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Question about vessel head diameter vs cost

Question about vessel head diameter vs cost

Question about vessel head diameter vs cost

(OP)
Hi all,

This is a question for those of you who are fabricators.  I would like to know if there are standardized head sizes that we buy from head manufacturers?  i.e., are head sizes comes in increments of 3" so a standard size in a 6' range is 6'-3", 6'-6", etc?

If so, then would the cost be significantly higher if I order a vessel head of 6'-2" as opposed to 6'-3"?  Or it doesn't matter at all?

The reason I'm asking is a Process Eng question how should he round the metric size of a vessel from imperial units.  He worried that if he calls out 1200 mm  (47" or 3'-11") then the cost will go up because it is not a "standard" vessel head size.   All these years, I never paid any attention to this issue.  I just design the vessel based on the process datasheet numbers and the fabricators builts it without any issues.

RE: Question about vessel head diameter vs cost

I think this depends upon the vessels.  My tank truck designs used 1/4" thicknesses and were formed over a mandrel.  Then OD's were available in roughly 6" increments.  

If the heads are formed with a dish pressed in the center and the knuckle rolled seperately then making different sizes is usually not that much of a problem.

Regards,
EJL

RE: Question about vessel head diameter vs cost

(OP)
OK, forget it.  I just got data from a local head manufacturer and he confirmed that there are indeed standardized heads and there is a significant cost increase by using non-standardized heads.

RE: Question about vessel head diameter vs cost

Depending on the tooling of your supplier, you should be able to get any size of head, and it should not be a premium.
Our supplier charges by the pound and there is no premium for oddballs.

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