ML20211D396

Preliminary Rept on Main Steam Bypass Piping Fatigue Analysis & Life Expectancy

ML20211D396
Person / Time
Site:	Fermi
Issue date:	10/03/1986
From:	Sun Y, Wang T STONE & WEBSTER ENGINEERING CORP.
To:
Shared Package
ML20211D357	List: ML20211D351 ML20211D360 ML20211D396 ML20211D421
References
NUDOCS 8610220186
Download: ML20211D396 (8)

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Attachment VP-86-0146-Page'9 of: 23 4 -

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PRELIMINARY REPORT ON MAIN STEAM BYPASS PIPING FATIGUE ANALYSIS AND LIFE EXPECTANCY t

MAIN AND REHEAT STEAM SYSTEM ENRICO FERMI - UNIT 2 DETROIT EDISON COMPANY By Y. S. Sun /T. Wang October 3, 1986 4

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8610220186 861016 1 PDR ADOCK 0500 P

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1. OBJECTIVE In order to assess the potential for flow / acoustic induced vibration damage to the turbine bypass piping at Enrico Fermi 2 plant, strain data for both the east and west bypass lines was measured at various power levels and dump valve positions.

The objective of this analysis is to reevaluate the fatigue damage and life expectancy on these lines using the actual strain data, taken on the modified piping system as opposed to results previously reported which were based on a theoretical forcing function.

2. ASSUMPTIONS The analysis made use of the following assumptions:

a. Once the calculated allowable stress cycles reach 107 cycles, the piping will be considered to last indefinitely.

b. Life expectancy of the bypass piping exposed to flow-induced vibration is calculated using a stress index of 3.0, which is used in conjunction with a factor of 20 on design life. This stress index is considered to be more realistic for the follow-ing reasons:

1) Edison has performed extensive NDT on the pipe welds between the bypass valve and the first orifice, and they have found that piping is free of all measurable inclusions.

2) The fatigue stress index is usually smaller than the code specified design stress index.

3. METHOD In accordance with fatigue theory, the alternating stress is calculated from the actual strain data. Since the through-wall shear stress calcu-lated from the stress differences between the principal stress in the radial direction and one of the principal stresses on the pipe surface is found to be higher than the surface shear calculated from the difference between the principal stresses on the pipe surface, the largest through-wall shear is used to check with the ASME S-N curve to determine the al-lowable cycles. If the allowable cycles exceed 10 7 cycles, the turbine bypass piping is considered to have indefinite life. If the allowable ':

cycle is lower than the 107 cycles, the design life of the turbine bypass piping is then obtained by dividing the allowable cycles into the equiva-lent stress cycles. The equivalent stress cycles are then calculated I; using the strain data curves and the ASME NC code rule. The expected  :

life expectancy is 20 times the design life. l

. l By using strain gage data and power spectral density (PSD) levels, an  !

effective stress cycle was calculated. An effective stress cycle, i 36 cycles /sec, was derived. This stress cycle was used to determine the ,

fatigue life.

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~P Page 11 pi 23 The fatigue life for the seven different valve opening positions con-tained in the test data was calculated based on two different stress indices. One stress index (5.45) is the ASME Code specified value and the other one (3.0) is assumed according to Assumptions b.1) and b.2) previously discussed.

The summarized results for both cases are tabulated and given in the next two pages for your consideration.

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LIFE EXPECTANCY (C 2 K2.= 5.45)

Operating Code Valve Shear Stress Alternate Allowable Cycles / Design Expected Opening Stress Index Stress Cycles Day Life Life

(%) (psi) 5.45 (psi) (S-N Curve) (36 Hz) (hours) (days) 24 4415 5.45 12031 1.24 x 108 3.0 x 108 9.92 8.27 36 6354 5.45 17315 1.98 x los 3.0 x 108 1.58 1.32 39 7294 5.45 19876 1.12 x 105 3.0 x 108 0.90 0.75 41* 7313 5.45 19928 1.1 x 108 3.0 x 108 0.88 0.73 50 5591 5.45 15235 3.52 x 108 3.0 x 108 2.82 2.35 68 4771 5.45 13001 8.07 x 108 3.0 x 108 6.46 5.38 97 3059 5.45 8336 7.86 x 108 3.0 x 108 62.88 52.40

• No-test data available. The life expectancy at 41 percent is estimated from the onsite data observed by DECO engineers. The actual strain data is not available to SWEC.

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Page'13 of 23 LIFE EXPECTANCY (C 2 K2 = 3.0)  !

Operating Code Valve Shear Stress Alternate Allowable Cycles / Design Expected Opening Stress Index Stress Cycles Day Life Life

(%) (psi) CK2 2 (Psi) (S-N Curve) (36 Hz) (days) (days) 24 4415 3.0 6623 2.46 x 107 3.0 x 108 8.2 Indefi-nite 36 6354 3.0 9531 3.89 x 108 3.0 x 108 1.30 26 39 7294 3.0 10941 2.01 x 108 3.0 x 108 0.67 13.4 41* 7313 3.0 10970 1.98 x 108 3.0 x 108 0.66 13.2 50 5591 3.0 8387 7.55 x 108 3.0 x 108 2.52 50.3 68 4771 3.0 7157 1.75 x 107 3.0 x 108 5.83 Indefi-nite 97 3059 3.0 4589 1.56 x 108 3.0 x 108 52.0 Indefi-nite

• No test data available. The life expectancy at 41 percent is estimated from the onsite data observed by DECO engineers. The actual strain data is not available to SWEC.

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4. CONCLUSION 1

a. The turbine bypass piping vibration level depends primarily on the dump valve opening position. Reactor power level and the operating mode (i.e., one line operating or both lines operat-ing) are seen to have little effect on the acoustic vibrations.

b. The highest vibration level was found in piping sections be-tween the dump valve and the first orifice. The critiral loca-tions in this region are the first two elbows downstream of the dump valves.

c. The flow orifice is seen to have little effect on the upstream vibration level, i.e., the region between the dump valve and the orifice, but the orifice does appear to confine the acous-tic chamber to the piping sections upstream of the orifice.

d. The through-wall alternate shear stress is more than two times the surface shear stress. Hence, the fatigue life is deter-mined from the through-wall alternate stress.

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e. Based upon the results of the preliminary analysis, the' follow-ing three zones of valve opening position are categorized to represent different degrees of operational safety.

Zone I Valve opening 0 to 24 percent and 68 to 100 percent.

In this zone the allowable stress cycles are greater than 107 cycles. The expected life of operation can be indefinite pro-vided the vibration level does not increase progressively from the measured level.

Zone II Valve opening 25 to 34 percent and 46 to 67 percent.

In this zone, the allowable stress cycles did not meet 107 cy-cles. The expected life expectancy is provided in the summary tables. It should be noted that the tables indicate cumulative life expectancy. Actual life expectancy will depend upon the actual time spent in the various valve opening positions.

, i In addition, because of lack of data between 24 percent and 36 percent, operation in the vicinity of 30 percent, specifi-cally 30 to 35 percent, should be cautious and requires confir- '

mation. We would recommend taking additional data in this region for further analysis.

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A'tfachment VP-8Q-0146-Page 15 of 23 Zone III Valve opening 35 to 45 percent This is a critical zone in which anything but transitory opera-tion should be avoided, since operation in this region affords the minimum life expectancy.

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Page 16 of 23 HOPPER AND ASSOCIATES ENGINEERS 210 AVENUE 1, SUITE E REDONDO BEACH, CA 90277 213-3164835 October 3, 1986 HA-10/86-532 Contract #274884 Suborder #D59113 Task #B7 PIS #N30-17 Detroit Edison Company Enrico Fermi 2 Job Site 6400-North Dixie Highway Newport, MI 48166 Attention: Mr. J. Contoni

Subject:

Preliminary Steam Bypass Line Structural Evaluation

Reference:

ME-PJ-86-0756; Transmittal of Strain Data on the Main Steam Bypass Lines; September 30, 1986.

Gentlemen:

As you requested, we have prepared a preliminary summary report describing our initial evaluation of strain data taken from the Fermi steam dumplines.

We look forward to continuing technical interchange with Edison on the subject.

If questions arise, please contact the undersigned.

Very truly yours, David M. Hopper Professional Engineer Enclosure cc: Mr. Gellety ,

Mr. Spiers Ms. Uema 1

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