ML20211D360

Main Steam Bypass Sys Testing Program Rept

ML20211D360
Person / Time
Site:	Fermi
Issue date:	10/16/1986
From:	Contoni J, Uema S DETROIT EDISON CO.
To:
Shared Package
ML20211D357	List: ML20211D351 ML20211D360 ML20211D396 ML20211D421
References
NUDOCS 8610220180
Download: ML20211D360 (8)

Text

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- Attachment VP-86-0146

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Main Steam Bypass System Testing Program Report Projects and Plant Engineering Fermi 2

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Written By:

J. Contoni S. Uema

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Attachment s VI)-86-0146 age 2y,23ceneral A test program was implemented by Detroit Edison that provided measured pipe wall strain data over the design flow ranges of the main steam bypass lines. The test program consisted of six test mns over three reactor power levels - approximately 4.9, 8.2 &

19%. At each power level two tests were run - one test with both bypass lines and the other with only the West bypass line. Pipe wall strain sta was obtained on 9-16-86 and 9-17-86 for valve positions at approximately 245, 365, 39%, 50% and 97% open.

The pipe wall strain sta has been forwarded to both Hopper &

Associates and Stone & Webster, (per NE-PJ-86-0756 and NE-PJ-86-0755), for re-evaluation of the bypass line life projections. Executive stmaaries of the final reports were received from Hopper & Associates (HA-1W86-532) and Stone &

Webster (NE-SW-86-0018) on 10-3-86, which are attached.

II. Hoooer & Associates Results Hopper & Associates approach for evaluating the bypass line fatique life was based upon a detailed fracture mechanics analysis in which a maximal constmetion code permissible weld flaw was asstzned at the location of highest stress. The test data validated the asstanption that the structural response in the form of pipe wall flutter has a random vibration characteristic. A statistical analysis of the strain data resulted in a time history for the alternating stresses, which was utilized to predict crack initiation and fatique growth to failure. This " threshold stress" level and its rate of occurrence per unit of time was used to predict service life of the line.

The report concluded that for bypass valve openings rarging from 30 to 40%, the measured maximal random strains exceed the crack growth threshold level of 100 microstrains. The predicted acctzculative operating life in the bypass valve operating range of interest was in excess of 130 days.' The critical fatique life prediction is conservative, since a non-destmetive examination performed on the pipe seam weld running between the bypass valve and the first orifice did not reveal any inclusions approaching the maximal constmetion code permissible size.

III. Stone & Wergter Results The Stone & Webster approach for evaluating the line fatique life j

is in accordance with micmscopic fatique theory. That is, the l

asstanption of a flaw in the material was not needed. The alternating stress calculated from the actual strain sta was compared to the altemating stress predictions from a NUPIPE conputer model.

• (This corresponds to a 40 year plant life, given our current operating.

procedures.)

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. Attachment VP;86-0146.

Th2 model gava equal forcing input credit to both flexural and Page 3 of 23 moment forens postulated to be acting on the piping. Thn dynamic alternating stresses consisted of the moment stress (calculated from the NUPIPE Computer Program - that is based on a theoretical forcing fbnction) and the hoop stress resulting from the piping flexural vibration. The calculated altemating stress was compared with the ANSI /ASME fatique life curve to determine the allowable cycles. For infinite life, the allowable stress cycles nust exceed 10 cycles.

Stone & Webster concluded that the critical bypass valve operating range was from 35 to 45% valve opening, dere the expected line life varies from 13 to 26 days. Infinite service life was predicted for valve positions from 0 to 24% open and from 68 to 100% open. This was based on the life expectancy & art for a stress concentration factor (C K ) = 3.0, see page 4 of the S&W 22 report. S&W used the C 2 = 3.0 & art instead of the Cf = 5.45 chart becau e it more accurately reflected the actbal physical field conditions, as they stated in item 2.b on page 1 of their report. Therefore the Cf presented just for infonnational purpose 5.2 = 5.45 & art was IV. Discussion 1.

Points of Agreewnt Both Hopper & Associates and Stone & Webster agreed on the general location of highest stress. The piping section of nost interest was between and included, the first two elbows downstream of the West bypass valve.

Also, both analyses predicted that the valve operating rarige Were limited life occurs is from 30-45% open.

2.

Points of Dingreamnt The differences between the two approaches are listed as follows:

a. Hopper & Associates analysis is based on random pipe wall flutter induced by a complex shock wave system at the bypass valve outlet. The analysis technique was macroscopic fracture me&anics.

b. Stone & Webster conducted a bending analysis in which sirrple flexing and moments are induced in the piping.

1. This analysis used a shear cone forcing function which was independent of shock wave effects.

Page 2 1

Attachment VP186-0146

2. Tha moment strtss rtsulting from bending is based on the Page'4 of 23 LVDT and cccelcrometzr d2tn that was obtnined for the 3/8" wall pipe for valve positions up to 25% open. This data was extrapolated from the 3/8" wall configuration to the 1" wall configuration. Such an analysis is sensitive to the accuracy of the displacement data and its extrapolation.

3. This analysis is also sensitive to where the bending / moment strains are applied.

V.

Conclusions; 1.

In order to validate or invalidate the basis of Stone &

Webster's analysis, Detroit Edison shall install strain gages on the first elbow downstream of the West bypass valve as specified by Stone & Webster per Attachment A (attached). With this strain data, obtained in the bypass valve posttion rarge of interest, contributions from bending can be evaluated. The actual alternating stress will be used to reassess the service life of the lines. It is expected that Stone & Webster's life prediction would be more compatible with Hopper & Associates as a result of this testing. This assessment would be corrpleted prior to using up 13 days of accmulated operation within the critical range of valve position.

2.

Nuclear Production will be required to keep tra:k of the operating hours of the bypass system while the valve positions are in the 305 to 45% opening rarge.

3.

The operating modes of the system are not restricted by Engineering. However, a cmulative running total of the hours as defined above is needed. This ensures the 40 year life of the lines is achieved.

4.

The need to perform additional nor>-cestructive examination of the bypass piping will be predicated on the results of the testing described in item 1 above and the emulative runrILng hours described in 2 above.

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httachMynt VP;86-0146 Page'8 of 23 Date:

October 3, 1986 File No.: 0801.05 NE-SW-86-0018 J.O. No.: 15680.11 Response Not Required To:

J. Contoni Lead Mechanical Engineer Projects and Plant Engineering Detroit Edison Company From:

T. S. Sz'bo a

Assistant Director, Nuclear Design Stone & Webster Engineering

Subject:

PRELIMINARY FATIGUE LIFE ANALYSIS MAIN STEAM TURBINE BYPASS SYSTEM i

SCP-86-019

Reference:

SWF-T-153, 6-6-86, Transmittal of Steam Bypass System Study Enclosed for your information and use are three copies of a preliminary fatigue life analysis of main steam bypass piping. This analysis is based on test data forwarded by S. Uema of Detroit Edison, P&PE.

This report is marked preliminary since it is based on the results of an' unchecked calculation. Per your request we will try to complete this calculation by October 17, 1986 at which time we will issue a final report.

Should you have any further questions, please contact the undersigned at (609)482-3542.

1. /

.T.-S.

Szabo Assistant Director, Nuclear Design Enclosures cc: R. Byrnes R. Strych (encl)

T. Chitester (encl)

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S. Noetzel D. Spiers A. Alchalbi SWMI Job Book /P. Kinkead SWEC Job Book /L. Purdy K. Floyd (encl)

T. L. Wang (encl) 4

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