ML20138H126
| ML20138H126 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 10/18/1985 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20138H123 | List: |
| References | |
| NUDOCS 8510280240 | |
| Download: ML20138H126 (3) | |
Text
.
Enclesure SUPPLEMENTAL SAFETY EVALUATION ON IMPLEMEl4TATION OF fCIG-01, REV. 2
" VISUAL WELD ACCEPTANCE CRITERIA FOR STRUCTURAL WELDIliG AT fiUCLEAR POWER PLANTS" FOR CLINT0fl i
POWER STATION (FSAR SECTION B.3.3.2)
B.3.3.2 Testing and Inspection of Weldments The staff concludes that the use of Nuclear Construction Issues Group (NCIG)-01, Rev. 2, 05/07/65, " Visual Weld Acceptance Criteria for Structural Welding at Nuclear Pcwer Plants" (VWAC) will provide adequate quality of non-ASl;E Coce Structural steel welds. These criteria are limited to non-ASME class welded steel structures wherc fctigue is not the governing design consiceration. Typical examples of structures to which these criteria may be applieo are raain building framing members and connecting members, supports for equipment and piping (ror-ASME Code), cable trays and conouit, HVAC duct supports, and miscellaneous steel including bracing and stiffeners, embedments, stairweys and handrails, doors and door frames, windows and window frames, gratings, covers, etc.
There are eleven criteria addressed in VUAC. For cracks, the same criteria as exists in AWS D 1.1 is specified; the welds shall have no cracks.
For underfilled craters, if proper weld size is achieved and cracks are absent, there is no reason for rejecting thcn, and therefore, they are acceptable.
i h For arc strikes, surface slag and wcid spatter, the VWAC criteria are based
$"; E more on the effects on structural strength rather than workmanship. Arc e"
strikes are acceptable provided cracks are not visually detectable. Weld U
gh spatter remaining after cleaning is acceptable. For surface slag, the i
P o
criteria are designed to prever.t the acceptance of a weld which shows a
-m$h gross lack of control by the welder.
Isolated surface slag which remains after weld cleaning has no structural significance.
I Criteria for the following types of defects / faults are also provided in VWAC:
A) fillet weld size 2.)
incomplete fusion c) weld overlap d) weld profiles j
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, the conservative approach used is to consider the length of weld in which a defect occurs as being non-existent, i.e., does not support any of the load.
Such cross section reductions are usually less than 12.5 percent.
There are some exceptions to this, particularly in thinner section members. This occurs because measurements of defects / faults are rounded off up to the smallest measurment unit specified.
For instance, a 1/32 inch maximum undercut 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.
Although the 16.7 percent maximum reduction is a theoretical possibility, it is not likely to
- occur, i
l 1
1 e
s 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.
The reasoning behind this is that if undercut is allowed to reduce the load carrying capability by a given number, other defects / 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 / 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 common engineering design practices result in significant margins above design requirements, such that a small reduction of 10 to 12 percent can be easily accommodated.
The present undercut criteria in AWS 0.1.1-85 is a practical demonstration of this.
The deviations from AWS D 1.1. as proposed in VWAC are relatively insignificant in that the redundancy of these structures and their individual welds, and the conservative design practices used, allow non-ASME Code structural steel weldments (which are not designed for fatigue) to use alternative criteria as provided in Criterion II of 10 CFR, Part 50, Appendix 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.
i
..- -.