ML20199H420
| ML20199H420 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Comanche Peak |
| Issue date: | 02/04/1985 |
| From: | Shao L NRC - COMANCHE PEAK PROJECT (TECHNICAL REVIEW TEAM) |
| To: | Noonan V NRC - COMANCHE PEAK PROJECT (TECHNICAL REVIEW TEAM) |
| Shared Package | |
| ML17198A302 | List:
|
| References | |
| FOIA-85-299, FOIA-85-59, FOIA-86-A-18 NUDOCS 8607030303 | |
| Download: ML20199H420 (3) | |
Text
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.t I:Eik)PEDU;l FOR:
V. Hoonan, Project Director Co lancim Peal. Project FR0!.:
L. Shao Leader, Civil / Structural S 1%chanical/Pipinq Tean SU.; JECT:
STATUS OF C0"ECHE PEA!; CIVIL /STRUCTUP/.L AjD MEC!!f6f'ICAL/ PIPING ALLEGATIO:lS i
- j Tnt attached for your infonnation is the status of Hechanical/Piring and I
Civil / Structural alleoations.
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N p-o L. C. Shao. Leader Civil / Structural and itschanical/ Piping Tea ~.
Conancl.e Peak Project
Enclosure:
At stated I
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o" C0r.Afi:4E PEEL civil /STRUCTURI STATUS 1.
Total No. of Allegations and Status of SSER hurber of Allegations Status of Draft SSER Completed To be Completed 1.1 Original Allegations 57 57*
0 1.2 New Allegations from CASE 24 0
24 1.3 Total Allegations 81 57*
24 2.
Closing Interview with Allegers Completed interviews with 4 out of 16 allegers. Attempting to locate and interview with 4 other allegers. Sent a closure letter to one other alleger. The balance of alleg'ers cannot be located or are not willing to meet with the TRT.
3.
Applicant Action Items In the process of working with the applicants on 5 applicant action iter.s.
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- Draf t SSER has been completed and reviewed by OELD.
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MECHANICAL / PIPING STATUS 1.
Totei h,. of Allegations and Status of SSER Number of Allegations Status of Draft SSEP Completed To be Completed 1.1 Originzl Allegations 147 147' O
1.2 New P.iscellaneous 280 280* (completed) 0 AllegEtions fror A-45 (by sampling 22 allegations) 1.3 New Allegations from CASE 9
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1.4 Total Allegations 436 427*(169) 9 2.
Closir.; interviews with Allegers Corpleted interviews with 12 out of 23 allegers.
One additional interview vill be heid. The balance of allegers cannot be located or are not willing tc r,eet with the TRT.
3.
Applicar.t Action items Applicant has not responded to 5 Applicant Action Items.
- Draf t SSER has been completed but not yet reviewed by OELO and management.
FEB 2 51985 MEMORANDUM FOR:
Vince Noonan, Project Director Comanche Peak Technical Review Team FROM:
L. C. Shao, Group Leader Civil / Mechanical Groups Comanche Peak Technical Review Team
SUBJECT:
REVIEW 0F DESIGN QA DRAFT 1 We have reviewed the subject draft and feel that this discussion has little impact on our TRT review since most of our review concerned fabrication and not design.
We have the following comments:
Page 6 - Item 13: We think support manufacturer should be changed to support designer since PSE would also be in this cycle.
Page 11 - Second paragraph, second sentence:
The TSDRs are not " controlled" like a CMC but they are logged and tracked by the technical services organization.
Therefore, the TSDR is tracked and until it is resolved the CMC (which is controlled) cannot be closed out.
(Ref. January 15 transcript, pp. 55-56.)
Page 15 - We do not see the difference between a snubber attached to the floor or ceiling under a dynamic load.
If you have a concern with one you will have a concern for both. We understand the concern that may exist for a strut attached to the floor which will be resisting dead weight and thermal in addition to the seismic loads. What is being described here can be construed to be that there is a stability concern for all pin ended supports that undergo a compressive loading.
These concerns would apply to all supports and restraints regardless of orientation that use clamps in conjunction with snubbers and struts.
Page 14 - We do not understand what the concerns are for the trapeze type restraints. Are the concerns just that they are different, or they are inadequate, or both?
Original Signed by L C. Shoe L. C. Shao, Group Leader Civil / Mechanical Groups Comanche Peak Technical Review Team J[.
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D. Eisenhut J Fair R. Masterson R. Bosnak
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FEB 6 1985 NOTE T0:
R. Bosnak D. Terao L. Shao J. Fair B. Saffell P. Chen FROM:
Vincent S. Noonan, Director Comanche Peak Project Enclosed for your review and coment is Don Landers response to the applicants motion for sumary disposition on Design QA.
Please forward all coments to me by COB Monday, February 11, 1985 (Mail Stop P-234).
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Vincent S. Noonan, Director Comanche Peak Project D
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Technical Report TR-62MB I In determining the acceptability of Design QA, two important issues need.to be revi,ewed. The first is to determine whether a D'esign Process is in place and functioning.2 The second is to determine wheth'er the existing Design Process is structured so that, if followed, reasonable assurance exists that the licensing commitments for a plant are complied with.3 The second issue above is the primary purpose of developing a process to control..the design.
Control. is intended to channel the efforts of the design groups to the goal of fulfilling licensing commitments.
This, in fact, may require some members of the design staff to do things differently than they are used to.
Also it may require approaches, techniques, analyses, etc., which are significantly different than the last nuclear power plant project com'pl eted by the. design -agent simply because the licensing commitments are different.
It" is important to recognize that both issues must be acceptable or questions with respect to adequacy of the design may exist.
For exampl e, a Design Process may be in p.l a c e, supported by procedures, subject to meaningful audits and verification and yet be flawed because it does not address the licensing commitments. Similarly a Design Process which addresses the licensing commitments may be in place but it is. not functioning properly and required audits and verifications are not being performed to demonstrate inadequate implementation and to provide corrective action.
I Note that this terminology has been used in these proceedings.
The author does not endorse its use in the context of the concern at Comanche Peak but will comply with current terminology.
2 This is essentially a review of paper.
For example, proper sign-offs exist, audits were performed appropriately, check lists were complete, etc.
This is essentially a review of technical adequacy.
For example, do6s the process assure implementation of a design that complies with applicable Regulatory Guides and Codes.
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Technical Report TR-621.6B 4,.
Two examples of the above situations were found by Cygna during the Independent Design. Verification.
The first is the issue related to mass participation.
Under questioning, during a January 10, 1985 meeting with the NRC, Cygna indicated that no procedure existed at Gibbs'and Hill (G&H) i to control this portion of,the Design Process. Therefore, verification and' QA audits using the process in place would not have indicated noncompliance with the licensing commitments for Comanche Peak. The second is the issue related to mass point' spacing.
Under questioning during the same January 10th meeting with the NRC, Cygna indicated that an acceptable procedure exists in the Design Process at G&H which addresses mass point spacing, however, in many cases this procedure was not followed. Design verification and QA. audits' failed to uncover the inadequate implementation of an existing procedure' which was. in place...to.. provide a design that
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complied with the licensing commitments. '
. It would appear that until the Phase 4 effort by Cygna the issue related to technical review of the Design Process to determine whether it controlled design such that the licensing commitments were satisfied was not performed..This opinion is reinforced by the fact that, at this point in time, Cygna is revising their Phase 1, 2 and 3 conclusions related to Design QA.
Having established that Design QA has two sides, a paper trail side and a technical side, it is necessary to look at the process in existence for Comanche Peak for piping and supports.
Pipe supports and' piping are so closely intertwined and technically interdependent that it is difficult to separate them.
In designing a j
piping system the designer makes certain assumptions concerning individual support configurations.
Al so, a piping designer usually cannot make appropriate judgements on the adequacy of a piping system without g.,. - -._
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Technical Report TR-6216B,
m reviewing.the iping layout with all of its supports.4.This is particu-l larly important when addressing an issue such as support stability since the-interaction between the support and the pipe is usually critical in
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making this ' determintion.
For example, for a pin-pin connection, the i
displacement,of the piping at the support location due to operating condi-tions (thermal expansion) can result in a reduction in the ability of the support to carry a load along its axis.
Also, the concern of the author with respect to support stability is directed towards anticipated water and/or' steam hammer. events which usually result in higher loads and dis-placeme'nts on the' piping system than does a seismic event. To accomplish the kind of review discussed above it is necessary to have an established l
and ! functioning link betw'een the group responsible for piping design and analysis and the group re'sponsible for support design and analysis.
In the majority of cases a utility constructing a nuclear power plant i
contraits with a design firm (usually one of the major AE's) to provide design services in the areas of piping and pipe supports (along with a number of other areas not relevant to this discussion). The AE is respon-sible for the design process interface controls and procedures required to i
develop construction drawings for piping and pipe supports.
The AE may elect to subcontract a portion or all of this work to a third party;.
however, responsibility for, and control of, the design of both piping and supports rests with'the AE.
This responsibility and control exists even when the third party uses its own Design QA Process and Procedures. The AE l
will review and' approve the process and perform audits to determine acc'ept-ability of implementation.
The above does not eliminate the. requirement that.the utility is ultimately responsible.
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i Your attention is" called to Welding Research Council Bulletin 300,
" Technical Discussion on Industry Practice," Section 1.7, page 26, December 1984.
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Technical Report TR-5216B.,
I 4
It is my understanding that, for Comanche Peah, TUGC0 contracted with G1H to perform piping design and also contracted with ITT Grinnell and NPSI to. perform support design. The only,G&H interfacing (or control) document imposed on ITT Grinnell and_NFAi_ wa s jpecTfication M5 43A.
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a contractual sense, therefore, TUGC0 was acting as an AE.
This role required TUGC0 to perform the activities necessary to assure that an overall process was in place, including necessary interfaces, and that the process was one that would provide control on the design so that proper engineering would result in construction drawings that complied with the licensing commitment. Some utilities have acted in this fashion, however, they do perform and control a significant portion of the piping and pipe support design and have significant experience in this area.
It is noted that this contractual approdch was not -unique to Comanche Peak for G&H.
They had the same type of contractual ' arrangement for the Fort Calhoun project.
No information is available concerning the design process for Fort Calhoun norTow it compared to that for ComanEPeak ~ particularly with respect to G&H role.
S In response to questions at four meetings with the NRC, TUGC0 indi-cated that the process for initial design, including issue of initial construction drawings, consisted of the following.
(1)
G&H performed preliminary free thermal expansion analysis and forwarded these to ITT Grinnell and/or NPSI.
(2)
Deadweight supports were located by Grinnell and,NPSI using the hanger spacing table established in ANSI B31.1.
Potential locations and directions of seismic restraints were established by. ITT Grinnell and NPSI.
Guidelines for spacin'g these re-straints were established by G&H and were based on frequency considerations.
l 5 August 9,1984, January 10, 1985, January 15, 1985 and January 17, 1985.
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(3). G&H then performed piping design and complete analysis, including location and selection of the type of pipe supports.
This required the normal iterative process of layout, analysis, sbpp' ort location, modification of layout, analysis, etc.
Eventually a design evolved that analytically complied with the licensing commitment.
(4)
Support locations, types and load combination data were sup-plied to ITT Grinnell and NPSI.
(5)
Support details (including selection of standard hardware) were developed and support analysis performed by ITT Grinnell and NPSI.
Cases could.arise_ where the. location of a specific support for the specified loadinh~was not acceptable (i.e., an adequate design could not be reasonably developed).
In such cases the support contractor would inform G&H and another iteration in the piping analysis process would occur.
(6)
Design and analysis was completed and supports were fabricated e
and shipped to the site. Review of the support details at G&H was not required at this time in the design process.
6 (7)
Modifications to supports required by field conditions were made by f'ald engineering (Texas Utilities responsibility) and a Component Modification Card (CMC) was executed.
(8)
The CMC was forwarded to the responsible support design agent (ITT Grinnell or NPSI) for review and approval.
(9)
A third pipe support group (PSE) was formed which was under the technical direction of TUGCO.
This group functioned just as ITT Grinnel and NPSI did although the engineering and administrative procedures differed between the three organiza-tions.
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(10) Also in this time frame, ITT Grinnell and NPSI sent support designers and analysts to the site to perform design, analysis, modifications, and review of CMC's.
These ITj Grinnell and NPSI personnel were administratively controlle'd by TUGC0 but utilized their own procedures in performing their required tasks. For ITT Grinnell these procedures were the same as those for the home office. NPSI developed specific procedures to be used by their personnel at the site.
(11) Any of the three organizations who had concerns with a CMC informed the initiating field engineer of that concern in a Technical Services Design Review (TSDR) memo.
(12) At a point in time when the pipe was installed and Brown and Root (B&R) felt confident that the support as designed or modi-fied would be able to be installed, an as-built walkdown was performed by TUGC0 personnel and a package forwarded to G&H for their
- review, reanalysis (as required),
comments and/or acceptance.
G&H comments or concerns with as-built condition were transmitted to TUGC0 in a G&H memo.
-(13) After piping reanalysis and determination of new loadings, the responsible support manufacturer would be supplied with the new loads by G&H to be used in their review, reanalysis, comments and/or acceptance, of the as-built support configuration.
For cases where. piping reanalysis was not required, the support designer would review, reanalyze, comment on and/or accept the as-built configuration.
(14) The documentation from G&H and the support design organizations was then forwarded to TUGC0 who reviewed the documentation and stamped those supports which were accepted by the support design organizations "as-built certified."
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Technical Report TR-6216B.
(15) This process continued on an interative basis until all piping and supports were acLepted.
(16) G&H in their review of as-built information was responsible for acceptance of the piping system (piping plus pipe supports) as complying with the licensing commitments.
As indicated, the Design Process at Comanche Peak was modified as the project evolved from design to design and construction.
This is not unusual in the construction of a nuclear power plant.
The author has some cdncerns with the process described above and with some aspects of implement'ation of that. process.-...These concerns do not necessarily result in a conclusion tha't tiie process or implementation is sufficiently flawed to result in a design that is not in compliance with NRC safety criteria or the licensing commitments of TijGC0 for Comanche Peak. The concerns are as follows:
Concern 1 TJ1e failure of the Design Ecocess to require G&H to review designs (and modifications) of pipe supports prior to fabrication and installation can result in a situation that is of concern.
Piping is not a " stand-alone" commodity.6 A basic premise in designing a piping system includes (but is not limited to) the fact -that support designs will reflect the assumptions made in the analysis of that piping.
This is of particular concern to the author as it relates to anticipated steam and water hammer resulting from plant operating transients. Since G&H was not. required to (and therefore did not) review support designs prior to their fabrica' tion 6 G&H agrees with this in footnote 13, page 17, of summary disposition.
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Technical Report TR-6216B.
and installation they are always dealing with an installed or " ready.for installation" situation.
This could impact the judgement of a reviewing individual..One may' be more wiJling to accept as installed situations rather than as designed situations.
This is not to be construed as a judgement that this occurred at Comanche Peak nor is it to be construed as a judgement on the adequacy (safety significance) of the design that exists at Comanche Reak.
Again, my major concern is related to anticipated transients such as steam _ hammer re,sulting from a turbine trip or water hammer resulting from pump switching and rapidly closing check valves. With respect to seismic loading it is my current ooinion (based on the data available to me) that 7
the existing. s.upports. wijl. be adequate.
This-is based on the fact that the CPSES piping was designed using l' wer damping values than are currently o
permitted.
Use of PVRC damping has resulted in reductions of peak accelerations of up to 50% with general reductions on the order of 35 to 40%. Further, test data indicates that piping systems with supports that are flexible, have gaps and pinned connections usually result in higher damping since a significant amount of energy is used up in deflecting the restraint, closing gaps and moving about the pinned connections.
Concern 2 The use of nomographs based on frequency to locate seismic restraints usually results in an excessive number of restraints.
This approach was used at Comanche Peak and apparently resulted in excessive seismic re-straints. This is verified, to a degree, by the fact that a majority of the seismic restraints are very lightly loaded. Lightly loaded restraints which are designed using a deflection criteria (i.e.,1/6-inch maximum) are usually very flexible.
Flexible restraints have been a subject of concern at CPSES.
7 Those restraints which are pinned vertically and have bumpers for out-of-plane displacement control are an exception and are discussed in Concern 3.
Technical Report TR-6216B.
Concern 3 The stabil,ity question has resulted in a number of analyses and some modifications to supports. In one area, on the main steam system, bumpers were added to prevent rotation of the support about the pipe. Cygna has not accepted this design as sufficient to provide stability.8 TUGC0 has performed seismic analysis with the supports in place and with the supports' removed and the resulting stresses are acceptable in both cases. However, the supports are still in place and, according to Cygna, will not function.
My concern is that the seismic analysis does not bound the real situation which could be that the support has become " tilted" or unstable and then a dynamic load is applied to the system.
Does the tilted support provide restraint in a direction that was 'not. intended?-- Once tilted does the support restrain thermal expansion? To assume that a support is acceptable because it is analytically not required may not " bound the problem" in every case. This would also apply to a support that was overstressed. To perform a piping analysis without the support in place and demonstrate acceptable stresses in the pipe and other supports is not always the worst case unless support failure is complete (or the support is physically removed) and does not impose a restraint on the system that was not accounted for.
Concern 4 A design process must provide a controlled communication between con-struction activities and design.
TUGC0 is right in pointing out thaff a Nonconformance Report (NCR) is not the only document for accomplishing this.
Examples of other techniques used in the past are a Field Change Request (FCR) and a Drawing Change Notice (DCN). -TUGC0 used a Component Modification Card (CMC) to provide this interface. However, some concerns exist with the implementation of this interface. The design process under-went an evolution as plant construction activity increased. The following
'8 January 10, 1985 Transcript, pp. 72 and 73.
Technical Report TR-6216B,
t 4
e discussion addresses the process from its initial to its final stage as now understood.
In the initial stages.(and for some time) CMC's on supports were generated by the Field Eng,ineering Group (a subgroup of TUGC0 Pipe Support Engineering - PSE) and were forwarded to the organization responsible for that support (ITTG and NPSI).
The CMC was placed in the system file by ITTG or NPSI and would be worked on as the piping system required rework or as TUGC0 requested.9 This resulted in construction of the modification continuing without review by the responsible design organization. In some cases, as-built analyses performed by G&H could have included supports with outstanding CMC's although the appropriate CMC would be included in
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the as-built package. Based on the defined process, this would mean that the effected support would not have been approved by the appropriate design organization at that time.
However, the support design organization was alsp involved in the as-built process and review of the support would have been acccmplished as a part of that process.
One could suggest that a method of controlling the number of outstanding CMC's on a given drawing (say 3 to 5), or controlling the time that a CMC can be outstanding, would force review, approval (or disapproval) and incorporation of the CMC into the drawing. This would reduce the turnaround time for approval and reduce the number of outstanding CMC's in a given as-built package.
Eventually, a site group was established unden. PSE which included ITTG and NPSI personnel. Under this organization CMC's were dispositioned by the.PSE group on site. This shortened the communicatio,n link and should have resulted in more rapid turnaround of CMC review.
However, no change to the process occurred (i.e., time limit on CMC or limit on outstanding number of CMC's on a given drawing) except that' the field engineer, who authorized construction to make a change to a support, had available, on site, the complete design resources of ITTG, NPSi and PSE.
9. January 15, 1985 Transcript, pp. 30 and 31.
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- i When ITTG, NPSI and PSE reviewed a CMC and found an unacceptable condition
( i,. e., stresses too high) they generated a~ handwritten memo (TSDR) noting the condition. This TSDR was sent to the field engineer responsible lor generating the original CMC.
The field engineer would reply back to the originator of the TSDR (on the original TSDR in a section set aside for a reply) noting the changes now recommended for the support can be found in. the next revision of the CMC.10 The support design organization was now responsible for reviewing the next revision of the appropriate CMC.
One area of concern with respect to QA control is that CMC's were handled by the site document control center and those individuals on the
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effected drawing distributilon list received _a <opy-of the CMC. Copies of the TSDR's were not controlled. There doe's not appear to be a definitive link between QA and design in the area of CMC's and absolutely none with' theTSUR's. Therefore QA could only determine that changes to design were
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occurring if they performed audits (which they did) and reviewed both the CMC's and the TSDR's.
This need not be a real area,of concern in the initial design stages where construction was not underway, however, once a construction drawing is issued it is important that QA be aware of changes that are planned to that drawing.
This is particularly important when those changes are already being built. QA can be effective in recognizing repetitive design changes and developing trends and then modifying their audit plan and schedule to focus on the effected areas.
TUGC0 (Chapman) states:II
" Applicants have established a procedure, CP-QP-17.0, " Corrective Action," to review documented conditions adverse to quality for the purpose of providing corrective action to. preclude repeti-tion of significant conditions adverse to quality. This proce-dure provides for Quality Engineering Staff to review design l
changes documented on CMCs.
The results of these reviews are 10 January 15, 1985 Transcript, p. 46 and Motion for Summary Disposition, July 3,1984, p. 53.
11 Motion for Summary Disposition, July 3,1984, p. 54. ~
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Technical Report TR-6216B.
tracked using trend analysis techniques as an objective method of ascertaining the need for corrective action to preclude repetition-of significant, conditions adverse to, quality.
Periodic reports summarize the results of the reviews, including trends, and provide recommendations, where appropriate, for cor-rective action with respect to identified conditions which are considered to be significant.
This is appropriate, however without receiving copies of TSDR's it is not clear that trends of field engineering to propose inadequate changes to design are not explicitly covered unless one assumes that the revision to a CMC resulting from a TSDR' defines that the reason for the revision was j
either a TSDR or a request by the reponsible des.ign organization.
Concern 5 i
G&H had a Site Stress Analysis Group (SSAG) at CPSES that was adminis-trated by TUGC0 but reported to G&H. Mr. Ballard of G&H states:I "SSAG was established to evaluate and approve proposed changes and modifications to pipe routing, pipe sup-port locations and/or pipe support type, as requested by site engineering groups. The evaluations are made employing the latest as-designed piping stress analy-sis. SSAG provides revised design information to the applicable site organizations.
All these activities are conducted'in accordance with CPSES Engineering In-struction CP-EI-4.6-9, Rev.1, entitled " Performance Instruction for Piping Analysis by SSAG" and Gibbs &
12 Motion for Summary Disposition, July 3,1984, p. 20.
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Technical Report TR-6216B.
t Hill Applied Mechanics procedures previously cited.
These documents have been established to assure that the SSAG activities are accomplished in a manner commensurate with the original as-design analyses'."
The concern here is related to the fact that SSAG performed their function "as requested by site engineering groups."
It is understandable that a modification to a pipe routing of considerable magnitude would have been routed through the SSAG.
It is assumed that this was accomplished through the use of CMC's as discussed for supports in Concern 4.
- However, a major modification to a support which could have an impact on pipe stresses may not be routed to the SSAG since the individual responsible for generating the CMC may not have considered (or recognized) the change would effect pipe stresses.
Concern 6 The following are discussions of those items which are specific in nature and yet, to a degree, have an impact on the design process.
6.1 Mass participation This issue is addressed in introductory remarks (see page 2) and is important from a design process standpoint and a support / pipe adequacy standpoint.
Based on the Cygna review it appears that the average mass participation of piping systems analyzed by G&H is in the order of 40%.13 One could expect that a seismic analysis cut-off at 33 Hz should normally result in 90% or greater of the total system mass.
For piping stresses this would usually be acceptable. For supports however the contribution of
~ 13 January 10, 1985 Transcript, p. 70.
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Technical Report TR-6216B -
rigid mode response could be-important, particularly for supports located close to large concentrated masses or where the support is providing axial restraint.
In these cases the total seismic load should fiiclude a rigid mode component equal to the ' floor ZPA times the weight of the supported component or segment of pipe. Based on normal expectations' a mass partici-pation of 40% is unacceptable. Further, the design process at G&H did not control this effect since a procedure was not available.
Reanalysis by G&H to include total mass participation will result in significant increa:e in some support loads.
This efect when coupled with the low suppo,rt stiffness (flexible restraints) could result in the need to modify supports (see Concern 2).
As a result of this mass participation problem it may be appropriate for"the CPSES engineering organizations to consider the latest Code revisions 14 with respect to damping.
This would result in a significant reduction in peak accelera-tions. However, should the new damping be adopted it is recommended that all of the requirements of WRC Sulletin 300 be adopted. There are signifi-cant discussions therein on interface control and responsibilities.
6.2 Support stability In addition to the discussion under Concern 3 which addresses s.ame specific restraints there are some generic concerns.
Many of the restraints and supports at CPSES utilize box beams with either pinned struts or snubbers connecting the box to structure. This is not a common design for seismic Category I nuclear piping. Box beams themselves are not uncommon, however they are usually rigidly connected to the building structure using standard structural shapes. A second type of support that
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is of concern is the trapeze style support which is composed of a structural member supported off the building structure by pinned struts or 14 Code Case N-411 - Adopts PVRC damping discussed in Concern 1.
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snubbers and attached to the pipe by a U-bolt or trunnion.
Again, this type of support is not a common design for seismic Category I nuclear piping.in plants, licensed to operate in the last 4 or 5 years.
(Trapeze type supports with U-bolts can be found in non-seismic piping at nuclear plants and in other facilities such as process and fossil plants.) A third concern is related to support application. That is, the use of struts or snubbers supporting a pipe from the bottom of the pipe to a floor or.
platform below the pipe. Since these supports are pinned they are unstable vertically as soon as horizontal displacement of the pipe occurs and system stability is provided only by the end conditions of the piping system or any horizontal restraints that exist. It has been pointed out that piping must be considered in conjunction with the existing supports and therefore
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the presence of pinnec supports applied in the manner described above must be judged based on the overall support system.
However, a reasonable designer would not provide this type of support in a number of locations on the same piping system and rely on pipe end conditions or horizontal restraints to provide stability.
For example, removal of the horizontal restraints for maintenance work (or as a result of a. snubber reduction program) could leave the system in an unstable situation.
For the pinned box beams and U-bolt trapeze supports it is nearly impossible.to. demonstrate by analysis that stability exists.
There are only two reasonable alternatives and they are:
(1) Perform a test of a system representative of a system at CPSES (system meaning pipe and supports). The test should provide dynamic input commensurate with the plant design seismic and operating transient conditions (water / steam hammer).
(2) Modify the supports.
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Technical Report TR-6216B -
t 6.3 As-built reconciliation The Jas-built reconciliation process has two functions.
The first, and most obvious, is~ to take dimensions, etc., 'of the actual as-built configuration of piping and supports and reconcile' those with the as-designed documentation.
The second is to have a qualified pi ping designer walk the system to develop an understanding of the overall geometry and to determine if the installation generally reflects the analysis.
The importance of this second step is obvious, the overall configuration is. there to see and one is not dealing with a number of different drawings trying to piece together a system.
The existing design process'~at CPSES"r# quired as-built informa-tion to be gathered by TUGC0 technical services personnel and forwarded to G&H applied mechanics personnel. Already the ideal situation where the G&H analyst or. members of the SSAG walked the system did not exist. However, this is not a fatal problem nor is it uncommon in the industry to have "others" gather as-built data.
It merely makes the problem of system acceptance and analysis reconciliation more difficult.
The as-built reconciliation program was started at the time that the piping was installed and Brown & Root determined that the supports not in place could be fabricated and installed as they were designed. -The number of installed supports on a given stress problem varied from 20% to 15 80%
at the time G&H started reconciliation efforts. Having only 20% of the supports installed has two impacts, one that could be positive and one that could be negative. The positive impact is that with only 20% of-the supports installed the G&H analyst should have had an early indication of what the support designs looked like and could have requested modification 15 January 15, 1984 Transcript, pp. 22 and 23.
Technical Report TR-6216B *
(if there was concern) prior to fabrication and installation of the remain-ing 80%.
That is, the undefined pressure to accept constructed supports was significantly less than one could hypothesize for the s,ituation where all of the supports were installed. The negative impact is that the piping analyst is not dealing with the complete as-built system and one can anticipate that a number of iterations will be required to complete the reconciliation process since modification to one of the remaining 80% of the supports could impact the total system including the installed 20% of the supports. Iterations such as this are not uncommon but sometimes tend to result in cursory reviews of already accepted situations.
One major concer.n with respect to as-built reconciliation is the situation where more than one pipidg. systen wis" supported by a frame,
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particularly frames which were pinned connected to building structure.
G&H, though aware of the fact that the frame supported more than one system, dealt with the support as a single support on the piping system under consideration at that time.16 The support designer was supplied with the loads on the frame for each piping system being supported and deter-mined the structural adequacy of the frame.
No one was apparently responsible for looking at the interaction effects inherent in a pinned frame supporting a number of pipes.
It is my opinion that this is the responsibility of the piping designer and G&H accepts that responsibility.17 6.4 Support mass Many of the support designs at CPSES result in considerable mass which is not acting at the outside diameter of the piping.
It is co.mmon practice to add support mass to the piping analysis and this is usually done at the centerline of the pipe since it normally involves a clamp.
In 16 January 15, 1984 Transcript, pp. 23 and 24.
-I January 15, 1984 Transcript, pp.11, 49 and 50.
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Technical Report TR-6216B -
the case of a box beam rigidly connected to the building structure the mass is not applied to the pipe and therefore need not be considered.
In the case of ~a box beam pinned to the building structure the mass acting 90 degrees to the direction of restraint should be applied to the pipe center-line.
A specific geometry that cannot have the mass applied to pipe centerline and be representative of the as-built condition is a support restraint that is pinned to the building structure and has a beam some distance from the pipe [ and the pipe 0.0.
The beam is attached to the pipe by welding a trunnion to the pipe and the beam.18 The effect of the offset mass rigidly connected to the pipe results in forces and moments on the pipe which will not be represented properly _by modelling the mass at the
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pipe centerline.
G&H apparently accounted for this effect on the main steam system only.19 10 This would normally be called a trapeze restraint but if used as a horizontal restraint on a vertical pipe that could be a misleading statement since a trapeze support is normally considered to be a verti-cal support on a horizontal pipe.
19 January 15, 1984 Transcript, pp. 61 and 61.
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Mr. J. B. George tf 2g"' )
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Texas Utilities Generating Company
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Corenche Peak Steam Electric Station Highey Fit 201 G
Glen Rose, Texas 76043
Subject:
Stability of Pipe Supports Texas Utilities Generating Company Corranche Peak Steam Electric Station Independent Assessment Program Job No. 84042
References:
(1)
N.H. Williams (Cygna) letter to V. Noonan (U.S. NRC),
"Open Items Associated with Walsh/Doyle Allegations,"
84042 2, dated January 18, 1985.
(2)
N.H. Williams (Cygna-) letter to V. Noonan (U.S. NRC),
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" Revision to Open Items Schedule," 84056.055, February 14, 1985, s(3) Affidavit of John C. Finneran Jr. regarding Stability of Pipe Supports and Piping Systems, dated June 17, 1984.
(4) Cygna Phase 3 Final Report TR-84042-1, Rev.1, November 20, 1984.
Dear Mr. George:
As comnitted to in Reference 1 and subsequently revised in Reference 2, Cygna has cocpleted an evaluation of the pipe support stability issue. This evalua-I tion considered the support designs reviewed by Cygna as part of Phases 2, 3 and 4 as well as TUGC0's position described in Reference 3.
Since stability is a l
very complex issue, we will summarize our position in six parts:
(1) Definition of Stability, (2) Dynamic Versus Static Stability, '(3) System' Stability, (4) l Cc s-tary on TUGC0's Position, (5) Classification of Cygna Review Scope, and (6) Cc.:lusions.
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Mr. J. 8. George Februa ry 19, 1985 Page 2 3
Definition of Stability Prior to performing an evaluation of this issue, criteria were developed to define what constitutes an enstable. pipe support.
Individual pipe supports can be classified into two broad categories:
(1) supports which, in the total absence of the pipe, are stable, and (2) supports which, in the total absence of the pipe, are unstable.
Implicit in our definition for the second category is the fact that the instability is a rigid body type which say be completely removed or accommodated by proper attachment to the pipe. That is, by restrain-ing certain degrees of freedom at the attachment to the pipe, such as with a pipe cla<mp, the instability nay be removed. Alternatively, by limiting the motion following instability through the pr'esence of the pipe and adjacent supports, the instability may also be eliminated. Since there is no stability issue with respect to supports of the first category, only supports of the l
second category need be discussed.
In order for a support of the second category to be stable, there are two l_
requirements to be met, one involving force transfer between the pipe and support and the other involving the geometric relationship between the pipe and i
l support. The force requirement is met if adequate forces, which develop instantaneously and can be relied upon by design, exist between the pipe and the support hardware to resist the factored load. The following definitions are i
provided for clarity:
develop instantaneously (immediately): Resisting forces are e
activated at the same instant that piping loads are applied. An example of forces which cannot develop intnediately are binding forces which require a rigid body motion of the support (rotation, translation) to become effective.
by design: The mechanism for and magnitude of the resisting forces are calculatable and known, or have been evaluated exten-sively by test or by use in the specific application.
e factored load: Applied load times a safety factor.
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In addition to the above described force requirement, the geometric relationship between the support and the pipe must remain within set limits during 'the
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operational life of the plant.
If sufficient clamping forces between the pipe and support are not present, small pipe movements nay cause large changes in the i
position of the support relative to the pipe. Piping system vibration occurring during start-up, normal operation or shut-down can cause the support to move j
(rotate, translate) relative to the pipe. This support movement is ur. favorable j
if, for a support initially perpendicular to the pipe, the direction of p,ipe 1
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msus Mr. J. B. George February 19, 1985 Page3 movement in the absence of the support is such that the dis;1 aced centerline of the pipe intersects the arc nede by the rigid body motion c' the pipe center within the support. The new position of the support on the pipe nay be well outside the displacement (eccentricity) envelope for which it was designed and for which stability has been assuredv Since the support di: not restrain the movement of the pipe during this process, adjacent supports must now resist an additional load for which they nay not be adequate. Theref:re, a sufficient condition for individual pipe support stabili.ty of the sected category is a design in which, upon the application of the factored load from the pipe, adequate resisting forces can be developed immediately and the position of the support attachment on the pipe does not move relative to the pipe with time.
Considering the definition presented above,' we will now dis:uss some specialized situations in which the instantaneous development of resisting forces required for stability does not occur. For these designs momentary instability (of the rigid body type) could be tolerated, provided that it can be demonstrated that sufficient forces eventually develop to completely remove the instability (i.e.,
stop the motion and allow the support to function as designed). For example.
when,considering the instability of a support which requires the development of binding forces to ultinately naintain stability, one could assume the support does not act and then determine the resulting pipe deflection in the released direction.
If that deflection is a sufficient multiple (say 4) of the deflec-tion required to develop the necessary binding forces, it then becomes appropriate to further investigate the ability of the supp:rt to resist both the binding force and the applied load.
During such an investigation, it is essential to demonstrate that the binding force mechanism possesses both sufficient strength and stiffness.
In other words, while certain designs any exhibit sufficient strength to develop and resist the necessary binding forces, they may not posssess sufficient stiffness to limit the rigid body displacement and thus resist the applied load. The alternative to this approach is to limit the consequences of the instability. This could be accomplished by showing that the piping and remaining supports are acceptable in the absence of the unstable support.
In either approach, before the design can be considered satisfactory, pipe stresses and otner support reactions must be checked for the new displace-ments occurring at the support and the pipe must be checkM for the effects.of the binding forces.
Dynamic Versus Static Stability The preceeding discussion addresses only stability due to statically applied loading. The question arises as to whether a support coul: be unstable statically under the application of nnximum load, yet staMe when the same load is applied dynamically. This is a very complex analytic p oblem to resolve which is further complicated by the fact that the maximum loading on a pipe l
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B". George February 19, 1985 Page 4 support is generally some combination of static and dynamic 1 pact. Cygna is unaware of any established precedent for the acceptance of statially unstable supports based on dynamic arguments.
In some cases dynamic loa:9g can contri-i bute to pipe support instability rather than helping to preclues it. The time phasing of static and applied seismic (random) forces can eithe exacerbate or alleviate individual support instability. Therefore, to demonst ate analytically that a statically unstable support is dynamically s able would require an extensive evaluation using large nonlinear dynamic nc:els and time-history analyses. Add to this the variety of possible geometric configuration.s and input motions that must be considered, as well as -the existene of static system preload (dead load plus thermal), and the problem becomes extremely costly to evaluate. This is a particularly unfavorable approac in view of the potentially inconclusive nature of the results.
For many of the same reasons stated above, any testing program 6tveloped to prove dynamic stability would also have to be very extensive. Tests which are severely displacement limited and sinusoidal (non-random) in natre can only prove that a support is stable under snall amplitude displacemen sinusoidal input. Such tests would not necessarily demonstrate stability u-der conditions which reflect the real nature of th,e random input motion.
System Stability Generally, the term system stability is associated with the arra gement of a structure's restraint configuration such that it is not possible for the struc-ture to undergo rigid body motion. We will refer to this as geometric sta bility. With respect to piping systems, geometric stability is assured when a pipe stress computer analysis is successfully executed. This computer analysis would have detected a system of supports which does not restrain each of the three translational and three rotational global degrees c' freedom.
Encountering such a geometrically unstable system is an extremely rare situation since almost all piping systems contain some type of anchor (e.5., equipment nozzle, penetration, structural anchor, etc.).
When discussing system stability as it relates to pipe support stability, the najor concern is the ability of the piping system to provide thE appropriate stabilizing restraint for each support. This type of global sta:ility can only
- be assured if each support is individually stable in its own ric-t, either through its design (supports of the first category) or by adequi:E attachment to the pipe (supports of the second category).
If individual supp:7 stability is not assured, system stability is not guaranteed. The instabili:. of one support can trigger the progressive instability of adjacent supports by ausing the limits of the forces and displacements to which the adjacent su;;3rts were 1
originally designed to be exceeded. This may result in the.forration of plastic
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'5llr" unun Mr. J. B. George February 19, 1985 Page 5 hinges in the pipe (due to overload) which in turn ney develop into a collapse mecha nism. This situation would not, however, prevent successful execution of a linear, elastic pipe stress ' computer analysis.
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Demonstration of system stability by removal of an unstable support from the system and subsequently showing that each remaining support can resist the new forces is not sufficient by itself.
In addition, it should be shown that removing the unstable support does not affect the stability of other supports.
That is, overall system stability should be reevaluated in the absence of the removed support.
Commentary on TUGCO's Position Cygna has reviewed the Reference (3) Affidavit using the criteria described above. The Affidavit (pages 2-8) discusses system stability and its relation to individual support stability.
In it, TUGC0 states:
"In addition, if the total support scheme does not provide proper multidirection support required by the piping configuration, the analyst will be unable to successfully run the piping) analysis computer program, (see Tr.12025 (Bjorksen testimony).
In sumary, the piping analyst assures the stability of the piping system by limiting deflections, which negates any need to assess stability sepa rately."
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Cygna agrees with the first statement, since this is our basic definition of geometric stability. The second statement, however, does not follow. A piping analyst does not limit deflections to those required to assure system stability, since, in general, these deflections are not known. Rather, the analyst inputs each support as a restrained node and reports the resulting deformations to the designer for consideration. Therefore, the issue is not piping system stability, but rather the stability of the individual support itself. The key point is whether the individual support can resist the applied load within'the initial eccentricities and displacement limits imposed upon it.
The stability issue is best illustrated in Figure 1(c) of the Affidavit, (page 4). The concern is not whether an adjacent support can provide a horizontal reaction component (since it is already known by analysis that it can and the system is geometrically stable), but rather whether the clamp (U-bolt) can provide sufficient resisting forces to prevent rotation of the clamp (U-bolt) about the pipe or slippa'ge along the pipe axis.
If the clamp (U-bolt) cannot provide sufficient resisting torque, the individual support is unstable and system stability as well as progressive support instability must be re-evaluated.
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w.m Mr. J. B. George Februa ry 19, 1985 Page 6 Of the specific support configrations discussed in 'the Affid'avit, the most unique is the box frame with zero-inch gap attached to a single strut or snubber (Affidavit, page 9). This is c..:sual because it relies solely on the relative thermal expansion between the pipe and frame during normal operation to create clamping forces. The resull.ing frictional forces which resist support rotation around the pipe and translatir, along the axis of the pipe would stabilize the support. The lower bound value cf stabilizing frictional force which exists over the operational life of tne plant was never determined eithEr analytically or by test. Furthermore, since clamping forces do not exist at ambient condi-tions, it is possible for the support to move (rotate and translate) relative to the pipe. This movement of the support could be caused by normal vibration during start-up, operation or shut-down, combined with pipe thermal translation conpatible within the rigid body displacement envelope of the support.
Subsequent to this movement the support may be in a position on the pipe which is outside of the displacement range for which it was designed and for which stability could be assured. Furthermore, due to the compatible rigid body motion of the pipe and support, the support would be unable to restrain the thermal movement (load) for which it was designed and adjacent supports would have to resist this load -- a load for which they were not designed. This situation may also develop at temperatures above ambient since the maintenance of zero gap over the life of the plant could be difficult to achieve.
For these reasons, Cygna classifies these supports, without modification, as unstable.
In Figure 4 of the Affidavit (page 13) three methods are shown which have been utilized to modify the box frase supports to improve their stability. Two of these methods
" indexed lugs" and " additional struts" only provide rotational stability. They do not prevent translation of the support along the axis of the pipe with time. Therefore both of these modification schemes result in supports j
which must still be classified as unstable. The third modification scheme, the addition of cinched U-bolts, can prevent both rotation and translation of the support provided it can develop sufficient lower. bound clamping forces. Since the final evaluation on the use of cinched U-bolts has not been completed, the acceptability of supports with this configuration remains an open issue at this time.
Cygna classifies all single struts with U-bolts and a thermal gap (Affidavit, page 15) as unstable since the stability of this type of support has never been analytically or experimentally denonstrated.
Cygna understands that all of these supports have been modified in an effort to enhance stability (Affidavit, pcge 18). Tnese modifications cor.sist of either cinching the U-bolts or adding supplementary steel that woulc prevent the rotation of the U-bolt crosspiece.
Cygna believes we have addressed those supports for which supplementary steel was added to create " stability bacpers" in Reference (4) Observation PS-02.
Cygna found these bumpers unacceptable since there were no calculations to I
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8%ssGv 5tsveCtb Mr. J. B. George February 19, 1985 Page 7 demonstrate that they possessed sufficient strength and stiffness to mintain stability. The stability of, the supports which were modified by cinc9ing the U-bolts remains open as part of the U-bolt analysis / testing program.
Double strutted frames (Affidavit, kge 19) supporting two or more pipes.were not encountered during any of the Cygna review phases. However, Cygna did find examples of double strutted frames supporting a single pipe and double strutted trapeze supports with U-bolts, which are configurations similar to those discussed in the Affidavit. As previously discussed for single strutted frames, both the double strutted frames and trapeze supports with uncinched U-bolts suffer from the problem of not having the demonstrated ability to maintain their relative position on the pipe over time.
In addition, the double struts cannot relied upon to resist compressive load until the frame (U-bolt) has rotated about an axis parallel to the struts and has bound itself in a cocked position against the pipe. Neither the stiffness requirements of the frame (U-bolt) necessary to r:aintain a stable position nor the binding forces and displacements required to restrict the unstability have been evaluated. Cygna therefore class,1fies these supports as unstable.
In the case of double strutted trapeze supports with cinched U-bolts, the most likely mode of instability is that due to rotation of the support about an axis parallel to the struts.
If the frictional resistance between the pipe and the trapeze crosspiece is not sufficient, the frictional bond will be broken and the entire destabilizing twisting moment mast be resisted by the bending strength (and stiffness) of the U-bolt binding against the pipe. Since neither the frictional forces nor the U-bolt have been evaluated for their capability to resist this nonlinear destabilizing moment, Cygna classifies this configuration as unstable.
The stability of a single strut or snubber with a cinched U-bolt (Affievit, page 27) is directly related to the resolution of the issue of U-bolts used as pipe clamps. Until the resolution of that issue, which includes the satisfac-tory determination that lower bound preloads can provide the clamping force necessary to resist the. factored piping loads, Cygna considers all such supports to the unstable.
Classification of Cygna Review Scope i
Cygna has examined the 226 pipe supports within the Phases 2, 3 and 4 review scope.
Thirty-seven supports were identified as supports which, in the total absence of the pipe, are stable. Of the remaining 189 supports which in the absence of the pipe would be unstable,124 possess sufficient positive attachment to the pipe to ensure stability. The 65 potentially unstable supports may be classified as follows:
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Mr. J. B. George February 19, 1985 Page 8 Single strut with box frame or cinched U-bolt (23)
Double strut trapeze with cinched U-bolt (25)
Multi-strut box frame,.(8)
Single strut with uncinched U-bolt, stability bumpers (2)
Double strut, double trunnion with cinched U-bolt (1)
Double strut trapeze with box frame (2)
Double strut trapeze with uncinched U-bolt (3)
Triple strut box frame (1)
There are two reasons for classifying these supports as unstable:
- 1) the unconventional methods used.to develop the restraining forces between the pipe and the support, and 2) the lack of any demonstration that the restraining forces developed by these supports are sufficient to maintain the support s stability. Supports wnich are designed with cinched U-bolts to provide the necessary positive connection to the pipe nay be reclassified as stable if the U-bolt testing / analysis program and the application of the results to the.
individual.-supports in question.is found to be acceptable.
It should be noted, however, that this program does not address the stability of supports which do not.use U-bolts, nor does it evaluate the twisting strength of U-bolts used in trapeze supports.
Conclusions Throughout this letter, Cygna has applied a very rigorous definition of rigid body instability. Cygna recognizes from a practical standpoint that many of these potentially unstable designs ney actually perform their intended function. However, we also recognize that the inability to quantify the actual behavior which nay help stabilize the support in practice necessitates that stability be viewed under more idealized conditions. For that reason the individually unstable supports identified above.and any similar configurations throughout the plant, should be evaluated using one of the following approaches:
Modify to provide adequate restraint at the pipe / support connection Demonstrate system stability in the presence.cf.the unstable
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Quantitatively show that the individual supports are stable e
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E"$n Mr. J. B. George February 19, 1985 Page 9 Please call to discuss any questions or clarification necessary since this is a complex subject.
Ti@tr 1 Very y'ours, N.H. Wi lams Project Panager NHW/ajb cc:
S. Treby (U.S. NRC)
S. Burwell (U.S. NRC)
V. Noonan (U.S. NRC)
D. Wade (TUGCO)
J. van Amerongen (EBASC0/TUGCO)
R. Ballard (G8H)
J. Ellis (CASE)
D. Pigott (Orrick, Herrington & Sutcliff)
J. Fianeran (TUGCO)
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