Reinforced Storage Tank Linings: Advantages and Applications

Reinforced Storage Tank Linings: Advantages and Applications The interior surfaces of steel storage tanks containing corrosive liquids must be lined internally in order to prevent wear and contamination originating both from the substrate and from the liquid stored inside the steel storage tank. In this context, a considerable number of reliable organic lining systems are available, and these are typically epoxy-based lining systems used in new construction. However, these generally also require maintenance to be provided for the tank throughout their design life. Indeed, the same systems can also be used within maintenance and repair coatings. However, if signs of corrosion-rusting begin to appear on the bottom of the tank, the steel plate thins and may even develop holes within the steel. In such a case, the tank owner has two options available. The first of these is replacing the worn steel, and this option is quite costly and requires the tank to be taken out of service. The second option is the use of a reinforced lining-lining layer. There are different types of reinforced tank lining systems available, and these can significantly affect the tank's downtime. This is due to the time required for the application of the lining layer. However, ultimately this type of application will benefit the user in the long term, and furthermore, lining layers applied to tanks will not show significant signs of rusting.

Reinforced Linings

Reinforcement systems using fiberglass in new construction provide significant advantages to the tank owner, while also providing benefits in terms of both elongation and flexibility. The lining's ability to stretch and elongate increases, which also increases the lining's capacity to seal holes. If signs of rusting are present on the bottom of the tank, this situation will cause the steel thickness at the tank bottom to fall below the minimum permitted level. In such a case, applying a lining will be beneficial in terms of preventing leakage. In this way, the increased flexural strength of the lining layer allows for greater movement to occur at the tank bottom during loading and unloading operations.

If only a rigid film layer is applied without any reinforcement layer, in this case the risk of the lining cracking increases due to movement at the tank bottom.

The reinforcement process also allows the applied lining to be applied in a thicker manner, in which case the risk of cracking decreases. This additional thickness will generally lead to a longer service life being obtained for the tank, due to the longer penetration time of the lining. These characteristics will also be beneficial during tank refurbishment. This is because, after years of tank use, the steel thickness decreases and signs of rusting that virtually turn into holes are observed. The recommendations stated in the American Petroleum Institute Standard API 650, titled "welded tanks for oil storage," generally specify elements for owners of tanks storing crude oil, while API 652 specifies lining types and inspection intervals. Again in this context, API 653, titled "linings applied to the bottoms of above-ground petroleum storage tanks" and "tank inspection, repair, alteration, and reconstruction," provides recommendations for tank owners. According to API 652, a thick film layer applied as lining on the tank bottom is defined as a layer having a thickness of more than 20 mils (510 millimicrons).

Linings involving a thick film layer may also include fiberglass reinforcement in order to impart the characteristics described earlier.

API 653 states that when a fiberglass-reinforced lining layer is used in the form of a thick film layer, the inspection interval may be longer compared to the use of a thin film layer. Indeed, according to API 653, the tank service life extends beyond 20 years (the tank can provide service for more than 20 years), and in this context, lining manufacturers normally recommend the use of a reinforced fiberglass lining in the form of a thick film layer if a wide inspection interval is to be used. Increased inspection intervals reduce the frequency of the storage tank's downtime. This is generally of great importance for tank owners, since tank downtime means lost revenue for tank owners. The method chosen for applying reinforced lining systems in the form of a thick film layer in storage tanks can also affect the tank's downtime and the expected service life of the lining in the tank. Various systems related to this matter are explained in the section below.

Hand-Applied Mat Reinforcement Systems

Traditionally, creating a reinforced lining system in the form of a thick film layer involves applying the lining in several coats and then hand-laying a fiberglass layer afterward. Chopped fiberglass used in this direction has advantages in terms of being uniform (homogeneous-consistent), and no signs of weakness are observed in any way. In hydrocarbon storage tanks, a 450-gram mat (15.9 oz) per square meter is generally used together with a thick film lining layer. Since this system requires hand application, it requires intensive labor and also involves a slow application rate. After surface preparation, holes, corners, and areas where welds have been made are typically sealed using a filler-sealant putty and then covered with stripe coating. This coating is done before the application of the first lining layer. While the lining is still wet, the underlying layer is applied and then a new layer is applied afterward. The lining layer is then rolled out with a roller. This removes excess air and ensures drying. A second layer can be applied if required. After the lining has cured, sanding the surface is generally good practice. The purpose of the sanding process is to remove protruding fiber elements. Afterward, a final topcoat gel layer is applied. Again, in such a case, if protruding fibers-elements are present after the gel layer has been applied, the relevant areas are carefully reworked.