By taking the three working loads into account, namely pressure, temperature and pressure/temperature coupling, several finite element models for pipe parts with different inner diameters were constructed respectively, and then the triaxial distribution of pipe stresses of the special acid-, temperature- and pressure-resistant brick and Asplit HB cement was analyzed by different inner diameters of pipe nozzle under three working conditions. The dangerous degree of different positions of the pipe nozzle during working process is clarified. The results show that for the special acid-, temperature- and pressure-resistant brick, the larger the radius of the pipe opening, the larger the maximum tensile stress in the radial and annular direction under the action of pressure load. Under the action of temperature load, the maximum tensile stress in radial and axial direction increases. Under the coupled pressure/temperature load, the maximum tensile stress in all three directions increases. For Asplit HB cement, the maximum axial tensile stress increases with the increase of the radius of the pipe mouth under pressure load. Under the action of temperature load, the maximum tensile stress in the annular direction increases with the increase of the tube orifice radius, while in the axial direction, the maximum tensile stress decreases with the increase of the tube orifice radius. Under the pressure/temperature coupling load, the maximum radial tensile stress increases with the increase of the orifice radius.