ML19209B095

Interim Deficiency Rept MCAR-32 Re Terminal Blocks & Failure of Disconnect Links Due to Cracking.Corrective Action Schedule Will Be Provided in Second Rept

ML19209B095
Person / Time
Site:	Midland
Issue date:	07/20/1979
From:	Bailey K BECHTEL GROUP, INC.
To:
Shared Package
ML19209B083	List: ML19209B082 ML19209B095
References
HOWE-226-79, NUDOCS 7910090162
Download: ML19209B095 (3)

Text

. -

,m _. , I n.,.-22o-79 Bechtel Associates Professional Corporat. ion '

SUBJECT:

MCAR 32 (Issued 7/20/79)

States Terminal Blocks, Cracked Disconnect Links INTERI$ REPORT 1, Revised

/.'.':

DATE: August 10, 1979 -

~

fi PROJECT: Consumers Power Company .

Midland Plant Units 1 & 2 Bechtel Job 7220 -

Introduction .

This report is submitted to provide the interim status and course of action required pursuant to MCAR 32 and Bechtel NCR 2362.

Description of Discrenanev During the electrical checkout by CPCo of non-Class IE staitup trans-for:ter OXO3A, 38 individual disconnect isnks out of 156 were found to be cracke.d. The initial failure was ident;fied when, in an a: tempt to reconnect a circuit af ter testing, the link failed to make connection.

Subsequent investigation by Bechtel on four cubicles in Class 1E 4.16kV switchgear 2A06 revealed seven individual States terminal blocks with cracked disconnect links. -

Probable Cause Failure of the sliding disconnect links could be attributed '.o the following:

1. Improper Installation It can be postulated that the cracks may have developed! by over-tightening the disconnect link screw. In the actual samples taken from the jobsite, the cracks were initially discovercd after field testing and retightening of the . sliding disconnect lina screw.

Overtightening would result in a concentration of stress forces at the sharp 90 degree corners of the sliding disconnert link which would in turn result in a stress crack. In an attempt to verify this as a suspect cause, Bechtel field personnel were mnable to

. produce similar cracks in identical sliding disconnect links.

Insiend of causing a crack in the link, the overtightamtmr resulted in a breaking of the sliding disconnect link screw.

P00RDHRR liis m MI&Mblio>

. t' Bechtel Associates Professional Corporatio6 ,

MCAR 32 .

Interim Report 1, Revised -

August 10, 1979 -

Page 2 -

2. Manufacturing Process ,

The cracks may be the result of a breakdown in the actual fabri

• cation process. Overstresses during shaping and forming could weaken the metal and aid in the development of cracks. .

3. Defective Material The material could be out of specification from that which would be required for the manufacturing process to produce an 3:ceptable dis connect link.

Corrective Action The subj ect ter=inal blocks are used extensively in all maj or electrical equipment, both Class 1E and non-Class IE. The terminal blocks are supplied as appurtenances to the major equipment and, therefo e, a large number of equipment suppliers are affected.

At this ti=e it is not possible to determine the magnitude of the discrepancy due to the actual construction of the suspect terminal blocks. Performance of a 100% inspection of each sliding disconnect link would require that each terminal block be removed from the asso-ciated equip =ent and be completely disassembled. Due to the location of the disconnect links in the block, a visual inspection of an installed block can only be made on approximately a quarter of the exposed surface of the link. ,

M As a corrective action, the terminal block manufacturer, as well as the major equipment suppliers, will be informed of the deficiency. The terminal block manufacturer will be supplied with a list of all the other equipment suppliers involved, will be requested to evaluate and determine the probable cause, and will be requested to stipulate what corrective actions are to be taken to identify and correct the non-conforming terminal. blocks. -

Safety Implication The identified discrepancy is of a nature that uould be suspect to a

, failure node. The fai ure mode would most likely be an electrical circuit disruption and therefore, pending the circuit function, could be classified as a fai. lure of the associated equipment to perform its intended function.

1

~

I '

Bechtel Associates ProfessionalCorporation

. ~ .

MCAR 32 Interim Report 1, Revised

• August 10, 1979 Page 3 i' Based on the potential failure mode and possible safety irnplication, this discrepancy is considered to be reportable in accordance with the Code of Federal Regulations, Part 50.55(e).

• Forecast Date on Corrective Action -

A schedule for.the corrective action will be provided in Interf= Report YGli./2 Submitted by: ~ '  : jA Ws t.

Approvedby['C'- MTbb-c3 Concurrence by: B.-

cs/j t

,- /

8/3/1 1115 284