ML20215K177

Proposed Topical Rept on Operability Assessment of ASME Section III Piping & Supports After Unanticipated Loadings

ML20215K177
Person / Time
Site:	LaSalle
Issue date:	09/30/1986
From:	COMMONWEALTH EDISON CO.
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ML20215K172	List: ML20215K171 ML20215K177 ML20215K183
References
NUDOCS 8610280011
Download: ML20215K177 (6)

Text

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TOPICALREPORT ON OPERABILITYASSESSMENT OF ASMESECTIONIIIPIPINGANDSUPPORTS AFTER UNANTICIPATEDLOADINGS i

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Prepared by COMMONWEALTH EDISON COMPANY September, 1986

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TABLE OF CONTENTS PAGE 1.0 Introduction 1 2.0 Background 1

3.0 Operability Criteria 2 3.1 Piping and Welded Att'achments 2 3.2 Piping Support Components and Structures 3 4.0 Examples of Use in the Past 4

5.0 Intended Use'in the Future 4 6.0 Conclusion 4

Attachment:

Sargent & Lundy Report " Low Cycle Fatigue Assessment of ASME Section III, Class 2/3 Piping for Unanticipated Loads."

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1 1.0. INTRODUCTION ,

i piping and support components in operating plants may at times experience unanticipated loads. The loads may be severe enough to cause the stresses in piping and/or supports to exceed the original design criteria as stated in the Safety Analysis Reports. The operability of the piping and supports, or otherwise, the ability of the piping and support components to continue meeting their designed service, comes into question. Since no formal or informal rules have been proposed, this report contains Commonwealth )

Edison's approach to assessing the operability of piping and  ;

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support components subjected to unanticipated loads at the LaSalle' '

l County Station, Units 1 and 2.

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1 2.0. BACKGROUND During snubber surveillance testing for Unit l's first refueling outage, 95 snubbers were found to have excessive drag loads and j I some were locked rigid. In accordance with Section 4.7.9(g) of the LaSalle Technical Specification, an engineering evaluation was performed on the components to which the inoperable snubbers were attached. The affected components typically included all components in a piping subsystem: piping, pipe clamps, shear lugs, standard pipe support components, auxiliary steel, structural attachments and structural steel. A subsystem typically begins and ends at anchor points, penetrations, nozzle connections and analytically-decoupled header connections. Therefore, the effects

! of a snubber failure is limited to the subsystem on which it occurs.

l The engineering evaluation performed on a piping subsystem as a l result of failed snubbers considers the effect of all past loads incurred by the subsystem, design and unanticipated. Design loads typically seen include; 1) dead weight, 2) pressure, 3) thermal, and 4) SRV (all/asy). Unanticipated loads include; l) increased loads from snubbers failing to perform their design requirement, and 2) water hammer loads if such an event occurred on the system.

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3.0. OPERABILITY CRITERIA I

j The criteria in the following sections will be used to determine if j a piping system component is operable.

i j 3.1. Piping and Welded Attachments l

Class 1 piping will.be evaluated per the fatigue evaluation

, requirements in ASME Code Section III, Subsection NB. ,

1 j However, the Code does not provide any low cycle fatigue

! methodology for Class 2 and 3 piping. The proposed approach-1 j to fatigue evaluation of Class 2~and 3 piping is a logical extension of Code rules in the low cycle range using the same test data and the factor of safety that form the basis of ASME Code Section III Subsection NC/ND 3650 fatigue evaluation requirements for load cycles-greater than 7000.

The criterion is discussed in detail in the attachment.

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The fatigue requirement is satisfied using the following )

l equations:

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l j N -= (245000/iS)5 Cycles l

. n/N i 1 i

where j n - Actual number of load cycles 1

N = Allowable number of load cycles

] , iS = Intensified pipe stress range. Code i

intensification factors are used.

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l m,, , - . . , _ . _ _ .. , , _ - , ,,..r,,._. .-_..-,,,-..r .,,.4.,,e---,,,, _ _ . _ . _ - . _ , _ , , , , ~ , _ - _ -

If the piping is subjected to stress cycles with more than one stress level, then the cumulative fatigue damage is calculated using the Miner's rule as defined below:

ny /Ny + n 2/N2 + ...... +n k "k i1 where n) = actual cycles associated with iS$ (j = 1, 2, f

....... k>

N. = Allowable cycles for Stress Level iS.

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iS: = Stress level associated with loading event j Further, the above approach could be used to evaluate mechanical loads. However, the piping stresses due to mechanical loads are checked against GE Report'NEDO-21985 functional capability criteria. If piping stresses exceed functional capability criteria, a walkdown of the affected piping will be performed to ensure no gross deformation of piping or cracking has occurred. Inspection of the highly stressed areas will be performed according to CECO NDE Visual Examination procedure VT-1-1. '

3.2. piping Support Components and Structures The stresses or load on standard component supports, auxiliary steel, structural steel or embedments due to postulated pipe loads will be checked against faulted allowables. If faulted allowables are exceeded, pipe support components and structures will be inspected for deformation or cracking per inspection procedures VT-3 and VT-4, as applicable.

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4.0. EXAMPLES OF USE IN THE pAST The above criterion has been used in the evaluation of some of the LaSalle Unit 1 piping for increased snubber drag force and/or snubber lock-up. Its use was limited to the evaluation of piping for past loads that were not anticipated during the original analysis. It was not used as a design basis for anticipated future loads. An example of its use is found in Appendix A of the

, attached report.

5.0 INTENDED FUTURE USE I

It is emphasized that the proposed (Markl) fatigue criteria for piping will not be used as a design basis. All piping in ASME Section III systems will continue to be designed according to ASME Section III Code. Th'e primary corrective action to prevent Code allowables from being exceeded is to prevent the recurrence of unanticipated loads.

The proposed operability criteria is intended only to act as a guideline in assessing the operability of piping system components and determining when visual inspection, NDE, and replacement is necessary. The operability criteria set forth in this report will be used when an engineering evaluation of piping system components is required as a result of failed snubbers, water hammer events, or other unanticipated loads. .

6.0. CONCLUSION The proposed operability criteria provides a way in which to assess the operability of piping system components. The operability criteria will establish the basis on when visual inspection and/or NDE is necessary to assess the operability of a component which has exceeded the original design criteria because of an unanticipated load. However, its use will be limited to the engineering evaluation of piping system components and will not be used as a design basis.

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