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-   -   Floating of a 1.6mtr x 19mm x 60 mtr steel tube (http://www.physicsforums.com/showthread.php?t=561820)

sbgce Dec20-11 09:48 PM

Floating of a 1.6mtr x 19mm x 60 mtr steel tube
 
Appreciate any comments regarding the following:-(I am not an Engineer)
We intend to launch (Mekong River) the subject steel tube (12mtr pipe welded together using the collar sleeve method) Flanges / gasket will be fitted at both ends of the tube. The flanges will have a 1" valve at the top and a 2" valve at the bottom. The plan is to float the tube (using two tugs) along side a barge then have two cranes(42 ton capacity each) to tie onto the pipe say 10 mtr from each end. once this is completed both 2" lower valves will be opened and then the 1" upper valve will be opened to control the flooding speed. final water depth when pipe is sunk (but still boyant is 6mtr - The river flow volocity will be approx 2mtr/min - I was considering welding some kind of baffle arrangment inside the tube (for stability) but as it has been coated I dont want to damage this . I am concerned that I may not get even (level) submerging when opening the valves. Also once the 1" valve is under water and the tube slowing submerging down to the 6mtr level - what effect will this have on the 1" bleed valve (back pressure??) At the 6mtr level the barge (by using winches) will slowly move the tube into position to connect (by Flanges) to a stationary pipe comming from the river bank.
Any comments would really be appreciated.

Thanks

nvn Dec21-11 09:05 AM

sbgce: By the way, the unit symbol for meter is m. E.g., 1.6 m, not 1.6 mtr. Also, always leave a space between a numeric value and its following unit symbol. E.g., 1.6 m, not 1.6m.

I think the pipe flooding rate will slightly decrease after the upper valve submerges (but this slight change in rate might not even be noticeable). And the flooding rate will continue at this same slightly slower rate thereafter, regardless of the pipe depth.

Therefore, I would say, let the upper valves submerge just below the water surface, and hold the pipe at that location with the cranes, and wait, until the pipe essentially finishes flooding. Now, with the pipe completely flooded, there is no opportunity for tilting (instability). Therefore, you can now proceed to lower the pipe to the desired depth.

PS: I think you can perhaps expedite final flooding by keeping one of the two upper valves, say, 100 mm below the water surface, and keeping the other upper value 20 mm above the water surface. Then, when air stops flowing out of the second upper valve, you can submerge the second upper valve, and hold the pipe at that location, per paragraph 3, until air stops escaping.

Danger Dec25-11 07:09 AM

Re: Floating of a 1.6mtr x 19mm x 60 mtr steel tube
 
Welcome to PF, Sbgce.
I'm pretty sure that I'm missing something here, because the scenario doesn't make sense to me. Why not just leave the pipes open, walk them into position with the barge cranes, and slowly lower them into position? If you're going to flood them anyhow, why would you bother to water-proof them in the first place?


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