#6 Fuel oil tank repairs

[Paperpete]

I am not sure that this is the right forum for this question. If any of you feel that there is a better one please respond and let me know.
I have a problem with a 70,000 gal oil tank. The sheetmetal roof is corroded. Actually several small holes has developed (approx. 1/8" diameter). When the top manhole was opened and I looked with a light and a mirror I could see that the structural members holding up the pitched sheet metal roof appeared to be in great shape. The walls of the tank also appeared to be in good condition. The problem I am facing is how to replace or repair the roof. I have recieved a quote for approximately $18,000 just to clean it!. I dont think that welding on top of this tank is a good idea unless it is completetly cleaned out. It may be possible to put a new sheetmetal on top of the old and fasten it down in some other way but welding.Could anyone give me some guidance or recommend a reputable company that could take on a job like this in the North East (Mass).
Thanks

 

[IFRs]

If the corrosion is from the uderside, then covering it may not be in your best interests.

If it is topside corrosion, you could add an aluminmum dome roof over the top of it, I think without taking the tank out of service.

 

[aybee]

you are correct, welding NOT a good idea unless the tank is cleaned out then Gas free ie no explosive vapour level...not cheap to do, Now I dont want to worry you but if the roof is holed and its probably come from the inside due to condensed water vapour then your worry is the connection between the roof support beams and the roof. You say the beams look ok ..if you are sure then you can concentrate on the roof only otherwise - open up, clean out scaffold up have a good look...better to spend the money than find out in year that the roof fell in.
If the beams are good I would do a UT survey on the roof to make sure that the rest of it is not about to rupture into 5000000 holes starting near the acess platform to make sure the UT guys doint fall thriugh the roof...may you are confident in this aspect as you have been over to the manhole.
if its structurally sound then you can consider patching it
with epoxy mastic/steel plate or spray over with polyurethan compound but once you do that you can no longer check it from the outside....more later

 

[aybee]

sorry about the last message..done in a hurry during lunch break. If you cover the roof you cant check on its conditon afterwards, so you will need to be sure you can live with that. You could fit an aluminium geodesic type roof over the top, not cheap though. I suspect that you have an API650 tank with a 3/16" roof which does not have much corrosion allowance and the underside is corroding more than you realise, there will be a patch under the 1/8" hole which has lost thickness worst part being where the hole is.If it gets bad enough you will get rust into the fuel oil system.
alternative to steel/epoxy patches is a plastic polyspray coating which will last you until you can plan/budget for a new roof..all these are temporary measures. you dont say how old the tank is, maybe its past its use-by date. I would do a UT scan about the bottom strake/floor plate area as well in case you got a water bottom you dont know about

 

[taylorg]

Paperpete,

A couple of questions:
What kind of fuel are you storing? (does it require heating to enable pumping etc?)
How old is the tank?
Do you have a 2nd tank you can use if the one you refer to is taken out of action for repairs/replacement.

Looks to me like you need to do some basic sums of the costs of repair versus replacement looking at the long term picture.
The cleaning cost you quoted seems high unless its a hazardous liquid.
Website below will give you a rough idea of the cost of a new tank.

http://www.mc-integ.com

Hope that helps!
GT

 

[Paperpete]

Thank you Taylorg.
To ansver your questions. The fuel is #6 fueloil, it does require heating before it can be pumped. The oil in the tank is kept hot with an internal steam heater and with an externernal heatexchanger (recirc loop).
The tank is about 40 years old.
I have no second tank to draw from. The oil supports an around the clock manufacturing plant with only one week a year outage.
The repair of the roof itself would be less then $20,000 but with cleaning and getting a second temporary tank (contained) and disposing of the cleaning debris etc. the total bill will probably be $80,000 or more. Hard to justify in our slow business. Looking for alternatives

 

[TBP]

Can you bring a railcar or two of oil in? They have internal steam coils, and you could rig a temporary supply from them, while the tank is being claned/inspected/repaired. As posted above, I'd check the tank floor very carefully as well.

Is the internal heating coil original? If the tank is opened, I'd check it too.

 

[Paperpete]

No railcar access, unfortunately. The heating coil use to be replaced every two years. Five years ago I finally replaced it with a stainless coil and have had no problems since. Once a year I have the steam/condensate side cleaned. One contractor suggested placing new pieces of sheetmetal in tar "gluing" them on top of the old roof. This may help me get by for a year or two until I can come up with a repair plan and secure capital for it.

 

[taylorg]

I would suspect that the tank is past its useful life, 40 years is pretty good going! (you must be somewhere dry and have an insulated tank?).

US$80,000 should get you a whole new tank complete with insulation and steam coil!

The most important thing here is to get the tank surveyed at the earliest opportunity, for the sake of safety if nothing else. If it turns out the roof is the only problem then you can look at a long term repair, either a non-welded solution such as those mentioned by aybee, or a whole new roof if possible.
However, I suspect that the survey/inspection will show that you need a new tank. This would mean a cheap temporary repair to the existing tank whilst you get the capital (ouch!) and construct a new one (do you have space for a new tank?). It would also mean that you don't have to take the whole plant down. Once constructed, you could use the old tank as a back-up until you secure yet more cash to dismantle it.

Let us know what you decide and how you get on!

 

[taylorg]

Forgot to ask an important question - what is the remaining life expectancy of the main plant? This could determine if a long term solution is worthwhile...

 

[zqew05]

Economy is down right now so I guess if you guys go for just fastening a new roof vice welding it, use a product called Silkaflex for adhesive/sealant function. We used on military hovercrafts to protect our fuel tanks from constant sea spray