Bolt Torque and Bolt preload query

[Danmecheng]

Hi All,

Currently going through a series of HX to calculate and verify torque values for girth flanges for an upcoming shutdown and pretty much doing a quick design sense check using the Appendix 2 calcs to determine the design minimum then following the guidance in PCC-1 appendix J , K and O to get the final assembly values. However when calculating the bolt preload to ensure the integrity of the bolts i.e. (tensile stress area x % utilisation x Minimum yield strength) can I ask for the yield strength value do you all normally use the yield strength for the bolt based at ambient temperature conditions or operating temperature conditions ?

I know standard practise is to applying between 40-70% yield and I like to use a utilisation of minimum 50% Yield but if you look at some of the exchangers the operating temp can be nearly 500°C so quite a difference in yield values compared to that of ambient condition so I assume it would be best to use operating conditions as to not over stress the bolt when it reaches its operational temp

This has caused abit of discussion in the office and keen to hear your thoughts on this and what you normally do ? I quite often use table Y1 of BPVC Section 2D to obtain the yield values at operating temps and find it quite good for this ?

Cheers

Dan

 

[lucky-guesser]

I've never done anything quite like this, but general practice is to design for worst case scenario. If you need and design for an overall SF of 2 at ambient, then your yield drops by 30% as you get up to operating temp, your SF isn't really 2 anymore.