API 650 Storage Tank - Shell Manhole for IFR Inspection

[MOHAMMED89]

One of our client requirements is to provide a shell manhole for IFR inspection. This manhole will be place on the shell at 3m elevation from the bottom plate.

They tanks will be equipped with a Carbon Steel Full Contact Floating Roof. Class I products are considered to be stored in these tanks. The tanks are 45m diameter by 22m high.

I would like to have your expert advice on the below queries:-

1. Providing Shell manhole on IFR travel region impacts on IFR movements.
2. Product clogging on the manhole neck.
3. IFR seal damage.
4. There will be spillage of product to the top of the IFR when the IFR is below these manholes.

Thanks in advance.

 

[HTURKAK]

Refer to API 650

H.4.6.3.2 Where propeller-type mixers are used, the support legs shall provide a minimum clearance of 75 mm
(3 in.) from the underside of the internal floating roof (or roof notch) to the tip of the mixer propeller. Deviations from
that spacing for any component (mixer, nozzles, shell manholes, seals, etc.) shall be noted on the data sheet and
discussed with the Manufacturer.


I agree with your comments ... The shell manway level SHALL BE below the min. operation level of the IFR.








I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[IFRs]

The easiest and most common solution is to weld a false shell plate on stand-offs to the inside of the manway cover plate that is flush or slightly inside the shell inside. For your tank these may not need to be rolled. Leave a small gap all around for drainage. IFR seals will have no trouble with it. I see this on almost 100% of the tanks I work on. I see lots of tanks with manways or nozzles in the second ring of the tank. If you or the environmental agency responsible for your community are concerned about vapors for the times that the IFR seals are below the top of the manway while the liquid level is above the bottom of the manway you can add a wiper seal to the false shell plate. I've never run into the issue of spillage but it would not be hard to angle the manway neck so it had a slight slope to it. Note that the liquid level will be below the manway when the IFR seals are still on the false shell plate, so the only liquid will be what remains after the manway drains out under the seals, which should be a very small volumne.