For many years 50% yield was a favored generic level for bolted flanged joints, however in pursuit of leak free performance this is no longer the case. In line with the guidance given in modern documents such as Appendix O of ASME PCC-1-2010 Guidelines for Pressure Boundary Bolted Flange Assembly [1] and with the increasing number of joints requiring corrosion resistant alloys often it is necessary and desirable to take bolts to values closer to their yield point or more accurately their 0.2% proof stress. The paper will examine the issues associated with tightening bolts to values well in excess of 50% of their 0.2% proof stress and analyze the effects on the during tightening and subsequent re-tightening. The analysis will include results of actual testing of bolts tightened to high stresses and give recommendations on a sound engineering approach to this practice which considers the risks and benefits. Analysis will also include a statistical evaluation of the effects of torque and tension scatter at high levels of target bolt stress.

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