, and dynamic testing of prototypical piping systems [3-2].
One objective of this program was to stimulate recognition of safety margins implicit in ASME B&PV Code rules for Classes 2 and 3 piping by demonstrating the existence of large design margins in piping and support systems when subject to seismic loads much greater than those acceptable according to the ASME Code.
3-3
Results from this effort and other similar experimental programs
[3-3, 3-4 and 3-5] have confirmed that piping systems are able to sustain extreme dynamic loads without plastic collapse, leakage, or loss of pressure-retention capability. Results of these programs demonstrate that piping systems have large inherent reserve margins under seismic loading. These programs have generated proposed changes to the ASME Code requirements that would remove seismic loading from a primary stress check in Code Equation 9 [3-61 (see Section 4.1 for detailed discussions).
Below, we briefly discuss two of the recent testing programs for piping systems, performed by ANCO L3-2].
The first system consists of a 70 ft. long, six-inch Schedule 40 pipe run.
The piping was subjected to accelerations as high as 15g and response accelerations over 50g were measured.
The second system consists of a 20 ft. long, four-inch, Schedule 40 pipe run.
Accelerations as high as 14g were input and response accelerations greater than 21g were measured.
a) 70 ft. Long, 6-inch Diameter, Schedule 40 Piping System The first piping system tested was a single run of A106 B carbon steel about 70 ft. long. It is shown in Figure 3-5.
Six-inch, Schedule 40 and eight-inch,. Schedule 40 piping was employed, with the larger diameter pipe located at the ends of the pipe run. The 6-in. and 8-in. pipe were joined together using standard 6 x 8 reducers. The pipe elbows were 90 long radius elbows. The piping was designed following ASME Code rules.
Comparison of analytical and test frequencies of this piping system is shown in Table 3-3.
The first natural frequency is 4.18 and 4.62 Hz from analysis and test, respectively.
Multiple tests were conducted with various magnitudes of dynamic input and support configations. The piping was pressurized to 1150 psig and driven with a 20 second input earthquake time history.
Selected test results are shown in the table below:
INPUT MAX. EXP.
RATIO TO
- RATIO TO **
MAX.
TEST CASE ZPA(G)
STRESS (KSI)
ASME LEVEL D SY STRAIN(%)
1 (XEQ3C1) 2.24 32.4 0.9
.93
.0677 2 (XEQ1) 4.32 42.12 1.17 1.2
.0953 3 (XEQ2) 4.86 47.16 1.31 1.35 0.1040 4 (XEQ3) 5.38 47 52 1.32 1.36 0.1070 5 (YEQl) 4.33 65 88 1.83 1.88 0.1153 6 (YEQ2) 5 55 74.52 2.07 2.13 0.1312 7 (YEQ3) 1.75 65.16 1.81 1.B6 0.1100 8 (YEQ4) 8.38 83.52 2.32 2 39 0.1400 Maximum Experimental Stress/2.4 Sh
- Maximum Experimental Stress/Sy 3-4
Various pipe cross-sections were instrumented with strain gauges. From measured strains at each pipe cross-section location, the maximum ASME Code Class 2 based piping stresses were calculated. In calculating the stresses, two assumptions were made:
(1) linear material behavior; and (2) using the stress intensification factor approach of the ASME Code for Class 2 piping (1980 Edition).
From the table above, it is observed that at just below Level D stress (Test Case 1),
the maximum measured strain in the piping was 0.06 percent.
The maximum input acceleration for this case was 2.24g.
Test Case 6 shows that at a stress level corresponding to 2 times Level D (or 2.13 S for the pipe material), the maximum measured strain was 013 percent. The maximum input acceleration was 5.5g for this test case. Test Case 8 shows that for a stress level corresponding to 2.39 S, the maximum measured strain in the piping was only 0.1 percent.
These experimental results show that low strains are obtained at stress levels greater than 2.0 Sy. Thus, a stress limit criteria of 2.0 SY is conservative.
To show the severity of the input for a particular test case, the input response spectrum for Test Case 6 is compared in Figure 3-6 to the input required to just achieve the Level D (using Class 2 stress intensification factor approach) stress condition in the piping system of Test Case 1. This test was about a factor of four greater than the input necessary to match the Level D stress limits in the frequency region of interest for the first piping system.
That is, the piping system successfully withstood an earthquake input about four times greater than the Code design rules would indicate to be acceptable. The piping system, in fact, withstood several more severe dynamic tests with no gross distortion or loss of pressure retaining capacity.
b) 20 ft. Long, 4-inch Diameter, Schedule 40 Piping System The second piping system consisted of a prototypical nuclear power plant piping segment which was tested by ANCO Engineers Inc., under EPRI sponsorship, to determine its ultimate dynamic load capacity.
The selected piping was a 20-foot run of 4-inch, Schedule 40 ferretic material with two elbows and three supports. An earthquake-like dynamic input was specified at each one of these supports. The piping tested is shown in Figure 3-7.
3-5
The piping run was designed in accordance with ASME Code Class 2 rules and was dynamically excited to varying response levels while under the Code maximum allowable internal pressure.
Figure 3-8 shows the horizontal dynamic spectra imposed on the piping. Also shown in Figure 3-8, for comparison purposes, is an SSE response spectra for a typical nuclear power plant sited in Southeast U.S. for Safe Shutdown Earthquake (0.2 - 0.3g). As may be seen, the test spectra input to the piping is seven to eleven times the SSE spectra in the frequency range of importance to the tested piping system (approximately 6 to 13 Hz.). This also implies that the test spectra input to the piping is about three times the 0.67 g Modified Housner Earthquake spectra for SONGS-1.
The first and second test frequencies of this piping system are 6 and 13 Hz, respectively.
Figure 3-9 is a comparison of the actual input test spectra with a spectra which produced stresses in the piping system equal to Code allowable (2.4 Sh). It is observed that the dynamic input to the test resulted in elastically calculated stressed, using the stress intensification factor approach of the ASME Code for Class 2 Piping (1980 Edition) equivalent to 4.0 Sy.
This stress level corresponds to twice the proposed SONGS-1 limit of 2.0 Sy.
At stress level of 4.0 no leakage occurred. Permanent deformations in several gions of the piping were observed, but there was no plastic collapse or loss of structural integrity in the pressurized piping, even with the extreme seismic input.
Based on the test data reported and strain levels achieved the 2.0 Sy stress limit represents a conservative, yet realistic criteria for piping systems at SONGS-1.
3.3 Summary The correlation study demonstrates that the use of the ASME stress intensification factor approach results in a conservative stress allowable of 2.0 Sy to correspond to the 1% strain limit for carbon steel and the 2% strain limit for stainless steel.
The elastic methodology which satisfies the strain limits is given by:
PDo + 0.75iM
< 2.0 Sh This procedure is conservative based on the following key points:
Moment-strain curves used in nonlinear analysis are very conservative (factor of greater than 2.0 at 2% strain) 3-6
Actual allowable stress from correlation studies is greater than 2.0 Sy Piping system testing shows strains five times less than nonlinear analysis at elastically calculated stresses of 2.0 Sy.
Therefore, the SONGS-1 elastic analyses screening approach results in a conservative estimate of strains in the piping system and ensures the satisfaction of the proposed strain limits.
3-7
Z 6g 0 f
53 FIGURE 3-1 AC-19 Mathematical Model
-Nonlinear Analysis (From Figure 5.1 of Reference [2-1],)
3-8
d,.
3O 41M4 z
3 sA CP a
FIGURE 3-2 MW-01 Mathematical Model - Nonlinear Analysis (From Figure 5.2 of Reference [2-1])
3-9
0 hO
-0 W
QA.
E O1 0O ad*
fili 0
xM us 0 aU
)
0n Un 0
n in M4 C
4 FIGURE 3-3 6-Inch Schedule 40 Carbon Steel Elbow Moment-Strain Curve (From Figure 5.7 of Reference [2-li) 3-10
Example: For a moment of 200 in-kips, experimental study shows 350 0.16% strain; ANSYS predicts 0.45% strain.
EXPERIMENTAL 300 r4 250 z 200 4
150 LOAD APPLIED PERPENDICULAR W
TO PLANE OF ELBOW 6" SCH 40 L.R. ELBOW 100
/CARBON STEEL 0.1 0.2 0.3 0.4 0.5
- STRAIN, PERCENT FIGURE 3-4 6-Inch Schedule 40 Carbon Steel Elbow Moment-Strain Curve (From Figure 5.8 of Reference [2-li) 3-11
NOTEs RADIUS OF CURVATURE OF ELSQWS - S*
(EXCEPT AS NOTED)
SCH40 rza REDUCER
- n.
II
- -e*FL?~
0J0WP SC4 Z
NELDING FLANG e
Le 9d*
VAL VE 10",RADJUS
'.Srx,*
REDUICER N-ELDIN6 PLANGE FIGURE 3-5 Geometry for 70 ft. Long, 6-inch Diameter Piping System 3-12
MW/CER I COWFI 5 Y FORC2NC CARTNOUAKE 2 CA 1707 9
51 V CNANNEL 14 DMFINC
- 0.030 20 r
Ill~i I
III I*
I H1 Test Input Spectrum Level 0 Spectrum 1312 Microstrain Peak 645 Microstrain so Peak 7 oill g
1I J
I Il fil
- 0. I-50t 0
FIGURE 3-6 Testing Spectra for 70 ft. Long, 6-inch Diameter Piping System Compared to that which would Produce Level D AllIowable Stresses 3-13
4.0 gI 3.0 z
2.2 2.1 1.4 1.6 2.0 1.0 Pinned Supports at Variable Support at
- Atators at Fts. 1.0.
1.4. and 4.0 FIGURE 3-7 Geometry for 2U ft. Long, 4-inch Diameter Piping System 3-14
I at" INGINEERS....
Test
- l ua S
Time 15:20 Date9/ 22 /8 1Recorded by a
Page Test Speciamn:
EPRI pipe test specimen Ia Purpose of Test:
attempted 8001 of yield test Direction:
Comints:
Channel 3 Response Spectra for piping input, Uaping - 2" point 1.0 Horizontal Response Spectra for plant sited in Southeast U.S.A. for safe shutdown earthquake 3-1 V5 go V1ane
^
I eKX N
a4"^14 FIGURE 3-8 Testing Spectra for 20 ft. Long, 4-inch Diameter Piping System, Compared to That for a Typical Nuclear Power Plant 3-1 5
Test I
gun 5
Tim 15:20 Date 9/ 2 2/ 81Recorded by B
Page
- Test Specimn:
EPRI pipe test specimen Ia Purpose of Test:
attempted 800% of yield test Direction:
tZ Comeats:
Channel 3 Usaping u 24 Test Spectra Spectra to Generate Kadimn Acceptable Stress Condition FIGURE 3-9 Testing Spectra for 20 ft. Long, 4-Inch Diameter Piping System Compared to That Which Would Produce Level D Allowable Stresses 3-16
TABLE 3-1 AC-19 Nonlinear Analysis Results -
Strains (From Table 5.6 of Reference [2-1])
Linear Analysis Nonlinear Analysis Location (See Figures 5.1)
Stress, ksi Maximum Strain, Percent Elbow 1 @ Node 2 49.7 0.49 Elbow 2 @ Node 7 39.6 Remained Elastic Elbow 3 @ Node 8 69.4 (2.0 Sy (1))
0.74 Pipe @ Node 14 53.8 0.21 Pipe @ Node 16 77.5 (2.2 Sy (1))
0.41 Tee 1 86.6 (2.5 Sy (1))
Remained Elastic Notes:
(1) S = 34.7 ksi 3-17
TABLE 3-2 MW-01 Nonlinear Analysis Results - Strains (From Table 5.10 of Reference [2-1)
Linear Analysis Nonlinear Analysis Location (See Figures 5.2)
Stress, ksi Maximum Strain, Percent Elbow 3 @ Node 8 23.1 0.10 Elbow 4 @ Node 14 55.0 (2.2 Sy (1))
2.0 Elbow 4 @ Node 16 31.8 0.42 Pipe @ Node 19 38.9 0.07 Tee 1 90.8 (3.6 Sy (1))
Remained Elastic Notes: (1) S = 25.0 ksi 3-18
Table 3-3:
Comparison of Analytical and Test Frequencies for 70-ft.
Long, Six-inch, Schedule 40, Piping System Analytical Direction of Analytical Test Test Mode Max. Component Freq.
Freq.
Mode No.
Of Eigenvector (Hz)
(Hz)
No.
1 Y
4.18 4.62 1
2 Y
6.76 7.11 2
3 Z
8.66 2
4 X
8.70 9.16 3
5 X
11.57 11.66 4
6 X
14.53 13.54 5
7 Z
16.24 8
Z 16.65 9
X 17.86 17.71 6
18.53 7
10 Z
21.68 11 Z
24.24 23.94 8
12 X
25.72 25.87 9
13 Z
28.96 28.06 10 29.30 11 3-19
4.0 CONSERVATISMS AND MARGINS 4.1 Categorization of Seismic Loadings In current ASME Code rules, seismic inertia stress is categorized as the primary stress and evaluated in Code Equation 9 as follows:
PD D
Class 1 piping:
B o+B M. < 3S (Level D) 2t 21 Class 2/3 piping:
PD0 0.75 i (Ma + MB) < 2.4 S (Level D)
+
h 4t Z
The 1980 edition of the Code for Class 1, 2 and 3 piping is used for the above equations and all terms are defined in the Code.
Studies have been performed, or are in progress, to investigate the technical support for the elimination of the primary stress requirement for seismic loading on piping. E.C. Rodabaugh stated in
[3-6] that because of the limited energy input of earthquakes to piping systems, earthquakes will not produce gross plastic deformation of piping systems.
The EPRI/ANCO piping tests [3-3]
also suggested that the real failure mechanism for earthquakes is not the formation of primary collapse mechanisms, but is fatigue-related.
A logical consequence of these studies is to remove moments due to earthquakes from Code Equation 9 and perform a separate low cycle fatigue evaluation. For example, E.C. Rodabaugh recommended in [3-6] that the allowable faulted stress ranges due to SSE should be up to 4.5 Sm for carbon steel and 7.9 Sm for stainless steel.
If seismic inertia stress is categorized as a non-primary stress, the 2.0 Sy allowable for pressure, gravity plus inertia loadings re.presents a conservative primary stress limit because seismic inertia is the dominant loading of the three.
Based on the EPRI/ANCO studies, the proposed 2.0 Sy limit has a margin of 1.5 -
2.5 against the experimental result.
4.2 Dynamic versus Static Loadings Current ASME Code elastic analysis stress response acceptance criteria do not differentiate between dynamic (such as seismic) and static loading events. It is well known that structures can withstand much greater loads if the loads are dynamic in nature; i.e., cycled on and off the structure. Since the ASME Code is based entirely upon the static strength of components, there is a seismic reserve margin associated with neglecting the dynamic aspects of the loading. Reference [3-7] describes one major study to quantify this margin in the particular case of nuclear power plant piping 4-1
systems. The results show that a dynamic load must be, on the average, 1.5 times a static load in order to produce the same stress and strain levels that are currently allowed by the ASME Code for Service Level D conditions (i.e., loads which include the design basis earthquake).
Also, materials testing procedures are based upon the pseudo-static application of loads (i.e., the loads are applied to the specimen at a very slow rate). It is well known that higher rates of loading result in an increase in the yield stress of the material - a phenomenon termed the dynamic strain-rate effect. Since the ASME Code considers both static and dynamic loadings, the specified minimum yield stresses are based upon the lower values appropriate for static cases. Reference [3-8] shows that the strain rate effects associated with seismic loading would result in a minimum increase in material yield strength of 11 percent. Figure 4-1 shows the effect of strain rate on yield strengt of mild steel [3-9i.
For example, at a strain rate of 2.5 x 10- in/in/second (which corresponds to the piping fundamental natural frequency of 6.Hz),
the increase in yield strength over the static yield strength is about 15 percent.
In establishing the allowable stress limit 2.0 Sy for the SONGS-1 approach, the benefit associated with the dynamic aspects of the seismic loading, as well as the dynamic strain-rate effect is conservatively neglected in piping analysis.
4.3 Operating Plant Earthquake Experience The El Centro Steam Plant was inspected by an NRC team following the October 15, 1979 Imperial Valley Earthquake [3-10]. The inspection was of interest to the NRC because the plant is similar to older operating nuclear power plants in both design and types of equipment installed. The NRC team observed only minor damage to the plant's structural and mechanical systems despite the estimated 0.5g peak horizontal ground acceleration produced at the site.
The large magnitude earthquake had its epicenter on the Imperial Fault, approximately 15 miles from the plant. When the earthquake occurred, Units 3 and 4 of the four-unit nonnuclear plant were operating.
The operating units tripped off-line when the station's power was lost. Unit 3 was restored to service within 15 minutes after the main shock. Unit 4 was restored to service within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
The plant's original design criteria specified a static lateral load equivalent to 20 percent of the dead and live loads. Following the earthquake, the NRC engaged LLNL to analyze Unit 4 [3-11]. To accurately predict the actual response of the Plant from the earthquake, the LLNL study used realistic assumptions for the analysis, thus eliminating many of the conservatisms that are used in the analysis of nuclear power plants.
For example, in the 4-2
soil-structure interaction analysis, soil damping ratios as high as 100 percent of critical were used.
The use of these highly damped soil springs provided a reasonable estimation of the forces induced in the structure as evidenced by the close relationship of the observed to the predicted base shears. It should be noted that for SONGS-1, the soil damping was limited to a maximum of 20 percent of critical, when in fact, experimental testing supported the use of damping as high as 50 percent of critical. It is reasonable to conclude that as a result of limiting the soil damping alone, we are severely overestimating the response of SONGS-1 structures, piping and equipment.
The LLNL study concluded that the forces experienced by the plant equipment were on the order of 2 to 9 times greater than the 0.2g specified design load. The reserve seismic capacity in the plant equipment is then at least of the order of 100 percent. Note that because of the highly damped soil properties used in the SSI analysis, the forces calculated from analysis represent a low estimate, if compared with the forces that would be obtained using more conservative assumptions, as was done for SONGS-1.
The reserve margin would be even greater if analysis techniques such as used for SONGS-1 were used.
The above conclusion was confirmed by observations of the actual response of piping systems at the plant.
Post-earthquake inspection indicated that no high-temperature or high-pressure piping failed during the earthquake. Piping failures were observed only in two lines, at locations that had been either weld-repaired or had been excessively corroded.
We can conclude that operating nuclear power plant structures, equipment and piping, such as those in SONGS-1, have considerable seismic reserve margins capable of sustaining an earthquake which far exceeds its nominal design capacity.
4-3
100 90 60 U) x 70 z
60 U) w 50 U) 40 30 20 10 0
10-6 Is' 10-4 0,
102 10-1 I
10 102 103 AVERAGE RATE OF STRAIN PER. SEC.
FIGURE 4-1 Relationship Between Material Yield and Strain Rate for Mild Steel (Reference [3-9])
4-4
5.0 REFERENCES
[1-1]
"Safety Evaluation Report of the Return To Service Plan, San Onofre Nuclear Generating Station, Unit 1," Docket No. 50-206, NRC Letter to SCE, dated November 21, 1984.
[1-2]
SCE Report No. 01-0310-1368, "San Onofre Nuclear Generating Station Unit 1, Seismic Program for Long Term Service," Submitted to NRC on March 8, 1985.
[2-1]
Impell Report No. 04-0310-0063, "SONGS-1 Functionality Criteria for Piping Systems in Response to the DBE Event," Revision 2, December 1983 (Transmitted to NRC in SCE Letter to NRC, from K. Baskin to D.M. Crutchfield, dated December 23, 1983).
[2-2]
ASME Boiler & Pressure Vessel Code, Case N-47-21, "Class 1 Components in Elevated Temperature Service,Section III, Division I," approved December 11, 1981.
[2-3]
Rodabaugh, E.C., "Position Paper on Stress Allowables for Piping,"
included on NUREG-1061, Volume 4, "Report of the U.S. Nuclear Regulatory Commission Piping Review Committee Evaluation of Other Loads and Load Combinations," December, 1984.
[2-4]
Imazu, Sahahibara, Nagota and Hashimoto," Plastic Instability Test of Elbows Under In-Plane and Out-of-Plane Bending," Paper E6/5, Sixth SMIRT Conference, Paris, France, August 1981.
[2-5]
Greenstreet, W.L., "Experimental Study of Plastic Response of Pipe Elbows," ORNL/NUREG 24, February 1978.
[2-6]
Teidoguchi, H.,
"Experimental Study on Limit Design for Nuclear Power Facilities During Earthquake," Japanese Report 50-170b Issued to U. S. NRC, February 1975.
[2-7]
Ibrahim, Z.N, Kitz, G.T., "Evaluation of the Functional Capability of ASME Section III Class 1, 2, and 3 Piping Components," ASME Paper 78-PVP-83 and Sargent & Lundy Engineers Report No. GEX 575U-UO, June 1978.
[2-8]
Marks' Standard Book for Mechanical Engineers, 7th Edition.
[2-9]
Harvey, John F., "Pressure Component Construction".
[2-10]
EPRI NP-2347, "Instability Predictions for Circumferentially Cracked Type-304 Stainless Steel Pipe Under Dynamic Loading," Volume 2, April 1982.
5-1
REFERENCES (continued)
[3-1]
Impell Report No. 01-0590-1355, "Quad Cities Unit 1 Functionality Study of Piping Systems in Response to the SSE Event", Revision 0, December 1980.
[3-2]
NUREG/CR-3893, "Laboratory Studies:
Dynamic Response of Prototypical Piping Systems," Prepared by ANCO Engineers, Inc. for the USNRC and EPRI, August 1984.
[3-3]
EPRI Report No. NP-3746, "Dynamic Response of Pressurized Z-Bend Piping Systems Tested Beyond Elastic Limits and with Support Failures," Prepared by ANCO Engineers, Inc. for EPRI, December 1984.
[3-4]
Sand, Lochan, Schoor, and Hass, "Experimental Study of Dynamic Behavior of Piping Systems Under Maximum Load Conditions Analysis," Kraftwerk Union, Federal Republic of Germany, ASME 1982 Orlando Conference, 1982.
[3-51 Ibanez, P., Keowen, R.S., and Renty, P.E., "Experimental Study of Dynamic Behavior of Piping Systems Under Maximum Load Conditions Testing." ANCO Engineers, Culver City, California, ASME 1982, Orlando Conference, 1982.
[3-6]
"Proposed Code Changes to Place Seismic Loading in the Fatigue Category," PVPC Technical Committee on Piping Systems. July 11,
,984.
[3-7]
Campbell, R.D., et. al., "Development of Dynamic Stress criteria for Design of Nuclear Piping Systems," Structural Mechanics Associates, Inc. Report No. 17401.01, Prepared for Pressure Vessel Research Committee, November 1982.
[3-8)
Smith, P.D., et. al., "LLL/DOR Seismic Conservatism Program:
Investigations of the Conservatism in Seismic Design of Nuclear Power Plants," Lawrence Livermore National Laboratory Report No.
UCRL-52716, 1980.
[3-9]
Maijoine, M.J., "Influence of Rate of Strain and Temperature on Yield Stresses of Mild Steel," Journal of Applied Mechanics, Volume II, ASME Trans.,
Volume 66, Pages A211-A218, 1944.
[3-10]
Levin H.A., Martore J.A., Reiter L., Jeng D., Heller L.W.,
"Reconnaissance Reports - Imperial Valley Earthquake, October 15, 1979," U. S. Nuclear Regulatory Commission, Washington D. C.,
Memorandum for Darrel G. Eisenhut (November 2, 1979).
[3-11]
NUREG/CR-1665 "Equipment Response at the El Centro Steam Plant during the October 15, 1979 Imperial Valley Earthquake," prepared by LLNL for the Office of Nuclear Reactor Regulation, October 1980.
5-2
Appendix A:
List of Piping Materials and Allowable Stresses
- I Max.
Operating Winter 1980 Code Temp.
2.4 Sh 2S Witr 2.4S /2S Material (F)
(ksi) h 25 (ks)
.4/
A312 TP304L 200 37.68 42.60
.88 A312 TP304 575 38.16 37.00 1.03 SA312 TP316 570 41.52 38.26 1.08 A106 B 545 36.00 54.44
.66 A53 B 340 36.00 61.20
.59 The apparent anomaly occurring in the table above, in which 2.U S is actually less than 2.4 Sh for two materials, is easily explained by considering the basis of the allowable stress Sh.
As defined in Appendix III, Article III-3000 of the ASME Code, Sh is defined as the lowest of:
Carbon Steel
- 1) 1/4 Su minimum (ambient temp.)
- 2) 1/4 Su (operating temp.)
- 3) 2/3 Sy minimum (ambient temp.)
- 4) 2/3 Sy (operating temp.)
Stainless Steel
- 1) 1/4 Su minimum (ambient temp.)
- 2) 1/4 Su (operating temp.)
- 3) 2/3 S minimum (ambient temp.)
- 4) 0.9 5y (operating temp.)
For SA 312 TP304 and SA 312 TP316, Sh is controlled by 1/4 Su at operating temperature and 0 9 S at operating temperature, respectively.
In these cases,.4 Sh is actually higher than 2.0 S as shown below:
For A312 TP304:
Sh = 1/4 Su @ 575*F = 1/4 (63.5) = 15.bb ksi (Code uses 15.9 ksi) 2.4 S = 2.4 x 15.9 = 38.16 ksi S @5750F = 18.5 ksi 2S = 2 x 18.5 = 37 ksi y
For SA312 TP316 S @ 570*F = 19.13 ksi Sh = 0.9 Sy @ 570'F = 0.9 x 19.13 = 17.22 ksi (Code uses 17.3 ksi) 2.4 Sn = 2.4 x 17.3 = 41.52 ksi 2 S
= 2 x 19.13 = 38.26 ksi A-1
100.
SA106 B AND A53 B 2 0.
40.-
2.4OSh z
S20.
- 0.
100.
200.
300.
400O.
500.
600.
TEMPERATURE (DEGREE F)
IKF'ELL CORPORRT TON MARTERIAL PROPERTIES APPLICABLE TO SONGS I LONG TERM SERVICE PROCRRM
100.
SR312 TF30'4L
- 80.
Lj 60.
~2.0 S LiL y
cm 40.
cr 2
.4A S
h S20.
1*00.
200.
300.
400.
500.
600.
TEMPERRTURE (DECREE F) ll/,ELL C0RF1ORRTION M.,TERIRL PrOPERTIES RFFLICR19LE TO SGNCS 1 LONG TERM SERVICE CRF FICURE A-2______
100.__
8312 TP304 8 0.
7
- z crw 60.
Lu cm 40.
-LJ z
~220.
- 0.
1,00.
200.
300.
400.
500.
600.
rE1F'ERRTuRE (DEGREE F)
~'L L C 0R F F.qT I N
!Y~rTE-RIPL F'.CF'ERTIAES rFPLIC!;5LE TO SCNCS I L3NG TERM SERFVICE F;K.. ;rr-F\\F FIGURE A-3
100.
SR312 TP316 2 80.
4n Lu60.
2.0 S m
m y
W 40.
2.4S h
z u
- 20.
0 I
I I
100.
200.
300.
400.
500.
600.
TEMPERATURE (DECREE F)
IMPELL CORPORATION MATERIAL PROPERTIES APPLICRBLE TO SONGS I LONC TERM SERVICE PROGRAM FICURE A-