Standard practice is to set flanges so the vertical and horizontal centerlines fall between bolt holes. Fitters say to two-hole a flange, or to make sure it's two-holed, because it puts valve stems and branch outlets square when matching flanges line up. A flange welded one-holed will not mate with equipment built the standard way without rotating everything.
Flange on the new spool is one-holed, it's going to put the valve stem cocked, cut it off and two-hole it.
Put a level on two bolt holes across the top of the flange; if the bubble's dead center, it's two-holed.
Also heard as
- two-hole
- straddle the centerline
- two-holed
Related terms
Raised face
A flange facing where the gasket surface stands slightly proud of the bolt circle area, concentrating gasket load.
Butt weld
An end connection where a beveled valve or fitting end is welded straight to beveled pipe with full penetration.
Dutchman
A short filler piece of pipe cut in to close a gap or correct a misfit between two spools.