Over the past two years, the accuracy and repeatability of equipment used to assemble bolted flanged joints have been studied, and progress has been reported in past papers. One of the findings has been that pneumatic torque wrenches demonstrated a broader plus/minus range on bolt stress from the targeted value (e.g., lack of accuracy) than manual or hydraulic torque wrenches. What was notable, however, was that the repeatability of the bolt stress that was achieved did remain consistent with the other types of torque wrenches. Since the repeatability has been shown to be consistent, attention has turned to investigating and determining the reason for the perceived lack of accuracy. One aspect that might account for this is the calibration of the pneumatic torque wrenches.
This paper outlines and documents the research that has recently taken place to identify the parameters that are key elements in improving the accuracy of pneumatic torque wrenches that might form the basis of development of a standard for calibration of powered torqueing equipment.