Limit State Formulations for TLP Tendon and Steel Riser Bodies

摘要

Existing limit state formulations for tendon and steel riser bodies used in tension leg platforms have been reviewed. These include API Bull. 5C3 (for casings), API RP 2A LRFD, BS1 Sub-sea Pipeline, Danish Pipeline Code, DnV Submarine Pipeline Standard and NPD Offshore Structures Regulations, as well as formulations proposed by Johns and McConnell (Battelle), Jensen and Pedersen (Technical University of Denmark), Loh (Exxon), Murphey and Langner (Shell), Tamano et al. (Nippon Steel) and Winter et al. (TNO). Ultimate strength formulations for tension, bending and pressure acting singly or in pairs of loads are compared. There are significant differences in the strength formulae for pressure load, mainly due to the treatment of initial ovality; and for bending capacity depending upon whether plastic or first yield bending capacity is utilized. Some formulae for interaction between pressure and bending, as well as pressure and tension, imply little mode interaction, while others, specially for low diameter-to-thickness ratio, indicate strong interaction, i.e. almost a linear relationship as in all formulae for tension combined with bending.