Bolt Torque and Turn of Nut 4

[ColmClonkirk]

Hi All,

Quick question - A supplier is proposing a joint with a torque of 350Nm and 120 degrees rotation. What would the 120 Degree rotation equate to in torque or is there a simple equation be available?

Bolt is 10.9 grade and M30

Thanks!

 

[TugboatEng]

The 120 degrees is to yield the bolt. There is no torque value because the stress/strain curve is flat during yield. If you you try to use an equivalent torque value you won't know if you're at the beginning, middle, or end of the yield region. You definitely don't want to be at the end...

 

[ColmClonkirk]

Thanks, but 350Nm would not take a 10.9 bolt near yield. I am not trying to use equivalent torque, would like to understand the load applied once 120 degrees rotation is applied.

 

[3DDave]

It depends on the free length of thread. How much elongation strain is there from the 120 degree turn?

 

[dvd]

Load depends on grip length. You could calculate the load based on stretch measured with a micrometer after 120 degree nut turn. Fastenal has a procedure -

https://www.fastenal.com/en/69/bolted-joint-design

 

[drawoh]

Thanks, but 350Nm would not take a 10.9 bolt near yield

It depends on how long the bolt is.

However messy this is in the field, the calculation is simple. You need to tighten the bolt to snug, whatever "snug" means to you and your installer. If everybody interprets "snug" correctly, your bolt is not yet strained, but any further tightening will cause it.

You have a clamped lengh[ ]L. You have a screw pitch[ ]p. You have a screw rotation[ ][θ]. Your grade 10.9[ ]bolt has an elastic modulus[ ]E. If your clamped joint is much more rigid than the bolt, the calculation of strain is easy, and that gets you stress on your bolt.

If your joint is not rigid, your calculation is more complicated, but what you need is strain on your bolt.

--
JHG

 

[ColmClonkirk]

Thanks Everyone - we can do the torque and 120 degrees in the field, I just wanted additional assurance to know the load in the bolt. I can get these tested in lab environment, and get measurement on elongation based on torque and additional 120 degree rotation.

 

The relationship between torque (difficult to measure with precision) and bolt tension is indirect and will depend on your guestimated friction factor.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dik]

Torque values can be 'tricky' at the best of time. Best to consider some other means of indication.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kingnero]

Torque + turn of nut is a very common method with very repeatable results. 350 Nm seems low for a M30, but is possible (if well lubricated, ...).
120° is much for a single step, but is possible (if very few bolts in the joint, ...).
Bickford's has detailed info on bolted joints.

 

[dvd]

Skidmore-Wilhelm is the way to go

 

[ColmClonkirk]

Great response thanks - Agree torque is low, a lot of bolts in joint but its not a standard joint. Will read Bickfords book, great pointer thanks!

 

[dik]

king: turn of nut, for sure... torque not so good. It's like wetting your finger and sticking it in the air to determine wind speed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r6155]

@ ColmClonkirk
1) Can you explain your "not standard joint"?
2) Use stud instead of bolt?
3) Use elongation control, not torque, not turn of nut
4) How long is this bolt?
5) For M30 use tensioner, not hand wrench
6) See ASME PCC-1

Tables for torque and turn of nut is the same for M30 x 100 and for M30 x500: ridiculous

Regards

 

[kingnero]

turn of nut, for sure... torque not so good

dik, are we talking the same thing?
I fully agree torque alone is worthless for an indicataion about bolt stresses.

Turn of nut however is always preceeded by a certain torque value (= a bit more than "snug tight"), in order to make sure both parts are fully seated against each other.

 

[ColmClonkirk]

1. Its metal into composite material, so certain limiting factors of the joint design as proprietary with Manufacturer.
2.Yes it is a stud. Control methods are difficult as blade hole, but we due to past issues we are working on using UT to prove
3.Torque is only option due to acceess/bolt lenght, can't tension unfortunately. We have a good idea of Nut factor due to lubrication used.
4.Stud is 465mm long
5. Can't tension due to access issue, insufficient room

Working on laboratory elongation measurement, and that will confirm elongation in stud and can use this in the field using UT measurement post torque.

Thanks

 

[Ron]

Agree with dvd!

 

[desertfox]

Hi ColmClonkirk

A rough estimate of the bolt tension can be found by looking at the thread pitch of an M30 bolt and if I assume it’s a 3.5mm pitch then:-

A full turn on a nut would move it along the bolt by 3.5mm and so a turn of 120 degrees would move the nut 1.166mm. Now if I apply this to a bolted joint then the compression of the members should equal the stretch in the bolt therefore and assuming a grip length of say 400mm then the tension in the bolt would be :-


F = E * Area * Strain

F = 200000 * 580.58 * (1.166/400)= 338.6 kN

For the area I used the tensile area of a M30 bolt.

The torque is not really an accurate method however again a rough ballpark :-

F = Torque/ (0.2 *d)

F = 350000/ (.2* 30) = 58.3 kN

If I add these two values together I get 396.9kN of bolt tension and the proof load for a 10.9 grade M30 bolt is 466kN.

Hope this might help.

I’m not sure how you intend to tighten this joint with limited access however I can’t see sending a guy with a wrench in to do this will be sufficient.



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

 

[r6155]

Turn of nut is not applied when the bolt length exceeds 12db. The required nut rotation shall be determined by actual testing in a suitable tension calibrator that simulates the conditions of solidly fitting steel.

Some problems with the turn-of-nut pretensioning method have been encountered with hot-dip galvanized bolts.

See Specification for Structural Joints Using High-Strength Bolts -RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS.

http://www.boltcouncil.org

Turn of nut is not allowed in ASME PCC-1

Regards

 

[dik]

That's where Skidmore, kicks in... and then you go back to 'turn of nut', once this has been determined. Most reliable.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik