The weldneck flange assembly is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the flange. The pressure tappings are provided through the flange which are at a distance of 25.4mm (1") from the relevant face of the plate. Weldneck flanges are prefered since the joint between flange and pipe can be subjected to radiography, to ensure quality of welding joint.
The slip on flange has a low hub because the pipe slips into the flange prior to the welding. It is welded both from inside and out to provide sufficient strength and prevent leakage. The slip on flanges are bored slightly larger than the OD of the matching flange. SORF flanges are not preferred where pressure tapping through flange is required, since after welding in line blocks the tapping holes which need to be redrilled at site after welding in line.
Orifice assembly with carrier raing and flange union is provided to facilitate pressure tapping, by means of corner tappings. This construction is generally used for lower sizes (less than 2"). However carrier rings can be used for higher line sizes also.