Effect of changes in the taper-hub shape on the strength of high-pressure flanges

Taper hub is the name of a ring of triangular cross-section which is integr al with the flange and pipe to strengthen their junction. Eleven models, ma de of pearlitic-ferritic spheroidal graphite or flake case iron were tested by tightening and pressurizing to failure at room temperature. Models with four different taper-hub lengths and three different fillet rad ii were tested. Flange fillet, pipe fillet and pipe strains due to increasi ng (measured) bolt tensions were recorded and converted to non-dimensional stress indices. An approximately linear response was found owing to tighten ing and pressurization up to the nominal rated pressure of the basic Britis h standard flange. Bolt tightening caused no stresses in the pipe remote fr om the taper hub. Pressure caused only small changes at the flange fillet. The lengths of the taper hub could be reduced to five pipe wall thicknesses without increasing stresses above those in the standard shape. Doubling th e fillet radius increased the nominal hoop stress in the pipe at burst from 67 to 78 per cent of the ultimate tensile strength of the spheroidal graph ite cast irons. A reduction in the hub length does not change the failure p ressure.