Abstract:

The basic principle of corrode groove on outside of steel pipe during storage was analyzed in this paper, namely the water film on the contacted surface of steel pipe, which gathered from humidity in the air, rain or gel, and the suspended particles in air, and the corrosive composition, such as SO₂, CO₂, O₂ and NaCl, in addition to the inhomogeneity of the organization and composition, which lead to the corrosion cell reaction, so that cause the corrosion initial from the contact surface of the between steel pipes, so as to form the corrosion groove.
At the same time, the corrosion groove with depth of 0.125t (t pipe wall thickness) on the pipe of Φ1016 mm×21 mm X70 API SPEC 5L was simulated using the FEM (finite element method), and the stress and strain distribution of the defect area near corrosion groove were solved at the inner pressure of 12 MPa, 10 MPa, 8 MPa, 6 MPa, 4 MPa and 2 MPa, respectively, which showed that no matter the pressure values were, the maximum stress and strain were lied at the bottom of corrosion defects groove and were in good linear relationship with the internal pressure increasing from 2 MPa to 6 MPa. When the internal pressures were greater than 6 MPa, they felled into the nonlinear model and to be yielded or even to be destroyed. In addition, the residual strength and the limit operation pressure of the corrode pipe with the defects groove of 0.125 t were calculated or simulated according to the theoretical calculation,the finite element method based on the stress, the finite element method based on strain, DNV-RP-F101, ASME B31G and experimental methods respectively. The results showed that the residual strength and the limit operation pressure of the defective parts solved by the finite element method based on stress were 424 MPa, and 15.34 MPa, respectively, which was very close to that of experimental method, the residual strength was 410 MPa and the limit operation pressure 14.78 MPa. Besides, the results also showed that it was feasible and effective to simulate the residual strength of the structure with corrosion defects using the finite element method.

Key words: Finite element methods (FEM), Storage, Corrode Groove, Stress analysis, von Mises equivalent stress