API Tank door cut: when to require stiffeners

[iangineer]

Can anyone point me in the direction of some calculations to help me determine if I should recommend stiffeners for a door cut into an API tank? Recently a 6ft x 6ft door was cut into the side of an ~80ft diameter tank to do some work, and I would think stiffeners would be needed for such a large cut, but the tank vendor said that it was a relatively small cut on this size tank and stiffeners are not needed.

I just need some way that I can quickly determine if stiffeners would be needed or not for future needs.

The recent tank is a clarifier and has a walkway from the shell to the middle where the rake motor is. Shell thickness is 1/4", height is 22ft. For this particular one, I recommended stiffeners and was told that it was no big deal to tack them on temporarily for the work, so it was fine. I'd like to be more certain next time.

 

[HTURKAK]

- IF THE DIAMETER IS ~80ft AND THE SIZE OF DOORSHEET 6ft x 6ft , I DO NOT THINK THAT BRACING OF SHELL IS NECESSARY AROUND THE DOORSHEET LOCATION AND I WILL NOT SEE ANY RISK FOR THE SHELL GOING OUT OF ROUND..

- IN PAST , MY COMPANY USED LARGE DOORSHEETS SUITABLE FOR HEAVY EXCAVATOR TO MINE THE SOLID SLUDGE IN THE TANK .ONE CAN IMAGINE THE SIZE OF THE DOORSHEET,

- API 650,653 DO NOT SPECIFY THE BRACING OF THE DOORSHEET HOLE BUT , I KNOW SOME COMPANY STANDARDS WHICH SPECIFY THE USE OF BRACING REGARDLESS OF THE SIZE ,

- IF THE BRACING THE SHELL IS NECESSARY OR NOT , COULD BE STUDIED WITH FEM MODEL ,

- I DO NOT THINK IT IS A BIG ISSUE TO BRACE THE SHELL WITH ANGLES OR CHANNELS ..

MY OPINION ONLY..

 

[Geoff13]

I agree with HTURKAK. A 6' x 6' door sheet is very small. It doesn't need stiffening.

We do add stiffening on large doorsheets, but this is only to hold the opening dimensions for ease of re-installation. Even a two-ring high doorsheet opening, for large equipment like HTURKAK discussed, wouldn't collapse a tank.

The stiffeners are stitch welded on prior to removal of the doorsheet. For larger openings our construction folks feel the work to add the stiffener is easily saved when they don't have to fight to get the doorsheet back in.

Assuming you are hiring contractors who are experienced at repairing tanks, I would leave the stiffener decision to them.

 

[iangineer]

I understand a 6' x 6' door is relatively small, but would it still be considered small on a 20ft diameter tank? Is there a ratio I can use, or some buckling calculation for tank walls that you know of?

 

[IFRs]

Is the door sheet large enough to require bracing? It's a pure judgement call, made by a qualified tank engineer. Shell thickness, weigh above the door sheet, environmental loads, expected construdtion loads, tank jacking, foundation stability, tank diameter, contractor competence, etc all enter into the decision. My suggestion is when in doubt, brace it - the cost is very small and the effort and cost needed to fix shell deformations can be quite large to be truly successful.

API 653 has only this to offer:

9.2.4.3 Large door sheets of the type shown in Figures 9.2, 9.3, 9.4, and 9.5 should have the top and/or sides of the opening stiffened to prevent a) sagging and deformation of the shell at the top of the opening, and b) shell deformations at the sides and upper corners resulting when the door sheet is first removed or when it is replaced and welded into the shell.

Installation of the stiffening members should be done prior to cutting the door sheet, providing it is safe to do so, and the members should remain in place until the door sheet is completely and satisfactorily reinstalled.

The specific arrangement and details of the stiffening should be determined by a storage tank engineer.

Door sheet stiffening, when used, usually consists of one or a combination of angle, channel, or wide flange section members.

HTURKAK - your caps key is stuck down - why are you SHOUTING at us? (perhaps that was not your intent?)

 

[HTURKAK]

Sorry for that..Shouting to any body cannot be an option for me .. I have problem with caps lock key and the reason is probably double alphabet ..