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

API 650 - tolerances for ?

API 650 - tolerances for ?

API 650 - tolerances for ?

Hello everyone. According to API 650 paragraph it is necessary to make some internal measurements in the tank before and after the hydrotest. What I understand is that with these measurements we could estimate some internal settlement at the bottom of the tank... but is there any tolerance for this? What is this code point for? Or are these values ​​that one must maintain so that during a future intervention of the tank in operation, we can make a comparative between data and see settlements over time?

RE: API 650 - tolerances for ?

Eduardo - not sure which edition of API 650 you are looking at and what "PH" means. But if you are looking at the pre- and post- hydrotest data I think the game is that the tank builder is contractually required to give the owner a tank that meets API 650 tolerances. Pre- and post- hydro data may help the owner understand if the tank fails to meet some criteria due to foundation settlement or if the tank builder did a bad job.

RE: API 650 - tolerances for ?

@ Eduardo1982
What edition of API 650 do you have?


RE: API 650 - tolerances for ?

Sorry.. i have updated my first post with correct paragraph in current edition of API 650.

RE: API 650 - tolerances for ?

I don't see that there is an actual tolerance applied to these measurements, they are simply reported.
I believe API-653 has procedures for evaluating bottom settlements that seem to be excessive.

RE: API 650 - tolerances for ?

API 650 is for new tank
API 653 is for in service tank.


RE: API 650 - tolerances for ?

An API 650 tank is new until it is put in service. Hydrotest is generally not considered "in service" since it is essentially NDE. The tank builder is responsible to deliver a tank that meets API requirements. API 650 does not have a tolerance on the bottom slope therefore it is a matter of the contractual agreement between the owner and the tank builder. The pre- and post- measurements will help the tank builder get paid, the owner be assured his new tank meets API 650 and the terms of the contract and help resolve disputes between the tank builder and the foundation builder.

RE: API 650 - tolerances for ?

Eduardo1982 (Mechanical),

You did not provide alot of info. here.. ( dia., height, foundation type , service ..)

API 650 specify tolerances for the foundation settlement ( uniform, differential ) however, silent for the internal settlement at the bottom of the tank..

There are some company standards which may be consider ,

Assuming the tank bottom is cone-up, the slope from the apex to the perimeter of the tank shall justify a minimum flow and there shall not be local depressions which may cause ponding of the content.

In general ,for typical soil conditions , the settlement at the center of the tank could be 3-4 times of the settlement measured at perimeter.

The bottom slope shall be chosen to satisfy a reasonable slope after hydrotest..

My opinion based on past our company experience..

PS. I have internet access problem and could reply with delay if you have further querries.

Use it up, wear it out;
Make it do, or do without.


RE: API 650 - tolerances for ?

@ IFRs
The hydrotest is not considered an NDE.


RE: API 650 - tolerances for ?

r6155 -
While perhaps not typically considered NDE, Hydro is listed in API 650 Annex T "NDE Requirements Summary".

RE: API 650 - tolerances for ?

@ IFRs
1) Hydro mentioned in API 650 Appendix T as NDE was an error.

2) On 12 February 1952 a large all-welded oil-storage tank collapsed during hydrotest at the Esso Petroleum plant at Fawley in Hampshire. Hydrotesting had commenced on 30 January following completion of the tank, but was halted when a 0.6m long vertical crack appeared in the bottom two strakes. The tank was emptied and the crack repaired. When the hydrotest was recommenced on the 11 February, the air temperature was near freezing and the water temperature +4°C. The tank split when the water reached 90% of the tank height, a continuous vertical fracture running through the parent plate of every strake. The shell was torn from the tank bottom and collapsed on the surrounding band, leaving the roof lying on the base.
Brittle fracture.


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


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