This paper presents a computational approach for the lifetime assessment of structures under thermomechanical loading. One of the main features of the work is the search for simplicity and robustness in all steps of the modeling, in order to match the proposed method with industrial constraints. Among the peculiarities of the engineering environment are the imposed commercial computer programs and the short time delays for manufacturing. The proposed method is composed of a fluid flow, a thermal and a mechanical finite element computation, as well as a final fatigue analysis. The efficiency of the approach is proved by comparison with experimental results on prototype manifolds. The numerical results match both the localization of the damage zone and the lifetime.