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Fatigue crack propagation tests are carried out on arc-shaped specimens prepared from MDPE gas pipes. Damage zone characterization is achieved using the diamond wafer sectioning technique from partially propagated and prematurely arrested cracks. Damage ahead of the crack-tip is used to assess a damage parameter and reliability based on statistical laws and subsequent use the PHIMECA Software. It is shown that a length and a width associated with a corresponding change in thickness at the fracture surface satisfactorily describe the damage zone size. The 3-parameter Weibull model gives the best reliability behavior and a critical lifetime of 82%. When considering separately both the Dugdale model and experimental damage zone measurements, it is possible to establish the evolution of the reliability index as a function of crack length. It is concluded that the reliability index approach based on damage provides a more consistent representation compared to analytical models. [ABSTRACT FROM AUTHOR]