Hi,
Does anyone have any technical information why weld-neck flanges are better than slip-on fanges or vise-versa?
I know they are both rated the same.
Its related to the flange-to-pipe weld quality not the flange face quality (rating of the flange). I have forgotten most of the details but the if you look at the size/shape of the weldment you will see that for a butt weld (achieved with the WN flg) it is possible to get a far more robust weld than a lap weld (with the SO flg). If you look up welding in Google, or get a good welding handbook, it will give you all the details
If this is B31.3 piping, also note that the stress intensification factor for a weldneck flange is 1.0 whereas for a slip-on flange it is 1.2. This may affect a stress analysis on the system.