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Vessel weight for lifting analysis

Vessel weight for lifting analysis

Vessel weight for lifting analysis

Hi all,

Is there a way to enter the empty weight of the vessel into Compress for use in a lifting lug analysis?  I'm trying to design lifting lugs and a tailing lug...and do it in a hurry (the fab shop needs this yesterday).  I know that usually I would run these calcs last - so all the vessel components would already be built in the model - but now I'm only designing the lugs for an existing vessel that will be lifted back into place (I know the total weight of the empty vessel).  So I don't need to build out all the nozzles and attachments, I only need their added weight so I can design the lugs.

And no, I have no idea what happened to the original lugs.  Maybe they floated this thing into place.  big smile

Is there a faster way to force Compress to use a weight I enter instead of having to build every vessel component?


RE: Vessel weight for lifting analysis

Forgot to mention...there is a very large structure located inside the vessel itself.  Not something I'm aware that I can model with Compress.  So, this accounts for a large portion of the lift weight (~20,000 # out of 54,000 lbs).

This is why I need to enter the weight manually.


RE: Vessel weight for lifting analysis

Perhaps create the basic shell/head of the vessel at the appropriate thicknesses to get that weight accurately and then add a packed bed of the additional weight and include it in the lift weight then design the lugs.


RE: Vessel weight for lifting analysis


A good and safe design shouldn't be done in hurry. Safety should always be a priority.

I would prefer modeling everything on Compress. You should have at least modeled the major components (i.e. cylinder, heads, supports). Also model internals such as trays or packed beds. It's quite easy to model them. You can add the weight of that large internal structure using the Load menu > Vertical Load. Input the vertical load of the structure, eccentricity (if any), position & angle, and click "Include in Lift Weight". Nozzles and manways account for a small portion of the total vessel weight. You can add them as a single combined load using the Load menu > Vertical Load and position it to the approximate center of gravity of the vessel erection weight. If this is a dressed vessel, model the insulation, fireproofing, L&P's, attached piping, etc.

BTW, how did you acquire the empty weight of the vessel? Did you get this from the old fabrication drawings? Remember that some fab drawings have a different definition of empty weight. For some fab shops, they make it the same as the fabricated weight. So it is better to model everything in COmpress or make a manual calculation to check if the empty weight includes everything attached to the vessel.

RE: Vessel weight for lifting analysis


And no, I have no idea what happened to the original lugs.  Maybe they floated this thing into place.
Once a vessel has been erected into place, some owners require that lifting lugs/trunnions be cut off. This has something to do with heat transfer, especially if the vessel is insulated. Or the vessel was lifted using  a top flange lug (i.e. lug welded on blind flange; blind flange connected to the top head nozzle). The top flange lug would be discarded after erection.

RE: Vessel weight for lifting analysis


I didn't mean to imply these would be designed in such a hurry that they wouldn't be done correctly.  My only point was that I need to save time if at all possible.  I would never, ever give time constraints a higher priority than doing it right.

I agree that the original lugs may have been cut off, but I am working from the original fabrication drawings.  I only half expected to see them there, and wasn't surprised when they weren't.  I've seen pictures of this vessel - there are lugs, but they don't look to be the right size (or placement) to have been lifting lugs.  No one at the site knows what they were for.  And the tailing lug was probably a tailing beam that was unbolted during the original lift.  Who knows?

This is not a "dressed" vessel and the weight I have is from the fabrication drawings.  I understand that this may be different depending on the shop (I started my career in a vessel shop), so I have made every effort to confirm the exact weight of the vessel as is.  Suffice it to say that the weight I have is very close to the weight that will be lifted next week.  It's as close as anyone involved is going to get.

Now, having said all that, I will try to add the weight of this structure (which, by the way, is not a tray or packed beds...this is something I've not seen before) as a vertical load.  Thanks for the tip.


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