The Effect of Bolt Size on the Assembly Nut Factor

This paper details recent testing that was performed as an extension of earlier work on nut factor and high temperature breakout performance of selected anti-seize products. Comparison is made between results obtained using bolt diameters from 3/4 inch to 2 inch, two different anti-seize products (Molybdenum and Nickel) and two different bolt materials (ASTM A193-B7 & ASTM A193-B8M). In addition, common equations used for the determination of achieved bolt load from a given torque are examined and compared from a practical perspective in light of the nut factor test results. The test methods that were used are designed to closely mimic actual bolt assembly in a process plant environment. The paper, therefore, presents useful information that will enable more accurate assembly of bolted flanged joints on pressure vessels and piping in any process plant environment.