ST-HL-AE-2653, Forwards Evaluation of Microbiologically Influenced Corrosion in Jacket Water of Cooling Sys of Unit 2 Standby Diesel Generators & Failure Analysis of Diesel Cylinder Liner Expansion Bellows. Unit 1 Shows No Corrosion
| ML20154C592 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/11/1988 |
| From: | Mcburnett M HOUSTON LIGHTING & POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| Shared Package | |
| ML20154C596 | List: |
| References | |
| ST-HL-AE-2653, NUDOCS 8805180237 | |
| Download: ML20154C592 (30) | |
Text
{{#Wiki_filter:l The Light ! PO. Ihn 1700 llouston. Tem 77001 (713) 228 9211 Ilouston 1.ightingk Power I May 11, 1988 ST HL- AE 2653 File No.: M10.05.02.02 I U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Units 1 and 2 Docket Nos. STN 50 498 and 499 Microbiological Influenced Corrosion in Unit 2 Standby Diesel Generator Jacket Water Cooline System This letter documents discussions between the NRC (E. Tomlinson) and lilAP (J. Bailey) concerning the discovery of Microbiologically Influenced Corrosion (MIC) in the jacket water cooling systems (JVCS) of the Unit 2 standby diesel l generators. In Unit 2, corroded conditions aere found in the JWCS during initial startup of the diesels. This piping was replaced as necessary, acid flushed and treated to prevent further corrosion. Expansion seals, which are used as a secondary seal to prevent JWCS fluid from entering the diesel lube oil surp, were later found to be damaged. Other damaged seals, identified using a pressure test, are in the process of being replaced. An evaluation was performed (attached) which considered the storage I history, material conditions, and system leakage detection capability. The l evaluation also includes an analytical review of damaged expansion seals which vere removed from the diesels. In summary, the evaluation concluded that the presence of MIC was a result of the storage conditions of the Unit 2 diesels. With replacement of l the identified leaking expansion seals in Unit 2, the existing seals, as well as the replacement seals, will serve their intended function. Further failures if experienced would be minor and would be detectable by normal surveillance tests in advance of diesel engine performance impact. l l l L2/NRC01/C \\ j
.\ Subsidiaiy of Ilouston Industries inwrporated 8805180237 880511 ,
PDR ADOCK 05000498 l P DCD _ _ . _ - _ _ _ _ _ i
llouvon 1.ighting & Power Company .i j ST HL AE 2653 ] Page 2 In Unit 1, although identical storage records exist, no signs of excessive corrosion as seen on Unit 2 have been observed. Inspections conducted to date have identified no failures. Analytically, it has been shown that expansion seal failures are unlikely even if MIC is present. Therefore, no further actions are planned for the Unit 1 diesel generators. ' If there are any questions, please contact Mr. J. N. Bailey (512) .' 972-8663. fM. A. McBurnett441 C lN Manager Operations Support Licensing MAM/JNB:dje i
Attachment:
Evaluation of Unit 2 Diesel Generator MIC l i l l l l 9 t i I L2/NRc01/G
ST HL AE 2653 File No.:M10.05.02.02 Page 3 cc: Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 1700 Houston, TX 77001 N. Prasad Kadambi, Project Manager U.S. Nuclear Regulatory Commission INPO 1 White Flint North Records Center 11555 Rockville Pike 1100 circle 75 Parkvay Rockville, MD 20859 Atlanta, CA 30339 3064 Dan R. Carpenter Dr. Joseph M. Hendrie Senior Resident Inspector / Operations 50 Bellport Lane c/o U.S. Nuclear Regulatory Bellport, NY 11713 Commission P. O. Box 910 Bay City, TX 77414 Don L. Carrison Resident Inspector / Construction [ c/o U. S. Nuclear Regulatory Commission P. O. Box 910 l l Bay City, TX 77414 l J. R. Nesuan, Esquire Newman & Holtzinger, P.C. s i g on Db 5 b36 l
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R. L. Range /R. P. Verret Central Power & Light Company 1 P. O. Box 2121 i Corpus Christi, TX 78403
- R. John Miner (2 copies)
Chief Operating Officer City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 R. J. Costello/M. T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296 Revised 03/18/88 L2/NRC/bb. i l l
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ST HL AE. 2653 Attachment Evaluation of Unit 2 Diesel Cencrator MIC L2/NRC01/G
I l Page 1 { STATEMENT OF CONDITIONS ON UNIT 2 f During prerequisite testing of ESF Diesel Generator No. 21, leaks were [ discovered in cylinder liner expansion seals on cylinders 10R, 5R, 2L, [ 3L and 4L. The expansion seal on 10R had a 1/4" hole and the ! expansion seals on SR, 2L 3L and 4L had pin holes. ! L l These seals are designed to allow the cylinder liners to expand and i contract while acting as the jacket water pressure boundary secondary seal between the cylinder liners and cylinder block. The primary seal is the metal to metal contact of the liner to the engine block. The exterior of the liner is plated with tin prior to being installed to j assure a tight "forced" fit. Some leakage may occur into the i expansion seal area especially during the standby mode, i The expansion seals on cylinders _10R and 10L were removed and shipped ; to the Bechtel Material Laboratory for analysis. Both seals exhibited ; evidence of Microbiological 1y Influenced Corrosion (MIC) and ; transgranular stress corrosion cracking. See attached report and j photographs in Appendix 3. "Failure Analysis of Diesel Cylinder Liner i Expansion Bellows." I t A pressure test at 35 psig was performed on the expansion seals to ! identify any other deficiences. The pressure test on Diesel No. 21 [ seal bellows identified deficiences to seal bellows on cylinders 1R j and 8R Diesel No. 21 had a total of seven (7) deficient seals. l Installation of new seals was completed by April 29, 1988 for all cylinders. The pressure test on Diesel No. 23 expansion seals revealed that cylinder 3L had a pin hole in the expandable metal portion of the seal and that 4L had seepage from the veld area close to the seal upper flange. Both seals have been replaced. No leaks were found on Diesel No. 22. STORAGE HISTORY All six diesel generators were fabricated in 1979. Prior to storage the cooling systems were flushed with a mixture of 504 glycol, 454 water, and 5n rust inhibitor. Five were stored outside, on rail cars, at the factory in Pennsylvania. Engine No. 7196 was stored elsewhere following testieg, in an environmentally controlled warehouse and shipped directly to site. The standby diesel generators installed in Unit 1 were shipped to the site over the period November 1981 through August 1983. See Appendix
- 1. "Standby Diesel Generators Storage and Shipment History." These engines were the last three manufactured, s/VGWb
l l Page 2 While at the site, prior to installation in the DGB, the Unit 1 diesels were stored i accordance with ANSI N45.2.2, Level B storage (in an enclosed area sith dry warm air) until installation in the Diesel Generator Building (DGB) in early 1984. In 1983, the three Unit 2 diesels were inspected at the factory and were found to show evidence of external rusting and other deterioration. Consequently they were refurbished at the factory to correct any problems created due to the extended storage period. After refurbishment, the cooling systems were flushed with a mixture of 50% glycol, 45% water and 5% rust inhibitor and drained. The Unit 2 diesels were shipped to the site in 1984 and installed in Unit 2 in April of 1986. While at the site, prior to installation in the DGB, thase diesels were also stored in accordance with ANSI N45.2.2, Level B Storage requirements. MATERIAL CONDITIONS The Unit 1 diesels were prepared for operation in the Summer of 1986. At that time, rust colored water was found in the jacket water coolant system, but the system exhibited no signs of deleterious corrosion. A velocity flush using water was used to c' -n the lines and the system. The Unit 1 jacket water systems were filled and inspected prior to starting the diesels with no evidence of leakage at the expansion seals found. While preparing the Unit 2 diesels for testing, their jacket water systems were found to contain severe corrosion damage. While a velocity flush was sufficient to remove the minimal rusting found in the Unit 1 cooling systems, Unit 2 required replacement of piping and an acid flush, prior to release for testing. On the Unit 2 expansion seals leakage was noted at the first filling of the jacket water system after the acid flush was completed. STORAGE & HATERIAL CONDITION CONCLUSION Although HL&P has been unable to determine the factor resulting in the difference, the Unit 2 diesels (but not the Unit 1 diesels) required corrective action due to corrosion both at the factory and here on site. Two of the Unit 2 engines required an acid flush at the factory i prior to shipment. All three required replacement of jacket water i piping and acid cleaning of the jacket water system on site. A review of Cooper-Bessemer data has not revealed any differences to account for the additional corrosion problems, s/WGW/b
Page 3 MIC CONTROL MIC control is an ongoing site prgrant. Various procedures are in use which have been proven to be eftective in MIC control. Due to the evidence of MIC presence, the Unit 2 jacket water systems, including the expansion seals, have been sterilized with hydrogen peroxide to kill any existing bacteria. All flush water used during startup cetivities has been treated to prevent MIC recontamination of the system. During operations, Low Halogen Nitrite-Borate-Tolytriazole is added to the jacket water coolant of both units to prevent general corrosion. The high PH of this fluid, >10, will prevent growth of MIC. The nitrite in the corrosion inhibitor will reduce the tendency for stress corrosion cracking by reducing the oxygen content and creating nitrate, The deaeration mechanism is nitrite reacting with oxygen to form nitrate. The nitrate formed is also an inhibitor of stress corrosion cracking. MEANS OF DETECTING LEAKAGE VISUAL TESTS: The Unit 1 expansion seals have been inspected, along with the rest of the diesel components, during the testing phase. This includes the l velocity flush of the jacket water r,ystem, start and stop tests of the { engine, and a 100 hour run performed on each diesel. No leakage has been noted during any of these inspections, l j In comparison, leakage was identified in two of the Unit 2 expansion seals during the initial fill operations. OIL ANALYSIS: The diesels are test run periodically, at a minimum of once a month. Lube oil samples are taken during the monthly test run. The lube oil l pump provides sufficient mixing of the oil to entrain any water l contamination with a complete volume change approximately every 3 1/2 minutes. The minimum detectable concentration in the sample, as analyzed, is 0.05% water in the oil, corresponding to a tot:a1 water volume of approxi'mately 1.05 galns. No evidence of water contamination of the oil has bs.a found in the Unit 1 machines. j I 1 s/VGW/b
I Page 4 I Should le.4kage of the cooling system fluid into the oil reservoir l occur, the monthly sample of the lube oil system provides a positive method of identifying that fact. With the detectable concentration of 0.05% and per Cooper-Bessemer, an allowable contamination of 1% (21 gallons) water in the oil, sufficient tolerance exists to recognize 1e:kage prior to impacting the operability of the diesel units. The absence of water it %e Unit 1 oil samples indicates that there is no leakage of water ints the crank case. Therefore, there has been no through wall damage due to MIC in the Unit 1 diesel expansion bellows. SUMP INDICATORS: Seal bellows leakage is one of several leakage paths for cooling water to the lube oil. The following is a tabulation of lube oil capacities and set points. Lube Oil Sump and System capacity - 2,100 Gal. Operating Level of Sump - 1,300 Gal. Remainder of System 011 - 800 Gal.
- 1. Capacity Per Inch Basis:
(a) High 011 Level Alarm - 65.2 Gal /In. of Depth (b) Normal Oper. Level - 66.1 Gal /In. of Depth (c) Low 011 Level Alarm - 67.3 Gal /In. of Depth
- 2. Distance From the Crankshaft to Alarm Settings:
(a) High oil Level Alarm - 22 5/8" (b) Normal Oil Level - 24 5/8" (c) Low 011 Level Alarm - 26 5/8"
- 3. Difference In Liquid Level By Gallons To Trip / Alarm:
(a) High Level - Average of 65.65 Gal. x 2 - 131.3 Gal. Addition (b) Low Level - Average of 66.70 Gal. x 2 - 133.4 Gal. Loss As shown above, the lubricating oil sump level alarms will provide only indications of gross fluid additions or losses from the sump. JACKET WATER COOLING SYSTEM STANDPIPE INDICATIONS: The jacket water cooling system level is measured on a standpipe. A discussion of the operating and standby modes is provided below, s/WGW/b
1 l l l Page 5 l The normal evaporation rate of the jacket water coolant, during the running condition of 170 F, is approximately 0.3 gph or 0.426 in/hr in the sight glass. During the coolant temperature rise of 50 F, from 120 F (standby temperature) to 170 F (operating temperature), the water level in the standpipe will rise 6.75" due to thermal growth. Because of this level increase, a low level alarm would not occur until 27 gallons of inventory has been lost during engine operation. The design of the interference fit between the cylinder liner and the engine block is such that little, if any, leakage would occur in the operating mode. In the standby mode a coolant loss of approximately 15 gallons would cause a local alarm (JACKET WATER STANDPIPE OFF NORMAL) and a remote alarm (ESF DIESEL GENERATOR TROUBLE) to sound in the Control Room. These alarms provide adequate leak detection while in the standby mode. CONCLUSIONS REGARDING LEAK DETECTION MIC has not been observed in the Unit i diesels during testing. Additionally, lube oil samples to date have shown no trend to indicate increasing leakage. Adequate systems exist, i.e. the lube oil sump level and jacket water cooling standpipe level, to alarm a catastrophic introduction of water into the crankcase or a significant loss of jacket water cooling system fluid. Therefore, continued operation of the Unit 1 diesels is justified. i l l ANALYTICAL REVIEW Two expansion seals were removed from the Unit 2, Diesel No. 21 and , sent for evaluation. One of the seals had already been observed to ' leak. The other was removed from the opposice side of the engine but was not leaking. (It was removed because of the accessibility due to the removal of the leaking seal on the opposite side). A combination of MIC pitting and corrosion cracking was observed in the leaking seal j while the other seal had evidence of the bacteria but no pitting or cracking. The acceptability of the remaining expansion seals was evaluated on the basis of design parameters provided by the diesel supplier and expansion seal manufacturer, and observations taken from the seals discussed above. The analytical review performed using fracture mechanics has shown that:
- 1. The majority of "partially through wall" cracks, if they exist in the expansion seals are categorized as non-propagating and will not grow over the life of the diesels.
l l l s/WGW/b ! l
Page 6
- 2. For any "partially through-wall" cracks that border on being through-wall, a leak may develop, but will be small and will not undergo any noticeable growth over the life of the diesels. Any undetected through-wall cracks will react the same and will not undergo any noticeable growth over the life of the diesels.
- 3. Corrosion pits, although not specifically analyzed, are bounded by the crack analysis. Consequently it can be concluded that pits will not develop into fatigue cracks during service.
A copy of the analysis is included in Appendix 2, "Effects of Corrosion Pits and Cracks on Bellows Seal Performance." OVERALL CONCLUSIONS UNIT 2
-The failure of the expansion seals due to MIC was a result of the same factors that tesulted in the poor condition of the Unit 2 jacket water cooling system components. The replacement of the deficient piping and expansion seals in conjunction with the acid cleaning and MIC Control processes have adequately resolved the corrosion effects.
The replacement of the leaking expansion seals will be performed before the unit becomes operational. The pressure test that was , performed provides assurance that no grossly MIC affected areas remain in the Unit 2 diesels. Analytically, it is not expected that there will be any further growth of already initiated pitting. If there is a failure, it will be of a very small size, thus allowing the oil sample program to trend any failures in the seals. Since the jacket water is appropriately treated, MIC and stress corrosion cracking are arrested and will have no further degrading effects on the seals. No further action will therefore be required on the Unit 2 diesel generators. UNIT 1 Based on the improved material condition of the Unit 1 engines and the favorable inspections, it is unlikely that MIC has occurred on the Unit 1 diesel generators. The stress and material analysis done for Unit 2 has shown that even if MIC has occurred, it is unlikely that new leaks will develop. If they do, they will be small and growth will be limited. If any leah.ge occurs, it will be detectable in oil samples in advance of a level damaging to the machine. Therefore, HL&P considers the condition of Unit 1 to be satisfactory with no further augmented inspection or pressure tests needed, s/WGW/b
I ST-HL-AE-Appendix 1 Standy Diesel Cencrators Storage and Shipament Illstory l I 1 l i l I l l l L2/NRC01/G
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i APPENDIX 1 STANDBY DIESEL CENERATORS STORAGE AND SIIIPMENT IIISTORY Unit Motor Date Factory Date To Date Date On Site No. TPNS Sr. No. Fab. Refurb. Site Rec'd Installed J. W. Flush i 1 3Q151MDC0134 7195 10/79 NA 8/83 9/83 4/84 7/86 - 1/87 l l 1 3Q151MDC0234 7196 11/79 NA 11/81 12/81 2/84 6/86 - 3/87 l i 1 3Q151MDG0334 7197 12/79 NA 3/82 4/82 3/84 8/86 - 11/86 l l 2 3Q152MDC0134 7192 3/79 7/83 4/84 5/84 4/86 Pending 2 3Q152liDC0234 7193 4/79 9/83 5/84 5/84 4/86 12/87 2 3Q152MDG0334 7194 5/79 8/83 10/84 11/84 4/86 1/88 - 2/88 Storage of diesel engines prior to shipment to site as follows: Motor serial number 7192 stored at point of fabrication. Motor serial number 7193 stored at point of fabrication. Motor serial number 7194 stored at point of fabrication. Motor serial number 7195 stored at point of fabrication. Motor serial number 7196 shipped to New York for testing and storage. Motor serial number 7197 stored at point of fabrication. Storage at point of fabrication outdoors on rail carc. When received onsite, each diesel was stored in an enclosure in accordance with ANSI N45.2.2 Level B Storage requirements,(warm dry air) until they were installed-in the buildings. s/WGW/b 1
ST HL- AE- 2653 Appendix 2 Effects of Corrosion Pits and Cracks on Eclimrs Seal Performance 1 l 1 i I l l i L2/NRC01/G
APR 05 '88 11:28 m m er 3s 10:27 se:mn. sr 2 uts. re-303e ;,2 Bechtel National, Inc. Ergireers-Constructors F f ty 9eale Street San Frarcisco.Cahfornia usumens 9 0 sca sess saa8ve's:: cA S4 49 To: 57r File. A/o M /o.o f. 0 1 . o A R. L. Randels File No. YC-048-01
Subject:
Ef fects of Corrosion Pics Date: April 4, 1988 and Cracks on Bellows Seal Performance From: Y. Chung Bechtel Job 14926-001, STP PAC 01C Of: R&D/ Materials & Quality Services Copies: R. A. Manley/F. C. Breismeister At: 50/15/35 Ext. 8-1489 T. T. Phillips R. W. Straiton R. A. White DCC 0241177
Reference:
Le tter from Y. Chung to R. L. Randels, March 1,1988 (SLN 8802-04) The letter referenced above transmitted a laboratory report, "Failure Analysis of Diesel Cylinder Liner Expansion Bellows." These bellows are used as expension seals in emergency diesel generators. The report contains the results of examination of two 16-inch Type 321 stainless steel bellows by Bechtel's M&QS. corrosion and stress corrosion cracking, which influenced wasIt concluded that the be11ews by iron bacteria ( Ga llionell a) . influenced corrosion). Bis is cocmonly referred to as MIC (microbiologically Figure 1 shows a sectional view of the bellows seal (item 10), which is secured to both the cylinder block and the liner by flanges. Cne of the two bellows exa: innd by M&QS is shown in Figure 2. n e design data (by Flexonics) for these bellows are presented in Appendix A. Basically, it is a single ply-single-expansion bellows with three convolutions. is 0.02 inch. Most of its life is spent as standby, We nominal vall thickness during which the bellows are pressurized with 120*F water to 10 psig. During operation, the pressure and temperature rise to 20 psig ud 170'F, respectively. One of the two bellows examined revealed corrosion pits and cracks, creating one hole about 1/2 inch in and netr the longitudinal diameter seam weld. and another about 1/4 inch in diameter, in report. See Figure 5(a) of the failure analysis s=all, 1/16 inch or less in the convolution.cracks and pits in other areas were Except for this failure area, most creci shich straddled a through-usil corrosion pit.One exception See Figure was 7(s)a of1/4-inch the long fallare analysis report. nies (' n d
MM'NTD
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PUO '- W Of 'E5 10:29 EE}TEL if 3 NIS , 7654038 p,3 R. 1.. Randels From: Y. Chung Page 2 April 4, Subiect: Effects of Corrosion Pits and 1988 Cracks on Bellows Seal performance
. Bechtel Job 14926-001 We bellows seals in the diesel engine generators were hydrotested at 35 psig subsequent to the discovery of the above bellows failure. Several leaked in Train A, 2 in Train C, none in Train B. It is possible that some of the bellows seals that passed the hydrocest may contain corrosion pits and cracks because of MIC.
Some of these pits and cracks may have penetrated the bellows wall by 50 percent or more, yet without leading to a hydrotest failure. This is because pressure boundaries with local wall thicknesses below the design minimum, for example, at the bottom of a small corrosion pit or at the tip of a small crack, can still withstand the design or test pressure. Unless a vall thinning occurs generally in a large area (e.g., 1/2 inch in diameter, or more in this case), the wall will not rupture during a hydrotest. For example, it has been shown that small pits or cracks with depthe more than 80 percent through the wall will not leak or rupture during hydrostatic tests.(1) It may be hypothesized, therefore, that the corrosion pits or cracks which have not caused leaks during a hydrotest can still cause leaks during service if they grow due to corrosion or metal fatigue. We have been asked to evaluate the effects bellows of corrosion pits and cracks, should they exist in some of the seals. We will consider potential bellows seal failures from two aspects: (1) metal fatigue, and (2) MIC. (1) Bellows Failure Due to Metal Fatigue Fatigue cracks occur in metal components when they are subjected to cyclic stresses (or strains). We peak stress values are much less than the tensile strength of the material in a high cycle fatigue. The bellows seal would experinnee a small number of relatively large stress amplitudes because of startuos and vibration shutdowns during and a large number of low stress amplitudes due to operation. i Figure 3 illustrates schematically the type of stress cycles that a bellows may experience. Figure 3(a) is a case where the bellows was extended by a small amount during installation in the cylinder block; the bellows can be compressed during installation. Figure 3(b) shows idealir.ed fatigue cycles and the definitions of stress tems. In fatigue, it is the stress range (6c = O of cycles which governs the material life. max ' Omin) and associated number he stress range would be the same regardless whether the bellows are extended or compressed during installation. In the bellows elements, fatigue cracks will occur, if at all, in the circumferential direction, along the convolution, rather than in the axial dire: tion. his is because, as shown in Appendix A, the stresses in the circumferential direction are much lower than those in the meridional (axial) direction. We stress ranges due to startups and shutdowns predominate over those due to vibration. (1) Machine Design, April 6, 1978, pp. 192-105. (A 2-inch CD tube with a 2.2 inch long x 0.012 inch wide slot, penetrating 83.2% of a 0.316 inch thick wall, passed a 6800 psi test.) 104 N bd
HFN Ub Od 11 61 PO4 W 05 'is 10:20 EECHTEL 5F 3 N151 MS-9039 # R. L. Randels From: Y. Chung Page 3 April 4, 1988
Subject:
Effects of Corrosion Pits and . Cracks on Bellows Seal Performance Bechtel Job 14926-001 We process of fatigue cracking consists of three stages: ' e crack initiation o crack propagation e final fracture (or perforation of the wall in the case of bellows) Bese separate stages cannot be accounted for by the classical fatigue analysis of metal components using the traditional S-N curves and Goodman diagrams. Wis approach relies primarily on statistical failure date of laboratory test l specittens for fatigue life prediction. Since the correlation between the specimen data and the perforcance of actual componente is poor, the S-N eurve approach has not worked well in fatigue life prediction. It has been userul, however, in providing conservative estimates of the so-called fatigue strength of a material for design purposes so that fatigue failures can be avoided altogether. In recent years, significant progress has been made in developing a more 'l accurate analytical tool for predicting a fatiguo life. Much of this work has been based on fracture mechanics. Unlike the traditional method, fracture mechanics accounts for the three stages of fatigue mentioned above (albeit i incompletely as yet in some aspects). It allows for existing flaws (e.g., pits or cracks) to be evaluated quantitatively by calculating crack growth rates for given stress cycles. A basic premise of fracture mechanics is that a single parameter K (stress intensity factor) can describe the stress distribution at the crack tip. Two important aspects of fatigue cracking in fracture mechanics have been recognized, as follows. A threshold stress intensity factor range (AKthreshold) exists below which a crack is nonpropagating regardless of the number of acres 2 cycles imposed. This is conservatively satimated at AK = 3 ksi/in for austenitic stainless steels. e The rate of f atigue crack growth da/dN can be expressed in tems of a stress intensity factor range 4K. %is is commcaly expressed, in simplified terms, as follows. da/dN = C(AK)n, where C and n are teaterial constants Figure 4(a) is a schematic relationship between da/dN and 6K and Figure 4(b) a data plot of fatigue cracking for A333 steel at ambient temperature, shown here as an illustration. In general, in Region B, the crack growth follows a l power-law behavior. h e ASME Section XI Task Group for Piping Plsw !. valuation l recorwends the following equation austeniticstainlesssteelpiping.{o2 fatigue crack evaluation This equation of flaws in will give conservative (high) estimates of fatigue crack growth rate as the code requirements are conservative. (2) Journal of Pressure Vessel Technology, vol.108, August 1986, pp. 352-366. 1047m O?
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APR 05 '88 11:3'2 P05 i p.Fo 05 '5 3 10: 51 EECHTEL 'EF 3 ( 415 ) M3-9033 R. L. Randels From: Page 4 Y. Chung April 4, 1988
Subject:
Effects of Corrosion Pits and Cracks on Bellows Seal Performance Bechtel Job 14926-001 da/dN = C E S (6 K)n where de/dN = C, n = change in crack depth, a, per fatigue cycle, in/ cycle material constant, n = 3.3, C = 2 X 10"19
=
(in/ cycle)/(psi /Tii)" S R ratio correction factor = (1.0 - 0.5R2 )-4 R = K min i
/Emax E =
environmental factor (equal to 1.0, 2.0, and 10.0 for AK = air, P'at, and BWR environments, respectively) Kmax -Emins (psi /IIi),and
)
Kmin Kmax= minimum and maximum values, respectively, of '{ applied stress intensity facetor , { The stress intensity factor K is related to stress c or the stress Intensity factor range LK to stress range Ac, as follows. ax = Acr ia F(a/t, a/c , b/c , ?) where F = shape factor t, b, e, ? = see Figure 5, a surface crack in a finite plate a = crack depth (or one-half the crack length in a through-wall crack) It can be seen enat the shape factor F is influenced by many factors. Numerical values for F are readily available in the literature for e/t up to about 50 percent; for example, graphically from Figures A-3300-1, A-3300-3, and A3300-5 in ASME Code Section XI. When a crack penetrates the wall by more than 50 percent, however, the shape facter is influenced greatly by the behavior of the remaining ligament, which may behave in a nonlinear manner. Therefore, it is difficultthrough breaking to definethe4K at the tip of a crack which may be on the verge of wall. In ductile and tough materials like the bellows material (Type 321 SS), K is higher at
? = 90 degrees (Figure 5) than at other angles, nus, the aspect ratio (depth / length) of a crack tends to be high as compared with the cracks in less ductile and tough materials like carbon steel, nis means that fatigue cracks in bellows seal would tend to be short (say, less than 0.1 inch in length) when they just break through the wall, leading to leak. (This does not apply to stress corrosion cracks.) Therefore, even if fatigue cracks develop at the bottom of a pit or at the bottom of a small stress corrosion crack due to stress cycles from startups and shutdowns, it will be a short crack which may "weep. " No massive leaks are possible. Furthermore, it is unlikely tha t 1047m f,
- APiG 5 '88 11i33 P06 A:R 05
- ES 10: 32 EECHTEL 'iT 3 ( 115) 765-9033 P.s R. L. Randels From:
Page 5 Y. Chung April 4, 1988
Subject:
Effects of Corrosion Pits and Cracks on Bellows Seal Performance Bechtel Job 14926-001 any of the presumed corrosion pits or stress corrosion cracks not detected by hydrotests will ever develop into fatigue cracks. W ie is because the followirs fracture mechanics calculations indicate that AK is either below 4K threshold or the crack growth rates are so low as to be negligible. Table 1 shows a summary of AK and da/dN calculations for assumed cracks of different sizes. Sample calculations of LK and da/dN are presented in Appendix B. According to these results, 6K for cracks with a depth less than 50 percentare operation of well the wall belowchickness 4X for stress rantes between standby and chreshold (about 3 kei/ E). D erefore, surface cracks even 1/2 inch or more in lenach with a depth less than 50 percent of the wall thickness will not grow no matter what the number of stress cycle is. Because of the difficulty in calculating 6K for the cracks with a depth more than 50 percent of the wall thickness, we calculated AK and da/dN for through-wall cracks for comparison pur thrcugh-wall crack is only 2.6 ksirG ; poses. thus, it6K willfornot a 1/8-inch long propagate. Even a 1/2 inch long through-vall crack will grow less than 1 microinch (10-6 inc h) per stress cycle or less than 1 mil in 1000 stress cycles.* It would seem reasonable to expect that 1/4-inch long crack with most of the wall thickness penetrated cycles. would have a crack growth rate lower than 1 mil in 1,000 stress middle) in the bellows seal that contained the mostEven with the longest the aboveare shutdowns calculations not indicate that the stress cycles due to startups andserious When compared with the stress ranges (5800 psi) due to startups a the stresses due to vibration are so low (3) that they may be ignored from fatigue consideration. corrosion pits are not as sharp as cracks. l As the above calculations show that ' even cracks will not grow due to fatigue, no corrosion pita in the bellows seal will develop fatigue cracks during service. (2) MIC Control The water peroxide asfor the bellows seal has been treated with a high dose of hydrogen biocide. Bis is complemented by adding triazole, sodium borate and sodium hydroxide. nitrite, and the water pH adjusted to 10 to 10.3 using sodium j effective in eradicating bacteria.ne high dose hydrogen peroxide treatment has been erevices, MIC becomes inactive in high pH environments.Even if they Werefore, survive under som recurrence of MIC in the bellows during standby and operation is not expected. j
*The month. e nergency diesel generators may be started up and shut down once a Au s , 1000 stress cycles is cont.ervative for a 40 year life.
(3) %e R. vibrational stresses are estimated to be 100 psi (Telecon between Randels of Bechtel and R. Miklos of Cooper, 3/28/88). ~ 104 7m f. e f.
T4PR 05 '88 11::$4 P07 AFF 05 'E 5 10: 33 EECHTEL F 3 i 41? ! N.54039 P. R. L. Randels From: Page 6 Y. Chung April 4, 1988 Sub}ect: Effects of Corrosion Pits and Cracks on Bellows Seal Performance
. Bechtel Job 14926-001 There is an tendency of extensive austenitic amount stainless of literature reporting that high pH reduces the For example, Theus and Staehle(4) steels to chloride stress corrosion crack. l 200'0 as the pit increases from 1 to 13.show an increage in time to failure at !
data. Sedriks(5) gives the most definitive Figure 6 (attached) shows the effect of pH, chloride ion content and temper 4 tyre on both stress corrosion cracking and pitting. 11hlig and Revic,(61 in addition to mentioning the beneficial ef fects of alkalinity , ! also statereduces nitrates, that eliminating st oxygen and addition of certain inhibitors, e.g. , ! Theus and Staehle(4)ress corrosion cracking of austenitic stainless steela. i also show the beneficial effects of reducing oxygen. Since effects. nitrite is added as an oxygen scavenger, it will have two beneficial First, reducing the oxygen content.it will reduce the tendency for stress corrosion cracking by f mechanism is nitrite reacting with oxygen to form nitrate.Second, it will create nitrat 1 is also an inhibitor of stress corrosion cracking.(7) The nitrate formed Conclusions 1) Fracture mechanics calculations on fatigue crack growth in stainless steel I bellows seals indicate that leaks due to fatigue cracking from existing I corrosion pits or cracks are unlikely. Most of the cracks (if they exist) that passed grow to cause aa hydrotest leak). will be dormant during service (i.e., they will not It is possible, however, leaks may develop from crecks or pits which just barely made the test. Any leaks from these flaws will be small.
- 2) It is possible to control the MIC which caused the bellows seal failure.
Recurrence of MIC leading to leaks is unlikely in high pH water environments in which the bellows are subjected to during standby and operation, p-% G .. YC:gf Chung (4) G. J. Theus and R. W. Staehle, Review of Stress Corrosion Cracking and Hydrogen Embrittlement in the Austenitic Fe-Cr-N Alloyw, Stress Corrosion Cracking and Hydrogen Embrittlement of Iron Base Alloys, NACE (1977). t ($) A. i J. Sedriks, Corrosion of Stainless Steels, John Wiley & Sons (1979). (6) H. 3. Uhlig and R. W. Revic, Corrosion and Corrosion control, third edition, John Wiley & Sons (1985). 1 (7) H. Hirano, et al., The Effect of Dissolved Oxygen and NO 3 Anions on the Stress Corrosion Cracking of Type 304 Stainless Steel in Water at 290*C, Corrosion (1983), 313. l 1047m (a5 )
hPR TJFT8 IT3b pud Acc .:5 'is 10: 24 EE:HTE'_ EF 3 (415> N 5-9028 3 TABLE 1 A Sue: mary of Stress Intensity Factor Range 4K and Crack Crowth Raten da/dN Calculations for Assumed Cracks Crack Size Stress Intensity Factor Range Cra:k Length (E) Depth (a) Crack Growth 6K Rate
'l'v p e (inch) (inch) ksi5i (inch) '
Parti 111y 0.06 0.01 0.8 through- 0.125 0.01 1.0 Nonpropagating wall 0.25 0.01 1.3 i Through- 0.125 0.02 2.6 Nonpropagating vail 0.25 0.02 3.6 0.50 0.02 0.2 x 10-6 5.1 0.7 x 10- l 0.75 0.02 6.3 1.4~x 10~; 1.00 0.02 7.3 2.2 x 10- 6 l l 1047m CM
AFG 05 '58 10:35 EECHTEL ST 3 M1D 762-9028 F.9 l Appendix A Bellows Design Data and Stress Calculations
. I d - outside diameter of cylindrical tangent, 16.625 inch (from Flexonics) t - wall thickness 0.020 inch l
w = convolution height 0.675 inch (from Flexonics) n = number of plies l 1 ! q = bellows pitch P = internal pressure Ps = 10 psig (standby),0.50 inch (from Plexonics) Po 20 psig (operating) 1 dp = d + w, gean diameter of bellows, 17.30 inch i t p = t(d/d p) , thickness corrected for thinning 0.0196 inch ! q/2W = correction factor for Graphs Fig. C18,19 5 20 = 0.37 q/(2.2)(dptp)b "
= 0.39 Cp = factor from graph Fig. C18 (from Std of the EJMA) = 0.74 Cf =
Fig. C19 = 1.52 Cd
=
Fig. C20 = 1.53 Los = bellows meridional membrane stress range due to internal pressures
= APw/2ntp = (10)(0.675)/(2)(1)(0.0196) = 170 psi M.
, = bellows meridional bending stress range due to internal pressures
=
(AP/2n)(w/tp ) C p
=
(10/2)(0.675/0.0196) 2 (0.74) = 4390 psi aCs bellows meridional membrane stress range due to deflections (ae)
=
(Eb tpde)/ 2w'Cf Ebs modulus of elasticity for the bellows
= (27.9 x 10 ')(0.0196)"(9.4 x 10'*)/(2)(0.675) 3 (1.52) = 10 psi 6e = (2.250 - 2.156) x 10-r= 9.4 x 10 " (from Flexonics) ass = bellows meridional bending stress range due to deflections (6e) 2
=(SEbpt ae)/(3w Cd) 8
=(5)(27.9 x 10 )(0.0196)(9.4 x 10')/(3)(0.675)2(1.53) = 1230 psi M, = ici+ Ac = 170 + 10 = 180 psi (sum of membrane stress ranges) 3 Mb " 00. + 10s = 4390 + 1230 - 5620 psi (sum of bending stress ranges)
As compared with the above stress ranges, the stress range in the circumferential diret. tion is .*nuch ,1ower, as follows, t.0 , bellows circumferential membrane stress range due to internal pressure
= (Pdp/2ntp )(1/(0.571 + 2w/q))
= (10)(17.30)/(2)(1)(0.0196) . (1)/(0.571 + 2.703) = 1350 psi
HiN F UO 'dd 11VJ/ P10 AFR 05 '.E8 10:36 EO:HTEL Er 3 i. air. rs; 1033 F.10 Appendix B Fracture Mechanics Calculations
- 1. Stress Intensity Factor Range 6K !
1.1 Surface Crack l l From ASME Section XI. A-3000 l 6K = AcmaM ha/Q +acb b!I ha/Q where oss , Scb = membrane and bending stress ranges, psi a = flaw depth surface crack < Q = from Fig. A-3300-1 l Mm = from Fig. A-3300-3 ! Sb = from Fig. A-3300-5 l t a a/L a/t M, Mh AK ksivlii 0.06 0.01 0.167 0.5 1.40 0.65 0.7 i 0.125 0.01 0.08 0.5 1.85 0.97 1.0 1 0.25 0.01 0.04 0.5 2.5 1.42 1.4 l
- 1. 2 Through h'all Crack 4K = Ac/Ea ac = Acm
- E0b = 5800 psi 1
- 2. Fatigue Crack Growth Rato da/dN = C.E S. (aX)n C = 2 x 10-19 n = 3.3 E=2 S=1 L a 6K da/dN _(inch / cycle)_
0.2 x IO-'
~
0.25 0.125 3.6 O.50 0.25 S.1 0.7 0.75 0.375 6.3 1.4 1.00 0.50 7.3 2.2 G>-lO
HPR OS '88 11:37 P11 MF 05 'E3 10:26 EECHTEL EF 3 (415 765-?018 p,11 O O O ,, O 2 4 1 3 1 l p~ 7" 13 w%/ W lf \ l l 1 g 1
, _ , e l l
l - s . 11 , s
.)f R .
4 M s
%@ ms
- 1. Screws.3/4-10(4) 9. Flange
- 2. $ crews,1-8 (6) 10. Expansion seal
- 3. Cyltader Liner 11. Gasket
- 4. Split Flange 12. Cylinder Block
- 5. $ crew and Washer 13. "Plastic"Gasket (12) 14. Water connection
- 6. Drain Flug 13. 0-ring $ sal
- 7. Gasket 16. Fire Gasket
- 8. Screws (8)
Figure 1 A sectional view of the emergency diesel engine cylinder block. Item 10 (arrow) is the bellows expansion seal. - G.~N .
" ' ~
APR Ob '80 11:38 P12 J.FP 05 '?2 10:37 EE:HTEL 5F 2 '415i 765-9038 ?,12 i
.~.. .
'W. :,x,
's
- /- ~ . -
. N . \
~ ,. .-
.j, (c. f"x .
- f. >
,...i , . ; . ., . --/. .- _
. - .. . , - - , .. _ m- . .. -; _ _ _._
*k- .. . ,. -
'-v,y N ,. .-.q .
.g .x. \ . . A
. - .- f , .
,- - /,
' .,%..,x x
~
g _., . ..
/ .,
,3 ~~ '~-n.,_. ._w . .
l s'
'N ,, -. 'q r
-s l j
Figure 2 One of the bellows seals exa: tined by MSQS l
6 k' 3r E , ric MP C5 'EG 10:38 EECHTEL ET 3 N15) 763-9023 P 13 1 I hydrotest
- n -- _ . . - % #
7 - operation os ' er- J " standby tension l 60 = c, . c o
#
- i" o
comoression (a) Bellow seal stress cycle spectrum e l. __
*[ ,. . . = _L ,
T v*4 (1) o_ = maximum stress in the cycle o, = mean stroso I"*' #"* j ..- -- --- ----
--~7 Tm e = minimum stress in the cycle
-6 e, = alternating stress amplitude = e" r 2 A
m u = r. e a :a - e - e.,.
*~ !
A = stress ratio = e"*
} 8a
} '- --- --- --- ~~~ ~
A = smplitude ratio = #'
~
l
- e. 1+R
**0 _T (3)
(b) Idealized fatigue stress cycles Figure 3 A simplified stress cycles for the bellows seal as compared with idealized fatigue cycles and defintions. 4
APR 05 #88 11:40 P14 Mc C5 '59 10:3? EECHTEL 5F I '415> 765-is]38 P 14 1 l l
. l l
I l 1 AK, kolin.0 ' 1 10 20 50 100 10 - f
,, o_ j o-4 9
10-s _ l I meren it p ,o
'o'- --
......, ucc.. .. . y Tie. weed I 1o**
4(C' t . 1 A f 41 t 0 i f >=AL peetti l 00 0 A89144 3_ i 8 'tw's 3 , e ,eend e . c o= ,i.wu pt A.mi.se....i.e,n . = slu l u -
, n te, .9
. u tenam at u s , >' ! eel 6N s CMK) O l inu .
i,.......... Ie '
" 10 ** - ' eo .P*"
U 4.......,. 1 . . . . .......
... ..I I -
3 l i 'g
....,... g ~
g ir* -a.-==*' I l g. cia.f , l _ 1od j I V 5 I i i .w., e u s - O
~ i 1
- i * .,
l .r.,,.
.e _ g j o -* _j I l [
4 i i i........
, i 1 i 1
- .i i........ l i -
4 ie' -
,,,,,..,,,,,,,,, i.......-.- i _ 3 o-7 l
. . . . . . . . . , i............i 2 l.'.*:" .'.**' ;
*8:***-'****** !
..... i .......i , m .. _
I
;ai i
i ."... .s. - . : i.,,......,. i,....."' 10
= >a s u. , i I i
-{8'
,y e i .
we an I _ 10 '
- ip (a) ! ; i i i l I i 10=7 10 20 40 60 100 oK, MPa m"'
(b) Figure 4 (a) Schematic relationship between fatigue crack growth rate da/dN and stress intensity factor range AK. (b) A plot of fatigue crack data for A533 steel at ambient temperature frW
~
M Uo ' 06 11:41 P13 4 ? CT 's5 10: 40 EEcHTEL sr 3 4. air , - 3_gg g 15 l l 1 l l 1 - i y I O i
)~ ~ .
/ ee
/ %,- c -
1 ,, 3 A l / 'o v X
! (iA a oJ
/
AJ~m~~,, L
.~ ~~.
l 2b t l l l Figure 5 A surface crack in a finite plate l b~li
Hek wo em 1184A yto ' m e er Es ic:aa se:m a. sr 3 <ais, res_ge33 ,g EXPOSURE TIME = 13,500 h (MAX.) B.R - - o- s c c - N -. -.....-../ 80 - -
- 0. o o 0 -
60 - - oo o - - pH12 40 - o os P o , KEY
- C: SCC 20 -
Q p ? 9 P= PITS S = STAINS 8.R - P ' ,cc c c - , O s NO l
- u. N
/ EFFECT J 80 -
s sP P ,'s, c - a: ~ 60 - - P P P' P - S< c: pH 7 -
)
w
- c. 40 -
s ss P P - 2 W 20 - 0, 0 o, s, P - H i 8.R - c cc p c -
\ ..,
/
80 - P 's, P C P c - 60 - - -p s c , P -
..., pH 2 40 -
o 'o p s P - os 20 - o s s - t i I i 2 3 4 0 10 10 10 10 CHLORIDE CONTENT, ppm Figure 6 Effect of pli on the chloride content and temperature required to produce cracking of Type 304 stainless steel in sodium chloride solution. (Af ter Truman) e it h' __ _ _
t ST-HL-AE- 2653 Appendix 3 Diesel Cylinder Liner Expansion Seal Bellt.ws Failure L2/NRC01/G
4-Bechtel National, Inc. g Engineers-Constructors G Fif ty Beate Street San Francisco.Cahfornia M44Adaress Po 8o:3965 SanFravsco CA 94119 To: iR..L. Randels File No . M no o s. c 2. .o?.
Subject:
Diesel Cylinder Liner Date: March 1,1988 Expansion Seal Bellows Failure Bechtel Job 14926-001, STP From: Y. Chung Of: R&D/ Materials & Quality Services Copies: R. A. Manley/F. C. Breismeister At: 50/15/B5 Ext. 8-1489 T. T. Phillips R. W. Straiton R. A. White , BLN 8802 DCC 0138177
Reference:
Memorandum from T. T. Phillips to R. A. White, 2/12/88 i A copy of our report on the failure analysis of expansion bellows from diesel cylinder liner expansion seals is enclosed . The results of our investigation show that the Type 321 stainless steel bellows failed due to pitting corrosion and cracking which was influenced by bacteria. t
,- /
.#eChung (f f ' -f 7
YC:g f ' i Enclosure
"~
RECEIVED n 4tCH 3 N ec var 25 1988 N L1 [ ** SEORGANIZATION
#14926
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