The relationships between the strain capacity in compression or bending of pressurized line pipes obtained by finite element analysis and that in compression predicted by an analytical solution are investigated in this paper. A series of finite element analyses was conducted to develop a database of the strain capacity in compression or bending of API X70 and X65 grade line pipes with diameters of 1420, 1220, and 1020 mm and pressurized to 9.8 or 7.4 MPa. The strain capacity of the line pipes obtained by finite element analysis is proportional to the strain capacity in compression calculated by the analytical solution.
Several semi-empirical design formulas have been employed in current design guidelines in order to predict the strain capacity of line pipes. Most of the design formulas deal with bending deformation caused by lateral ground movements (JGA, 1982; Gresnigt, 1986; Murphy and Langner, 1986; Zimmerman, Stephens, De Geer, and Chen, 1995, for example). However, one design formula focusing on axial compression is used to withstand the ground motion (JGA, 1982). Suzuki and Toyoda (2002) derived an analytical solution to predict the strain capacity in compression (SCC) of an unpressurized line pipe expressing the stress-strain curve by the Ramberg-Osgood formula (Ramberg and Osgood, 1943). Moreover Suzuki, Zhou, and Toyoda (2008) derived another analytical solution representing the strain hardening properties by an exponential function.
SCC and strain capacity in bending (SCB) of line pipes were obtained by conducting a series of finite element analyses (FEA). API X65 and X70 grade line pipes with diameters of 1020, 1220, and 1420 mm, stress ratios of 1.020, 1.030, and 1.040, and pressurized to 7.4 and 9.8 MPa were used for FEA. Wall thicknesses were calculated according to the working condition coefficients of 0.60 and 0.75 (SNiP, 1986) and other values between the two thicknesses were also taken into account. The stress-strain curves were featured by the stress ratio σ2.0/σ1.0 where σ1.0 and σ2 0 meant the engineering stress defined at the total strain of 1.0 and 2.0%, respectively.
