Shipping Spiders 2

[ConstantEffort]

Can anyone recommend a resource for the design of shipping spiders? Anyone have some rules of thumb? Or even a go by?

My vessel's D/t approaches 150.

A previous tower of similar size arrived out of round after road shipment, even with weld-in rings every 2' for the field-installed trays. Between our inspector and the AI, we take it that the vessel was round once upon a time.

 

[Duwe6]

Typically, the best way is to have the bracing tacked in to the vessel by the manufacturer. You REALLY do not weant to turn somebody else loose in a new vessel, because decent bracing needs to be tacken in, not just wedged in.

And I hope you refused delivery of that column. With trayrings spaced that often, somebody mishandled it after hydro. No reputable [or semi-reputable] AI would sign off a hydro & Code Stamping for a misshapen vessel. The Code allowable out-of-round and crookedness are fairly stringent.

 

[MJCronin]

Good information on shipping spiders here:

http://www.nsrl.ttu.edu/personnel/J.../publications/1991Cokendolpher_Latrodecta.pdf

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[gr2vessels]

Haha, the best of this week! Poisonous spiders for out of roundness, that's great! On the other hand, with very little support from shell, you (ConstantEffort) might need to consider two or three saddles for transport, only the spiders won't give much support.
Cheers,
gr2vessels

 

[ConstantEffort]

Thanks for the replies... honest or comedic.

This go around we have called for some spiders to be force fit and tacked in by the vessel fabricator. What these spiders look like is the problem. 2 lengths of small angle forming four 90deg pie pieces? 4 lengths of wide flange keeping the slices down to 45 degrees?

Figuring the compressive forces on these spiders is the problem I suppose. Is anyone willing to share some ideas on how to approach this?

 

[Duwe6]

I'd use 3 or 4 pieces of angle, and keep the length-size ratio at 50:1 or less. Wide-flange would be overkill for this short of a span.

 

[KLee777]

Get your hands on a copy of Dennis Moss' "Pressure Vessel Design Manual." There are whole chapters on transportation and erection of vessels, including shipping saddle designs, spiders, and lugs.

 

[ConstantEffort]

Get your hands on a copy of Dennis Moss' "Pressure Vessel Design Manual." There are whole chapters on transportation and erection of vessels, including shipping saddle designs, spiders, and lugs.

Thanks for the recommendation. I have the 4th edition through Knovel and read through chapter 10 "Transportation and Erection of Pressure Vessels." The only mention of temporary support for transportation loading says that a spider might be employed if a shipping saddle cannot be located near a naturally occurring stiffening element (page 633). Searching the entire book, that's the only mention of spider and appears to be the only relevant mention of "temporary."

Where in the book is spider design covered?

 

[KLee777]

Hmm, I don't have a copy as someone at my former place of employment swiped it (nice, huh?). Can't say what's in the current edition, but it used to be in there somewhere. I used it to design a shipping spider for a particularly challenging column once. But alas, I've since moved to the dark side and went to work for an owner/operator, and my design skills aren't nearly as sharp as they used to be.

Try Megyesy's "Pressure Vessel Handbook." That's another extremely useful reference for items such as this. Usually one of the older engineers will have a copy.