shell stresses in a carbon steel stack from sling loads while lifting

[jimmyhutmacher]

We fabricated a 65ft long, 12ft diameter carbon steel stack, lined it with 4in of refractory and now we have to lift it onto the trailer for shipment to the customer. The current plan is to have a sling at each end in a basket configuration. The problem I have is that I don't know if the shell can handle the stresses from the slings. The worst case scenario is the shell delfecting significantly and the refractory cracking. I'm struggling to find a resource that addresses the stresses in the shell of a stack (or tank) due to sling loads. Any guidance or a resource other than FEA would help! Thank you

 

[JohnGP]

In the most simplistic form, the stack is a simple beam with a distributed load due to self weight combined with the refractory lining weight. If the lining is effectively bonded to the shell then the bending stresses will be shared across the combined section. You may need FEA to analyse what is happening in the lining then.

I would be concerned about any deflection potentially causing cracking in the lining. For lifting onto transport, multiple cranes could be used, but the bigger problem will be at site when it has to be lifted into a vertical position.

 

[jimmyhutmacher]

Thanks for the reply. As far as analyzing the stack as a simple beam in bending, the stresses are minimal, so no concerns there. And erection in the field is done by another outfit so design of the lift is their responsibility. I'm mainly concerned with local deformations of the thin shell due to the forces imposed by the (2) slings. I actually found decent formulas in Roarke's Formulas for Stress and Strain in thin rings, Table 17, Case 13 (i think that's the case, don't have it in front of me currently), but the stresses i'm getting are astronomical, hoping there's another resource to compare them to. And at this point FEA's probably not an option.

Since the ultimate tensile and compressive strenghts of the refractory are in the range of 300 to 550psi, I'm assuming that the refractory offers no additional strength to the steel itself.

 

[JohnGP]

It's deflection that is going to be the killer for the refractory.

 

[robyengIT]

I see two ridiculous things in your statements :
1 - You designed something cumbersome without keeping in mind handling and lifting in your workshop ?? What about vibrations and shocks during transport ?? Whose responsibility is it ??

2 - on site You say that is their responsibility handling and lifting : they can't go to the moon with the bicycle You gave them !! If You deliver the stack horizontal how can they lift it in vertical position ??? You should inform them how to do and give them the lifting points !!

 

[jimmyhutmacher]

Thanks for your insights roby. There are obviously many details you don't have and i'm not going to get into them. To reiterate my question: i'm looking for resources that address stresses in a shell due to slings in a basket configuration.

 

[JohnGP]

If your responsibility for stack integrity ends once the unit is on transport, then the answer is clear - use more cranes and slings. It's a simple lift if carefully controlled, and that way you avoid having to worry about the effect of any deflection on the lining. I'm surprised though that the customer did not request an installation procedure, even if the onsite contractor was responsible for developing one.

 

[MikeHalloran]

I was going to suggest jamming a timber diaphragm inside at the sling locations, but then I guessed that it would crack the refractory if it were too tight a fit. So, better to reinforce the outside.

A simple search found a bunch of YouTube videos about erecting stacks.
All of them seemed to have an external reinforcing ring of some sort at the lifting points.

One of the larger ones had a polygonal ring around it just above the midpoint with two trunnions extending radially out. It was lifted and rotated from horizontal to vertical with a single spreader that was a little longer than the stack diameter, and a single rope from each end of the spreader to each of the trunnions. I don't know whether the trunnions were permanent or not.

All of the stacks shown lying on the ground or on a truck were supported by U-shaped saddles, clearly custom bits, and not allowed to just lie on the ground or the truck bed.

Does your stack have _any_ external reinforcement, e.g. for attaching guy wires, or for tying it down to a truck bed without distortion?






Mike Halloran
Pembroke Pines, FL, USA

 

[DSB123]

I think that as you lift this the refractory inside will definitely be damaged and need repair. As Roby says when you design/manufacture an item that is not the end of it. The item must be such that it can be safely transported and installed in its final position. It is your responsibility to ensure the design is fit for purpose from manufacture through to installation.

 

[IFRs]

You said "As far as analyzing the stack as a simple beam in bending, the stresses are minimal, so no concerns there." I would analyze the stack as a simple beam for deflection and use this to decide how many slings and shipping supports to use. Note: flat beds are not "flat" and they will deflect under load - both your load and dynamic loads from bumps in the road.