Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Limiting a tank's capacity

Limiting a tank's capacity

Limiting a tank's capacity

Due to a EPA request, I have to physically and permanently limit our fuel oil storage tank from 1 million gallons to 985,000 gallons.  Level indicators and administrative controls are not acceptable.  I can find no reference in API on reducing a storage tank capacity.  How would I best limit this tank's capacity to comply with the EPI and API code?  I have been asked to put concrete in the bottom and I know that is not an option, but I cannot find anything in API that backs me on this.

RE: Limiting a tank's capacity

Is the tank already double bottom'ed? Maybe you need to add a new bottom? Depending on diameter, something on the order of 6" above the existing bottom should work. Not uncommon...


RE: Limiting a tank's capacity

How about adding 15,000 gallons of distilled/de-ionized water?  It should all separate and end up at the top, giving you the buffer you need?

RE: Limiting a tank's capacity

The tank has to be physically modified so that it can never hold 1 million gallons again.  Shell vents, overflows, etc can be removed and are not acceptable.  I would like to add a cone/cylinder to the bottom of the tank to displace 15,000 gallons, but this alteration "could be altered again" to restore capacity - see below.  I am interpreting the requirement below as installing a second floor or lowering the top as the only option.  I am just trying to find the lowest cost solution to this issue.

This is our requirement from the EPA:

 2.5.3 Definition of Storage Capacity
Under the SPCC rule, if a container has the requisite capacity, it does not matter whether the container is actually filled to the capacity of the container. If a certain portion of the container is incapable of storing oil because of its integral design (e.g., mechanical equipment or other interior components take up space), then the shell capacity of the container is reduced to the volume the container might hold (67 FR 47081).

Generally, the shell capacity is the rated design capacity rather than the working/operational capacity.

2.5.4 Tank Re-rating
Shell capacity should be used as the measure of storage capacity, unless changes are
made to the design shell capacity in a permanent, non-reversible manner. For example, when the integral design of a container has been altered by actions such as drilling a hole in the side of the container so that it cannot hold oil above that point, shell capacity remains the measure of storage capacity because such alteration can be altered again at will to restore the former storage capacity.

When the alteration is an action such as the installation of a double bottom or new floor to the container, the integral design of the container has changed, and may result in a reduction in shell capacity.  An addition or modification to a field-erected storage tank should be performed in accordance with industry standards and the original design specifications. Relevant industry standards include American Petroleum Institute (API) Standard 653 "Tank Inspection, Repairs, Alteration, and Reconstruction" (API-653). This standard includes additions or modifications to shell penetrations such as overfill diverters. However, even where such modifications are done in accordance with standards, the tank may not be considered re-rated to a lower capacity; the capacity remains equal to the original rated shell capacity. An owner or operator may reduce the
capacity of a tank only by changing the shell dimensions (i.e., by removing shell plate sections).  Since SPCC requirements are based on shell capacity, modifying a vent, overflow, or other tank appurtenances that reduce the working fill capacity does not affect SPCC requirements.


RE: Limiting a tank's capacity

Welcome to the world of EPA wasting the public's money.  We had a client with a similar situation and owner could not afford to include an emergency response plan for tanks at and over 1 million gallons to his SPCC. The EPA would not grant any modification to this 1 Million gallon tank. This tank was in excellent shape; it had been  internally inspected and undergoes annual fire marshall inspection.  So ultimately the tank was drained and dismantled.
And we wonder why all the jobs are going to China, India and the likes.  The EPA is a diservice to the US.

RE: Limiting a tank's capacity

Wow, all that work for a 1.5% volume change!

I'm guessing that this is not a floating roof tank.


RE: Limiting a tank's capacity

That is correct - fixed roof

RE: Limiting a tank's capacity

I wish I had a simple idea for you.  seems like you're between a rock and a hard-place.

i'm sure you've already been in contact with tank vendors/manufacturers to get them involved.  Chances are one of them has had to go through this with someone else before.

RE: Limiting a tank's capacity

Seems to me the choices are either raise the bottom or lower the roof, and it would mainly be a matter of cost efficiency to choose between them.  Try contacting some vendors that do tank modifications and see what they can do.

RE: Limiting a tank's capacity

Could you pour a concrete slab inside the tank to take up the volume needed?

RE: Limiting a tank's capacity

I think you should go back to the EPA and tell them not to be so stupid and use a bit of common sense. For me re-locating the overflow will limit the capacity to whatever you need.

On the reasons why jobs are going to India,China etc is the short-sightedness of the Project Managers/bean counters seeing this as being cost effective BUT they never actually consider the overall cost when the job takes two to three times as long with quality taking a huge "hit". But hey perhaps they will learn when more accidents occur and hopefully they end up locked away for negligence!!

RE: Limiting a tank's capacity

Concrete was discussed, but I feel confident that pouring concrete would not be in compliance with API.  If this was performed, the bottom of the tank could never be inspected again without removing the concrete.  Also, the tank is full of #2 diesel fuel, that would most likely deteriorate the concrete and we would start pumping pieces of concrete into our boilers.

RE: Limiting a tank's capacity

A new overflow is not acceptable ???/!!!!

"Shell vents, overflows, etc can be removed and are not acceptable." ???

Yup.... and someone could add a couple of shell courses in the middle of the night and get your capacity back.

It sounds like this is EPA code for "make the shell shorter"...no other solution is acceptable.



RE: Limiting a tank's capacity

Would it just be cheaper to comply with the regulations for a million gallon tank?  Modding a tank so it skirts just under a limit doesn't feel quite right somehow.


RE: Limiting a tank's capacity

EPa would not accept an overflow for our client's 1 Million gallon tank.

RE: Limiting a tank's capacity

I just received notice that the entire site's capacity must be under 1 million gallons.  So, I will have to reduce this tank's capacity by 300,000 gallons.  I am going to cut the shell and lower the roof.  Thanks for all the comments.

RE: Limiting a tank's capacity

So, what I understand from this forum is that the EPA dictates tank design details....and states acceptable nozzles, overflows and vents ? Is that correct ?

Send the Nazis a large blank sheet of paper....have them draw and detail an acceptable tank farm.

Otherwise, you will have a very long guessing game ahead of you.

And people wonder why all industry has moved to China....


RE: Limiting a tank's capacity

If you wanted to, you could sue the EPA.  A welded overflow nozz is an API-approved method to limit tank capacity.  The EPA does not have the authority to override API Code without a clear-cut statute.  With nothing formally in their regulations stating that API-approved method(s) are no longer acceptable, they "don't have a leg to stand on".  Get your Senators involved in this.

RE: Limiting a tank's capacity

Adding a double bottom with concrete between would have to be less expensive than lowering the roof.  Bringing suit to the EPA is not a draconian measure - it is simply the way things get done.  Have you complained up the EPA ladder?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close