ML19323H646

Addendum 1, Investigation of Preservice Failure of Midland Reactor Pressure Vessel Anchor Studs, for Bechtel Corp

ML19323H646
Person / Time
Site:	Midland
Issue date:	06/06/1980
From:	TELEDYNE ENGINEERING SERVICES
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ML19323H644	List: ML19323H643 ML19323H646
References
TR-3887-1-ADD-1, TR-3887-1-ADD1, NUDOCS 8006160008
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Text

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BECHTEL PROFESSIONAL ASSOCIATES CORPORATION  !

777 EISENHOWER PARKWAY

) ANN AR80R, MICHIGAN 48106

)  :

J' TECHNICAL REPORT TR-3887-1 ADDENDUM 1

)

INVESTIGATION OF PRESERVICE FAILURE OF MIDLAND RPV ANCHOR STUDS

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JUNE 6, 1980

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• Tas:WNE ENGNEEMG SGMCES 303 BEAR HILL ROAD-WALTHAM, MASSACHUSETTS 02154 y- 617 890-3350

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Technical Report

) TR-3887-1 Addendum 1 WTI:1 ITf(NE M954G SERVCES 3887-1 Addendum 1 1.0 Introduction Tcledyne r.-ineering Services (TES) under contract with Bechtel Associates Pr- sional Corp. (BAPC) has conducted an investigation of preservice f ailures of two reactor vessel anchor studs at the Consumers Power Co. Midland Plant, Unit 1. TES has previously reported the results

) of this investigation in Technical Report TR-3887-1. Since preparation of that report, a third stud has f ailed, and material from that stud was suppliec to TES for further testing. This report describes the results of tests conducted on the third stud, which is identified as 35 outside.

J 2.0 Conclusion l .

This investigation was primarily concerned with determining whether

) the failure of stud 35 was comparable to the previous two f ailures. Based on the results reported here, it is TES's opinion that the mode of failure (stress corrosion leading to cleavage fracture) is the same as for studs 3 and 36, and the results presented here do not change the conclusions or b .

recommendations contained in TES report TR-3887-2 Rev. 1, " Acceptability for Service of Midland RPV Anchor Studs".

l 3.0 Test Program l

3.1 Introduction l

l The following tests and inspections were conducted on the third stud:

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1) Visual and Non-destructive examination using wet fluorescent magnetic particle techniques.

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2) Hardness Survey on the portion of the stud received by TES.

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) Technical Report 1R-3887-1 Addendum 1 WM SERVICES

3) Chemical Analysis for conformance to AISI 4140.

4) Fractography

5) Plane Strain fracture toughness (KIC}

3.2 Stod Dissection In the Midland Unit 1 plant, the third stud (35 outside, from heat

) 000) to fail was adjacent to the second failed stud (36 outside). Unlike the two previous failures which were at or above the concrete surface, stud 35 f ailed in the embedded end approximately 6 feet ,below the surf ace (Figure 1). The stud was saw cut approximately four inches from the

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fractured end and this cut portion provided to TES for further testing.

TES cut the fracture surface from the stud, approximately 3/4" from the end of the sample. Then another (1/4") section was cut for chemical

) analysis and hardness testing, and the remaining material used to prepare three fracture toughness specimens. The dissection plan is shown in Appendix A.

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l 3.3 Non-destructive Examination Prior to dissection, TES performed a visual and wet fluorescent mag- i netic particle examination on the 4" length of stud. l 3.4 Hardness Testing TES performed a hardness traverse across the diameter of the stud on 3

the slice from immediately behind the fracture surface, and along the length of the stud. Also, the hardness was measured at the fatigue crack front on the fracture toughness specimens.

) 3.5 Chemical Analysis A portion of the slice used for hardness testing was used for chemical analysis.

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Technical Report TN TR-3887-1 Addendum 1 NERNG SERVICES b

3.6 Fractography Consumers Power Co. personnel had effected a cleaning of the fracture by repeated replica stripping. This, combined with the fact that ahe D

fracture had not oxidized excessively resulted in a very clean fracture surface. TES was able to conduct a direct examination of the fracture surface using a scanning electron microscope.

D 3.7 Plane Strain Fracture Toughness Three L-R oriented 0.4T compact tension specimens were removed from the stud as shown in Appendix A. These specimens were designed and tested D

in accordance with ASTM E-399-78.

4.0 RESULTS 9

4.1 Non-destructive Examination No indications of additional cracking were found on the portion of the stud examined.

9 4.2 Hardness Testing Hardness traverse results are presented in Figure 2 along with pre-O viously reported results for studs 36 and 3. The results shown in Figure 2 dra also rhown in Table 1. Stud 35 showed a pronounced hardness gradient across the diameter, similar to the gradient in stud 36. There was also a hardness gradient along the length of the portion examined by TES, pre-sented in Table 2.

The hardness measured at the f atigue crack tip in the fracture tough-

, ness specimens from both studs 35 and 3 are shown in Table 3.

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) Technical Report TR-3887-1 Addendum 1 W N bE 94GeEstNG SBWICES

) 4.3 Chemical Analysis Results of the chemical analysis are shown in Table 4 along with results for studs 36 and 3 reported in TR-3887-1, AISI specification

) limits, and material certification results for heats 0 and 000. The results for this stud are consistent with the material certification results for heat 000 and the AISI specification.

) 4.4 Fractography The fracture surface is shown in profile in Figures 3 and 4, and in plan view in Figure 5. Figures 7 through 16 provide the results of a

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scanning electron microscpe examination, and Figure 6 provides a key show-ing where each photograph was taken.

This stud was different from the two previous studs in that there were 3 multiple origins, and at least three separate cracks which combined to form the final fracture surface. Also unique was the fact that, as shown in Figure 3, the fracture occurred in the nut, and not at the first engaged thread, resulting in a few stripped threads on the stud (Figures 3 and 4).

3 Further, the fractures initiated on a thread face rather than the thread '

root. (Figure 4)

The fracture surface of stud 35 consisted of intergranular fracture

) at the origins and transgranular cleavage over the remainder of the frac-ture, with a sharp transition between the two regions, as shown in Figures 11, 13 and 15. At the transition there were small regions of dimpled i fracture. Dimple fracture was only seen at the transition, and nowhere

) else on the fracture surface.

l One facet on the fracture surface was more heavily oxidized than the other facets. The entire facet was oxidized except for an annular ring 3 around the outer diamter at the origin. However, the region of transition l from intergranular to transgranular cleavage did not bear any relation to the transition from oxidized to unoxidized region. TES does not consider this feature to be important in this failure investigation.

) Technital Report TR-3887-1 Addendum 1 WM SBWICES

) The origins of all three cracks were more annu.ar, than thumbnail, in shape. However with visual examination it is possible to see the outline of what may have been thumbnail shaped cracks, which joined to form the annular cracks. The measured depths of the intergranular to transgranular

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) cleavage transition were 4.8 mm (Figure 8), 3.3 m (Figure 10), 4.1 mm (Figure 13) and 6 mm (Figure 15).

4.5 Fracture Toughness Testing

)

Fracture toughness results are presented in Table 5. Of the three specimens tested two are valid with respect to ASTM E-399-78 requirements.

The other specimen was invalid because the crack front was not straight

) enough to meet E-399. Because stud 35 failed in the nut, a fracture mechanics evaluation to compare the measured toughness values to flaw sizes as was done for stud 3 was not possible.

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TABLE 1 HARDNESS TRAVERSE, STUD 3 AND 36

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Location From Edge

• Stud 3 Stud 36 Stud 35

) 1/8 46.0 45.5 48.8 l

1/4 45.5 46.0 46.6 3/8 45.0 44.5 46.5 1/2 45.0 44.0 42.5

) 5/8 45.5 40.0 40.0 3/4 46.5 40.0 39.5 7/8 45.5 39.0 38.0 1 47.0 37.0 38.0

) 1 1/8 47.0 37.0 35.7 1 1/4 46.5 37.0 37.3 1 3/8 46.0 38.5 37.7 1 1/2 49.5 39.5 38.5 3 1 5/8 50.0 39.0 39.2 1 3/4 46.0 46.0 41.5 1 7/8 46.5 45.0 43.1 2 45.0 46.0 47.9 l 3 2 1/8 46.5 48.0 48.2 l ,

• (inches)

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) Technical Report TR-3887-1 Addendum 1 TN N MCES

) TABLE 2 LONGITUDINAL HARONESS TRAVERSE

) STUD 35 Location

• Hardness

) HRC 1 1/8 48.0 1 3/8 47.5

) 1 5/8 47.5 1 7/8 46.0 2 1/8 45.5 2 3/8 43.0

) 2 5/8 43.5 2 7/8 45.0 3 1/8 43.0 3 3/8 44.0 3 5/8 44.0 3 7/8 44.0

• From fractured end of specimen J

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D Tec.hnical Report TR-3887-1 Addendum 1 SeTAsry(E SSNCES D

4 TABLE 3 p Hardness Test Results on CT Fracture Toughness Specimen At Fatigue Crack Front p Stud Specimen Hardness Ave.

35 1CT-03 40, 40, 39.5 2CT-03 39, 39.5, 38.0 3CT-03 41, 41, 41 D ,,

39.9 3 FCl 46, 45.5, 48 FBI 45, 46, 48 3 46.4 D

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70 EE o.u TABLE 4 -

k3 Composition of Failed Anchor Studs Compared with Specification and Material Certification AISI Material Material 4140 Certification Certification

' Element Stud 3 Stud 36 Stud 35 Nominal

• Report, Heat 0 Rsport Heat 000 C 0.434 0.420 .425 0.38 - 0.43 0.40 0.42

'Mn 0.969 0.930 .840 0.75 - 1.00 0.90 0.86 P 0.012 0,014 .010 0.035 Max.** .010 0.013 S 0.015 0.015 .017 0.040 Max. .018 0.020 Si 0.240 0.240 .310 0.15 - 0.33** 0.25 0.33 Cr 0.970 0.990 1.010 0.80 - 1.10 0.94 0.96

' Ni 0.027 0.022 .020 - - -

Mo 0.184' O.180 .180 0.15 - 0.25 0.18 0.19 Cu 0.021 0.023 .050 - - -

Al '

O.027 0.037 .030 - - -

Ca 0.005 0.011 - - - -

B 0.001 0.001 - - - -

• From Metals Handbook Vol. 1, 9th Edition 1978 page 127

• • 040 max. for phosphorus and 0.20 to 0.35 for Si from Metals Handbook Vol. 1 8th Edition 1960, page 61.

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g Technical Report TR-3887-1 Addendum 1 9p qq SBNICES TABLE 5 Plane Strain Fracture Toughness (KIC)

, for Stud 35

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KIC (Ksi ICT-03 48.5 2CT-03 54.9*

3CT-03 56.1 3

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Figure 6 Map of fracture surface shown in Figure 5. Numbers refer

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to figure numbers of this report and show where photographs for figure were taken. Dashed lines outline entire region ,

examined with the scanning electron microscope.

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Figure 7 2000X Typical intergra,nular fracture near an origin.

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Figure 8 1000X Mixed mode (intergranular and dimpled) fracture.

) This type of fracture was always seen near the transition from intergranular to cleavage fracture.

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3 J Figure 13 1000X Transition from intergranular fracture to transgranular cleavage. Again, some dimpled fracture (arrows) is apparent at the transition.

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.g Figure 15 750X Transition from intergranular (top) to transgranular cleavage (bottom) fracture.

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