Length/Diameter (L/D) Ratio

[hubert88]

Hi guys,

Anyone knows is there any requirement in ASME Section VIII mentioned about the length/diameter ratio?

If no, any guideline/rule of thumb to follow?

P/S: It is an 2:1 elliptical horizontal pressure vessel

 

[TGS4]

Internal pressure: no. External pressure or other situations where there might exist longitudinal compressive stresses: the L/D ratio comes into the calculations, but there is no limit per se.

 

[SnTMan]

It is an 2:1 elliptical horizontal pressure vessel

????

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Jano6924]

The L/D ratio is used for cylinders, see UG-28(c)(1) in ASME VIII-1.

For elliptical heads you don't need the L/D ratio, see UG-33 in ASME VIII-1.

Regards.

 

[Jano6924]

Sorry, I forgot that for dished head with a skirt, then the skirt (or flange) of head shall be calculated as a cylinder per UG-28. For the dished portion of head you use UG-33.

Regards.

 

[hubert88]

Sorry that I didn't write it clear about my question.

Basically, we are proposing a pressure vessel with ID: 2000mm and TL/TL: 5500mm.

But the client commented the length/diameter ratio (5500/2000 = 2.75) is too small.
Usually, it needs at least 3.

So, my question is, does the ASME Section VIII mentioned about this requirement?

 

[JohnGP]

Firstly hubert, ASME Section VIII itself is not concerned with L/D ratio except when considering vacuum design. Check the formulae for thickness calculations. Secondly, the L/D ratio will, or should, result from process considerations and not just from a general guideline.

You’ve also not stated the function of the vessel. A slug catcher will likely have a different L/D ratio than a separator, or a compressor suction drum, for example. The process requirement will generally dictate whether a vessel needs to be long and skinny, short and fat, or vertical/horizontal.

 

[jte]

What's the L/D of a sphere? Are we to design all spheres to a 3:1 ratio? And how, precisely would one do such a thing?

What's the L/D of a common household propane container - as with the 20 pound tanks usually used for grills in the US?

The ASME is a mechanical organization. Whether or not the container functions as the process engineer intended it to is not a concern for Section VIII. Sounds to me as though your client got some rule of thumb from a process engineering perspective and is now trying to ask "intelligent sounding" probing questions since he has little experience to base a conversation on.

 

[r6155]

Please see Pressure Vessel Design Manual by Dennis Moss 4th Edit. Procedure 2-16: Optimum Vessel Proportions and you can find L/D ratio 3, 4 and 5. The maximum volume for the least surface area, and weight..............and more.

Regards
r6155

 

[JStephen]

Shipping clearances, lifting capacity, overhead crane clearances, available plate lengths and rolling capacities, available head sizes enter into it.
If there is no other criteria, specify volume only and let fabricators pick the most economical dimensions- which may vary from fabricator to fabricator, from place to place.

 

[georgeverghese]

Industry practice for optimum dimensions for horizontal and vertical vessels, at least from a cost perspective, is for L/D to range from a minimum of 3 to a max of 6 - this is usually applied to vapor liquid separators and gas scrubbers. Higher L/D (approaching 6) leads to a lower plate thickness and easier fabrication in most cases.