ML20081A011
| ML20081A011 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 02/15/1984 |
| From: | MISSISSIPPI POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20081A006 | List: |
| References | |
| NUDOCS 8403020410 | |
| Download: ML20081A011 (74) | |
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&/w GRAND GULF NUCLEAR STATION UNIT 1 , FINAL REPORT ON DIVISION I AND II TDI DIESEL GENERATORS February, 1984 9403020410 840221 PDR ADOCK 05000416 8 pm
T-4 D maj i 4-{s NUCLEAR PLANT i.NGINEERING FINAL REPORT ON GCNS DIVISION I AND II TDI DIESEL GENERATORS REPORT NO: 84/005 DATE: Februsry, 1984 I PREPARED BY: MECHANICAL AND OPERATIONAL ANALYSIS SECTIONS NUCLEAR PLANT ENGINEERING / 02- -84 DATE REVIEWED BY: / DATE APPROVED BY: / DATE f l
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.I .6 TABLE OF CONTENTS I.ag,e, ABSTRACT. . . ........................... I
1.0 INTRODUCTION
. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2.0 PISTONS . . . . . . . . . . . . . . . . . . . . . . ........ 9-11 i 3.0 CYLINDER HEADS. ... . . . . . . ... . . . . . . . . . . . . . . 14-15 4.0 CONNECTING RCD EEARINGS . .. . ... . . . . . . . . . . . . . . 18-20 5.0 PUSH RODS . . . . . . . . . . . ... . . . . . . . . . . . . . . 24-25 6.0 CRANKSHAFT. . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-30 7.0 L.P. FUEL LINE FAILURE. . . . . . . . . . . . . . . . . . . . . . 35-36 8.0 H.P. FUEL LINE FAILURE. . . . . . . . . . . . . . . . . . . . . . 37-38 9.0 CRANKCASE CAPSCREWS . ..... . . . . . . . . . . . . . . . . . 39-40 10.0 TDI PRODUCT IMPROVEMENTS. . . . . . ................ 41 11.0 QUALIFICATION / RELIABILITY TESTING . . . . . . . . . . . . . . . . 43-45 12.0
SUMMARY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47-48
13.0 CONCLUSION
S . ........................... 49
14.0 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50-51 ATTACHMENT 1 - RESPONSES TO SIXTEEN PROBLEMS IDENTIFIED IN TDI OWNERS GROUP MEETING WITH THE NRC ON JANUARY 26, 1984. . . . . . . . . . 52-65 ATTACHMENT 2 - PISTON MANUFACTURING DETAILS . . . . . . . . . . . 66-69 TABLES TABLE 1 DELAVAL ENGINE SPECIFICATIONS . . . . . . . . . . . ..... 4 TABLE .1 GGNS D/G OPERATING DATA . ... ............... 5 TABLE' 1 DIVISION I AND II APPROXIMATE P.UN HOURS UNDER LOAD SINCE PISTON SKIRT MODIFICATION IN NOVEMBER, 1981 . . . . . . . . . 6 TABLE 1 D/G LOADINGS. . - . . . . . . . ................ 6 iii
AL-TABLE OF CONTENTS (CONTINUED) P_agg TABLE 2 RESULTS OF INITIAL INSPECTION OF GGNS MODIFIED AF PISTONS . . 12 TABLE 2 RESULTS OF ADDITIONAL INSPECTION OF GGNS MODIFIED AF PISTONS. 13 TABLE 3 INSPECTION RESULTS OF DIVISION I CYLINDER HEADS . . . . . . . 16 TABLE 3-2 --INSPECTION RESULTS OF DIVISION II CYLINDER HEiDS. . . . . . . 17 TABLE 4 CHEMICAL SPECIFICATIONS LIMITS FOR ALC0A B850 6-T5 ALUMINUM. . . . . . . . . . . . . . . . . . . . . . . . . 21 TABLE 6 SH0REHAM AND GGNS CRANKSHAFT DATA. . . . . . . . . . . . . . . 31 TABLE 6 CRANKSHAFT STRESSES AS REPORTED BY VARIOUS ANALYSES. . . . . . 32 TABLE 6-3 . CRANKSHAFT LIQUID PENETRANT INSPECTION RESULTS . . . . . . . . 33 TABLE 10 TDI PRODUCT IMPROVEMENT SIMS . . . . . . . . . . . . . . . . 42 TABLE 11
SUMMARY
OF QUALIFICATION AND VALIDATION TESTING. . . . . . . . 46 FIGURES FIGURE 2 LOCATION OF STUD BORE AREAS WITHIN PISTONS-. . . . . . . . . 8 FIGURE 4 CONNECTING ROD BEARING DESIGN & NOMENCLATURE (SCHEMATIC) . . 22 FIGURE 4 COMPARISON OF CONNECTING ROD / BEARING CHAMFER ARRANGEMENTS. . 23 FIGURE 5 WELDED BALL CONNECTOR ROD. . . . . . . . . . . . . . . . . . 26 FIGURE 5 FRICTION WELDED PUSH ROD . . . . . . . . . . . . . . . . . . 27 FIGURE 6 CRANKSHAFT COMPARISON. . . .. . . . . . . . . . . . . . . . . 34 FIGURE A2-1 PISTON COMPARISONS . . ... . . . . . . . . . . . . . . . . 69 iv
0 JRA7T ABSTRACT This report contains a detailed description of the program of preventive maintenance, replaccment of components with improved quality products, engine testing, and engineering evaluations which have been undertaken by MP&L, GGNS Unit 1, to enhance reliability and to assure with a reasonable level of confidence that the Transamerica Delaval, Inc. (TDI) diesel engines at Grand Gulf . Nuclear Station (GGNS) will perform their required safety function. The report also addresses implementation of vendor recommendations, NRC directives, problems encountered on TDI engines at other locations, in
. particular, the LILCO plant at Shoreham, potentially significant items identified at a TDI Owners Group meeting and other sources of operating experience information.
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1.0 INTRODUCTION
Grand Gulf- Nuclear Station, Unit 1 is equipped with three diesel generators, two of which are supplied by Transamerica Delaval, Inc. (TDI). These ' two diesel . generators are sources of emergency power to the GGNS Division I and. Division II ESF buses. The' third D/G set, dedicated to the HPCS system, is supplied by the - Electro-motive Division (EMD) of General
, Motors.
This report provides a detailed description of a program undertaken by MP&L to enhance the reliability and performance of the two TDI diesel generators at GGNS Unit 1. The report contains a description of activities of preventive maintenance, replacement of various components with improved quality products, and testing of the two TDI diesel generators. The improvement. program includes specific actions which have been or are i being'taken to correct the problems experienced with TDI diesel generators during the -start-up testing phase of GGNS Unit 1. Potential problems identified to MP&L as a result of the experience with TDI diesel generators
'at other nuclear installations, in particular the LILCO plant at Shoreham, are also addressed.
The main emphasis of this report is to provide the results of an engineering evaluation of the two TDI diesel generators at GCNS Unit I for ~ their reliability and performance. This evaluation is intended to provide reasonable assurance to the NRC that the TDI diesel generators will perform their required safety function. Sections 2 thru 9 of the report contain descriptions of repairs or
-modifications which have been performed. Section 10 concerns TDI's product improvement program. .Section 11 focuses an the testing programs, both the testing done in the past and the testing performed after completion-of
- the piston skirt changeout. A summary of the overall engineering evaluation is provided in Section 12. The conclusions reached from these evaluations are provided in Section 13.-
Attachment - 1 provides details of concerns raised at a meeting of the TDI
. diesel generator owner's group with the NRC on ' January 26, 1984, their
[ ! applicability.to Grand Gulf and their resolution. l Attachment;2 provides a summary of various piston skirt designs that have l been or are in use in the GGNS TDI diesels. (: .. . Table.1-1 provides a list of the principal design specifications for GCNS Unit 1 TDI diesel generators. 7
- Table 1-2 shows the total operating hours, starts., valid tests and valid
[ ' failures for: the GGNS TDI D/Gs. Table 1-2 also shows that the ratio of L . valid failures (1) 'to valid starts (128) results in an excellent start L reliability in excess of 99 percent. c-. f l l. 2
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u ;;; - " s~ 1.0 (Continued) Table 1-3 shows . the Division I.and II approximate run hours under load since the ' origin ally furnished piston skirts were modified in November,
. 1981.
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Table-1-4'shows the procurement specification estimated electrical loads and = the present electrical loadings for the Division I and II' diesel generator. The significant work activities completed on the Division I and II engines are:
'All piston skirts.have been replaced with skirts of improved
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o design, o All 32 cylinder heads inspected and eight cylinder heads with rejectable indications have been replaced, o :All Division I and Division.11 connector push rods have been 1 replaced with components of improved design, o All connecting rod bearings have been replaced, o Inspection of both crankshafts has been completed, and o Rework of turbo piping and components using ASME welding, pro-cedures and materials. These: work activities are intended to enhance engine performance and reliability. They have insignificant - impact on engine specifications,
~ design criteria, subsystems or performance characteristics.
None ' of the work activities affect the design considerations listed in Table 1 of IEEE 387-1977. As such, these work activities are considered
" minor" design changes as defined by IEEE .387-1977. Therefore, the post i'
' maintenance qualification and availability testing of these diesels was planned according to the guidelines e.stablished in IEEE 337-1977 for minor l, changes. . Additional testing was also performed.
c. 3
s. TABLE 1-1 DELAVAL ENGINE SPECIFICATIONS Model DSRV-16-4 Quantity 2 Engine Serial Number 74033-2624 & 74034-2625 Service Stationary generator for nuclear service Fuel Mode Diesel Configuration 45* "V" type No. of Cylinders 16 Bore (in.) 17 Stroke (in.)- 21
- Cycle Model 4 stroke Total Displacement (cu. in.) 76,266
, Crankshaft Rotation CW (from Flywheel end) Firing Order IL-8R-4L-5R-7L-2R-3L 6R-8L-1R-5L-4R-2L-7R L 6L-3R ! Continuous Rating (kw) 7000 f i I - Overload Rating (kw) 7700 Crankshaft Diameter (in.) 13 , Crank Pin Diameter (in.) 13 i' ' [ s
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TABLE 1 CCNS D/G OPERATING DATA Division I Division II Shop and Pre-Oper.'Run Time _(Hrs). 535 252 Since Date of OL Run Time (Hrs) 736 560 Total Run Time (Hrs)( 1271 812 TOTAL NO. OF STARTS ( } Delaval Shop Runs ( } 310(2) 5 Pre-Operational Runs 60 60 Since Date of OL Runs 154 105 Total Starts ( 524 170 NOTES: 1. Source of Information - Delaval Technical Manuals.
- 2. Division I engine had 300 prototype runs for reliability testing.
- 3. Data as of February 1, 1984 4, Valid Starts: Div I - 76 Div II - Sj!,
128 Valid failures: 1 (Div I) 2 Start Reliability: 99.2% Valid starts and failures are as defined in Regulatory Guide 1.108.
h.~~~ rg TABLE 1-3 DIVISION I AND II APPROXIMATE RUN HOURS UNDER LOAD SINCE ORIGINALLY FURNISHED PISTON SKIRTS-WERE MODIFIED IN NOVEMBER, 1981 TO FEBRUARY 1, 1984 r
-Load, + 5% Division I Hours Division II Hours 50 14 12 50 .60 -450 316
, 60 - 99 7 7 100 272 197 110 14 10 TABLE 1-4 D/G LOADINGS Division I Division II Procurement Specification 5730 KW 6100 KW Design DG- Rating 7000 KW 7000 KW Loss of Offsite Peser Loads 3627 KW (51.8%) 4745 KW (67.8%) Post LOCA Loads- 4711 KW (67.3%) 3914 KW (55.9%) Total Connected ESF Bus Load 5963 KW (85.2%) 6397 KW (91.4%) c , --- --m. - u- - --
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a , 2.0 PISTONS-
2.1 DESCRIPTION
MP&L received information from TDI that during a recent reassembly of the three TDI diesels at the Shoreham station, an inspection of the piston skirts revealed linear indications exceeding 1/16 inch in length in 23 of 24 modified "AF" piston skirts. As a result.of this finding TDI generated a 10CFR21 report recommend- ' Ling that GGNS and San Onofre inspect 25% of the modified "AF" piston skirts in'each engine for linear indications. MP&L subsequently found rejectable indications in three of the four modified "AF" piston skirts during the~25% inspection on the GGNS Division II engine. All piston skirts on the Division -II D/G were then inspected. The results of these inspections are shown in Table 2-1 and 2-2. The inspection f- criteria used for the inspection is described in Step 2.3 of this section. 2.2 ENGINEERING EVALUATION Failure Analysis Associates (FaAA) performed an inspection and analysis of the modified type "AF" piston skirts which were removed from the Shoreham . diesels. After comparing the GGNS Division II piston skirt inspection results with the Shoreham evaluation results, l FaAA concluded that the GCNS Division I piston skirts could contain fatigue cracks of the same approximate depth as the Shoreham engines. . As a result of these early evaluations MP&L replaced all piston skirts in the two Unit 1 TDI engines with the improved "AE" style skirt provided by TDI. (See Attachment 2 for Details of Piston Designs). , i -MP&L _ worked with TDI in the final phases of production and inspection [- of ' theset piston skirts to - assure . that they are free of rejectable l indications L(as evidenced by fluorescent magnetic particle examina-
- tion).
ji . Preliminary results~ of ~ an evaluation 'as reported by FaAA indicates l: l that the' "AE" type piston will exhibit substantially lower stresses
- than=the replaced modified "AF" type under similar loadings. FaAA has
[~ also indicated that some related information has been compiled on j existing TDI engines using.the "AE" pistons. The "AE" pistons in the TDI supplied Kodiak engine-(more than 6000 hours'of run time) and the TDI R-5 test engine (approximately' 680 hours of run time) exhibit no rejectable indications. At's meeting of-the TDI D/G Owners Group on February 8, 1984, LILCO L indicated that a'Shoreham TDI engine is about to undergo a 100 hour p -full ~ power test. .LILCO has agreed to provide MP&L with piston skirt inspection results upon completion of the test. ( TDI also has undertaken a program to further verify the adequacy of I the "AE" piston design.' Static loadings . of fully instrumented "AE" p pistons.in the cold' condition are being performed by TDI. Results of the testing will become available to MP&L when completed. b L 9
d hg -g' # A 2.3 LPISTON INSPECTIONS (1) Division II modified "AF" piston skirts were nondestructively examined with liquid fluorescent dye penetrant and/or wet fluorescent- magnetic -particle processes. The specific area of
; concern was the filleted transition area between the skirt / crown stud hole bore and the skirt wall. All critical filleted areas of each modified "AF" piston skirts were initially inspected with the liquid fluorescent dye penetrant process. The results of
-this. initial . inspection are summarized in Table 2-1. The
.following criteria was used in recording possible indications:
- 1. all indications were to be evaluated, and
- 2. a linear indication is defined as an indication in which its length is greater than three times its width.
Numerous indications were found, ranging from 1/32 to 9/16 inches in length. The following additional inspections were performed to determine if the linear indications were superficial in. nature. Each linear indication was ground and/or sanded to a-2 - depth of approximately 0.062 inches. These indications were re-inspected using the liquid fluorescent dye. penetrant or wet fluorescent magnetic particle process. Linear indications were found ranging from 1/32 to 1/2 inch in length. The results of these additional' inspections are summarized in Table 2-2. To characterize these indications, a confirmatory metallurgical analysis will be performed. The analysis will. attempt to deter- , 'mine the mode of cracking,- characterize ^ the crack propagation rate, and estimate the depth. (2) All replacement "AE" picton skirts were nondestructively examined by TDI using the wet fluorescent magnetic particle process prior to installation in the engines. All TDI nondestructive examina-tion procedures were' reviewed and approved by MP&L. The follow-ing criteria were established as levels of unacceptability:
- 1. any. linear indication greater than 3/16 inch long,
- 2. rounded indications with dimensions greater than 3/16 of an inch, 3, four or more rounded indications in a line separated by 1/16 of an inch or less, edge to edge, and J
- 4. cracks and hot tears.
y; These acceptance criteria were derived from ASTM Standard E 125-63, reapproved 1980. 10 -
x a 2.3~ (Contin'ued) All piston skirt castings were accepted to the above criteria. It should be noted that all acceptable indications that were found were documented by appropriate records. 2.4' MANUFACTURING DETAILS , The maitufacturing details for the "AF", modified"AF" and "AE" p,.ston - designs have been provided to MP&L by TDI. The evolution of IDI's piston design is relevant to this report. As such, the details of
. manufacture for each of these piston designs is presented in Attachment 2.
-It is important to note ' that the "AE" design utilizes a reinforced
^(lower str; esed) casting and a half-stack Belleville washer arrange-ment.- Also, "AE" skirts are heat treated to produce stress relieved nominal 100,000 psi tensile strength nodular iron. The "AE" style skirt is ' interchangeable with existing R-4 piston crown and requires only minor hardware changes.
2.5 CONCLUSION
S As a result of the Division II modified "AF" piston skirt inspection, the piston skirts in the Division I and II D/Gs have .been replaced
'with the type "AE" piston skirts.
. Based. on preliminary results of analytical work being performed by FaAA and . the operating experience and subsequent inspection of the piston skirts on the TDI Kodiak and R-5 test engines, MP&L has con-cluded that the "AE" design is capable of . performing the required
' function at all running loads. . MP&L will continue to monitor piston
- skirt validation evaluations by the' vendor, consultants and the TDI D/G owners group, i
11 l-
'D TABLE 2-1 RESULTS OF INITIAL INSPECTIONS OF CGNS MODIFIED AF PISTONS IN THE DIVISION II D/G -
Indication Length (Inches)(1) Piston Stud Hole Bore Area (2) Identification #1 #2 #3 #4
#1RB None 1/8 3/32 1/4.1/32,I/16
#1LB None 1/32 None 1/16
#2RB None 1/32 None 1/4,1/16
#2LB 5/64,1/16 None 3/16 1/8,1/32
#3RB 1/4 1/32,3/16 None 1/2
.#3LB 1/32 1/32 None 3/16
#4RB None None 1/4 None
#4LB 1/16,1/8 None 3/32,1/8 1/16
#5RB 1/32 1/32 1/4 1/4
#5LB 3/32,3/32 1/8 9/16 3/8
#6RB 1/4 3/16 None 1/4
#6LB 1/32 None 1/16 1/32
#7RB None .None None 3/32
#7LB None None None 1/32
#8RB 3/32 None None None
#8LB 1/16,1/8 None- 1/16 1/4 General Notes:
(1) All inspection performed using Liquid Fluorescent Penetrant Process. (2) See Figure 2-1 for location of the stud bore area within piston skirt. 12
4 4' TABLE 2-2 RESULTS OF ADDITIONAL INSPECTION OF GGNS MODIFIED AF PISTONS IN THE DIVISION 11 D/G Indication Length (Inches)(1) pg,g , . Stud Hole Bore Area (2) Identification #1 #2 #3 #4
#1RB --
1/8 (MT) NAD (MT) NAD (MT)
#1LB --
NAD (MT) -- NAD (MT)
#2RB --
NAD (PT) -- NAD (PT)
#2LB NAD (PT)_ --
NAD (PT) NAD (PT)
.#3RB 1/4 (MT) 3/16 (MT) --
NAD (MT) _ i
#3LB 1/8 (MT) 1/8 (MT) --
3/16 (MT)
#4RB -- --
1/4 (MT) --
#4LB 1/8 (MT) --
1/8 . (Kr) 1/16 (MT) iSRB NAD (MT) NAD (MT) 1/4 (MT) NAD (MT) f5LB NAD (MT) NAD (MT) 1/2 (MT) 1/4 (MT)
#6RB NAD (MT) NAD (HT) --
1/4 (MT)
#6LB NAD (MT) --
NAD (MT) NAD (MT)
#7RB -- -- --
1/32 (MT)
#7LB -- -- --
NAD (MT)
#8RB NAD (MT) --
#8LB 1/8 (MT) --
NAD (MT) 1/4 (MT) General Notes: (1)' PT indicates Liquid Fluorescent Dye Penetrant Inspection. (2) MT indicates Fluorescent Magnetic Particle Inspection. (3) See Figure 2-1 for location of the stud bore area within piston skirt. (4) -- Not performed.- No discontinuities present during initial inspection. (5) NAD No apparent defect. 13
m i FIGURE 2-1: LOCATION OF STUD BORE AREAS WITHIN PISTON
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s 3.0' CYLINDER HEADS f
3.1 DESCRIPTION
During disassembly of the Division II engine for piston inspections, . red rust was reported in the area of the exhaust valve seats on the #5 right bank head. Subsequent color contrast dye penetrant inspections i showed cracks in the stellite exhaust valve seat overlays. Because of the: rusting, it is postulated that one of the cracks may extend
- into the water jacket.' s 3.2 INSPECTION AND ENGINEERING EVALUATION Ae a result of these cracks, an investigation has been initiated to determine the extent of the cracking and required corrective action.
The investigation. has been divided into two parts; short and long
,. term. The short term investigation was initiated to determine-if the extent .of ' cracking is ~ generic- to all heads at GGNS. All cylinder
- heads on both- Division I: & II D/Gs were removed ' and were ncndestruc-tively . examined . in the area of the stellite seats with a color contrast solvent removable dye' penetrant process. The following criteria were established as levels of unacceptability:
r
- 1. Any cracks orf linear indications >
- 2. Four or more rounde'd indications in a line separsted by 1/16 inch or less, edge to edge 3.- Any rounded indication with dimensions greater than 1/16 inch 4.- Linear' indications are those indications in which the.
length is more than three times the width While only the #5 right bank Division 11 cylinder head, an apparent L - through wall crack, one of other 16 heads on the Division .II D/G and
- six of the 16 heads on the Division .1 D/G were determined to have rejectable indications. No other visual evidence .of cracking was found in the cylinder heads. A description of the' indications found l
' during these_ inspections are detailed for Division.I in Table 3-1 and- ,
! Division II in Table 3-2. I p~ To - address the long term concern, a failure investigation has been ! initiated. A metallurgical evaluation will be performed to determine the cause of crack initiation, and the crack propagation mode. 3.3 CORRECTIVE ACTION Based on the .short term - investigations , MP&L has replaced the two r heads on the Division II D/G and the six heads on the Division I D/G with heads that were examined and determined to have no rejectable linear indications. No further action is planned, pending the results L of the long term investigation, l '. 14 ( i T w e--,,, ,w.-,-y.-e-- ,,,em-_,y -,y , , - - , , ,c, , , , , -
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3.4 CONCLUSION
S Two heads on Division II and six heads on Division I were determined to have rejectable indications. However, as demonstrated by the operability of the D/Gs prior to the replacement of these heada, the ability of the Unit 1 D/Gs to perform their safety function was not impaired. The replacement of these eight heads with heads free of rejectable valve seat indications provides additional assurance that the potential for head cracking from this source is minimized. To provide further assurance that any significant cracks in the heads will be detected, additional surveillance will be performed following D/G operation to detect the presence of water in the cylinders. These surveillances will be in addition to the current surveillances which are designed to check for the presence of water prior to manually initiated D/G starts. 15
TABLE 3-1 INSPECTION RESULTS OF DIVISION I CYLINDER HEADS Head Identification Inspection Results Number ILB No Apparent Defects IRB No Apparent Defects 2LB Linear Indications on Fusion Zone Between Casting and Stellite Valve Seat 2RB No Apparent Defects 3LB No Apparent Defects 3RB No Apparent Defects
'4LB No Apparent Defects 4RB Linear Indication in Stellite Valve Seat SLB Linear Indications in Stellite Valve Seat SRB No Apparent Defects 6LB Linear Indication in Stellite Valve Seat 6RB Linear Indications in Stellite Valve Seat 7LB No Apparent Defects 7RB No Apparent Defects 8LB No Apparent-Defects 8RB Linear Indication in Stellite Valve Seat 16
TABLE 3-2 INSPECTION RESULTS OF DIVISION II CYLINDER HEADS Head Identification Inspection Results Number ILB Incomplete fusion 5/16 inch long on intake valve seat 1RB No Apparent Defecta 2LB No Apparent Defects 2RB No Apparent Defects 3LB No Apparent Defects 3RB No Apparent Defects 4LB - No Apparent Defects 4RB No Apparent Defects SLB No Apparent Defects SRB Twelve linear indications ranging from 3/16 to 3/4 inch. All indications transverse to stellite overlay on two exhaust valve seats. All cracks are contained within the valve seat except for one, which extends from stellite into cast head material. 6LB No Apparent Defects-6RB No Apparent Defects 7LB No Apparent Defects 7RB No Apparent Defects 8LB No Apparent Defects 8RL No Apparent Defects 17
4.0 CONNECTING ROD BEARINGS
4.1 DESCRIPTION
Shoreham has experienced cracks in connecting rod bearings. These cracks were discovered (See Reference 2), when LILCO disassembled the thres.. diesel engines at Shoreham (TDI Model DSR-48) to investigate a crankshaf t failure (See Section 6.0). A complete inspection found that four of the forty-eight connecting rod bearing shells contained cracks. Even though the Grand Gulf D/G design is significantly diff-erent (i.'e. , GGNS has articulated connecting rod design and reduced connecting rod bearing loads) an inspection and evaluation was per-formed to determine if this concern e :ists at Grand Gulf. 4.2 ENGINEERING EVALUATION, SHOREHAM BEARINGS A schematic of a cracked Shoreham bearing is shown in Figure 4-1. FaAA performed ' an analysis (Reference 18) on one of the cracked Shoreham bearings. The cracked bearing was checked for its chemical and physical properties. A scanning electron microscopy (SEM) analysis of the fracture was also performed. In addition, dimensional
. checks were made for wear. The chemical and physical properties met the current design specifications except for elongation. The elonga-tion was found to be below specification, however, since the test specimen was not standard, this led to results that were inconclu-sive. . Reference chemical properties for B850.0-T5 are shown in Table 4-1. A Shoreham SEM examination of the fracture face indicated that voids in the bear- ing shell may have been crack initiation locations.
~In compression, voids in the " overhang" area would not pose a prob-
'lem. However, the bearing / rod arrangement on the Shoreham diesels did not support the end part of the bearings (Figure 4-2). This unsup-ported end combined with the . yawing of - the crankshaft would put the internal diameter surface into tension. The surface ' porosity acting as a stress inten- sifier may have contributed to crack initiation in the ' unsupported end (" overhang" area). Also, the subsequent shell thickness measurements showed the bearing to be within the manufactur-p ing tolerances, i.e., no appreciable wear.
l 4.3 GGNS D/G INSPECTION ( The ' inspections delineated below were performed on Division Il D/G l components. New bearings were installed in both divisions as part of l the five year planned preventative maintenance program. This ex-l pedited.the return to service of the diesel and extended the replace-l ment - period of the bearings. The integrity of these replacement bearings was based on an' exact part number exchange, visual inspection of the bearings before installation, and favorable results from the inspection / evaluation performed on the original' bearings, i. i 18
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> 0 4.3 (Continued)
~
- 1. 'All of'the connecting rod bearings were dimensionally checked for wear and for signs of unusual or abnormal wear patterns. -
- 2. Two (25% of total) of the connecting rod bearings were inspected by liquid penetrant (PT) and radiography. The radiography tech-nique utilized an x-ray tube radiation source and obtained a 2-2T film sensitivity yielding at least of 0.015 to 0.020 inches reso-lution. The PT inspections used a liquid fluorescent dye pene-trant process and met the requirements of ASTM Standard E165.
No rejectable indications were found. Tests ~ to check the chemical and physical properties of two (25% of total) ' original connecting rod bearings are planned. Thesa tests will be performed in accordance wich applicable ASTM Standards. These tests are considered confirmatory in nature and are not required to justify D/G operability.
- 3. The " overhang arrangement" of two bearings / connecting rod assem-
.blies was dimensionally checked for unsupported bearing material.
.The chamfers on the connecting rods and rod bearings were dimen-sionally checked to determine if the " overhang arrangement" exists and to verify that the connecting rod configuration was of the correct design.
4.4 lNSPECTION RESULTS The initia1' Division II D/G inspections indicated the following: ;
- 1. Review of the radiographic film showed that any bearing porosity-was less than 0.030 inches, however, some linear type indications were present. All linear type indications were directly traceable to minor- gouges and marring located on the bearing
, ~ surfaces ~ which occurred during disassembly. As indicated in preliminary . information by FaAA, porosity of less ~ than 0.030 inches .is predicted to -be . of little consequence to the satisfactory. operation of the bearings.
.2. The results of the dimensional inspections confirmed that the.
bearings were within manufacturing tolerances. No signs of unusual. or abnormal wear patterns were noted. This indicates that there was no misalignment between the connecting rod assemblies
~
and the crankshaft. i: 3.- The results of the chamfer measurements indicate that there is no
- l" overhang" arrangement on the #7 connecting rod / bearing assembly.
.However, the results indicate that the #2 connecting rod / bearing assembly has an " overhang" of approximately 0.016 inch (i.e.,
0.016 inch of unsupported bearing material). This amount of
" overhang" is insignificant compared to the 0.25 inch " overhang" on the Shoreham bearings at the time of bearing cracking.
i 19 t w w- , ,
. . _ , . , . . . , .,,,m...e .g ,,,,...-,---.--n -..r.
. -r-,. , ,,.,,,-,.,e. . ,... . m-- -.w. .., ,, . - ,,, .%,,-,.--+m,.2
i l l 1 l 4.4 (Continued)
- 4. The results of the Liquid Fluorescent dye penetrant examination indicated that no cracks were present.
4.5. CONCLUSIONS The differences in design between Grand Gulf and Shoreham (i.e., articulated connecting rod design and reduced connecting rod bearing loads at Grand Gulf) preclude the types of problems that Shoreham has experienced. However, inspections were performed to verify the ade-quacy of the bearings. Inspections of the original Division II D/G connecting rod bearings showed that no appreciable wear or unusual wear patterns were present. This confirms proper alignment of the connecting rod assemblies to the crankshaft. Radiographic inspection of two original Division II D/G connecting rod bearings found no porosity of a size greater than 0.030 inches, which is judged to be insignificant. No rejectable indications were found on any of the bearings inspected by liquid dye penetrant methods. Added assurance regarding integrity of the replacement bearings is being provided by confirmatory analyses. These analyses include de-structive and non-destructive testing as well as analytical work being performed by FaAA. 20
r L .
= e 9
TABLE 4-1 CHEMICAL SPECIFICATION LIMITS FOR ALC0A B850.0-T5 ALUMINUM 4 Element Composition % Si 0.4 Max Fe 0.7 Max Cu 1.7 - 2.3 1 Mn 0.10 Nhx Mg 0.6 - 0.9 Ni 0.9 - 1.5 Sn 5.5 - 7.0 Ti 0.20
-Other E ements-l 0.30 Max Al Remainder I
21
.- . _ . - . - . - - , - . - - . - _.- ,-. .~-- - .- -- -... -. . .--.
FIGURE 4-1: SHOREHAM CONNECTING ROD BEARING DESIGN AND NOMENCLATURE (SCHEMATIC) End Annular groove
, Cil hc.
1 O c w ol pin CR.Acx Spreader , [Alumir.t back r groove _ l abbit * [ ole Parting flae overlay on surfac 34 ,
\ I LE NGiT W OF CR.ACir--
( insid's diameter Longtn
/
/
t 9 FIG. 4-1
FIGURE 4-2: COMPARISON OF CONNECTING ROD / BEARING ~ CHAMFER ARRANGEMENTS CONNECTING ROO 03-340 - 0 3- o c
*# $ ;M A ,
s.- ..g m v . .
- 245*CHF.
, _ 4 BRG. SHE*:L , a 0 3 - 340 - 03% 0 A L~
cv . N A= 69.42 sNs 2 fl*DIA . R (II" CMAHKPIN} SCHEMATIC 0F SHOREHAM "0VERHANG ARRANGEMENT" INDICATING UNSUPPORTED BEARING MATERIAL CONNGCTING rod 02 340-II- AJ
~N N
,$x45'CHf.K _
B R G . S H E L t. A ' fg 54S* CHF. 02- 340-o4- AG l
\
= % A ,,yg,g_7 gy$2 l
13"DIA. gy (13" CRANKPIN) o l SCHEMATIC 0F GGNS BEARING ARRANGEMENT WITH BEARIhG MATERIAL SUPPORTED FIG. 4-2 l l - i I
-v l
.
- l 5.0 PUSH RODS 5.1 - DESCRIPTION.
10n August 11, 1983, during the performance of unrelated maintenance, a rocker arm connector push rod was found to have a cracked weld.. The push rod ball . disengaged from the shaf t as the push rod was removed ifrom the Division I engine. The defective connector push rod was replaced and the Division'I engine was tested and returned to service
. with additional ' connector . push rod inspection criteria specified.
During;a subsequent inspection of the Division I engine, 14 of 16 ,
. connector push rods .were discovered with cracked or separated welds.
This inspection - revealed one of the connector push rod balls was cracked in addition to the weld cracks previously observed. During the inspection of the Division II engine in December, 1983, 13 of 16 connector push rods were also found to have cracked tube-to-ball welds. 5.2 ENGINEERING EVALUATION ~AND CORRECTIVE ACTION There were two. types of push rod designs used at GGNS. The main push rods had a tubular steel shaft fitted with hardaned steel end pieces which were attached to the tube with four plug welds near the ends of the tube. According . to TDl, an estimated. 2 percent of this design developed cracks in or adjacent- to the plug welds on the rods. The connector push rod consisted of a-tubular. steel body fillet-welded to carbon steel ball bearings. This design is the type which exhib-Lited defects at Grand Gulf and is shown in Figure 5-1. A 1 1/2-inch high carbon steel ball bearing.is fitted to 1 1/4-inch OD tubing with 1 a - 1/4-inch wall. The inside edge of the tubing has a 45' chamfer
- which results in a 7/8-inch circular seating ring for the ball at the end of'the tube. The ball is attached to the tube with a continuous 360* fillet weld. . The materials of construction are as follows
- ,
l' Ball Material: AISI 52100 l Tube Material: ASTM A519 Weld Material: UNIALOY 850 (: The first connector push rod found defective was subjected to metal-l lurgical evaluation (Reference 3). The initial weld defect resulted
- from lack of penetration of the fillet weld with the tubing. Destruc-tive examination of the ball and weld on the opposite end of the de-factive connector push rod revealed additional cracks in the heat-
'affected-zone ~(HAZ) of the ball bearing. The welds exhibited lack of penetration and slag inclusions in the crevice area behind the weld.
I The metallurgical evaluation' concluded that the ball material is difficult to weld. The possibility of finding underbead cracks all around.the ball in the HAZ is very high, i' 24 i L t- . _ - - - . _ _ . . _ . . . , . , _ . _ . . . _ . , _ _ ..- _ _ _ _. _ . _ . _ _ _
v .. . 5.2 (Continued) Previous operational experience did not indicate that the cracks would , propagate out of the HAZ since the connector push rods are loaded in l compression. Furthermore, none of the MP&L defects or other reported l defects were associated with underbead cracking. Rather, all previous j defects of this design were associated with insufficient weld penetra-tion. Consequently, MP&L concluded that a push rod exhibiting these defects would not result in engine failure. MP&L proceeded with an interim inspection program, until replacement connector push rods free of defects could be obtained. The discovery of a cracked connector push rod ball in the Division I diesel, however, demonstrated that the underbead cracks could, in fact, propa-gate through the ball material. A new replacement connector push rod design (Figure 5-2) had been developed by TDI. This new design consists of a tubular steel shaft which is friction welded to cylinders of alloy steel on each end. These ends are then machine finished and hardened. The tube material is ASTM A-106 Grade B steel; the ends are AISI 8740/50 steel. During December, 1983, MP&L engineers reviewed all aspects of the connector push rod fabrication and observed procedural qualification runs at Delaval's push rod fabricator in Los Angeles. Samples of the quali-fication run were analyzed by MP&L and determined to be acceptable.
5.3 CONCLUSION
S The connector push rod problems described have been corrected with the new push rod design that is installed in the Division I and II D/Gs. MP&L plans no further action on push rods, however copies of metal-lurgical evaluations of the old and new push rods are being provided to the TDI D/G owners group. In addition, a connector push rod with
-at Jeast 100 hours of full power operation will be provided to th 9
TDI D/G owners group for laboratory fatigue-proof testing to 10 cycles'to verify a saticfactory endurance limit. 25
+
FIGURE 5-1: WELDED BALL CONNECTOR . 03-390-04-AB 1 F -0 05 - 074 FILLET WELD EACH END ms s s s- __
, ss s s ss /
_ _ _ _ ;l> - - @ _ _ __- \ r y T i; .. i
+ ;
' I $ __ __ _ _ d,(__ __ _ _ _ __ L A
~ J i
I 1 1 FIG. 5-1
FIGURE 5-2: FRICTION WELDED PUSH rod . 02-390-07-AH
~
02-39 O- Cr7- AF O2-390-07-AF FRICTION WELD EACH EMO q ( -________ --- - > .. . .
. - _y. -
___________[--
-- - \
1 y -
"* 4% ,
4 FIG. 5-2
- .- -- - -. - ~ . .- - _.. . ..
4 %
- 6.0 -CRANKSHAIT -
6.1 DESCRIPTION
The concern over the design adequacy of the crankshaft was prompted by a crankshaft failure that occurred at Shoreham with their TDI supplied
-standby diesel generators. Investigation by FaAA revealed that the cause of the crankshaft failure was high cycle fatigue. This led the NRC to issue IE Information Notice No. 83-58 which identified Grand Gulf as having TDI supplied standby diesel generaters with possible crankshaft design deficiencies.
, 6.2 ENGINEERING EVALUATION Investigations were immediately conducted by MP&L on the applicability
.of the failures at Shoreham to the Grand Gulf TDI diesel generators.
, A' physical comparison '(Reference 19) of the DSR-48 (in-line eight cylinder)-series engine crankshaft that failed, with that employed in the DSRV-16-4 (Vee-16 cylinder) series at Grand Gulf revealed . some important differences. Among the significanc design improvements on the Grand . Gulf engine are the larger web size and shape, larger crankpin diameter, larger pin fillet . radius and the use of counter-weights. In addition, it was learned that TDI may have used potentially -non-conservative (1st generation) design harmonic coefficients in 1974 when the Shoreham stress analysis was performed. The original GGNS design stress calculations utilized later 1975 (3rd generation) harmonic coefficient values. At the request of MP&L TDI clarified the use of the GGNS 1975 Vs -1983 post-Shoreham 4th genera-tion coefficients and- recalculated the GGNS D/G shaft torsional stresses using the latest coefficients (Reference 4). The changes made in the newest harmonic coefficients were an analysis refinement that ' resulted from analytically generated .results being compared to actual test-results.. The changes were minor and did not
~
F substantially' affect the analysis.. The TDI results indicated that the GGNS crankshaft stresses were significantly less than the maximum
-allowable DEMA standard and also were only 60% of the stresses in the-1
-failed crankshaft a t' Shoreham. This confirmed that a substantial design margin existed in the GGNS crankshafts.
To verify the adequacy and results of the TDI crankshaft design analysis, MP&L requested Bechtel to evaluate TDI's analytical methods. Bechtel concluded that' the analytical methods used to predict crank-shaft stresses by TDI are in accordance with industry standard prac-tice and appear to be properly applied (Reference 5). ' t
-The results of the Bechtel analyses are summarized below:
o The shaft configuration lends itself to a simple dyramic model which adds assurance to the accuracy of the calcula-tion. The calculated first mode natural frequency has been i confirmed by results of the torsiograph test, while the ' predicted single mode shaft stresses are within the ' DEMA allowables. 28 i
, , ~. , - _ - - - - - - . _ , - - . , , , , - - , , . , , , , , - - , , _ . , , _ - , . - - - - _ _ . _ - - - . . - - ..
6.2 ~(Continued) o The harmonic coefficients, cylinder firing sequence, and engine configuration are such that the response of the major orders .of critical speed are minimized. The harmonic '~ coefficients have not been verified but it appears that a significantly detailed effort has been undertaken by TDI to provide accurate values.
~o The TDI analyais did not combine the response . from the -
various harmonics of a given mode and of other modes to calculate total stress. .. However, because of the expected-random ' phasing, the reduced effects of higher modes, the first mode stress margins compared to DEMA, and the torsiograph results..the total stress remains acceptable, o A comparison _of the Grand Gulf and Shoreham crankshafts has been - provided in Table 6-1. The improvement in 'the web area, fillet radius, properly applied counterweights, and shot-peened fillet radius surface finish provide for a significant reduction in stress concentrations. o The torsiograph results provide verification of front end angle of twist and an indication of shaft stress even though it is not a direct stress measurement. One important piece
- . of information suggested by the torsiograph tests is that the first mode dominates the response of the crankshaft.
This would tend to confirm TDI's use of first mode response to predict crankshaft stresses. , o To address the total stress in the circular portion of'the shaf t, - Bechtel performed an independent dynamic analysis using the normal mode method and applying modal superposi-tion (Reference 16). Five sets of harmonic coefficients were ' considered in the analysis with the most important. being the actual measured gas pressure values obtained from an engine of the same configuration and BMEP. The harmonic co- efficients used by TDI are in good agreement with-these derived from the measured gas pressure values. The results of the single order and total stress calculations are tabulated in Table 6-2 along with other crankshaf t stress results for comparison. o It should be noted that TDI's analytical crankshaf t _ stress determination is based on individual harmonics within a given mode. TDI did not determine the stress for a specific harmonic due to the response of all modes, or to sum the effects of all harmonics and stresses from ~ experimental
. shaf t ' deflection measurements to which a theoretical de-flection/ stress relationship was applied. The theoretical
-deflection /st'ress relationship is based solely on the characteristics of the first mode, whereas, the measured
- deflection includes the response of all modes.
29
._ _ _ . ~ . _ , _ - _ . _ _ . . _ _ _ _ _ . . _ _ _ . _ . .
6.2 (Continued) o The value of overall stress reported by FaAA for the , Shoreham crankshaft represents the average stress taken over the peak stress excursion. To provide a meaningful com-parison a similar average stress was computed by Bechtel for the GGNS crankshaft. An average stress is a useful value for comparison with DEMA standards since the measure of stress reversal is directly related to fatigue life. The peak stress . calculated by Bechtel for GGNS crankshaft is 6034 psi. Both the peak stress and the averaged reversed stress for the GGNS crankshaf t are within the limits for allowable stress published by DEMA. More importantly it should be noted that the total GGNS crankshaft stress is lower than the FaAA calculated stress for the new Shoreham crankshaft, even though the rated output of the GGNS diesel is twice that of the Shoreham diesel. As a' further verification of crankshaft adequacy, during December, 1983, and January, 1984, the Division I and II engines were disassem-bled for maintenance and replacement of existing piston skirts with improved piston skirts. The Division I and II crankshaf ts were in-spected using accepted NDE methods. No rejectable indications were discovered. All the rod bearing journals were examined using a liquid fluorescent dye penetrant process. The entire journal surface was inspected with particular attention to the journal fillets. All linear indications were evaluated with respect to integrity. The results of the examina-tion are shown in Table 6-3,
6.3 CONCLUSION
S The method of analysis used by TDI has been reviewed and is in accord-ance with industry standard practices. Additionally the total stress values not addressed in TDI analysis have been calculated based upon measured gas pressure input and are shown to be within the DEMA limits.- Liquid penetrant examination has shown no defects to exist on the journal fillets. The total stress analysis results are lower _than DEMA recommendations and when combined with acceptable liquid penetrant examinations alle-viates the concerns over the design adequacy of the CGNS crankshafts. 30
9 '.. TABLE 6-1 SHOREHAM AND GGNS CRANKSHAFT DATA Shoreham R Series Grand Gulf RV Series Web Width. 21 in. 25 in. Web Thickness 4 1/2 in. 5 1/8 in. Web. Shape Flat Sided Round Crank Pin Dia. 11 in. 13 in.
' Fillet Radius 1/2 in. 3/4 in.
Fillet Finish Not Shot Peened Shot Peened p P 4 f 31
/
TABLE 6-2 CRANKSHAFT STRESSES AS REPORTED BY VARIOUS ANAI.YSES Single Order Stress (psi) Total Average Stress (psi) Crankshaft Bechtel FaAA TDI Bechtel FaAA TDI Sh:reham (11" pin) - 5790(15) 4570(2) - 8910(15) 5314(2) Shoreham (12" pin) - 3300(I ) 2990(17) - 5640(17) 4208(2)
- G3NS (13" pin) 2389(16) -
1967( } 5084(10) - 3507(2,4) General Comments: (A) DEMA limit for single order stress is 5000 psi and 7000 psi for the total stress. (B) References to the source of information are identified in parentheses. (C) .The differences between the TDI and Bechtel calculations is primarily due to Bechtel's summation of stresses from all modes (modal superpositions) and TDI's method of including only harmonics with a single mode. j 32
1, _. 1 l l l l i TABLE 6-3 CRANKSHAFT LIQUID PENETRANT INSPECTION RESULTS Rod Bearing Journal Nurber Inspection Results Div I All Journals Indications were present - evaluated as wear surface marks and marring caused by micrometer measurements. No apparent defects. Div II
#1, #2, #3 Indications were present - evaluated as wear surface
#4, #5, #6 marks and marring caused by micrometer measurements, and #8 No apparent defects.
Div II 4 of7 No indications present - No apparent defects 33
FIGURE 6-1: Crankshaft Comparisons . 13* CRAfEPIN gg CRANMPIN i3' SHAFT 1
- y S 1
sf SHAFT
'~~~
2 - - CouMTEr. WEIGHT g
~
'l I .
A c ^JI $ I T3 e
.4. - ) )
) _
\
N - 4 6 SHOREHAM - REPORTED NO COUNTERWElG;tTS ROTATED 90* GGNS CONFlGURATlON z SHOREHAM CONFIGURATION i
#2 4:3
( #4' 4 S S6
>A *' '
.3 q>
-<n p- ct j
l C- , i g, i. _ b; i hI a 3 ij
. _ _ --j. i' 16 CYLINDER M-ss3s a u-653.0 i
'r -
'h-i:
l
- - - - - ~ - -
-k- --- 1 '-- ~ ~
ll ' . r ~
.imm W L..nsd '
sr=>n ! ---- - M i'
~
--..~. - - . .- - - . - .
r 7.0 'L.P. FUEL LINE FAILURE
7.1 DESCRIPTION
On. September 4, 1983,the Division I D/G was started for maintenance operation. The_ engine was manually stopped and the outside fresh air fans secured when a fire was reported at the engine. The fire was
' caused by a break in a piece of 1-inch fuel oil supply header. The break sprayed fuel oil onto the exhaust gas piping to the left bank turbocharger. Closer examination revealed that the tubing cracked circumferential1y along a line between the two ferrules of the Swagelok connector which connects the 1-inch tubing to the cross connect pipe between the the right and left bank fuel oil supply lines. The fire required extensive rework and replacement of various components.
7.2 ENGINEERING EVALUATION The three possible causes of the tubing failure which were identified in.the analysis by Middle huth Services (Reference 6) are as follows: ? (1) improper tubing material. (2) improper fitup and assembly of the tubing connector, and (3) vibration loading. (1) The strength of a Swagelok type connection depends on controlled deformation of the' tubing - between the body of the connector and
~
i the front. and back ferrules. Consequently, the tubing must be ductile enough to deform significantly without cracking. Swagelok recommends .an ASTM' A179 material. Hetallurgical analysis revealed that the tubing composition, hardness and ductility were all within the specified ranges for ASTM A179 r material and that the tubing was acceptable for the application. ' The 0.049-inch tube wall was the minimum recommended by Swagelok,
.but more than adequate for the operating pressures. The tubing was replaced with Delaval standard spares.-
(2)- A Swagelok representative fron..the Oakland Valve and Fitting Company, inspected the failed tubing and the associated Swagelok connector which had been sectioned for analysis. The Swagelok representative stated that the tubing had been properly deformed and that fitup or assembly problems would have been very un-likely. The Swagelok fitting was replaced with Delaval standard spare material. (3) Vibration and fatigue were the most likely causes of the failure. The ' assembly of the Swagelok fitting forms a small' ledge which acts as a stress concentrator. There were no supports on this section of tubing, although Delaval drawing 02-450-13 shows a clamp or support as item number 7. i 35
. . - - , , ., ,y - ,-----.,ry_._ y-,-,__.-,,,,,,7.- .,.,,-e-.-ww y-- ,,wr- '-'r'- -- *P--*-+-=*'
I l l l (3) (Continued) l l Analysis revealed no evidence of cracking at the other end of the tubing at the fuel oil filter Swagelok connection. The crack in the failed section of tubing initiated at the root of the ledge. The crack was initiated and propagated by high cycle fatigue mechanisms. This particular section of tubing had been subjected to unusual vibration loading by a defective left bank turbo-charger. The root cause of.the failure was determined to be the unusual vibra-tion loads imposed by the defective turbocharger combined with the i absence of any supports to isolate the Swagelok connector from vibra-tion . loading. The defective, out-of-balance turbocharger (combined with a period of operation after the turbocharger mounting bolts were discovered to be loose) is suspected as the initiating source of vibration. The fuel oil header, to which the failed tubing section connects, is mounted to the turbocharger mounting pedestal. This turbocharger, however, was replaced prior to the ultimate failure of
, the tubing which resulted in the fire.
7.3 CORRECTIVE ACTIONS MP&L designed and installed a tubing support for this section of tubing on both standby diesels. In addition, following completion of
-all rework related to the fire, the engine was subjected to a mainte-nance run to verify that all components were functioning properly.
During the maintenance run, the engine was instrumented for vibration analysis. The results of the vibratory analysis ' revealed that the engine exhibited vibration levels which were well within the limits which could be expected . from this type of machinery. These actions were described to the NRC in Reference 12.
7.4 CONCLUSION
S The root cause of the low pressure fuel line failure was attributed to unusual vibration loading and the absence of any supports to isolate the . Swagelok conne'ctor from this loading. The corrective actions
.taken alleviates the loads imposed on these lines. Therefore, further failures-of these lines are not expected.
36
L . L
, s 8.0 H.P.-FUEL LINE FAILURE 8.I DESCRIPTION Shoreham experienced a failure of a fuel injection line during pre-operational testing. TDI . filed a 10CFR21 notification on July 20, 1983 to alert the NRC to a deficiency involving a possible draw seam on the ID of the high pressure fuel injection lines supplied on TDI
~
diesel generators. The tubing failures at Shoreham were attributed to the draw seam which acted as a stress riser and failed when subjected to repeated operating cycles (about one million cycles). At approximately the same time of the notification, a high pressure fuel injection line. on the GGNS, Unit 1. Division I diesel generator failed. An analysis of the failed tubing attributed the failure to the tubing manufacturing flaw. 8.2 ENGINEERING EVALUATION AND CORRECTIVE ACTION
-All.'of the GGNS D/G fuel lines were original equipment, except one on each division, and had been subjected to more than ten million operat-ing cycles. Therefore, they were considered free of defects of this type. The two lines that were not original equipment had been re-placed during startup testing because of leakage around the fittings.
One . of these two replacement -lines subsequently failed, as stated above, at approximately one million cyclee. Based on the results of an analysis performed by Middle South Ser-vices, .the failed tubing exhibited a - crack which initiated from a manufacturing flaw on the inside surface of the tube. The flaw, which ran-the entire length of the failed tubing section, was formed by a defective mandrel during the initial extrusion phase of the forming
~
~
process. - Additional rolling operations lapped over the flaw, which
.was about 6-8 mils deep. The fuel injection line operating pressure, which cycles between atmospheric pressure and about 5000 psi, provided the fatigue loading which produced cracks along the stress riser pro-vided by the manufacturing defect. The preexisting flaw acting with the fatigue stresses generated by the cyclic operating pressures pro-duced the failure. These evaluations and actions were described to the NRC in Reference 12,
8.3 CONCLUSION
S The TDI 10CFR21 notification indicates that the failures occur at approximately one million operating cycles and that fuel lines that
.have in excess of ten million operating cycles without failure are satisfactory. All of the original lines on the Division I rnd II
^
diesels . were. - therefore, considered free of internal flaws of this type because they have in excess of ten million operating cycles and have . not failed,- One line on the Division I diesel, the one that failed and was replaced, and one line on the Division II diesel were not original lines and were considered suspect. Replacement lines
-were ordered and installed in place of these two lines.
37
8.3 (Continued) This problem is, therefore, considered resolved for the GGNS, Unit 1 TDI diesels. e 38
9.0 CRANKCASE CAPSCREWS
9.1 DESCRIPTION
During the performance of a 24 hour run test on March 15, 1982, the Division II D/G tripped on a " Generator Differential" which was accom-panied by an observed electrical arcing flash inside the generator. In a subsequent inspection of the generator it was found that the stator insulation had been damaged and that a 15/16 inch capscrew head from a 5/8 UNC X 1-3/4' inch long capscrew had imbedded in the stator and damaged the generator. It was determined that the capscrew head was from a capscrew on the diesel's rear crankcase cover that had sheared off and entered the generator through the air gap on the end of the generator. The generator was replaced with a generator from Unit 2 and all rear crankcase cover capscrews on the Unit 1, Division I and II diesels, were replaced with new replacement capscrews. An independent lab performed an analysis (Referencu i) of the 42 capscrews removed from the Unit 1. Division I and II diesel genera-tors. A (eview of the analysis produced the conclusion that the failure mode was due to a low-stress fatigue front expanding from an initial small crack. It was also noted that the failed capscrews had a decarburized skin which may have contributed to the failure. On October 4, 1982, the rear crankcase cover capscrews were checked for the correct tightness (60 ft-lbs). Three of th'c capscrews on the Division II diesel generator were found to be less than 60 ft-lbs (20, 23 and 35 ft-lbs). Any capscrew not within i 2 f t-lbs of the 60 f t-lbs was to be torqued to within the acceptable range. When the capscrew that was found at 20 f t-lbs was tightened, it sheared off approximately one inch from the bottom side of the head before reach-ing 60 ft-lbs. 9.2 INSPECTION AND TESTING The Division II D/G was instrumented by Nutech in January of 1983 and data was obtained during an operational test run. The test data indicated that the highest vibration amplitude occurred during the startup and shutdown of the diesel, with capscrew stresses at 6000 psi. The vibration amplitude was much less during steady state opera-tion at 450 RPM, with the capscrew stresses at 3000 psi. However, the test results were inconclusive as to the root causes of the vibration sou ce. The present information indicates that the capscrews failed by a combination of metallurgical and transient vibration factors and that the failures are unique to the Division II D/G. 9.3 CORRECTIVE ACTIONS The main thrust of the corrective action taken was the design and installation of protective screens for the generator air gaps. The failure of the rear crankcase cover capscrew, by itself, would not 39
9.3 (Continued) prevent the diesel from performing its safety function. On the other hand, the entry of foreign material into the generator could cause failure, therefore, the screens were installed to protect against a similar mode of failure. At the same time fatigue resis-tant, high strength capscrews and tab washers were installed to extend the life of these capscrews. One of these capscrews was pulled from each division and subjected to destructive analysis. While there was no sign of crack initiation there were signs of frett-ing on the threads of the capscrew removed from the Division II D/G. The expected life of these capscrews has not been confirmed. After the metallurgical report is evaluated, the schedule for removing another bolt from the Division II D/G for analysis will be determined.
9.4 CONCLUSION
S Although MP&L is continuing to inspect the crankcase cover capscrews and isolate the source of cyclic loading, the possibility of failure of one of these capscrews no longer poses a threat to diesel generator operability due to the installation of protective screens on the gene-rator air gaps. 40
.=- . _. .
' 10.0 TDI PRODUCT IMPROVEMENTS TDI has a product improvement program which addresses both changes that are required to ensure diesel generator operability / reliability and changes :
that are developed to extend component life, allow easier maintenance operations, or use improved manufacturing techniques. The TDI program classifies changes as follows: (1) changes required to correct 10CFR21
-deficiencies, (2) changes developed to improve diesel generator performance or reliability (not as a result of a potential defect) and issued to custo-mers under TDI's Service Information Memo (SIM) program, and (3) changes developed by TDI.that are determined by TDI to b relatively insignificant to diesel generator operation and therefore do no necessitate immediate customer notification.
The TDI program of product improvement has included applicability reviews for the diesel generators installed at Grand Gulf and the applicable changes have been identified to MP&L (Reference 2). The TDI Nuclear Check List for. SIMS identifies those that are applicable to TDI diesels at nuclear stations. The thirty-three SIMs -identified by the list were reviewed by MP&L . to determine which SIMs could be considered product in-provements. Four categories; product improvement, instructions, informa-tion and guidelines were utilized for the review. Eight of the thirty-three SIMs reviewed were considered to be product improvements, nine SIMs as . recommended instructions, ten SIMs as informational and six SIMs as guidelines. . A listing of the'eight SIMs considered product improvements is provided in Table 10-1. Review of the vendor manual for the TDI diesels and other documents indicates that the eight product improvement SIMs have been incorporated on the Unit 1, Division I and II diesel generators. A continuing review will be performed for TDI SIMs as they are received to determine their applicability to the GGNS TDI diesels and appropriate actions taken, as deemed necessary. d w ~ 41
TABLE 10-1 TDI PRODUCT IMPROVEMENT SIMS SIM NO. SUBJECT 64 1. Increase link rod torque - 735 to 1050 ft/lbs
- 2. Increase rod bolt torque - 1 1/2 in bolt 1200 to 1700 ft/lbs 1 7/8 in bolt 1800 to 2600 ft/lbs
- 3. Product improvement designed to increase reliability
'4. Deletes SIM 270
- 5. Use in conjunction with SIM 332
- 6. Incorporated during "AF" piston skirt modification in November, 1981 307 1. Change in ring end gaps on new piston rings in 4 valve R & RV engines
- 2. Incorporated 313 1. Information on removing intake manifold supports on 4 valve RV engines to reduce oil leakage at the camshaft covers
- 2. Incorporated 324 1. Modification of type "AF" piston skirt
- 2. Incorporated on Unit 1, Unit 2 "AF" piston skirts have not been modified
- 3. The modified "AF" piston skirts have been replaced with the "AE" style piston skirts on the Unit 1, Division I and II D/Gs 324A 1. Information for reuse of piston crown studs
- 2. Incorporated 332 1. Never harder washers on connecting rod bolts RV engines
- 2. Incorporated 360 1. Information on possible problem of air start valve capscrews being too long
- 2. Incorporated on Unit 1, Div I and II, tracking document issued for Unit 2 361 1. Information on potential problem with commercial grade cable in certain engines and panels
- 2. Incorporated on Unit 1 Division I and II engines - Cable replaced with Class IE qualified cable, tracking document issued for Unit 2 42
11.0 QUALIFICATION / RELIABILITY TESTING 11.1 HISTORY 2 All the GGNS Unit I diesel generators have been tested and qualified in accordance with the requirements of. Regulatory Guides 1.9 and 1.108 and IEEE Std. 387-1977. The Division I and Division II engines were shop tested by TDI, including a 300 prototype test run on the Division I engine as required by IEEE 387-1977.. On-site testing was done by Bechtel and MP&L before fuel loading in June, 1982. Since then the engines - have ' been tested in accordance with the plant surveillance test procedures, as described in the plant technical specifications. 4 A special 7-day performance test was performed on both of the TDI engines : under a directive of MP&L management (Reference 10) before l the present maintenance and parts replacement work was started in December,-1983. To verify the operability and reliability of the Division I D/G following~the D/G rework after the fire the 18 month functional test ; was repeated for the Division I D/G. The 18 month functional test included the following:
- 1. Starting air receiver capacity test
- - 2. Testing of D/G trips and response to ECCS actuation signals
, 3. 100% load rejection
- 4. Simulated loss of offsite power followed by the loss of and restart of the D/G
- 5. Simulated loss of offsite power in conjunction with ECCS actuation signals
- 6. 24 hour load test
- 7. LOP /LOCA test This 18 month functional testing was completed. satisfactorily.
The following _ sections outline the recent tests that were performed on the Division I and II diesels following completion of maintenance work, before each of the two engines was returned to service. 11.2 REQUALIFICATION TESTING REQUIREMENTS Testing ' requirements for modifications to a previously qualified
-diesel generator unit are set-forth in IEEE Std. 387-1977. The recent
. maintenance and parts replacement work on the two TDI diesels had no significant impact on engine specifications and design criteria, related subsystems, .or engine performance characteristics. Nor, did these work activities involve changes in plant load characteristics 43 y m I
. d. - _.- _ _,. , - - . _ _ .... .-- .. _ ,=_ .,_ _.= _ .-- .- _ . _ _. - , _ - - _ _
I 11.2 (Continued) l l for the two TDI engines. No modification of the generator or related , electric or instrumentation circuitry was performed. Therefore, none l of the design considerations listed in Table-1 of IEEE Std. 387-1977 l were modified or altered. As such, the various tasks performed during the current maintenance activities were considered minor design changes aus defined by IEEE 387-1977 criteria. Appropriate testing was conducted to verify satisfactory operability of the engines. 11.3 REQUALIFICATION TESTING DESCRIPTION FOLLOWING PISTON SKIRT REPLACEMENT
'The requalification testing is described in the following section.
11.3.1 To perform TDI's recommended breakin run, following the installation of the "AE" piston skirts, the engines were started and run at 300 rpm and no load for about 15 minutes. During this run the D/Gs were inspected to ensure thac the rocker arms, valves, push rods, fuel injection pumps, nozzle holders. high ' pressure fuel injection lines and drip return headers were secure, functioning properly and that there were no fuel leaks. The engines were then stopped, the crankcase side door covers removed and various internal 4 components checked for indication of excessive heat. The covers were replaced and the engines run at 20% load for about one hour. After this run the engines were inspected as above. The engines were then run at levels varying
' between 25% to 100% load for approximately 8 hours. After this run' hot crankshaf t. web deflection checks were per-formed. The engines were then allowed to cool and another inspection as above was performed.
11.3.2 The load rejection tests were accomplished by performing Test #3 of Surveillance Procedure Nos. 06-0P-lP75-R-0003 and 06-OP-1P75-R-0004 " Standby Diesel Generator (SDG) 11 (12) 18 Month Functional Test". These tests demonstrated the capability to reject a full load (7000 kw) without exceeding speeds or voltages which could cause tripping, mechanical damage, or harmful overstresses. 11.3.3 In addition to the required testing, 24 hour run tests were ( . performed; 2 hours at 110% load followed by 22 hours at 100% load. These tests demonstrated the capability of the D/G to carry the rated load for an extended period. 11.3.4 The starting, load' acceptance and design load tests were accomplished by performing Surveillance Procedure Nos. 06-OP-1P75-M-0001 and 06-0P-1P75-M-0002, " Standby Diesel Generator (SDG) 11 (12) Functional Test". These tests demonstrated the ability of the D/G to start and reach rated frequency and voltage within 10 seconds after the start signal, the capability to be loaded to at least 100% load within 60 seconds and to operate for at least one hour at full load. 44
( 11.4 TESTING NOT REQUIRED FOR REQUALIFICATION , The main consideration in developing the requalification test program described in Section 11.3 above was that any engine component or subsystem that was replaced, modified or repaired would be adequately tested, followed by an integrated testing of the total diesel genera-
-tor system. ~Accordingly, an engine component or subsystem that was ,
not affected by the maintenance activities and was previously quali-fied, was not tested individually or in conjunction with engine test-ing. l 11.5 D/G RELIABILITY ENHANCEMENT TESTING MP&L has developed comprehensive maintenance programs and established operating practices to assure a high level of diesel generator reli-ability. This program was developed using vendor recommendations as well _ as good engineering practice and operating experience. This program covers the diesel generator as well as its supportive equip-ment. Critical diesel generator parameters such as jacket water temperature, lube oil temperature, jacket water standpipe level, generator bearing oil level, turbocharger lube oil flow, starting air pressure, heater
-operation, and alarm checks are performed once per 8 hours; while other various supportive equipment is checked once per day by the
_ Operations Department. These checks will assure that the diesel generators are in - a satisfactory state, and that potential problems i are identified. During the monthly surveillance test, operating parameters are checked to verify that the diesel generator is operating as required. The
- generator operating parameters monitored are voltage, amperes, fre-
_quency, VARS, DC volts-field, DC Amps-field, RPM and watts. The engine operating parameters monitored are lube oil temperature and pressure, Jacket water temperature and pressure, turbocharger lube oil pressure, lube . oil filter differential pressure, fuel oil pressure, fuel oil filter differential pressure, combustion air pressure, crank-case vacuum, RPM cylinder temperatures, and exhaust stack tempera-
-tures. The monitoring of these parameters aids in detecting any prob -
less which would affect engine operation and reliability. 11.6 ADDITIONAL DEMONSTRATION TESTS *
-Since the discovery of the failed crankshafts at Shoreham, additional
~ testing / monitoring of the D/Gs at Grand Gulf has been implemented (Table 11-1). This includes the completion of a 7-day equivalent test
~
run on both D/G units, 24 hour run tests (22 hours @ 100 percent and 2 hours e 110 percent power),Ladditional miscellaneous 100 percent power tests, monitoring of vibration levels by Technology'for Energy Corpo- ' ration (Reference 8), increased emphasis on pre-action planning sessions for persons involved in planned operational and maintenance
. activities and an improvement in the working relationship with TDI (Reference 10 and 11).
i b 45
TABLE 11-1
SUMMARY
OE QUALIFICATION AND VALIDATION TESTING TESTING PRIOR TO INSTALLATION OF "AE"- DEMONSTRATION PISTON SKIRTS REQ SURVEILLANCES . Qualification Testing (I) X Preop Testing ( X
. Tech Spec Testing (3) X
. 4%' 9 18 ONTH FUNCTIONAL TEST, DIVISI_0N I D/G 7-Day Equivalent Test X Vibration Test Runs X "AE" PISTON SKIRT INSTALLATION Piston Inspection X Crankshaft Inspection X Rod Bearing Inspection X TESTING FOLLOWING INSTALLATION OF "AE" PISTON SKIRTS Break-In Run X Load Reject X 24-Hour Run - 2 Hr @ 110%, 22 Hr @ 100% X Additional 100% Power Runs X Monthly Surveillance X X (1) Qualification Testing includes 300 Start Prototype Tests Performed by TDI. (2) Includes Starting, Load Acceptance, Overload, Design Load, Rejection, Reliability, Electrical and Subsystem Tests. (3)- Includes Monthly Surveillance and 18 Month Functional Tests. 46
;( __ -. . . - .= - - - . - - - . . - _ ~ .- . - -- . _.
12.0.SUHFRY f Spec'ific actions have been taken to correct problems identified during testing of the Division I and II TDI diesel generators and to also evaluate and resolve problems identified to MP&L as a result of experience with TDI diesel generators at other nuclear installations. Significant actions that have been completed, or are planned, are as follows. o The suspect modified type "AF" piston skirts in the Division I and II_ D/G have been replaced with new type "AE" pistons. The i new type "AE" piston skirts were inspected prior to installation to ' assure they were free of the type of rejectable indications found on the type "AF" piston skirts and to establish documented , baseline data for the new skirt. These actions serve to enhance , the reliability of the GGNS Unit 1 TDI diesel generators. o During removal of cylinder heads on the Division II D/G the stellite overlays on the exhaust valve seats on the #5 right bank
- . cylinder were discovered to have cracks. There was also incom-plate fusion on the intake valve seat of the #1 left bank head.
Inspection of the Division I heads found six with rejectable in-
'dications. The eight heads with rej ectable indications were ! replaced with heads that had no rej ectable indications. To
- address a long term concern, a failure investigation has been initiated to determine the cause of the crack initiation and the crack propagation mode.
o As a result of the. connecting rod bearing failure identified at Shoreham, MP&L initiated an inspection of the connecting rod bearings and connecting rods during the scheduled piston replace-ment on the Division II D/G. The inspection results indicate that the integrity of the bearings is good and not affected by previous service. A final analysis for chemical and physical properties is planned. E o Numerous weld failures between the D/G connector push rod ball and tube have been discovered. MP&L concluded that it was not i likely that a failed push . rod would - result .in engine failure. However, during a recent inspection one of the push rod balls was cracked in addition to the weld cracks. _At this point a new re-placement design was pursued. The new design has been determined-
--to be acceptable by MP&L and replacements have been installed in the Division I and II diesels.
o Due to the crankshaft failure at Shoreham an engineering evalua-tica of differences in design between the Shoreham and GGNS TDI ~ diesel crankshafts was performed. This evaluation shows that the potential for the type of failure experienced at Shoreham does not exist at GGNS. During the piston skirt replacement the Division-I and II crankshafts were inspected. These inspections did not indicate defects of the type found at Shoreham. 47
,_ _, - _ _ _ _ _ - - - . , _ . ~ _ _ . _ _ _- 7
12.0 (Continued) o A fire in the Division I D/G room on September 4,1983 was determined to be caused by the break of a low pressure fuel oil line. Analysis indicated that.the line break was caused by a combination of unusual vibration loads imposed by a turbocharger that had been replaced several weeks before the fire, and the absence of any supports to isolate the Swagelok connector from vibration loads. Tubing supports were designed by MP&L and installed on the Division I and II diesel-generators. o 'A 10CFR21 notification to the NRC by TDI dated July 20, 1983 identified a possible draw seam on the ID of high pressure fuel oil lines supplied on the Division I and II D/Gs. 'A high pressure fuel oil line on the Division I D/G also similarily failed. An analysis of the failed tubing attributed the failure to a manufacturing flaw (draw seam) in the tubing. The TDI letter of July 20, 1983 indicated that the failure occurred at approximately one million operating _ cycles and that fuel lines that have in . excess of ten million operating cycles without failure are acceptable.. Using this rationale, all of the original lines on the Division I and II D/Gs were considered to be free of flaws of this type, however, the replacement for the failed line and one line on the Division II diesel were not original lines and were considered suspect. Replacement lines were ordered and installed in place of the two suspect lines. o The generator on the Division II D/G was damaged and replaced in mid-year of 1982 when a head from a capscrew on the rear crank-case cover sheare.d off and entered the generator via the genera-tor air gap. Protective screens have been installed on the Division I and II generator air gaps to prevent recurrence of damage to the generator from an incident of this type. Subse-
-quent testing indicated that the problem of the capscrew shearing
~
was unique to the Division II D/G and that the failure was due to low stress high cycle fatigue, however, test results were incon-clusive 'as to the root causes of the vibration sources. High strength capscrews and tab washers were installed to extand the life of the capscrews. Periodically a capscrew will be removed from the crankcase covers and subjected to destructive analysis in an attempt to obtain further information for identifying the root cause. o Following piston skirt replacement, qualification / reliability testing in accordance with IEEE Std. 387-1977 was performed on the Division I and II diesel generators. Testing of the D/Gs prior to this planned maintenance included the_ satisfactory com-pletion of a 7-day equivalent test run on both D/Gs. Post main-tenance testing included breakin runs, twenty-four hour runs, load rejection tests and surveillance tests. 48 3
13.0 CONCLUSION
~In conclusion, the specific corrective actions, engineering evaluations and testing that have been completed, enhance the reliability of the D/Gs and provide assurance, with a reasonable level of confidence, that the GGNS TDI engines will adequately perform their required safety function.
s 4 49
1
14.0 REFERENCES
i
- 11. FaAA Preliminary Report on GGNS Modified AF Piston Skirts.
'2. TDI Letter Dated.12-15-83 " Nuclear Power Plant Standby Diesel ;
Generator User's Group Minutes of November 30, 1983, Meeting".
- 3. . Metallurgical Evaluation of Diesel Engina Purh Rod Weld From Grand Gulf Nuclear Leation-Unit 1 Emergency Diesel Generator (Division I),
prepared by Middle South Services. 4.- TDI Response to MP&L.for NRC Request of Additional Information on TDI , D/Gs, Dated November 2, 1984. i
- 5. Preliminary Standby Diesel Generator Crankshaft Design Analysis Review Grand Gulf Nuclear Station, prepared by Bechtel Power Corporation.
- 6. Metallurgical Evaluation of Diesel Engine Fuel Oil Line Failure from Emergency Diesel Generator - Division 1. Grand Gulf Nuclear Station -
Unit 1, prepared ~ by Middle South Services, i
- 7. _ Metallurgical Evaluation of Diesel Engine Fuel Injection Tube from Grand Gulf: Nuclear Station -
Unit 1 Emergency Diesel Generator
' Prepared by Middle South Services. ,
- 8. Test Evaluation Report on the Grand Gulf Nuclear Station Division I
.and Division II Diesel Generators (TEC . Report No. R-83-033), prepared by Technology for Energy Corporation.
9.. ? Engineering Investigation of the Failure of Rear Crankcase Cover Capscrews,for the Delaval Standby Diesel Generators at MP&L, GGNS, , LETCO Job No. G-8847, Dated August 17, 1982, by Law Engineering t Testing Company..
- 10. PMI 83/12569, J. P. McGaughy.to J..B. Richard Letter on D/G t Enhancement.
11.. PMI 84/0210, J. E. Cross to J. F. Pinto Letter on Plant Staff Response to NRC D/G Questions.
~12. AECM-83/0689 -JGCNS Diesel Generator Reliability Report, October 26,
+' 1983.-
- 13. fAECM-83/0724, GGNS Diesel Generator - NRC Request for Additional
.Information, November 15, 1983.
-14. AECM-84/0030, GGNS Diesel Generator - NRC Request for Additional
_ Information, January, 18. 1984.
~
- 15. FaAA-83-10-2 PA07396 - Emergency D/G Crankshaft Total Stress Analysis
. Summary, February 2, 1984. > 50
,, .v-c., ~ -c ,,,e , . , , , , . . - . , + . - - . _ - , . . ~ -- - . , - ~ , , ,..,- _ . . , , , , , - -
14.0 (Continued)
- 16. Bechtel Standby Diesel Generator Crankshaft Total Stress Analysis
. Summary, February 2, 1984.
- 17. FaAA-83-10-02 PA07396, Analysis of the Replacement Crankshafts'for Emergency Diesel Generators, Shoreham Nuclear Power Station, October 31, 1983.
- 18. FaAA-83-10-16, PA07396, Emergency Diesel Generator Connecting Rod Bearing Failure Investigation Shoreham Nuclear Power Station, October 31,-1983.
- 19. AECM-83/0653, Applicability of Shoreham Diesel Generator Crankshaft Failure to GGNS, October 14, 1983.
l l l t I I 51
, . . .,, . . . _ . .__ . _ . _ _ . _ _ _ _ _ - . _ . _ _ _ _ _ . ~
ATTACHMENT 1 TO THE FINAL REPORT ON GGNS DIVISION I AND II TDI DIESEL GENERATORS RESPONSES TO SIXTEEN POTENTIALLY SIGNIFICANT PROBLEMS IDENTIFIED IN TDI OWNERS GROUP MEETING WITH THE NRC ON JANUARY. 26, 1984 4 FEBRUARY, 1984 52
1.0 INTRODUCTION
A meeting of the Transamerica Delaval, Inc. (TDI) diesel generator (D/GS owners group with the NRC Staff was held on January 26, 1984. During the meeting the owners group presented a slide summarizing significant potential probler.s with TDI diesels. These potential problem areas are detailed below: o Crankshaft o Connecting Rod Bearings o Pistons o Cylinder Heads o Cylinder Liners o Cylinder Block o Engine Base o Head Studs o Push Rods o Rocker Arm Capscrews o Connecting Rods o Electrical Cable o Fuel Injection Lines o Turbocharger o Jacket Water Pumps o Air Start Valve Capscrews Further details of these concerns, their applicability to Grand Gulf, and their resolution are described in the following sections. 53
2.0 CRANKSHAFT A summary of the concern and its resolution on Grand Gulf is provided in Section 6.0 of the Final Report. 3.0 CONNECTING ROD BEARINGS A summary of the concern and its resolution on Grand Gulf is provided in Section 4.0 of the Final Report. 4.0 PISTONS A summary of the concern and its resolution on Grand Gulf is provided in Section 2.0 of the Final Report. 5.0 CYLINDER HEADS A summary of the concern and its resolution on Grand Gulf is provided in Section 3.0 of the Final Report. 6.0 CYLINDER LINERS
6.1 DESCRIPTION
A concern has been raised regarding cylinder liner damage in TDI D/Gs. One incident was listea for GCNS, AECM-82/157, dated April 15, 1982, transmitted the final report on PRD-81/45 dealing with the separation of piston crown from the piston skirt during testing of the Division II D/G. An additional deficiency noted in this report was damage to a cylinder liner on the Division I D/G. The damaged cylinder liner was discovered during disassembly of the Division I D/G for corrective action for the piston skirt / crown separation. The damaged Division I cylinder liner was found to be grooved in three places. These grooves were approximately 10 inches long and 1/16 inch deep. As indicated in the PRD final report, the grooving was probably caused by debris that entered the cylinder during assambly or initial startup. 6.2 ENGINEERING EVALUATION AND CORRECTIVE ACTION The grooved cylinder liner was replaced with a new liner. The Division I lube oil was flushed and replaced and the lube oil sump was cleaned. At a meeting between MP&L, LILCO and TDI on February 2, 1984, TDI indicated that the only case of a cylinder liner failure occurring without sotne other initiating event causing it, occurred on the ship 54
7 6.2 (Continued) Columbia. This damage was attributed to the high vanadium content of the light-heavy fuel oil and the high ash content of the lube oil (heavy _ oil) . Despite the . cracking of the liner which resulted from the use of these oils, the engine continued to perform its function. The CGNS TDI diesels use light fuel oil with a lower vanadium content and utilize light lube oil. During the piston skirt changeout on the GGNS Unit 1 TDI engines, the cylinder liners subjected to a close visual inspection before and af ter having the liners to receive .the new rings. No obvious damage was discovered during these inspections.
6.3 CONCLUSION
S Based on lube oil cleanup efforts, recurrences of the subject problem is considered to be resolved. To date, no known cylinder liner fail-ure has been the root cause of a TDI engine failure. Neither liner material, manufacturing process _ nor design are con-sidered to be the root cause ' of the damage on the Division I GGNS engine. Inspections of the Division I and II D/G cylinder liners during the piston skirt changeout did not reveal any indication of liner damage. Based on the above conclusions and root cause, cylinder liner failure is not expected to occur at GGNS. 7.0 CYLINDER BLOCK
7.1 DESCRIPTION
The non-nuclear industry has reported cracks occurring in the area around the cylinder liner landing. Cracks may also propagate from the head stud / stud bore.to the jacket cooling water passage. 7.2 ENGINEERING EVALUATION
- If this cracking -were to occur and propagate into the jacket water j passage it would be possible for an extremely low flow of jacket cooling water to come into contact with the head studs and cylinder head. This flow would be prevented from entering the cylinder by two spiral wound head gaskets. It is unlikely that jacket cooling water would enter the firing chamber (cylinder) and only a very slow loss of Jacket cooling water to the outside of the engine would be evident.
To prevent this cracking TDI has indicated that proper torque must be placed on the cylinder head studs. 55
p I..( y: , . 7.3 CORRECTIVE ACTION AND COMCLUSIONS MP&L considers that no corrective action is required for these condi-tions, since the postulated condition would not interfere with the operation of the engine and because the proper torque of 3600 foot-
. pounds, as reconenended by TDI, has been applied to the head studs of the GGNS Unit 1 TDI D/Gs.
d I 56
. .~ ~ . , - . . _ . _ _ . _ . - -
- 7. - -
J
\a; \ < (i 8.0 ENGINE BASE
8.1 DESCRIPTION
Linear indications have been found on the bearing base journal of
. several . marine diesel engines. These indications were apparentiv caused by improper torquing of the bearing holddown studs during assembly of the engine.
8.2 CORRECTIVE ACTION TDI issued SIM #286 to correct this problem. This fix resulted in an increased preload being placed on the holddown studs. 8.3 : CONCLUSIONS Grand Gulf's TDI D/Gs were assembled after SIM #286 was issued. GGNS
. installation of main bearing bolt nuts, as witnessed by GGNS Plant Quality, indicate that correct preload values were verified during recent engine disassembly.at the site on all main bearing studs. This problem, therefore, is net expected to occur at Grand Gulf since no defects have been repori .d to have occurred in engines using the proper. torque.
9.0 HEAD STUDS
~ This concern is related -to the cylinder block concer's described in Section 7.0 of this Attachment. Refer to this section for further details.
10.0 PUSH RODS A summary of the concern and ' its . resolution on Grand Gulf is provided in Section 5.0 of the Final Report. 11.0' ROCKER ARM CAPSCREWS
11.1 DESCRIPTION
Shorkham : has L experienced problems recently with fatigue failure of rocker arm capscrews. . 11.2 ENGINEERING EVALUATION AND' CORRECTIVE ACTION t" . These- failures were apparently caused by undertorqued poor quality capscrews. New polished capscrews made of ASTM A-193 material were
- installed to correct the problem.
n
+ .- -.4 r - _.,-_,-----,,.se . -.~v.-~, -y -e. . , - _ . . . - - , -_
7 y-. y nw, y,...'f' *'T Y*? P-T v 'r**-77
. - _ - ~ _ . _ _ _._ _ - - _ _ - _ . . _ _ _ . . _ ___ ,y __ . - _ - - . - _ - - = _ _ _ _
1
11.3 CONCLUSION
S GGNS rocker arm capscyews have not experienced this type of failure after greater than 10 cycles of operation. Since these capscrews are I original components of the diesels, and have been properly torqued to 365 ft-lbs, no failures of the type are expected. 12.0 CONNECTING RODS
12.1 DESCRIPTION
4 TDI has informed MP&L of several incidences of connecting rod failure. At a meeting between MP&L, LILCO and TDI, on February 2, 1984, TDI defined the historical problem with connecting rods. Cracking of the. connecting rod link assembly in a master rod-longitudinal plane
~ through the bottom of upper bolt holes (See Figure 12-1) has ' occurred on several non-nuclear applied diesel engines built by TDI.
i 12.2 ENGINEERING EVALUATION AND CORRECTIVE ACTION TDI Vee-type engines of a comparable size to GGNS Division I and II ' utilize either 1 1/2 or 1 7/8 inch connecting rod bolts. The original design of the GGNS engines (TDI's earlier design) uses the larger of
. , the two bolt eizes. ' TDI originally specified that these bolts should W" be torqued to 1800 foot-pounds.-
. TDI initiated an evaluation of the - problem based on the operating
.1- ,
' history of the engines with failed or cracked connecting rods. For example, several instances of connecting rod cracking were reported to
\ .
;;; have' occurred in a marine. diesel on the ship Columbia. The average
. hours of operation between occurrence'was approximately 10,000 hours.
l ,
. Evidence of fretting in _the " rack-teeth" almost always accompanied
- connecting rod failure or cracking.
[ t, -The first design change to reniedy the situation was a decrease in the
', 1 connecting rod bolt diameter to 1 1/2 inches. Decreasing the. connect-
, ing rod bolt diameter effectively increased the amount of base metal whern cracking was occurring. Since the cause of the cracking was
! . x. '
'thoeght to be . relative motion between the ro i parts and flexure of
~
connecting rod parts, an increase in the base metal adjacent to the 4' ,
. crack initiation site should increase stiffness and hence decrease b
o
. incidence of cracking or failure.
P
- A de.creasefin' cracking. frequency was noted. However, connecting rods
% .w ? . - using both 1 1/2 and 1 7/8 inch bolts were still reported exhibiting
%' ^
cracking._ It was then thought that fretting of!the " rack-teeth"'was U s .due to. lack of' clamping force between the connecting rod link and the master rod and box _ assembly. TDI : issued- Service Information Memo
"(SIM) .64 to - rectify . the suspected - clamping force problem. SIM 64 m . effectively increases- the required torque on 1 1/2 and 1 7/8 inch
! connecting tod bolts from 1200 to 1700 foot pounds and from 1800 to
. y 2600 foot-pounds', respectively. This denign change greatly reduced theireported cases of connecting rod cracking. ,,
W
* ~
2 7, - n 58
~E 9"
, m., N lR 2 , . . , . . . ; , ,J, m._,.m__ _ __.._ . , _, , ,,, m, , _ , _ . , . . . _ _ _ . _ , _ _ _ _ , , _ , _ _ , _ , . . . _ ,
12.2 (Continued) The GGNS Division I and II engines were originally assembled at the vendor's shop using the pre-SIM 64 torque values. Therefore, the GGNS engines have been run part of the present total sum times with the connecting rods torqued to pre-SIM 64. torque values and the balance at post SIM 64 torque values. The table below indicates the approximate run times on the Division I and II engines before and after SIM 64 was implemented: Division I Divialon II At Assembly 0 0 Before SIM 64 332 44 After SIM 64 939 768 Present Run Times 1271 812 At a recent TDI D/G owners group component selection committee meeting, the owners group diesel generator specialists agreed that the type of cracks reported by TDI would propagate very slowly. The cracking of connecting rod parts on non-nuclear diesel engines were reported to have occurred at relatively large run times (greater than 10,000 hours).
12.3 CONCLUSION
S To date,.all engines using the 1 7/8 inch connecting rod bolts exhi-biting failures or cracking have been suspected of being under-torqued. .Further, no known failures have occurred on connecting rods using 1 7/8 inch bolts that were properly torqued. All torques used on the subject bolts at GGNS have been verified to be in accordance with SIM 64. Based on low probable propagation rate of incipient cracks, relatively
-low run hours on Division I and II at pre-SIM 64 torques, and the expected low future run times, (estimated 200 hours / year) cracking of the GGNS connecting rods is'not expected.
59
. . l 113.0. ELECTRICAL CABLE )
13.1' DESCRIPTION
' Memo (SIM) No.'361 concerning certain Class 1E cable which failed the IEEE'383-1974 insulation flame test was issued by TDI. The content of
- this SIM-is' detailed in Tablez 10-1. This SIM identified the affected cable as being the shielded cable from the terminal block to the Air-pax. tachometer relay in the engine control panel, the shielded cable from the Airpax magnetic pickups to the junction boxes on the side of the engine and the multiconductor cable from the engine side mounted
. junction box.co the Woodward governor actuator.
Another notification from Delaval received by MP&L on October 20,'1983 (API-83/0974),:idicated that the manufacturer's temperature rating for the cable _ insulation may be exceeded during operation of the diesel generator.. Delaval recommended that these cables be replaced with 90*
- rated cable.
- 13.2 ENGINEERING ~ EVALUATION AND CORRECTIVE ACTION It.was determined by Nuclear . Plant : Engineering that this potential deficiency could create a substantial safety hazard. A Design Change Package (DCP-82/3196). was : implemented for Unit 1 in which the in-stalled commercial. grade shielded cable on the Division I'and II D/Gs was replaced with Class 1E IEEE 383-1974 qualified cable.
- Further ' investigations into_ the problem subsequently revealed that
'Bechtel Design-Specification M-018.0, Section 6.8.2.6, calls for com-pliance~with Design Specification Appendix N which requires compliance with IPCEA Publication No. S-19-81, Section 6.
- InrespondingtoANI-83/0974 it was determined that the affected cable
.had previously'been replaced on the~ Unit 1. Division I and II'D/Gs.
Therefore, no further: action-was initiated for Unit-1. Bechtel has issued NCR 6762 to track this' concern.for_the Unit.2 D/Gs.
13.3 CONCLUSION
S This. issue is considered closed for the Unit 1.D/Gs. The replacement electrical, cable meets the appropriate requirements of IEEE 383-1974 and TDI's recommended temperature rating. 14.0 FUEL INJECTION LINES-A' summary of the corcern and. its resolution on Grand Gulf is provided in Section 8.0 of'the Ti u t Report. A 4 6
- 60
15.0 TURBOCHARGER
15.1 DESCRIPTION
+
t Turbocharger vibration has been identified as the cause of several problems with D/G engine mounted components. Turbocharger abnormalities resulted in broken mounting bolts. When
..the turbocharger is not anchored correctly, the intercooler and the jacket water piping ara forced to partially support the turbocharger and thereby absorb a larger amount of fatigue stress. This stress would normally be absorbed by the turbocharger mount. Since neither of -these two auxiliaries - was designed to support the turbocharger, they both developed cracks and broken welds.
c ' Table 15-1 presents a summary of past problems, causes, and corrective action taken. Further details are provided below: 15.1.1 CRACKED WELDS AND BASE METAL ON INTERCOOLERS Cracks developed in the base metal on the top of the inter-cooler along an extruded seam. This sean. has since been redesigned by.'Delaval and a piece of flat bar stock welded over the top _of the extruded vee shape to stiffen it. The stay' rods extend from one side of the intercooler to the other through a heavier block of steel on the outside. The rod is then welded to this heavier block, this is the weld which- broke on the right bank intercooler. Several other stay rods were observed to have deficient welds and were also cut out and rewelded. 15.1.2 . CRACKED WELDS ON JACKET WATER PIPING There were several cracked welds which developed on flanges and fittings where the jacket water system ties into the turbochargers. Since more'than one repair was necessary_the header was refabricated using standard pipe, fittings, and ASME Section III Welding & NDE Criteria in order to work l with codes with which MP&L maintenance and engineering l personnel were acquainted.- L 15.1.3 LOW PRESSURE FUEL OIL HEADER FAILURE On September 4, 1983.-the main fuel -oil line feeding the Division I engine headers failed due to fatigue. The oil sprayed onto the turbocharger exhaust gas hader transfor-mation piece - and ignited. All affected components were repaired or r'eplaced. The failed' tube and.Swagelok fitting were subjected to a metallurgical evaluation, and the cause L .of the ' failure was identified as high cycle fatigue com-pounded by the absence- of tubing supports. Further dis-cussion is provided in Section 7.0 of this final report. 61
i I 15.1.4 INDUSTRY EXPERIENCE l Turbocharger problems at other nuclear plants have also been experienced. Recently, Shoreham has experienced a failure of turbocharger thrust bearing in two of their engines. 15.2 ENGINEERING EVALUATION AND CORRECTIVE ACTION The Division _ I D/G left bank turbocharger has exhibited signs of unusual vibration and misalignment in the past. Improper turbocharger alignment and running of the engine with broken / missing turbocharger mounting bolts, has produced conditions conducive to fatigue crack initiation and propagation in adjacent supports and components. During the rework of the Division I engine after the fire, the turbochargers were removed and re-seated twice before proper fitup was attained. The result was an engine that had no noticeable areas of high vibrations, as attested to by Technology for Energy Corporation when they instrumented the Division I and Division II engines after the fire rework was completed. Thrust bearing failures similar to these at Shoreham have not been identified at GGNS and are not expected because of the differences in design of the lubrication systems. The failures of the turbocharger - thrust bearings at Shoreham have been attributed to probable lack of lubrication during manual engine starting. Shoreham's TDI D/Gs lube oil systems utilized two lube oil pumps, one
.an engine driven lube pump and the other an electric driven lube oil heater pump (See Figure 15-1). GGNS's system is apparently unique to
.us and one other DSRV-16-4 in that our D/Gs lube oil system utilizes three lube oil pumps, one an engine driven lube oil pump, one an electric driven lube oil heater pump and the other an electric driven auxiliary lube oil pump (See Figure 15-2).
Presently, on a manual start Shoreham does not have the means of supplying oil to the turbocharger thrust bearing other than through a turbocharger . lube oil drip system. The turbocharger lube oil drip system is also used at GGNS and is essentially the same as Shorehams. However, prior to a manual start of the D/Gs at GGNS the engine is prelubed for two minutes or less with the auxiliary lube oil pump which pressurizes the turbocharger thrust bearing with lube oil. This precludes the type of failures reported at Shoreham. There have been several occasions when the turbocharger mounting bolts have failed. The main reason for these failurer,has been misalignment of the ' turbocharger with its associated piping and components. The recent failures can also be attributed to misalignment. An engineer-ing evaluation of the turbocharger mounting arrangement is being per-formed and procedures designed to preclude misalignment have been im-plemented. 62
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15.3 CONCLUSION
S The susceptible areas in the piping and components around the turbo-chargers have been identified by past failures. The. integrity of these areas has been enhanced by the use of approved ASME code welding, procedures, and materials during rework. Since these enhancements, the weld and component failures have not reoccurred. With implementation of the alignment procedures, future failures of the mounting bolts are'not expected. Upon completion of the engineer-ing evaluation of the turbocharger mounting arrangement any required design changes will be implemented and reported to the TDI D/G owners group for generic consideration. I
.63
- --. . _ . - _. . ~ . . - , . , _ . ..
TABLE 15-1 ENG7NE HOUNTED COMPONENTS PROBLEMS CAUSED BY TURBOCHARGER VIBRATION ITEM DESCRIPTION OF PROBLEM CAUSE CORRECTIVE ACTION l 1 Cracked welds and base metal Fatigue compounded by high Repaired welds and base metal cracks on.intercoolers. vibration from turbocharger. cracks. Reseated turbocharger to eliminate undue stresses caused by misalignment. 2 Cracked welds on Jacket water Fatigue compounded by high Repaired w' elds. Refabricated flanges and piping headers. vibration from turbocharger. header to ASME III Class 3 reseated turbocharger. 3 Low pressure fuel oil header Fatigue compounded by high Replaced fuel line and fittings failure resulting.in Div I vibration from turbocharger. reseated turbocharger, fire.
. . FIGURE 15-1: Illustration of Shoreham TDI Diesel Generator Lube 011 System (Reference Telecon Shoreham)
Filter Y $ Orifice g, 1 o Sight Glass M e Drip Lubrication
} g Supply Turbo a
Pressurized Oil Supply % Prelube Flow Shoreham
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+
Filter a CO CO Engine L.O. Driven Heater Pun.p Pump Fig. 15-1 1
- _ - _ _ - - _ - - - - - - - - - - - - - - - J
FIGURE.15-2: Illustration of GGNS TDI Diesel Generator Lube Oil System Filter
}
-1. e 0rifice. %1 I
Dri b ication f A Turbo Pressurized gs Turbo Oil Supply g o t L
+
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-Flow "
GGNS -
}
^ Main Hdr. 4 L.O.
h fHdr. az
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16.0 JACKET WATER PUMPS
16.1 DESCRIPTION
i Shoreham has experienced a jacket water pump shaf t failure. l 16.2 ENGINEERING EVALLIATION ! This problem apparently affects only the in-line engines. No jacket water pump shaft failures have been reported on Vee-type engines to date.
16.3 CONCLUSION
S As of this time, MP&L has been unable to obtain evidence of generic jacket water pump shaft failures on DSRV-16-4 engines. Since this problem appears to be unique to in-line engines, it has not and is not. expected to occur on the GGNS diesel engines.
~
17.0 AIR START VALVE CAPSCREWS
17.1 DESCRIPTION
i en May 13, 1982, T7I reported a potential defect concerning the cap-screws that are used to retain the air start valves in the cylinders heads to the NRC under the provisions of 10CFR21. The 3/4-10x3 inch long capscrews were suspected of bottoming out in the tapped holes in the cylinder heads. -This could result in insufficient or unequal clamping forces being applied to the air start valve. 17.2 ENGINEERING EVALUATION AND CORRECTIVE ACTIONS TDI recommends machining 1/4 inch off the existing 3 inch capscrews or replacement with 2 3/4 inch long capscrews. DCP 82/4059 was issued to implement corrective actions. The air start valve cap-screws on the Unit 1, Division I and II D/Gs were modified by machin-ing 1/4 inch off the :.ength. MCAR-142 was issued to track the con-cern for the Unit 2 D/Gs.
17.3 CONCLUSION
S Corrective action is considered complete in regards to the air start valve capscrew problem. c - - _ _ _ . - - _ . . - _ _ , ._ . _ .
- . y.
i . jf ATTACHMENT 2 TO THE FINAL REPORT ON GGNS i 2
- DIVISION I AND II TDI
, -DIESEL GENERATORS s
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- I i
PISTON MANUFACTURING DETAILS t FEBRUARY, 1984 k i i a e f 1
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ATTACHMENT 2 PISTON MANUFACTURING DETAILS
; 1.0 GENERAL As reported by TDI (Reference 2), all 450 RPM rated " Enterprise" R-4 series engines have been furnished with two-piece pistons which incorporate a cast steel piston crown attached to a cast modular iron piston skirt by means of four studs. <This piston design has evolved since its inception in 1969 to incorporate design improvements for high reliability and less costly manu-facture. As horsepower ratings of engines increased in the mid-1960's, Transamerica Delaval and other medium speed diesel engine manufacturers
- abandoned the older style single piece piston design. The two piece piston is' inherently better equipped to deal with the higher thermal inputs of
-high Brake Mean Effective Pressure (BMEP) engines, because it allows thermal growth of the crown without causing excessive bending stresses in
-the skirt. The two piece piston design is also better equipped to handle the higher pressure and inertia. loadings of the increased horsepower engines. The modular iron skirt has passed through several design changes.
Five different designs have been used and are identified by TDI termino 1-
-ogy as "AF", modified "AF", "AN Old Style", "AN New Style", and "AE".
2.0 'CCNS BACKGROUND Only the "AF", modified "AF" and "AE" piston skirts have been used at CGNS. - The "AF" piston skirts were originally supplied by TDI on the Division I
;and II GGNS engines.- When problems were encountered with material quality
' of the washers (piston crown / skirt bolt) and GGNS experienced a piston crown / skirt separation, MP&L responded by upgrading hardware in accordance
-with SIM 324.to the modified."AF" piston skirt design. The cracking dis-covered later' on _Shoreham modifie'd "AF"' piston skirts and rejectable indi-
- cations found-at inspection prompted MP&L to change out all piston skirts at GGNS to the latest "AE" design piston skirts.
3.0 PISTON TYPES 3.) "AF" AND MODIFIED "AF" PISTON SKIRTS 1"AF" pist'on skirts use spherical washers on the four studs which sttach the crown to the skirt. These spherical washers provide Lfastener flexibility. These' commercially supplied washers proved to have inconsistent quality and large variations in heat treatment and manufacturing tolerances.- As a' result, a small number of the washers failed in service, resulting in piston, skirt / crown separation. One such separation occurred on the Division II D/G during field testing. To solve'the spherical washer problem, the d'esign was modified to Lincorporate's " full stack"'Belleville washer arrangement resulting in a modified "AF" piston skirt. i:
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l 3.1 (Continued) The "AF" style piston skirt casting received the following heat treatment: o Heat to 1750 degrees F. (near the upper critical tempera-ture) for 3 hours. Normalize (air cooled) in still air. This results in a pearlitic structure with 100,000 psi tensile strength. o Re-heat to 1050 degrees (slightly below the lower critical temperature) for 3 hours and cool in still air. This tempering process produces the desired ductility in the
-nodular iron.
3.2 "AE" Pistons The "AE" piston, the latest R-4 piston skirt design, just concluding
, research development testing, incorporates the field experience on the R-4 series engine and the R-5 series engine.
The "AE" design utilizes a " half stack" Belleville washer arrangement. All "AE" skirts are heat treated to produce stress relieved 100,000 psi tensile strength nodular iron. All piston skirts in the TDI units at GGNS Unit I are being replaced with this design. The "AE" style skirt is interchangeable with existing R-4 piston crowns and requires only minor hardware changes. i
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