This paper explores torque wrench accuracy, one source of the overall inaccuracy associated with bolted flange joint assembly. The accuracy and repeatability of various pneumatic torque wrenches were tested and analyzed. Pneumatic torque wrenches were benchmarked against a hydraulic wrench which has a lower perceived bolt load scatter. The testing was performed on two mock-up flanges, NPS 8 Class 150 and NPS 16 Class 300 raised-face flanges with spiral-wound gaskets. The analysis compares the accuracy and repeatability of the following: each tool versus its manufacturer’s claims; duplicate models of the same tool; and overall tool type (pneumatic or hydraulic) versus another tool type. Because accuracy is closely related to tool calibration, torque wrench calibration method and frequency are also discussed.

There are several methods of applying axial load through torque that have been used within the industrial assembly of Bolted Flanged Joint Assemblies (BFJA’s). The most common tool used within the industry is the manual torque “clicker” wrench which traditionally allows an assembler to reach 600ft/lbs. While companies make wrenches that achieve higher amounts of torque, they are harder on the assembler to use so other tools, such as hydraulic and pneumatic torque wrenches (Powered Equipment), that require less physical strength are used instead. This paper will discuss the accuracy and repeatability of pneumatic and hydraulic wrenches and compare them to the manufacturer’s/industry standards.

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