Dome roof thickness

[Dream91]

I have one tank with 5 m dia & dome roof.

Roof minimum thickness is 18 mm .

How I can reduce the thickness ? is it advisable to add rafters to reduce the thickness ?

 

[JStephen]

If this is an API-650 tank, the thickness on a 5m dome roof would normally come out the minimum thickness- 5 mm or whatever it is.
If you're coming up with 18mm, I would suspect an error somewhere, possibly applied load off by a factor of 10 or something like that.
If the load really is very very high (design vacuum or very high snow load), then using the minimum allowable roof radius will reduce thickness.