ML20148G794
| ML20148G794 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 01/22/1988 |
| From: | Dante Johnson, Mayer E, Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | |
| Shared Package | |
| ML20148G775 | List: |
| References | |
| TAC-65992, NUDOCS 8801270035 | |
| Download: ML20148G794 (40) | |
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I REPORT OF HELIUM CIRCULATOR S/N C-2101 AND INLET PIPING S/N 2001 REPAIR AND MODIFICATION ACTIVITIES January 22, 1988 FORT ST. VRAIN NUCLEAR GENERATING STATION Public Service Company of Colorado Prepared By: d M /. -
O. S V.ohnson Circulator Project Manager Verified By: [h M E. L. Mayer V Senior Engineer Verified By: n (Attach. 1) B.A.Ringff
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Quality AssMrance Enaineer Approved By: / E [ W ~ /SW
- 0. W. Warembourg 7' Manager Nuclear Engin=ering 4
TABLE OF CONTENTS Pa.se 1.0 Purpose .......................... 1 2.0 Summary and Conclusions .................. 1 3.0 Inspection and Repair ............ . .... 2 4.0 Component Failure Assessment ............... 6 5.0 Component Design Considerations ............. 9 5.1 Colt Material Selection .............. 9 5.1.1 Li',erature Review and Survey ........ 9 5.2 Fastener Review .................. 16 5.2.1 Fastener Material Changed .......... 14 5.2.2 Fastener Material Not Changed ........ 17 i 5.3 Preload Requirements ...... . . ..... 18 l
l 5.4 Spring Plunger Addition / Insulation Ccver ingagement 19 5.5 Chamfer C-2101-431 Ccunter Bore .......... 20 6.6 Thread Lubricant Change .............. 20 6.0 Quality Assurance Requirements For Helium Circulator Fastener Procurement ........ .... 21 7.0 Circulator Inspection / Replacement Criteria ........ 23 7.1 Determination of Intervals . ........... 23 7.2 Inspection Intervals ........ ....... 24 7.3 Tech Spec Upgrade ................. 25 7.4 Circulator Operability ........... . . 26
Ease 8.0 Monitoring ........................ 26 0.1 .Present Monitoring System . . . . . . . . . . ... . 26 8.2 Speed and Wobble. Computer ............. 29 8.3 Enhanced Wobble Monitoring ............. 29 8.4 Loose Parts Monitoring ............... 30 8.5- Continuing Circulator Operability .........-30 9.0 ' Review of Water Chemistry / Treatment ........... 30 9.1 Past Water / Steam Chemistry ............. 30 9.2 Present Water Chemistry Procedure Requirements ... 31 9.3 Proposed Water Chemistry Procedure Changes ..... 32 9.4 Water Chemistry / Treatment Overview ......... 33 ,
10.0 Secondary Coolant System Material ,
Effects Review .,.................... 33 11.0 Refurbishment Plan and Schedule ............. 33 11.1 Inlet Pipe S/N 2001 Repair ............. 33 11.2 C-2101 Repair- ...... ............ 33 i 11.3 Parts .'chedule ................... 34
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Page 1 of 35 1.0 PURPOSE The purpose of this report is to provide information relative to design changes and controls to be implemented on helium circulators at Fort St. Vrain as a result of damage to circulator C-2101. This report also addresses the damage and repairs associated with circulator C-2101 and inlet piping (penetration assembly) S/N 2001.
2 . ')
SUMMARY
AND CONCLUSIONS Helium circulator S/N C-2101 was removed from service in July, 1987 as a result of excessive shaft wobble indications and a purified helium interspace leak. The circulator was subsequentiy shipped to GA Technologies (GA) for inspection, evaluation and repair.
From the results of a metallurgical analysis performed on components from circulator C-C.101, it has been determined that caustic stress corrosion cracking (SCC) was the i'11tiating cause of component failure. A common environment to all the failed and damagcd components is steam utilized for the turbine drive, suggesting this was the source of caustic contamination. The presence of caustics has been verified by a review of the water chemistry system records. There was also a period when significant levels of caustics were utili;;ed in the chemical treatment program for the auxiliary boiler.
Fort St. Vrain's revised water chemistry procedures have made beneficial differences in the quality of condensate and steam.
This, coupled with the more stringent water chemistry requirements described by this report, will reduce the potential for caustic SCC in plant components.
As a further precautionary measure, a study was undertaken to find alternative bolting material which is more resistant to caustic SCC than the originally inst.alled material. The study resulted in the decision that Inconel X-750 in a solution annealed and overaged condition be used where possible. One application where Inconel X-750 could not be used is for the l steam ducting to bearing cartridge connection. Due to the high l material strength requirements for this application, high strength Alloy A-286 will continue to be used.
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Page 2 o' 35 Fasteners 'in the steam area of each circulator will be replaced in an outage scheduled for Spring, 1988. Subsequent to this, a replacement interval for fasteners exposed to feedwater/ condensate and reheat / auxiliary boiler , team has been developed which will mandate replacement (subsequent to initial
- installation) prior to completing an additional 40,000 operating hours. In addition, during any future circulator refurbishment, all fasteners (with a few exceptions) will be replaced. This includes fastener replacement in the steam, primary coolant, bearing cartridge and service line areas of the helium circulators.
3.0 INSPECTION AND REPAIR Helium circulator S/N C-2101 was removed from service in July 1987 as a result of excessive shaft wobble indications and a purified helium interspace leak. Following its removal it was shipped to GA Technologies in San Diego. On August 14, disassembly of the machine commenced, directed by a team of PSC and GA engineering and metallurgical staff. Specific details of failures and nonconformances were documented in accordance with '
GA's Quality Assurance Manual.
Initially, the circulator disassembly was confined to removal of the circulator Felton wheel (90-C2101-407), the turbine stator assembly (90-C2101-460) and turbine wheel assembly (90-C2101-440) (reference Figure 1 for configuration details).
l At that point the damage to the downstream upper oriented face of the turbine wheel was exposed. The labyrinth spacer (90-C2101-416), the labyrinth seal (90-C2101-421), the
' insulation cover (90-C2101-402), tha spring plunger (90-C2101-300-53) and the labyrinth seal securing screws (90-C2101-300-46) were also observed as being extensively damaged or destroyed. The sintered metal fiber insulation rings (90-C2101-415 and -417) and backing plate (90-C2101-419) could l
not be found.
Two of the fifteen 3/4 inch diameter bolts (14 solid core,1 center drilled), which secure the bearing cartridge to the steam ducting, were broken off with their head sections missing and their threaded sections still present in their locating holes.
One of the fourteen solid core bolts (90-C2101-300-45) had failed in the shank. After removal, one more -45 bolt was found cracked near total failure in the shank approximately 1" below
. the bottom of the head. The pressure tap bolt (90-C2101-300-52)
I had failed in the shank above the first thread. This center f drilled bolt provides the means of sensing the static pressure l on the downstream side of the turbine wheel.
Page 3'of 35 f//// Y ////s,
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LA8YRINTH SEAL BOLT 11 BOLT (FROM BACKSIDE)
N Stru t f / \\\\ NNNN CIRCULATOR STEAM TURBINE'PELTON WHEEL DETAIL FIGURE 1
Page 4 of.35 Part of the metallic debris trapped in the upper dished face of the turbine wheel was identified as the remnant of the head of either the missing -45 or -52 bolt previously referenced.
During inspection of the vacant steam ducting counterbore hole
! for the missing ~52 bolt head, a fine hair-like crack was observed, running the length of the bore. The crack did not l extend to the apex of the collar where the interspace seal is made nor did it penetrate through the steam ducting weldment to havt caused an interspace leak.
Cracks were also observed in all of the 90-C2101-431-4 struts in the vicinity of the weld connection between them and the 90-C2101-431-5 forging. Each of the sixteen struts were cracked around 40% of the strut periphery, resulting in a reduction in the strut cross sectional area of approximately 15%. Subsequent inspection has shown that steam ducting dimensions are within tolerance. The struts will be weld repaired to return the support area back to the original configuration.
The helium compressor and the bearing cartridge assembly were disassembled anc inspected. The condition of these components was good other than normal expected wear. When compared to past circulator refurbishments (C-2102 and C-2104, which also experienced fewer operating hours than did C-2101), these components are generally considered to be in as good or better condition. There was no damage on the bearing water / primary coolant side of the circulator attributable to the steam side failures. All fasteners examined in these assemblies show no signs of degradation or SCC.
A complete report addressing the disassembly and refurbishment of circulator C-2101 including the elements of technical specification surveillance SR 5.2.18 will be prepared and issued by GA Technologies following refurbishment activities.
Inner piping assembly S/N 2001 was also sent to GA Technologies for inspection, repair and certain previously identified modifications. No failures were observed in bolts and fasteners associated with the inner piping. Each of the convolutions in the 6" bellows was found cracked. This failure is common to all inner piping assemblies repaired to date. Modification of the expansion joint is being implemented to eliminate this type of failure. A crack in the steam deflector weld was also found.
This weld cracked due to insufficient weld depth and has been repaired. Figure 2 shows details of the penetration and inner piping.
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Page 6 of 35 4.0 COMPONENT FAILURE ASSESSMENT A detailed metallurgical evaluation was performed under PSC Lab Report No. 138 (Attachment 1) on twenty-four different components including fasteners, expansion joint, steam ducting, and turbine wheel. This included visual examination, scanning electron microscopy, energy-dispersive spectrometry, metallographic examination, x-ray diffraction and chemical analysis.
Failure or damage has occurred in several different materials including 410 martensitic stainless steel, A-286 austenitic stainless steel, carbon steel, 4140 steel, 5% chrome steel, Monel 400 and Inconel 600. SCC was identified in several components including 410 SS bolts, A-286 SS bolts, carbon steel spring plunger, and Monel 400 lockwire. Table 1 summarizes the results of the metallurgical evaluation. In addition, caustic SCC was identified in the NG5250-A-27 Inconel 600 6" diameter bellows and high concentrations of sodium were identified on crack surfaces. Sodium, which is considered the initiator of caustic SCC, was also found in the corrosion products from the C-2101-460-10, 11 and NG5250-A-59 cap screws. Given the appropriate conditions, caustic will cause corrosion and SCC in 410 SS, A-286 SS, carbon steel, 5% chrome, 4140, Inconel 600 and Monel 400 materials.
A common environment to all the failed and damaged components is steam utilized for the turbine drive suggesting this was the source of caustic contamination. From a review of water chemistry records (Reference Section 9.0), significant levels of sodium hydroxide and sodium phosphate could have been carried over into the circulators from auxilicry boiler steam. High levels of caustics in this steam is considered to be the major cause of the corrosion and SCC observed. Other caures of corrosion and SCC were considered such as hydrogen sulfide which could result from the degradation of molydisulfide lubricant.
l However, since SCC was found in nonlubricated components, such i as the 6" expansion bellows, Monel lockwire and fractured I surface of the pressure tao bolt, molydisulfide degradation is not considered to be the primary cause of SCC.
SUMMARY
OF MLIABLURGICAL EXAMINATION TABLE 1 l 1 1 1 101AL l NO. I !
1 PARI No. I NAME l PdATERIAL I i.UMBERl EXAMINEDI OBSERVATIONS l l i I I I l l__ l Pitting and SCC in threads in all 8 bolts I I l labyrinth Seal l l l*
l C2101-300-46 l Mounting Botts l 81055 4 1 12 8 l examined I l i I I .l_ 1 l l
l l Spring Plunger l Carbon l l 1 l C2101-300-53 l l St sel l 1 l 1 1 Pitting and SCC in threads l l l l l l l 1
l_
l Steam Ducting l l l l l l C2101-300-52 1 Pressure lap Bolt l A-2E6SS l 1 l 1 i SCC in shank and threads l I l__I_ l l l l 1 l l Steam Ducting l l l [
l C2101-300-45 i Bolting l A-286SS l 14 l 14 l SCC in shanks and threads of 8 of 18s bo l t s l l 1 l 1 l l l
", 1 1 inconel I l l Cracking bolt hole 9 ac 10 likely from l 1 C2101-300-23 l Steam Ducting l 718 l 1 l 1 l mechanical rubbing damage l l l_ I l l l l l Steam Iurbine Stator l [
l l l l l C2101-460-81 l Cap Screws l 410SS l 4 1 3 i Pitting and SCC in threads of 3 cap screws 1 1 l l l l l 1
l l Steam lurbine Stator l l l l SCC along face of threads instiating at i I C2101-460-10 i Cap Screws 1 410SS I 16 l 16 I manuracturing derects in 10 cap screws i I I I I I l I
l t ockwi re ror 460-10 l I I l l l
l ---
1 Bolts l MONEL-400 l 1 1 1 l SCC l l l l 1 l l ._
l l l Socket llead Cap I l l l SCC at the apex of a th road initiating at a l l C2101 - 300-8 4 1 Screws I 84 10SS l 84 l 4 l manufacturing defect in one cap screw l l l l l l l
ll_ _ _t abyrinth Spacer I l l l l l
l C2101-300-27 l l 430SS I 1 1 1 l Damage due to mechanical rubbing l l l 1 1 1 l l
l Labyrinth Seal l l l l l l
l C2101-300-28 l l 4305S l 1 1 1 l Damage due to mechanical rubbing i l I l l l l 1 l Insula tion Cover l l l l l l
l C2101-300-11 1 1 830SS I 1 1 1 l Damage due to mechanical rubbing l 1 l_ l l_ l ,1 l l
l l Steam Iurbine Rotor i l l 1 l Slight pitting of disk along dovetail notch l l C2101-84 :42-2 1 Disk l 422SS l 1 l 1 I
l l l . l _ _ ___ i l i
! 1 l Pelton Wheel flo tt l INCONLL ! l I l l l C2101-300-38 l l 718 l 1 1 1 1 No appa rent damage 1 l I I I I I l_ _____
l l Pelton Wheel Lock l INCONEL l l l l o",
l C?101-300-14 l Washer 1 600 l 1 1 1 l No apparent damage l l l l l l c 1 1 -
l I l Pelton Wheel Nut l INCONIL 1 1 I l C2101-300-15 l l 718 1 1 l 1 1 No apparent damage i u I I I I i l o I
l
SUMMARY
Of METAttURGICAl. EXAMINATION
- ~-
TABLE 1 (zontinued) ^
q' I I I l TO1AL l NO. I 1 NAMC l MA1ERIAL l MUMBERI EXAMINEDI OBSERVATIONS .l i PART NO. I I l l 1 1 I l 1 Crack like indications (possible SCC) at l l Nozzel Support Socketl i l .l l NCS250-A-59 11 Cap Screw l 4140 1 24 1 3 l threads & head of shank Junction or 2 out or 1l i _1 . 1 I __I 1 3 screws l Nozzle Bolt Assembly l 5% l l l SCC at head to shank Junction in 2 of 3 bolts.1l l Chrome i 6 1 3 i Ceneral and pitting corr. In all 3 bolts l NG5250-A-57 !i l l l l I I I l No apparent damags l l 1 Lockwire for l l l I
l ---
l NC5250-A-57 Bolts 1 304SS 1 1 1 1 1 I
I I i .
I I I 1 Pitting and general corrosion. 1 l Special Stud i 5% l i 1 l
l Chrome l 16 l (1 3/4" l _l I NC5250-A-42 l l l I i l _1 Section11l Pitting in all four and. SCC through enti re l l l Bellows Support Ring i l l l
4140 1 40 1 4 I cross section in one cap screw l MC5250-A-68 l Cap Screw 1 I l I I l 1 1 i
l Lockwire f or i INCONLL l l l No apparent damage l I 1
--- l NG5250-A-68 Cap 1 600 1 1 1 1 1 l l'
! I l j l l_Sc[ews l l SCC l l Expansion Joint l INCONLL l 1 l NG5250-A-27 1 (Bellows) 1 600 1 1 l 1 1
( l l I l l 1 l Derlector Plate l Ca rbon l l l Cracking due to inadequate weld,also shallow l l 1 l corrosion fatigue cracking 1.
l NG5250-A-50 l l Steel 1 1 1 I
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b Page 9 of 35 5.0 COMPONENT DESIGN CONSIDERATIONS Subsequent to the disassembly, inspection and analysis of components from circulator C-2101 and inner piping S/N 2001, design changes were determined necessary to decrease the probability of failure similar to that which occurred in C-2101.
5.1 Bolt Material Selection Stress corrosion cracking was found in certain bolts exposed to reheat and auxiliary boiler steam in Circulator C-2101 (as discussed in 4.0 Component Failure Assessment).
As a result of the discovery of SCC, a study was undertaken to find alternative bolting material which is more resistant to the caustic SCC identified in C-2101.
Acceptance Criteria for alternative bolt materials is as follows:
- 1. Minimum yield strength of 95 ksi at room temperature, 85 ksi at 600*F (based on fastener strength requirements).
- 2. Superior resistance to SCC from exposure to steam or water containing caustic, chloride, or sulfide at temperatures up to 600 F.
- 3. Broad data base on mechanical properties and SCC behavior.
- 4. Availability of materials.
- 5. Thermal expansion characteristics compatible with surrounding steel and nickel base alloy structures.
5.1.1 Literature Review and Survey A survey of the literature was conducted to determine materials most resistant to SCC in steam or water with caustic, chlorides, and molydisulfide degradation products such as hydrogen sulfide.
Contacts were made by telephone with individuals Anown to be knowledgeable about and who have had experience with SCC, or who had investigated bolting materials resistant to SCC, primarily in the nuclear industry. Information and opinions were also sought from material cuppliers/manufacturert. with regard to the materia's most resis+ ant to SCC in the above environments.
1 i _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Page 10 of 35 As a result of this literature review and telephone survey, the list of candidate bolting materials shown in Table 2 emerged. Also included in Table 2, for comparison purposes, are the properties of some bolting alloys currently used in the FSV circulator regions that contact reheat / auxiliary boiler steam.
The review of the literature showed the following:
- 1. There are no commercially available alloys with required mechanical properties that have demonstrated immunity to caustic-induced SCC.
Almost all commercial and nickel base alloys are subject to SC# in the presence of caustic at elevated temperatures. However, some available data indicates that, in certain heat treatment conditions, Inconel Alloy X-750 offers more resistance to caustic-induced stress corrosion crack propagation than many other alloys.
- 2. For a number of the alloys shown in Table 2, data on elevated-temperature caustic stress corrosion were not available.
- 3. The high-nickel-content alloys such as Inconei Alloys 718 and X-750 exhibit superior resistance to chloride-induced SCC.
- 4. The resistance of the alloys to molydisulfide degradation products is not fully defined.
However, in general, high-strength, low-alloy steels offer lowest resistance, and nickel base alloys offer greatest resistance.
- 5. Under PWR core bolting conditions, Inconel l
Alloy X-750, in certain treatment conditions, i offers the greatest resistance to SCC initiation and propagation. Inconel Alloy 718 offers good resistance to crack initiation under these conditions, but poor resistance to crack propagation.
1 _ . _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ ___
Page 11 of 35
- 6. The susceptibility of most alloys to SCC is a relatively sensitive function of heat treatment condition. For example, under PWR core bolting conditions: Inconel Alloy X-750, in one heat treatment condition is the most SCC-resistant; whereas, the same alloy, in a different heat treatment condition, is one of the least SCC-resistant. It is important, therefore, in material selection, to consider both the alloy and its metallurgical / heat treatment conditions.
TABLE 2 l CANDIDATE BOLTING ALLOYS Minimum Minimum UNS No. Specification Specification 9r Yield Tensile Hgat I ren Etrength ksi Strenqth ksi Notes Alloy A ti l_ No, }pecif4 cation A286 UNS-S66286 ASME-SA453C-660 1650' + 1325'i 16 hr 85 130 Botting 1800* + 1325*F 16 hr AMS-5737 1650' + 1300*F 16 hr 95 140 SPS Cold worked, solution, and ( 180 )( a ) 200 Bolting p rec i p i ta t ion-ha rdened 718 UNS-N-7118 ASME-SB637 Solution and precipitation- 150 185 Ba r and ha rdened forging SPS Cold worked and precipitation- ( 180 )( a ) 220 Bolting ha rdened X-750 UNS-N07750 ASME-SB637 2100*l, stabi l ize and precipi- 90 140 Ba r and tate fo rg ing 1800*F and precipitate 115 170 Ba r and forging
[PRI heat treatment 100 160 Ba r and fo rg ing None Solution 1800* and 160(b) 200(b; Botting V-57 rione 175(c) Fo rg ing 1350*F 16 hr 125(c)
MPl$9 None None Solution 1800* and 265 280 Bolting 1350*f 16 hr Solution 2000 and 120 155 Botting W545 UNS-S66545 1350' 20 hr and 1200* F 20 hr ASIM-A193 Quenched and tempered at 105 125 Bolting 87 AISI-4140 ASTM-CRDT 1100*F AISI-501 ASIM-A193 Quenched and tempered at 80 100 Bolting B5 ASIH-CRB5 1100*F ASSI-410 ASIM-A193 Quench and tempe red a t 85 110 Bolting B6 AS1V-CRB6 1100*F
.A o
(D (a) Estimated values -
(b) Cold worked and aged N (c) Aged only O W
LD l
Page 13 of 35 Overall, the literature data indicated that Inconel Alloy X-750, when used in the solution annealed and overaged condition, offered a range of stress corrosion resistance that suggested it was the better choice for the circulator operating conditions.
The discussions with knowledgeable people from industry produced information similar to that summarized above, with additional commr.,s as follows:
- 1. Elevated temperature caustics produce conditions that can initiate stress corrosion in nickel base alloys as well as iron base alloys. The consensus was that no alloy could be relied upon to fully resist caustic SCC under the kind of conditions believed to have occurred in the circulator reheat / auxiliary boiler steam exposed system.
- 2. Inconel Alloy X-750, in the solution annealed and overaged condition, was generally favored as the most stress corrosion-resistant, higher-strength bolting material available today for many high-temperature water / steam applications.
- 3. Nickel case alloys like Inconel Alloys 718 and X-750 are considered more resistant to chloride-induced SCC than iron base alloys like Alloy A286. However, in caustic environments, Inconel Alloy 718 is only slightly better than Alloy A286, whereas, correctly heat treated Inconel Alloy X-750 appears considerably better than either Inconel Alloy 718 or Alloy A286 in caustic.
- 4. Little relevant data is available on other potentially interesting alloys like V57, MP159, and MP35N.
Overall, the bolting material identified as having superior resistance to SCC was Inconel Alloy X-750, in the solution annealed (2025 25'F, 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) and overaged (1300 F 25 F, 20 to 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />) condition. This heat treatment has been recommendea by EPRI draft specification 2322-16322-HC2.
-~
I Page 14 of 35 5.2 -_ Fastener Review A review of fasteners and locking mechanisms which are exposed to reheat / auxiliary boiler steam within the circulators was performed.
This review resulted in the list of fasteners and lockwashers listed in Table 3.
5.2.1 Fastener Material To Be Changed The review of the effects of SCC on the original materials in Table 3 resulted in the recommendation that certain bolts / fasteners be changed to Inconel X-750 with heat treatment as follows:
anneal at 2025'F 25'F, hold for 1 to 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> Solution and cool within material five minutes to 800 F or less; the temperature should as thereafter quickly be cooled to room as possible and precipitation
(+2, hardened at 1300 F 25 F for 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />
-0 hours) and air cooled. No hardness requirements have been specified since the minimum required strength and ductility of the material is obtained through heat treatment.
The mechanical properties of the bolts / fasteners shall have:
1.
an ultimate tensile strength of 160,000 PSI minimum,
- 2. a yield strength (0.2% offset) of 100,000 PSI minimum, and
- 3. a minimum of 20% elongation, in 2 inches.
The above requirements correspond to those in EPRI proposed for Use in specification 2322-16322-HC2 "Alloy X-750 Light Water Reactor Internals" prepared by Stone and Webster Engineering Corporation. The
' heat treatment conditions recommended for the X-750 FSV helium circulator bolts are those defined as the "core draft internal basic condition" in the EPRI specification.
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IC-2101-300-38 l I u r ta i ne/ P. W. ll 640 l Inconel i 136.86 5 77.68 1 60.0 11 inconel l 136.86 l 17.68 l 60.0 l(.021" - .024")l l l tie bolt l I 718 l l H 118 I IQS 1 l l u 1 I i 1 1 I H I I I i 1
- C-2101-300-14 i Pelton nut i 640 l inconel 1 35.0 1 30.16 1 60.0 ll Inconel 1 35.0 1 30.16 8 60.0 l ----
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) I sockwasher i I 600 l I I I 600 1 I I I i 1 I I I i 1 1 1 I I IC-21ol-300-15 l 640 I loconel l 20.59 l 60.0 l Inconel l1@78.97 1 'O.59 l 60.0 1 ----
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I i 1 1 I 1C-2101-300-29 I tal>y seal bolt i 600 l AISI 1 40.5 1 18.31 I 1.8 1 inconel 1 35.9 l 11.97 I 1.1731 ---- 1 ,
I l lockwasher i I 430 SSI l l l l 600 l I I I l i i l i I I I I l 1 i l i 1C-2101-300-44 l Broit-steam I 750 l AISI l 69.0 h>6.6 1I 1.8 1 inconel I 93.3 1 36.9 l 1.1731 40 in.-lb. l l l stator l l 410 SSI I I I X-750 I I l l l 1 1 I 1 l l 1 1 I I I I i 1C-2101-300-% i .tolt-steam l 500 l A286 1 167.0 1 114.5 1 42.7 i A286 l 167.0 l 8.5 1 36.7 I (.008"I l l I duct brg. assy. 1 l l 1 1 1 1 ! 5 I I I I I J l i I I i i i I IC-2101-300-46 1 Ital t-laby sea l 1 600 l ASIM A1931 T1.7 $6.6 1 1.8 l Inconel l 95.0 , 36.9 l 1.1731 40 in.-Ib. l l l l l CRD6 l @l l l X-750 l l l 1 l i
1 1 1 1 I I l i I I I 1C-2101-300-52 I liolt-press. 1 500 ll A286 1 167.0 1 132.0 1 42.7 I A286 l 167.0 11A2.9 1 36.7 I (.008")
l l tap i l I i i l i IQ5 l l l l l l 1 I l I l l I h 5 in.-Ib.
IC-2101-300-53 l Sp r a ng p l unge r i 600 1 Carbon l steel l@22.1 l
l 1 I
1 I
I loconel l l X-750 1 95.0 1 I
1 I
1 I
11 l
l l l I I I I I I I I i I I I 1C-2101-460-10 i Bloit-turbine 1 750 l AISI l 69.0 49.D 1 1.8 1 incenel l 93.4 1 36.9 l 1.1731 40 in.-Ib. I I ]_tw y cal j l_f00 SSI I I I X-750 l I I l l l
l h Shear Hers: GA0H 13. Pl??, GADR85
@ Ilased on _, Inrgin;_[inf!b}
..15 x nom Oia. x stressed a rea except at no cd otherwise y
@ Her. NIC-87-OS60 f'or preload evaluations .
@ Ilased on measured bolt stretch $
a
@ Her. SAL HDuk app. I.
@ Based on 0.2 s'riction coerricient ( o rig i na l designi instead or O.15 o
{N
Jant t 3 (continuedi i i I .
_ O'llClhAL i ffW l l l MAXIMUM l MIN. YIf tDI PR[ TOAD l l l MIN. Yl[LDIPR[tOAO,1 1 TORQUE .l l l l l l T[Mr ll l 4 itMP. I STRES lPRELO I l 4 TEMP. ISTRESJ llPREto DI OR I I LitM NO. l __UthCHittliMi IL_G) l _i Mall!!! ALIi _ !G 8 __xs 3I kts 4 JMimLAL_1 kSt l_f@lG3 _Ed I (STRETCHI I-1 i I 7 1 I .
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Ic-yl01-460-11 i Boit-asign. 750 l AISI l 69.0 i
)49.45li 1.8 l Inconel I 93.4 1 36.9 l 1.1731 40 in.-Ib. I j i i sleeve l l 4to SSI I i i X-750 1 l l l 1 1 1 i i i I i 1 1 1 l l IfP-91-M-19-4-42 l Stud-steam I 650 l SA-193-851 60.0 I
)25.49 l 5.761 SA-193-871 81. fi 1 33.98 1 7.681 60 ft.-Ib. l l 1 intet ,
i I I I I I I I I l ,
i 1 1 1 l l 1 I I I I I f P- 71-M- 19-4-41 1 Nut-guido ! 650 l Cold l1@22.5 l h 9.52 1i 5.768 Cold 1@22.5 l 12.69 1 7.681 l l 1 tube I i rotted i I rotied 1 I Q6 l l 1 1 1 1 I steel I i 1 I steel 1 1 1 I l l 1 1 I I 1 I I I I I I trP-91-M-19-1-57 I aont-poston 1 500 i SA-193-851 60.0 ,361.94 1 1 4.8 I loconel l 96.0 1 68.82 1 5.33l 22.5 ft.-ib.i l I water nozzle l l l l l l X-750 l l l l l l l I I l i 1 I i i l i IIP-91-M-19-5-59 1 Bolt-nozzle 1 650 l SA-193-BFI 81.0 78.9 l 1.581 Inconel I 94.5 I 67.54 l 1.351 35 In.-Ib. I l I support i l i i 1 X-750 l l l l l l l l l 1 l l I I 1 l l Isr-91-M--19-9-68 I sin e t-be l lows 1 650 i SA-193-Bil 81.0 21.14 1 3.0 l encones I 94.5 1 28.2 1 4.0 1 22.5 ftMIb.l.
I I support ring i I i l 1 X-750 l i I I l l 1 1 1 1 I i 1 1 1 1 I Ife-91-H-19-14-1221 Holt-thermat l 650 l SA-193-871 81.0 38.05 1 5.4 I incono: 1 94.5 1 28.2 1 4.0 l' 22.5 ft.-Ib.I l.
I l sleeve to steam i 1 l l 1 X-750 l l l I i 1.plR i O2 I I I I I i 1 I i i I
@ Shear
@ Rers: CADR13. Pi22 GADR8')
Based on Torque;_(lDZlkl
@ . I 's x NOM Dia. x stressed area except at noted othe vise
@ Ref. NI G-8 T-O'/60 f or preload evaluations
@ Based on measured bolt stretch
@ Rer. SAE ilDUK App. E
@ Dased on 0.2 i riction coerricient (original designl instead or O.15 c3 LD E
M
Page 17 of 35 i
l All lockwashers and lockwire exposed to steam are being changed to or will remain Inconel 600. The lockwasher material of Inconel 600 (C-2101-300-14) examined from C-2101 showed no signs of SCC.
Inconel 600, although not as resistant to SCC, was chosen over Inconel X-750 for its ductility properties and its acceptable level of resistance to relaxation. This material has adequate strength for the application. Inconel 600 also has superior resistance to SCC compared to the other existing materials, which are primarily carbon and low alloy steel, and 300 or 400 series stainless steel.
5.2.2 Fastener Material Not Changing The 3/4" steam ducting to bearing assembly bolts (90-C2101-300-45, -52) are installed with significant preload to provide proper seating of an 0-ring seal and provide adequate pressure difference capability. These preload requirements are shown in Section 5.3.
Due to the high stresses incurred in this application, Inconel Alloy X-750 is not suitable as a replacement. Since these bolts need to be of higher yield strength, high strength (200 KSI minimum tensile strength) A-286 has been chosen for continued use based on the following:
- 1. The original A-286 performed satisfactorily for more than 60,000 operating hours.
- 2. The bolts are captive with respect to the circulator rotating element (i.e. individual bolt failures will not result in impingement of loose parts on the rotating element). The failure of the bolts in this area would result in a loss of secondary interspace pressurization. This interspace pressurization is controlled by technical specification and readily recognizable by the surveillance testing program.
- 3. Consistent with PSC's commitment to change Technical Specification SR 5.2.18 (details discussed in Section 7.0), an enhanced circulator inspection program and fastener replacement interval is being implemented.
This program has been developed based on a review of operating history and disassembly / inspection records.
Page 18 of 35
- 4. More stringent water chemistry controls have been and are being implemented (discussed in Section 9.0) which will reduce the allowable concentration -level of caustics in the steam system.
The steam inlet piping mounting stud material is being changed from SA-193-B5 to SA-193-B7 due only to material availability. The mounting studs will only be changed during a complete inner piping refurbishment, which is currently being done on inner piping S/N 2001. The studs will not be changed out to a caustic resistant material for the following reasons:
- 2. There are 16 studs holding the inner piping to I
the steam scroll. The probability of all 16 studs completely failing is highly unlikely.
i j 3. The preload stresses on the connection are I less than 60% of yield, 3 condition which makes it less likely to initiate SCC in the studs.
The turbine /pelton wheel tie bolt and nut (Inconel 718 material) are not undergoing a material change for the following reasons:
- 1. The tie bolt and nut from circulator C-2101 were inspected (Ref. Metallurgical Report
- 138) showing no indications of SCC.
- 2. The preload stress is approximately 56% of yield which makes the connection less susceptible to SCC.
5.3 Preload Requirements The preload for each fastener listed in Table 3 has been analyzed for each application. The preload stress has been minimized to avoid SCC while exceeding a preload value below which fastener loosening might occur.
The method for preloading each fastener has also been evaluated. The most critical preload stress applications have been determined to be in the steam ducting to bearing assembly bolts (C-2101-300-45 and -52). Since these bolts are fabricated from A-286 material, they are not as resistant to caustic SCC as Inconel X-750. They also requirc a high preload stress to maintain the pressure boundary connection.
=
c Page 19 of 35 _
! For these reasons, the determination of preload stress for n i the C-2101-300-45 bolts using ultrasonics to measure bolt ;
elongation is being investigated. The system being _
considered is a Stressmic V828 manufactured by Stresstel -
Corporation. In anticipation that this system will meet 3 our needs, special manufacturing requirements have been -
imposed for the A-286 bolts to ensure flat parallel ends of adequate finish to accommodate the measuring device q requirements. These .nethod s will determine the bolt ;
length prior to and subsequent to installation. (
A Since the original torquing application for the -45 bolts -}
provided sufficient preload to maintain the pressure 4 boundary (i.e. interspace to secondary coolant), testing y will be performed to ensure the calculated 8 Mils of 9 v.longation needed to provide desired preload is not above the elongation developed by torquing at 400 to 410 ft-lbs. 1 If the elongation resulting from the applied torque of the .
400 ft.-lb. range is consistently below the calculeted 8 ;
Mils, then the preload application method for this 6 connection will be re-evaluated. Applications will be .
controlled by GA under Shop Traveller and by PSC 3 Maintenance procedures.
The turbine /pelton wheel tie bolt (C2101-300-38) will be preloaded using a micrometer caliper to measure the bolt ,
length before and after tightening. This installation will be accomplished under GA Shop Traveller and PSC Maintenance procedures, ]
i The remainder of the fasteners listed in Table 3 will be i
~
preloaded using a precision torque wrench. This will limit torque to the calculated values. Allowing for a 130*6 accuracy, the preload stress will generally be -
These installations will be maintained below yield.
controlled under GA Shop Traveller and PSC Maintenance -
procedures. _
Spring Plunger Addition / Insulation Cover Engagement 5.4 The spring plunger, which locks the insulation cover in place could allow the insulation cover to disengage if failed. To eliminate this single failure mechanism, a second spring plunger will be installed to redundantly prevent insulation cover rotation. Since this modification is not considered to be feasible insitu, it .
will be implemented during complete circulator refurbishments. The direction of installation will be e changed during the initial circulator bolt replacement, proposed for the Spring of 1988, so that turbine rotation -
will force the insulation cover towards 100*; engagement. _
These modifications will not affect the function of the components and will increase their reliability.
b r
Page 20 of 35 5.5 Chamfer C-2101-431 Counter Bore The counter bores in which the 3/4" bolt heads seat, (C2101-300-45,-52) currently have a square edge on them.
This edge contacts the fillet radius at the bolt shank to head interface, which could result in a line of stress concentration upon contact. To eliminate this stress concentration point, the counter bore edge will be chamfered. This modification will be implemented during the initial bolt replacement program.
5.6 Thread Lubricant Change Industry practice in recent years has been to eliminate the use of molydisulfide lubricant at elevated temperatures, and in the presence of moisture. While the molydisulfide is not considered to be the primary cause of SCC in C-2101 (SCC was also found in non-lubricated components), a review of other lubricants has been completed with the preferred lubricant being Dow Corning Molykote 505. Molykote 505 does not contain any molybdenum disulfide nor is it similar to silicon molykote. Molykote 505 is a paste containing an inorganic solid lubricant stable up to 2000 F in a mineral oil base.
Besides reducing break-away torque, the lubricant is designed to provide protection against corrosion. An analysis of the Molykote 505 will be performed to identify its constituents. The results of this analysis will be utilized to ensere material and environmental compatibility. If constituents are found which could enhance SCC, this compound will not be used. Nickel l
Never-Seez Pure Nickel Special and Felpro Grade N 1000 are also being pursued and will undergo the same evaluation as the Molykote 505.
Mechanical means will be used to remove the molydisulfide lubricant from the bolt and screw holes in the FSV helium j circulators. Thread taps and stiff stainless steel wire brushes rotated by a drill motor will be used to loosen the lubricant.. The loosened material is then to be removed by blowing it out of the holes with pressurized air and/or by vacuuming to pull out the loose lubricant particles.
Evaluation of chemical means suggested by suppliers of moiydisulfide lubricants to remove the lubricant shows them to be dangerous and impractical. Suggested chemical means are very hazardous, do not completely remove the lubricant, and may result in contamination of the circulator with residues which may cause SCC.
I
Page 21 of 35 6.0 PROCUREMENT QUALITY ASSURANCE REQUIREMENTS FOR HELIUM CIRCULATO To ensure a high quality fastener, avoid manufacturing defects, and ensure fastener cleanliness from manufacturing contaminants, the followingonQuality implemented all Assurance (QA) requirements are being procurements:
current helium circulator fastener 1.
All procurement activities are per GA's QA Manual, PSC Engineering Procedure ENG-16 and PSC Quality Assurance Procedure Q-4.
2.
Approved suppliers per the PSC approved vendors list and/or GA QA Manual are being used. (10CFRSO Appendix 8 and/or ASME Quality Systems Certificate and/or source inspection).
- 3. Vendors are requ1 red to establish in their subtier procurement documents those requirements necessary to assure that each item delivered has been controlled, manufactured and inspected in compliance with the requirements of the GA or PSC purchase order.
- 4. Vendor (s) are required to obtain written approval of all nonconforming items prior to shipment.
- 5. Traceability of all materials is required.
- 6. All fasteners of each type / size are required to be from the same heat of material (within a given purchase order).
7.
Chemical required.
and mechanical certified mill test reports are 8.
Furnace charts. for all heat treating, are required.
9.
All completed fasteners are required to be fluorescent penetrant inspected per ASME Sec. V Article 6. No linear indications in shank or threads is permitted.
- 10. Substitutions and/or weld repair are prohibited.
- 11. All rolled threads are to be rolled per applicable sections of MIL-S-8879 or MIL-S-7742.
- 12. Vendor special processes must be performed by qualified personnel, procedures, and equipment.
- 13. Vendor shall provide a certification of compliance for each heat treating, non-destructive examination or similar process performed on this hardware.
l Page 22 of 35
- 14. Detrimental materials (possibly those contained in cutting fluids)_will not be used if they cannot be effectively removed.
- 15. Vendor visual and dimensional inspection is required.
- 16. Receiving inspection (as a minimum) will include:
a) 100% visual inspection b) Dimensional inspection with sampling per MIL-ST0 105 0.
c) Verification of chemical analysis and tensile strength of two (2) fasteners from each lot.
d) Random verification of hardness per MIL-STO 105 D.
e) Cleaning of all fasteners in alcohol or equivalent.
- 17. Vendor shall certify compliance with all purchase order requirements.
- 18. 10CFR21 shall be imposed on vendor (s).
Due to the high stress requirements of the C2101-300-45, -52 bolts, the following additional requirements will be applied:
- 1. Prior to fabrication all material shall be ultrasonically examined per ASME Sec. V, Article 5, Para. T-535. Any imperfection which causes a response in excess of 20% of the reference amplitude shall be cause for rejection.
- 2. GA to witness ultrasonic testing of material.
- 3. GA to witness dye penetrant testing of finished hardware.
- 4. Source inspection of final hardware.
- 5. Vendor to submit NDE procedures for GA review prior to their use.
I _ _
)
Page 23 of 35 7.0 CIRCULATOR INSPECTION / REPLACEMENT CRITERIA A review of the operating history and disassembly / inspection records has been perfortred. From that review and the hours of operation of C-2101 prior to failure, a conservative inspection / parts replacement interval was developed to include the following:
- 1. Insure initial replacement of all C2101-300-45, -46, -52, and C2101-460-10 fasteners. Also replace the C2101-300-53 spring plunger. Perform a visual inspection of all components removed for fastener replacement. These activities are scheduled to be completed during a Spring, 1988 outage.
- 2. Repeat the fastener replacement and component inspection within a time frame not to exceed 40,000 circulator operating hours.
- 3. Complete disassembly and inspection per Attachment 2 of a second circulator within a 10 year time frame frt.m the first circulator so inspected per Surveillance SR 5.2.18 (reference Section 7.3).
- 4. Inspection results from any circulator examined or inspected for any reason will be evaluated and factored back into the established programs to reflect any required adjustments.
7.1 Determination Of Intervals Operating history and disassembly / inspection records of three circulators C-2101, C-2102, and C-2104 were examined in an effort to establish a reasonable inspection / replacement interval for various circulator components. The review of eperating history indicates that 64% to 72% of operating time of the circulator has been on steam.
Complete disassembly and inspection of circulator C-2102 at 17,142 hours0.00164 days <br />0.0394 hours <br />2.347884e-4 weeks <br />5.4031e-5 months <br /> (12,249 on steam; 43 thermal cycles) revealed no failed components. This disassembly and inspection was a Technical Specifiestion surveillance requirement (SR 5.2.18). Circulator C-2104 was disassem' a and inspected at 49,037 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> (34,921 on steam; ,M 4ermal cycles) for repair of the turbine end
- damaged " , ted foreign material. One 90-C2101-300-46 ne .0-C2101-500-51 fastener were found fastenu failed. L~ 'stor S/H C-2101 disassembly and inspection at 63,893 hours0.0103 days <br />0.248 hours <br />0.00148 weeks <br />3.397865e-4 months <br /> (41,091 on steam; 136 thermal cycles) revealed extensive failure of turbine end assembly fasteners and hardware with resulting significant turbine end damage. All twelve 90-C2101-300-46 fasteners and 20%
of 90-C2101-500-45, -52 fasteners had failed.
Page 24 of 35 Since no failures were found at 17,142 hours0.00164 days <br />0.0394 hours <br />2.347884e-4 weeks <br />5.4031e-5 months <br /> and two unrelated fastener failures were found at 49,037 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />, an inspection interval somewhere above 17,142 hours0.00164 days <br />0.0394 hours <br />2.347884e-4 weeks <br />5.4031e-5 months <br /> but below 49,037 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> would seem reasonable. The extensive failures at 63,893 hours0.0103 days <br />0.248 hours <br />0.00148 weeks <br />3.397865e-4 months <br /> may indicate an_ accelerated failure rate as operating hours are extended above 49,037 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. The two unrelated fasteners found failed on C-2104 at 49,037 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> would not of themselves result in further failures or -cause .any damage since both are captive.
Based on the above, a conservative inspection interval of 40,000 circulator operating hours (combination of steam turbine ~and pelton wheel drive) has been established.
7.2 Inspection Intervals The inspection intervals and the inspection methods to be applied are included in the inspection schedule shown in Attachment 2. The inspection schedule basically duplicates that used by GA for the first SR5.2.18 inspection but with the following changes: 1) The inspection interval has been shortened for the turbine end components found failed in C-2101, 2) Scheduled replacement of critical turbine end fasteners that may be susceptible to caustic stress corrosion has been included, and 3) A schedule for inspection of the steam inlet and water piping assembly has been added.
Subsequent to initial fastener replacement, an inspection / replacement interval of 40,000 circulator operating hours will be applied to the circulator steam turbine end components outlined in Section 5.0. During any future circulator refurbishments, all fasteners, with the exception of the speed probe attachment fasteners (90-C2101-500-40, -51), the Pelton wheel tie bolt and nut (90-C2101-300-38, -15) and the inlet piping mounting stud assembly (FP-91-M-19-42, -44), will be replaced. This includes fastener replacement in the primary coolant, steam, bearing cartridge and service line areas. The Pelton wheel tie bolt and nut and inlet piping stud assembly are not being replaced for reasons discussed in Section 5.0. The speed probe attachment fasteners are non-critical to continuing circulator ope ation.
Page 25 of 35 7.3 Technical Specification Upgrade As a result of the failures observed on circulator C-2101, an enhanced ISI Technical Specification surveillance test, SR5.2.18 will be developed. Based on historical information, a required inspection / replacement program at 40,000 circulator operating hours is being added to the current 10 year disassembly and inspection requirements.
This will include the inspection of the turbine end and inlet piping components and the replacement of specified fasteners. The inspection / replacement requirements will receive further evaluation based on the results of fastener replacement scheduled for the Spring of 1988.
Given the positive results of tSe primary / bearing cartridge side inspection of circulator C-2101, as well as previous inspections of C-2102 and C-2104, there is not sufficient technical information to assess the present ten year interval of inspection specified by SR 5.2.18. It is therefore PSC's intent to remove a circulator either during the Spring of 1988 or,-at the latest, during the fourth refueling. This circulator will be disassembled and refurbished under the provisions of SR 5.2.18. The results of this future circulator inspection coupled with our past experience will be utilized as a basis for evaluating the SR 5.2.18 inspection interval. It should also be noted that the provisions of SR 5.2.18 (with a few exceptions) have been applied in the refurbishment efforts on C-2101 to provide a greater data base for evaluating the SR 5.2.18 inspection intervals.
Operation history; refurbishment / repair results, both historical and future; and the continuing operational monitoring program will all be evaluated as elements of the circulator ISI Program. These elements will be utilized to adjust the program as necessary. In the interim the following requirements have been established:
- 1. Insure initial replacement of all C2101-300-45,
-46, -52, and C2101-460-10 fasteners. Also replace the C2101-300-53 spring plunger. Perform a visual inspection of all components removed for fastener replacement. These activities are scheduled to be completed during a Spring, 1988 outage.
- 2. Repeat the fastener replacement and component inspection within a time frame not to exceed 40,000 circulator operating hours.
- 3. Complete disassembly and inspection per Attachment 2 of a second circulator within a 10 year time frame from the first circulator so inspected per Surveillance SR 5.2.18 (reference Section 7.3).
I
Page 26 of 35
- 4. Inspection results from any circulator examined or inspected for any reason will be evaluated and factored back into the established programs to reflect any required adjustments.
7.4 Circula. tor Operability The inspection intervals coupled with the material upgrade described in Section 5.0, the enhanced monitoring system described in Section 8.0 and the improved water chemistry controls described in Section 9.0 will provide assurance of operable circulators. Results from continuing circulator inspections will be trended, evaluated and utilized to make necessary adjustments to the program.
8.0 MONITORING As a result of the failures associated with circulator C-2101, a comprehensive monitoring and trending program will be implemented to enhance circulator performance and assist in early detection of any future circulator failures. Circulator shaft wobble is currently being monitored on an interim basis with the use of dedicated oscilliscopes until a continuous monitoring system can be implemented.
8.1 Present Monitoring System Circulator shaft vobble is presently monitored by four dedicated oscilliscopes and data is recorded daily per test T-369. Wobble is also being checked after any unplanned circulator speed changes. The data accumulated to date has not shown any significant wobble increase with speed. The wobble data to date indicates that there is some scatter, but the data remains close enough to the baseline so that the scatter has not been significant.
Surveillance SR-RE-17-W is run on a daily basis to balance the cables to the speed modifiers. This imbalance is caused by the bridge circuitry drifting between their two locations, one at the circulator and the other in the control room. The imbalance is being evaluated as a part of the long term enhanced monitoring program.
Instrumentation utilized to support wobble monitoring and surveillance tests is controlled and calibratec as a part of the safety related instrumentation program.
PSC has developed an enhanced circulator performance trend analysis. The data shown in Table 4 is being trended to evaluate circulator operating characteristics. Included in this data are the circulator bearing cartridge differential pressures, which are being logged manually.
l .
Page 27 of 35 The current method o f. monitoring, displaying and documenting the wobble signal on a daily basis provides assurance of proper circulator shaft operation. The information show obtained is being stored, analyzed and trended to any degradation or changes in circulator rotational dynamics, in support of continued circulator operation and ongoing circulator assessments.
4 1
1 e
Page 28 of.35' The -following data is recorded continuously on the plant data logger:
TABLE 4 GROUP I "A" CIRC. "B" CIRC. "C" CIRC. "D" CIRC.
SPEED ST-2105 ST-2111 ST-2106 ST-2112 STEAM TURBINE CONTROLLER OUTPUT SC-2105 SC-2111 SC-2106 SC-2112 BEARING WATER FLOW FM-2183 FM-2185 FM-2184 FM-2186
- BEARING WATER CARTRIDGE 6P PDI-21285-1 PDI-21285-2 PDI-21286-1 PDI-21286-2 BUFFER-MIDBUFFER PDT-21389 PDT-21391 PDT-21390 PDT-21392 GROUP II COLD REHEAT PRESSURE PT-2243-1 (L I)
COLD REHEAT PRESSURE PT-2244-1 (L II)
STEAM TURBINE EXHAUST PRESSURE PT-2243-2 (L I)
STEAM TURBINE EXHAUST PRESSURE PT-2244-2 (L II)
GROUP III STEAM TURBINE PRESSURE RATIO PM-2243 (L I)
STEAM TURBINE PRESSURE RATIO PM-2244 (L II)
STEAM TURBINE EXHAUST TEMPERATURE TE-2255-7 (L I)
STEAM TURBINE EXHAUST TEMPERATURE TE-2256-7 (L II)
GROUP IV PRIMARY COOLANT PRESSURE PT-1110 AVERAGE CIRCULATOR INLET TEMPERATURE (L I)
AVERAGE CIRCULATOR INLET TEMPERATURE (L II)
- Not currently recorded by the plant data logger (recorded manually).
Page 29 of 35 8.2 Speed and Wobble Computer The speed and wobble computer system (PDP 11/10), which was functional during initial plant start-up, has not been functional in the past due to parts unavailability and system complexity. The system utilizes a minicomputer and d display panel to Compute the actual bearing clearance based upon the phase relationship between upper and lower displacements.
At this time the system has been refurbished and appears to be functional. The interface cable has also been replaced, making the interface functional. Efforts are under way to load the speed and webble program to check for system operability as part of the enhanced monitoring project.
A Nicolet Oscilliscope representative has demonstrated a model 4094 digital oscilliscope that has alarm capabilities. The scope contains a micropressor and it appears that it could replace the function of the existing computer. The scope is currently being evaluated for use in the system.
8.3 Enhanced Wobble Monitoring In an effort to increase monitoring capabilities, an enhanced monitoring program is being developed which will provide continuous wobbie monitoring, alarm, data acquisition and storage, trending and diagnostic capabilities. The major problem with the development of the system is that the slots in the shaft at the speed probes cause an incompatibility with standard monitoring systems on the market. An interface with the existing probes must first be developed. This will allow a monitor to hook up with the existing speed cables external to the circulator. If this interface cannot be established, then the other two options are to install wobble pick ups into the bearing cartridge or fill in one of the two upper and lower slots in the circulator shaft. Both options would have to be done with the cartridge disassembled and would be extremely long term. Another problem with using the existing wobble system is drifting of the bridge balance circuitry which requires frequent recalibration. If the interface circuit does not remedy this situation a long term system redesign would be required.
Page 30 of 35 If the problems can be resolved, Bently Nevada, who 1:
working with PSC to develop the system, would require one month to gather information and one month to develop a prototype on paper with another month required to physically build the customized prototype. After that time a month of operational data collection would be desired with another month to construct the finalized system. Final installation could then take place within approximately one week, which at best would be mid 1988.
8.4 Loose Parts Monitoring A loose parts monitoring system is being considered which would consist of transducers (noise pick ups) placed near the turbine stage and in a natural collection region with a monitor located in the control room. A meeting with Babcock and Wilcox (B&W) took place on 11/10/87.
Questions were raised concerning the ability to gain access to the monitoring regions and the degree of sensitivity required to detect loose parts. It was agreed that a preliminary investigative task would be proposed by B&W to try and determine the feasibility of applying a loose parts monitoring system. The objective of the task is to prove whether the technique is practical and to determine the optimum sensor location.
8.5 Continuing Circulator Operability Although the enhanced wobble monitoring system and a loose parts monitoring system (described in Sections 8.3 and 8.4 above) are long term, the present monitoring system (described in Section 8.1) provides a more than adequate means of monitoring and trending circulator operation. We are continuing in cur efforts to enhance this monitoring system with additional information from the existing speed and wobble computer (described in Section 8.2).
9.0 WATER CHEMISTRY / TREATMENT REVIEW 9.1 Past Water / Steam Chemistry The three main modes of operation at Fort St. Vrain for the secondary coolant system are shutdown, powering up or down, and power operation. During shutdown, the plant uses condensate /feedwater to drive the helium circulators.
During shutdowns or when powering up or down, the condensate /feedwater is converted to steam in the auxiliary boilers. This source of steam in turn drives the circulators via the reheat steam piping system.
During power operation, the condensate /feedwater is converted to steam in the steam generators which then drives the circulator steam turbine via the reheat steam piping system.
r y Page 31 of 35 The chemistry of the condensate /feedwater during plant shutdown has generally been of good quality and therefore is not considered as the caustic contamination source for the recent hardware failures in C-2101. The sodium contained in the condensate is not harmful to- the equipment and components because the condensate is in the water phase and the sodium levels are not high enough to deposit onto metal surfaces.
The chemistry of the auxiliary boiler's steam during powering up or down modes and shutdowns has not always been of good quality. For a period of 18-20 months, from December 1983 through July 1985, the boilers were being treated with a phosphate treatment program which consisted of the injection of sodium compounds directly into the boilers. During some routine maintenance on the auxiliary boilers' steam header, deposits of sodium compounds were found near a valve and subsequent analysis samples of the auxiliary boiler steam indicated 79-820 ppb sodium. The boiler systems were not systematically cleaned out after finding the deposits and consequently the sodium continued to contaminate the auxiliary boiler steam whenever that steam was required.
The chemistry of the condensate /feedwater converted to steam during power operation has generally been of good quality. Sodium levels have seldom exceeded the allowable limit of 20 ppb specified in FSV procedures. However, based on a review of EPRI guidelines and literature on SCC, these allowables are considered to be too permissive.
9.2 Present Water Chemistry Procedure Requirements The controlling procedure for the chemistry of the condensate /feedwater during plant shutdown (PSC Procedure WCP-302) specifies a limit of 1000 ppb for sodium when the demineralizers are bypassed and 20 ppb when they are in service. These limits are in keeping with EPRI guidelines and the additional limit of 20 ppb is more restrictive than EPRI. Sodium levels of 1000 ppb in the condensate itself are not harmful to circulator components when utilized as a pelton wheel drive source.
The controlling procedure for the chemistry of the auxiliary boilers' steam during plant shutdowns and powering up or down modes (PSC Procedure WCP-311) does not specify a limit for the sodium. This is because the condensate /feedwater procedure mentioned previously specifies the allowable sodium levels as the plant rises or comes down from power operation, and this is the originating source for the auxiliary boiler.
Page 72 of 35 The controlling procedure for the chemistry of the condensate /feedwater during power operation is the same procedure as during plant shutdown. It specifies a limit of 20 ppb for sodium and this limit is less restrictive than EPRI guidelines.
9.3 Proposed Water Chemistry Procedure Changes The allowable sodium limits do not need to be changed for the condensate /feedwater during plant shutdowns. These limits are considered reasonable since sodium levels of 1000 ppb in the condensate cannot cause SCC of helium circulator -components at the temperatures present during plant shutdown. However, since there is the potential for sodium buildup on components due to the wetting and drying effects of the pelton wheel's operation during shutdown periods, the 20 ppb limit will be maintained as specified in WCP-302.
Since the procedure for the auxiliary boiler steam did not require the sampling and analyzing of that steam, this procedure will be changed. Even though the quality of the boiler feedwater is controlled by the condensate /feedwater procedure, it is important to keep a tighter control on the boiler steam since it has been the major source of caustic contamination. A modification design package u currently being developed which will install an auxiliary circulator boiler steam sampling system during the Spring, 1988 circulator bolt replacement outage. The procedure will be changed to require sampling of auxiliary boiler steam when it is being used for plant start-up or shutdown, or when the circulators are being driven by it.
If the sodium exceeds 3 ppb, Procedure WCP-311 will require cleaning up the auxiliary boiler systems. This procedure change will take place immediately and in the interim will utilize a temporary station for sampling.
The allowable sodium limits for the condensate /feedwater during power operation (above 30% reactor power) will be changed in Procedure WCP-302 to require a maximum of 3 ppb at the outlet of the demineralizers.
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O.4' Water Chemistry / Treatment' Overview Fort; St. Vrain instituted some new . water chemistry procedures in 1985 and 1986 which have made some
' beneficial differences in the quality _of the condensate' and steam. It is considered that these new procedures plus the changes mentioned above will ensure the integrity of plant components and reduce the potential for_ SCC. One of the contributing factors to.the recent bolting failures of circulator C-2101 was caustic initiated SCC attributed-to the poor water chemistry prior to 1985. Specifically, the sodium compound treatment of the auxiliary boilers produced high levels of caustics in-the auxiliary boiler steam. The plant will_ not use this treatment program again .so this will decrease' the chances for SCC.
10.0 SECONDARY COOLANT SYSTEM' MATERIAL EFFECTS REVIEW Due to the. presence of the caustics identified in the water chemistry review, it is necessary to review the secondary _
coolant system for the effects of the caustics throughout~the system.- This review will be a long term project which will determine components .that could have been affected by caustics and an inspection / evaluation program during routine maintenance for replacement of suspect parts as may be required.
-11.0 REFURBISHMENT PLAN AND SCHEDULE The failure of circulator C-2101 mandated that several parts undergo a design change. The most significant of these changes is the material change of bolting and fasteners. The failure also required that several repairs be initiated and replacement-parts be ordered. A circulator and inlet piping repair schedule is shown in Figure 3.
11.1 Inlet Pipe S/N ?001 Repair The repair of the inlet piping assembly is progressing on schedule. There have been only minor setbacks with little
, impact to the schedule. It is to arrive at Fort St. Vrain on February 3,1988.
11.2 C-2101 Repair j
! In the repair of C-2101 two significant setbacks have been encountered. The steam ducting weldment was identified as i
being cracked. This repair, if successful, will be i
completed by the end of February, 1988. If the weld repair is not successful, a new steam scroll will be required. This would delay the completion of the total i C-2101 repair until the end of 1988.
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Page 34'of 35 The compressor rotor was contaminated with little chance of success in decontaminating it to the background level required for vendor high speed spinning, Que to:the contamination difficulties the spinning was not completed until late December, . which impacted the end date of the schedule. This pushed the C-2101 repair completion to approximately mid-April, 1988, 11.3 Parts Schedule All parts required for the Spring,1988 circulator outage have been ordered. Although all the delivery dates have not been established, it is expected that the parts will be received to support the above schedule, I
AUG 87 , SEPT 87 , OCT 87 , NOV 87 ,
DEC 87 ,
JAN 88 ,
FEB 88 , IAAR 88 ,
APR 88 ,
CIRC DISASSY & EVALUA TiOf4 REFURBISit PARIS & SUBASSYS ,
RE-ASSY BEARING CARTR RE-ASSY CIRC a
i I
TEST l
STEAM SCROLL T O O Lif4G & Ir tSPECTIOtt i SillP I C 1 RECEIVE WELD REPARS I AT FSV i a l
FINISil MACH!tJE l INNER pipit 1G I DISASSY REPAIR & REASSY 2
o SillP
- a RECEIVE M AT FSV o a %
FIGURE 3 '
FORT ST. VRAIN CIRCULATOR C2101 & INNER PIPING 2001 REPAIR SCHEDULE
ATTACHMENTS Number Description 1 Metallurgical Analysis of Components From Helium Circulator C-2101 2 Helium Circulator Inspection Schedule
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