As per API 650 Cl.3.6.1.5, no shell course shall be thinner than the above it. In addition, API 650 Fig. F-2, detail-i(Appendix-F), allows higher thick plates above the lower thick shell course for stiffener ring of roof. Considering this we are using 1200 mm width and 16 mm thick top course over 8 mm thick shell course. This also helped us to avoid one number of circumferential joint. But we are unable to input this in TANK software. Since, it is given an error as follow: "the specified thickness of current shell course is thinner than the course above it". Please advise us whether we can use this configuration.

It is not necessary to "double post".