An experimental and analytical investigation into the 3D hot bend of API 5L X65 pipeline

Pipelines for natural gas transmission may be subjected to plastic deformation by an outside force such as ground subsidence, ground liquefaction, hot bending, cold bending and mechanical damage. Plastic deformation affects the tensile properties and fracture toughness. Tensile test, Charpy impact test and S-N fatigue test were conducted on an API 5L X65 pipe to investigate the mechanical properties of pipeline subjected to plastic deformation during 3D hot bend. Tensile and fatigue test revealed that yield strength, tensile strength and fatigue strength of the extrados of the 3D bend were higher than those of the intrados of the 3D bend. However, Charpy impact energy of the intrados of the 3D bend was higher than that of the extrados of the 3D bend. There is no variation of strain at the crown according to the numerical analysis to the 3D hot bend. The equivalent strain up to 19 % shows in the side of the intrados of the 3D bend. The equivalent strain up to 15 % displays in the side of the extrados of the 3D bend.