Davit arm design

[hakkik]

I need information about davit arm design. Davit shall carry a 30" CL900 blind(~1800kg weight.)used as bolted cover for a vertical vessel. Any help(Company spesific designs, design guides, etc.) will be useful.

Thanks

 

[bhushan76]

You can refer to chapter 6 of Pressure vessel design manual by Dennis Moss , Third edition.

 

[pennpiper]

Try here for some information on Davits and Cranes.

http://pipingdesigners.com/phpBB3/viewtopic.php?f=1&t=2230&p=4379&hilit=Davit#p4379

 

[rneill]

You might want to buy the PIP vessel construction details as these include detailed fabrication drawings for various davit arm assemblies.

http://www.pip.org

The document you would be interested in is "VEFV1100"

 

[11echo]

"IF" I understand where you’re coming from on this question, you don't need ANY design for a davit. You're requesting a "vessel" from a manufacture, just request a blind davit at a specified location and they "should" just plug in a davit that will do the job. "IF" you plug in your own design, they "may" do as you request, but probably take no responsibility for that davit so if something goes wrong with it, so your company will be on the line for that problem.

 

[bhushan76]

No 11echo, any reputed vessel fabricator will not deny to take the responsibility of ANY part of vessel fabricated by them. Vessel fabricator will check the design provided to them and if found okay they will take the responsibility.
If they find any gaps in design they come back to the purchaser highlighting the gaps.

 

[Crompto29]

bhushan76,

What if this isn't a reputed fabricator?

I would expect a good fabricator to take a look at external custom designed components like davit arms. But what about an average fabricator.

I have never come across a fabricator that checks the designs of complete externally designed, drawn and certified vessels.

For a large high quality fabricator I worked for, if a customer supplied professional fully certified fabrication drawings there was no need nor payment to carry out yet another design check. In one case this did result in a sub chamber imploding during testing, however the customer supplied a full set of checked, approved and 3rd party certified, drawings.

 

[jamesl]

It is stated in U-2 that "The Manufacturer of any vessel or part to be marked with the Code Symbol has the responsibility of complying with all of the applicable requirements of this Division and, through proper certification, of assuring that all work done by others also complies."

When I worked at fabricators, we always checked to make sure the vessels were properly designed and meet code requirements in fabrication details, even if the client is big and reputable. If you take other people's design for granted, you could be in big trouble.

BTW, PIP does not cover 900# manway davit.

 

[jte]

Not only do the PIP's not cover Cl-900 flanges, they do not cover 30" flanges of any rating.

I guess I would expect that a "good" fabricator would spot check customer supplied designs for non-code components such as the manway davit being discussed. They've seen plenty of designs, and if the given design is substantially weaker in some respect, that should raise a red flag. How many vessel fabricators run numbers on the adequacy of components like tray support rings? But I'd bet that if I had an 8' diameter column and specified a tray support ring that's 1/16" thick I'd get some communication back from the fabricator to make sure I was positive that's what I wanted.

I would expect the fabricator to do his U-2 duty of checking the Code compliance of the Code components of a provided design. I've had fabricators "adopt" my calc's by putting their title block or logo in addition to or instead of mine. That's fine - as long as they either satisfy themselves that my design is reasonable (not "exactly right") and are willing to trust me with their liability.

jt

 

[rneill]

Sorry, should have double checked the scope of Davit arms in PIP before giving that reference. I guess I haven't had to deal with the high pressure, large closures before and so never much noticed the limitation on size and class in PIP.

 

[hakkik]

Thank you all,

Moss's book and PIP document helped very much. I almost completed the design but some problems remain.

Davit support to flange(not blind) connection. Davit support can only welded to WN flange. WN flange is not a cylinderical surface thus using Moss's way a bit problematic. But i also think using FEA is an overkill. I have to find another way for calculating welded connection or make some (conservative)assumptions and wait the proof test. Any idea, comment or guidance on this matter?

sorry for the quality of the sketch

 

[vesselfab]

Move the lower plate down a few inches past the seam

the distance between the plates is not set in stone

 

[Justolejim]

A 30" Blind weighs about 3316 pounds u se 4 kips design The davit is made up of a 2" schedule 80 pipe bent into a 90 degree elbow 20" approx. leg in lifting direction and about 12" in short dimension - weld an inside triangular brace plate corner plate to the elbow. this is the davit arm allow for 5" approximate to the short side to fit into a 2-1/2" sch 40 sleeve that is welded to the tank wall by means of 2 side plates bracket about 3/8" thick- I like a brass sleeve in the 2-1/2' pipe to cut down on friction of the davit. In the long end of the davit drill a 5/8" hole through the entire 2" 90 that we have fabricated - and use an I bolt through the hole to attach to a 3/8" rood "I" welded to the flange. You can calculate the fixture as a counter leaver beam the stress in the shell from the support bracket by the moment induced through the length of the arm x the weight -
Have a good day