ML19294C256

Final Deficiency Rept Re Cracked Disconnect Links.Caused by Stress Corrosion Cracking.Manufacturer & Suppliers Informed of Deficiency.Links in Class IE Circuits Will Be Tested & Terminal Blocks Will Be Sent to Sandia by 800305

ML19294C256
Person / Time
Site:	Midland
Issue date:	02/29/1980
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML19294C254	List: ML19294C253 ML19294C256
References
NUDOCS 8003070379
Download: ML19294C256 (4)

Text

Enclosure to Heve-52-80 STATUS REPORT STATES TERMINAL ELOCKS, CRACKED DISCCNNECT LINKS Descriution of Discrepancy During the electrical checkout by CPCo of non-Class lE startup transforner 0x03A, 38 inuividual nickel plated brass discenneet links cut of 156 vere found to be cracked. The initial failure e3s identified when, in an attempt to reccaneet a circuit after testing, the lit.s failed to tighten and make a good coanection. Subsequent investigation by Bechtel en four cubicles in class 1E h.16kV switchgear 2A06 revealed seven individual States ter=inal blocks with cracked disconnect links.

The subject terminal blocks sre used extensively in all majcr electrical equipment, both Class lE and non-Class lE. The terminal blocks are supplied as appurtenances to the major equipment and, therefcre, a large number cf equipment suppliers are involved.

Caus e The narrow breaks, or flaws, are believed to be causet by stress ccrresica cracking which prcpagated by both transgranular and intergranu'-" "-a^ king.

The stress correcicn is believed to be the result of excessive ccid verking of the brass and the subsequent exposure of the brass to a cerroding egent during the nickel plating process. Also, refer to paragrnphs h and 5 of

" Corrective Acticn."

Corrective Acticn

1) The terminal block manuf acturer and the med er equipment suppliers were informed of the deficiency.

2) Tae terminal bicek manufacturer was supplied with a list of all the cther equipment suppliers involved and was requested to evaluate and determine the probable cause (refer to paragraph h below) and to stipulate what corrective acticas need to be taken to identify and correct the nonconforming terminal blocks. The terminal block manufac-turer has replied that terminal blocks sold to equi

• ment manufacturers are not traceable to any specific batch er period c.f manufacture and that only isolated instances of f ailures have been rep < rted in the past. The terminal block manufacturer has, however, agreed to provide known good links to replace all cracked links, as required.

3) An inspection plan was developed f cr determining the extent cf cracked links in the major equipment using States terminal blocks. The inspection activity has been ccmpleted. The attached su==ary lists the results of this inspection.

40 80030

2 .

Status Report States Termin al Blocks, Cracked Disconnect Links h) The termine block manufacturer and CPCo independently conducted metallurgical failure analyses to determine the probable cause of the sliding link cracks. These met allurgical analyses have been reviewed and the cause has been determined to be as stated in the "Cause" section of this report.

5) A search was initiated of the cperations records of CPCa f acilities to identify any other link failures of States terminal b ocks. No extensive failure problems with the sliding links were found, only isolated cases.

6) The status of delivery of Class lE equipment centaining States terminal blocks was re<ieved to determine which pieces of equipment have not yet been shipped to the jobsite. This review was intended to suppcrt _

considerations for potential in-process (ie, prior to shipaent) cor-rective acticn that might reasonably be applied to equipm ent that has act yet been shipped. Since les= than 10% of the equip =r.nt renains to be shipped, it is believed to 'se most cost effective to shin them to the jobsite, install them, a d proceed as cutlined in items 2 and 3 under " Planned Actions", belc.. Accordingly, in-process corrective action is nct believed t o be appropriate in this case.

Safety Implication The identified discrepancy s of a nature that would te suspect to a f ailure mode; that is, ene in which the screv dces not hold the links in a tight positic:. and thus dces nct provide circuit continuity. The failure =cde could cauce an electrical circuit disruptica and, therefore, depending cn the circuit function, cculd be classified as a failure of the associated equipment to perfcr= its intended function.

Repo . ability Based en the potential failure mode and possible safety implication, this discrepancy was censidered to be reportable in acecrdance with the Ccde of Federal Regulations, Part 50 55(e).

Planned Acticns Construction and precperational testing vill continue with the existing links based en the folleving conditions:

1. A review of cperating history at other CPCo plants has indicated that no generic problems are kncun to exist with the States sliding disecnnect link terninal block.

2. All of the links in Class lE circuits vill be exercised during pre-operational testing. Links that fail to provide an electrical

3 '

Status Report States Terminal Blocks, Cracked Disconnect Links connection or which are found to be broken vill be replaced with links which are known to be good.

3. CPCo will centinue investigative efforts, including takins advantage of any industry informatien which may became available to determine lcng-term mortality statistics. If the links are determined to be un-acceptable for lcng-term operation, then suitable shunt / jumpers will be installed en all Class lE circuits prior to fuel lead.

WEBird February 29, 1980 WRB/lr Attach =cnt: Summary of Incpection Plan Results b

H6ve-5g_gn Attachment to Status Report

SUMMARY

OF INSPECTION PLAN RESULTS Cra cked Screw Did Not Group Description Links Tested Links

• Tighten 30 16 0 I Q-Listed 480V Load Centers 178 11 3 II Q-Licted 460V Motor Control Centers Q-Listed 4.16kV Switchgear 45 13 0 III 120 11 4

. IV Q-Listed Main Control Panels V Q-Listed Auxiliary Control 44 11 1 Panels VI Q-Listed Miscellanceus Equipment 82 11 0 VII Non-Q-Listed Miscellaneous Equip =ent 501 73 8 Totals I of Total 15% 1.6%

• Cracks found by visual inspection under 10 power magnification with high intensity lighting. Includes links where screws did not tighten.

• • Inspection not performed. Either equip =ent not delivered to jobsite as of date or equippent was found not to contain States terminal blocks.

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