Tank Restoring 2

[MechEngOI]

I would like to know your opinions or recomendations of the following case:


A 70 ft diameter by 32 ft Height API 650 Oil Storage Tank builded in 1995 suffered overpressure and crack on the roof to shell joint. After an ispection the damage reported was:

-6 out of 25 Shell plates had distortions. (See attatched picture)
- Most of the self supported roof U beams fell off or were deformed, approximately 70 % of its diameter were damaged and the main central column showed displacement.
- High level of Corrosion were detected on the annular ring
- Instrumentation were found OK ( Opening vent , relief valves, level meter)



After Reviewing API 650 , API 653 and API 2000.


The decision:

-Replacement of the entire roof and supports, includes: U beams, roof plates , central column.
-Replacement of the 6 distorted shell plates.
-Reinforcement of the annular ring and a medium or small percentage (will be determine by MPI an LP) of the remaing floor plates and welds.
-Shell plates are going to be cut on the weld since the whole plate is replaced
-Openings on the existing shell plates and roof plates are going to be build from scratch following AS-BUILT Drawings.



Note:

-Replacemente and repairs include Testing , calibrating , Maintenance, painting and procedures following the AS-BUILT design and drawings.
-Currently the tank is working with a very low level just enough to avoid pumps from cavitate

 

[JStephen]

I think that the best approach would be to inspect the tank very thoroughly (inside and out), then get prices both to repair it and to replace it altogether. Try to get prices from companies specializing in repairs and from those specializing in new tank erection; they are not necessarily the same.

If you don't have a thorough inspection, it can be very easy to discover additional work that needs to be done when repair work is already underway.

The tanks I've seen that were damaged by overpressure had damage all around the top ring, but not down lower in the shell as shown on the diagram. On the other hand, I've seen tanks with wind damage on one side like that.

On the distorted plates, I don't know that there's any reason to replace a whole plate. It would be just as easy to cut in the middle of a plate as to cut at a seam.

 

[MechEngOI]

Hi JStephen

I would try to check prices and compare repairing vs replacing where it could be done.

A more extensive inspection can be done but the idea is to approach the best solution with the previous inspection

I will attatch some pictures of the shell plates , I'm not sure if they can be repairing whitout the material loosing their properties (A 36).

Thanks Again for your tips and recommendations

 

[MechEngOI]

Here is another picture of the shell plates

 

[Duwe6]

RE: wrinkled plates, only the creased ones require replacement. You will be amazed how many dents a good 'tankie' can pull out, thus salvaging the plate, the welds, and not requireing any X-ray 'RT' or ultrasound 'UT'.

Three more thoughts;

Avoid RT in favor of UT; the results are quicker and the testing can be done w/o shutting down the work.

Involve an API-653 certified Inspector before the repairs start, to check your proposed work and testing. jStephen'srecommended full survey and evaluation should be done by an API-653, so it would be best to get one ASAP.

Lay the new roof plates [cheaper to install new than salvage old ones, usually] last, to allow the tankies to work in daylight and let their welding fumes to escape w/o powered ventilation. Happy workers that can see well are much more productive.

 

[MechEngOI]

Thanks for your tips Duwe6. I was not considering about pulling out dents thinking on what you said on the roof plates, that is cheaper to install new than salvage old ones. Why is it different ?

 

[Duwe6]

The roof plates are harder to work with. Shell plates can be pushed using the far side of the tank, and pulled in using temporary lugs on the floor/far wall. Can be pulled out with a chain hoist anchored to the contractors work truck.

With a roof, ask the tankies which they can do cheaper, and how much of a positive effect there will be having the roof off during the shell work. You won't save money by buying a new roof, but a cost analysis of the whole job may show that a new roof is "free". It takes a lot of work to fix a roof.

 

[MechEngOI]

Very Helpfull Tips Thanks Duwe6

 

[unclesyd]

Aside from all the very good advice given above a little more information would help like what is the process fluid the tank sees, can it be cleaned for entry and welding, how long can you be offline, seam welding details, etc.
As stated above a through inspection is paramount and while this is going on I would have a representative from a tank company close by as he can quickly tell you what are possible repair possibilities. make sure you get your jurisdictional authorities involved early on.
From your pictures it looks like the tank was exposed to a vacuum it was not designed for.

PS:
If the tank representative isn't a grizzly old veteran and doesn't give out ball caps or jackets look for a new one.

 

[MJCronin]

Perhaps it would also be a good time to review the original tank design pressure, the correct tank vent sizing and the operation of the tank/system to ensure that this does not happen again...

I am curious about the original cause of the over/underperssure that caused this destruction.