Thermal expansion for buried Pressure vessel located in sand filled pit

[D2HANDLE]

Hello all,

I am working on a vessel which is to be installed in a concrete pit. The pit will be filled with sand after installation of vessel as per local regulation requirement to prevent leakage of the process gas to outside atmosphere.
Vessel operating temperature is 230-C and the material of construction is CS.
Design and fabrication code is ASME VIII Div. 1.

Since the concrete pit will be filled with sand after installation, my understanding is that there will be no room for expansion of the vessel during operation since the free expansion of vessel will be restrained by the sand and the concrete pit.

Could you kindly advise how can we design the vessel for restrained expansion so that there will be no overstress of the vessel due to restrained expansion during operation?

Any ideas are welcome......thanks for your help.

Regards,
D2HANDLE

 

[TGS4]

Unless you provide some capacity in the burial for the thermal expansion, something is going to break - thermal expansion doesn't like being restrained...

Check out EEUMA 190.

 

[MJCronin]

"The pit will be filled with sand after installation of vessel as per local regulation requirement to prevent leakage of the process gas to outside atmosphere."

Please explain how that works ... Where in the world will this vessel be located ?

After the process gas works it way through the sand, what advantage is gained ????

By placing a hot CS vessel in a sand filled pit you will only ensure accelerated failure .... from thermal constraint of the vessel and accelerated external corrosion.

What MBA/local regulator came up with that idea ?



MJCronin
Sr. Process Engineer

 

[racookpe1978]

Outside pressures, movement and settling of the sand mix? Corrosion and water seepage (water adhesion next to the CS underground will require some kind a tar or epoxy sealant?) Expense? Delays in construction? Do they think the sand will prevent or absorb leaking process gasses and fluids? Slow an explosive reaction?

What the bloody hell do they think they are trying to do? (Other than destroy the tank integrity.)

-320 degrees?

 

[D2HANDLE]

Hello TGS4, MJC and Rookpe1978 for your valued opinions.

I am also not sure how and why sand filling shall be able to contain the release of harmful gases from the pit, should this happen.But there shall be a concrete slab at the top of pit and this may help for leakage issue in some way.

Well…the vessel shall be installed in one of the former soviet bloc coutries.And we are not familiar with all of the local regulations.. so we have to believe what our local consultant advises us, and they told us that as per the regulation, the Pit must be filled with sand.

But looking at the issue, we are tying to reverify with another local consulatant about the requirement for sand filled pit for this Vessel.
To tackle thee external corrosion, special paint devised for buried vessels, is planned to be applied.
I shasll keep the forum members updated with further developments.

Regards,
D2HANDLE

 

[saplanti]

I guess,this is the cheap designer approach to confined spaces regulations.

 

[racookpe1978]

No, building this "thing" inside a deep hole in the ground IS a confined space nightmare! Welding that deep? Painting, lifting and providing safety harness/retrieval ear for the people down in the hole?

Getting ventilation to get the air exchanged down there? it combines the worst of "not a tunnel" with the access to the bottom of "a deep vertical pit" with the hassle of "excavation".

 

[saplanti]

Let's not forget the thermal expansion under the differential temperature between construction and operation conditions.In case the diameter is large, obviously the length will be long with thin wall with/without internal design pressure. Therefore there will be expansion. and consequently restraining action by the sand. This cannot be controlled in the longitudinal direction without a proper compaction in the send, and will create more problem. In the radial direction again the same problem exist. However if there is no pressure in the tank, there will be some plastic dislocations, which may be acceptable in case there is no internal pressure in the tank, under the thermal load under uneven sand bearing forces.

 

[racookpe1978]

Sand, however, is both very loose - when dry and clean - AND very tight and semi-rigid (when damp and packed or pre-loaded with even mild pressure or very "fluid-like" - when very wet and pressurized.

Therefore, the very large vessel WILL "float up" in its surrounding sand bed as the container shrinks and swells with thermal expansion, as the sand settles and adjusts over time and with varying water percentages in the sand around the container, and with the varying internal weights of the container.

Over time, the sand around the tank will tend to loosen (up high around the tank) and then drop and settle further down (below the tank) thus creating a lifting force much like bouyancy in a liquid quicksand. Not anywhere near that quick, but the lifting force will need to be addressed somehow.

 

[chicopee]

What will the content of the tank be and once the product is heated to 230 dC will that temperature stay consistent? if the temperature remains consistently high, in my opinion, the sand will displace, if not compacted by the concrete cap, and the tank should be under minimal restraining stresses. Make sure the tank is coated with material compatible for underground application and that the tank is cathodically protected.
Before proceeding with this project, find out if other such installations within this country are in existence and if there were any problems associated with thermal expansion.

 

[SnTMan]

From what I read on here these days, I think many more of 'em outta be buried

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[FoxRox]

Does the sand have to be up against the vessel shell to meet the regulation? Perhaps you could put it inside a metal box or cylinder and let that structure deal with all the sand and expansion issues.

There are thousands of buried fuel tanks around the world. How do they do that without breaking things?

 

[TGS4]

FoxRox - most underground fuel tanks are at ambient temperatures, and therefore do not have the thermal expansion issues.

D2HANDLE - the previous underground vessels (mounded, actually) that I have designed that had thermal expansion had a non-collapsible foam applied on the vessel surface. More foam was provided at the ends, and special sleeves were provided for nozzle protrusions. Nozzles and other openings (think manways) will get bent rather quickly without special consideration.