API 650 design using TANK software

[oldisgold981]

Hello
i am using TANK software by heaxagon (formerly intergraph TANK) for calculation of API 650 Tanks.
tank is 7m diameter and 7.2 meter height. self supported cone roof with internal pressure of 0.25Kpa.
in the roof calculation it is giving warning that "design pressure is greater than Pmax " as per F4.2.
but in my opinion Annex F is not applicable as the weight of the roof plate ( t = 12 mm ) is more than the uplift caused by internal pressure.
should i just ignore this message as in my opinion there is no need for Annex F calculation or am i missing something ?

 

[Geoff13]

What is your roof corrosion allowance? As noted at the top of your screenshot the corroded weight is used.

I would NEVER recommend ignoring error or warning messages. What you should do is understand what Code rules have made TANK feel Annex F is applicable. Once you understand this you will either understand why F.4.2 applies, or correct the input to TANK that caused it to use Annex F. If you continue to feel that Annex F is not required then you should contact Hexagon so they can review your tank model and correct TANK if that's required.

Also, when you send your calculations to the Purchaser how are you going to explain "I just ignored this warning because someone on EngTips said I could."?

 

[oldisgold981]

Thank you Geoff13 for your response.
Roof corossion allowance is 3mm.
I posted here may be someone else have also encountered the same problem. May be in the new version they have fixed the issue. As per my understanding i dont see the need for performing Annex F calculations as the pressure is 0.25 KPa and the uplift is less than the roof weight.

 

[Geoff13]

I have never used TANKS, but I would hope that somewhere earlier in the output it notes it's going to use Annex F and why.

 

[JStephen]

F.4.2 is to determine if the pressure is okay based on an unanchored tank. If you have already specified, or the program has already determined, that the tank is to be anchored, F.4.2 does not apply, and should not have been used in the first place.
Presumably, if the allowable pressure is calculating zero here, then anchors were required under 5.11.2.1.

 

[oldisgold981]

Thank you @JStephen for your response

moments for 5.11.2.1 are as follows all conditions along with sliding are ok
Mw = 136013 Nm
MPi= 33674 Nm
MDL =157834 Nm
MDLR =115810 Nm
Mf =275181 Nm
MWs =60794 Nm


as per 5.11.2.1 no anchors were required.
below are the tanks complete calculations for roof evaluation.

 

[Mindaugas_Kukis]

Hello,


got this problem before till I get what it is about. It's in roof to shell junction cross section. First enter info in foto below then click 3 dots and, if the area is enough you will get max pressure bigger than entered and this error will dissapear

 

[oldisgold981]

Thank you mindaugas for your reply. i have already done that the compression area is not the issue . its enough i am still having the same error.

 

[zelgar]

Looking at the formulae and the results, it appears that the reason for the error is that you're getting a negative pressure for the equations: Maximum Pressure per F.4.2 Equation 1 and Maximum Pressure per F.4.2 Equation 2. In both of these equations you're subtracting RMW which has a value of 1203820. Looking at API 650 RMW (Mw) is the overturning moment about the shell-to-bottom joint from horizontal plus vertical wind pressure.