How to avoid shell buckling during API650 tank repair 4

[jrafael95]

Hi everyone, my problem is:

There are several tanks and I need to standardize the double bottom installation process. It's my first time dealing with API650.I have to open some space in the shell. How I design the supports around the shell to avoid buckling?

I have with me API650 and API653, but i didn't find anything about shell buckling due openings.

 

[IFRs]

Welding C-Clips to the tank on 10 foot [3 meter] centers. Slot the shell leaving 2 or 3 inches of metal between the slots, at the C-Clips. Better yet, consult with a local company or two who have experience with tanks your size.

 

[HTURKAK]

Dear Jrafael95 (Mechanical),
I hear that , you want to repair the bottom of existing tanks with double bottom method and you have API 650 and API 653 with you..

API 653 9.10 describes the repair of tank bottoms and and Figure 9-5- Typical Welded-on Patch Plates on Tank Bottom Plates and 9.10.2 describes the replacement of Entire Tank Bottom.

I understand that ,the repair of bottom with welded on patch plates is not sufficient .

Repair with double bottom refers to two steel bottoms constructed by slotting the tank shell above the lower bottom and installing a new bottom 100-150 mm above it. In order to install new bottom, the shell must be raised with shell jacking method .For this purpose,
1) lugs are welded to the shell near the base, in general the spacing is about 15 ft. Jacking shall proceed around the tank circumference in small increments in order to Prevent damage to the shell and to the bottom. Shims are placed as the jacks are moved around, and the tank can be raised to desired elevation.


2) Another method, jacking under the bottom of the shel. For this purpose, small pits will be excavated under the shell of the tank in order to place a jack.

If you provide detailed info. (no.of tanks, service, roof type, diameter, height, age of the tanks, reason for double bottom repair...)., you may get better comments...

 

[IFRs]

Jacking is not required if you cut the tank shell twice, about 1" apart, making a slot. Slide the new bottom plates in and then when you cut off the shell tabs and C-Clips the tank settles down onto the new bottom.

 

[jrafael95]

Dear friends @IFRs and @HTURKAK thanks for the repplies!
I apologize for the lack of info in this post, it's my first time in this forum.

The tanks have single bottom. I need to make a step by step procedure (in compilance with API650 and API653) to install a double bottom in these tanks. It's dimensions are:

(Diameter;Height) in meters:
(13.12, 12.60)
(10.66, 9.01)
(4.38, 5.20)
(5.65, 5.89)
(9.25, 11.66)
(11.46, 9.76)
(11.46, 7.32)

I need to know if I need to install shell bracings before door sheet instalation and how to do the calculation of them.(the best reference I found is:

https://www.eng-tips.com/viewthread.cfm?qid=223392)

 

[HTURKAK]

Dear jrafael95 (Mechanical),
I do not look to web everyday so my responses in general with delay.

The requirements for the installation of a replacement bottom over an existing one are given in API 653 9.10.2 . Your concern as i understand, the stability of shell around the door sheet opening. I don’t think any problem is If the size of the opening in the range of 2 m . but should be confirmed with calculation. In case of stability risk, temporary vertical stiffeners could be welded (typical, C120 ) to both sides of the opening from the outer face. The new double bottom which will be installed into the tank performed by the "shell slotting method." as mentioned by IFRs (Petroleum) . This method is O.K. if there is no levelling problem of the foundation.

The dimensions of the existing tanks are substantially small and i think the roof is self supported cone roof. The weights of the tanks should vary between 4tons ( for smallest ) to 40 tons(for largest) and the foundations should be flat slab (circular, octogonal..etc) rather than ring foundation.

I will suggest the following procedure (i think feasible option if Crane avaible) = i) completely severe the tank Shell with Shell slotting 4-6 in. Above the old bottom, ii) Remove the Shell and roof to a temporary place (Shell should be supported on sand bags), iii) install membrane on the existing bottom and pour R.C. concrete for filling material iv) erect the new bottom and then erect the existing Shell and roof . Provide at least two manways for big dia. Tanks for ventilation during welding and cleanning. Good Luck...

 

[jrafael95]

Dear HTURKAK, thanks again for the answer.

Yes, all the tanks have self-supported cone roof and some of them have internal floating roof (gasoline tanks). As I didn't find anything in API 650 and 653 about shell temporary support calculation method, we'll do some calculations and proper engineering judgment.

 

[IFRs]

The attached presentation may be of interest to you.

Please let us know what calculations you perform and how they turn out.

 

[jrafael95]

@IFRs, this EXACTLY what I was looking for! Thanks a lot.

Well, about the calculations, probably another company will do, but I think they will sketch the tank without door sheet in some finite element software and analyze, or just weld some beams on it without calculations. Anyway, when i get this answer i'll post here to you guys.

Thank you all for the help,someday I hope to help people in this forum like you guys helped me

 

[Geoff13]

The attached presentation may be of interest to you.

jrafael95
Having worked with John for years before he moved to TIC, I'll tell you that this will be very reliable information.

I will note that page 13 of the presentation is a RISA-3D output, not FEA. This is too simple a problem to need FEA, or even RISA-3D. I'm sure John only ran RISA-3D to show the expected deflected shape of a tank with a door sheet opening.

 

[jrafael95]

Geoff13, thanks for the aditional info!

 

[IFRs]

Geoff13 - I was not sure if John or TIC would object to posting this document in this forum, but I thought it was in the public arena since it was shown at a conference that anyone could have seen if they paid the admission fee. If you or John or TIC is concerned or objects, I will get it removed, pronto.

 

[Geoff13]

IFRs : Personally I think the presentation is just standard industry practice, good engineering and API 653 requirements, without much that would be proprietary to them. But I guess we'll find out if John or TIC are on Eng-Tips.

 

[IFRs]

Geoff13 - Yes, we should find out!!! I was disappointed that API did not give any guidance on the minimum size of structure to put around the opening, or any simple formula for that. I realize that there is technical difficulty in doing so, but it would have continued the cookbook style that has been so successful worldwide.