[ew6082]

It's more like a re-usability factor in mechanical design. Higher safety factor tends to equal fewer cracked welds down the road in anything exposed to vibration and shock. I've only ever heard of one lifting fixture weldment that used a safety factor of 1.0. Every single welded joint was taped instead of painted, and peeled off and fully mag particle tested between each use.

Keep in mind that weld strength is not one single number, it is a wide range. You can inspect a weld with X-ray, UT, MT, and PT methods to narrow the range, but there are still variable heat input, soluble hydrogen content, pre-heat and post-weld heat treatment factors that ALL affect the final hardness/brittleness and ultimate strength of a welded fabrication.