Ammonia storage tanks are integral part of any ammonia plant and the safety and integrity of these tanks are of utmost importance to the operating companies and to the communities near to where they are located. It is normal practice in urea fertilizer plants that surplus and unconsumed anhydrous ammonia produced by ammonia plant are stored in a suitable storage tanks. Ammonia storage tanks typically have few corrosion problems. Incoming ammonia with purity more than 99% contains maximum 0.3% water and less than 5 ppm oil. Accordingly, the only corrosive agent is the presence of water which settles on tank`s bottom because of density inequality comparing with the oil. The best way to inspect ammonia storage tank is discharging the tank completely and doing internal inspection. This paper describes the methodology for discharging, inspection, repair and putting into service of an ammonia storage tank that located at a urea fertilizer plant (KHPC) in Iran and has been inspected in 2008 after twelve years of operation.