Refurbishment of a Burnt Oil Storage Tank

[Mechanigenic]

Hello Everyone,

I have a serious problem at hand.
In the oıl fıeld I am workıng ın there ıs an ongoıng project whıch ıncludes refurbıshment or repaır of a burnt oıl storage tank. The tank is a 40.000 BBL capasity tank with a diameter of 85 ft and a height of 40 ft. Design code is API 620. The fire burned the insulation on the shell and on the roof and the especially one side of the tank shell was exposed to excessive heat. Deformation on the upper courses can clearly be seen due to thermal expansion as they have 10 mm, 8 mm and 6 mm thickness.

On the other hand first course has 15.5 mm thickness and has not shown obvious deformation such as buckling and waving as the other courses. It has lost its straigtness and bended as if it was a baloon and inflated from inside of the tank.

I have read the API 579 and API 653 to see if there are and dimensional tolerances mentioned which I can use to detect the shell plates which needs to be replaced without hesitation. Hardness tests and microstructure analysis will be done, but my question is, which dimensional inspections can spare me time and detect which plate to replace?

Can I make banding inspection on the shell plates and cancel out the ones which show deformation over 1" for example?
Please see the attached photos.
Your replies will be highly appreciated.

 

[LittleInch]

I don't know of any to specifically cover this so my normal first port of call is to go back to the original build spec, in your case API 620 and apply the dimensional tolerances. your aim, is to return the tank to an "as new" condition so the same dimensional tolerances apply as a Minimum.

If it's the same as API 650 then for your size tank radius tolerance is 20" and local out of plumbness 2.4" ( 1/200 of tank height) or as specified in the original plate condition.

At the least it gives you a base case to work from and then some small areas you can judge individually

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Mechanigenic]

Thank you LittleInch for your answer.

There is a section in API 579 (Fitness for service) where it describes how to check if the deformations on the shell are within acceptable range or now, however, it requires too much data and also involves very complex formulas that I don!t even dare to try using. I am trying to get away with the dimensional tolerances which I can handle easily.

 

[pdiculous963]

Mechanigenic - serious tank distortion due to a fire incident requires a detailed analysis. If it does not pass the original fabrication tolerances outlined in Table 8.5 of API 579, I recommend you enlist the service of an expert who routinely deals with explicit distortion modeling.

 

[IFRs]

You can use a laser scanning service to get all the data you need. You will probably never meet any standard of flatness or verticality. However it is essentially just a tin can and it will hold liquid with some degree of certainty. Your biggest issue is brittle fracture leading to a catastrophic outpouring of the entire tank contents. Your tank got soft and then hard again, frozen into a new shape. How much risk is there? Is this a water tank or an acid tank? Is it critical to life and limb? Is it a danger to the public if it breaks open? Is it in the middle of a residential city or out in a brown field? Even if you replaced all the deformed steel I'd still want hardness testing done on the transition areas to determine if the material is brittle. Of course a full-height hydro at MDMT is needed. What are the design vs operating temperatures, pressures, vacuums, etc? Many questions, much risk. Panic is not needed but careful and deliberate evaluation for fitness for service and how much repair is warranted before a complete replacement is in order... Of course, my thoughts only, and you get what you pay for...