High pressure flange connections for LDPE plants are commonly designed using lens ring gaskets and bolted flange connections. The rules given in the ASME Code Sections B31.3, VIII Div. 2 or VIII Div. 3 for bolted-flange joints offer no guidance for the calculation of threaded flanges.
In this paper, an approach is presented that considers internal pressure and external loads on a flange connection and fulfills the requirements of ASME Section VIII Div.3 and ASME B31.3. Of specific interest is the dimensioning of bolts due to the bending moment with a method that avoids the over-conservatism of the rules given in ASME VIII Div.2 and ASME B31.3. Furthermore, a simplified calculation for threaded flanges considering the stress classification and stress limits given in ASME VIII Div. 3 and using Finite Element Analyses is described.