Corroded Bottom Floor Plates Replacement

[Inchtain]

I am seeking your help in comparison between choosing the single bottom with geomembrane liner and CP protection; and the double steel bottom with leak detection and CP protection for the replacement of a Crude Oil Surge Tank floor replacement with reference to the International Standards.

Which are the advantages and disadvantages of each repair procedure?

Tank Data:
Construction Code API 650 Appendix F, Edition 2001
Design Pressure / Vacuum 3.45 kPag / 0.5 kPag (51 mmH2O)
Working Pressure (kPag) 0.9 ÷ 1.5
Contained Fluid / Blanketing Gas API 38 Crude Oil / Nitrogen
Max. Operating Temperature (°C) 90
Actual Working Temperature (°C) 57
Dimensions (m) Height 14.6 - Diameter 37.2
Nominal Capacity (15,900 m³ )(100.000 barrels)
Material Bottom: ASTM A 283 Gr. C
Annular & Shell: SA A 516 Gr. 70
Roof: S235 J0Roof Structure: S275 J0
Corrosion Allowance (mm) 1.6
Bottom/Annular/Roof Plates Thickness(mm)8 / 10 / 7
Shell Plates Thickness (mm)
1st course 14
2nd course 13
3rd course 11
4th course & up 10

 

[LittleInch]

Single bottom will be cheaper, easier and faster to install, but could leave you with leaks if the internal surface coating is breached and the crude has water or other material which corrodes the floor.

Double skin bottom will tell you if there is a primary leak and then contain it, but will still need repairing after that, so it depends on the impact of a tank floor leak on the environment or risk.

what was the identified cause of the failure of the original floor?

 

[HTURKAK]

I am seeking your help in comparison between choosing the single bottom with geomembrane liner and CP protection; and the double steel bottom with leak detection and CP protection for the replacement of a Crude Oil Surge Tank floor replacement with reference to the International Standards.

It is not clear for me .. A sketch may help to get your point. If you cut the shell and install new bottom above the existing one , by definition this should be classified as double bottom .
My points are ;
- This subject has been discussed in past with several threads and you may look to them,
- API 653 explains the requirements pls look 9.10.2.1.1 through 9.10.2.1.6. The common practice is shell slotting (complete severing of the tank wall ) 100-150mm above the bottom .
- You may prefer the use of 100mm concrete spacer to avoid CP. Radial grooves could be added for leak detection.
-If you choose sand for spacer material , you will need C.P. for external corrosion.
- Old German standard defines double bottom as , the bottom has two layers the layers seal welded at perimeter and a negative pressure is applied to detect if one of the bottoms leaks.

My understanding for double bottom is similar to API 650 Figure I.5—Double Steel Bottom with Leak Detection at the Tank Perimeter (Typical Arrangement)