Floating Suction With Aluminum Internal Floating Roof

[lokesh rahul]

Dear all,
We are operating Aluminum IFR with floating suction. We found the floating suction getting stuck at a particular height. Hence are draining the product. In the process one side IFR is stuck with floating suction arm and the other side has come down. We have observed this from tank roof.
Request expertise advice on how the floating suction can be brought down along with floating roof once the product is drained.



Regards,
Lokesh

 

[mk3223]

Just wondering if IFR tilted is possibly because of leak of the pontoon, instead of the suction arm.
Suggest to involve the local Tank Contractor to investigate the incident.

 

[IFRs]

The floating suction may have come off the track sideways and become lodged betweenn pontoons or beams. The floating suction may have gone past a safe angle and come off the track and become stuck.

 

[LittleInch]

Got a drawing or sketch of this arrangement?

I've never heard of a floating suction with an IFR before because of the interaction between the two.

Why do it?

And please don't double post.

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[IFRs]

Floating suctions under aluminum IFR is not all that strange for me. I'm doing one now in fact for a 150 foot tank. A couple years ago I made two 24" for each of 3 tanks.

 

[LittleInch]

Fair enough. Do they usually come with wires to pull it down so that you can lower the roof?

Or just rubbing strips on the roof?

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Also: If you get a response it's polite to respond to it.

 

[JStephen]

You can run into issues if air or vapor is trapped in the floating suctions during initial fill.
Normally, in the design of a floating suction, you'd want substantial excess buoyancy to allow for variations in density, dimensions, thicknesses, product specific gravity, jet effects, etc. But if it's under an aluminum IFR, they may have very little dead load available to resist uplift. So it becomes kind of a balancing act.
There may be a cable or chain to limit maximum lift angle on the floating suction, and if that is broken, that could cause the problem.
If the tank has a light product, it might be possible to float the floating roof above the problem spot, then slowly pump water back into the floating suction and bring it down. Some calculations would be in order before trying this,
If the floating suction is filled with air and the outlet is above liquid level, it may float in that position.

 

[IFRs]

"Fair enough. Do they usually come with wires to pull it down so that you can lower the roof?"
In my experience - seldom but it can be done, has been a very long time since I've seen or made one.

"Or just rubbing strips on the roof?"
Usually a roller on the end of the swingpipe and a track on the underside of the IFR.

"You can run into issues if air or vapor is trapped in the floating suctions during initial fill."
I put a initial fill bleed hole in the top of the pipe at the end

"Normally, in the design of a floating suction, you'd want substantial excess buoyancy to allow for variations in density, dimensions, thicknesses, product specific gravity, jet effects, etc. But if it's under an aluminum IFR, they may have very little dead load available to resist uplift. So it becomes kind of a balancing act."
Quite correct, I've used 125 to 250 pounds net up for years.

"There may be a cable or chain to limit maximum lift angle on the floating suction, and if that is broken, that could cause the problem."
Correct, or if the painters disconnected it (yep that happens!)

"If the tank has a light product, it might be possible to float the floating roof above the problem spot, then slowly pump water back into the floating suction and bring it down. Some calculations would be in order before trying this,"
Never tired that but it might work. If the chain is broken or missing, this will be a disaster if the swingpipe goes past vertical, in which case the IFR doomed. Last time I was involved in a disconnected chain, we held the IFR up using chains and lowered the liquid level until the swingpipe angle was good, then lowered the IFR down onto it, emptied the tank, connected the hold-down chain and went on our merry way.

"If the floating suction is filled with air and the outlet is above liquid level, it may float in that position."
Not sure what response to generate for this...

 

[HTURKAK]

In addition to the above comments, i would like to add ;

- API 650 Item 5.8.11.1;

... Floating suction lines shall be provided when specified on the Data Sheet, Table 4. Floating suction lines
using rigid articulated (having one or more swing joints) pipe shall be designed to travel in a vertical plane and prevent
damage to the floating roof and the suction line through its design range of travel. These lines shall be designed so
that the vertical plane is as close as possible to, and in no case greater than 10 degrees off, a radial line from the tank
centerline to the nozzle. Adjustments shall be made to clear internal structures.

- The max. operation level should be limited such that the angle from the horizontal would be around 50 degrees. This can be provided with using weight chain. One end of the chain is connected to float and some portion lays down on the tank base. AFAIK , damage to the IFR is due to allowing the arm to get too steep.


He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[LittleInch]

lokesh,

First thing you need to do is refloat the deck and level the deck before you damage it and the tank more than you have already.

Then see IFRs comment about holding the roof up from the top side with chains, ropes or similar in a flat position before it get tot he point where it is stuck, lower the level a few metres more so that the arm drops below 45 to 50 degrees then lower the roof slowly back down and continue to drain it out until you can get people inside the tank to either re attach the chains or replace the floating arm swivel or both.

Let us know how you get on.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.