Issue 49

H. Berrekia et alii, Frattura ed Integrità Strutturale, 49 (2019) 643-654; DOI: 10.3221/IGF-ESIS.49.58 651 Using a stepwise method simultaneously with the method (scheme) implicit Newton, which ensures good convergence [17]. The method developed above gives versus of the internal pressure of the pipe, the value of the damage, and the accumulated plastic strain and stress components at each instant until a macroscopic crack initiation at the defect corrosion. This allows determining the maximum lifetime that a corroded pipe could support in the case of a longitudinal corrosion defect. The maximum lifetime is the lifetime value corresponding to the critical value of the damage D C (corresponding to crack initiation). Figure 8 shows the damage as a function of cycles number for retained corrosion defects. It is noted that the damage is initiated in the material for a number of cycles equal to N 0 (microscopic crack initiation) and the microcrack propagates until a macroscopic crack is obtained for a number of cycles equal to N R . Figure 8 also highlights the effect of the degree of corrosion (extension and width of the defect) on the pipe lifetime . 0 6000 12000 18000 24000 30000 36000 42000 48000 54000 0,000 0,025 0,050 0,075 0,100 0,125 0,150 0,175 0,200 0,225 0,250 0,275 0,300 Déf-95 Déf-75 Déf-65 Déf-60 Déf-45 Déf-30 Déf-25 Déf-20 Déf-10 Déf-5 Damage Number of cycle Figure 8 : Damage as a function of cycles number. Based on Figure 6, we can transform the numbers of cycles in lifetime, that is to say in number of days or years knowing that: 1 cycle = 10 days Cycles number Days number Defect N 0 Nr N 0 Nr Defect-95 44 7143 440 71430 Defect-75 88 14286 880 142860 Defect-65 132 21429 1320 214290 Defect-60 154 25000 1540 250000 Defect-45 176 28572 1760 285720 Defect-30 198 32143 1980 321430 Defect-25 220 35715 2200 357150 Defect-20 242 39286 2420 392860 Defect-10 264 42858 2640 428580 Defect-5 286 46429 2860 464290 Table 4 : Number of cycles according to corrosion defect.