External Settlement Surveys

[Cristian N]

I was wondering if anyone had experience performing external settlement surveys on in-service storage tanks. I see a lot of 3rd party inspection companies tend to incorporate settlement surveys in their external visual inspection reports.
[ul]
[li]I know API 653 has minimum required points in accordance with the tank's diameter.[/li]
[li]Edge settlement surveys are performed during out of service/external inspections.[/li]
[/ul]

Essentially, what I am asking is, are settlement surveys performed from the outside, really effective? If they are, how effective are they on a double bottom tank?

 

[HTURKAK]

Pls look API 653 APPENDIX B-EVALUATION OF TANK BOTTOM SETTLEMENT and excerpt from the same;
( During operations, settlement measurements should be taken at a planned frequency, based on an assessment of soil settlement
predictions. For existing tanks that do not have initial settlement data, a program of settlement monitoring should be based on prior service history.)
and
(B.1.2 If at any time settlement is deemed excessive, the tanks should be emptied and reI eve led. Releveling of a sizable
tank is expensive and rather difficult to achieve )...


Regarding the double bottom, is that for leak detection ? What is the service?

I will suggest you to look also ( API RECOMMENDED PRACTICE 575 Inspection of Atmospheric and Low-Pressure Storage Tanks )..

If this is a real case, pls post some details , some sketches double bottom detail ,and settlement survey to get more valuable comments..

 

[IFRs]

If you are expecting or experiencing ongoing tank settlement due to foundation or sub-soil issues, taking periodic external elevations would not be that unusual and in fact would be a splendid idea. The presence of a double bottom would not affect this at all.