When a chemical storage tank fails, the costs can be significant to the business or government entity. Regulatory concerns, environmental cleanup, lawsuits from property damage, and injury to employees are costly exposures.
This article will look at the reasons why chemical storage tanks fail.
Steel Storage Tank Failure
Chemical storage tanks constructed from stainless steel are subject to failure in two main areas.
- Steel chemical storage tanks are fabricated with sheets of metal. The sheets are welded together to form the tank. The weld seams are where leaks can occur when the weld quality is poor.
- In addition, chemical attack can break down the integrity of the metal itself. For example, sulfuric acid can become very aggressive if concentrations are below 93%, resulting in acid etching. Acid etching reduces the structural integrity of the stainless steel tank. The chemical concentrations can then become altered due to improper venting, increased humidity, or different concentrations from the supplier. Visual, x-ray, or dye inspections are recommended to detect leaks in steel chemical storage tanks, paying particular attention to weld seams.
Fiberglass Storage Tanks
Fiberglass is a multi-layer composite construction with an outer layer of resin. Once the resin layer is compromised with a crack, it typically impacts and compromises the structural filament layer of the tank. Chemicals will tend to find the cracks and expand the leak. In addition, the leak can develop into a catastrophic failure of the tank.
Polyethylene Chemical Storage Tanks
There are two types of construction of polyethylene both create storage tanks are free of welds or seams:
- Linear (non-molecular bonded)
- Cross-linked (molecular bonded)
Linear poly storage tanks have the potential to come apart at the polymer chains. This is due to the lack of molecular bonding and reliance on static attraction to gain its strength known as van der Waals force. Caution must be exercised when selecting this material, as it is designed to be a general purpose material used in many applications from toys to containers. When designing this type of tank it is very important to consider how susceptible it is to crack propagation. The installation of a fitting creates an environment that can lead to cracks, which is why fitting areas need to be inspected for cracks with linear polyethylene plastic tanks. A linear poly plastic tank under pressure or even static load can experience a catastrophic failure, similar to what happens when dropping a gallon of milk that splits apart.
Cross-linked polyethylene chemical storage tanks are covalently bonded or molecular bonded. They are extremely resistant to stress cracks. Just like all chemical storage tanks, special attention must be paid to the mechanical fitting on a cross-linked poly chemcial storage tank. If stress occurs due to over pressurization or hard piping, spider or micro cracks will form. The advantage of cross-linked polyethylene is that it will not catastrophly fail. It will, however, require you to cut the compromised section out of the tank and install a larger fitting or replace the tank. While this may be more costly, the risk of large cracks and catastrophic failure of cross-linked polyethylene storage tanks is minimal.
Storing chemicals safely and avoiding the expense of a chemical leak or catastrophic failure of a storage tank is always a concern. Carefully consider the materials and construction of the storage tank and the chemicals which are being stored.