Oil Storage Tanks: API 650 Design and Floating-Roof Basics An oil storage tank is a welded steel vessel built to API 650 for bulk hydrocarbon storage from 100 to 150,000 m3, with floating or fixed roofs controlling vapor. External and internal coatings of epoxy or urethane defend against corrosion, backed by cathodic protection for a 30-50 year life. Engineered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel) for refinery, terminal, and depot duty. What an Oil