Justification for a New Industry Standard for Torque Wrench Calibration

Abstract

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. Calibration is the measurement of a device’s output to a known standard and adjustment to within specific tolerances if necessary. There are several different codes and standards that are followed in the industry, but these practices are normally left up to interpretation. Common sense tells us calibration of torque wrenches on a periodic basis would be advisable. Many in the industry have different policies that are inconsistent when considering several factors of a calibration program. This may be because there is not data available to justify the cost of such a calibration program or misconceptions on what calibration is and when it should be completed. An analysis of the data reveals exactly why regular, periodic calibration of torque wrenches should be an important part of any maintenance program. By using certain methods of calibration, one can mitigate the risk of an un-calibrated torque wrench affecting one’s facility. This paper includes general trends for a sample of torque wrenches that received calibration in order to compare the overall accuracy of the wrenches prior to calibration versus post-calibration. The study was conducted on data obtained from the calibration of hundreds of wrenches over a five year period. This may be considered a reasonable snap-shot of the inaccuracy of torque wrenches that may be expected in the field if recent calibration has not been performed. Due to the highly prevalent misconceptions regarding calibration found in the petrochemical and oil industry, there needs to be an industry standard for torque wrench calibration. Our hypothesis for this paper states that each torque wrench that is used in the field, whether it is new, used, or repaired, shall have an individual calibration performed at no less than a 12 month interval. This standard will prevent material damage to the installation and operation of equipment by correcting both slight deviations from accuracy tolerances and, especially, extreme outliers. The material presented in this paper will show justifcation of an industry standard that should be adopted.