Dear Sir,

I was checking one of our vendors calculations for a tank. They have used TANK ver. 2.50 software.
Although 1.5 mm corrosion allowance has been specified, the resisting weight (and therefore the resisting moment)has been calculated considering the weight of shell, roof plate, roof structure and columns, all in uncorroded condition.
in my opinion it is not in accordance with para. 3.11.2 of API std.
Does the software calculate the resisting weight for uncorroded condition or our vendor has made a mistake in entering the input data?

Regards

TANK computes the wind resisiting moment (for Section 3.11) based on corroded shell weight.

One thing some people miss in Section 3.11 is to deduct the uplift from any internal pressure.

What do you mean by uplift??

Is it the uplift from INTERNAL PRESSURE ?

Or

Is it the up-lift from the vertical outwaard pressure on the roof created by WIND ?

Yes, uplift due to internal pressure. See the definition of "W" in Section 3.11.2.

I understand that this is in API 650..

But why not/ and what is the idea behind of NOT including the weight of the roof in the up-lift equilibrium of the tank.

Because in the assumption that there is no roof then:
1/- There is no effect of the internal pressure on the roof.
2/-The up-lift forcedue to wind on the roof is zero.

Well I am lost!!

I can't help you with "why a certain item is in (or not in) the code".

However, Addendum 4 which most people just received does add uplift force due to wind. This will be in TANK 3.00. (I have no release date for 3.00 yet, I just started working with Addendum 4.)