Saddle without ribs? 1

[robertogrramos]

Hello,

I'm new in this site and at this kind of work. But I was asked to verify some calculations of a pressure vessel design.
The design is of a horizontal water boiler with 1500 l capacity (800mm radius) and 4,0 kg/cm2 pressure.
I'm researching the subject, my main sources are ASME Division 1, Zick's paper and Dennis Moss's book.
In this design the support of the vessel have no ribs, just the wearplate, web and baseplate (about 6mm thickness). In my research I never found any saddle without ribs, but I'm new at this.
So my question is, is this common? Or even allowed?

Thanks

 

[marty007]

It certainly wouldn't take much axial force to buckle the saddles. Is the vessel supported axially in another way?

 

[TVSN]

It is not a common practice to provide only web plate to support the vessel, for the reason stated by "marty007" above.

Since only limited design data is available in the question, approx. check yields a thick of 2 to 3 mm, considering this thickness, if the overall weight of the equipment is very less and no other force acts, providing web plate only as a support option can be evaluated. However, as "marty007" said axial force required to buckle the saddle would be very less so this would force to consider high thick plates.

 

[DSB123]

The answer to you question requires substantial additional data such as:
1. Thickness of web
2. height of web
3. width of web
4. loading on saddle
5. temperature
6. material
7. is seismic loading to be considered

Slenderness of the web may require stiffeners. if the web is thick then it may not need stiffeners. With the information given no-one can give you a definitive answer.

 

[robertogrramos]

Thanks guys!
Frankly just the fact that you didn't found a saddle wihtout ribs something absurd was allready helpfull.
I guess I'll just recommend to include ribs in the design, it's not like it'll require a lot of added material or manpower to do it. Then, I'll do the calculations considering the ribs.

 

[chicopee]

One additional reference in regard to your OP is "Pressure Vessel Design Handbook" authored by Bednar. My book, being a 1981 copyright, has section 6.8 dealing with stiffners in saddles pertaining to your question. There may be updated copyrights.

 

[r6155]

Something is wrong in your data: 800 mm is radius or diameter?
If diameter is 800 mm ribs/gusset may not be required. Also wear plate may not be required.
See PIP (Process Industry Practice) VEFV1104 Standard Details

Regards
r6155

 

[Skipdeiter]

Pressure is low, vessel is relatively small.
Short of the saddles being 3 meters tall, inside ribs would be excessive and a waste of parts and hours.

 

[saplanti]

High saddles always create problems to the vessel shell connected under axial and lateral loads of the vessels. The same problem is also valid for the transportation. Therefore saddles should be as low as possible (to be able to work with bolting and thermal insulation). In your case you can use low saddle and the remaining height can be filled with structure (steel or concrete). This will allow you to use an industrial standard saddles with/without ribs (needs to be checked by calculation) to work with for the vessel. I suggest you to look for the steel saddle calculation reference (I cannot remember the std number at the moment) in the PD5500. The reference std gives you the calculation method for the pressure vessel with steel welded saddles.