ML20054C004
| ML20054C004 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 03/23/1982 |
| From: | Wigginton D WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20054B982 | List: |
| References | |
| AE528P-39P8203, AEA-FRPE-145, AEA-FRPE-145-DRFT, NUDOCS 8204190365 | |
| Download: ML20054C004 (23) | |
Text
/
- AEA-fRPE-145 PRELIMINARY ZION STEAM GENERATOR IMPACTED TUBE ENDS RECOVERY EVALUATION
1.0 INTRODUCTION
The Zion Unit 1 Steam Generator 0 inlet channel head was subjected to impacting by a foreign object. This object was determined to be a pipe cover.
It is approximately 24.0 inches in diameter, when installed, weighs approximately 40 lbs., and is made in three hinged-together pieces (to permit installation). The pipe cover moved within the channel head by the reactor coolant flow. The cover, or parts of the cover, impacted areas of the channel head; however the only area of noticeable impact is the underside of the tube sheet where the tubes project approximately 0.2 in.
As discussed in Section 4 below, this impact should not affect *.he structural integrity of the steam generator or the reactor pressure boundary. Nor does it keep the steam generator from parforming its primary, heat transfer, funption. However, the principal causes for concern are:
a.
Were the tube to tubesheet welds integrity compromised?
b.
Were the tube ends d? formed sufficiently to preclude entry of eddy current examination probes or tube plugs?
This recovery evaluation describes the results of work to determine the potential for weld cracking, and to develop and qualify a technique for restoring the tube ends to a geometry sufficient to accept an eddy current inspection probe or tube plug.
dNAgy 4
l l
8204190365 820401 i
PDR ADOCK 05000295 P
I
2.0 CONCLUSION
S The following conclusions were reached:
The impact to the Zion Unit 1 steam generator 0 inlet tube ends, caused a.
by the inlet port cover, was relatively minor and consisted primarily of cending deformation to soma of the tube ends.
Such impact does not appear to be sufficient to compromise the heat transfer capability of the unit.
b.
Based on laboratory tests, and other plant related experiences, no tube to tubesheet weld cracking is expected and none has been observed in the examinations to date.
The observed bending of the tube ends could result in an insignificant c.
increase in the fatigue usage factor.
d.
Based upon engineering judgement, it is believed that no tube end repair is necessary unless:
1.
The tubes are to be repaired new to facilitate future eddy current probe acceptance or to facilitate future plug installation.
2.
Tube end tearing is found at the tube to tubesheet weld tip, in which case the tube end would be machined off to the tip of the weld.
A process for restoring the geometry of the tube ends tn accept an eddy e.
current probe or tube plug was successfully qualified.
I f.
The wall thinning after tube end straightening is within the original manufacturing process allowance.
l l
i AE528P/39P8203
i 3.0 RELATED EXPERIENCE 3.1 Plant I Relatively early in its life, some brot?n bolts from the reactor were transported to the steam generator. There, they were confined to the inlet channel head and impacted the tube ends.
In Plant I, the steam generator tubes project through the tubesheet a short distance and are welded to it with circumferential fillet welds (essentially like the Zion steam generators).
The impacting broken bolts affected the tube ends minimally. The tube ends were slightly deformed and a few bolt pieces lodged in some tubes. The repair consisted of a reaming operation in whien all tubes were machined to restore the inside diameter. Welds were inspected and no detectable cracks were found. All pieces of the broken boits were recovered except for a few that could not be extracted from the tubes.
In these few cases, the tubes were plugged.
3.2 Plant II In the other plant, a bolt, nut, and washer were found in one of the steam generator channel heads following the cold hydro test, during which the main coolant pumps were run. A peening type deformation of some of the tube ends was observed.
In Plant II, the steam generator tubes project below the tubesheet by a small amount, and are welded to the tubesheet using fillet welds. This configuration is similar to that of Zion Unit 1.
Four types of tube end impact were identified.
In the first, the tube end was virturally unchanged.
In the second, the tube end was no longer round.
In I
the third type, greater deformation occurred.
In the fourth type, consider-able tube material was missing. Detailed examination of five of the more severely impacted tube ends reve:
" no weld cracking.
AE52SP/39P8203
8 The repairs being undertaken at Plant II include different operations for the four types.
For the first type, only hand dressing to remove sharp edges is being used.
Light rerolling or reshaping the tube end is used for the second type.
For the third type, the tube end is being resurfaced by machining.
For the fourth type, both resurfacing by machining and selected rewelding may be needed.
4.0 TUBE END EVALUATION 4.1 Examination The form and extent of the impact to the tube ends in the Zion Unit 10 steam generator was determined through a series of examinations. These are summarized in the following.
4.1.1 Visual Examination An initial visual examination was performed by an engineer from the Westinghouse Tampa Division, the steam generator manufacturer. The type and extent of the impact to individual tube ends was assessed.
It was found that a large number of tubes appeared to be affected, a significant number of these are close to the steam generator divider plate, and that the flow passages into the tubes do not appear to be significantly reduced.
4.1.2 Video Examination A video tape of the bottom of the inlet tube sheet was made and sent to the Westinghouse Tampa Division.
There, it was studied in considerable detail and a map was made showing regions with varying degrees of apparent tube end impact.
AE528p/39P8203 e
4.1.3 Photographic Examination Several complete sets of photographs of the bottom of the inlet tubesheet were made at various magnifications. Two photographs comprised the first set and e
these were used to orient the others. A series of' numbered plugs had been
~
inserted into tubes, on a regular pattern, and these aided considerably in orienting the higher magnification photographs.
The second set of photographs, at a magnification of approximately IX, was This mosaic is shown in used to form a complete mosaic of the tube sheet.
5 Figure 4-1 and a typical portion of a constituent photograph is shown in The weld and tube ends were reviewed in detail by Westinghouse Figure 4-2.
Tampa, NTD, and NSD personnel.
The basis of this review was to determine if the impact could have compromised the structural integrity of the tube to tubesheet weld.
Each photograph was studied and tube ends that required additional review were identified.
Small stickers were placed on the mosaic to identify these 190 tube ends (see Figure 4-1).
These tubes were studied further by means of photographs at a magnification of i
approximately 2.5X.
Figure 4-3 shows a portion of a typical photograph.
Those tube ends with deformation that could affect the tube to tubesheet weld l
were identified.
Eighteen fall into this category.
Photographs at approximately SX magn.ification indicates no impairment of these welds.
l I
Every tube in the mosaic was also studied to determine if an eddy current Of the 3388 tubes, 1085 were judged to be marginal probe could be inserted.
in this regard.
4.1.4 Helium Leak Test Helium at 18 and 30 psi, in varying concentrations, was placed on the secondary side in the steam generator.
The primary sides of the tube to tubesheet welds were examined for helium to detect any cracks or leaks in the weld. The results were inconclusive.
AF528P/39P8203
4.1.5 Examination Results The results of the examination show that while many tube ends appear deformed sufficiently to prevent the insertion of an eddy current probe or tube plug, only a few (approximately nine) appear to be sufficiently affected to require closer examination and possible corrective action. The overall assessment is that the impact on the tube ends at Zion is minor to moderate.
4.2 Tube End Impact Tests The objectives of these laboratory tests are:
To duplicate the tube end deformation observed in the Zion Unit 1 D steam o
generator.
l To evaluate photography as a method for inspecting the weld region.
o To develop and qualify a technique for restoring the tube ends to a o
geometry sufficient to accept an eddy current inspection probe or tube plug.
To verify that the repair technique does not cause weld deformation or o
cracking and that tube wall thinning is within the original manufacture process allowance.
The test samples prepared are mockups which are similar to the bottom condition of the tubesheet. One mockup, with three tubes is shown in l
Figure 4-4.
This figure shows these tube ends following impact and repair.
In order to simulate the affected condition, the tubes were impacted two ways; one used in inward impact, the other used a fatigue (i.e., reverse bend) impact.
For each impact condition, three different impact loads were used; light (15 -30* bending), medium (45 -60* bending) and heavy (90* bending).
l Also various local spots on the tube ends were deformed by the impact load to simulate the conditions in the Zion steam generator, which are shown in the photographs (see Figures 4-2 and 4-3).
AE528P/39P8203 6
Before the tube ends were impacted, the conditions of the weld areas around tube ends were recorded by 4X magnifying photography, focused at 18 inches, and using Kodak plus-X pan 135 MM film. After the tubes were impacted, the weld areas were examined by photography, radiography and metallurgical sectioning.
The results of the tests, via the photographic and radiographic examination of the deformed tubes, showed no indication of weld degradation. Metallagraphic sections through the weld / tube interface did not disclose any cracking, as shown in Figure 4-5.
The tube-end showed cold work at locations corresponding to the original deformation (See Figure 4-5).
Tube wall thickness measurements were taken on three test samples at the tube-end, weld tip, weld base, and two additional locations into the simulated tubesheet. The locations of the axial and circumferential measurements are shown in Figure 4-6.
A summary of these measurements is oresented in Tables 4-1 to 4-3." The results indicated that the wall thinning after the l
rework operation is within the four to six percent permitted for the original manufacture.
Results of this test program indicated that the impacted tube ends observed at the Zion plant should not result in any loss of structural integrity to the tubesheet weld.
Once it was established that the tube-end impact deformation observed in the Zion Unit i D steam generator was judged insufficient to lead to tube /tubesheet weld cracking, a tube end repair process was developed and qualified to return the tube end to a minimum dimension of 0.770 inch. After measuring the tube ID within the original rolled region, the tube ends in a qualification test block were impacted and deformed to various conditions to simulate those seen in the Zion steam generator.
Figure 4-7 shows both as-fabricated and impact deformed tube ends.
AE528P/39P8203 7
The repair process consisted of using a tube entry rework tool in combination with a series of rolling operations.
For lightly deformed tube ends, the tube entry rework tool was used to open up the tube ends to a minimum dimension of 0.770 inch. Other lightly deformed tube ends were reworked using an Airetool
- 840 roller. For medium or heavily deformed tubes, a combination of a tube entry rework tool with three different size Airetool rollers was evaluated.
Repaired mockup tuba ends in the qualification test block are shown in Figure 4-8.
4.3 Stress Report Review and Analysis 4.3.1 Introduction l
The region of extensive tube impact deformation is limited to the tube ends beyond the tube /tubesheet weld. To evaluate the tube /tubesheet weld, the following approach was taken. The region where the stresses exceed the l
material yield strength was determined. This material was then assumed to be unable to carry any load. The stresses (primary plus secondary plus peak) were then scaled by the ratio of the length of the weld leg before the tube deformation occurred to the length of the weld leg in the elastic region after the deformation.
4.3.2 Extent of Yielding The extent of yielding in an impacted tube to tubesheet weld was determined as follows:
o,eo4
=
w o.o si NJw p.-.
i 3
v A
h -e-(\\
l AE528P/39P8203 8
I Material: 58-163(Ni-Cr-Fe)
S = 27,900 psi at 600*F (Code) y S = 42,100 psi at 600 (Minimum Test) y Yield moment at Section A-A assuming rigid / perfectly plastic stress strain relationship 2
MO " I/43 t y
O = 1/4(27,900)(.05)2 = 17.4375 in lb/in (Code)
M 0 = 1/4(42,100)(.05)2 = 26.3125 in 1b/in (Minimum Test)
M Determine thickness required to remain elastic throughout the section:
>.05(1.5)1/2 =.06124" (Section B-2)
> 6M, n/2 or t t
l yi Maximum distance between A-A and B-8, x
=.06124
.05 =.011 max Assume the following stress distribution between sections A-A and B-B' l
[Y
_fL~
s k
=
m AE528P/39P8203
1 The resulting moment is:
M = ([ - L][ +8+g2}e,=
)2,
h =.05 + x where x = distance from Section A-A Solve for L L = (3[(.05 + X)2j)l/2 4
y
._M =
,(.05)2 o
4 4
y L = [.075x +.75x ]I/2 2
x L
~ ~ ~ ~ ' "
.000
.0
.002
.0124
.005
.0198
.007
.0237
.010
.0287
.01124
.0306 Figure 4-9 shows the yielded portion of the tube to tubesheet weld.
t l
l t
c AE528P/39P8203
I 4.4.3 Fatigue Evaluation A fatigue evaluation of a weld on a deformed tube end follows.
Membrane Stress = f(t) 2 Bending Stress = f(t )
2 b+Q+F)bythefactor[09276' # \\ = 1.26 Scale total stress (P
+P L.
m 4
The hot side minus tne outside diameter stress difference, S3 - S1, for a central hole is the largest principal stress difference under both normal and upset loading conditions. This stress difference is located at the base of the crevice between the tube and the tubesheat.
The modulus of elasticity for the SB - 163 (Ni-Cr-Fe) material at 600 F is 6
E = 29.2 x 10 psi. The fatigue curves in the ASME code are based on a 6
modulus of elasticity E = 26 x 10 psi. Therefore, the allowable fatigue stresses must be multiplied by the ratio of 26/29.2.
The fatigue usage factor is made up of the following components:
a.
For 5 cycles, the principal stress varies between 116,221 and 51,321 psi, which are the primary and secondary hydrostatic test stresses, respec-tively. The total stress is:
(1.26)(116221 + 51321) = 211,103 psi and S',3, = 211,103 (j)(,{} = 93984 psi AE528P/39P8203 11
From the ASME code, NALLOW = 1600 cycles and u = 1600 = 0.003 b.
For 18,300 cycles, the principal stress varies between 0 and 64,391 psi, which is caused by the plant loading and unloading from cold shutdown to full power. The total stress is:
(1.26)(64391) = 81133 and 2 (29.2)= 6121 psi
)
S' alt = (81133)
From the ASME Code, NALLOW = 130,000 cycles and 18300 = 0.141 u = 130000 6
i c.
For 10 cycles, the principal stress varies between 54,536 and 55,541 psi, which is caused by all other loading conditions, including the primary to secondary pressure variations. The total stress is:
(1.26)(55541 - 54536) = 1266 and l
AE528P/39P8203 12 l
From the ASME Code, NALW = - and u=h=0 d.
The total fatigue usage factor is Iu = 0.003 + 0.141 + 0 = 0.144 < l.0.
For comparison, the total fatigue usage factor for non affected tubes is Zu = 0.063 < l.0.
I 4.3.4 Conclusion These calculations demonstrate that the total overall fatigue usage factor for the Zion 51 Series steam generator tube /tubesheet welds is well within that allowed by Section III of the ASME Code.
5.0 REPAIR PROCESS QUALIFICATION PROCEDURE t
The repair process was qualified in accordance with Westinghouse procedure qualification and quality control programs.
6.0 REPAIR PROCEDURE OUTLINE The repair procedure for the Zion Unit I D steam generator tube ends includes l
both " hands-on" operations as well as automatic operations. The principal operations include:
Slide Hammer tube inside diameters to open sufficiently to accept a.
camlocks (for supporting automatic equipment) and hard rollers, b.
Hardroll tube inside diameter with small hardroller to open the diameter sufficiently to accept the large hard roller.
i AE528P/39P8203 13
i c.
Hardrool tube inside diameter with large hard roller to open the diameter sufficiently to accept an eddy current probe and, possibly, tube plug.
d.
Inspect the reworked tube ends to confirm that acceptable diameters were achieved.
i n
h i
4 d
AE528P/39P8203 14
TABLE 4-1 : WALL.HiICKNESS MEASUREMENTS AROUND TUBE FOR SAMPLE # 1.1 Wall Thickness Measurements Sectioning Locations
, g,,
"C" "D"
"E" 1
.0510
.0519
.0515
.0504
.0520 2
.0486
.0509
.0508
.0506
.0504 3
.0516
.0522
.0504
.0504
.0501 4
.0525
.0486
.0506
.0496
.0495 5
.0497
.0522
.0492
.0488
.0492 6
.0448
.0498
.0478
.0482
.0477 7
.0477
.0486
.0470
.0480
.0478 8
.0482
.0484
.0465
.0466
.0480 9
.0477
.0476
.0470
.0467
.0479 10
.0521
.0525
.0499
.0508
.0510 11
.0519
.0523
,0502
.0500
.0516 12
.0537
.0515
.0500
.0505
.0520 Max. % of 4.8%
7%
6.8%
4.6%
Wall Thinning See Figure 4-6, for measurement locations Ncminal wall thickness 0.050"
TABLE 4-2: WALL THICGESS MEASUREMENTS AROlND 'IUBE FOR SAMPLE # 1.2 Wall Thickness Measurements Sectioning Locations "C"
"D" "E"
1
.0510
.0510
.0518
.0505
.0490 2
.0510
.0527
.0544
.0544
.0526 3
.0505
.0533
.0520
.0513
.0503 4
.0520
.0524
.0514
.0513
.0500 5
.0505
.0526
.0530
.0527
.0510 6
.0526
.0527
.0511
.0513
.0499 7
.0507
.0507
.0481
.0495
.0483 8
.0473
.0503
.0484
.0489
.0483 9
.0484
.0490
.0470
.0489
.0477 10
.0484
.0483
.0480
.0434
.0465 11
.0480
.0485
.0482
.0475
.0469 12
.0493
.0490
.0486
.0482
.0477 D*5 3.4%
6%
5%
7%
Wall i
Thinning l
See Figure 4-6 for measurement locations Nc:ninal wall thickness 0.050"
TABLE 4-3 : WALL 'IHICKNESS MEASUREENTS AROUND WBE FOR SAMPLE # 1.3 Wall Thickness Measurements Sectioning Locations "B"
"C" "D"
"E"
,,An 1
.0503
.0522
.0514
.0514
.0522 i
2
.0521
.0519
.0505
.0506
.0506 3
.0498
.0500
.0488
.0494
.0498 4
.0447
.0483
.0490
.0490
.0483 5
.0482
.0473
.0487
.0477
.0483 6
.0542
.0514
.0485
.0475
.0474 7
.0457
.0495
.0489
.0474
.0474 8
.0487
.0497
.0493
.0486
.0474
.0493
.05 00
.0496
.0490
.0488 9
.0505
.0511
.0510
.0509
.0506 10 11
.0514
.05 24
.0510
.0510
.0515 12
.0522
.0533
.0510
.0516
.0520 Max. % of Wall 5.4%
3%
5.2%
5.2%
H inning See Figure 4-6 for measurement locatiens Ncminal wall thickness 0.050"
4 i
1 ZION
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FIGURE 4-1 Zion "D" Steam Generator Inlet 7bbe Sheet - bbsaic
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Figure 4-2 Zion "D" Stea:a Generator Inlet Tube Sheet Section (Rcws 2 to 8, Colt =ns 85 to 89,1 X apprcx.
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FIGURE 4-3, Zicn "D" Steam Generator Inlet Tube Sheet Section (Rows 3 to 5, Cohn:ns 85 6 86),
2.5 X approx.
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FIQlRE 4-4 Zion %besheet Mockup with 'Ihree Impacted and Repaired hhc Ends
I
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x Wf Y
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-150' 270*'
30*
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anikjTJ.y:id
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k,r%:WM:
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60*
180*
300*
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210*
330' a.. a. !wm t-Y-37cy V'*Tok
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a t
u0-220-0*
FIGURE 4-5 Meta 11ographic Sections at 30' Positiens Around Circirference of Deforned and Repaired Tube Sa.:ple 1.3
~ 5x
O' 30 12 '
1
/
f 11 2
C/S 60 Block 10 Tube -
3 L
,c-
\\
S 4
/
8 5
%o 7
3_
6 i
Polished Face i60*
casa. Weld Sectionine Locations l
l "A"
- .062" l
Reference a _._
--- {^
8 "B"
- .125" Line "C"
- .250" c-
"D"
- .500" Clad l
,'E"
- .750" e
o-E-
I.D. Measurement Locations 1
hbe/Tubesheet Sa::ple Sectioning 6 I.D.
FIG. 4-6 l
Measurement Locations
.