Issue 50

M. Belhamiani et alii, Frattura ed Integrità Strutturale, 50 (2019) 623-637; DOI: 10.3221/IGF-ESIS.50.53 635 to 2 3 as validated by Hill’s equation (Eqn.. 8) and said before (Fig. 8). The present FEA results shows for   < 0,3 the hoop stress is dominant in plastic collapse. Figure 14 : The variation of the PLP* with crack angle for the repaired bonded composite system. Fig. 14 shows the variation of PLP* with 2 ,  it can be seen that the repair system increases the plastic limit load for all circumferential cracks where the PLP* reach a stable level of about 80% for 2  > 80°. In the other hand, we can say that the repair system react three times better in the longitudinal case than the circumferencial cracks. This is due to the level of reaction of the composite overwrap. CONCLUSIONS n this work, a numerical limit analysis of API 5L X65 PSL2 steel pressure vessel structure has been studied. Within the scope of this study, the following conclusions can be drawn: 1. A non-linear proportionality behaviour of the value of maximum of J integral with loading. 2. The crack propagation in depth is more dangerous than the longitudinal crack 3. at 150% of the thickness of the pipe the maximum value of the J integral remains constant and independent of the crack length. 4. The composite overwrap reduces the J integral level for a constant value (1.1 J/mm²) beyond 75% of c/t 5. It can be concluded that increasing the patch length may be detrimental to repair when it exceeds 15.75 (L / t). This limit of patch length gives us an economic benefit to reduce the global cost of the repair operation. 6. The results show that the present FE analyses agree well with Hill’s works with maximum error about 3%. 7. For a/t greater than 50%, our results converge to Carter’s model. 8. For the axial through-wall cracked pipes the FEA solution is more conservative than Folias’s solution if ρ <1.5 where it converges to Folia’s solution if ρ>1,5. 9. We note the repaired technic elevate all values of plastic limit load to an average value of PLP = 34 MPa independently to the crack geometry. 10. For through wall circumferential cracked pipes larger crack lengths   > 0,3 the analytical solutions agree with the FEA results whereas Kastner et al under predict the FEA solutions. 11. The repair system increases the plastic limit load for all circumferential cracks where the PLP* reach a stable level of about 80% for 2  > 80°. I