Lift vertical vessel by skirt

[FoxRox]

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

 

[racookpe1978]

Weight of PV?
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.

 

[FoxRox]

Thank you for your reply. To answer your questions:

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.

 

[SnTMan]

FoxRox, it sounds like what you are describing is known as "tailing" a vessel, turning it from horzontal, as shipped, to vertical, as installed.

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

 

[jte]

SnTMan got it right. A vessel this size isn't particularly special (add a zero and we'll perk up a bit), but it would be prudent to run the calc's. The Pressure Vessel Design Manual by Moss and Basic covers this in Procedure 10-3. The basics of the skirt base plate evaluation are derived from Roark's 3rd or 4th Edition, the rest is essentially statics.

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.

 

[SnTMan]

(add a zero and we'll perk up a bit),

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

 

[FoxRox]

Thanks for the feedback. I see how using trunnions near the CG would be ideal for the "tailing" procedure. Unfortunately, the vessel in question ships with loads of accessories already mounted on it which makes trunnions impossible. When going from horizontal to vertical, our crane operators have to pick it from four lugs on one side, two at the top and two at the bottom. They then lower the bottom until the whole vessel hangs freely from the top two lugs. Then, they gently balance it on the edge of the skirt and tip it into the vertical position. I'm not a fan of this procedure, as it appears to put excessive stress on the edge of the skirt. But they assure me that it is common practice and they've never had a problem with one bending. So, when this pick is performed, the two lugs on the skirt have to support about half the weight of the vessel at approximately a 45 degree angle toward the top of the vessel. Not only that, but since the lugs double as gussets, they are mounted in a radial position, so the crane will be pulling sideways on them. Certainly not ideal.

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