AIFR 1

[Vicky07]

Hi.
I came across an aluminium IFR that has 8 " floats. The floats are placed linearly and not around the rim sections.
[li]There are product stains on the deck panel around the emergency drains, legs and deck seams.[/li]
[li]The inlet flow rate is around 600 Kl/hr.[/li]
[li]No diffuser is instaled in the inlet nozzle.[/li]
[li]Some vapour smell is felt on the tank roof when the tank is in operation.[/li]

So my questions are:
1. How do the stains come over the deck panel? Is it because of the product spill or due to vapour condensation(or due to poor panel quality? The panel laid is of Al. 3000 series ).
2. If at all there is spillage of product over the IFR, in any case, does the inlet flow rate affect this? If so, how much should the inlet flow rate be maintained to avoid this oil spill over the IFR?
3. Why do we feel the smell of HC vapour over the tank roof? ( Is it due to the deck drains )
4. If some floats are to be placed around the periphery, will it make any change to this oil spill?

The buoyancy calculations are correct and it exceeds twice the dead load of the IFR.

Please share your thoughts.

Thanks
Vicky

 

[LittleInch]

A diagram and any pictures would help, but assume this is an Internal Floating Roof tank with some sort of roof structure.

I've never seen Kl/hr before - 600 m3/hr? what size pipe and velocity?

How is the roof monitored / operated when it gets to low level / sat on legs?

what is the jointing between the panels? Welded or rivets?

Excess velocity from the inlet if it catches the roof could lead to some spillage onto the roof as could excess flow when flowing in from a low level position.

An IFR will always leak some vapour and hence the internal space is normally Zone 0 ( permanent explosive atmosphere). Seals don't seal 100% and there are a number of roof penetrations and it takes only a small amount of vapour to be "smelt". The human nose is really very sensitive.

If the roof is really light and subject to some bending during operation as the drag from the seals makes itself known then locating floats closer to the rim might make a difference? Can't tell from this distance.




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

 

[Vicky07]

Thank you @LittleInch.

I've never seen Kl/hr before - 600 m3/hr? what size pipe and velocity?

Yes. It is 600 m3/hr. The inlet size is 12" and its velocity is around 2.3 m/s.

How is the roof monitored/operated when it gets to low level / sat on legs?

At low levels, the flow is restricted to 300 m3/hr.

what is the jointing between the panels? Welded or rivets?

The sheets are overlapped and connected with SDST screws.

 

[LittleInch]

Ok, 2.3 m/sec isn't too bad, but if it hits something could create a small pressure enough to drive some liquid through any holes or vents.

If the IFR sits on its legs then as the liquid comes up to point where it floats you can get little jets shooting up any penetrations in the shell before the roof lifts off and floats.

Connected with screws??

A drawing would help...

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

 

[IFRs]

The fact that there is 100% excess buoyancy does not mean it is properly distributed nor that the pontoons are not leaking. A better indication of buoyancy is the presence and locations of float lines on the pontoons, visible in an out-of-service inspection. Pontoons around the outer edge are normally used because the rim with seal(s) is heavier than the rest of the deck and there is no buoyancy on the other side ( where the tank is ). The self-drilling self-tapping sheet metal screws used to join the sheets provide a poor seal at the sheet overlap. These screw are also often SS410 which is a violation of API 650 (which you may or may not be using). Stains at the drains, legs and deck seams suggests multiple issues. Drains are in low points where the skin sags, deck seams are are at high points in this system and legs usually are taller than that. You may have had vapors in the inlet stream that bubble liquid onto the deck but I suspect that you simply have an old deck or one put together with poor details that was the least expensive thing available at the time and it simply performs badly due to a multitude of poor details possibly compounded by sloppy installation. If many of the deck seams leak and many of the drains leak and many of the legs leak you just have a poor example of a deck and while you can check off the box "IFR" on a form somewhere you can't expect to get the good performance of a higher quality deck. Self-drilling screws in particular points to the cheapest version ever on the market. You may see it get worse over time to the point that it is worthless. Given the safety and environmental hazard consider an out-of-service inspection and budget for a new, more expensive version.

 

[Vicky07]

Thank you @ IFR's
presence and locations of float lines on the pontoons, visible in an out-of-service inspection.
The float lines are normal. All the floats are 50% submerged. This is why the doubt occurs that how the product is oozing over the deck?(observation of stain marks)
Self-drilling screws in particular points to the cheapest version ever on the market.
Without using SDST screws, what are the other options of clamping the deck panels?