Frequency of Torque Tool Calibrations and Field Torque Verifications

The past calibration papers have discussed the importance of accuracy, repeatability, and verification of calibration methods. Through these papers it has been seen that the method of calibration is critical to achieving the proper bolt load as there is no current standard followed for calibrating “powered equipment.” The frequency of calibration and the practice of field torque verification has not been previously addressed in either research or by the tool manufacturers. The only timeframe that is currently followed is based off ISO 6789-2 “Assembly tools for screws and nuts — Hand torque tools” [1] which states that manual torque wrenches shall be calibrated once every 12 months. There are also no manufacturers that have stated the frequency of calibration since there is no current information of how many times a wrench is used or correlation of the setting of the tool with the amount of use it has seen. This paper will address the process of calibration & field verification of torque tools during an oil refinery turnaround. During this turnaround, the tools used were calibrated prior to first use and after they were used for the day. Through over 2700 data points, this paper will show three different types of tools, and their suggested rate of field verification. They include manual torque wrenches, hydraulic torque wrenches (both low profile and square drive), and pistol grip torque wrenches (both battery and pneumatic).