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It is proposed a new methodology for calculating safety factors in triaxial casing design, regarding Ultimate Limit State (ULS) models. The definition of an equivalent axial force allows an unified graphical approach, in which both ULS and Serviceability Limit State (SLS) envelopes are represented in the same space. A review of the ULS casing design proposed in the standard is presented, and some considerations are made on the usage of Klever-Stewart and Kever-Tamano models. Both are defined for combined load analysis but are not effective for triaxial casing design routine, for they only compare the applied internal/external pressures to the design limit. Thus, two additional limit states are verified: axial and triaxial. Furthermore, the ULS envelopes (Klever-Stewart and Klever-Tamano) are plotted in the same load space as the SLS envelopes, allowing for an analysis on both limit states in a single graphic …