Bulkheads for external floating roof

[crvhybrid]

Hi
Any criteria/guidelines for number of radial bulkheads in the floating roof? We have a old floating roof that does not have bulkheads in all the inner rings (only the outermost ring) and have been having leaks in the rings. we intend to install radial bulkheads to solve this. Intention is to increase stiffness so that the welds don't crack over time due to flexure. Thanks

 

[HTURKAK]

What is the number of bulkheads at the outermost ring and how many inner rings are there ? Pls post some details ( at least a descriptive sketches showing the dia, no. of compartments at the outermost ring , and other rings ) to get better responds.

 

[crvhybrid]

What is the number of bulkheads at the outermost ring and how many inner rings are there ? Pls post some details ( at least a descriptive sketches showing the dia, no. of compartments at the outermost ring , and other rings ) to get better responds.

Thank you. It is a 60m dia.tank. It has 6 rings of approx. 5.9m each and 3m for the centre ring. Tank with 19 bulkheads in the outermost (6th ring) and none for the rest. What would be the basis for adding bulkheads for the other rings?

 

[JStephen]

For a pontoon-type roof, API has a requirement that the roof float when any two adjacent pontoons and the center deck are compromised. Using fewer pontoons gives you a larger flooded area under this assumption, may require taller pontoons, additional strength, etc. But this reasoning wouldn't really be applicable to your case. The number of bulkheads may also be tied to the number of outer legs.
So I would say just a matter of judgment in your case.
One item, you are adding weight to the roof, so you are making a change in stress distribution and floating characteristics, although somewhat minor.
One item, it's not immediately obvious to me that welding those bulkheads will accomplish what you want to accomplish.

 

[crvhybrid]

For a pontoon-type roof, API has a requirement that the roof float when any two adjacent pontoons and the center deck are compromised. Using fewer pontoons gives you a larger flooded area under this assumption, may require taller pontoons, additional strength, etc. But this reasoning wouldn't really be applicable to your case. The number of bulkheads may also be tied to the number of outer legs.
So I would say just a matter of judgment in your case.
One item, you are adding weight to the roof, so you are making a change in stress distribution and floating characteristics, although somewhat minor.
One item, it's not immediately obvious to me that welding those bulkheads will accomplish what you want to accomplish.

Thank you. Hopefully adding bulkheads adds to overall stiffness that reduces localised high stress and prevent weld crack. We also will check that the roof legs don't touch the bottom plate during operation.

 

[HTURKAK]

Thank you. It is a 60m dia.tank. It has 6 rings of approx. 5.9m each and 3m for the centre ring. Tank with 19 bulkheads in the outermost (6th ring) and none for the rest. What would be the basis for adding bulkheads for the other rings..

API 650 is silent for the no. of compartments and radial bulkheads . In your case , i will suggest the followings acc. to my experience and understanding,
- The no. of 19 bulkheads ( so 19 compartments ) is strange. I will expect an even figure and a reasonable radial angle . Pls count them again , could be 20 compartments,
- Assuming 20 bulkheads , the other no. of bulk heads ; second ring 16 bulkheads, third ring 12 , fourth ring 12 and fifth ring 4 .
Make sure that the radial bulkheads should be staggered to provide limited flexibility for the roof.

My opinion only..

 

[crvhybrid]

API 650 is silent for the no. of compartments and radial bulkheads . In your case , i will suggest the followings acc. to my experience and understanding,
- The no. of 19 bulkheads ( so 19 compartments ) is strange. I will expect an even figure and a reasonable radial angle . Pls count them again , could be 20 compartments,
- Assuming 20 bulkheads , the other no. of bulk heads ; second ring 16 bulkheads, third ring 12 , fourth ring 12 and fifth ring 4 .
Make sure that the radial bulkheads should be staggered to provide limited flexibility for the roof.

My opinion only

 

[crvhybrid]

Thank you. we have 20 bulkheads and 20 compartments in outermost. Yes, as you suggested, somewhat our proposal initially but the consultant reduce number of bulkheads to only 8 for the 2nd ring from their design check. But since there is very little text on this, guess it will do.
Regards

 

[LittleInch]

Do you have a drawing of the current roof or sketch?

I'm a bit confused by what you mean as bulkheads as opposed to pontoons. Is this a double skin deck?

Weld cracking should no be happening and it points more to poor quality welding for me.

Also you comment about roof legs is interesting - Is this what has been happening? Even in their retracted state?

Was the tank liquid level left below roof height for a long time sitting on its legs?

Simply adding bulkheads sound like a sticking plaster to me when you actually need a new roof.