Residual stresses and deformations that generated by pipe forming and pipe welding act as harmful factors causing deformation, buckling, and fatigue behavior of a pipe. In this paper, the effect of residual stresses and deformations due to three roll bending and butt-welding on the flexural behavior of a steel pipe is introduced using nonlinear finite element simulations. Numerical analysis of three roll bending pipe forming process is conducted to consider the residual stresses due to pipe forming. The forming analysis of three roller bending pipe has to consider the material nonlinearity and the geometric nonlinearity due to large deformation of a plate and take account of the contact nonlinearity due to the change of contact condition between roller and plate. Also, a fully coupled thermal-mechanical analysis is performed to simulate the butt-welding of a pipe. The moving heat source and the heat transfer coefficient is implemented by the ABAQUS subroutine DFLUX and DFILM model. Also, the flexural behavior of a pipe is evaluated by the four-point bending analysis that considers the result of three-roll bending pipe analysis and butt-welding pipe analysis as the initial condition. Mises stress, axial strains, and the moment-displacement relationship of pipes are measured through the numerical analysis because the main failure model of the pipe under bending loading is the local buckling (wrinkling) of the pipe wall.