The strength of tubular members of the fixed steel offshore structures is usually evaluated through common guidelines such as API RP 2A (ASD), or EC3 (Eurocode) and DnV OS C101... (LRFD). In the paper, the method of strength assessment in accordance with API, EC3 is compared with a direct method based on nonlinear numerical models. According to API, strength of the tubular is checked based on frame elements. According to EC3, the strength is checked by cylindrical shell elements. According to numerical method, the pipe is modeled by shell elements. The tubular strength is checked by the comparison of the actual stress based on non-linear analysis and yield strength limit of material. The three methods mentioned are used to evaluate the strength of an existing fixed steel platform at Vietnam sea. The three methods give similar results for assessing tubular strength. Along with that, it also confirmed the suitability and applicability of the evaluation method through numerical models.