API 650 Hydrotest Water Filling Rate 2

[Regi1989]

Hello guys,

I have a concern with regards to the required volumetric flow rate for filling a tank to be hydrotested. Is there such thing? I was thinking i need this data for sizing the required pipes and pumps to be used by using Q=AV. Though API 650 gave Water Filling Rate at Section 7.3.6.5, these aren't volumetric flow rate right? We may consider these as velocity, isn't it?

Any idea for the pipe and pump sizing? All comments are highly appreciated. Thanks in advance.

Cheers!

 

[LittleInch]

You've answered your own question. 7.3.6.5 give you a filling rate expressed in height. You simply need to convert this to volume based on the square area of your tank. The filling rate can be converted to a height (volume) per minute or second. Don't exceed this flowrate ( gpm or l/sec or m3/hr ).

Your sizing of the pumps is based on flow and the pressure / head you need to pump from wherever your water supply is to the tank plus the max height of the tank.

" these aren't volumetric flow rate right?" Wrong - They are volumetric flows, but do vary depending on the height of the water in the tank

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

 

[zdas04]

There are real issues around rate of pressurization, but not fill rate. If you are filling a vented tank you can fill it as fast as you are able to. Once you shut off the vents and begin pressurizing the tank you need to slow it way down because the test pressures are so low that it is very easy to overshoot your test pressure and break something.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Just to be clear - 7.3.6.5 states filling rates are to be in line with those on the data sheet or as specififed in the table if settlement tests are being carried out.

May not apply here, but if you've got a floating roof (internal or external), fill rate before the roof lifts off is often very low and then the roof normally has a maximum lift speed.

Also "Any idea for the pipe and pump sizing?", Well if you give us the size of the tank and the nozzle sizes and how far away the water is from the tank then we might get somewhere....

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

 

[Regi1989]

Thanks zdas04 and LittleInch.

For example, the tank has a dimension of 21mIDx22mH. Bottom course thickness is 14mm, thus maximum filling rate is 460mm/hr (below top course) and 300mm/hr (top course). Assuming maximum design level is same as tank height (which is really not, how to compute for this? Client didn't advice though) total required time to fill up the entire tank is 45.72hrs. Including time allowances of approximately 6mins per reading for settlement readings, 24hrs holding period at fully filled tank, and assuming emptying time is same as filling time, the total estimated hydrotest time for the tank is 115.94hrs. Are my assumptions correct or is there a better way?

For the volume flow rate, computed area of the tank is 16.4sqm while velocity is at 0.46m/hr; hence, volume flow rate is 7.544cbm/hr. Does it mean i should not exceed this flow rate during filling/emptying the tank? Should i also use this flow rate for the pump sizing?

With regards to the pipe sizing for hydrotest, how? Should i just follow any nozzle size among the roof nozzle? There are 4" level switch, 6" gauge hatch, 10" vent, 24" manhole, and 1-1/2" stilling wells.

Thanks a lot for all your inputs guys.

 

[LittleInch]

Err. maybe its my maths but a 21m diam tank has a surface area of 346 m2 not 16.4. Thus for a fill of 0.46m/hr = 160 m3/hr, 0.3m = 105m3/hr

Otherwise your assumptions are correct. I'm not sure about discharge rate, but certainly allow for the same as filling.

Use this flow rate as a maximum flow rate to fill and empty your tank for the bottom courses for hydrotest so size your pump accordingly. Probably a 6" pipe would be OK, but 8" would be better.

Definetly don't use the vent - are you mad? - so use the manhole, but I don't understand why you cant use one of the nozzles which is intended to be used when the tank is in service??

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

 

[Regi1989]

Hi LittleInch,

Yes you're correct on the area of 346sqm. I don't know where i got the 16.4

Anyway, I now understand the volumetric flow rate issue, but why choose 6" or 8"? Is it because we should limit the water velocity up to 2m/s?

No advice from the client with regards to the service nozzle (if there is). If manhole will do, then its fine.

Thanks a lot.

 

[LittleInch]

I couldn't work it out either....

6" or 8" is just a good size for that flow of pipe where yes, velocities are reasonable, but pipe isn't too big. You could probably get away with a 4" if you want - there's no real limit on velocity in this instance, but 6" or 8" has lower pressure losses.

If you're having to put in temporary hoses up to the roof(?) then 2 x 4" would be similar.

If you can't used the service nozzles I'm not sure how you're going to drain it unless you dangle a submersible pump from the roof.

You don't seem to know a lot about this tank, which worries me a little. What is your role in this hydrotest?

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

 

[Regi1989]

Hi LittleInch,

There is a drain nozzle on the shell (i believe).

I am doing a preliminary design and estimate cost for the required hydrotest.

Are there any items that i missed? Thanks a lot for your help LittleInch, really appreciate it.

 

[LittleInch]

Don't think so.

It's pretty basic and normally you use the tanks own gauging system,

Depends on what type of tank it is and whether you allow for it, but often the owner wants the tank "strapped", i.e. accurately measure the water in and the equate that with the level readings.

Once you've emptied it often you need to clean it and enter the tank to sweep out all the water.

Normally there are fill and sometimes separate discharge nozzles on the tank or a manhole which you can adapt a flange to have your fill nozzle on the ground, which is much easier than trying to fill from the top.

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

 

[Duwe6]

If filling thru a shell nozzle [best IMHO] don't forget to use a properly rated valve. And have a blind cover for if that valve leaks/weeps when you switch to the roof to finish filling the last couple of inches. NEVER trust brand-new tank instrumentation for the initial fill, even if its calibrated for water. Sit on the roof and watch the level, unless there is a trustworthy overflow nozz.