The new API (American Petroleum Institute) RP 2A (Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms) will have two co-existing versions: API RP 2A-WSD (Working Stress Design) 22nd edition and API RP 2A-LRFD (Load Resistance Factor Design) 2nd edition. API RP 2A-LRFD 2nd edition will adopt most of the technical provisions of ISO 19902:2007 1st edition, which was originally derived from API RP 2A-LRFD 1st edition. In parallel, ISO 19902 2nd edition is being prepared for publication. The objective of this paper is to present key technical alignments in the harmonization of the latest editions of API RP 2A-LRFD and ISO 19902 in the following aspects:
unity check (UC) of tubular members with hydrostatic pressure,
UC of conical transitions, and
minimum capacity requirements of tubular joints.
Based on findings from the AKADEME project (Energo Engineering, 2016), API RP 2AWSD 21st edition and ISO 19902:2007 1st edition have reasonably good alignments of UC ratios for tubular members without the hydrostatic pressure checks. When hydrostatic pressure checks are included, UC ratios vary depending on whether members are in axial tension or compression. API RP 2A-WSD 21st edition and ISO 19902:2007 1st edition have identical member code check equations when members are in axial compression with hydrostatic pressure. For members in axial tension with hydrostatic pressure, API RP 2A-WSD 21st edition code check equations provide a reasonably conservative fit to existing test data. For conical transitions, API RP 2A-WSD 21st edition computes UC ratios using the tensile strength instead of yield strength. ISO 19902:2007 1st edition checks the combined longitudinal, hoop and local bending stresses, resulting in more conservative UC ratios. The Norwegian NORSOK standard checks the combined longitudinal and hoop stresses without considering local bending stress, and checks local bending stress separately. Review of a study performed by Maersk/DNVGL shows that ISO 19902:2007 1st edition produces the most conservative results while NORSOK produces the most reasonable (least conservative) results comparing with Finite Element Method (FEM) analyses. It is recommended to consider adopting the NORSOK conical transition code check equations for future revisions of API RP 2A-LRFD and ISO 19902. The minimum capacity requirements for tubular joints in API RP 2A-WSD 21st edition and ISO 19902:2007 1st edition are different. It is well known in the offshore structure community that the ISO 19902:2007 1st edition minimum joint strength requirement is overly conservative. As such, adopting the API RP 2A-WSD 50% effective strength requirement is recommended.