The fastening of the high-strength bolt must be carried out twice, the first time is the first screw, the initial tightening is 60%-80% of the standard axial force (that is, the tensile force) of the bolt, and the torque value of the initial screw shall not be less than 30% of the final screw torque value. The second tightening is the final screw. In order to evenly stress all the bolts in the bolt group, the initial and final screws should be strictly in the fastening order. Operate symmetrically in the "meter" shape.
The bolts that have been initially tightened should be marked for confirmation to prevent leakage. The bolts installed on the same day should be finally tightened on the same day. Bolts must not be installed on rainy days, and the friction surface should be in a dry state. The final twisting torque must be carried out according to the set value requirements.
For electric torque wrenches that have a set torque, the bolt should be able to rotate at least 30° from pre-tightening to tightening. Do not use the electric wrench again for bolts that have reached the set torque, otherwise, the torque may be unconsciously increased, and the load on the bolt and the electric wrench may also be increased and may even damage the bolt and wrench. Pressure vessels, if the preload is too large, will break or the gasket seal will fail due to too large bolt tension.
Operate in strict accordance with the operating procedures of the electric torque wrench. Be sure to reset to zero after each wrench to avoid metal fatigue of the spring. The torque value of the calibration wrench should be calibrated periodically and its deviation should not be greater than 5%.
It should be noted that when the electric wrench is working, turning between the high-speed gear gear and the low-speed gear gear will not damage the wrench, but the torque value of the high-speed gear gear and the low-speed gear gear is different. When the electric wrench is working, the hand should be kept away from the reaction arm.
Assuming that the torque or preload force of the solid bolt is accurate, but due to external forces, temperature changes, vibration and other factors, the preload force will still change after a period of time, and it must still be checked.
