ML19254E783

Final Deficiency Rept Re Excessive load-pin Clearance in QA Level I Pipe Support Struts.Strut Assemblies Will Be Redesigned to Incorporate Struts Equipped W/Close Clearance Spherical Bearings in End Connections

ML19254E783
Person / Time
Site:	Fermi
Issue date:	10/23/1979
From:	Casiglia J, Colber W, Sigetich M DETROIT EDISON CO.
To:
Shared Package
ML19254E780	List: ML19254E779 ML19254E783
References
EF2-50-590, NUDOCS 7911020317
Download: ML19254E783 (4)

Text

• / RECEIVED

'00T 241979 Detroit a. W. BARR Edison ENRICO FERMI UNIT 2 PROJECT

' ENGINEERING October 23, 1979 EF2-50,590 To: R.W. Barr Project Quality Assurmace Director From: M.G. Sigetich h Supervising Engineer,

/ EG44

Reference:

1) Letter on Docket 50-341 dated August 28, 1979 from Mr. G. Fiorelli, USNRC Region III to Mr.

Edward Hines, Detroit Edison Company

2) EF2-46,349 dated September 28, 1979

3) EF2-50,242 dated September 21, 1979

Subject:

Report of Engineering's Evaluation of an Identified Design Deficiency in QA Level I Pipe Suoport Struts Pursuant to the rules of 10CFR50. 35(e), Item 3, attached is a copy of the subject report.

Written by: J.H. Casiglia

/sp Approved: , [/

W.F. Colbert /,/v[7 Project Engineer cc: T.A. Alessi W.M. Street L. Bertani R.A. Vance T.H. Dickson H.A. Walker ,

W.M. Everett Doc. Control W.J. Fahrner F.E. Gregor D.L. Schweikhart 1262 296 R.J. Stanley i

7911020

y .4 Attachment to: EF2-50,590 ENRICO FERMI POWER PLANT UNIT 2 DEFICIENCY REPORT EXCESSIVE IDAD-PIN CLEARANCE IN QA LEVEL I PIPE SUPPORT STRUTS INTRODUCTION During a postulated seismic event, the inertial and differential anchor movement loads developed by the Category I piping systems are transferred to the building structure by the pipe support system.

The magnitude, direction and characteristic nature (force, moment, displacement, etc.) of the loads is predicted by the computerized piping system stress analysis. The overall validity of that analysis is der?, dent upon the accuracy with which the physically-installed support system satisfies the structurally-related (orientation, stiff-ness, etc.) assumptions, concerning the support system, which were made during the performance of the analysis.

Pipe support devices, which are capable of resisting both tensile and compressive loads and transferring these loads to the building structure, are known as struts. When modelled analytica1'.y in the 7 1 ping analysis, the strut is assumed to be structurally rigid along its axis and yet provides no restraint to movement or rotation of the piping system in other directions.

In order to achieve the required axial structural rigidity, the strut is provided with close-fitting pinned connections at the pipe attach-ment point (clamp) and structure attachment point (rear bracket). In order to provide for required off-axis flexibility, the pinned connec-tion must be provided with a slight clearance betw;en the pin and its mating connection.

It has been determined by both analytical studies and industry ex-perience that as long as the total cumulative clearance in the pinned connections at the ends of the struts does not exceed approximat:1y 1/16-inch, in the axial direction, the validity of the stress analysis is not compromised.

DESCRIPTION OF THE DEFICIENCY In order to provide the re u - d off-axis flexibility for the QA Level I struts used on Ferm 2, the originally specified acceptance criteria permitted up to 1/? , .nch diametral clearance between each load pin and its mating connection.

Upon closer engineering evaluation of the potential effect of this specified clearance, it was established' that cumulative " stack-up" of the tolerances between each pin and its mating connection on a strut assembly could result in a total of k inch of free axial move-mentbetweenthebuildingstructureandthesupportedpipe,duripg postulate. seismic event.h, g}

se i Attachment to: EF2-50,590 Page 2 DESCRIFFION OF THE DEFICIENCY (contd) It was also determined, during the course of the above described in-vestigation, that specific criteria to insure that threaded portions of the strut end plus (bolt studs) were not in the load-bearing por-tion of the connection were not specified; and approved strut designs with threaded portions of the load pins in the shear plane of the end connection had been released for construction. The above constitutes a departure from good design practice and poses the potential for further increase to the clearance in the strut end connection due to crushing of the thread crest under compressive load-ing. It was concluded that the potential for excessive displacement between the building structure and the supported QA Level I piping compromised the integrity of the seismic analysis of that, piping. Therefore, pur-suant to the rules of 10CFR50.55(e) item 1 (i2 ), a reportable design deficiency existed. NUCLEAR REGULATORY COMMISSION NOTIFICATION In accordance with the rules of 10CFR50.55(e), Item 2, verbal notifi-cation of the above design deficiency was provided to the NRC Region III staff, by the Fermi 2 project Quality Assurance director en Oc-tober 2, 1979. CORRECTIVE ACTION All QA Level I strut assemblies not presently so-designed, will be redesigned to incorporate struts which are equipped with close-clearance spherical bearings in the end connections. These bearings provide the axial rigidity required for proper performance of the strut, while still allowing for the necessary off-axis movement capability to permit free thermal growth of the piping system, as required by the design and accounted for in the piping stress analysis. SAFETY IMPLICATION OF THE DEFICIENCY An engineering assessment of the potential effects of excessive tol-erance in strut end connections concluded that during a postulated site seismic event, impactive loads which are not accounted for in the piping analysis or support system design, would be generated. If the magnitude of those loads were sufficiently high, the potential for support system structural failure and attendant overstress of the QA Level I piping would exist. ' e Q k -

r , Attachment to: EF2-50,590 Page 3 SAFETY IMPLICATION OF THE DEFICIENCY (contd) It has been concluded that by redesigning the QA I struts, as pre-viously dascribed, the originally-provided design margins against structural failure of critical piping systems due to earthquake load-ings will be preserved and the piping systems will be capable of per-formirs their intended safety function. Prepared by: K H. Casigliaf PE Engineering Work Leader Approved: / M.G. Siget'ich (/ Supervising Engineer, EG44 Approved W.F. Colbert , PE Project Engineer, EF2 O 326.-}}