Storage tank with compartments

[zsa]

Hey all,

Got a design query that I need your input on. A client wants us to design an atmospheric storage tank (for methanol) with compartments. He provided us with a picture of what he wants, a copy of which I'm attaching for your reference.

My question is this- for the compartment 'walls' is it okay to just provide a wall built-up from plates that is welded to the inside of the shell (on either side) or do the compartment walls need to be braced (e.g by using angles)? Is there any 'standard' pertaining to such a design(I could not find one) or should this just be designed according to good engineering practices?

Thanks,

Z

 

[IFRs]

No standard that I am aware of, if one of the compartments can be full while adjacent ones are empty it will be an interesting design project. Don't forget seismei effects and the unusual restraint at the tank shell. If you can change it to circular divisions it gets easier.

 

[LittleInch]

This "design" is a nightmare.

No it is not "okay to just provide a wall built-up from plates that is welded to the inside of the shell (on either side) "

If this thing is any bigger than a couple of cubic metres, the forces on that dividing plate on the wall, floor and centre join are large and complex. Making it three rather than 4 compartments will also make it more complex to model and build.

I can only presume that the client is trying to be clever and thinks he can have three tanks for the price of one and a half.

If it was that easy there would be a standard for it. It isn't at all easy and there is no standard.

The only way would be to FEA this design with all its reinforcements, bracing, stress concentration, additional forces and moments on the shell and floor....

A standard API 650 tank is very highly stress utilized and cannot take any other significant loads. You will end up with a much thicker tank and floor, larger foundations, special fabrication, much higher design costs. In short an interesting exercise, but one I believe doomed to be more expensive than three smaller tanks.

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

 

[MJCronin]

I agree with LittleInch....

About 12 years ago, the consulting firm that I was working for went through a series of structural evaluations of several API-650 pie shaped tank designs that the client's young engineer came up with. Very similar to the sketch provided.

The client's newbie engineer claimed he was going to save lots of money with his new, revolutionary ideas... we told him that this idea had been evaluated many times before ...

At the client's direction, we evaluated several "internal pie shaped" and "concentric circle" designs.

Bottom line:

- As compared to individual tanks, these multi-compartment designs are ALWAYS MORE EXPENSIVE

- Unless they are VERY small, square and rectangular tanks are also much more expensive than simple API-650 designs. (This has been discussed repeatedly on eng-tips)

- Multi compartment API-650 tanks can be designed, fabricated and certified. They will have thicker shells and floors than similar single compartment tanks.

- Inspection of internal shells is nearly impossible.

Oh .... later on, the project was transferred from the client newbie to a senior member of the client's staff. (MBA) He complained bitterly about the money spent on evaluating different tank designs and refused to pay.

Same as it ever was ..... same as it ever was ....

MJCronin
Sr. Process Engineer

 

[IFRs]

Circular tanks within circular tanks are not unheard of, I've put internal floating roofs in them in the distant past but not in the last 30 years or so.

 

[LittleInch]

I remember looking at a circular tank inside a tank one time and the forces and thickness you needed to go to when the outer ring is full and the inner one empty was huge. Basically think vacuum collapse and you're part way there.

Also maybe it's just the view angle but it looks like its been built as a slight funnel shape, i.e. sloping walls?

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

 

[zsa]

Thanks for the input guys. I just checked with my supervisor and he told me the client wants to store methanol in all three but he wants to have the compartments based on a bad experience in the past where a low grade/bad batch was decanted into the tank which already had some product and the entire batch went to waste. They want to use compartments to empty the tankers in the different compartments available and then get some tests done to ensure that the product is of reasonable quality.


This is what I just found out; I did not attend the meeting with the client.

LI: the sloping walls may be an inadvertent visual effect. That is not a requirement

 

[LittleInch]

Seems like a sledgehammer to crack a nut.

Sure an off spec tank is a right royal PITA, but does it really justify all this grief - but then I guess the client didn't know or think about the issues.

Just build a tank for immeadiate offload or test the stuff before you offload....

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

 

[IFRs]

I also don't see the value. Build three small tanks. You have to run separate piping anyway, if the three are in a line the piping will be quick and clean. Also, if you are required to use internal floating roofs the three small tanks will be far easier and cheaper.

 

[JStephen]

Agree with the others above. It'll be cheaper to build three small tanks.
Tanks make very efficient use of the shell when they are round, and that shell is entirely in tension. Using non-round surfaces requires large stiffeners, much extra analysis, extra detailing, extra welding. And the final product won't meet any particular standard, either.