Pipe used as a spreader bar 3

[tnteng]

Can anyone help - I am designing a spreader bar and will be using pipe as the spreader bar. The padeyes on the top and bottom of the spreader bar will be made of one piece of flat bar that slides through the pipe and is welded to the walls of the pipe. I have checked the buckling in the pipe due to the compressive loads of the padeyes and I have checked the stresses in the padeyes themselves as well as the welds that hold the padeye plate in the pipe. My only concern is what local stresses the pipe will see due to the loads that the padyeye plate imparts to the pipe (bearing or buckling) and how those would be checked.

Any suggestions?

Thanks,

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[Cockroach]

Essentially you are taking collapse of a slender column or rod. Analyse with Euler Buckling for Columns. I would also check the structure itself for stability. This would be the typical truss type analysis, depending on your exact geometry which is a bit nebulus right now.

I would also look at material strengths and computation of maximum allowable loading thereof. It sounds like you have already done this, but specifying a maximum allowable load would be the proper thing to do.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[tnteng]

Thanks Cockroach,

I have already analyzed the pipe for buckling using the AISC ASD formulas. I am now only concerned with any local buckling or bearing that the pipe would see in the vicinity of the padeye/plate.

Thanks again,

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[micjk]

why not padeyes at the end of the pipe dual chokers to the lifting device hook. this will eliminate any chance of buckle provided it's not grossly overloaded.

 

[desertfox]

Hi tnteng

You need to check bearing and tearing of the padeyes where you put the bolts or shackles through the padeye holes.
Also I notice you have checked for buckling but in terms of the crippling load I presume. If the spreader bar is in bending which I thought it would be then you need to check deflection of the bar this may also put extra stresses in the padeye welds.Can you give material and sizes of pipe and padeyes so we may help you further.

regards desertfox

 

[tnteng]

Thanks Desertfox,

The pipe is 12" sch 40 or 80 (not decided yet). The padeye plate is 2" x 7" A-36 flat bar or plate. The padeye plate is oriented at a 45 deg angle relative to the spreader bar. As I described before, the padeye plate is slid through slots that will be cut into the 12" pipe and welded up. The slings at the top of the spreader bar are sized to result in a 45 deg angle up to the master link. The padeyes under the spreader bar are loaded with a vertical downward load. As I see it there will be virtually no vertical load on the welds except for the load due to the weight of the spreader bar.

I have checked the tearout and bearing at the location of the shackle pin on the top padeye. On the bottom padeye I checked tearout and bearing as well as the combined bending and axial stress that is seen at the section where the weld will be.

For the pipe itself, I checked the stability against buckling due to the combined effects of the dead weight of the pipe and the compressive load due to the lift using AISC Spec formulas H1-1, and H1-2.

Should I be concerned about the local buckling or bearing near the welds and how would the welds need to be sized?

Thanks for the support.

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[desertfox]

Hi tnteng

Okay I see what your doing the padeye is one piece from top to bottom at each end and so the tube is just acting like a spacer between two padeyes.
Well the welds should be sized according to American Welding Society which specifies the following working stresses for welds as follows:-
1/ tensile= 13000lb/in^2

2/ compressive= 18000lb/in^2

3/ shear = 11300lb/in^2

I am assuming your using fillet welds for your spreader in which case the welds would be considered to fail in shear ie use 11300lb/in^2.
To calculate the weld area you multiply the length of the weld by the throat dimension of the weld, assuming the weld as equal legs ie- say .125"

throat dim = sin45 degrees * .125"

so for a 1" long fillet weld with a .125"leg length the weld area = 0.088388"

The above figure for shear stress is based welds running parallel to the loading direction and welds that run perpendicular per unit length to the loading tend to be stronger so to err on the safe side the same stress figure is used.
Finally i am based in the UK so the figures I have quoted for stress come from a very old reference book so you might wish to check they are still okay to use.
The size of fillet weld leg lengths are usually governed by the thinnest of the two materials to be welded ie:- if your tube was .125" thick and a plate was .25" thick then your maximum fillet leg length would be .125".

Hope this helps

regards desertfox

 

[tnteng]

Desertfox,

Thanks again. You did not comment on any local buckling that might be present near the padeye welds. Should this be checked with some assumption made with regard to the local bending or buckling in the pipe?

Thanks,

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[desertfox]

Hi tnteng

What sort of weight are you going to lift with this spreader? I was thinking once you have stressed your welds around the end of the padeyes with a suitable safety factor I didn't see a problem, however I think you would have to refer to a finite element stress analysis (beyond my field) to find out any local stresses and exactly what was happening in those regions. Two further comments one is how frequently is this spreader going to be used as fatigue of the welds may have to be considered and finally when you calculated the buckling load for the tube did you also take into account the offset ie;- the bending moment caused by the compressive load not passing central through the tube centerline.

regards desertfox

 

[unclesyd]

If I’m reading you correctly you are making a spreader bean not a bar. It is my understanding that when you slit the pipe that ends the bar aspect as far as the Regulators are concerned. If hang the lifting points/pad eyes from the pipe you are in whole new set of design conditions.

You might want to look at this site as they have some information on spreader bars.

http://www.tandemlock.com/index.asp

 

[tnteng]

Thanks to all who responded.

desertfox,

The spreader bar is rated to lift 65,000# and is designed wih a safety factor of 4.0. Fatigue is not an issue for this spreader bar. I had considered the offset buckling load. I was originally considering making the padeye plate an "angle" shape with the vertex at the centerline of the pipe. That would result in the compressive load passing through the centerline of the pipe. I had then changed the design to a straight flat bar for simplicity. I may need to go back to the angle shape.

Thanks,

Tony Billeaud
Mechanical Engineer
Franks Casing Crew

 

[desertfox]

Hi tnteng

The site that "unclesyd" referenced in his post has a 6500lb spreader beam and the design is similar to yours with a length of 12 foot betweeen padeye holes. Notice though the offset for the compressive load is limited to 5.5". I think the deflection due to the offset load would be
the driving force as to whether or not you revert to your original design of padeye.


regards desertfox