Bolt Length Calculation 8

[SHIoffshore]

How many threads shall be remained after tightening of bolt and nut?

Bolt length calculator which I found on the internet mentioned that 1/2 diameter of bolt should be added for a tolerance but not mentioned about the references like standards or regulations.

Please let me know if there is any standard or regulation stating above.

Thanks

 

[CoryPad]

Remaining in which direction? In this clamp length or projecting beyond the nut?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MintJulep]

See faq725-1331

 

[Ussuri]

If using bolt tensioners you will need to leave a significant length to allow the tensioner to attach. This would depend on the type of tensioner used.

 

[MotorVib]

The generial rule I have used is min 1 times the bolt dia for steel on steel but 1.5 times dia is what I would rather see. For Steel bolt in AL or cast iron 2 times or more.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[evelrod]

I retired over ten years ago, but at that time, most inspectors in Los Angeles would buy a 'flush nut' if it were fully torqued. With the advent of TS fasteners the question is largely moot. Not a good idea to try for a flush nut if you are using load indicators...inspectors frown on that.

Rod

 

[chicopee]

My rule of thumb is three full threads.

 

[evelrod]

chicopee, I always liked 'three threads' too. However in a building with tens of thousands of fasteners....Those 2.5 extra threads can add up to big bucks. Like I said, if the specs call for it, ok. Otherwise, most go for saving wherever they can.

Rod

 

[MotorVib]

3 is good if you have good threads and steel in steel

I feel better with what I have posted above. Bolt cost are small thing when compared to a joint problem. (I have worked with bolts from #10 to 2.5 inch)

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[rmw]

Probably the only thing I remember from one of those ME courses that I took was the derivation of the "3 thread" rule. I've always appreciated that Professor for taking the effort to make us go through that. Sorry, I can't do it now, however. Once was enough to convince me.

rmw

 

[chicopee]

I have not seen calculations done on free threads but I have seen an analysis done on bolt threads under engagement with nuts a few years ago and if I remember correctly that was with three full threads and the analysis concluded that additional threads under engagment did not contribute significantly..

 

[plasgears]

Thread length tolerance can rise up and bite you in the hind quarters. Mfrs tend to make to the low side, so you need to add to the three thread rule, if you want to end up with three.

 

[HotStab]

For subsea equipment, a general rule I use is one thread or two at maximum. More exposed threads would increase the difficulties in disassembly. In subsea equipment, exposed bolts threads might be damage by corrosion or calcareous deposit.

 

[HeviiGuy]

In most of the world, critical subsea flanges are almost always tightened by the use of bolt tensioners rather than torque wrenches. This enables all bolts to be tightened simultaneously with a great degree of accuracy and speed not possible through torquing.

The extended length beyond the nut of bolts (studs, actually) intended to be tensioned is the equivalent of at least 1 times the diameter for topside/shore applications. For subsea flanges, it's usually 1.5 to 2 times.

The extension is only required on the end of the stud which is to be tensioned. The typical 2-3 threads is sufficient on the other end. In most cases with pipe flanges, this means that, on one side of the flange, every other stud will have the longer extension. Then, on the other side, the configuration is repeated with the exception that the tensioners are indexed by one. Thus, 50% of the tensioners are installed on one side of the flange while the other 50% are installed on the opposite side of the flange.

It sounds a bit convoluted to the uninitiated but it's really quite simple (and darn effective!)

Ciao,

HevïGuy

http://www.heviitech.com

 

[HotStab]

The concept "critical flanges" shall be carefully assessed. In most cases (something more than 90%) bolts and studs of subsea oil and gas production equipment are still tighten with torque wrenches. In fact bolts and studs compromised with pressure containing are a minority regarding the quantity of structural and simple fixture bolts required in any subsea equipment. And even among the well pressure containing flanges just in very special situations, for example flowline field connections, tensioners are used.
For hydraulic tensioner connection an extension of threads beyond the nut is usually required, but for the wrench tighten bolts and studs additional threads might lead to problems for a future maintenance work. However it is not a rule, it is just a recommendation.