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Sleeve Nuts

Sleeve Nuts

(OP)
I have been wracking my brains over the theory behind sleeve bolts (some people call these compensators).

It is a sleeve to extend the stud for high temperature service.

Every time I try to do the theory I seem to come up with a different answer. Example: one time I try to maintain constant gasket stress by holding gasket strain between ambient and operating (bolts colder than flange); another I will try to ensure that the gasket does not unload in shut-down. Every time I come up with different answers, some of which do not even seem realistic.

However, sleeve nuts have been used countless times, so where am I going wrong???

In the 1990s I had a book called 'Theory and Design of Pressure Vessels' by Harvey, which had the theory behind this (about page 435 - I used to catalog pages when I was young and keen!). Lent it to my Client's engineer-weasel and never saw it again - Thank You Shanghai Chemical! - Hope you enjoy it.

In a similar vein, I am trying to work out whether Belleville washers make sleeve bolts redundant (another subject I think addressed by Harvey).

Tough for me to ask for a freebie on this, but with the downturn in O&G I cannot really face buying another copy of Harvey just for this one question.

Thanks for your time.

RE: Sleeve Nuts

Bolt sleeves increase the grip length of the bolt, which in turn decreases the stiffness of the bolt - total elongation is Δl=l*F/(A*E), where:
Δl is the total elongation due to the axial force F
l is the grip length of the bolt (i.e. from inner nut face to inner nut face)
F is the axial force in the bolt
A is the effective cross-sectional area of the bolt
E is the Young's Modulus

During events which result in a change in temperature from installation, the thermal expansion imposes its own Δl. Depending on the situation, this may increase or decrease the axial force on the bolt. But, the longer the bolt, the less that the value of F will change.

Belleville washers work on a similar principle, by adding some springy-ness between the flange surface and the nut face. The goal in both is to maintain as constant a bolt force (and hence gasket contact force) as possible, throughout a temperature change.

RE: Sleeve Nuts

(OP)
Excellent! Many Thanks!
I wanted a way to get a sleeve washer to equal Bellevilles, but came up with three different answers (depending on parameters). Your answer appears to work. Thanks again!

RE: Sleeve Nuts

a) Pressure Vessel Design Manual 4th Ed., by Dennis R. Moss and Michael Basic

Studs. Studs used for high pressure applications are integral to the overall design, the performance of the joint,
and functioning of the vessel. For these reasons, it is imperative that every design detail receive the appropriate
attention.
Typically the threaded shank of the stud creates a stress concentration. Numerous tests have shown that this is the most likely area of failure. To preclude this, and minimize stress concentrations, a generous radius is machined into the shank of the stud at the location of the first thread. This is critical for cyclic service or high temperature operation. Any time high temperature or fatigue are involved, the studs should have a generous radius machined at the root of the first thread.

Sleeve Nuts. Sleeve type nuts are utilized whenever normal spacing of nuts based on wrench clearances cannot
be met or is not desirable. Sleeve nuts are a smooth sleeve of metal that is internally threaded. The nuts may have a nut machined to the top of the cylinder to accommodate hand or wrench tightening. However, they are not designed for manual tightening.
Most high pressure applications do not utilize wrench tightening anyway. So why base the bolt spacing based on
wrench clearances?
In this case, the nut is not there to create the stud tension, but only used to secure the elongation of the stud. Sleeve nuts achieve this goal with a minimum of metal. Sleeved nuts may have holes drilled in them to facilitate the turning of the nut during stud elongation.
Sleeve nuts have longer threads to develop full strength as opposed to nuts. Sleeve nuts should have a minimum of
10 threads to ensure full strength.


b) AD 2000 MERKBLATT B7 BOLTS

2.2 In order to make a bolted connection as elastic as possible, it is recommended to design it with neckeddown bolt to DIN 2510. Neckeddown bolts should be applied if the design temperature exceeds 300ºC or if the design pressure is higher than 40 bar. Care has to be taken that adequate effective bolt length is available which can be increased e.g. by sleeves to DIN 2510. The length of the bolt shank must be at least twice the thread diameter
2.3 Neckeddown bolts are regarded to be bolts having a shank diameter ds≤0,9 dk or having dimensions according to DIN 2510. Bolts with no reduced shank are regarded to be rigid as far as design is concerned.

Regards
r6155

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