Flange Stud Bolt Lengths Based on Tightening Method

[Krausen]

I wanted to revisit a closed thread to ask a question on stud length requirements based on tightening method. As I understand, stud bolt tensioning devices are the most accurate torquing method for flange studs. I'm working with high pressure ASME B16.5/B16.47 steel pipeline flanges requiring upwards of 3000 ft-lbs of final torque per nut. These levels of torque obviously cannot be achieved by hand tools or hand-operated power tools. I've been assuming these are typically installed with hydraulic torque wrenches. For various reasons, these stud lengths have been specified & ordered to provide approx. 2 exposed threads beyond each nut after final torque. However, now I'm concerned that if the contractor wishes to use a hydraulic bolt tensioner instead of torque wrench the studs may not be long enough since these devices require longer stud lengths to mount the tensioner device to pull the studs during installation. Does anyone have any comments or experiences with this issue?
thread725-355979

 

[racookpe1978]

If the studs are purchased and are enroute to the job site, the contractor either has to use them with a calibrated hydraulic stud wrench, or replace them with qualified longer studs and use his stud tensioner.

 

[desertfox]

Hi Krausen
Your concern is valid, if the contractor needs to tension these studs hydraulically then you will need a length of stud protrusion beyond the nut of at least one bolt diameter.
check out this site:-

http://www.tentec.net/tensioners.php

 

[Krausen]

Thank you sirs. I'm afraid I'm going to need to address this somehow on this project.

 

[ricklts]

Krausen,
I'm no longer in that business, but there are hydraulic torque wrenches available thru 30,000 and 60,000 ft/lbs capacity. While not as inherently accurate as tensioners, they do produce a reasonable preload, and can be used successfully for applications such as yours.

Stud tensioners from several manufacturers, TenTec, SPX, Hydratight, etc. are readily available to contractors as rentals from many sources. As are the Torque Wrenches, and usually from the same sources.

Good luck,
Rick

 

[Duwe6]

Use the hydraulic torque wrenches that rikits mentioned. Precise stud tensions are NOT necessary. What is required for any flange to seal is that the tension on all bolts/studs to be EVEN. And,of course, that the clamping force is adequate to 'energize' the gasket. And it takes an amazingly low torque/pretension to achieve that clamping force.

You will only have to ensure that the studs and nuts on each individual flange all came from the same batch, i.e. no mix-and-match stud sets. One flange, one batch # // heat # for the studs. And also make sure that ALL of the studs are liberally lubed with the same anti-seize grease. Now, whatever input in foot-lbs a torque wrench applies at that flange, each stud will have an identical preloaded tension, and that flange will be evenly bolted up all the way around. Evenness in tension, and starting the torque-up of the flange with the elements aligned and parallel are the most important components. Second most important is to gradually increase the torque/pretension is stages; a good bolt-up needs to progress from 'snug' to 1/3-torque - 1 'trip' around the bolt pattern, 2/3 torque - twice around the pattern, full torque - three times around the pattern. Whether the preload is 10kips, 15kips, or 25 kips in nowhere as important as these elements.