Design of a Large Rectangular Flange

Abstract

A large rectangular flange (5’ wide × 12.5’ Long) was designed using finite element analysis for a horizontal mixer vessel. The mixer vessel contained a large horizontal agitator with the shaft protruding through the two flat ends of the vessel. The horizontal vessel was split in the middle horizontal plane creating a large rectangular opening to be sealed by the two large rectangular flanges. The size of the flange, the type of gasket, the bolt preload required to obtain a reasonable seal made it a design challenge to design this bolted flange assembly. To start with, an estimate was made based on the calculation of the thickness of the flange using an equivalent circular flange. The finite element analysis of the whole assembly was preformed using the FEA software ANSYS. After several iterations, an acceptable solution was found with acceptable flange and bolt stresses. The seating stress in the gasket was also above the recommended gasket seating stress. Thus, the flanged joint was designed to be in compliance with ASME B&PV Code, Section VIII, Div-1. The vessel and the bolted flange assembly was successfully fabricated and hydrotested based on this design and it is successfully operating in the field.