Would nut rotate by torque wrench even if completed by hydraulic tensioning

[HH Choi]

Hi there,

I would like to ask advice about applying torquing where hydraulic tensioning has been completed.

One of reports describes that some nuts on flange joint are rotating (I mean tighten) by torque wrench (hydraulic or manual) when apply torque value per ASME PCC-1, even if it has been completed by hydraulic tensioning. Please note that it was just different method and the interval was quite short, in few days. However observed nut engaging. The joing was supposed to be 50% hydraulic tensioned, and processed following vendor (SPX SRT3) procedure. I would like to mention that readiness, tensioning value and work sequence were conducted in a correct manner.

I recognize various factors are affecting on tensioning and torquing, but the question is could nut rotate even if it has been tensioned idealy? For example,, say 100 is the ideal level to hydraulic tensioned, and it is 100% achieved. On this condition, what will happen if try to rotate nut by hydraulic torque wrench? I think nut should not move if torqued idealy in 100 level, but in reality it moves because of +/-30% tolerance to achieve target. How do you think?

Many thanks in advance.
Regards,

 

[TugboatEng]

Hydraulic tensioning provides an accurate result. Why would you screw that up by torquing it?

 

[HH Choi]

It was not planned to use torque wrench at tensioned joint, but a informality check using torque wrench. I agree to have consistent method for tightening.
But not sure what made nut rotate even if hydraulic tensioned per vendor procedure.

Maybe it was not correctly ready and/or tensioned, or torque value was over-estimated. But if not, I mean work is conducted correctly, would nut rotate after hydraulic tensioned?

 

[TugboatEng]

If the fastener is very long it can twist without the nut advancing on the thread. Once the torque is released the fastener will return to it's original position.

 

[HH Choi]

Well,, fastener length would not be a factor to rotate nut, in this case. It was not so long.

 

[desertfox]

If the bolts were hydraulically tensioned then I would not expect the nut to rotate freely when a torque wrench was applied unless the torque value was set significantly higher than that equivalent of the hydraulic tension force. That said you only need one method or the other to tighten the bolts ie either hydraulic tensioning or torque wrench.
A hydraulic tensioned bolt is far more accurate in its clamping force than relying on torque.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[HH Choi]

Thank you for all,

Regards,