Roof seal for Floating Roof Storage Tanks 3

[mylexicon]

What are the pros and cons of using "Tube seal" vs. "Mechanical seal" or vice versa to seal off the gap between the roof and shell of an Atmospheric Storage Tank?
I work on this project which involves erection of 500,000 BBL Atmospheric Storage Tanks for storing Heavy Crude Oil and the supplier/fabricator is quoting his offer considering the tube seal option. The Tanks are 100 meters in diameter and the roofs are of double deck type.
To give you a view of the site; it is located in a highly saline, hot & humid environment with ambient temperatures ranging between 15 to 45 degrees celcius throughout the year, and rainy seasons are parctically non-existent.
How do these two types compare in operation, service life, maintenance?
Your recommendations are highly appreciated.

regards,

drno

 

[BigInch]

Take care. When it rains it RAINS!

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[IFRs]

Tube seals test better in the lab but wear out quickly and become hazardous waste. One small burr on the tank shell and the tube seal is torn, then it soaks up product and pulls away from the shell. Mechanical seals are less efficient in the lab but last longer and are more resistant to shell burrs. Insist on all stainless steel construction. In either case, buy materials and installation from a well known and experienced vendor who will measure and examine the tank prior to installation and has the financial strength to stand by their work.

 

[mylexicon]

BigInch
If you already know this, then ignore this thread.
However, if this tank was to be erected in a rainy climate we certainly would have to worry about rain.
Floating roofs usually come with roof drainage systems which are gravity drained through hoses hanging off the roof deck and submerged inside the tank contents. Subsequently lead through drainage piping at the bottom of the tank to a closed drainage system.

regards,

drno

 

[bingopin]

I work in a chemical plant and deal with tanks smaller than refinery tanks. We do not measure the performance of the seals, rather, everything is based on visual inspection. Once a year you don breathing air look through the top hatch. Any anomalies seen in the seal require the tank to be taken out of service and the seal repaired or more likely replaced. My experience matches IFRs information. Log or tube seals just do not do not hold up well. I've seen them fail after less than one year of service on rundown tanks that cycle 2x in 24 hours. A mechanical shoe seal will give much longer service life. Typically, shoe seals have a pantograph configuration pushing the shoe against the tank wall along with an additional wiper seal below the shoe. We no longer install log seals at all.

 

[mylexicon]

IFRs
How exactly do you mean when saying:
1)"Tube seals test better in the lab..."
2)"Mechanical seals are less efficient in the lab..."

Do you mind elaborating a bit on the above statements? What kind of tests do they perform on these 2 types of seals that render these results? If it is too much trouble describing the tests, perhaps you can refer me to the article, source, or publication where this was discussed.

many thanks,

drno

 

[MJCronin]

lexi..

This topic does not really belong in this forum..

However, it has been discussed in:

http://www.ast-forum.com

-MJC

 

[mylexicon]

MJCronin

Thanks a bunch. great site.