TANK vacuum calculations seem to be working in a stand alone mode, isolated from the rest of the modules. Material properties and thicknesses are to be input which can easily be picked up from the General Tank Data Input. Also the value of vacuum input here is ignored in the Wind and intermediate stiffeners calculations. As per note in 5.9.7.1 Code equations assume an inherent vacuum of 25mm WC and anything greater is to be factored in so as to reduce the maximum unstiffened shell height H1. True TANK gives independent calculations for Vacuum as per Appendix V, but with the code being obscure in this area of overlap, both wind and vacuum results need to be satisfied.The incidence of additional vacuum has to be taken cognizance of in the Chaper 5 calculations.

Regards,

So we have to do the most obvious thing - otherwise we're constantly justifying the operation of the software and/or changing the software to satisfy the most current suggestion.

Send your suggested computations in to TechSupport and we'll take a look at your interpretation of the Code.

The intent of the code is to reduce the maximum unstiffened height due to incidence of pressure/vacuum greater than its considered value in its basic equation.

API Basic Pressure = 1.72kPa
For 50mm WC Vac ie additional Vac of 25mmWC = 1.96kPa

Ratio = .878

Hence if Max H1 works out to 5mts, Modified Max H1 due to higher Vacuum would be 5x.878 = 4.39mtrs

A value which satisfies both Section 5 as well as Appendix V would have to be considered.

Regards