Tightness of piping fasteners query 5

[Sally Smith]

Hi,

A colleague told me it is not a concern that the below (secondary) nut isn't properly secure and maybe suggested it should be loose. I think they may be wrong. If it's there it should be tight, right?

Can anyone confirm please?

Thanks in advance!

 

[1503-44]

Removed is probably better.
Why 2?

 

[Sally Smith]

Thanks but I still believe it should be tight.

Additional security in case of vibration works them loose.

 

[The Obturator]

First of all, what is the reason for the two nuts? against vibration, shaking loose? Has the stud length been purposely extended to cater for an additional nut?

You might want to enter 'jam nuts', 'double nuts' or locking nuts' in the search above. It's been a subject covered a few times.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

There are better ways to do it IMHO, but double nut is seen a lot.

But it doesn't work if they aren't actually tightened up on each other...

Interesting article here

https://www.boltscience.com/pages/twonuts.html

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sally Smith]

Thanksa lot, folks. I think studs are deliberately long to accomodate double nuts. Fairly common in the industry I believe. Agreed there are better solutions.

Thanks, Littleinch, but that link is down.

 

[LittleInch]

Sorry. I added an l at the end. Try this.

https://www.boltscience.com/pages/twonuts.htm

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sally Smith]

Thanks! The person in question actually said it was supposed to be like that.

 

[1503-44]

If vibration is going to shake those off, there's some other far worse problem. If it is a very hot line with high cyclic duty, 2 nuts might stop loosening, but they have to be jambed.

 

[Sally Smith]

Thanks, 1503-44. Hot line but no vibration.

It seems we all agree: they should be in contact to prevent self-loosening.

 

[Sally Smith]

I agree that ideally a thin nut should be placed first then a thicker fastener on the outside but with what we have they should be tight against one another, and not loose.

 

[1503-44]

Why not two ASTM A 193 HH

https://boltport.com/products/heavy-hex-nuts/

jam nuts

https://boltport.com/products/jam-nuts/

Asme fastener specs

https://boltport.com/standards/asme/

 

[goutam_freelance]

You can check the self locking feature by using:

f is coefficient of friction
Lambda is lead angle of thread.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[racookpe1978]

Hah1 I had always been told that the thicker nut goes first, gets torqued in 1/3 increments to maximum to carry the desired load, then the the thin nut - properly torqued! - is tightened on the outside.

Per that reference, it is exactly the opposite.

 

[1503-44]

Work around that problem with 2 x HH,

Yes that seems strange, the thin one first.
If you use the same torque on each, the thin one would have a much higher torque /length of thread, so friction might be greater and less likely to move while the second provides axial force backup. Do you think?

 

[KevinNZ]

Certainly not standard practise for pipe flanges. Anyone seen this as an option in the flange or piping codes?

 

[LittleInch]

Definitely a little bit odd for a flange which needs a fair amount of tensile force to maintain the sealing force. Unless right on the outlet of something like a compressor or pump I don't understand how vibrations will cause a flange bolt to loosen and not also be spurting fluid everywhere.

They look pretty meaty flanges and nuts - class 1500?

but whatever they are doing, you need then to be tightened against each other for sure...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.