ML20076E418
| ML20076E418 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 01/25/1983 |
| From: | Dollansky K ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY |
| To: | |
| Shared Package | |
| ML20076E390 | List: |
| References | |
| TR-V-MCM-003, TR-V-MCM-3, NUDOCS 8306010087 | |
| Download: ML20076E418 (14) | |
Text
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6.2 Report No. TR-V.-NC:4-003 6.2 Metallurgical Examination of Diffuser /R.C.P. Casing Bolts Returned from Arizona Unit 2 (791350) by K. W. Do11ansky, P.E.
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1-25-1983 8306010007 830518 PDR ADOCK 05000528 S
PDR P.enort 83-0002 APPEilDIX II
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Eigne rcken R.C.?. ciffuser/ casing bolts were returneo frcm Arizona Unit 2 for examination. One bolt was found to be broken during the de-staking operation. The type of failure was identified as hydrogen induced stress corrosien cracking.
The remaining seven were used to pull the diffuser /wecges into cosition.
This operation broke the bolts. All bolts were initially.
cracked which was attributed to stress corrosion cracking.
All aight bolts originated fran the same lot which was examined and discussed in Report TR-MCM-ll2.
2 "eport 83-0002 APPEllDIX II.
Intrecuction.*nd Backorcund j
This report is in contindation of Report TR-MCM-112, dated 11-24/82, submitted to CE-KSS with Memo MC.V-82-274 on 11-30-1982.
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C-E Winosor received from CE-KSB eight broken socket head cap screws (threaded halves only) for examination.
These broken bolts were returned from Arizona Unit 2 following recent rework activities.
One of the eight cap screws was found to be broken during the de-staking operation (pump S/N1110-2B, identification "8109-200-016-1 Thread").
The remaining seven were used to pull the diffuser / wedges into position prior to installing the new replacement cap screws, and it was this operation which caused the final breakage of the bolts.
It was reported by CE-KSB that these bolts were the original new onis which have never been through operation at either CE-KSB or Arizona Unit 2.
A list cf the eight bolts with identifications is shown in Attachment (1).
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i Peport 83-0002 APPENDIX II l
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Examinatien All eignt bolt samoles showed similar ' fractured surfaces, i.e., an oxidized incioient crack and a clean final fracture (see Fig.1). Also the surface (shank and :hreao) of all samples was covered with a dark grey oxide, suggesting that the bolts had been exposed to an oxidizing medium such as, for instance, primary coolant (this would be contrary to infomation received from CE-XS3; see Introduction of this report).
We selectad for the examination bolt sample "8109-200-016-1, Thread" (sample 1) which broke during the de-staking operation, and bolt sample "8109-200-016-3-1 Thread" (sample 3-1) which is representative of all seven bolt samples listed under 2., 3. and 4. in Attachment (1), i.e., rough surface of the final fracture as compared with the fractured surface of sample 1 (Fig.1) e The colts came fran the same lot discussed in Report TR-MCM-ll2 and
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consequently were made frcm the same grade of steel (Type 410) folicwing the same manufacturing procedure (see Report TR-MCM-ll2).
Metallographic examination of the samples 1 and 3-1 revealed the microstructure to be tempered martensite with a grain size of about ASTM No. 7 (Fig's 2 and
- 3) and with clearly distinguishable former, austenitic grain boundaries (see also Fig. 3 in Report TR-MCM-ll2, the presence of the 'ormer, austenitic grain boundary was discussed in this report).
The micro hardness of both samples was found to be OPH 468-470 (500g load),
corresponding to about Rc 47.
Tne fractured surfaces of the two samples were examined on the scanning electrcn microscope (SEM).
The crack which initiated the failure of the two bolts (see Fig. 1) is shown in the left photographs of Fig's 4 and 5.
As can be seen the cracks are intergranular and follow the former, austenitic grain boundaries visible in the photomicrographs of Fig's. 2 and 3.
The appearance of the crack surface (left, Fig's 4 and 5) is almost identical with that of Fig. 5, Photo A of Report TR-MCM-ll2, including scme secondary cracking between adjacent grains. 'e. cort 83-0002 APPENDIX II
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The right chotographs of Fig's 4 and 5 show the fractured surfaces of the final break of the samples 1 and 3-1, respectively (clean portions of the fractureo surface in Fig. 1). The finer appearance of the fracture of sample 1 is believeo to oe oue to the fact that this bolt broke by delayed hydrogen cracking wnereas bolt 3-1 broke by overstressing when used to pull the diffuser /weoges into position.
Conclusions The initial cracking of all eight bolts occurred by hydrogen induced stress corresien cracking as discussed in detail in Report TR-MCM-ll2. Bolt 8109-200-016-3-1 broke finally by delayed hydrogen cracking just as the bolts No.13 and 15 examined and discussed in Report TR-MCM-112. The remaining seven bolts broke 3after initial stress corrosion cracking, when they were used to pull the diffuser / wedges into position.
It is believed that they also would have 5
faileo sooner or later by delayed hydrogen cracking.
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1 APPENDIX II
.teport 83-0002
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.s-ATTACHMENT {1)
Chronology of Arizona Unit 2 RCP Diffuser Ring Segment Bolting Sccket Head Cao Screws, P/N 8109-200-016 were received from the Arizona Unit 2 Site on January 14, 1983. A total of eight (8) broken cap screws were returnec fran two different pumps - S/N 1110-2A and 1110-28.
Four major categories have been established as follows:
1.
One socket head cap screw was found broken upon de-staking of the locking sleeves frem 1110-28.
Labeled as:
8109-200-016-1 Head; 8109-200-016-1 Thread.
The remaining seven socket head cap screws can be separated into three groups according to the location of the fracture.
2.
Three socket head cap screws failed at the head / taper / shank transition.
l Labeled as:
8109-200-016-2-1 Head; 8109-200-016-2-1. Thread.
8109-200-016-2-2 Head; 8109-200-016-2-2 Thread.
8109-200-016-2-3 Head; 8109-200-016-2-3 Thread.
3.
Two socket head cap screws that failed approximately one inch from the head cearing surface.
Labeled as:
8109-200-016-3-1 Head; 8109-200-016-3-1 Thread.
8109-200-016-3-2 Head; 8109-200-016-2-2 Thread.
4.
Two socket head cap screws failed approximately 1-1/8 inch to 1-1/4 inch from head bearing surface.
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Labeled as:
8109-200-016-4-1 Head; 8109-200-016-4-1 Thread.
8109-200-016-4-2 Head; 8109-200-016-4-2 Thread.
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eoort 83-On02 APPENDIX II
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k se DIFFUSER / CASING 1
BOLTED CONNECTION N\\
s Report 83-0002 FIGURE 1
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TABULATED
SUMMARY
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O!!FUSER BOLT Fall.URES y
DURING tlECHANICAL TESTS AT CE-KSB i
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TEST PUMP TEST DURATION NUMBER OF STARTS LOCATION OF SIX*
NO. OF BOLTS y
NilMBER ll00RS FROM AMBIENT TEMP.
VANE DIFFilSER llALF BR01;EN C0ft4ENTS 8:
1 500+
3 Right 2
(See Note 1) g h (Test 1 - 3) 17 h(Test 2581,2681) 50 2
Right 1
(See Note 2)
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20 (Test 10182.10282 50 2
Right 2
(See Note 3) 3,,,(20A
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Test 10582,10682) 30 2
Right 2
(See Note 4) k ( (200 m g Test 10782) 30 1
Left 0
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v 20C 3 (Test 10882 30 1
Right 4
(See Note 5) e
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200 New bolts and S
8 (Test 10982) 30 1
Left 0
Diffuser Wedges.
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- Looking down the discharge, as viewed from behind the casing.
I Note 1: Two bolts were found broken and the ring segment was found sitting on the impeller. The exact location of the broken bolts is not certain, but it is thought that they were the " bolts bridging the gap."
Note 2: One ring segment bolt found broken on the ring segment " bridging the gap" on the six vane diffuser half.
Note 3: One bolt was on the ring segment " bridging the gap" on the six vane diffuser half, and the second bolt was on the adjacent ring segment on the six vane diffuser half.
Note 4: One bolt was on the ring segment " bridging the gdp" on the six vane diffuser half, and the second bolt was on the adjacent segment on the six vane diffuser half.
Note 5: Four ring segment bolts ultimately found cracked on the five vane diffuser half.
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- 1, #17,
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Ring Segment Bolt
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Report 3.~i-@02 FIGURE 3
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DIFFUSER WEDGE ASSEf1BLY l
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Report 83-C002 FIGURE 4 l
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