Downstream Oil & Gas facilities operate continuously, producing hundreds of thousands of barrels a day. The cost of stopping this process and shutting down a refinery has been estimated by owners as up to €100k per hour. In order to ensure that production can always take place raw materials (commonly crude oil) are stored on site in large storage tanks. Shutting down a 40m tank has been estimated to cost €40,000 per day. As a result, keeping these tanks in service and especially avoiding unplanned outages is key to the smooth running of the refinery, so internal linings to prevent degradation of the tank are one of the many key reliability concerns of the tank operator.
Industrial petroleum storage is usually concerned with the storage of hydrocarbons in large diameter above-ground storage tanks. The tanks are most commonly made from carbon steel. Carbon steel is an ideal material as it is readily available in most areas of the world at reasonable costs. The steel also has the required properties of being easy to form and construct into a large storage tank (diameters of up to 100m (300ft) and up to 20m tall (60ft)). The hydrocarbons can be stored in the form of crude oil before it is processed or the finished petroleum products such as gasoline, diesel and jet fuel. Carbon steel is also resistant to chemical attack from these hydrocarbons (unless there are impurities such as sulphur).
Considering these properties, why does the steel require a lining? In most storage tanks there is a high likelihood of water being present – this water may have come with the crude oil as contamination or entered the tank via rainwater or humidity in the air. This water gathers underneath the hydrocarbon and can cause corrosion of the carbon steel tank. The level of water is not usually very high and is therefore in contact with the tank floor and the base of the walls. For this reason, many hydrocarbon tanks are lined base and a short way up the wall. 1m (3 ft) up the wall is commonly specified, or up to the first strake (the height of the first row of plates used to construct the tank).
If a tank contains a cargo which is aggressive to carbon steel, a lining can then be applied to all areas of the tank (floor, walls and ceiling) to protect the tank. It is often cheaper to manufacture a tank from carbon steel and protect with a lining rather than to make the tank out of a corrosion resistant alloy such as stainless steel. Jet fuel tanks are lined to protect the jet fuel, rather than to protect the steel from corrosion – they would also be completely internally lined. Complete internal lining creates a much more complex project as scaffolding is often required to prepare, apply and inspect the lining at height.
Any entry into a confined space such as a tank should have a thorough health and safety review prior to work starting. Confined space entry is a potentially dangerous activity requiring specialist support to ensure all work is carried out safely.