Alternative Torquing Sequences

[miningman]

I have learned a lot from these threads over the last few months and I recognise that experienced people do not rely on torque values alone for flange assembly, but I am going to do so. Rating is Class 300, 24 inch, with an ultimate required torque supplied by my EPCM QA/QC people of 1600 foot lbs. Any leaks would be embarrassing rather than lethal, since duty is water.

Assuming I want to restrict myself to four passes with the torque wrench, is there any benefit or potential consequences to using say, 300, 600, 1200, 1600 or alternatively 250, 500, 1000, 1600? Any relevant comments or opinions welcome.

 

[TGS4]

Refer to ASME PCC-1 - Table 2, which recommends:
1) Hand-tight (star-pattern)
2) 20%-30% of target torque (star-pattern)
3) 50%-70% of target torque (star-pattern)
4) 100% of target torque (star-pattern)
5) 100% of target torque (circular pattern)
6) Wait a minimum of 4 hours, and repeat 5) above.

That's actually a 3+ pass approach. I would recommend that you purchase PCC-1 for all of the details.

 

[miningman]

TG, I had not overlooked your steps 5 and 6 , I was refferring to the initial 4 steps only.

However,your post summarizes my problem!! 50-70% is a range of 800- 1120. Surely there must be some advice available from people who have done this in the field on a regular basis.

 

[HeviiGuy]

Hello miningman,

First: It's good to see you here and to know that your property hasn't gone on Care & Maintenance as so many others have!

Second: I promise not to mount my "Torque is Evil" pulpit ;-)

...However,your post summarizes my problem!! 50-70% is a range of 800- 1120...

Indeed, it's frustrating! However, such a loose procedure is not to be unexpected in an uncontrolled process which is already fraught with so many unknowns. In the context of having to hope that the final preloads and their distribution is close to what's required, this range of 320 ft-lbs really isn't such a big deal; the joint's reliability is already based on a (granted, educated) wing and a prayer :-(

Simply pick some torque values (pick the higher end of the scale) and tighten your bolts in three stages with a final two passes at 100%. Like you say, it's only water. If the flange leaks, tighten 'er up some more. If the leak stops, congrats! If not, get some new flanges (because the existing ones would have likely rotated) and try it again. If you're not too unlucky, the second attempt should work. If that one doesn't either, then you might wish to revisit your strategy and perhaps incorporate a bit more control into the process.

Good luck

* I've attached a file which might come in handy when trying to calculate bolt load, torque, elongation etc...



Ciao,

HevïGuy
www.heviitech.com

 

[HeviiGuy]

miningman,

You wouldn't happen to be pulling "the good stuff" out of the Carlin Trend, would you? If so, I'll be there at one of the properties next week on a training contract and would be happy to meet with you before flying home.

Ciao,

HevïGuy

http://www.heviitech.com

 

[miningman]

Hevi , thanks for the suggestions and invitation , but no , Im based in Canada and only have peripheral knowledge of activities in Nevada.