In the present work the calibration is presented of a partial safety factor format for the verification of the hull girder in bending conditions. The calibration is performed by means of a second level reliability model, based on a FORM/SORM procedure. All the steps of the calibration process are described, including: choice of the failure equations inherent to the problem, characterisation of the stochastic model for the second level analysis, application of the analysis to a calibration set, selection of a target reliability, identification of proper ranges of variability for the partial safety factors, choice of a criterion of closeness of the code to the target. The procedure is in the present case applied to a homogeneous set of longitudinally framed, double hull tankers. The result of the study is a reliability-based formulation for the checks of mid-ship sections: formats of this kind are suitable to be adopted as Rules by Classification Societies.