Buried Solvent Storage Tank

where are you located?

You may refer NFPA 30 (chapter 23 Storage of liquid in tanks - underground tanks)

i am from PAKISTAN.

Do you have NFPA30 in soft copy?

Unfortunately i don't have a soft copy. I don't know what rules are applicable in Pakistan but NFPA, UL, API are internationally respected.

You may ask your insurance company to suggest something. The link mentions some of the codes and standards, if this may help: -

http://www.epa.gov/oust/cmplastc/standard.htm

SA516-70 is a common pressure vessel plate. Your atmospheric tank might not need so much; SA36 might even do. Corrosion is likely to be the major issue, and probably should be the focus of your investigation. Off the top of my head, I don't recall what works for ethanol/ethyl acetate.

Actually, its a buried solvent storage tank.

When vessel is buried, there will be external pressure offered by soil.

One problem is how to calculate the external pressure.

The external pressure will depend on the soil characteristics (density, cohesion and angle of internal friction), the depth, the surcharge and whether you are in a flood area.

What will you contribute to the design?

In this case, my contribution to design is to calculate the weight of tank for cost estimation and safety rules.

Do calculate the buoyancy as well. They make excellent boats too _{(been there, done that, secondhand T-shirt now on eBay...)}.

ohsa [occupational health and safety adminastration] here in the usa has all the information you need to install a buried tank that's used to store famable liquids.

you can find the information online.

By follwing the rules of UL-58 I have done basic designed(thickness,length,material of construction). but i dont understand the concept of beouncy force,(how to make it(vessel) stable)

Thanks all

Adiba Nasir

Chemical engineer

Consider the empty vessel submerged in water. What techniques are used to keep it submerged against the buoyancy upthrust (rhetorical question - NNTR)?

External soil pressure will vary with soil type, location of water table, etc. Some soil types can "fluidize" in case of earthquake, and can float a partly empty tank to the surface. This can be prevented by putting a slab of reinforced concrete below the tank, and anchoring the tank with straps or the like. A geotechnical engineer can assist with this, and in complying with local seismic regulations.

ok . I have got the point.

thanks

Another consideration are regulations to prevent water table contamination in case of a leak in the tank and provide the means to detect and prevent such leaks.

The preferred solution is to build a concrete chamber with at least one manhole, space to walk around the tank, a suction pit in the bottom, venting, and then place the tank inside with its support saddles bolted to the bottom slab of the concrete "room". finally, cover the chamber with a concrete slab on top provided with manhole, venting, bulkheads for piping and instruments, special fittings for tank filling, etc. This way the problems of buoyancy, external corrosion, leak detection, water table contamination are prevented or solved.

internal corrosion is no problem if carbon steel is used for methanol - ethyl acetate storage. But SA-36 is no longer an acceptable material for vessels made for flammable liquids sotorage.

Try to get NFPA Code 30, look for "nfpa" on Google or other search engine and follow the links to buy it in soft form. Whatever the cost is, it is a very good investment. specially if it lets you avoid a very costly failure later on. API codes are very good too. And do not forget the local codes; check with a local gasoline dealer; they know the codes and how to solve all problems of underground storage tanks for flammable liquids.

The vessel is designed at atmospheric pressure and ambient temperature.

SA-36 may also be used as per UL-58.

vessel is FRP coated to avoid corrosion.

The preferred solution is mounted vessel but as specified by customers, its buried vessel.

SA 36 has the adequate strenght but since the 70's it is not listed as an acceptable material for vessels operating under pressure (ASME CODE Sect VIII) or for flammable liquids. In addition to its strenght there are other characteristics of this steel plate material, such as its ductility, etc.

I recommend to check the ASME code and choose another steel grade. The cost difference, if any, is rather small.

By Roark equation , we can calculate external pressure being exerted onthe vessel by soil.

this equation has following factors

1-Es=modulus of elasticity of steel(29.5x10^6psi for structural grade A36 carbon steel)

2.ts=thickness of shell

3.L=length of tank

4.r=radius

5.u=poisson's factor(0.287 for structural grade A36 cs)

6.P=Buckling pressure

now from Es and u , we are using value of A36,

thats why i recommended material A36

Basically UL-58 is for STEEL UNDERGROUND TANKS FOR FLAMMABLE AND COMBUSTIBLE LIQUIDS.

here i have confusion whether to use A36/SS

UL-58, as per clause 7(materials)

7.1,7.2 gives some specification for CS to be used.

UL-58 table 3.1 gives minimum thickness for SS & CS against maximum diameter and capacity of tank.