No no no no - Rajkumar25, I admire your thirst for knowledge, but listen to your elders, especially gr2vessels and send a data sheet to a tank design and fabrication company. Once you place an order you can then request a design report which should set out how they have designed the tank including soil conditions and foundations, wind load, seismic, thermal load, number of nozzles, internal coating, internals, type of roof, rain load etc etc. In my experience tank shells are designed with virtually no spare stress allowance at all and that is why tank nozzle loadings are normally so small. Let some one who knows what he's doing do it and then read the report and calcualtions. Don't try and learn this way - you could easily make some huge errors.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way