BOLT TENSIONING 1

[GAL02]

Dear all, Good morning!

Hopefully all of your doing well and taking care during the pandemic.

Well! I have a query regarding the usage of Bolt tensioning, as a general practice we do torquing to achieve flang joint integrity from smallest to larger size bolts but
what is the guideline or threshold point to use bolt tensioning i.e. from which bolt size we should apply bolt tensioning and why from that size of bolt?

Have a good day!

With regards

 

[NRP99]

Check ASME PCC-1.

 

[CuMo]

Some plants in Europe require bolt tensioning for bolting above 1"UNC or 1.25"8UN.

 

[GAL02]

Dear all, Good morning!
Thanks for your response, I have gone through ASME PCC-1 but there is a two-way guideline.

Anyhow, understand that there is no such confirmative guideline to say use from this size & why it's so.

With regards

 

[r6155]

@ GAL02
As an engineer, you will need to use your best judgment.

Regards

 

[desertfox]

GAL02

Bolt tensioning is used when a really accurate bolt tension is required ie within say 3% of a given bolt tension, torquing on the other hand is only accurate to about 25% plus or minus. There will be a bolt size that prohibits using a torque wrench for practical reasons ie the bolt force required that would exceed the strength of the operator to achieve that torque with a wrench.

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

 

[r6155]

Use studs (not bolts).
For stud lengths greater than 5 times the nominal diameter, use elongation (torque is not allowed).
I always use elongation, the installer is responsible for achieving the required elongation value.

Regards

 

[iangineer]

At my plant, we specify tensioning for bolt diameters 2" and larger.

For stud lengths greater than 5 times the nominal diameter, use elongation (torque is not allowed).

Just curious. Is this just your rule of thumb, or do you have any reference that supports this? Wondering if I should note this in our bolting procedure.

 

[Andrew ONeill]

In my experience, rule a judgement thing. Usually more about economics and schedule than anything. Once you get to about 2" stud size, tensioning is usually quicker, and arguably safer than torqueing.

Andrew O'Neill
Specialist Mechanical Engineer
Rio Tinto
Australia

 

[r6155]

@ iangineer
I used the reference in ASME PCC-1 2019 8.2 Note 7
“A bolt having an effective length shorter than 5 times its nominal
diameter is generally considered to be short.”

I consider that the torque value is not the same for different lengths of studs. The elongation considers the length of the stud.
Then I use elongations value for all stud diameters.
Sound engineering practices and judgment should be used to determine the applicability of a specific method to achieve the required elongation value (hand wrench, hydraulic tensioner, .etc)

I hope I have been helpful.

Regards

 

[BJI]

The cautionary note is for lengths less than 5x the diameter not greater than 5x. Short studs are stiffer and much harder to assembly accurately. Bolts with higher flexibility (longer length) torque quite well. Bolt spacers are sometimes used for this reason. When it comes to tensioning, the load loss factors need to be known with some accuracy, and this involves interaction of the flanges as well as the bolting. For more information refer to ASME PCC-1 Appendix Q-4.

 

[iangineer]

I appreciate the information. Checking the bolts on most of the flanges I deal with (typically RF flanges), it looks like they all have a length longer than 5x the diameter. It doesn't make sense to me to recommend tensioning on a 2" 150# RF flange. I don't see anywhere that torquing a bolt with length >5x diameter is not allowed.

The plant I work for has a bolt torque tool that uses PCC-1 App O for torque calculations. I use this tool in conjunction with some flange-check calculations to find an appropriate torque. Our existing procedure is to tension bolts 2" and larger and hydraulically torque bolts requiring 500 ft-lbs of torque or more. Otherwise, a manual torque wrench is used.

(somewhat unrelated to this thread): Looking deeper into it, I kinda fell into the rabbit hole of when to use washers per PCC-1. Appendix M says they are optional in the first line. However, in Figures 1 and 2 of PCC-1 Section 10, Note (1) says "Washers are required only when torquing methods (versus use of hydraulic tensioners) are used for bolt tightening." I found a bunch of threads about washers in this forum and basically settled on needing washers if: (1) a joint is often unbolted/rebolted (2) CS bolting on high alloy steels (3) on bolt holes >1/8" larger than bolt (the thread said 1/16", but the holes I deal with are mostly 1/8" larger). That section 10 Note (1) is a bit confusing, though, since very few of the flanges in my plant utilize washers and most are torqued.

Any discussion or thoughts on these would be appreciated.

 

[desertfox]

Hi iangineer

I think washers should be used on most bolted joints because they help to spread the load from under the bolt head / nut and in addition they help to prevent bolt heads embedding into the clamped surfaces when the clamped material is softer than the bolt material.

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

 

[GD2]

GAL02,

There are Bolt Tensioning Tools from 3/4 Bolt size. What is important is that there must be enough (usually 1 bolt dia) extension of bolt thread to mount the tensioning tool. Not every flange joint will have it. For these flanges, you will use torque wenches.

GDD
Canada