Issue 49

H. Berrekia et alii, Frattura ed Integrità Strutturale, 49 (2019) 643-654; DOI: 10.3221/IGF-ESIS.49.58 653 Figure 10 shows the cycle variation at rupture as a function of the length and width of the corrosion defect during pipe service. It is noted that the lifetime at rupture in the vicinity of the corrosion defect decreases when the length and width of the defect increase. 0 20 40 60 80 100 10000 20000 30000 40000 50000 0 20 40 60 80 100 lifetime N R at rupture width of corrosion defect in mm Extension of corrosion defect Figure 10 : Number of cycles at rupture. C ONCLUSION n this study, a method was developed to highlight the weaknesses of the ASME / B31G method using the concept of damage mechanics. The prediction of damage initiation from an existing corrosion defect of steel pipes has been investigated using numerical approach. A constitutive coupled behaviour-damage based on the concept of effective stress and on finite element method to determine a critical value of stress at the vicinity of corrosion defect. A Finite element simulation is based on the steel elastoplastic constitutive law and on the chosen mesh for a good relative convergence accuracy of the damage values. For the depth of defects does not exceed 10% of the pipe thickness, we have shown that defects can resist to the hydrostatic pressure test or a constant service pressure without damaging the pipe. However, these defects do not resist to pressure variations, which may generate a phenomenon of fatigue causing a failure of pipe. Therefore, failures can occur for corrosion defects when the depth value reached 10% of the pipe thickness, while the ASME / B31G method states that no rupture of pipe occur in this case. However, it has been shown that the concept of damage mechanics allows determining the optimum depth defect in order to predict the failure of pipe. R EFERENCES [1] ASME B31G (2009): Manual for Determining the Remaining Strength of Corroded Pipelines [S]. American Society of Mechanical Engineers, New York. [2] Caligiuri, R. D. (2015). Critical crack path assessments in failure investigations, Frattura ed Integrità Strutturale, 34 125-132; DOI: 10.3221/IGF-ESIS.34.13 [3] Zampieri, P. Curtarello, A.Pellegrino, C. Maiorana, E. (2018). Fatigue strength of corroded bolted connection Frattura ed Integrita Strutturale, 12 (43), pp. 90-96. DOI: 10.3221/IGF-ESIS.43.06 I