eight shell manholes.

[Jay_]

Hello!
I need a professional opinion,
I am working on a large storage tank 16m dia x 14m height.
The basic design of the tank is done, but the client wants to heat up the product inside electrically and he proposed/insists on heating elements through the tank shell.
He proposed 8 shell manholes, 1 basic manhole, and 7 manholes so the heating elements can go through them, now since the 8 manholes are going to be in the same shell plate sequence, i am afraid that it will damage the integrity of the tank, the manhole dimension is 24 inches,
The first shell course thickness is 8mm as per the api650, should i increase it to 10mm or what should i do since the api650 doesn’t discuss this kind of matter?
Thank you in advance!

Detailing is a hobby,

 

[MJCronin]

Electrical heating of a large tank ??? .....

What is the desired maintenance temperature ? Will there be forced recirculation of the product to evenly distribute the heat ??

Over time, electrical heating will be very expensive to operate.....

Is natural gas service not available at the plant site ?

I am willing to bet that a gas-fired simple steam or thermal fluid system would be far cheaper to run over time. The tank should be fully insulated and configured with single or multiple serpentine coils internally.

Manholes are expensive. I am also willing to bet that a storage tank with internal coils is cheaper to purchase than one with so many manholes.

Has a study been made on these alternatives ??

MJCronin
Sr. Process Engineer

 

[IFRs]

For a tank this small you may not need seven heaters. I've seen calculations for a 36 meter tank with four electric heaters. There are electric immersion heaters 7.7M long - enough to go almost half way across. That said, each manway is reinforced and does not subtract from the tank strength. If equally spaced they will be on 6.28M centers - it would look a bit odd but I personally would not worry about the tank integrity. Be sure to use Annex M in APi 650.

 

[Jay_]

This type of tank have been requested by an a client and he was and is still insisting on electrical and 7 Nos. Of them. I will try to recommend him the cheaper case as what you said! Thank you so much for your continued professional help!

Detailing is a hobby,

 

[MJCronin]

Please keep us posted on the final design ....

Any drawings that you can share with us ???

I have always been a strong advocate of strict drug testing for new clients ......

MJCronin
Sr. Process Engineer