In this study, crack growth rate in a standard steel elbow as a result of open and close bending moments has been investigated based on failure mechanic concepts and determination of crack growth in ductile materials. In this work, crack growth in elbows with various geometries has been investigated using finite element method. In following, assuming a primary crack in through wall circumferential or axial, subjected to in-plane closing/opening bending moment have been carried out on standard steel elbows. Finally, crack growth rate in elbows was calculated and maximum allowed crack moment and moment which causes failure were measured. Results which had been obtained from crack growth finite element modeling were compared with experimental results. FEM results are seen to have agreement with experimental results and it was shown that in elbows under close bending moment, displacement values which eventuate in failure are lower than values which result in failure in elbows under open bending moment. In finite element analysis, by increasing the elements and reducing the elements' dimensions in crack region and applying different shapes such as circle and elliptic for elements in this region, better agreement with experimental results was achieved.

Keywords: Elbow, pipes, steel, allowed moment, crack growth, open and close bending.