Flange Connections Design Resistances in Light of the LRFD Methodology Presented by DNV ST-F101 Standard

Abstract The LRFD methodology presented in DNV ST-F101 standard is based on design resistance of the component as well as the load categories which are defined in relation to the probability of appearance. In addition, different safety classes are defined for systems with different severity as well as the test and material requirements. The code itself is often used for subsea pipeline design and in particular for designing pipe dimensions. With a quality understanding of the system, existing loads and design method; the code allows to design more robust and better fitted systems then most of the other codes. That will affect the economic aspects which is often beneficial for operators. Currently the flange connections design is not described in detail, and other codes and standards are referred to. This can lead to solutions that are not in line with the safety level presented by the DNV ST-F101 standard, often being overly conservative or much “bulkier” than necessary. In this paper, guidance and recommendations for how to harmonize the design of flange connections with the safety level and test/material requirements defined in the standard, using the LRFD methodology, is presented. Based on the flange example, the allowable loads and capacities are presented for different codes and compared to the proposed approach based strictly on DNV ST-F101 methodology. The detailed method and recommendations presented in this paper are proposed to be included to the next DNV ST-F101 code revision.