One/two point pick for tailing lugs 1

[KLee777]

I have a large tower (~90' tall, ~200,000#) that will be lifted from the horizontal and placed vertically into service. I have two flat lifting lugs at the top of the vessel (each designed to carry the entire load in case of failure during lifting). Two cranes will be used to lift the vessel and the tailing lug(s) is/are to be located within the type 2 basering on the skirt. The skirt is 1/2" thick.

From your experience, would a one or two point pick on the basering allow for easier setup of the vessel? I have never seen one of these lifted and am trying to find out if I could use only one tailing lug successfully. I have yet to do the calculations on the tailing lugs.

Any advice you could offer would be greatly appreciated.

 

[jte]

KLee777-

If by "type 2 basering" you mean a baseplate with anchor bolt chairs topped by a continuous top ring then you are off to a good start. A one point pick has advantages in the field compared to having to use a tailing beam. Perhaps the most significant is that you don't have to send in a crew to unbolt the beam while the vessel is on the hook so that you can set it down. If you build an internal beam then you can leave it in, but some won't like it due to the tripping hazard/interference.

So, try hard to make a one point pick work. Increase the thickness of the baseplate and top ring, decrease the ID of the baseplate as required to get the section modulus you need for the ring. Increasing the skirt thickness is also an option. There will be some cut point where a thicker skirt is cheaper than the additional fabrication of additional reinforcement or going to a two point pick (don't forget field hours in the cost).

I've sometimes advocated reducing the stresses during lifting by filling the vessel with helium or hydrogen. Just float the darn thing up. Or, better yet, pulling a full vacuum on the vessel (gotta check those compressive loads, though). Haven't had any takers yet...

jt

 

[MJCronin]

KLee...

I have a little experience with setting vertical feedwater heaters (about 50kips --48 ft long by 8 foot diameter) in a nuclear power plant in Maine. Although, they are not quite as big as your unit, I believe that the methodology used in rigging would apply.

In my opinion, the most common way to lift and set a long horizontal pressure vessel is to use two pipe trunnions at the top and a single tailing lug.

A crane lifting the top of the vessel (with a spreader beam) uses two adjustble chainfalls with chains looping around the welded trunnions (each trunion was designed for entire vessel load). Another crane would be at the tailing lug just for the initial part of the lift.

As the top crane lifts, the chains rotate slightly as the vessel goes to vertical. The bottom of the vessel is placed on cribbing. The top of the vessel swings to just beneath the spreader beam. The tailing lug is diengaged from the second crane.

At this point, the vessel/tower is supported entirely from the top crane and it is place in final set position.

This has been done many times, obviously much attention must be paid the to trunnion design on the thin tower shell and the geometry of the trunnion/chainfalls/spreader beam must be carefully evaluated.

My recollection/opinion only

MJC

 

[codeeng]

jte
Interesting theory on the full vacuum/light gas. I guess we need to be careful about how we anchor vessels in these services.

 

[KLee777]

Wouldn't it make my job SO much easier if we could, though.

Looks like the tailing lugs might require some thinking "out of the box" due to its large diameter and thin skirt...am not allowed to increase thickness of skirt because it's already been fabricated.

Thanks for your help....much appreciated.

 

[codeeng]

KLee777
You can refer to PV Design Manual (3rd Edition) by Moss for some useful data on vessel lifting arrangements and vessel shipping. There are lots of different tailing options. In the end though you should have it reviewed by someone experienced in rigging.

Good luck

 

[altoid3000]

Iteresting discussion very much relevant to something that I am working with at present. I dont have much experience so I can only ask questions.

Can someone direct me to some reading about the different stresses involved during the lifting process. I guess when you lift the tower, one important factor to worry about is the base ring going out of shape due to the bending moment. How do you design for this moment? Would you provide two tail lugs with pads on the inside surface of skirt just to beef up the section? Or would you provide one thick tail lug with a bracing bar all across to distribute the moment equually? Please direct me to some credible formulae in some good books or design handbooks. I understand there are a lot of different ways of analyzing this problem. If you know something that is different, please direct me to the source.