Lift vertical vessel by skirt
Lift vertical vessel by skirt
(OP)
I am trying to verify that it is safe/legal/code-compliant to lift a vertical heater treater by lugs on the skirt when going from horizontal to vertical or vise-versa. More specifically, we are replacing four of the gussets on the skirt with thicker gussets that have a hole in them for a pick point. We use Compress for our pressure vessel design, so I am usually confident in the code-compliance of our vessels, but Compress does not include the capability to put a lug on the skirt. The company owner is a life-long welding and rigging expert and wants to save money on standard side-mounted lift lugs if possible. He see's no problem with lifting by the skirt.
My concern is that the skirt, when designed to code, is only rated to hold the weight of the vessel vertically, not sideways with two point loads. I don't want to end up up with skirts bent out of shape or have a crane accident. The approximate gross weight of the vessel in question is 25,000 lbs.
Is this even addressed in sect 8 div 1? I can't find it. Do I need to do an independent FEA analysis to verify the lug/skirt strength? I have that capability, but it would take ages with the hardware I have to work with. If anyone knows of a precedence for this or a reasonably simple way for me to verify the safety of these lugs, please share.
Thanks!
Luke
My concern is that the skirt, when designed to code, is only rated to hold the weight of the vessel vertically, not sideways with two point loads. I don't want to end up up with skirts bent out of shape or have a crane accident. The approximate gross weight of the vessel in question is 25,000 lbs.
Is this even addressed in sect 8 div 1? I can't find it. Do I need to do an independent FEA analysis to verify the lug/skirt strength? I have that capability, but it would take ages with the hardware I have to work with. If anyone knows of a precedence for this or a reasonably simple way for me to verify the safety of these lugs, please share.
Thanks!
Luke





RE: Lift vertical vessel by skirt
Skirt specific design?
Height, welds, holes now present, thickness, other ribs or gussets?
Height of total PV + skirt?
Lifting it -> Then putting it back down straight with no other movement?
If the PV is any significant height or weight or both, you need a specific structural and crane engineering company to do a specific lift calculation.
Expensive? Not compared to dropping the PV as it rotates sideways across three other PV and refinery vessels and ALL other piping in the vicinity.
RE: Lift vertical vessel by skirt
Weight of PV? approximately 25,000 lbs.
Skirt specific design? not sure what you mean.
Height, welds, holes now present, thickness, other ribs or gussets? It is a typical skirt design with many gussets, four of which are replaced with heavier gussets with holes to lift from.
Height of total PV + skirt? about 24 feet
Lifting it -> Then putting it back down straight with no other movement? No. The purpose of lifting from the skirt is for switching the vessel from vertical to horizontal or vise-versa, such as when loading or unloading it for transport. The vessel will be two-lined by the crane and then gradually stood up or laid down. I have additional lift points at the top for moving the vessel into place. Those are not a problem.
If the PV is any significant height or weight or both, you need a specific structural and crane engineering company to do a specific lift calculation. That is probably not an option. If a specific lift calculation needs to be documented, it will be me who has to do it.
Expensive? Not compared to dropping the PV as it rotates sideways across three other PV and refinery vessels and ALL other piping in the vicinity. I am aware of the risks, hence my hesitation.
RE: Lift vertical vessel by skirt
Vessel is ideally lifted from trunnions located near (above) the vessel CG, and lug(s)on the skirt. By lowering the skirt, the vessel is turned from horizontal to vertical. Keeping the trunnions near the CG minimizes the load on the tailing lug(s) and skirt.
And no, not covered by Sec VIII Div 1, more likely to be found in something like PV Design by Moss, etc. Vessels were handled in this manner for many years before FEA became commmon. Plus side, 25K is not that heavy as vessels can go.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Lift vertical vessel by skirt
So... my recommendation is that you have your boss spend a small fraction of the anticipated savings on a book which will allow you to confidently achieve the savings.
RE: Lift vertical vessel by skirt
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Lift vertical vessel by skirt
I have a copy of that book on order. Hopefully one of the examples in there can give me some insight.
Thanks for the recommendation,
Luke