Issue 49

D. E. Belhadri et alii, Frattura ed Integrità Strutturale, 49 (2019) 599-613; DOI: 10.3221/IGF-ESIS.49.55 612 F) Effect of the repair method: In reality, the composite does not have a single thickness but is wound around the pipeline by several layers. By taking this evidence we have assumed two repair configurations, at first, we consider a single layer of a composite of 4mm thick, the second, we apply a repair with four (4) layers of composite and four (4) layers of adhesives to the same thickness. Fig. 21 shows the distribution of SIF along the front of cracks, it is clear that the two configurations do not present a big difference for the three modes. This result presents an e xcellent agreement with those of M. M. Benziane et al[29] C ONCLUSION he results obtained numerically by the three-dimensional finite element method enable us to draw the following conclusions: 1. We note the presence of three failure modes along the semi elliptical crack front. The maximum value of the SIF along the crack tip is that of the mode K II . 75% of the crack front is influenced by the mode II, 20% by mode I and only 5% of the crack front is commanded by the mode III. 2. For longitudinal elliptical cracks the risk of rupture of pipelines is more dangerous on the internal fronts than for external ones. 3. The repair on the external side is better with an efficiency of 81% for the mode III. This is mainly due to the direct contact of the lips of the crack with the composite which ensures a good transfer of the concentrations of the constraints of the pipe through the adhesive to the composite. 4. The composite repair technique is effective for the two crack geometries studied. 5. the rectangular crack is governed only by mode 1, while the semi elliptic crack knows the interaction of the three modes of fractures I, II and III. 6. The reduction of stress intensity factor by the composite patch leads us to conclude that the fatigue life can be improved. 7. The increase of the thickness of the patch leads to the decrease of the SIF for the internal and external crack positions. A thick patch allows a good absorption of the constraints. 8. It is necessary to optimize the characteristic and geometric (thickness, length) of the composite to have an effective repair. This can lead to low cost repair and hence decrease the cost of energy. 9. The use of a layer of composite or the decomposed in several layers to simulate the real case showed that there is not a big difference compared to our results. This confirms that only the first layer of the composite which absorb the maximum stress of the pipe. R EFERENCES [1] Mohitpour, M., Golshan, H., Murray, A. (2003). Pipeline design and construction: a practical approach. 2nd ed. New York, NY: ASME Press; 2003. pp. 499–518. [2] Chapetti M.D., Otegaui, J.L., Manfredi, C., Martins, C.F. (2001). Full scale experimental analysis of stress states in sleeve repairs of gas pipelines. International Journal of Pressure Vessels and Piping, 78, pp. 379–87. [3] Koch GH, Brongers MP, Tompson NG, Virmani YP, Payer JH. (2001). Corrosion cost and preventative strategies in the United States. Federal Highway Administration, Office of Infrastructure Research and Development, pp. 260–311. [4] Matheas, J.D. (2005). Etude du comportement mécanique de patchs composites utilisés pour le renforcement de structures métalliques aéronautiques. pp. 13-21. PhD thesis. N d’ordre : D.U. 1587 EDSPIC : 323. [5] Andrew, J., Patrick., composites- case studies of pipeline repair applications, Clock Spring Company, L.P., Huntingdon, UK. [6] ASME B31.4. (2003). Liquid transportation system for hydrocarbons, liquid petroleum gas, anhydrous ammonia and alcohols. New York: American Society of Mechanical Engineers; 2003. [7] ASME B31.8. (2003). Gas transmission and distribution piping systems. New York: American Society of Mechanical Engineers; 2003. [8] Alexander, C.R., Francini, R. (2006). State of the art assessment of composite systems used to repair transmission pipelines. Paper no. IPC2006-10484. In: Proceedings of the 16th international pipeline conference, Calgary, Canada September. pp. 25–29. T