oil and vapour come out from roof legs 1

[mustafa2014]

Dear all,

our tanks is a floating roof double deck dim.88m.The problem is that oil with vapor come out from some legs. I have checked the pontoons and are okay.
As far as I know if there is a vapor should come out from vents. you will find attached some pics.

 

[Duwe6]

Your photos were taken looking into the sun; can not tell if the oil is from the leg or a leak at the base of the sleeve for the leg.

If it is from the leg, you are getting hot fumes condensing and dripping down the sleeve. The 'fix' would be to add a wiper seal to the sleeve. Is the oil in the tank hotter than the air temperature?

 

[mustafa2014]

Dear Duwe6,

No thing with the base of sleeve it is coming out throw legs

 

[Duwe6]

Try putting a 'wiper' collar inside the sleeves to seal off the legs. Use foam material similar to what is used for secondary seals on internal floating roofs. They should have been sealed during construction, but maybe they were not actually sealed.

 

[IFRs]

Picture 1 shows a lot of liquid, looks like too much for vapor condensing unless over a long but the oil does not look old. The whole sleeve is wet, this looks like liquid coming up out of the sleeve.

Picture 2 shows the same - same leg?

Picture 3 is different - the sleeve is not stained, this could be a small leak at the repad?

Picture 4 is similar to pictures 1 and 2

If these are the only legs that have this issue, are they above the fill line and could the fill condition be turbulent enough to splash liquid up through these sleeves? If not the liquid fill, are you pigging into the tank, which could cause similar turbulence?

 

[mustafa2014]

Dear Duwe6,
Is that wiper as a seal accepted by API 650 BECUSE OUR TANK IS API650>??

Dear IFRs:
your answer really interesting we do some times pigging in the pipeline to the tank. I have attached new photos they may give you all complete picture.

Cold you explain to me more what do you mean by "are they above the fill line and could the fill condition be turbulent enough to splash liquid up through these sleeves?"

is there any relation if the current crude in the tank has lower or higher API??

 

[IFRs]

API 650 does not regulate emissions. You need to review your EPA permit to see if controls on the legs are required.

To the extent that thinner liquid can flow easier, or splash through thinn places, yes, the API of the liquid is a factor.

If you have a liquid only diffuser and you bring gas into the tank through that line, there may be turbulence, it can be dramatic and it can create enough action to bring liquid up through sleeves. If the legs in question are in one area omly, see if they are in line with or above the fill pipe.

 

[IFRs]

Can you make a quick sketch showing in plan all the legs, and those that are leaking, we need to look for patterns. Include the shell nozzles and internal piping locations, rolling laddre, gauge poles and other penetrations. What type of rim seals are there? Also, did this oil just appear recently, over a long time, after a severe weather event, after a pigging operation, after a very high fill, after the deck was landed and the tank refilledtc. Gather as much data as you can, even if it does not seem relevant (you never know what is relevant), etc.

 

[mustafa2014]

Dear IFRs,

I will pass to you all information you requested within today. Please keep in tuch

 

[mustafa2014]

Dear IFRs,

Please find attachment Nr.1 the sketch for the the tank I will send you the other DWGS

 

[mustafa2014]

ATTACHMENT 2 SEAL SYSTEM

 

[mustafa2014]

Attachment 3 Tank DWG

please note that our tank is just 7 years old. this thing happened some days ago , the weather was quit hot and MAy ( I am not sure) after the deck was landed and the tank refilled.

 

[IFRs]

Sorry for the random nature of this paragraph.

This looks like a typical external double deck floating roof with a pantograph shoe seal and secondary compression plate seal. These types seldom have buoyancy or strength issues unless there was serious erection quality issues.

If the roof drains were closed and deck was overloaded with water from a storm, I would think that more legs would show oil and you would have widespread staining.

Since it is a double deck style, bad welds around the leg sleeves are an unlikely issue and since only a few legs are showing this, severely leaking compartments are not likely either.

It is hard for it to be vapors since the underside of the floating roof is normally in full contact with the liquid and while there could be some, you'd need a lot to condense into that much liquid, particularly in the hot summer months.

The sleeves are very tall and getting the floating roof that low in the liquid is quite unlikely.

I'm liking the idea that there was a turbulent fill event that splashed liquid up through these few sleeves, perhaps pigging or butane blending, etc. Bear in mind that getting liquid up through these small spaces in the leg sleeves is not easy, it would have to be quite turbulent.

If the rolling ladder froze up and held the floating roof down, I'd expect to see more and widespread liquid staining in other areas.

Question: do you have fill and suction pipe drawings?

Question: were the legs changed from low to high and position and back recently? If you pull a leg up, it may hold some liquid which might spill out.

Question: please help me understand what items 21 on page 9 of 12 of the tank drawings set are used for ( spherical caps )

Question: what does the floating roof company say?

Question: Were these legs always pinned in the low position or could the pins have been missing allowing the legs to telescope up and down as the floater came down to low liquid level, possibly bringing liquid up through, then they were "found" and "fixed"?

It's hard to find the cause without being there, getting a complete operational history, talking to those on site, etc. I'm basically shooting in the dark hoping to hit something. I am likely way off base and it will turn out to be something completely different.

Good luck, keep your ears and eyes open and let us know what happens!

 

[mustafa2014]

Question: do you have fill and suction pipe drawings? I will check

Question: were the legs changed from low to high and position and back recently? If you pull a leg up, it may hold some liquid which might spill out. [pre]no but even if this happen you a mouse hole in the bottom of the leg unless is blogged by sludge

Question: please help me understand what items 21 on page 9 of 12 of the tank drawings set are used for ( spherical caps )

Question: what does the floating roof company say? we have not called them yet, and you can not trust them especially if there is a mistake in design of the tank. [pre][/pre]

Question: Were these legs always pinned in the low position or could the pins have been missing allowing the legs to telescope up and down as the floater came down to low liquid level, possibly bringing liquid up through, then they were "found" and "fixed"? no one touch the legs for seven years[pre][/pre]

 

[mustafa2014]

Question: please help me understand what items 21 on page 9 of 12 of the tank drawings set are used for ( spherical caps)....I think that is the bottom end of the leg where there is a mouse hole

 

[LittleInch]

Mustafa - that is a big tank. My guess is that if the roof was grounded or got very close to the bottom, those legs may be hitting some debris or flex in the tank floor and therefore slightly bending the roof. Depending on how fast you filled the tank??, it may not simply have been possible for all the air / vapour to travel to the vent before finding a way out via the leg holes. The upstands seem quite low - if you want to fix it I would simply increase the length of the outer sleeve, maybe even using a screwed connector to avoid welding in the tank to increase the height by say 500mm

It doesn't look like it is a constant thing, but a one off event caused by air / vapour sliding around the top of the fluid / tank. I couldn't actually tell where your vents were or how many as the pdf drawings in red and yellow were very difficult to read.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[IFRs]

LittleInch - I printed his documents to PDF using "make all color black" then they were readable. Making a pdf out of a pdf, as it were. Bending the roof might leave evidence such as wrinkling, etc. The thickness of the roof at the legs is substantial - it would have to bend a long way. Some legs with puddles are close to the rim, we did not see evidence of the rim bending...

To increase the sleeve length, we would have to block the pin holes and make longer legs.

Mustafa - the drawings show mouse holes and spherical caps - you don't use both. Probably not a big deal, I was just curious.

There are rubber devices available that can be retrofitted on the legs to reduce emissions, these will also serve to minimize splash up through.

If this was a one-time event, clean it off, monitor operations and observe the deck for more oil.

 

[LittleInch]

On such a big roof, the bending wouldn't have to be very much or even just flexed when sitting on the legs to corner a small amount of vapour in a spot where it wouldn't travel to the the vents. It's clear the oil leakage is just a fairly small spurt, so I think trying to solve it remotely and without 50% of the information especially the operations immediately preceding it is a bit of a wild goose chase. I was talking about just extending the sleeve by either screwing on a connector - there is some room between the pin and the top, or welding on an extra sleeve, or simply pushing on a plastic tube. There is no pressure involved here, just a bit more head to stop any fluid spurting out.

If the tank has been there 7 years and it's only happened once then it's not a systemic problem and might not happen again. It probably hasn't been cleaned or entered since going into service so who knows what the inside floor now looks like.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[mustafa2014]

Dears
I am really appreciated your reply.

IFRs,
Could you please send me more information regarding rubber devices

 

[IFRs]

Try google and "leg sock" or "leg seal"

I was thinking of thest

http://ateco.com.tr/product/emission_control_device/leg_seal.html

but from the original manufacturer, whose name eludes me right now.