Investigation of the Ratcheting on Corroded Places with Different Shape and Depths in Elbow Pipe under Internal Pressure and Cyclic Bending Moment

In most industries, such as Petrochemical and Nuclear power plants design of pipelines which operate under high pressure is important. Especially when the pipelines are subjected to external cyclic loads for example during earthquakes. The situation becomes more severe when chemical reactions cause corrosion in pipe walls. In this case, ratcheting effect due to the cyclic mechanical load is magnified due to the corroded region and it becomes a major concern. In this paper the ratcheting behavior of corroded elbows have been investigated using finite element based software ABAQUS and numerical solution method. Two forms of corrosion: spherical and cubic geometric shapes are used with two depths of one and two millimeters on the sensitive areas such as symmetry axes in the intrados, crown and extrados of the elbow Finally results suggests the corrupting influence of corrosion in term of ratcheting and consequently increase this corrupting influence with increase depth of corroded and also its reliance to the geometry of applied corrosion. So the ratcheting on corroded place with cubic shapes is larger than spherical shapes. The results show that the ratcheting in the circumferential direction is too large compared with the axial direction.