Many thanks for the interesting comments. Allow me to react:
- Indeed we think of the bolts like springs. The figure on wikiuploads is very instructive to visualize this first principle. @Scuka, I gratefully downloaded it. Yet, I also agree with desertfox that you have to consider the flange as...
When assembling flanged joints, a typical target bolt stress is 40-70% of its SMYS, see e.g. ASME PCC-1 Appendix O. If you look at the allowable stresses for bolt materials (e.g. SA-193-B7) in ASME II Part D, you will find that these are much lower. That is, when assembling a regular flange...