ML20138A871

Sser Supporting Util 850725 Proposed FSAR Change, Incorporating Nuclear Const Issues Group Rev 2 to Visual Weld Acceptance Criteria for Structural Welding at Nuclear Power Plants Into FSAR Table 3.8-2 & Section 3.10.3.2.2

ML20138A871
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	10/07/1985
From:	NRC
To:
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ML20138A851	List: ML20138A846 ML20138A871
References
NUDOCS 8510110114
Download: ML20138A871 (3)

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i ENCLOSURE

, BYRON STATION, UNITS 1 AND 2 BRAIDWOOD STATION, UNITS 1 AND 2 DOCKET NOS.: STN 50-455/456/457/458 .

4 SUPPLEMENTAL SAFETY EVALUATION REPORT l 3.8 Design of Seismic Category I Structures i 3.8.3 Other Seismic Category I Structures 4

I The staff concludes that the use of Nuclear Construction Issues Group (NCIG)-01, Rev. 2, 05/07/85, " Visual Weld Acceptance Criteria for Structural Welding at Nuclear Power Plants" (VWAC) will ensure adequate quality of non-ASME Code structural steel welds. These criteria are limited to non-ASME class welded steel structures where fatigue is not the governing design consideration.

Typical examples of structures to which these criteria may be applied are main building framing members and connecting members, supports for equipment and piping (non-ASME Code), cable trays and conduit, HVAC ducts and duct supports, l and miscellaneous steel including bracing and stiffeners, embedments, stairways

$ and handrails, doors and door frames, windows and window frames, gratings, Covers, etc.

There are eleven criteria addressed in VWAC. For cracks, the criteria is the f , same as in AWS D 1.1 " Structural Welding Code" - the welds shall have no cracks.

l ," Underfilled craters are acceptable if proper weld size is achieved and cracks l are absent.

I For arc strikes, surface slag and weld spatter, the VWAC criteria are based

more on the effects on structural strength than on workinanship. Arc strikes are acceptable provided cracks ce not visually detectable. Weld spatter re-maining after cleaning is acceptable. For surface slag, the criteria are

, designed to prevent the acceptance of a weld which shows a gross lack of control by the welder. Isolated surface slag which remains after weld cleen-ing has no structural significance, i

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Criteria for the following types of defects or faults are also 'rovided p in VWAC:

a) fillet weld size b) incomplete fusion c) weld overlap d) weld profiles e) undercut f) surface porosity g) weld length and location The basis for the acceptance criteria in VWAC is the amount of reduction in cross sectional area caused by the defect or fault. In such calculations,

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'the conservative approach used is to consider the length of weld in which a

-- defect occurs as being non-existent, i.e., it does not support any of the load. The standards usually allow such cross section reductions up to 12.5 percent.

There are some exceptions to this, particularly in thinner section members.

This occurs because measurements of defects or faults are rounded off up to the smallest measurement unit specified. For instance, a 1/32 inch maximum under-cut for the entire length on one side for 3/16 inch thickness material results in a 16.7 percent reduction in area. Because the 1/32 inch undercut will not be uniform along the entire length, most of the undercut will be less than 1/32 inch in depth. However, the defect or fault is rounded up to 1/32 inch.

Therefore, although the 16.7 percent maximum reduction is a theoretical possi-bility, it is not lik.ely to occur.

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The 12.5 percent " benchmark" was chosen based upon the presently allowed percent reduction in area affected by the undercut criteria in AWS D 1.1-85 for the most limiting case in the thinnest member. This is because if undercut is allowed to reduce the load carrying capability by a given number, other de-fects or faults that would result in a reduction of similar or less magnitude should also be acceptable.

The acceptance by engineering evaluation of thousands of field weldments with similar defects or faults not meeting the criteria of AWS D 1.1 has resulted in the decision to use the weldments "as is" without repair. This is possible because comon engineering design. practices result in significant margins above design requirements and a small reduction of 10 to 12 percent can be easily ac-comodated. The present undercut criteria in AWS D.1.1-85 is a practical demonstration of this.

The deviations from AWS D 1.1 as proposed in VWAC are relatively insignificant since the redundancy of these structures and their individual welds, and the conservative design practices used, allow non-ASME Code structural steel weld-

[ ments (which are not designed for fatigue) to use alternative criteria as pro-

'vided in Criterion II of 10 CFR, Part 50, Apendix B. We find these criteria are appropriate and provide adequate integrity of the affected structures and accordingly, General Design Criterion 1 of Appendix A to 10 CFR Part 50 has been met.