Tank Settlement Survey 1

[Whin]

Is it necessary to perform a routine soil settlement survey for in-service tanks that are supported by concrete ring wall, or is this requirement applicable only to tanks that rest on an earthen foundation (without ring wall)? Could someone provide a relevant reference standard for this requirement? Thanks in advance...

 

[HTURKAK]

Refer to API 653 , Appendix B which is normative.
Evaluation of Tank Bottom Settlement
...
B.1.1 ...... 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.
...
The monthly routine in-service inspection shall also include a visual inspection of signs of settlement.

 

[LittleInch]

"Necessary "? Not really, but depends on what the ground situation is and whether there are any visual clues that settlement has occurred.

And foundation can settle or subside given poor ground conditions or undermining by e g. water flow

 

[Whin]

Refer to API 653 , Appendix B which is normative.
Evaluation of Tank Bottom Settlement
...
B.1.1 ...... 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.
...
The monthly routine in-service inspection shall also include a visual inspection of signs of settlement.

Settlement survey was taken during hydrostatic test after tank construction, subsequent external visual inspection (5yrs of service) doesn't shows any signs of settlement. Is it mandatory to have another set of settlement survey as planned frequency?

 

[LittleInch]

"Mandatory" implies legislation so no, but would seem to be a good thing to do a 5 or 10 yearly basis. Really doesn't cost that much.

 

[HTURKAK]

Settlement survey was taken during hydrostatic test after tank construction, subsequent external visual inspection (5yrs of service) doesn't shows any signs

My points are ;
- The settlement measured during hydrostatic test is immediate settlement . Time dependent Consolidation settlement is totally different story. Depending on the soil conditions , ( for normally consolidated clayey soils with high GWL ) the consolidation settlement may last several years . Sometimes 30 years .
- The standard says ( ....During operations, settlement measurements should be taken at a planned frequency, based on an assessment of soil settlement predictions....) . That is , the settlement analysis is a prediction only and for settlable clayey soils if you can predict with in an error of 20 % limit , you are lucky.
- Again standard is clear . Look to the soil data, geotech report and settlement prediction calculations , initial test settlement and past inspection reports and decide accordingly if new survey and a program of settlement monitoring should be necessary.

( P.S. Settlement in MEXICO CITY at some locations was several meters ).

 

[Andrew ONeill]

My typical experience is an operating facility would survey every 5-10 years, but do it as a whole site survey, typically there will be other structures (e.g. stacks) or large buildings or strain critical equipment where some sort of survey is also a good idea. Normally just group it into that work.

 

[Whin]

Refer to API 653 , Appendix B which is normative.
Evaluation of Tank Bottom Settlement
...
B.1.1 ...... 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.
...
The monthly routine in-service inspection shall also include a visual inspection of signs of settlement.

If there is no signs of any settlement in 10yrs of operation (during routine visual inspection), is it nescessary to conduct the soil settlement survey?

 

[HTURKAK]

If there is no signs of any settlement in 10yrs of operation (during routine visual inspection),....

This thread is released almost three months ago .
You cannot visually detect if there is an internal bulge settlement with exterior inspection . Refer to Annex B2 Measurements of Bottom Settlement (Internal) Tank Out-of-service.
If the code is silent for a specific case , one of the options is using engineering judgement.

 

[Whin]

If there is no signs of any settlement in 10yrs of operation (during routine visual inspection), is it nescessary to conduct the soil settlement survey?

API 653 , Appendix B can be applicable for concrete ring wall tanks?

 

[Geoff13]

Are you just going to keep asking the same question until someone says "surveying isn't required"? Well, that's not me. LittleInch and HTURKAK are on the right track, and very knowledgeable forum members.