Piping systems connecting critical equipment such as pumps with non-standard flanges should be designed so that all components have compatible strength. One such non-standard flange design is the so-called finger flange, used on the discharge flanges of large pumps. A finger flange uses slots instead of holes for the bolts. This design is common for certain types of equipment in use today, such as large slurry and water pumps.
In this study, finite element analysis is used to model a finger flange bolted to a standard ASME B16.5 weldneck flange and understand the areas of weakness in the overall joint. Seating stresses caused by bolt load are calculated as well as stresses experienced by the joint during operation with additional pressure applied. Stresses are compared for the region of highest stress at the junction of the hub to the pipe shell. Various aspects of the geometry are modified to evaluate the effect on flange stress.
The slots were found to have minimal effect on flange stress. Increasing the wall thickness reduces the stress in the finger flange. Bolting the finger flange to a thicker standard flange increases the stress in the finger flange. Uneven bolting was simulated by tightening a bolt and leaving the surrounding bolts loose. In this situation the finger flange experienced significantly higher stress than a standard flange exposed to the same uneven load. Gasket stress and displacement were similar between a finger flange joint and a standard joint.