Abstract: The pre-tightening of flange bolts is an important factor to ensure the sealing effect and prevent leakage of the flange connection system, and how to determine the tightening torque of flange bolts is the core issue in the flange pre-tightening process. This paper highlights the common methods for controlling the pre-tightening force of the flange connection system. In order to ensure the safety and reliability of the flange connection system, the paper puts forward a set of calculation methods for reasonably selecting the bolt tightening torque. Meanwhile, it points out the main differences in the selection of flange pre-tightening force and yield strength ratio in domestic and foreign specifications. And on this basis, the paper proposes a practical and reliable method for selecting the constant torque wrench to control the flange pretightening and sealing in engineering.

Key words: pre-tightening force, tightening torque, flange, gasket, double-screw bolt