No abstract

Abstract. In this paper, the stresses of plate-fin structures at the different operation parameters were analyzed in actual operation process of LNG plate-fin heat exchanger based on finite element method and thermal elastic theory. Stress characteristics of plate-fin structures were investigated at the different operation parameters of that. The results show that the structural failure of plate-fin structures is mainly induced by the maximum shear stress at the brazing filler metal layer between plate and fin while by the maximum normal stress in the region of brazed joint near the fin side. And a crack would initiate in brazed joint near the fin side. The maximum normal stress is also main factor to result in the structural failure of plate-fin structures at the different temperature difference (between Natural Gas (NG) and Mixture Refrigerant (MR)), MR temperature and NG pressure of LNG heat exchanger. At the same time, the peak stresses obviously increase as the temperature difference, MR temperature and NG pressure increase. These results will provide some constructive instructions in the safe operation of LNG plate-fin heat exchanger in a large-scale LNG cold-box.

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.