FINITE ELEMENT MODELING OF FATIGUE CRACK GROWTH IN CORRODED PIPELINE

Ensuring the safety of pipelines in the oil and gas industry is important to prevent financial losses and human injuries. One of the threats of pipelines is corrosion effects and it may occur locally and by repeating changes in loading and operation pressure conditions, it could lead to the phenomenon of fatigue in corroded pipelines. In this research, the corrosion of the inner surface of the API 5L Gr. x52 pipeline using ASME B31.G. and the finite element method was studied and the obtained results along with experimental results were compared. It was found that the effective area method of ASME B31.G. with a maximum error of 3.83% compared to the FEM had good compatibility with the FEM and the laboratory method. Then, by taking into account the phenomenon of fatigue due to working pressure changes, crack growth due to both fatigue and corrosion was studied simultaneously by theoretical methods and extended finite element method. The effect of various factors and conditions on the formation and crack growth due to fatigue by considering the effects of corrosion on the inner surface of the pipeline using XFEM was investigated. By the failure pressure of corroded pipelines, the fatigue crack growth would be investigated and by obtaining stress intensity factors using Paris law and XFEM, results would be investigated in terms of important factors in the fatigue crack growth and the significance and effect of depth and length of cracks on the stress intensity factors will be detected by the results of XFEM. Using the results, the effects of various factors such as corrosion area characteristics, crack geometry including crack depth, crack length, and fluctuations in fluid working conditions including work pressure in fatigue crack growth were investigated. In the model 61%, the first mode of the stress intensity factor of the theoretical method with an error of 0.43% compared to the XFEM showed good agreement with the results of the theoretical methods and the XFEM in the field of fatigue crack growth.