05000280/LER-1980-063-01, Vascomax Cap Screw in Steam Generator a Leveling Pads Broke During Disassembly. Caused by Stress Corrosion Cracking.Screws Replaced

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Vascomax Cap Screw in Steam Generator a Leveling Pads Broke During Disassembly. Caused by Stress Corrosion Cracking.Screws Replaced
ML18139B157
Person / Time
Site: Surry 
Issue date: 03/09/1981
From: Joshua Wilson
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18139B155 List:
References
LER-80-063-01X, LER-80-63-1X, NUDOCS 8103130477
Download: ML18139B157 (2)
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LER-1980-063, Vascomax Cap Screw in Steam Generator a Leveling Pads Broke During Disassembly. Caused by Stress Corrosion Cracking.Screws Replaced
Event date:
Report date:
2801980063R01 - NRC Website
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CCCK&T NUMBER 68*

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VENT CESCrUPTION*ANC PROBABLE CONSEQUENCES@

((II] I During disassembly of "A" Steam Generator Leveling Pads. in accordance with*ETA C!JI]..J

  • 30017 ~ a Vascomax cap screw was broken.
  • The screw had been loosened and was being

([JILi turned out when it failed.. Preliminary investigation revealea *the failure_ h@sL C[II].

  • 1 begun be£ ore removal..

This event. is reportable as per Technical Specification 1.... --

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50-280 REPORT NO:

80-063/0!X-1 EVENT DATE:

11-19-80 VASCOMAX CAP SCREW F~

.1. DESCRIPTION OF EVENT:

-* I> ----*-***-----*-----------*

During* disassembly-of "A" Steam* Generator* leveling Pads, in accordance with ETA 30017, a Vascomax cap screw was broken.The screw had been loosened-and was being turned out when it failed.

Preliminary investigation revealed that.

the. failure of the bolt 'had begun before removal..

  • ... '"'1'
2.

PROBABLE CONSEQUENCES' AND STATUS OF REDUNDAN'r -~QUIPMENT:

The other cap screws did not have any visible evidence of cracking.

and safety of the* public were not affected.

3.

CAUSE

The.health The failure of the cap screw has been attribut:ed-to~stress-corrosion cracking which initiated at surface-pitting at the intersection of* the cap screw. bearing surface and the-cap: screw shatik*~:. A stagn}lnt _space_ at __ *th:i,.s ----------'-*

location. coupled;/with a material susceptible

screw selected::for detailed examination indicates that stress corrosion cracking had initiated in this-bolt as we11.-*Tnis second bolt had been removed without breakage.

4..

Il1MEDIATE. CORRECTIVE ACTION:

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The remainder.:of the broken bolt was. removed.

5.

SUBSEQUENT CORRECTIVE ACTION:

The failed bolt, as well as one bolt which. had been removed intact, were**

evaluated. by Lehigh University to determine _the.. made of fail~re (Refer to "Cause")__

6. "ACTION TAKEN TO PREVENT RECURRENCE:

TheVascomax cap screws have been replaced with cap screws of a superior material (ASTM A~574) as a part of the steam generator replacement project.

This. ~e.plaeement was already** accbmp-lished on Up.it _;l_L __..

7.
GENERIC lMPLICATIONS*:

The potential for failure, especially stress corrosion of this material was a major factor in.the scheduled bolt replacement.

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