Contact US

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!

*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

Life span of storage tanks

Life span of storage tanks

Life span of storage tanks

Hello comrades,
I have 2 questions.
1. I'd wanted to know. How is life span of a welded storage tank factored into the calculation of the shell plate thickness according to API 650
2. I discovered quiet recently that shell plates that were stored in the open and had been sandblasted for construction had their thicknesses reduced significantly. A cursory check on the thicknesses on each sample revealed that the thicknesses of the shell plates were just a mm or two below their minimum design thicknesses. My question is can these be still considered useful or they still have some usefulness but reduced life span?

RE: Life span of storage tanks

API-650 does not address life span directly. The owner is allowed to specify a corrosion allowance, also internal and external coatings as applicable, cathodic protection systems, various stainless steel alloys, etc. API-653 has requirements relating to corrosion rates and inspection intervals, and if that information is available, it can be factored into the new tank design as well. Note that there are steel tanks in service that are over 100 years old.

On the loss of thickness observed- that sounds like something abnormal. If the corrosion was extensive prior to the blasting, I suppose it's possible. I would also consider if the plates were mis-identified, or thickness testing performed incorrectly, etc. But in general, they should be the specified thickness when the tank is built.

RE: Life span of storage tanks

I agree with JStephen ..... Neither API650 nor any other Storage Tank Code or Standard specifically addresses tank life.

Be aware that storage tank life is controlled by the sole mechanism of internal and external corrosion. In nearly all situations, the tank life is not controlled by swings of pressure or thermal loadings, like would occur for pressure vessels and piping.

(An exception to this would be the flat-bottomed, high-temperature salt storage tanks in a Solar Energy Generating Plant)

Be also aware that, as the decades pass, the useful life of the tank may change due to new coatings, changes in maintenance or service, etc.

The only reasonable way to determine the useful life of the tanks that you manage, is to inspect surfaces and take thickness readings ...

I suppose, in some indirect way, when the tank purchaser decides upon a Corrosion Allowance, he is making a choice about tank life

Sr. Process Engineer

RE: Life span of storage tanks

1) I agree with JStephen and MJCronin
2) Plate thickness below design thickness is not allowed to fabricate new tank. Something is wrong with the thickness of the measured plates.
The Acoustic Emissions Examination (AEE) is the best practice for the expected service life.


RE: Life span of storage tanks

Interestingly API 650 does refer to "service life" in a few locations without really defining it or using it anywhere.

The best description comes here: 3.7 corrosion allowance
Any additional thickness specified by the Purchaser for corrosion during the tank service life. Refer to 5.3.2

5.3.2 doesn't add much.

If your plates are below the minimum design thickness than you can't use them and comply to API 650.

Either build a smaller tank ( less height) or buy some new plate.

I think API 650 basically assumes that the tank won't corrode more than the corrosion allowance (if any).
If it does then you need to assess it in a fitness for purpose assessment, normally to API 653 for API 650 tanks. However you can't do that for a new tank. That would not be permitted.

So yes the plates are still useful, but not for your original tank but a smaller one where the min design thickness is less than your "sandblasted" plates

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

RE: Life span of storage tanks

Agree with LittleInch ...

Corrosion allowance is a de-facto tank lifetime gauge... Your sandblasted plates can serve as materials for a redesigned smaller tank.

As a point of reference, even the sellers of baked-on coatings for "Glass-fuse-to Steel" tanks only advertise a 30 year service lifetime.


Sr. Process Engineer

RE: Life span of storage tanks

Note that per API 650 an underrun of 0.01" [0.3mm] is allowed for shell plate. This referrs to the as-deliverred plate thickness from the mill or supplier, it was not intended for your situation and is probably too small to help. My best suggestion is to recalclate the allowable liquid heights for each plage, use all the material you have for upper tings and bring in new steel for the bottom ring.

RE: Life span of storage tanks

Try with joint eff. E=1


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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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