ML20129K103

Exam of Fasteners from Salem Nuclear Generating Station

ML20129K103
Person / Time
Site:	Salem
Issue date:	07/10/1995
From:	Bowerman B, Czajkowski C, Roberts T BROOKHAVEN NATIONAL LABORATORY
To:
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ML20129K094	List: ML20129K092 ML20129K103
References
NUDOCS 9611080148
Download: ML20129K103 (20)

Text

-.

Examination of Fasteners from the Salem Nuclear Generating Station C. J. Czajkowski B. S. Bowerman T. C. Roberts 1

Materials Characterization and Innovative Technology Group Environmental & Waste Technology Center Department of Advanced Technology Brookhaven National Laboratory Upton, New York 9611000148 950710 PDR TOPRP EXIENL C

PDR j

1.

Introduction Examination and testing of two stud bolts and four nuts were conducted at Brookhaven National Laboratory (BNL) for the U. S. Nuclear Regulatory Commission (NRC). These were cariied out to confirm portions of a root cause analysis conducted by 1

the NRC licensee at the Salem Nuclear Generating Station.

2.

Tests and Results I

Two stud bolts and four nuts were received at BNL accompanied by documentation j

(shown in Appendix A) which identified the stud bolts nuts as 7/8 x 5 %. The bolts and nuts appeared to be unused and fabricated from a non-magnetic steel. (See Figure 1.) Markings on the ends of the stud bolts and the nuts (shown in Figures 2a and 2b) are standard, j

j identifying the material and manufacturer. B8 on the stud bolt shows that the material

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conforms to ASTM A193/A193M; the nuts' marking, 8B, connotes ASTM A194/A194M (Ref.1). The "V" mark is the manufacturer's code marking.

j Dimensional Characteristics 4

l The dimensional characteristics of the stud bolts were determined according to System j

21 and System 22, of ANSI /ASME Bl.3M (Ref 2). For external threads, System 21 l

requires testing for GO maximum material, NOT GO functional diameter, and major diameter. System 22 is more restrictive, in that more parameters must be checked: GO maximum material, minimum material, major diameter, minor diameter, and root profile.

4 Various gages may be used and measuring instruments may be used for determining thread characteristics under ASME Bl.3M. Under System 21, GO and NOT GO threaded ring gages, respectively, are generally used for the first two parameters, while an optical comparator can be used for the major diameter. Other types of snap gages, pitch micrometers, thread measuring wires, etc., are acceptable as described in the ASME standard.

GO and NOT GO gages are functional tests in which a bolt or threaded stud is threaded into the gage, which resembles a threaded nut. The GO gage, which determines that maximum material is not exceeded, is passed'when the bolt of interest can be threaded through the gage and beyond. The NOT GO gage is passed when the bolt of interest can Dol be threaded into the gage for three turns. The NOT GO gage measures functional diameter.

The optical comparator magnifies and projects an image of the thread profile on a screen. Profile dimensions are checked using appropriate linear and angular scales on the instmment, and by use of overlay charts of thread profile, radius, or other parameters.

Flank angles, thread crest, root radius, axial plane pitch, and other parameters of interest.

Most commonly, major, minor, and pitch diameters are identified, then measured using table transverse readouts.

BNL Central Shops Division, as part of its support function, has an Inspection Group

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which maintains the capability for System 21 and 22 characterization methods. Using these methods, the Inspection Group evaluated the stud bolts according to dimensional limits specified in ANSI / ASME Bl.1-1989 (Ref. 3) for 7/8-9 UNC-2A threads, and " accepted" them. (The inspection report is Appendix B.) The inspection report notes that the minor diameter was measured at 0.727 inches, and that the specified maximum minor diameter should be 0.7368 inches, according to the Machinery's Handbook (Ref. 4). The Handbook l

contains specifications from ANSI /ASME Bl.1 dated 1966. The more recent specifications dated 1989 (Ref. 3), call for a maximum minor diameter of 0.7408. In either case, na minimum value is specified, so the threads meet specification as determined by System 21 l

and System 22.

l Hardness Tests For the hardness tests, a one inch section was removed from each stud bolt. Four measurements using the Rockwell A scale were obtai eu cn the face of each bolt. Average values (see table below) corresponded to a Rockwell amaness of 90.5 on the B scale. The specification for ASTM A193 material in a Class B8 Class bolt is a maximum 96 on the Rockwell B hardness scale.

Stud Bolt Rockwell A*

Rockwell B6

1. 1 55.75 i 90.5

1. 2 55.75 90.5

a. Average of four mdaEurements,

b. Conversion value.

Hardness test were also conducted on the four nuts. Three measurements on each 4

bolt were averaged to obtain the Rockwell A values, which were then converted to the Rockwell B scale value shown. ASTM A19'/194M specifies a nardness range for Grade 8 nuts of 60 to 105 on the Rockwell B hardness scale. These nuts meet this specification.

Nut Rockwell A*

Rockwell B6

1. 1 62.5 0.0 101.1

1. 2 61.0 i 0.9 98.5 l

1. 3 60.7 1.8 98.1

1. 4 61.5 1.8 99.5 l

a. Average of four measurements,

b. Conversion value.

i l

Static Load Tests Static load tests were initiated to monitor the load relaxation behavior of the stud bolts. A block of tool steel was machined to permit access for strain gage leads while maintaining flat surfaces for uniform contact with the nut faces, and nominal clearance for the stud bolts. (See Figure 3 for a schematic representation of the static load block..)

The nuts were installed without lubricant and tightened to a torque calculated to induce 50% yield stress in the stud bolt, as directed by the NRC Project monitor. The calculated torque,121 fr-lbs, was applied using a calibrated torque wrench. The nuts were re-torqued after approximately 30 minutes, as described in an EPRI report on bolting practices (Ref. 5).

Prior to installation, two precision strain gages were bonded to each stud bolt, which had been machined at its midpoint to provide a flat surface for the strain gage. The machining was just sufficient to remove the threads, and the strain gages were aligned with the bolt axis. The gages (Micro-Measurements, Romulus, MI) were calibrated on installation to yield direct readout of microstrain (microinches/ inch) on a digital strain indicator (Model V/E-20A, Vishay Measurements Group, Raleigh, NC). One of the pieces from the hardness tests was fitted with a gage to monitor and compensate for ambient temperature changes.

Readings were taken daily for about two months, at which time, since there were no changes in the readings, the static load test was terminated. The raw strain data are tabulated in Appendix C, and the temperature compensated data are displayed in Figure 4.

Figure 4 ir Ates that the stud bolts, after an initial elongation, maintained a constant strain for the durauon of the test.

3.

Conclusions Two 7/8-9 UNC x 5 % stud bolts were tested for dimensional characteristics, hardness, and performance under static load. The bolts were found to be acceptable under both System 21 and System 22 gaging requirements. The bolts and the nuts met hardness criteria specified in ASTM 193/193M and ASTM 194/194M, respectively. The bolts maintained a constant elongation under a staic load test for two months.

4.

References 1.

Industrial Fasteners Institute, Fastener Standards. Sixth Edition, Industrial Fasteners Institute (1988).

2.

ANSI /ASME Bl.3M-1992, " Screw Thread Gaging Systems for Dimensional Acceptabili:y - Inch and Metric Screw Threads," American Society for Mechanical Engineers, New York,1993.

3.

ANSI /ASME Bl.1-1989, " Unified Inch See v Threads," American Society for Mechanical Engineers, New York,1989.

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4.

E. Oberg, F. D. Jones, and H. L. Horton, Machinery's Handbook A Reference for the Mechanical Engineer. Drafstman. Toolmaker. and Machinist, Industrial Press, Inc., New York (1979)/

2 5.

J. Bickford and M. Looram, " Good Bolting Practices, Vol.1: Large Bolt Manual" EPRI-NP 5067, Electric Power Research Institute (1987).

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Appendix A Documentation Received with Fasteners 1

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Appendix B BNL Central Shops Inspection Report

- CENTR AL SHOPS DIVISICN ST.OOKHAVEN NATL 3N AL LABOR ATORY INSPECTION REPORT Date Acct. No.

1.L.R. No.

W.O. No.

P.O. No.

Insp. No.

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Appendix C Strain Gage Data from Static Load Test l

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1. 1 Stud

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Gare#I Gage 44 Gage #5 Gage #6 Gage #7 3/l7NS 950 69

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$17 874 505 783 3/20/95 940 72

-I 3 515 872 502 78I 3/21N5 820 72

-12 518 874 504 783 3/22N5 915 69

-10 506 873 506 779 3/2385 940 72

-13 515 872 504 781 3/2495 950 72

-13 515 871 503 777 3/27N5 9 16 71

-15 515 871 499 779 L'2fL95 926 72

-13 515 872 500 780 3/29N5 852 72

-14 515 871 Sol 780 1/30N5 1247 73

-12 516 872 501 781 3/1885 845 72

-11 517 874 504 782 414N5 819 71

-13 516 873 500 780 4/5N5 850 71

-14 514 370 501 780 4 %95 9 10 71

-16 513 869 498 777 4/7N5 847 67

-14 516 873 499 779 4/10N5 900 73

-10 516 872 505 782 4/IIN5 841 72

-12 515 871 502 780 4/12N5 858 69

-12 516 872 501 778 4!!IN5 841 72

-7 520 877 508 786 4/1495 842 72

-9 516 873 509 784 4/17N5 902 72

-12 514 871 501 779 4/1895 536 72

-11 516 873 502 781 4 'l9N5 858 69

-10 518 874 505 783

e lhte Time Temperature Stud

1. I Stod

1. 2 (T)

Gage #1 Gage #4 Gage #5 Gage #6 Gage #7 2O lM5" 1040 81 0

0 0

0 0

2GIM5' 1047 81 0

502 865 489 773 2/21N5' 1817 81

-3 498 861 486 769 d

2/28Mi til7 81

-3 516 875 499 784 2GIM5 1315 83

-3 516 873 499 782 2GIM5 1610 67

-15 515 873 499 774 2'2235 900 70

-17 516 873 499 781 2S3M5 900 72

-l 8 515 872 498 780 2/24N5 845 71

-16 518 876 501 784 2/27/95 852 71

-19 513 870 4%

778 2n8/95 1011 68

-17 517 874 498 787 U195 841 73

-13 517 874 502 783 3/2N5 911 72

-15 514 871 500 781 3/395 856 71

-I7 514 870 498 779 3/6/95 855 73

-13 516 873 500 781 3/7MS 1018 73

-13 516 873 501 782 3/lL95 906 73

-11 519 876 505 785 3.9N5 1839 70

-Il 515 872 507 784 3/ IONS 846 70

-18 512 868 5(X) 779 3/l4N5 830 78

-13 517 873 503 783 3/15MS 1000 70

-l1 517 873 503 779 3'I A95 10 9 72

-11 517 874 95 783

Date Time Temperase Srmt

1. 1 stud

1. 2

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1640 81 0

0 0

0 0

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502 865 489 773 2/21N5' 18I7 81

-3 498 861 486 769 2/21/95*

1817 al

-3 516 875 499 784 2/2 tN5 1315 83

-3 516 873 499 782 2/21/95 1610 67

-15 SIS 873 499 774 2/22/95 900 70

-17 516 873 499 781 2/23/95 900 72

-18 515 872 498 780 2/24/95 845 71

-16 518 876 Sol 784 2/27/95 852 71

-19 513 870 4%

7 73 2/28N5 101I 68

-17 517 874 498 787 3/1/95 Ell 73

-13 517 874 502 78) 3/2/95 911 72

-15 514 871 500 781 3/3/95 856 71

-17 514 870 498 779 3/6N5 855 73

-13 516 873 500 781 3/7/95 1018 73

-13 516 87)

Sol 782 3/L95 906 73

-11 519 876 505 785 3/9N5 1139 70

-Il 515 872 507 784 3/I0/95 846

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-l8 512 868 500 779 3/14NS 830 71

-Il 517 873 501 781 3/15N5 1000 70

-11 517 873 Sol 779 1/IN91 1050 72

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