ML20002D994

Ro:During Feb-Mar 1971 Refueling outage,3-inch Section of Tee Piping W/Cracked Welds Removed.Caused by Incomplete Fusion & Suckback in Root Pass.Metallographic Exams to Be Performed.Sketch & Photo of Removed Tee Encl

ML20002D994
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	06/17/1971
From:	Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8101230761
Download: ML20002D994 (6)

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June 17, 1971 ru Dr. Peter A. Morris, Director Re: Docket 50-155 Division of Reactor Licensing DPR 6 (ZEK)

United States Atomic Energy Commissirm Washington, DC 20545

Dear Dr. Morris:

Attention:

Mr. D. J. Skovholt During the February-March 1971 refueling outage, a short section of three-inch 304 stainless steel clean-up system piping was replaced due to five welds of questionable quality located in this piping. The replaced piping vae at the tee where the clean-up system return water mixes with poison system injection water and water displaced from control rod drives when they are notched. The intention to replace this piping and the welds was reported in the 13th Semiannual Report of operations far the Big Rock Point Nuclear Plant.

It was obvious after sectioning the removed piping that the velds did not meet Code standards. These welds showed what appeared to be incomplete fusion and "suckback" in the root pass.

Vnile the pieces of the welds were being prepared for shipment to the two vendors involved in the weld inspections, it was noted that the three-inch tee removed contained four slight cracks. These were on the ID of the tee and approxid.ately one third to one half of the pipe wall thick-ness deep. They are not located in the heat-affected weld zone, but in the radius curvature as shown in the attached pictures and sketch. This is where the higheot density of thermal cracks appeared on the previously failed tee reported in the 5th Semiannual Report of operations dated Ibcember 20, 1966.

The original tee failure in May of 1966 was attributed to thermal shocking of the tee material due to the mixing of excess control rod drive 0

hydraulic water at approxicately 80 F with clean-up system return water at approximately 500 F.

A new tee was installed in May 1966 and the piping system was modified in September 1966 such that cool, excess control rod drive water is mixed with clean-up demineralizer effluent which is at approximately the came temperature.

The cracking appears to be very similar but much less extensive t' nan that observed in 1966. The 1966 failures were attributed to a thermal-induced fatigue failure.

It is noted that the original tee had a service l

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Juns 17, 1971 life of approximately two and one half vee _r: under severe thermal operating conditions. The newly installed tee operated under those same thermal con-ditions for approximately five months prior to the piping modifications.

Assuming the results of planned tests will show the cracking to be due to thermal-induced fatigue, it is sumised that the cracking condition on the recently removed tee was induced during its initial five months of opera-tion under the severe thermal mixing conditions.

Samples of the recently removed tee have been shipped to South-west Research Institute so that metallographic examinations can be performed to determine the cause of failure. When the results of the metallographic examinations are available, further information vill be submitted.

Yours very truly, RBS/ map Robert L. Haueter Electric Production CC: BHGreer Superintendent - Nuclear Div of Comp USAEC

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_3 P-Petone oATg OF 00CUMENT:

DATE RECEIVED N o.;

Seasoners Feuer Company June 17, 1971 Jane gl 1971

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NO ACTION NEC($$ARY O co ar~T O

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CLA&5aFa POST OFF*CE F4LE CODL

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W 50-155 DESCRIPTsort (Must Be Unctaesshed)

REFERRED TO DATE RECElvtD SY DaTE Ler reposting an incident in which ziemann 6-2 L-71

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a 3-inch tee dat was removM i t..

w/9 cys for ACTIOT welds contained four sli C c cr w/stech sketch of Removed Section ePN STRDUTION:

5"c'o5va" 3-inch SCH80.....

% g Pile Cy AEC PDR C -Rm-F-506-A Conoliance (2)

R. Pricy & stafC B. Thonoson Morris /Schroodar

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