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Fixed Roof Tank

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#1 sudheer


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Posted 27 June 2007 - 05:34 AM

Dear Forum
Can I know various reasons for failure of fixed roof tank which is operating for fuel oil service. It would be better if one can provide the symptoms to look out during such failure.

#2 Art Montemayor

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Posted 27 June 2007 - 06:20 AM


Please be specific. What, exactly, are "such" failures.

You've told us you have a problem - but you failed to tell what the problem is.

#3 sudheer


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Posted 27 June 2007 - 10:43 PM

Sorry for writing in short. Let me explain in detail
What can be reasons for failure of fuel oil tank when its level is low (10%), temperature is around 50°C, No pump in or pump out. Last pumpout from the tank was around 48 hours back. The failure mode is sinking of roof inside the tank.

#4 Art Montemayor

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Posted 28 June 2007 - 03:06 PM

Are you saying that your fixed-roof, fuel oil storage tank has suffered a collapsed roof while it was in operation with a low liquid inventory, a temperature of 50 °C and no inventory changes taking place? You also add that the roof collapsed 2 days after the last oil pump out. Is this a valid interpretation?

If the above is correct, then the first thing I would suspect is that the fixed roof failed due to corrosion. It just rusted from the inside out. Of course I’m assuming that the tank did not operate under a gas blanket system – either natural gas or nitrogen. Without specific information, that would be my first guess.

#5 Adriaan


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Posted 29 June 2007 - 09:43 PM

Mmmmhmmmmm ....

the - to me anyway - obvious answer would be that the tank cooled, causing a partial vacuum in the tank. Did it rain in those two days? (rain causes rapid cooling)

With a 50 °C temperature and an almost empty tank that would mean a significant enough pressure drop (depending on the environmental temperature) IF said tank does not have a vent / vacuum breaker / blanketing system (or said system were clogged up, something sadly not all that unusual in oiltanks as the vapours - in my experience - can make NASTY condensates [even crystalline ones]).

Tanks can withstand some OVER pressure but it only takes a relatively small UNDER pressure for a tank to buckle. As the (round) wall is stronger than the (flat or conical) roof deformation of the roof would be expected (buckling). For the roof to actually SINK in, however, I would agree with Art Montemayor that there must have been structural damage to the tank to begin with. I would not, however, expect this to be caused by rusting from the inside out (given that it is an oil tank) but rather from the outside in (many a time have I seen tanks (conical roofed ones) with the 'catch board' edge along the roof fouled and therefore retaining (rain) water there, causing the tank to rust.


check tanks regularly to see if rainwater runs off unimpeded, check appendages (vents etcetera) to see if they aren't clogged up and finally check the state of the tank insulation (if rainwater seeps in the temperature will drop sharply)

#6 proinwv


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Posted 05 July 2007 - 10:31 AM

Hi Guys,

From reading all the previous I suspect that the information is incomplete or that more has occurred to cause the failure than was thought.

While all of the comments have validity it seems that the "facts" need to be reviewed and re investigated.

#7 indy


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Posted 24 July 2007 - 09:30 AM

without much information from the poster, for me, the collapse of the tank was due to a vacuum peak




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