ML19351E414
| ML19351E414 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/09/1980 |
| From: | Proft T PARAMETER, INC., TECHNIMET CORP. |
| To: | |
| Shared Package | |
| ML19351E412 | List: |
| References | |
| CON-NRC-05-80-251, CON-NRC-5-80-251 78429, IE-120, NUDOCS 8012100073 | |
| Download: ML19351E414 (29) | |
Text
{{#Wiki_filter:s Sheet'l of 29 s l Metallurgical Analysis of Failed Turbine Casing Bolt from Arkansas Power & Light, I tit 1 Report No. IE-120 September 9, 1980 Prepared for: United States Nuclear Regulatory Commission 1 Office of Inspection j and Enforcement ' NRC Contract 05-80-251 gt tfhp PAR: NRC-IE-80/81, Task 04
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s a r=b an s* $ e r, n c. C O N $ U til N G E N GIN f f R 5 ftM G R O V E, wl1 CON 5tN NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or impl ied , or assumes any legal liability or responsi-bility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. I
CO T O 4379 SOUTH HOWELL AVENUE MILW AU K E E. WISCONSIN 6320/ 414:4 b3 0054 TEGINIhET REPORT NO. 76429 PARAMETER REPORT NO. IE-120
SUBJECT:
ANALYSIS OF FAILED TURBINE CASING BOLT FROM ARKANSAS POWER AND LIGilT, UNIT 1. NRC CONTRACT 05-80-251, PAR: NRC-IE-80/81. TASK ORDER NO. 4 l BY: Til0 MAS L. PROFT, P . ii . DATE: SEPTEMBER 9, 1980 1 l l l l l
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O ,__3 y O g i _ .5 _ft_LI_V_ 5_ s , CORPQRATION 4379 SOUTH HOWE LL AVENUE M ILW A U K E E. WISCONSIN 53207 September 9, 1980 414/481 0054 REPORT NO. 78429 I. DESCRIPTION AND PURPOSE: A failed 3/4" diameter fastener was submitted. The fast - ener was identified as a bolt, but was by definition a stud, with a nut at each end. The stud had fractured on one of the threaded ends at what appeared to be the first engaged thread. This stud was reportedly removed from a flange on the tur-bine casing of the emergency steam drive auxiliary feed-water pump at Arkansas Power and Light Company, Unit 1. The Arkansas Power and Light Company had reported to the
.RC-IE that a steam leak was observed at this connection.
Visual inspection had found five out of a total of eight studs had failed. The failed studs were consecutively located on the flange, reportedly from the 7 o' clock to 1 o' clock positions. It was also reported that the tur-bine had experienced an overspeed recently. Previous problems had been reported with water slugging, which may have caused vibrations or excessively high loads in the system. The studs were reportedly to have been manufactured according to ASTM A-193 Grade B7. The purpose of this investigation was t'o provide metal-lurgical analysis of the failure, as outlined in Contract Number NRC-05-80-251, Task Order No. 4. II. CONCLUSIONS: A. The stud material did not conform to that specified I for ASTM A-193 Grade B7, which requires a quenched ; and tempered 4100 series alloy steel. Microstructural and chemical analyses showed the material to be cold drawn AISI 1215.
, Sqptember 9, 1980 REPORT NO. 78429 Page 2.
1I. CONCLUSIONS: (Continued) B. Based on Rockwell B hardness tests, the estimated tensile strength of this material is 90,000 psi. Estimated yield strength is approximately 70,000 psi. The specified AST!! A193 Grade B7 material requires a minimum tensile strength of 125,000 psi and a mini-mum yield strength of 115,000 psi. C. Scanning electron microscopy showed that failure occured primarily by brittle transgranular (cleavage) fracture. Some areas of mixed mode intergranular, transgranular, and ductile dimpling fracture were also found. D. EDAX analysis on the fracture face and adjacent threads showed the corrosion products to contain cal-cium, potassium, silicon, aluminum, magnesium, and small amounts of sulfur, chlorine, and phosphorous. It appears that these corrosion products are the result of exposure to steam and the surrounding insulation material after fracture occured. Corrosion was not a causative factor in this failure. E. No evidence of corrosion pitting or fatigue cracking was found in the adjacent threads or on the other threaded portion of the stud. F. Failure appears to have occured by brittle fracture, initiating at three different points along the root of the first engaged thread. Failure probably occured in less than 10 cycles. G. The cold drawn 1215 material used would be expected to have much lower resistance to the type of frac- . ture found than the specified ASTM A-193 Grade B7 I material.
- 11. Only one of the five failed fasteners was submitted for analysis, and therefore no conclusions can be drawn as to the mode of failure in the other four studs .
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September 9, 1980 REPORT NO. 78429 Page 3. III. TESTS AND RESilLTS: A. Visual Examination. Figures 1 through 4 show the failed stud as received. Note that fracture occured along what appears to be the first engaged. thread. Figure 5 shows the fracture surface as received. The heavy layer of corrosion product s and pipe insulation material prevented any fractographic analysis at this point. Figure 6 shows the unfailed threaded portion of the stud after removal of the nut. Stereo-microscope
- examination of the thread roots and subsequent cican-ing and dye penetrant inspection could reveal no cracking on this end of the stud.
B. Energy.Dispersive X-ray Analysis Before Sectioning. Before the stud was occtioned, energy dispersive X-ray analysis was performed on the material in the , roots of the exposed threads of the unfractured end. Figure 7 shows the electron image of the area analy::ed. Figure 8 details the results o f semi-quantitative analysis at the point indicated by the arrow in Figure 7 The analysis shows unusu,11y high levels of silicon, phosphorous, molybdenum, co?cium and capper. Only traces of sulfi.r and chlorine vere found. C. Energy Dispersive X-ray Analysis of Fracture Surface After Sectioning. Figure 9 shows the stud after sectioning. Section B was used for hardness testing and metallography. Section C was used f'or spectrographic chemical analy-sis. Section D, containing the fracture surface , was used for EDAX analysis, scanning electron microscopy and subsequent metallography. Figure 10 shows the electron image of the area at the alzow in Figure 5. i I l l
Se'ptember 9, 1980 l Rl! PORT NO. 78429 Page 4. III. TESTS AND RESULTS: (Continued) C. EDAX Analysis of Fracture Surface Af ter Sectioning. TContinneil) The area indicated by the arrow is shown at higher magnification in Figure 11. The corrosion products in this area were EDAX analyzed, the results of which are detailed in Figure 12. The high aluminum and silicon found are presumably f rom the steam piping insulation material. The calcium and potassium are the result of exposure to the 1ive steam. Sulfur and chlorine, while present, are not at levels expected to initiate a corrosion induced fa ilure.
. Figure 13 shows one of the fibers visible in the lower left of Figure 11. EDAX analysis of this fiber is de-tailed in Figure 14. The analysis indicates the fiber may be asbestos, although contamination by the steam and su'osequently formed corrosion products prevent accurate assessment of the magnesium, calcium and iron
- ratios, which are used to identify asbestos.
i Figure 15 shows the corrosion product on a typical area of the fractu.e. This heavy layer of corrosion prevented any fractographic analysis before cleaning. Figure 16 is an EDAX analysis of this area. The re-l sults are typical of several other areas on the frac-ture face. D. Spectrographic Chemical Analysis. The following details results of st i ec trographic chemi-cal analysis performed on cross section C of the stud: Element Percentage C .09 Mn 1.12 S .341 P .091 Si 4 01 Cr .03 Ni .02 Mo 4 01 Pb 4 01 Cu .02
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September.9, 1980 REPORT NO. 78429 Page 5. III. TESTS AND RESULTS: (Con t inued) D. Spectrographic Chemical Analysis. (Continued) The material conforms to the check analysis limits of SAE or AISI 1215 material. This material is a re-sulfurized, re-phosphorized grade of carbon steel used primarily for its free machining properties. Due to the high phosphorous and sulfide stringer con-tent, this material is not recommended for critical high strength applications. E. Meta 11ography on Bolt Shank. Figures 17 and 18 show the microstructures found on transverse and longitudinal samples prepared from section B. The structure consists primarily of ferrite, with small patches of pearlite and large manganese sulfide stringers. This structure is typi-cal of an SAE 1215 material. To verify the composi-tion of the inclusions, the polished longitudinal tion was examined with the scanning electron micro- _ cope in the hackscattered and X-ray mapping modes. Figure 19 shows the backscattered electron image of one of the stringers. Figure 20 is a sulfur X-ray map of this same area. The concentration of sulfur X-ray signals verifies the inclusion is a sulfide. F. Hardness Testing. Rockwell B hardness tests were taken at mid-radius on a cross section of the bolt shauk. Hardnesses at 900 interva 'anged from Rkw B89.5 to Rkw B91.2. From these hardness tests, the tensile strength is estimated to be approximately 90,000 psi. The speci-fied material, ASTM A-193 Grade B7 requires a .nini-mum tensile strength of 125,000 psi. While a ninimum hardness is not stated in the ASTM speci ficat ic n , hard- : ness level at a tensile strength of 125,000 psi would l be approximately Rkw C25. ! l 1
u 4 l l 1 September 9, 1980 (
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RiiPORT NO. 78429 Page 6. III. TESTS AND RESULTS: (Continued) F. liardness Testing. (Continued) The hardness level and microstructure indicates that the m.iterial is cold drawn. While this would elevate the vield strength to anproximately 70,000 psi, the ductility and resistance to brittle fracture would be further degraded. G. Scanning Electron Microscopy on Fracture Surf ace A f ter Cleaning. In order to determine the mode of failure, the frac-ture surface was cleaned in a mixture of phosphoric
. acid and glycol, with subsequent rinsing and ultra-sonic cleaning in acetone.
Figure 21 shows the appearance of the fracture surface after these cleaning operations. The letters refer to areas examined by scanning electron microscopy. The electron image of region A is shown in Figure 22. Figures 23 and 24 show the fracture features within the crescent shaped area of region A on Figure 22. Fracture in this area is primarily by transgranular cleavage, with some indications of intergranular cracking. Pitting on the cicavage planes was caused by corrosion subsequent to fracture and partially by the phosphoric acid cleaning solution. Figure 25 shows the fracture features found in region B of Figure 21. Again, at this location, fracture was primarily by transgranular cleavage. Figure 26 shows the fracture features at region C of Figure 21. Again, failure is primarily by transgranu-iar cleavage, with some indications of intergranular cracking. Figure 27 shows the electron image of region D. Macroscopic features indicate this to be the primary origin of fracture.
September 9, 1980 REPORT NO. 78429 Page 7. III. TESTS AND RESULTS: (Continued) G. SEM on Fracture Surface Af ter Cleaning. (Continued) Figure 28 shows this region at higher magnification. Failure is primarily by transgranular cleavage, with small areas of ductile overload and some intergranular cracking evident. Figure 29 shows the fracture features at region E. Again, failure is primarily transgranular with some indications of intergranular cracking. Figure 30 shows region F at low magnification. This area is shown at higher magnification in Figure 31.
- Again, fracture is primarily by cleavage, with some evidence of intergranular cracking.
Fracture features at region G are shown in Figure 32. At this point, failure was primarily by ductile dimp-ling. These features indicate that failure occured in a brittle manner, initiating at three points, regions A,D, and F of Figure 21. Failure may have initiated at all three of these locations with the same impact load, or, several separate loads may have been applied to cause final failure. No evidence of fatigue crack-ing, stress corrosion, or any other slowly progressive type of failure could be found. 11 . Meta 11ography on Cross Section of Fracture. After scanning electron microscopy was completed, the i fracture surface was sectioned along the diameter. Figures 33 and 34 show the structure at the crack surface in the root of the thread at region D of Figure 21. Figure 35 shows the crack surface at higher magnifi-cation, approximately 1/8" from the thread root. Note that cracking is primarily transgranular (arrow 1). Some secondary cracking is evident along the grain ; boundaries at the interfaces of the pearlite and ferrite ' grains (arrow 2). i l
~ September 9, 1989 REPORT NO. 78429 Page 8. III. TESTS AND RESULTS: (Continued) I. St:perficial liardness Testing Nea r Fra :ture. Rockwell superficial 30N hardness readings were taken on the polished cross section approxiiaately 1/16" from the crack surface. Rockwell 30N readings ranged from 78.0 to 80.0. These readings convert to Rockwell B93.0 to 96.0. While slightly higher than the Rockwell B89.5 to 91.2 readings obtained on the shank section, they are within the range of accuracy expected for hardness conversions from the superficial scale. No evidence of carburization, corrosion, pitting, or
.other surface damage could be found near the crach origin or in the roots of the adjacent threads.
Respectfully submitted, TECilNIh!ET CORPORATION e G J= 3 _, , y
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Til0h1AS L. PROFT , P .E. 2 L PROFT 5 Vice-President 5 31 15/09 $@ o ( a,.gtWAu.c: .- TLP/mP Nn /-t. . Attachments g n,u,,,o
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- i Fig. 10 -
Electron image of region shown at arrow in Figure 5. Arrow in this Figure indicates corrosion product shown at higher magnification in Figure 11. (SEM 14X) l l
. , , . _ . . ~ _ , , - . . . . _ , . _ _ . - _ , . . . . - - _ . _ _ _ - _ . , _ _ . . _ _ . _ . . . . . _ _ - _ _ _ _ _ _ _ , . , . . . . _ _ , . . _ . . . . - . _ . . _
a f September 9, 1980 . REPORT NO. 78429 ! D Q} i e- - - - , ,_ - . .
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di
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! . l Fig. 11 - Corrosion product at arrow in Figure 10. White l appearance is due to electron charging, a result j of the corrosion products' non-conductivity. EDAX i analysis of this r.rea is detailed in Figure 12. (SEM 50X)
- -1 ENTP
- : EOLT FRAC S-2 l
.7 ZAF V=21.5 !=35.0 T=26.6 ELEr1 LINE STD i AL K Q=100.O SI K P K ;
K CL K V K l CA K l FE K < ] +&++++++++ l
- 9. 262 ";AL j 38.716 ";SI
.521 *P .
. 47 ? *:S
- .410
- CL I
1.093 *sK 29.411 %CA 21.110 *-;FE i ->0 END l Fig. 12 - EDAX analysis of corrosion product shown in Figure 11. I l l l
- - _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ . . _ _ _ _ . , _ _ _ _ _ _ . . . _ _ _ , . _ _ . _ _ . _ . _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ -1
September 9, 1980 D* j' '\Il U D db
- Ju *[D '@h
- LB' ~E REPORT NO. 78429
.m
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L. l Fig. 13 - Higher magnification view of insulation fiber seen in lower left of Figure 11. (SEM 500X) I l 1
-)1 EriTR :: BOLT FPC S-3
-:2 7 ZAF V=21.5 S=35.0 T=26.6 STO l
, ELEM LIfiE MG K O=100.0 l AL K j SI K K K S K CA K , Mri K FE K
++++++++++
9.137 *:MG 9.325 *:AL 31.052 *:SI
.615 %K 1.038 %S 22.104 *:C A 1 .577 *:Mri l :'6.14 8
- FE
-> 0 EriD Fig. 14 -
EDAX analysis of fiber shown in Figure 13.
l September 9, 1980 0 REPORT NO. 78429
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Fig. 15 - Electron image of corrosion on fracture surface, typical of entire fracture area. (SEM 500X)
->1 EriTP :: BOLT FRAC S-4 I
->7 ZAF s/= 21. 5 5=35.O T=26. 6 ELEt1 LIr1E STD AL K O=100.O T15 K SI K S K CL K CA K t1il V FE K
++++++++++
1.102
- SAL
. 3 05 ";t16 5.909 *;TI
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- 1. 218
- C A 1.084 *s Mil 88.153 '<FE
->0 Er4D Fig. 16 -
EDAX analysis of area shown in Figure 15. l 1
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. ig . 17 -
Transverse section through bolt shank. Structure consists of ferrite with small areas of pearlite at the ferrite grain boundaries. Roundish grey areas are manganese sulfide inclusions. (200X) g;. . g,.,4
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September 9, 1980 n h i! .! REPORT NO. 78429 D [h Qul[I$uuuh&,' Uj W Wm On 1Kyp'g%yggglF.%9;;ygiggy;gg.qgg C fy,x"qtw WMw; ; + w : x.<y.w mlw.,y g. .s g a r , p +'.;
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T .. , a%w& ;:,t.u,u i m . : .:;t .,.1 . . .+.-. m., , x, 1 :.s . l Fig. 19 - Backscattered electron image of polished longitudinal i cross section showing large sulfide stringer. (SET 1 1000X) i l i i I l i I 1 i ; i '
.. , n .. . a,.
i-
.3. (q..g
, ,3 .
n w+ .3'.(1: . st;_%:; . . s.. = l .. 8 Fig. 20 -
. fur map of same area shown in Figure 19, confirring inclusion to be a sulfide. (SE11 1000X) l l
1
- _ _ . - . - _ ~ . , . . . - . _ _ _ . . . . . _ _ _ . - - - . _ _ _ _ . . _ _ _ _ _ ___ _
I l I i Sqrtember 9, 1980 ig!
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REPORT NO. 78429 (L _
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Fig. 21 - Fracture surface of bolt after phosphoric acid and , , ultrasonic cleaning. Letters refer to regions examined ! by scanning electron microscopy.
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e , .. Fig. 22 - Electron image of region A. Note secondary cracking at arrow 1. This region appears to be a crack origin, with cracking starting at the root near arrow 1, progressing approximately 1/8" into the bolt before forming a shear step at arrow 2 to join the main fracture surface. (SE>l 17X)
l i September 9, 1980 6 g n:, .x z,t ~ . W\ . m. g v. .g e N$.. -
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Higher magnification view of fracture features near outer edge of crescent shaped area in Figure 22. Fracture is primarily by transgranular cleavage. l Some areas of intergranular cracking are also present j (arrow). (SEM 425X) t
.R l
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l i 9 ~i.; 9pg.,a, c j Fig. 24 - Fracture appears in region A at higher magnification. A5 l l Fracture is primarily by transgranular cleavage. ; Pitting on cleavage faces was caused by initial I corrosion and subsequent phosphoric acid c1 caning. l (SEM 1000X) 1 __.-_ _ __._ _ ..._-. . -._- , .... .. . , - _ . - , - - ~ . . _ . . . - . _ _ _ . - , - - - _ _ _ . . _ . , _ . . . . _ - - - - . . _ . - . . . _ . -
l September 9, I'80 i l 4 REPORT NO. 78429 I* s. I t.,
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- q. - ,
2N? M T.lMOl?% A (; 9 -
.2 Fig. 25 -
Fracture features at region B. Again, fracture is primarily by transgranular cleavage. (SEM 1000X) e -
'e \
.=
<j '. . *y
~
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j s, , l
? py
[ h': Al . Fig. 26 - Fracture features at region C. Fracture is primarily by transgranular cleavage, with some intergranular cr cking. (SEM 500X)
-m l
Spptember 9, 1980 - fj)f?';jj!(3;an i ' gg" (h{};,!!\ihDJJU L g' "i O ,t REPORT NO. 78429 g i ( >
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' = t.O y;g.l4 Fig. 27 -
Low magnification image of region D. Macroscopic features indicate this was the primary origin of failure. (SEM 100X) l 8./
.(. .. ; ft ;. 5 ;
s
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j k . p , Fig. 28 - liigher magnification view of fracture in region D. Fracture is primarily transgranular cleavage. (SEM 500X) 1
Se,Ptember 9, 1980 ,2 mrrn hp Jil', m, 1,M R14 REPORT NO. 78429 e h}Ng\1 bifM.EJ!!U\ T6S Si '.il
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Fig. 29 - Fracture features at region E. Failure is primarily by transgranular cleavage with areas of intergranular cracking (arrow). (SEM 500X)
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r- 9. l M $ 2" e-.. . MNC:v;Ss ?.l p.:qgm h;f & [j [ g % ha #W.da;&M111 Fig. 30 - Low magnification image of region F. Macrosconic features indicate this area was a third fracture origin. (SEM 20X) l
i , . September 9, 1980 ; fit "1 y,;ijgjktN[S ga D REPORT NO. 78429 by '$G~ ~ g .!';*.
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I pf l j, . .l. l y i- ' h. - [j , 1 Fig. 31 Fracture features in area F. Fracture is again by transgranular cleavage, with secondary intergranular cracking. (SEM 1000X) i
^
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Fracture features in region G. This area appears to be one of the last areas to fail as indicated by the primarily ductile dimpling fracture mode. (SEM 500X)
. . Sqptember 9, 1980,7 -0 p 5. @Iv.q [N E kf .n\0 l 0 . >
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L ' REPORT NO. 78429 ' 1 J
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Fig. 33 - Photomicrograph taken on cross section through l fracture surface at location D. Arrow indicates
; origin of crack at thread root. (50X) .t
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h M'@mp .: m E f_wwf ,hbh %a _ % n u.an E Fig. 34 - Same as Figure 33 at higher magnification. (100X) i l i 1
, .. September 9, 1980 - ,- n REPORT NO. 78429 .h .k -
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'%se;dA I Fig. 35 -
Higher magnification view of fracture surface. Note fracture is primarily transgranular (arrow 1) with 1 secondary cracking along pearlite, ferrite grain boundaries (arrow 2). (200X) l 4 l i l l l I
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