Flange Joint Live Tightening

[TXY]

Hi guys,

Looking for advice on performing live tightening on flange joint at 120degC. Prior to start up, it was torqued with the recommended 4 torque passes (30, 60, 100, 100% check). It has been some time since start up and the end user contacted to perform live tightening. My question is whether it is still necessary to perform 4 torque passes for live tightening. Or a clockwise check pass with 100% torque would suffice. Thanks in advance.

Cheers
XY

 

[LittleInch]

Doing anything to a live system has a significant increase in risk compared to doing anything to one which is not live.

Why does the end user think it need checking?

Is it leaking?

 

[NovaStark]

Hi guys,

Looking for advice on performing live tightening on flange joint at 120degC. Prior to start up, it was torqued with the recommended 4 torque passes (30, 60, 100, 100% check). It has been some time since start up and the end user contacted to perform live tightening. My question is whether it is still necessary to perform 4 torque passes for live tightening. Or a clockwise check pass with 100% torque would suffice. Thanks in advance.

Cheers
XY

Much like what LI says, if it isn't leaking, there wouldn't be any need to do an online tightening as that could impart more damage than benefit.

Is this a known problematic joint or operates in some condition where bolt relaxation is a sigifnicant issue ? 120 degC doesn't seem like a large enough temperature to cause it.

 

[TXY]

Thanks for the responses.

End user advises that it is leaking; although they don't seems overly anxious with this. I do not have any joint history as the initial start up tightening was performed by other bolting contractors. Information provided to me as of now is 24" 900# RTJ Flange connection with target bolt load 534kN (~27,000psi bolt stress). In my opinion, this is kind of low.

And back to my original question, in the event of live tightening, what would be the recommended procedure? ASME PCC-1 seems to be rather silent on this. My thoughts are 30% and 60% torque passes would likely not turn the nuts at all, so wondering if there are any merits of going thru the motions. And considering to minimize operators' exposure to this work, I'm inclined to propose that a direct 100% torque pass would suffice. Any thoughts?

 

[NovaStark]

If your bolts are B7 bolts, the yield is around 105 ksi at ambient conditions, so the 27 ksi is around 25% of the value.

Usually, we try to go to 50-60% depending on the situation.

With an RTJ gasket, you can try a slightly higher torque value however, note that the with torqueing of these gaskets, strain hardening can occur. So it should not be a repeated exercise.

 

[r6155]

Elongation control is the best practice, not torque. Checking elongation is easy.

 

[TGS4]

I'm with @r6155 here - elongation - likely by the turn-of-nut method - is going to be more robust in this situation. For torquing, you are assuming that you have the same nut factor as when the lubricant was new. It is not new any more. As a result, you won't know what your actual nut factor is.

Perhaps get a second opinion on the target bolt load. I know that it seems on the low side, but RTJs are different, and higher bolt loads can cause cracks in the flange at the bottom of the ring receptacle. Also, make sure that this is a PCC-1 Appendix O bolt stress, and not one from an ASME VIII-1 Appendix 2 calculation.

 

[LittleInch]

My thoughts are generally don't do it.

RTJ flanges are not the same as RF and tightening the bolts or even just checking they are all at their 100% torque ( noting the issue that 100% torque might no be the same as 100% of their intended stress due to rust, wear, lack of grease etc) may very well not cure the leak and if the leak is due to a crack or corrosion of the flange sealing surface you could easily increase the leak flow or lead to failure of the gasket ring.

In terms of bolting etc, PCC1 is for for new joints in the main. You may want to look at PCC-2 and the applicable section would seem to be article 311 on "hot bolting", noting the requirement to reduce to 25% of normal or max operating pressure.

Or use a flange sealing kit / company until you can de-pressurise the joint and actually see what the problem is.

What exactly is "some time" after installation, what does this pipe contain, what is it operating pressure and has anyone considered that tightening the bolts at 120C when already less stress is already present is a good thing when they cool down.

So in summary you need to think very carefully IMHO, if this operation will actually work or whether you will just be causing more damage or be back in a few weeks time, when the original fault just re occurs.

 

[r6155]

In this example, the nut rotation is not applied for verification: impossible.
Ultrasound is applied, compared to the original ultrasonic elongation report.