Tank made from large diameter pipe

It would probably work. How long does it have to work for? Issues to consider: foundation, stability in wind or seismic loading, freezing potential, corrosion, entry manway, fill and empty nozzles, maintenance. If you are designing per a code like API 650, there are minimums loads and thicknesses. If this is for your back yard look for local codes. If it is for critical supply to a hospital that's a whole different ball game

Lots of people make very cheap steel tanks to no recognised code - shop built, designed to be transported on a standard 8 ft wide flatbed trailer.

I would be surprised if this could be done cheaper as they optimise the steel thickness by height or just have it all set up to not fail in service.

Unless you literally build it in situ remember you need to transport it, lift it, secure it in place.

I would also reinforce the top with either some angle or some cross braces.

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Not sure this will be a lower cost alternative. You may look API 650 App. A and App. J . The minimum shell thickness 3/16 in. For API 5 L the minimum wall thk. for 80 in dia. 0.562 in.

However, if you find a waste pipe with low price, this can be an alternative. You will add min .thk. bottom plate, top angle and some lifting lugs for transport and erection .For wall thk. 0.50 in and more , i do not think you will need temporary internal struts.

Thank you for the replies!
Answers and additional input.
Looking to make it last 15 years or so
The bottom plate for the tank will not need to carry the load of the water. The tank is intended to be anchored on a foundation constructed for the load, etc.
Freezing should not be an issue.
For corrosion protection, I will either powder coat it, or epoxy, or 3 part paint system.
The tank will require some nozzles for fill, drain, etc
No Manway required
The tank does not need to be build to API or any code. But I will need a structural engineer check the material thickness and anchor clips that will be added to the tank.
It is not a backyard project. It is for a water treatment system for industrial use.
The 8ft diameter limit is considering truck transportation across the US.
Optimize material thickness could be done, but I am looking at the possibility of minimizing cost, hence, I would think the cutting and welding of different thickness material will be higher in cost vs a 96" dia pipe.
For transportation and handling, lifting lugs will be added
Reinforcement can be done, but not preferred. The intentions will be to get a structural guy to check it and minimize additional bracing, etc

Additional input:
The goal of the tank is to produce a large quantity of identical tanks to treat wastewater. The tanks 8ft dia x 20ft high each will also contain a strainer block or strainer screen that supports a floating media. The water tank (mainly will contain wastewater, municipal type) and will be filled and drain about twice a day. (Fill, treatment, drain, every 12 hours, repeat).
The tank does not need to be build to any code, but since we are building about 20-30 tanks. I want to invest in getting a structural engineer check optimize the design, material thickness, anchor locations, bracing, etc.
So my intention is start the whole design using a standard product, in this case s 96" pipe. I want to believe this will be a low price start and adding a tank floor and nozzles will be the lowest cost possible to build these tanks.
Any other input or past experience using large pipes to build tanks will be appreciated!

Generally, pipe in that size will be rolled out of plate and welded. Very few service/pipe centers are going to stock 96" pipe.
And tanks in that size will be rolled out of plate and welded.
So there's no real advantage to using "pipe" unless you just happen to have it on hand at low cost.
For a manufactured product, consider specifying either API-650 Annex A or AWWA D100.

Using pipe to make a tank is commonly done for small-diameter pressure vessels, say 24" or less, where the pipe is readily available in a range of thicknesses. But not in 96" OD>