Roof air rising
Roof air rising
(OP)
I woukld like to know how to calculate the right pressure for roof air rising of a tank.
I have been involved in some but only as an observer. I would like to know if someone can help me on this issue.
I have been involved in some but only as an observer. I would like to know if someone can help me on this issue.





RE: Roof air rising
RE: Roof air rising
RE: Roof air rising
RE: Roof air rising
In https://ferrysibarani.wordpress.com/2009/10/29/air... you can see also the balancing wires in order to keep the roof in equilibrium.
Is there is any rule to calculate how many points around the tank and type of cable to be used?
RE: Roof air rising
Interesting project. Thanks for posting the pictures.
RE: Roof air rising
1. Get from the engineering drawing the roof weight + roof nozzles + other accessories. Total weight = W Ton. Let say = 200 Ton.
2. Calculate the roof surface area Just calculate the flat surface. It is not necessary to calculate the dome. The area is A M2. Let say = 1500 M2.
3. Pressure P = W / A Ton/M2. = 200 / 1500 = 0.1333 Ton/M2 To get mm H20 this number must be multiply by 1000. Hence = 0.1333 x 1000 = 133.3 mm H20
4. There is also friction between the seal and the shell. It is estimated about 13 mm H20
5. Total pressure required to raise the roof = Item 3 + Item 4 = 133.3 mm H2O + 13 mm H20 = 146.3 mm H20
6. Get the blower or fan performance chart.
7. From the blower perfomance chart we will know how much air can be produced by the blower at total pressure 146.3 mm H20
8. Estimated leakage could be estimated 70 M3/hr per M tank circumferential.
9. Net air produced by the blower : item 7 - item 8.
10. Roof raise speed could be calculated : Item 9 / Item 2.
11. How long it will take to raise the roof could be calculated = Tank height / item 10.
The blower,seal, roof balance during raising, tank roundness and plumbness are the main factors during air raising.
RE: Roof air rising
Your comment confirm my calculations.
But what about the balancing wires? How many we must use and type of cables?From I saw in the past and from the pictures it looks that they are around 9 to 11mm diam. which looks to small in order to do the equilibrium of the roof during the way up.
Could you comment on this?
RE: Roof air rising
The size of the wire rope is 1/2".
The empiric method to calculate how many wire rope we need is : tank diameter in Feet / 10. Must be even number. Let say tank diameter is 30 M or 98.4 Ft. So the number of wire rope or A-frame would be 98.4 / 10 = 9.84 round up to 10 .
We did many air raising by using the above calculation.
RE: Roof air rising
It means that balancing wires is a empiric data accordingly your experience.No maths involved.
RE: Roof air rising
RE: Roof air rising
Concerning the number of balancing wires and accordingly thumb rule of Syahar we need to have 20 wires instead of the 16 used ( diam:206´/10=~ 20).
I do not know if I am right but 16 or 20 are in the same range if we consider it as a "thumb rule" which of course depend of the experience of each company.
Am I right Syahar?
RE: Roof air rising
RE: Roof air rising
Number of A frame (wire rope) = tank diameter in FT / 10 and round up to the next even number is minimum requirement. Like your case 206' diameter you can use 22 A frame.
It is right each company has their own experience and it was proved. Off course there is a factor the easiest and economist way.
Let me give you an example. One company ask us to cut the shell on the first shell ring to make an opening for their temporary door sheet. On this temporary door sheet they will install blowers and access for the crew going to inside the tank during initial lifting. After roof air raising we have to fit up and welding and NDT that cut out shell plate. They don't like to utilize shell man way for access.
Other company they are utilizing shell man way for blowers and other shell manway for crew access. If they need 2 blowers just make tandem. Or they fabricate adaptor like Y from 24" pipe. The vertical leg of this Y connected to the shell man way. The diagonal of this Y connected to 2 blowers.
The 13 mm H20 is additional pressure need to be added for friction including pulley to wire rope.
RE: Roof air rising
RE: Roof air rising
Off Course no secret in today technology. Before only CBI the one who did roof air raising. Now many companies can perform roof air raising.
I have been involved for roof air raising preparation, pressure calculation and execution when I was young :).
I have seen and installed 2 type of seal.
1. Wire mesh on the shell side and plastic on the wire mesh side. So the wire mesh is between the shell and plastic.
2. Metallic sheet on the shell side and plastic on the metallic side. So the metallic sheet is between the shell and plastic.
RE: Roof air rising
As far I remenber, we welded some wire pins on the border of the roof in order to fix the wire mesh. This mesh was like a roll covered by plastic.
Is what you have done in your first option Syahar?
From your experience what is the avarege distance between the roof and the course? Is it the same for metalic shell and concrete shell?
RE: Roof air rising
Yes that is the 1st option.
I have seen and installed 2 type of rod to roof underside in order to fix wire mesh or metallic sheet.
1. Use weld rod 3.2 mm bend it to U shape and tack weld to the underside roof.
2. Tack weld 6 mm bolt to underside roof. Fix the wire mesh or metallic sheet and install the nut.
I have seen from almost 0 to 25 mm the gap between the roof and shell.
Unfortunately, I have never seen air raising for tank with concrete shell. But if the shell is steel with concrete on the external surface of the steel, it would be the same principle.
RE: Roof air rising
Perhaps: the corresponding system discharge results in the roof lowering without risk, or NRVs / valves etc are installed.
Obviously these hazards may already be under control in your application, though maybe they need to be considered in your application.
Regards,
Lyle
RE: Roof air rising
Nevertheless, if everything goes wrong, the roof can be goes to the original position slowly as the air escapes between shell and the roof via the wire mesh instaled. The balancing wires will keep the roof in a stable position during the descend.
RE: Roof air rising
There is a checklist to ensure all procedures had been followed. Off Course back up blower and generator shall be available. The fuel in the generators and blower rotation direction shall be checked.
I have experience when the roof is raise about 1 foot we lowering down by opening the roof manhole wider. And the roof went down slowly.
But it would be different case if the roof already raised in half way.