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DOUBLE DECK FLOATING ROOF DETAILS
3

DOUBLE DECK FLOATING ROOF DETAILS

DOUBLE DECK FLOATING ROOF DETAILS

(OP)
Meyers only has a cross section and a vague picture. Does anyone have CAD drawings or PDF files for a DDFR showing details for tank of diameter 300 ft (say), eg pontoon layout, location of support legs, etc, any information will be appreciated. The principle of design as per appendix C of 650 is understood, however looking forward to any advise, guidance or experiences.  

RE: DOUBLE DECK FLOATING ROOF DETAILS

2
For what purpose do you need this information?  What do you need guidance and advice for?  Repairs?  Performance?  Replacement?  I have some powerpoint slides that may help visualize the basic arrangement, but you seem to already have that information.  Leg spacing and specific structural details were usually vendor specific.  Do you know the manufacturer and the date of installatioin?

RE: DOUBLE DECK FLOATING ROOF DETAILS

(OP)
Preparing a preliminary design for tender for 300ft diameter tank. This is a new one for the company I work for and seeking information as per original thread.
Thanks

RE: DOUBLE DECK FLOATING ROOF DETAILS

If you like, post your email and I will send you a set of specifications.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFRs

I am a Mechanical Engineer mainly in the design of Distillation tower and tower internals.  But can you send me you power point slides (on double deck floating roof tanks) to me on the below mentioned email id for the sake of academic interest.

Thanks in advance

my email chennaidevan1974@yahoo.com

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFR
I do appreciate , if you could send me the specification
for floating roof.

I thank you in advance.
magi_n@hotmail.com
maji@safineh.net

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFR
I do appreciate , if you could send me the specification
for floating roof.

I thank you in advance.
nkumaresan@technip-coflexip.com

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hey please send me the information ...

THX in advance.

fracontr@hotmail.com

RE: DOUBLE DECK FLOATING ROOF DETAILS


hi, i am new member.
i would like also  if you could send  those specifications for floating roof

thanks in advance

aviv @ludan.co.il

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFRs (Petroleum)
I too would be gratefull if you could send me your specs.
My e-mail address is as follows:
joseph.ortega@clough.com.au

Additionally I am at present involved with some tank issues and have the following questions:

For a floating roof tank what are the tolerances prescribed with respect to tank shell verticallity and plumbness. The API tank code and the British code BS 2654 state that the tolerance can be a max of 1 in 200 over the tank shell height. This means that at the top of a 15m tall tank the allowable tolerance would be +/- 150 mm. Would a floating roof seal be able to accomoate sucha tolerance - or am I mis reading the codes?

I was also advised of the following experience by  a colleague:
Whilst hydro-testing a tank with a floating roof tank the floating roof actually buckled (if thats the correct word to use here) due to the difference in temperature between the tank and hydrotest water. The tank was in a hot climate (ambient temp 40 degrees C +) and the shell was quite hot and the sea water was at about 20-25 degrees C.
Has anyone had similar experiences?

RE: DOUBLE DECK FLOATING ROOF DETAILS

roca -

I will be happy to send you what I have, though I fear you will be disappointed as it is just a simple drawing.  If you need more details, please ask.

Wouldn't the 1/200 criteria yield
15M = 15,000MM / 200 = 75MM tolerance, not 150MM?

I read that to say that the tank can be +75MM in one place and -75MM in another place but not +75MM and -75MM in the same vertical slice.  In that case, most seals should be OK.

API 650 section 5 gives the 1/200 criteria but also says that for tanks with internal floating roofs, apply the criteria of this section or Appendix H, whichever is more stringent.

API 650 appendix H (internal floating roofs) calls for the seal to be able to accommodate a +/- 100MM [4"] of local deviation between the floating roof and the shell.  Appendix H also calls for the columns, ladders and other appurtenances to be plumb within a tolerance of +/-75mm (+/-3in.).

API 650 appendix C (external floating roofs) is less specific, calling for seals to provide a reasonably close fit to the shell surfaces, and that an adequate but minimum number of expansion joints shall be provided.

If your tank is worse than a standard seal can deal with, ask your seal vendor for a special seal.  Allentech (sales@allentech.com) has designed floating roof seals for tanks that are more than 12" out of plumb.

I'm not surprised that steel floating roofs change shape when they are floated or when their temperature changes rapidly.  A stiffer floating roof (pontoon or double deck) would suffer much less than a "frying pan" type.  

What was the damage like?

Note that API 650 appendix H has footnotes on pan type floating roofs, one of which I have copied here:

These designs contain no closed buoyancy compartments, and are subject to flooding during sloshing or during application of fire
fighting foam/water solution. Also, without bracing of the rim being provided by the pontoon top plate, design to resist buckling of the rim must be evaluated. These types are considered a fixed roof tank (i.e., having no internal floating roof) for the siting requirements of NFPA 30.

Was this any help?

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFRs
Thanks for the reply
And your correct - 1/200 of 15m is 75 mm - I must brush up on my maths....!!
Regards
joe

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFRs,

I am new member here. I would very appreciate if you could send me a set of the spec. of external floading roof.

my email: lee@protank.com.my

Thank you and best regards,
Laikin

RE: DOUBLE DECK FLOATING ROOF DETAILS

IFR, do you have any info on a rule of thumb about the fill rates?  We have a 222" diamenter, 32" height tank with a floating roof, and we are using mechanical shoe seals.  The product is oil.

RE: DOUBLE DECK FLOATING ROOF DETAILS

The liquid velocity through the inlet pipe is generally not more than 25 feet per second, more typically 15 feet per second.  Inside the tank, the liquid velocity as it exits the inlet pipe must be reduced to 3 feet per second or less (per NFPA and API).

What is the size of your inlet pipe?

If you are concerned about the maximum speed that your floating roof can handle, start with 1 inch per minute and see where that gets you.  That would be about 34,500 barrels per hour.

RE: DOUBLE DECK FLOATING ROOF DETAILS

IFRs
Thank you for your time, the pipe size we use at the inlet and outlet is 24". I compared the rate you gave me with what we use, 25 bbl/hr, and we have a much lower rate which tells me that is not the cause of the problem.

Oil is getting on top of the floating roof, after several inspections, our best guess is that the roof is binding somewhere on the columns making the roof hang from one side and after a while it releases itself splashing the product out.  The columns have seals, but no guiding system which makes the roof free to move horizontally and to rotate.  Another observation is the probability of some friction involved with the mechanical shoe seal around the shell.

What do you think it is the problem? any suggestions/comments?

RE: DOUBLE DECK FLOATING ROOF DETAILS

Is the floating roof internal or external, aluminum or steel?  DO you know the original manufacturer?  If steel is it a pan, bulkhead, pontoon, center pontoon or double deck?  What brand perimeter seal and when was it installed?

Would you like us to visit, inspect and report?

RE: DOUBLE DECK FLOATING ROOF DETAILS

It is an internal, pan steel decks floating in contact with the product.  It was installed in the late 70's and the original perimeter seal were double wiper seals, but  we changed them to mechanical shoe seals 10 yrs ago.  I do not know the brand of the seals but they were fabricated by Tank SEal Technologies.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Well, it could be a lot of things.  We have seen many reasons for oil to be on floating roofs.  It could be an overloaded area, corrosion, deformed rim plate, leaky weld, a damaged sump, a damaged leg sleeve, seal friction, tank deformations, etc. etc. etc.  

If you have a substantial amount of oil on the roof, I'd treat it as a potential emergency and get a definitive answer and remediation plan put together ASAP.

Where and how much oil is on the roof?  When was it first noticed?  Does it go away and come back?  How active is your tank?  Is there evidence that the oil seeped up from below or ran down the rim or column wells?  Do you have pictures?

While I will continue to try to help here, this forum may not be the best method for determining your problem and avoiding a major "event".  If you would like to discuss setting up an inspection trip, send me a note at Sales@Allentech.Com and I will call you.

RE: DOUBLE DECK FLOATING ROOF DETAILS

IFR
Thank you, I'll keep you in mind.
You mentioned some reasons that I had not thought about!!  From the information we have right now, I think the seal friction is what is making the roof hang; Since the original design was changed, from wiper seals to mechanical shoe seals,making it produce more friction.

We took immediate action, and right now we are in the investigation process, but to answer your questions; most of the oil was in the foam dam area  and there were
some pools all around the floating roof.  It does not go away and come back, it accumulates. This is the 3rd time, 1997 being the 1st.  The tank is very active.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Seal friction is an odd choice, because presumably it worked fine for years, and only now (1997) is trouble?  Are you saying that each time this happens, it is cleaned up and does not repeat itself for another few years?

RE: DOUBLE DECK FLOATING ROOF DETAILS

Yes, since the mechanical shoe seals were installed, it took 3 years for oil to appear on the roof.  We cleaned it and in 3 years we faced the same problem and for the third time 2 years later.  It seems that the mechanical shoe does not let the roof find its free point or in other words does not let the roof move freely as with the wiper seals.  Does this make any sense?

RE: DOUBLE DECK FLOATING ROOF DETAILS

It almost sounds like there is a tight spot where the tank shell deforms inwards and binds the seal, holding down the floating roof but only once in a blue moon do you fill the tank to that height.  If this is the case, I'd worry about filling the tank much beyond that elevation for fear of sinking the roof.  Excess friction or seal binding can permenantly deform the outer edge of a pan floater which can (and has more than once that I know of) lead to sinking the roof.

Is it possible that these episodes involve filling the tank so high that the floater is rammed into the tank roof structure or foam deflectors?

Do you pig, blend or use mixers?

RE: DOUBLE DECK FLOATING ROOF DETAILS

We use mixers.  We do not fill the tanks TOO high to ram the floating roof to the structure.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Not sure if this is relevant, but at a refinery, we had an external floating roof tank with double wiper seals.  We bought some waxy crude (Cintas?) that left a thick film on the inside of the tank as the roof went down.  When the tank was filled back up, the upper seal wiped the oil off the wall and onto the roof.    

RE: DOUBLE DECK FLOATING ROOF DETAILS

Well, It seems I'm not the only one looking for details 'bout DDFR.

I've "figured out" some information on:

www.cbiepc.com/cbi/products/floating-rooftanks_design.html

It's just general information, So if someone of you just have more detailed informatión (I mean drawing, basis for design & sepecs) I would really apprciate to send it to me at:

jcbb47@yahoo.com.

I understand that structural design should be tied to tank dimensions, and sould comply with Appedix C of API-650. Anyway, I'm looking for basis theary about bouyancy that let me get a prelimiar dimension of the floating roof (in current stage of the the project I'm ivolved now don't let me wait for final verdor detials).

Thanks a lot everybody colleges.
Best regards.
jcbb47
BS Mechanical Engineer.

RE: DOUBLE DECK FLOATING ROOF DETAILS

A double deck floater will sink into the liquid about 5".  Does that help?  What specifically are you needing, design-wise?

RE: DOUBLE DECK FLOATING ROOF DETAILS

Thanks for your attention.

Well, actually what I need is more theory (basis, fundamentals, principies, best practices, tipical geometry, etc.) that let me make a preliminar design (dimensioning).

However, It doesn't matter roof diameter ? If volume equivalent to this 5" under liquid is displaced by roof - then mass of roof divide by this volumne will be density of roof, and this last figure should be equal or less that fluid density on tank (Even when API-650 states 0.7 SG of fluid for design) (Arquimedes).

Whatever, all what I've said is just my opinion. That's why I need more theorical basis to support my design.

Design-wies would be a good for starting.

RE: DOUBLE DECK FLOATING ROOF DETAILS

jcbb47 - The drawing I sent you has the floating weight, you can use that to estimate the displacement.  API650 has a section on the design requirements of floating roofs, but it won't help you do the engineering.  You will need an engineer for that.  Basically, it is a simple structure that needs to support the API design loads when floating or when supported on its legs.  Perhaps contacting a manufacturer will help??

RE: DOUBLE DECK FLOATING ROOF DETAILS

jay165 - I would suggest that you switch to a shoe seal with wax scrapers.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Thanks a lot.

Excellent information. What I did is just make a calculation (spreadsheet) trying to estimate desck separation (roof hieght) in order to verify bouyancy (Total weight / Total volumen <= 0.7 x 62.4 lb/cu.feet). I've compare results with estimated weight on your informatión (300' diameter, 6 pontoons, etc...!) and results were a pretty good approach (just what I needed). I'll be improving (testing & comparing results) the spreadsheet before trying to make it shareware.

Once again, Thank you very much.

RE: DOUBLE DECK FLOATING ROOF DETAILS

Georginr
Do you use pressurised nitrogen to clean your inlet and outlet pipes. This could also be the cause of the problem if cleaning is done when floating roof is in the lower portion of the tank.

RE: DOUBLE DECK FLOATING ROOF DETAILS

tkequipments

Thank you, I am going to look into that!!

RE: DOUBLE DECK FLOATING ROOF DETAILS

Hi IFR

could you please send me information/ typical specification of double deck and if possible other type of floating deck.

Thanks

RE: DOUBLE DECK FLOATING ROOF DETAILS

Well guys , I am still waiting for some information regarding how to design very roughly roof decks.

I would like to exchange some ideas, spreadshhets, Mathcad
forms about API 650 and 620 Tanks
 

RE: DOUBLE DECK FLOATING ROOF DETAILS

carthago,
I doubt anyone will share much about floating roof design.  It a skill honed while in the employ of major tank fabricators.  There are many sad stories about folks that have tried to design such items for the first time.  Usually the problems that arise are due to not understanding the importance of how construction methods factor into the the design process.  Anything you find published will be specifically vague on the really important stuff.  It's quite an interesting topic and was a pretty cool thing to learn when I worked for a major tank building firm many years ago.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

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