Last at attention has brought to the failure of oil gas pipelines which fatigue stress corrosion cracking (SCC). This phenomenon generally happen suddenly and dangerously . Even small considerable changes on internal pressure of oil gas in transfer pipeline will lead to fatigue in the pipe. Combining the fatigue and stress corrosion leads to fatigue stress corrosion. Failure rate caused by this phenomenon is higher than fatigue and stress corrosion and is commonly takes places in the near neutral pH environments. In this study the life time of buried oil gas pipes calculation is investigated. Outer surface cracks in different sections of the pipe near welding line as well as cracks on the welding line are considered. Residual stresses due to welding process make critical cracks around welding line. Cracks with different dimensions are modeled in Finite element software (ABAQUS) and the least dimensions of the crack to initiate fatigue stress corrosion are calculated. Then pipes with different welding conditions are investigated and critical sections are determined. also the effect of reducing residual stresses due to welding on the life time and the position of the critical crack is determined. There is a time which is needed for cracks to reach a critical size and after this time cracks grow due to fatigue corrosion failure. Time of this failure is also calculated. The results of numerical calculations with ABAQUS engineering finite element software done in this dissertation obtained here can be mentioned and summarized as below: 1. Location of Critical sections in transfer pipelines with various welding conditions is different. This section are 2.3mm to 2.5mm far from welding line for the case study in here. 2. The minimum size of crack to initiate fatigue stress corrosion cracking has been calculated for special condition to be 2.5mm. 3. Life time of pipeline with different crack size in different welding conditions were calculated. This time can be varied from 37 year to 44 year depending on residual stress from welding. 4. In this phenomenon The cracks grow elliptically and the initial shape of the crack has not influence on the final crack shape. Key Words Stress Corrosion Cracking, Fatigue, Pipeline, Residual Stress, Crack Growth
