Bearing Requirement for Large Pressure Vessel Davit 1

[sisaacs]

I've been tasked with designing a top davit for a filter, and the design weight of the top blind flange is 6,750 lb. I've designed a few davits in my career using Procedure 6-1 in the Pressure Vessel Design Manual (Moss) but none with such a large load. The davits I have designed have all been the basic "sleeve a pipe into a larger pipe and add a ton of grease so it'll rotate easily" type, but my customer (vessel fabrication shop) is asking if we should go to a roller bearing or other bearing type for a davit loaded this heavily. I'm hoping someone with relevant experience can answer two questions:

1. Is a bearing required here? Where's the load limit at which a bearing starts to make sense?
2. I'm an oil & gas structural guy; I don't really know how to go about specifying a bearing for this application (or for any application, really). What kind of bearing would make sense? I know I'm likely going to need to loop in a mechanical engineer on this, but I'd like to have some ideas.

The davit will have a 5-ton manual chain hoist for lifting the top flange.

 

[SnTMan]

sisaacs, i have supplied a number of davits as part of shell & tube HX designs. Most were nothing special and were usually detailed to a company standard, so no real design needed. I have had a couple where it was obvious something a little more special was needed. I have detailed out oil holes a number if times. Don't recall ever fitting a grease zerk, but it could be done.

1) Don't know of any stated limits. I'd think if a reasonably close fit between davit arm and sleeve is made then perhaps a plain (bronze, oilite, etc) thrust bearing would be beneficial. Plain sleeve bearings could be furnished as well. A roller thrust bearing could be furnished, but I'd worry a little about weather.

2) Talk to a bearing apps engineer.

I have always thought it a little odd that no provision is made for turning the davit. I have thought of a couple of lugs to put a pinch bar thru, or for larger davits, to attach a chian fall to.

Best of luck,

Mike

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

 

[sisaacs]

SnTMan, thanks for your advice, it's very helpful. I've often wondered about the lack of provision for turning the davit as well; I would guess that if a couple of operators can't move it by hand they just loop a sling around the davit arm and use a chain fall, probably cursing engineers the whole time

 

[r6155]

1) Diameter of the pressure vessel?
2) As information See PIP Standard VEFV1119 Column Davit up to 2000 lbs load
3) I consider 100% powered davit crane is required.

Regards

 

[sisaacs]

r6155:

1) 54" OD, 3.25" wall thickness
2) I am aware of the PIP standard; I am here to discuss ways in which a davit supporting nearly 7,000 lb would differ from one supporting up to 2,000 lb.
3) It is definitely not required, but I agree that a manual hoist is not the most user-friendly choice. I will point out to my customer the amount of chain the operators will need to pull through the 5-ton manual chain hoist they've selected (roughly 300 feet) and they can decide if they want to use a powered hoist instead. It's possible that the end user's plan is to procure the unit with a manual hoist and then swap it out for a powered hoist right away using opex budget.

 

[jtseng123]

sisaacs,
I just finished one project with several vessels fabricated in China. They did design davit sleeve with bearings at each end for rotation, also furnished a chain hoist at the davit arm, exactly what you are talking about. I can not give you the details, but the bearing is Chinese standard GB/T 297-2-15, material 32314, GB/T 288-2013,material 22220. Or you can contact Morimatsu (Jaingsu) Heavy Industry Co.