Issue 49

A. Guillalet alii, Frattura ed Integrità Strutturale, 49 (2019) 341-349; DOI: 10.3221/IGF-ESIS.49.34 346 Figure 4 : Geometry of pipeline avec crack on the external surface Variables Description μ St Distribution a Crack depth (mm) 0.2t, 0.4t, 0.6t, 0.8t Fixed c Crack length (mm) a/c=0.125c-0.25c- 0,375-0,5-1-1,5-2 Fixed D Outside diameter (mm) 1219,2 0,0121 Normal t Pipe thickness (mm) 12,1 0,605 Normal P Maximum operating pressure (MPa) 8 0,08 Normal K Ic Fracture toughness (MPa.m 1/2 ) 137 13,7 Normal Table 1 : Random variables and their statistical proprieties Results and discussions a- Parametric study Reliability index is calculated using different configuration of crack shape and depth ratio. The used Reliability method is Importance sampling at the design point method described in section 3. Results of this study are presented in form of variation of reliability index. Fig. 5 illustrates the variation of reliability index with different crack to depth ratio for three cases: deep crack ( a/c=2 ), semicircular crack ( a/c=1 ) and shallow crack ( a/c=0.5 ). The calculations are made in deep point. The first observation is that reliability index decrease with increasing crack depth ratio. It seems that for all depth ratios shallow crack has reliability index lower then semicircular and deep crack. The difference is greater as depth ratio is increased. Figure 5: Variation of reliability index with depth ratio at different shape ratio. Moreover, the variation of reliability index with different shape ratios at fixed crack depths is investigated. Two cases are considered in Fig. 6: Case 1: reliability index estimated at deep point Case 2: reliability index estimated at shallow point