Bending Moment in Flange Design, Capacity, Allowable Loads and FEA Methodology

Abstract There are many types of flange and clamp connectors in use and described by different standards. Most of them are based on the linear elastic methodology and allowable stress concept (ASME, API flanges). More modern designs (ISO 27509 and NORSOK L-005 Compact Flanges, NORSOK U-001 subsea flanges) are based on elastic plastic principles and plastic collapse capacities. For all of them defining the tensile structural and functional limits is relatively transparent and seamless process. Often the external allowable Bending Moment load at rated Pressure is one of the most critical characteristics for subsea use and High-Pressure connections. To predict capacity and allowable Bending Moment is more complicated especially for modern flange types. In this paper author will focus and explaining already existing design methods with relation to the FEA assessment and modern connections structural and functional capability. The topic will be discussed based on the Compact Flange (ISO 27509 and NORSOK L-005) connection example and in related structural FEA long term functionality check based on DNVGL-RP-F112 recommendations (Hydrogen Induced Stress Cracking for subsea Duplex and Super Duplex material). In the presented example the focus will be on the flange itself, but the attached pipe also be included in the evaluation. The topic discussed in the paper and the conclusions are included in the FEA recommendation in the newest national NORSOK L-005 flange design code release.