Question about vessel head diameter vs cost

[vesselguy]

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.

 

[eliebl]

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

 

[vesselguy]

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.

 

[weeeds]

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.