API 620 high compression area requirement

[BZ29]

Hello experts:

I have sometime came across large API 620 tanks having significant design pressure, which requires a very large compression area. i tried using all of the available Compression-ring Juncture options, but still there used to be a big difference.
eg. presently i have following tank

Dia: 24m
Height: 20m
Dome roof
Design Pressure: 65kpa (cannot be reduced)
Design temperature: 80 degree Celsius

required compression area is near about 144 sq.in / 93000 sq.mm, while the maximum i was able to provide is 43 sq.in / 28000 sq.mm.

One of the senior engineer asked to add welded rafters and girders to dome roof for estimation, but hesitant to share any information, whether how is he calculating it or might be he is just estimating by experience.

Is there any calculation for this kind of approach or is there any other better way to solve this?

 

[Geoff13]

With that large required area I'm going to guess your roof has R/D close to 1.2. There should be a notable reduction is required area by going to R/D = 0.8.

My gut says you should be able to get more area than you say with Figure 5-6 Details (e) thru (g).

I don't agree with the idea from your senior engineer. The compression bar area is independent of whether the roof is a self-supporting dome, or if it's supported by a bunch of rafters and girders.

 

[BZ29]

Yes, i was using R/D as 1.2. Now i have changed it to 0.8 which reduced the required area to half. But actual issue is, that software was not calculating the compression area correctly as per the selected detail. Now i have calculated it manually and it was significant increase in area. So the issue was resolved.

Thank you for your guidance Geoff13

 

[Geoff13]

Hopefully you will send your calculation documenting an error to the software company for them to correct.

 

[BZ29]

Yes, sure. I will reconfirm it again before sending them an email.