Limitations of Zick's Analysis? 2

[KLee777]

Can anyone tell me if Zick's Analysis is limited to certain geometries? I know very little about it other than the original analysis was performed for 2 saddles.

The vessel I'm looking at is very long (60'+ best guess), contains numerous stiffening rings and I don't know the diameter yet. I'm considering using CodeCalc if this is appropriate.

Just wondering?

Thanks.

 

[stanier]

Go to

http://www.paulin.com.

they have suitable software and also some technical papers.

 

[PVGuy]

Klee777,

The Zick paper makes lots of assumptions and includes lots of limitations (that is if you want to stay 100% within its scope). It assumes: 2 saddles, saddles are equal distances from their respective tangent line, the total weight of vessel and its contents are evenly distributed from 2/3 depth of "left" head to 2/3 depth of "right" head, the left and right heads are identical, and a few other assumptions just for fun. Now, do not get me wrong, because the paper is very useful and I am sure it was very difficult to write. However, I suggest looking at some methods that are derived from this paper that allow for a broader scope of vessel geometries. The TEMA red book has a pretty good method for vessels supported on saddles in its Recommended Good Practice Section. Though TEMA is written for shell and tube exchanger fabricators, it is still very use for those who do not do this or do it infrequently. I like some of the saddle design equations in the various design hand books but I do not have one that allows for A-symmetric saddle placement or uneven weight distribution. Good luck.

 

[MJCronin]

Klee...

I agree with "stainer"....

The paulin software would enable you to perform a detailed stress analysis of a unique horizontal pressure vessel. I am willing to bet that less tha 2% of all horizontal vessels are this long

It sounds like you have a very long expensive vessel that would justify this kind of analysis.

I am assuming that there are only two saddles.....(!!??)

Unless you have a lot of experience in this area, I would seriously consider having this FEM analysis done by experienced others, with a PE stamped calculation as a deliverable.

My opinion only

-MJC

 

[JStephen]

I would like to point out that some of the limitations of the Zick paper are easily negotiated. For example, the equal saddle spacing, the assumed distribution of load, the identical heads are all just assumptions that go into deriving the beam bending moment and saddle load equations, and these equations can be adjusted for other conditions.

In the case of a vessel with many stiffening rings, you could apply the Zick method to it by simply neglecting the stiffening rings (or locating a support AT a stiffening ring). If this gives you unreasonably large stresses, then look at more sophisticated designs.

 

[jte]

I agree with the sentiment that Zick (and Chicago Bridtge and Iron which employed him) did the PV community a great service by doing the experiments and writing the paper. As JStephen noted, certain adjustments are easily made to accomodate nonsymmetrical vessels.

I think that one significant assumption which most current users of Zick's method conveniently forget is that the paper was based on vessels with wear plates. These wear plates were not connected to the saddles: The saddles were made of concrete. Thus the typical modern welded steel saddle is a bit different from that which Zick studied. Besides being loose and of substantially different Young's Moduli, the bearing of the saddle was distributed over the entire width of the saddle. Compare that with typical welded steel saddles which have the web of the saddle, perhaps 1/4" to 1" to carry that load along with the outer flanges and occasionally interior ribs. I'd still like to see a study which correlates Zick's approach of steel on concrete to modern steel on steel saddle design.

jt

 

[LSThill]

TECHNICAL PHOTO GRAPH:

http://www.codeware.com/photoalzamil.html

by Al Zamil Heavy Industries, Saudi Arabia [www.codeware.com]

http://www.codeware.com/photodacro.html

by Dacro Industries, Edmonton, Alberta, Canada [FEA
by paulin research group houston, texas, www.paulin.com]

 

[JStephen]

That first picture looks like saddles on a horizontal tank.

The second picture looks like a vertical tower with temporary saddles for transport. Presumably, the far end is flat (IE, skirt with support ring, not just a head).

Both are impressive photos, thanks for pointing them out.

 

[DSB123]

JStephen,
Think you are right about the second photo. Nothing to do with horizontal vessels just transportation saddles for a vertical column.

 

[JohnGP]

DSB123,
When being transported horizontally, a vertical vessel doesn't experience normal process loadings obviously, but the shell still sees a couple of saddles there so the transport loadings need to be analysed, and Zick's method can be used for that.

It would be a bit unfortunate to have your column turn up with severe buckling because someone forgot to check the transport loadings.

Cheers,
John

 

[LSThill]

Technical Note: Thank you Sir: JohnGP (Mechanical).

Technical Reference: Pressure Vessel Desing Manual Dennis Moss, Third Edition: PROCEDURE 7-1 Transportatin and Erection of Pressure Vessels: Shipping Saddles.

Table 7-1 Barge Shpping Forces and Summary of Loads/Forces on Vessel During Transportation. Load Diagram for Moments and Froces Case 1, - case 4.

Procedure 7-2 Erection of Pressure Vessels
Procedure 7-3 Lifting Attachment and Terminology

Procedure 7-4 Lifting Loads and Forces
Procedure 7-5 Design of Tail Beems, Lugs, and Base Ring Details.
Procedure 7-6 Desing of Top Head and Cone Lifting Lugs

Procedure 7-7 Desing of Flange Lugs
Procedure 7-8 Desing of Trunnions
Procedure 7-9 Local Loads in Shell Due To Erection Forces
Procedure 7-10 Micellaneour

Goble Team Members: the above technical reference may help you in your desing.

Note: 27 Feb 2006 Location: BROWN BOOK SHOP/TECHNICAL. 1517 SAN JACINTO ST, (713) 652-3937. HOUSTON, TX 77002 has (3)three: Pressure Vessel Desing Manual by Dennis Moss, Third Edition.

http://www.brownbookshop.com

 

[DSB123]

JohnGP,
I fully understand that vertical vessels transported horizontally must be analysed for the location of the saddles - it's not news to me. The point is that the original question was about horizontal vessels under process conditions (i.e. full or partially full) To cite a vertical vessel in this context is , in my opinion, not valid as the vertical vessel is not transported with liquid inside and is subject to additional transport loads.

 

[JohnGP]

DSB123,
No problem, I won't hijack the thread by further debating this issue, but just wanted to highlight the fact that vertical vessels on transport saddles are still horizontal vessels for a time, and this becomes particularly important for vessels with lower design pressures.

 

[JoeTank]

JohnGP is right on the mark about low pressure vessels with thin shells and the problem of proper support during shipment! Here's a star.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com