Experimental Research on Preload Loss of Stainless Steel High-Strength Bolt Connections

The law of preload loss is an important basis for determining tightening technology and quality inspection in high-strength bolt connections. The bolt preload of 10 groups of stainless steel high-strength bolted standard specimens was tracked for a long time under six kinds of faying surface treatments， such as the grit blasting， heavy brushing， mechanical scoring， anti-slip coating， hot rolling， and mirror surface. The results showed that the preload decreased rapidly after final tightening， with the loss rate gradually slowing over time. The preload loss within the first hour after the tightening accounted for 50% of the total loss， and the loss stabilized after 24 hours. Larger slip resistance coefficients of the friction surfaces resulted in greater bolt preload loss. The laws of bolt preload loss for all specimens in the test were statistically analyzed and fitted. The results showed that for the specimens in the test， the final loss of preload with a 95% assurance rate was about 7.2%， which was similar to that of high-strength bolted connections in steel structures under the same conditions. Based on the results of this study， it is suggested that the preload inspection of stainless steel high-strength bolt connections should be conducted within 6 to 24 hours after final tightening.