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Re: Horizontal vessels-Friction forces

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Thank you, Tom. I feel good.

Rajendran
--- Tom.Hunt(--nospam--at)d-fd.com wrote:
> Padmanabhan,
> 
> We do a lot of heat exchangers and other horizontal
> drums for refinery and
> power work where thermal expansion is a major
> concern.  It appears that
> your propane tank will see only ambient temperature
> changes but none the
> less should be considered.  Our horizontal tanks are
> slotted on both ends
> because the tanks are purchased early in the job and
> the "fixed" end is not
> determined until our pipe stress group runs their
> numbers.  Once the fixed
> end is determined our standard drawings call out for
> a 1/4 inch plate
> washer to be field welded to the saddle after
> installation.  At the sliding
> end we double nut and leave 1/16 inch clear from the
> bottom bolt to the
> saddle.  Most of our designs use a galvanized slide
> plate at the other end
> and Teflon plates and pads for only very heavy
> vessels.
> 
> Your co-workers are correct at the sliding end, if
> the slotted holes are
> long enough and all is installed correctly the
> sliding end anchor bolts
> should not see any load from thermal expansion.  In
> fact, one of our
> clients (Shell) do not use any anchor bolts on the
> sliding end but instead
> weld bars on the outer ends of the slide plate to
> act as guides.  However,
> the fixed end bolts should be designed for the full
> friction load.  Thermal
> loads are not necessarily instantaneous and will
> build up forces until the
> sliding end actual moves and after that it
> theoretically remains at that
> load.
> 
> Your bolts at both ends will definitely need to be
> designed for transverse
> seismic and note that UBC section 1632.1 does not
> allow you to deduct the
> friction resistance from the seismic force.
> 
> A 500 kip vessel warrant's the use of Teflon slide
> plates.  Note that
> Fluorocarbon changed it name to Furon and now has
> sold off their slide
> plate division.  It is now an independent company
> named Seismic Energy
> Products.
> 
> Regards,
> 
> Thomas Hunt, S.E.
> Duke/Fluor Daniel
> 
> ----- Forwarded by Tom Hunt/DFD on 03/02/01 12:18 PM
> -----
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>                     Padmanabhan                     
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>                     Rajendran            To:    
> seaint(--nospam--at)seaint.org                                   
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>                     <rakamaka@yah        cc:        
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>                     oo.com>              Subject:   
>  Horizontal vessels-Friction forces                 
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>                     seaint                          
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> 
> 
> 
> As far as I am aware of, horizontal vessel,
> supported
> on two saddles, has slotted holes on one of the
> saddles (sliding end) and standard holes on the
> other
> saddle (fixed end). Horizontal force of friction due
> to thermal expansion/contraction of the vessel is,
> then, equal to the product of coefficient of
> friction
> at the sliding interfaces and the vertical reaction
> at
> the sliding end. Consequently, one of the loading
> for
> which the anchor bolt on the "fixed" end should be
> designed for is the friction force. Because this
> loading is transient, one may use a higher allowable
> stress or use a reduced load factor. This is what I
> have learned and practiced for about 10 years.
> 
> I have changed jobs and the lead engineers
> (mechanical
> and civil) in this company tell me that the above
> noted friction force need never be considered in the
> design of anchor bolt. Their reason is that the
> vessel
> moves on the sliding end (and, probably on the fixed
> end also because the hole diameter on the fixed end
> is
> larger than bolt diameter)and, any friction force
> that
> may develop is so quick and instantaneous that the
> bolt will not experience it. The tank in question is
> a
> propane storage tank with an operating weight of 500
> kips. Based on my experience I figured that the
> friction force will be very large and that in order
> to
> reduce it, I suggested using Teflon sliding
> surfaces,
> such as Fluorogold product. The engineers here say
> that Teflon sliding pads do not work well and that
> the
> pads easily come off the equipment. They also told
> me
> that it is common to have both saddles with slotted
> holes and that they have never heard of using
> friction
> reducing sliding surfaces on horizontal vessels!
> Each
> of them has more than 20 years with reputed and
> large
> consulting engineering companies, whose design
> standards echo what I have been practising.
> 
> Rick Drake and Christopher, in particular, (because
> I
> believe that both of you have refinery and pipeline
> experience), am I overly conservative in my design
> approach and is my design criteria in error?
> 
> P. Rajendran
> 
> 
> 
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