Issue 49

H. Berrekia et alii, Frattura ed Integrità Strutturale, 49 (2019) 643-654; DOI: 10.3221/IGF-ESIS.49.58 644 project. By way of example, the rehabilitation of the GZ1 Hassi R'mel-Arzew gas pipeline carried out by DRC / SONATRACH for the SC5-TA section, ie 108 km, was based on a comparative study between two variants: -Installation of a new line of 108Km with acquisition of new tubes. -Reuse of recovered tubes that have already been used for some thirty years of service or from remaining projects and rehabilitated according to the conditions of the ASME / B31G method [1] which confirms the reuse of the tubes at the maximum operating pressure of the gas pipeline at 70 bars. The example of the gas pipeline GZ1: translates into an overall cost of around 24.892 DA per linear meter for a rehabilitated tube (Tube + Coating + Pose) while if a new section was put the cost would have been 35.065 DA lm. In conclusion, DRC / Sonatrach opts for the first variant which consists in realizing a significant financial saving, ie the use of rehabilitated pipes. The ASME / B31G method [1] used by DRC / SONATRACH for the determination of the new operating pressure of a corroded pipe assumes that a pipe with a depth of corrosion defect not exceeding 10% of its thickness can be reused at the operating pressure without any risk and this regardless of the extension and the width of the corrosion defect. Many researchers have investigated the effect of corrosion and fatigue phenomena on the life-cycle of materials and structures. Based on the visual, metallurgical, and fractographic analyses as well as calculations using established ASME methodologies, Caligiuri has studied the rupture of natural gas pipeline in San Bruno, California [2]. He observed that the failure was caused by the combination of a missing interior weld, a ductile tear, and fatigue cracking. Zampieri et al. have investigated the influence of the corrosive phenomenon on the fatigue strength of a friction type joint made of high strength preloaded bolts [3]. They observed that the accelerated corrosion process applied to the specimens caused a not negligible reduction of the fatigue strength of joints. These authors have studied the fatigue behaviour of a bolted connection with high strength bolts using finite element method in order to determine the fatigue life cycles of the studied joint. These results suggest that other factors may influence the decrease in fatigue resistance of the corroded connection, such as a variation in the slip coefficient between plates or a certain amount of loss of bolts pretension, which may resulted in a decrease in the friction resistance of the connection and consequently a bearing type behaviour of it [4]. Based on Continuum damage mechanics (CDM), Gabriel Testa et al. [5] have used the Bonora damage model (BDM) to predict the strain limit capacity of X65 steel grade used for pipeline application. it was shown that numerical simulation with CDM could be used to carry on “virtual experiments” for the determination of the material fracture toughness with high degree of accuracy. Using conventional mathematical methods, B31G, RSTRENG-1, Shell-92, DNV, PCORR, and Fitnet FFS, Terán et al. [6] analyzed a combined corrosion defects, which joins together a general corrosion and a pitting corrosion defects to predict the failure pressure of corroded steel pipelines. It was found that the failure pressure predictions of general corrosion combined with a pit are affected by the length and depth of two corrosion defects. In our study, we develop constitutive equations taking into account behavior-damage coupling of material to highlight the weaknesses of the ASME / B31G method [1] and show for defects whose depth does not exceed 10%, these defects can survive hydrostatic testing but will develop during service when the pressure is variable [2]. Our research work will focus on developing a method to highlight the weaknesses of the ASME / B31G method [1] and its subsequent modifications. ASME / B31G code is one of the solutions for an assessment of the influence of corrosion defects on pipe integrity .Since it is often regarded as too conservative. Considering a behavior-damage coupling of the material, finite element numerical simulations were carried out on XC65 steel pipes with pitting in the axial direction. Depending on the size of the corrosion defect (length and width) [3].for a depth equal to 10% of the pipe wall thickness, the critical or dangerous area where the equivalent Von Mises stress is maximal is determined by the finite element code ANSYS [7]. The calculation of the crack initiation conditions in the critical area is obtained from the history of strain components taken as the output of the finite element calculation. M ODELING o model the pipeline, we used the ANSYS Workbench 15.0 [7] software with two cases, a model with a rectangular defect and a model with a parabolic defect. Given the symmetry of the pipeline, we modeled a half cylinder. The dimensions of the structure are length, radius and thickness. Thus, we have been able to model the corrosion of the X65 steel pipe taking into account the geometry of the defects, the boundary conditions and the mesh. T