Conical-flat ends instead of spherical heads

[DavidCR]

In our shops we have to construct and repair many pressure vessels for different aplications mostly cylindrical air receivers, steam headers, cold water headers.

We don´t need to ASME stamp our vessels but we follow ASME VIII Div 1 rules and use PVElite software on our designs.

We don`t have the means to construct formed heads (toriespherical, etc.) it takes to much time for us to aquire them to others. To save time, for some applications, it is easy for us to use, instead of a formed head, a conical transition section to a diameter were a circular flat head is possible to be used without the need of ribs or fins to reinforce it. Of course we plan to do it only in some cases were the diameter and pressure don´t require excessive thickness in the conical section and the flat head.

We use the rules of ASME for conical sections and welded circular flat plate (UG-34 sketch (e) for example).

I´d apprecuiate a lot coments about the usage of such a "frustum of a cone" end instead of a curved head.

 

[waskillywabbit]

I assume you are constructing and repairing non-ASME stamped vessels.

I don't see anything wrong w/ what you are doing as far as putting a welded cover on a transition but I see your only real savings here as being a quick turnaround time as you aren't waiting 6 weeks or longer for a formed head to be delivered.

Some things that come to mind:
*more material costs (thicker flat cover)
*more labor costs for welding (support rings, adding long seams, etc.)
*discontinuity stresses in the shell and transition
*spacial limitations

I can't imagine having a PV come into our shop for repair that has a formed head on it and suggesting to a customer to take your approach. While certainly acceptable, it just seems unusual to my experience.

Do you have a dimensional and thickness basis for where your method is cost effective or just a time saver?


Brian

 

[codeeng]

I see no problem with this type of closure. A little unusual thats all.

 

[DavidCR]

Thanks for your coments.

I agree that it is not necessarily cheaper, in our case for example, we can build an urgent air receiver that is needed for perforation works in a tunnel.

I live in Costa Rica and since the global situation of steel, buying items like formed heads can be difficult. We have good welders and big stocks of plate in our shops, so it´s easier for us to use this type of solutions.

Yes it´s unusual and they are starting to call them "pigs" or "torpedos".

We don´t stamp our vessels, but I´m courios if the design considerations should be different if we were talking of a vessel designed as if it were stamped. (?)

 

[GenB]

It looks that your Compan~ia is a large facility and if that is the case I would invest on a forming machine.
It is nothing wrong with your desind, but instead of just a flat plate in The US is used a pan head, that is a flat with a 1-2in. skirt with 1/4 or more radious(note:if the end becomes too thick by design, the skirt can not be formed so a plain flat will be used)
er

 

[waskillywabbit]

DavidCR

If you are using PVElite to design the "heads" to ASME code then they could be stamped if everything is in order. I don't think there are any other design considerations, just an unusual looking result!

Brian