Field Calibration and Accuracy of Torque Wrenches

In most cases, it is assumed that a manual or hydraulic torque wrench will deliver the requested torque value if set correctly. However, torque wrenches have moving parts that will be subject to wear. They are also subject to harsh operating conditions in the field, which elevates the risk of damage. It is common sense that calibration of wrenches on a periodic basis would be advisable. This activity is regulated and required in some industries, such as automotive and wind-power generation. However, in the Petrochemical and Oil & Gas industries there are relatively few companies that practice regular calibration. In part, this may be because there is not data available to justify the cost of such a calibration program. It is not until the calibration program is underway that the value can truly be determined. In this paper, the results of field calibration of several hundred torque wrenches is presented and an analysis of the data reveals exactly why calibration of torque wrenches should be an important part of any leak-free bolted joint program.