This study, application of reverse engineering concepts to a compressed air tank, leads us to calculate tank shell in static and fatigue, by using of formulas and software. Furthermore, unsatisfying results from basics formulas of cylindrical and spherical shell, lead us to use standards methods: ASME code and Indian standards to design torispherical head tank. Then obtained results showed that, design a tank with torispherical head by ASME code is more safety than Indian standards. It was proved that, Indian standards is the most economic, because the life consumption of tank is only 3,8 % against 0,73% by ASME code. However, those two methods showed that, the stress in knuckle is superior to admissible strength in case of testing pressure (design pressure), but inferior with maximum operating pressure. This explains the using of ring to reinforce the knuckle in some case.