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Earl   AST Forum  

Bottom plate in welded steel petroleum storage tan

Wednesday, August 29, 2018   By: ksm208@gmail.com [1945] 0 Stars
In a newly constructed ATF tank due to settlement the slope of bottom tank is towards annular plate. Due to this water settles around critical zone in tank bottom.

This is not allowed in ATF tank to overcome this another plate is welded from shell to bottom so that slop is toward the center of the tank.

My query is whether this welding will have effect on load on bottom plate and if so what else is suggested to correct the slope of bottom plate from outward to center.


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Thursday, August 30, 2018   By: Orlando Costa [201] 2 Stars
You mean you have the suggestion of soldering plates under the existing plates bottom. Thats right?

I would think about another suggestion: depending on the diameter of the tank, it would weld plates to compensate for the inclination required using API 653, see itens 9.10 and 9.9.2 as a reference.

Of course, a project correction document signed by an Engineer certified by API 653 will be required. Considering details such as nozzle level, need to fill the space between the plates, dimensions required of the new plates to avoid tensions and others.

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Friday, August 31, 2018   By: Orlando Costa [201] 2 Stars
However, the plates to correct the problem would be welded over top the existing bottom.

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Wednesday, September 05, 2018   By: Orlando Costa [201] 2 Stars
Depending on the dimensions as the angle of inclination of the existing bottom and others details of your tank you can use API-653 - to - Replacement of entire Tank Botton.

I worked on a similar case in the past. See an attached sketch.


Click on picture for full size view or to view PDF!

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Monday, September 03, 2018   By: BABRTs973 [53] 5 Stars
Was this tank built with a cone up, cone down or flat profile. If it is a cone up or flat you may have to raise the nozzles to slot the shell for new sketch plates allowing drainage away from the shell.

Not knowing the size diameter and height also makes for a shot in the dark.
If it is a cone roof less than 10 meters diameter you may be able to lift the tank and reprofile the base material for drainage to the center then set the tank back on the foundation.

But never in any circumstance should plates be laid on the existing floor and filet welded to the shell. The shell needs to be notched and the sketch plates inserted through the shell and welded on both sides.

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Sunday, September 23, 2018   By: Karsadi [652] 4 Stars
Dear Sir,

Maybe other ways can be considered as follows
To change the slope of the existing bottom tank, it can be done by installing a new bottom plate above it, without dismantling the old bottom plate and installing a new bottom plate above it by making the bottom slope in accordance with the plan by implementing Double Steel Bottom Construction
If a double steel bottom is used, the details of construction shall provide for the proper support of the primary bottom and shell for all operating conditions. The design shall be evaluated to verify that the primary bottom and shell are not overstressed. The evaluation shall consider all anticipated operating conditions such as design metal temperature, maximum design temperature, fill height, hydrostatic testing, seismic conditions, and tank settlement.

The evaluation is not required if the primary bottom is uniformly supported on both sides of the shell and is not structurally attached to the secondary bottom or primary bottom support.

For double steel bottom systems that use steel members such as grating, structural shapes, or wire mesh to separate the bottoms, ingress of water between the bottoms will result in local accelerated corrosion rates. If the perimeter of the bottoms is not sealed, corrosion protection of the tank bottoms shall be provided.

Thus hopefully it provides an overview of the benefits.

Best Regards

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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