Numerical Investigation of the Strain Characteristics of a Natural Gas Transportation Pipeline Crossing Tunnel

To ensure the safe operation of a natural gas transportation pipeline (NGTP) crossing tunnel, a model is established to analyze the strain characteristics. Some factors affecting the strain are considered in this paper. The results show that the strain failure of a NGTP crossing tunnel may occur in the two elbows of the NGTP located at the tunnel entrance and the position in contact with the fixed pipe clamp near the tunnel entrance. At the same time, the strain of the NGTP crossing tunnel is obviously affected by the temperature change of natural gas. So, the temperature change should be controlled within 8 K in the actual operation process. The wall thickness, the length of the NGTP, and the slope angle of the crossing tunnel are also main factors to affect the strain of the NGTP crossing tunnel, while the operation pressure and mountain slope angle have little effect when the operation pressure is 6–11 MPa. The maximum value of Mises equivalent strain is also obviously affected by the pipe diameter when it is more than 273 mm. Meanwhile, a prediction model for the maximum value of Mises equivalent strain is also established by the nonlinear fitting method and the deviation is within ±15% between the calculations and simulation results. The above conclusions will provide a theoretical basis and data support for the safe operation and design of NGTP crossing tunnels.