Water Storage Tank Fill over the top

[Moezam]

We have an over the top fill pipe with dia size of 1 m to a water storage tank without a internal drop pipe. The hight of the water drop is 17 m. Is there a requirement to increase the thickness of bottom plate considering there will be no drop pipe to the tank bottom? What consideration should be taken (free board splash, etc) ? What is a sufficient thickness for the bottom plate (6 mm?) Note the steel tank volume is 12,000 m3.

 

[LittleInch]

What's the depth of water in the tank at low level?

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[Moezam]

The water depth is 2 m at low level.

 

[HTURKAK]

I am not sure i understand the correctly.. as far as i understand , the water is spilling from the inlet pipe at 17 m elevation..
Is this potable water tank? the volume 12000 m3 implies cylindrical tank with dia 30m and ht 18 m etc..
Will you provide more details ( a sketch showing the sizes, inlet and outlet piping etc..)

 

[Moezam]

Thanks HTURKAK. You are correct. Its is a potable water cylindrical tank with Dia of 30 m. The inlet pipe tank centerline is 1.5m from tank top. The connection is flanged. The outlet is 1 m dia from tank bottom. There is no drop pipe for the inlet connection.

 

[MJCronin]

Very tough question .... Was this tank constructed IAW API-650 or AWWA codes ? ..... 6mm bottom plate thickness ???

Someone with a very old water tank may be able to answer this question. But, I cannot believe there is any analysis out there about this.

My guess is that as long as you maintain a 2m minimum depth on the tank while filling , you will be all right.

During your periodic tank inspection, ( 5 years?) I would request a more detailed ultrasonic inspection on the tank floor in the area of question.

I also have no problem with the welding of an erosion plate on the tank bottom if any wastage of the impact area is noted.

I also would not be surprised that a carbon steel tank has erosion in this area from years of AERATED water filling.

(BTW, The careful detailed engineering of inlet and outlet tank connections and impact plates is VERY IMPORTANT on ACID TANKS such as Sulfuric acid)

Give up more dimensional and other details about your storage tank construction

How old is the tank and what kind of internal coating do you have in the area in question ???

MJCronin
Sr. Process Engineer

 

[JStephen]

I think more often than not, there would not be any analysis done on this.
You could treat the incoming flow as a jet impinging on a flat plate, and find corresponding pressures on the bottom. If those exceed the allowable bearing, that would be the main issue to look at.

 

[LittleInch]

I'm sure i've seen before the velocity profile of a water jet impinging on a water surface, but can't find it now. But from memory at 2m deep the jet will hardly impact the tank bottom, but you need to be careful when first filling it.

YOu could reduce impact by either installing a dip pipe, or adding a fan or other device to reduce the jet effect.

But fee fall like this will generate waves and high humidity water vapour which will corrode the rest of your tank well before the floor start to corrode.

Actually just reread this and is the inlet pipe 1 metre diameter?? How full does this pipe run? If it's a full pie I think you'll hit the far wall first??

Give us a bit more info and we might get somewhere.

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