Bolt Tightening Sequence

[SteveTC]

My Client has requested a bolt-tightening sequence to be included in the installation guidelines document for an Offshore Flexible Riser 2-piece Hang-off Clamp which has a horizontal circular PCD bolt group and a vertical rectangular bolt group.

Do Engineers usually just specify 3-stage spiral sequence (just like most car engine head-bolts)or is there some kind of calc I should be doing??

 

[CoryPad]

SteveTC,

Most multi-bolted joints use a cross or star pattern in two (or more) stages: tighten all joints to snug condition, then tighten to final level. Some critical flange joints (e.g. liquid/gas sealing requirements) use matrix algebra to calculate interaction coefficients to arrive at the desired preload for all bolts.


Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[diamondjim]

I agree with Corypad but would recommend at least two
stages in tightening. Use 1/2 the torque value thru
the first sequence, and then repeat with the full
torque value for the final round. We normally recommend
3 stages in tightening if it is critical.

 

[yates]

If the joint is important enough to merit a pre-determined joint tightening sequence, then the sequence used to tighten the joint before leak/pressure/endurance/vibration testing should be reproduced in the field. If none of this testing was done then it is academic (and of no proven usefulness) to calculate and require a particular sequence.

 

[DSB123]

If it's considered a critical flange connection then any potential for breaking the flanged assembly should be done under a controlled procedure also to prevent damage to the flanged assembly. I have come across instances where a bolting-up sequence is deemed a requirement along with an un-bolting sequence for the same flange. The bolting up sequence is dependant upon the number of bolts but is similar to that highlighted by CoryPad but the levels are 30%, 70% , 100% then 100% again (i.e. a four stage bolting sequence) with the un-bolting being to release the bolts to around 30% of the final level and then full unloading.

Hope this helps.

 

[arto]

Check out ASME PCC-1 "Guidelines for Pressure Boundary Bolted Flange Joint Assembly" for an official standard procedure on bolt tightening.