Issue 49

E. Abdelouahed et alii, Frattura ed Integrità Strutturale, 49 (2019) 690-697; DOI: 10.3221/IGF-ESIS.49.62 694 three composites, boron / epoxy and the most resistant patch in areas where the temperature is high for the repair of cracked transport pipelines. Pipeline Steel API 5L X70 , e pipe = 4 mm Composite Patch e patch =2mm, P int =Variable Adhesive FM-73, e a = 0.2 mm Crack length a=5mm P int (bar) 0 20 40 60 80 100 K 1 (MPa.m 0.5 ) 0 10 20 30 40 50 60 Boron/epoxy Glass/epoxy Carbon/epoxy Figure 4 : SIF variation according to the internal pressure T(°C) 0 10 20 30 40 50 60 70 K 1 (MPa.m 0.5 ) 0 2 4 6 8 10 12 14 16 18 Boron/epoxy Carbon/epoxy Glass/epoxy Pipeline Steel API 5L X70 , e pipe = 4 mm Composite Patch, e patch =2 mm Adhesive FM-73, e a = 0.2 mm Crack length a=5mm Figure 5 : SIF v ariation according to the temperature of the external environment The temperature of the external environment as well as the type of the patch composite clearly played a determining effect on the stress intensity factor levels. On one side the temperature weaken the adhesive accumulating the load on the pipeline and on the other hand the quality of the composite of the patches conditions the absorbed quantity of the loads, the more the composite is rigid more it allows the adhesive to transfer more than charge. However, this transfer is limited by the capacity of the adhesive, which will be limited even more by the presence of temperature as a climatic load on the structure. Effect of crack depth Fig. 6 shows the evolution of the stress intensity factor at the bottom of the composite patch repaired API 5L X70 steel pipe crack as a function of the crack depth change with respect to the thickness of the pipeline. We noticed that the KI increases when increasing the depth of the emerged crack, so the stresses are very important at the front of the crack. It is deduced that the quality of the repair decreases in cases where the crack is very deep. It is also noted that the effect of the composite quality of the patch follows the same variation as that of the stress intensity factor. This effect also retains the advantage of its quality regardless of the parameters analyzed. The more the crack depth increases, the more the repair affects its effect.