Slip on pipe flanges are typically provided with a raised or flat face. When a raised face is necessary for slip on pipe flanges, the standard height is 1/16 inch for slip on pipe flanges fewer than 400#. For slip on pipe flanges of 400# and up, the standard slip on pipe flange raised face height is 1/4 inch.
The slip-on flange
is positioned so the inserted end of the pipe or fitting is set short of the flange face by the thickness of the pipe wall plus 1/8 of an inch, which thus allows for a fillet weld inside the SO flange equal without doing any damage to the flange face. The back or outside of the slip-on flange or SO flange is also welded with a fillet weld.