Question regarding the basics of liquid tank design. ('SMALL' 8m tall, 3m dia) 2

[human909]

Okay. I don't won't to be one of those posters asking extremely basic questions. Buuuuuut, I will do so and suffer any flaming I deserve.

I have a upcoming job with small liquid tanks (8m high, 3m dia). It isn't something I've ever done before but I'm sure I can work it out without asking the community. But I'd figure it can't hurt asking. I deal with all sort of stuff and have extensive large silo design experience which are arguable more complicated.

Anyway from a cursory inspection it seems that custom once off fabricated liquid tanks are likely more driven by ease of fabrication constraints rather than hydrostatic loads. Of course there is wind and seismic to take into account but I suspect the answer will as much come down to robustness and fabrication requirements rather than structural strength.

Am I missing anything here?

 

[LittleInch]

You need to know liquid SG and design pressure. If these are "atmospheric" tanks then most of them at that size are not designed to any specific code only "vendor design". I.e. they've built a whole load of them and none of them have collapsed. Search on this forum (button on the top left) for tank design codes and you'll see what I mean. There are a few generic design codes which are not onerous for this size of tank.

Build to some sort of a code or standard and the costs go up.

3m x 8m is probably just within the scope of a "shop built" tank, transported and then lifted in position. Again a whole heap cheaper than building it in situ, once you go bigger diameter than you can road transport - prob max 3.5m maybe 4m at a push.

Internal coating required / a good idea? If you have water and keep it at a constant level then you get corrosion in the splash zone. Also the floors tend to corrode pretty fast.

And a few spare nozzles at top and bottom and on the roof. Always a good plan.

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

 

[human909]

Thanks LittleInch for replying. I appreciate it and I'm aware it is a pretty basic question. You've given me the essentials and enough talking points. I'll chase down relevant codes myself of course.

If these are "atmospheric" tanks then most of them at that size are not designed to any specific code only "vendor design". I.e. they've built a whole load of them and none of them have collapsed.

Yeah I figure this would be the case. The client is a mechanical design and fabrication firm and would have FAR MORE experience in these items than me. They have probably supplied many that haven't been 'engineered'. However their customer likely requires a suitable engineering certification and I've become their go to engineer on many of the projects as they don't have anybody suitably qualified internally. So it likely is just a certification with very limited design for the liquid tanks.

3m x 8m is probably just within the scope of a "shop built" tank, transported and then lifted in position. Again a whole heap cheaper than building it in situ, once you go bigger diameter than you can road transport - prob max 3.5m maybe 4m at a push.

Yes that would be the plan. I've done similar with silos.

Internal coating required / a good idea?

At a guess it is likely stainless steel, but I'll have to confirm with the client.

And a few spare nozzles at top and bottom and on the roof. Always a good plan.

Good tip. I this case the client has this handled. I've seen a 3D model of their planned design, but I still need to chat to them to clarify the scope of the work they want from me.

 

[LittleInch]

A fairly standard design is a " 30 x 9"

30ft long, 9 ft diam, but usually mounted horizontally.

Why do they want tall skinny tanks? Foundations are much harder.

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

 

[JStephen]

For a small vertical tank, the actual shell design is typically just based on minimum thickness per the design codes.
In the US, these would typically be built to API-650 Annex J or UL-142 if storing flammable products. NFPA 30 or IFC (fire codes) may regulate construction as well. Non-code tanks would still fall under ASCE 7/ IBC requirements in most places in the US. I don't know what standards are used elsewhere.
Anchorage is for wind, seismic, pressure, or overpressure due to fire exposure.
Tanks of those dimensions are not uncommon, due to site constraints and ease of transportation, assuming shop-built tanks.

 

[human909]

Why do they want tall skinny tanks? Foundations are much harder.

That was my first thought, that they are an inefficient shape for storing liquid. However I believe you half answered the question that the are being road transported. The other reason is likely to minimise the bunded area required which is likely an EPA requirement.

For a small vertical tank, the actual shell design is typically just based on minimum thickness per the design codes.

The client currently has them at 6mm thick in their preliminary design which seems a bit crazy thick. The may want me to help them economise, or maybe they are happy with their standard design...

They are for storying and mixing "polymer" exact substance unknown at this stage.

 

[JStephen]

In API-650 Annex J for shop-fabricated tanks, minimum shell is 0.25" over 10.5' diameter, 0.1875" under that, and I believe 0.1875" for stainless in either diameter. So 6 mm is not unreasonable. That's based more on handling than on actual operational loading.
UL-142 allows somewhat thinner tanks.
When you attach anchor bolt chairs or platform clips to the tank, super-thin shells become a problem.
I would say first thing is to figure out if there is any kind of building code or fire code applicable to the installation and go from there. I assume "polymer" means it's flammable or combustible.
Also look at venting requirements.
Check if there are any kind of emissions requirements.
Dimensions in meters implies not-in-the-USA, EPA requirement implies in-the-USA, but confirming where these are would narrow it down some.
For stainless, make sure the purchaser and fabricator are in agreement about what kind of surface finish is going to be furnished, and to what extent segregation of materials and tools will be maintained if critical.

In the USA-
Usually the city, county, parish, or state will have a building code (IBC of whatever year); that in turn references ASCE 7 of whatever year, and that's where your wind, seismic, snow, flood loading originate.
They will also have a fire code(s), usually winds up with NFPA 30 involved; that will affect how tanks are spaced, what fire protection is required, etc.
Normally, you can find out online which codes, which years are applicable. Normally local libraries (in that jurisdiction) have copies of those codes if you don't.
The overall facility will have to comply with federal EPA emissions requirements, and that will determine whether floating roofs are required, etc (typically not for very small tanks).
There may be state tank registration rules as well.
OSHA rules will affect ladders, stairs, handrails.
Tank details per the tank standard.
Anyway, it can get very involved trying to wade through all this if you don't normally do it, whether it's a 1-barrel or a million-barrel tank.
It's very easy to get into a situation where "they" assume you checked some aspect, you assume "they" checked some aspect, and it doesn't get checked.

 

[human909]

Thank you JStephen for another comprehensive reply.

In Australia the our environment regulator is also called the EPA in most if not all states. In my local state the act to create the EPA passed in the same month as it passed in the US and was one of the earliest in the world.

Anyway, it can get very involved trying to wade through all this if you don't normally do it, whether it's a 1-barrel or a million-barrel tank.

Agreed. Though many the things you list I have extensive experience in. Just not liquids handling and emissions. Most of that will likely be well outside my scope. But that still needs to be clarified. I confident I can suitable define the scope required and address it. Thanks for the advice and wise words of warning. We never want engineers stepping too far away from their areas of competency!

But gradually pushing our areas of competency is how we grow. This job is far from complex.