Water Tank Design

Hi,

In your place, I'd start with a simple reconignsing to know how much space do you have available to check the maximum diameter you can have.

Then, put in the paper or in excell the equation calculating the vessel, and then do some changes to obtain the maximum volume with the minimum material in the walls. It's gonna be funny, but I won't do it for you, I don't know how much space you have. But keep the heigh as low as possible, because this is the dimension that will increase the pressure inside, of course.

After arriving to an initial size, check out the ASME standard for pressure vessels. There you will find all the wall dimensioning you'll need, and I'm affraid no one will build it if you don't use the standard, it's safe for you and for your customer. It's a kind of too much conservative, but works.

After having the vessel design ready, go consulting a good civil engineer, to make the foundations for you. Don't forget that you'll be placing 500 ton in the terrain.

If the storage tank designed to be atmospheric, it shall be in accordance with WWA (Water Works Associatioin) or API 650 (or API 620) (API : American Petroleum Institute). The atmosheric water storage tank (not considered to be a pressurized vessel) can't be designed in accordance with ASME Code for pressure vessels.

Relation between tank diameter & height depends mainly on the height of tank and the pressure due to water column at lower point, taking into consideration the soil bearing load (Soil Data Report is required) to withstand the total tank load.

Well, this is an important information. I think this is the basic rule in USA, so, if you're there, follow it! It's mandatory, and that's all.

I have successfully used ASME before, for low pressure reservoirs, that's why I mentioned it.

By the way, the API 620 takes care of tanks with internal pressure equal or less that 15 psig. If your tank is deep enough to increase pressure above it, watch out.

With it being just a water storage tank I would first find a Diameter that both meets; Area available and Ease of ordering material to build. Then with that you can determine your height.

Thanks for your help. The space is not a problem.

I mean we can design several water tanks with the same capacity and different combinations of diameter and height, which are all conform with API 650 but one of them is minimum cost design.

Endeed the soil bearing is a key factor for water tank height choice.

I was curious, and tryied to establish a mathematical solution for your problem.

I expressed total volume and area in function of radius and heigh. Then, I inserted it in excell in the form of an interactive equation to find a solution. Of course, it diverged. Then, I looked for the algebric prove for it (calculating the first and second derivates), and found that, first, volume equation has an inflection point just at the origin. Second, the area equation doesn't even, because of the linear component in its formula. Trying to solve the problem, the solution is not a real number.

The volume grows with the square of the radius. The total area too, in a different way. My advice, if valid, is to use diameter equal to heigh, check calculation and material thickness required, check suppliers, look for the cheaper material available, and then try to reduce heigh to fit a light and cheap material that can handle the job. The material price will dictate your reservoir shape, at last. Try some alternatives and keep the cheaper.

Thanks for the advice. It's a good approch I'll use it!

When designing a tank, you will usually have a few constraints, like you say manufactures stock is a typical one, but other common considerations when designing size by volume are:

Ground bearing capacity which is affected by the area of the base of the tank or that of the foundation you can set below.

Surronding space restriction in both diameter and height; in the form of existing structures, overhead obstruction and access.

If the tank is to be below grade; how deep can you excavate due to equipment, safety or bedrock? Will the water table be an issue (seen plenty of tanks pop up through the ground like a submarine due to not enough ballast and high water table)?

If the tank is large and prefabricated, can you transport it and maneuver it on site, does equipment capacity limit size (Lift Radii, Lift Capacity etc)?

Limitations from material mechanical properties.

Cost implications of any of the above.

Your asked for "criterion." The criteria are: (1) footprint and tank base elevation available in your application; (2) head increases with tank height; (3) tank volume increases disproportionately greater with incremental increase in tank diameter than with the same incremental increase in height. So, if footprint space is limited, you're stuck with more need of air space (and rights). If air space/rights is limited, tank radius must increase--but with possible sacrifice of head pressure. So determining the envelope must precede (and govern) how criteria are applied. From there, it's straightforward.

Rectangular Tanks(in feet) : L x W x H x 6.22 = Gallons

Round Tank(in feet) : D sq. x L x 6.22 = Gallons

Convert metric to imperial and play along with the length, width & height as per your requirement.

Perhaps This Would Be Of Assistance To Your Efforts

http://ferrocement.com/tankBook/indici.en.html

Happy Tank Building !

Cheers

Bondjamesbond@rock.com