Research on Pre-tightened Status' Change of Bolt under High Temperature and Countermeasures

The stress and strain of the pre-tightened bolt and flange heated to high temperature from ambient temperature would have a change and have an influence on sealing performance.Firstly,the changes of strain and sealing performance were analyzed under the hypothesis that the stain of different parts was uniform.Secondly,the stress and strain under the state of pre-tightened,heated and re-tightened process were analyzed by FEA software.Lastly,the effect of creep and stress relaxation on axial stress of bolt was estimated.Following conclusions were drawn,the bolt pretightened at ambient temperature should be re-tightened to sustain the status of sealing performance when working at high temperature.The re-tighten stain was equal to thermal strain difference of flange and bolt.The re-tightened bolt should be loosened to avoid damage of spacer when cooled to lower temperature.The axial stress of bolt should not sustain high level otherwise the sealing performance would be deteriorated in a short time.It was suggested that the bolt should be tightened at regular intervals.