Aboveground storage tanks (ASTs) are designed to store fluids (known as product) such as crude oil, intermediate and refined products, chemicals, waste products, water, and water/product mixtures. The storage and types of products govern how the ASTs are constructed; important factors such as desired storage conditions, temperature and the volatility of the product influence its size, shape, and the material of construction. ASTs can be constructed out of carbon steel, alloy steel, aluminium or other metals, depending on the service requirements and the intended product being stored. However, the vast majority of ASTs is constructed out of carbon steel.
ASTs operate under no (or very little) pressure, and are often cylindrical in shape, perpendicular to the ground with flat bottoms. They are available in different shapes and configurations: vertical and horizontal; open top and closed top; flat bottom, cone bottom, and slope bottom to name a few. They have either a fixed or floating roof. Fixed roofs can be different shapes such as cone, geodesic dome, and umbrella.
The tank bottom can have varied amounts of internals including sumps, roof supports, mixers, diffusers, and heater coils; the floors can also have repair patches from previous inspections. This is an important factor when doing inspection as the condition of the floor, as well as the obstacles, can affect the percentage of floor that is covered with inspection technology and requires manoeuvring around obstacles.