ML20062H704

Comments on J Halapatz 800616 & 25 Memos to Pawlicki & R Gamble,Respectively.Implication That Weld Drawbead Repair Has Significant Potential for Line Break Is Not Accurate & Neglects Previous Safety Evaluations & Svc Experience

ML20062H704
Person / Time
Site:	Sequoyah
Issue date:	06/27/1980
From:	Gamble R Office of Nuclear Reactor Regulation
To:	Pawlicki S Office of Nuclear Reactor Regulation
Shared Package
ML20062H675	List: IR 05000327/1980012 ML20062H670 ML20062H676 ML20062H682 ML20062H690 ML20062H693 ML20062H695 ML20062H700 ML20062H704 ML20062H707 ML20062H710 ML20062H713 ML20062H719
References
NUDOCS 8008210269
Download: ML20062H704 (2)

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June 27, 1980 NOTE TO: S. S. Pawlicki, Chief Materials Engineering 3 ranch Division of Engineering FROM: R. M. Gamole, Section Leader Component Integrity Section

SUBJECT:

DIFFERING PROFESSIONAL OPINION - SEQUOYAH PRESSURIZER PIPE WELD Based on my previous discussions with J. Halapat , acd NRR and IE staff over the last six months, I have some comments concerning the contents of the June 16, 1980 memorancum J. Halapat: to S. Pawlicki and the June 25, 1980 memorandum J. Halapat: to R. Gartle.

First, I believe that many of the individual technical points made by Mr.

Halaca:: are generally correct and nave merit. Certainly, it is cifficult to interpre: radiograchs to detect sensitization for the repair weld and accitional radiographic examination might better characterize the degree of sensi:1:ation in this repair. Further, there is concern for material degradation and sensiti:stion from excessive heating during repair welding, especially for austenitic stainless steels; better cocumentation and a more representative mock-up would have been helpful in evaluating the repair. Finally, NRC Pioe Crack Study Groups have evaluated similar concerns aDout IGSCC in austenitic stainless steel piping, In fact, the PWR Pipe Crack Study Groue draft recor:

recommends that a study be comoleted to define generic limits on the allowable extent of repair welcing on pipe.

However, in my judgment, the extracolaticn of these individual items to the conclusion or imolication tha: this recair has significant potential for a line treak' is not accurate and neglects previous safety evaluations and a significant amount of service experience. First, some cegree of sensitization probably exists in most welds in 3WR and PWR stainless steel piping. While tne cocuments to cefine tne degree of sensiti:ation for the repair weld may be less inan cesired, the metallogra:nic work done by TVA anc the IE evaluation incicate that

ne repair weld is no worse than the occulation of full penetration welds in LWRs. Second, tne presence of sensiti:ec material does not automatically pro-duce cracking and to imoly ina: the weld will be subject to cracking similar to tna in SWRs ignores evidence provided by many years of PWR service excerience.

There nave ceen over 100 cracking incidents in SWR primary systems and none in NR pressurizer lines. Further, even if cracking occurs, operating experience inoicates na: IGSCC has been detectec by either inscection or leak detection ,

< before excessive leakage results. Additionally, analyses by the last two NRC Pice Crack Study Groucs and various exoerimental ca:a indicated tha; even very 8 0 08g10 269

5. 5. Pawlicki large tnrougn wall cracks in comeination with faulted loading conditions are unlikely to result in large losses of coolant from stainless steel lines.

Since : believe tna: the repair weld is reoresentative of the population of pressuri:er welcs, I would not recomend furtner studies to define :Me cegree of sensitization for Me recair weld. Similarly, at this point, a third party inscection would not seem to provide significant accec assurance of integrity because of :ne attention given to this weld by IE and Decause no cracks or c:ner weld defects have been reported.

In sumary, I believe Mr. Halapa:: has raised valid coints accu: :ne metal-lurgical anc cocumentation aspects of :nis repair. However, nis focus on the presence of sensiti:ed material overlooks :ne safety issue. Successful service experience of sensitized welds that co not crack, analyses and excerimental cata :nat snow :ne potential for significant coolant loss is unlikely in stain-less steel lines naving IGSCC, the small leakage rates associated with inservice IG35C and successfui excerience in detecting small leaks indica:e ina: acceptacle system safety margins will ce maintained.

q & vb~ \k R. M. Gamole, Section Leader C:mponen: Integrity Section Materials Engineering Branen Division of Engineering cc: J. Halapat:

R. M. Gamole i

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