ML20099F222

Forwards Addl Info on Independent Assessment Program Phase 3 & Cinched U-bolt Testing & Analyses Program.Contact Between Pipe & Crosspipe Overestimated & Contact Between Pipe & U-bolt Incorrectly Assumed to Extend for 180 Degrees

ML20099F222
Person / Time
Site:	Comanche Peak
Issue date:	11/16/1984
From:	George J TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	Williams N CYGNA ENERGY SERVICES
References
NUDOCS 8411260317
Download: ML20099F222 (15)

Text

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TEXA i UTILITIES GENERATING COMPANY P, o. box 1002 GI EN ROSE. TEXAS 76043 November 16, 1984 /:7 M

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t's. N. H. Williams Project Manager CYGNA Energy Services 101 California Street, Suite 1000 Stsa Francisco, California 94111-5894 '

COMAhCHE PEAK STEAM ELECTRIC STATION Independent Assessment Program Phase 3 Cinched U-Bolt Testing & Analyses Program Additional Information REF: 1) J. B. George (TUCCO) letter to N. H. Williams (CYGNA), dated November 1, 1984 - same subject

2) N. H. Williams (CYGNA) letter to J. B. George (TUCCO), " Status of Cinched U-Bolt Testing and Analyses Program", 84042.018 dated October 1, 1984

Dear Ms. Williams:

Reference i provided in its attachment the information requested by Reference

2. Included in the attachment as part of the answer provided to Item 2 of Reference 2 were results of a finite differetree heat transfer analysis con-ducted for an uninsulated and an insulated U-bolt configuration on a 10-inch pipe.

A rechecking of the modelling of the contact areas between the U-bolt and the pipe and the pipe and the crosspiece has indicated that the contact be-tween the pipe and crosspiece was overestimated and thac the contact between the pipe and the U-bolt had been incorrectly assumed to extend for an arc or 1800 Accordingly, we are providing in the attachment to this letter the results obtained for the uninsulated case of the pipe at 2500 F and the in-sulated case with the pipe at 350 F, where the boundary conditions of the model are changed to reflect the more realistic contact areas. We will be glad to discusr the details of the model, if CYGNA so desires.

Please call if you have any questions.

Very truly yours, TEXAS yTILITIES GENERATING COMPANY

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/ . .-. c 0 69c O' eor j Vice President / Project General Mar:ager JBG/RCI/gh 4  ;

cc: S. Burwell R. Iotti J. Van Amerongen D. Wade I f

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ATTACHMENT 1 Revision to Item 2 of Reference 1.

Please replace Item 2 response with the following:

A. The answer to this question is best worded by first restating that the choice of 2500F for the 10-irch pipe temperature is a compromise choice which bounds the majority of the systems in the plant, and where used with an uninsulated U-bolt configuration is also representative of the case where the pipe temperature may be 3500F but the U-bolt configuration is insulated.

Second, it is important to point out that there is a cingle cinched-up U-bolt which is used on the 10-inch portion of the RHR system. This is support RH-1-024-007-S22R which is on line 10-3H-1-24-601-R-2, which is connected to the outlet line of the RHR heat exchanger. The maximum normal temperature seen by the line is 2800F during initiation of RHR operation. Only under upset conditions, where component water cooling may be lost, can the maximum temperature of this line reach 3500F. There are no cinched-up U-bolts on the inlet side of the RER heat exchangers.

Third, it is germane to point out that the tests conducted on the 10-iu.h pipe specimens had a corresponding average temperature of the U-bolt equal to approximately 1500F. For the particular configuration examined here, i.e.,

stainless steel pipe and carbon steel U-bolt, the approximate 1500F represents the equilibrium temperature of the U-bolt. The following describes the tem-perature history during the thermal cycling test and the creep test for both the U-bolt and the crosspiece.

Thermal Cycle 1:

The pipe reached the test temperature of 250 F at 30 minutes, but then con-tinued to climb to over 2800F before settling back down ot 2580F. The U-bolt radius and leg stabilized around 1950F and 1500F, respectively, near the end of the cycle. See Figure 3.

Thermocouples 2, 9 and 10 on the crosspiece reached temperatures of 1290F, 136 F and 1440F, respectively, at the end of Cycle 1. These are less than the equilibrium temperatures reached during the creep test. Figure 4 shows that temperatures had not leveled off. Refer to Figure 9 for location of thermocouples.

Thermal Cycle 6:

The pipe reached an equilibrium temperature of 2500F within 20 minutes. The U-bolt radius and leg reached 18301 and 144 F, respectively, arcuad I hour.

See Figure 5.

Thermcouples 2, 9 and 10 on the crosspiece reached temperatures of 1250F, 1320F and 1390F, respectively, at the end of Cycle 6. These are less than the equilibrium temperatures reached during the creep test. Figure 6 snows that temperatures had not leveled off.

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Page 2

• Creep. Test:

, The pipe reached an equilibrium tecperature of 2500F in less than i hour.

The U-bolt radius stabilized at 1850F within i hour. The U-bolt leg sta-

.bilitad at 1480F within-2 hours. _See Figure 7.

Thermocouples 2, 9 and 10 on the crosspiece reached equilibrium' tempera-tures of 1380F, 1460F and 1540F, respectively, around 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. See Figure 8.

10" Specimen Summary:

With a pipe test temperature of 2500F, the U-bolt reached thermal equili-brium during each cycle of the thermal cycling test, but the crosspiece didn't. The entire assembly reached thermal equil$brium shortly into the creep test. A summary-is provided in Table 1.

Results of finite difference thermal analyses are very sensitive to the assumed area of contact between the pipe and the U-bolt and the pipe and the crosspiece.

When the U-bolt is cinched, the line contact between the pipe and the U-bolt extends for an arc which is less than 1800 , and the precise extent of which depends on the cinching force and the spacing of the bolt holes in the crosa-piece. Similarly the cinching process tends to produce a loss cf contact at some points between the crosspiece and the pipe due to-either bending cf the crosspiece or local deformation of the pipe. This loss of contact, however small, profoundly affects the heat transferred from the pipe to the crosspiece.

A heat transfer model has been executed for the uninsulated U-bolt configura-tion with the following assumptions. Heat transfer from the pipe to the U-bolt is along an are near the apex of the U-bolt. At the diametral location there is a small gap (less than 1/16") between the pipe and U-bolt. No gcps are assumed betwe(a the U-bolt and the crosspiecc (the assumpcion is believed to be inconsequential since both elements are roughly at the same temperature at that location). Heat transfer between the pipe and the crosspiece takes place through a line contact extending 2 inches along the pipe, and via gap conductance, along the circumference of th pipe and through a gap increasine t from zero to 1/128" linearly from the end of the contact area to the end of i

the place. Likewise, the heat transfer between the pipe and the U-bolt also considers the gap conductance with areas immediately adjacent to the line of contact and extending out to the U-bolt radius. This model produced results j which more closely match the results of the test.

)' Results of the analyses are shown in Figure 1 for the uninsulated case. In Figure 2 similar results are shown for the insulated case. The only difference between the latter analyses and that of the uninsulated configuration are the pipe temperature, which in the latter instance is 3500F, and the presence of j insulation.

I For the uninsulated case the average temperature of the U-bolt in the curved j portion is 175-1800F, while the straight portion is at about 150 F. For the insulated case the corresponding temperatures are approximately 3000F and j 2600 F respectively.

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Page 3 The effect of the temperature rise on the clamping forces acting on the pipe and the U-bolt for the two cases of 2500F pipe, uninsulated U-bolt and 3500F pipe, insulated U-bolt, can be estimated by comparing the relative growth of the pipe to U-bolt for the two cases, neglecting any deformation of the pipe.

Since only relative growth is pertinent here, the one-directional growth of the U-bolt due to thermal expansion given as Yi where Yi= 43 TL where L is the projected length of the U-bolt which is given as 2R and T is the temperature differential between the average U-bolt temperature and ambient (or a reference temperature), is compared to the diametral growth of the pipe, Y2 , which is given as Y2= dz AID The worst case relative expansion will occur for the stainless steel pipe and the carbon steel U-bolt. For the 10-inch pipe (10.75 OD), coefficients of thermal expansions (= 6.3 X 10-6 in/in/0F at 150-1800F or 6.6 X 10-6 at 260-300 F and d,= 9.4 X 10-6 at 250oF or 9.53 X 10-6 at 350 F and a reference ambient temperature of 700F, the relative expansion for the two cases con .

sidered, i.e., 2500F pipe with bare U-bolt, and 350 F pipe with insulated U-bolt are as follows:

1. 2500 F AY = 0.011755 inches

2. 3500F AY = 0.0137 inches i

). 3. Finite Element Analysis 3h' = 0.0141*

(* Finite Eleme.nt Analysis used 210 F.)

As seen from the above, theoretical, steadystate heat transfer analyses would predict that the case of 3500F pipe expanding against an insulated U-bolt j could result in a differential pipe expansion which would be soproximately 17%

j Jarger than could be expected for a 250 F pipe with uninsulated U-bolt. How-

, ever, the finite element analysis has been conducted in a manner that would encompass the case of 3500F insulated U-bolt. As saen from the third row of relative expansion, the finite element analysis, which used a pipe temperature of 210 F but maintained the U-bolt temperature at 700F, would yield a relative expansion which is comparable to the case of 3500 insulated.

Another point to be discussed, is that the test has provided information on the transient thermal expansion differential between the pipe and the U-bolt.

As seen from the data which is attached as Figures 3 and 5, the maximum temperature differential Fetwecn the pipe and the U-bolt occurred when the U-bolt has reached a representative temperature of about 101-1050 while the .

0 pipe had been heated to 250-255 , a difference in temperature of approximately 1500F. This difference is well simulated in the finite element analysis where there is a c',astant ditference in temperature of 140 F. It should also be remembered that for these temperature differentials, the amount of stress caused by the thermal expansion is not very significant.

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4 U-BOLT TilERMAL AND CREEP TEST DATA EVALUATION 4

I TIME REQUIRED TO REACll .

EQUILIBRIUM TEMPERATURE, *F EQUILIBRIUM TEMPERATURE, HOURS U-BGLT U-BOLT  % U-BOLT U-BOLT ,

PIPE RADIU9 I.EGS T/C 2 T/C 9 T/C 10 PIPE RADIUS 1.ECS T/C 2 T/C 9 T/C 10 I

1 -" INSUI.ATED SPECIMEN I

TilERMAL CYCLE 1 559 498 451 * *

• 2.5 2.5 2.5 * *

• I T l THERMAL CYCLE 6 560 530 440 * *

• 2.0 2.25 2.75 * *

• g CREEP 564 495 451 322 340 365 2.0 2.0 2.0 3.0 3.0 3.0 y r-IIE C 250 195 150 * * * .50 1.5 1.5 * *

• TilERMAL CYCLE 6 250 183 144 * *

• 25 1.0 1.0 * *

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CREEP 250 185 148 138 14o 154 1.0 2.0 2.0 3.0 3.0 3.0 1.I

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'l2" INSULATED SPECIMEN .

l THERMAL CYCLE 1 560 * * * *

• 4.0 * * * * *

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j l CREEP 563 440 353 154 175 251 4.5 11.5 12.5 14.5 14.5 14.5 l - - I -

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• TilERMAL EQUILIBRIUM WAS NOT ACllIEVED.

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