IMPORTANT CONSIDERATIONS TO SAFELY STORE AND HANDLE CORROSIVE ACIDS AND BASES IN INDUSTRIAL PLANTS
When specifying vessel and piping materials for handling and storing corrosive acids and bases, many lean on their educational training, personal experience and familiarity with products. If a carbon steel, stainless steel or fiberglass-reinforced plastic (FRP) vessel was specified for a similar situation in the past, the plant or operations manager is likely to choose it again, regardless of the expected service life.
Relying on personal experience can be valuable, unless there is definitively a better option available. Considering alternatives and the reliability they have delivered in existing applications can help plants recognize greater performance, a longer service life and lower lifecycle costs.
To accurately evaluate materials, key comparison factors must first be considered.
The Most Important Factors for Vessel Material Selection
For tank and piping selection in acid storage and distribution, the most important factors dependent on the specific application are:
To derive these answers, compare materials according to three factors.
Factor #1: Compatibility with the Chemical and Expected Conditions
It almost goes without saying that the tank or piping material should be compatible with processing conditions and chemicals.
But, compatibility is a spectrum.
Very rarely is a material entirely compatible with a specific acid or base. Rather, one material is more compatible than another because it withstands wear better or for a longer period than other materials when in contact with the given chemical.
For example, steel vessels are commonly used to store acids. Carbon steel is likely used for many sulfuric acid tanks because it is considered compatible enough. Metals, however, are generally more susceptible to corrosion over time than many nonmetallic alternatives. Steel may be what a plant or operations manager has experience with, but it likely will require more frequent repairs or replacement than an alternative, like CPVC.
See how CPVC performs against 400+ chemicals by viewing the Corzan® CPVC Chemical Resistance Table.
Factor #2: Compatibility with a Broad Range of Chemicals and Conditions
Another important consideration is the compatibility the material has with a broad range of chemicals, not only those that are anticipated for the tank’s intended use. It comes down to designing for a high safety factor.
If the material is only compatible with the expected chemicals in the tank, a small deviance or inadvertent reaction could cause failure from the vessel. Carbon steel is a good choice for 98% sulfuric acid, but if the concentration is allowed to dilute down to 90% sulfuric acid the tank owner will soon see a change in corrosion resistance.
Tank materials should also be able to handle temperatures beyond the expected range.
Unintended chemical reactions, latent heat (as chemicals change from a liquid to a vapor state) and other unexpected events should all be designed for.
In some tanks, for example, chlorine is pushed through a caustic solution that forms sodium hypochlorite (bleach). Typical heat cycles corresponding to the sun rising combined with the relatively unstable solution can present some unsafe conditions if not properly designed for. If the vessel is exposed to heat from the sun or environment, sodium hypochlorite will generate oxygen as it decomposes, increasing the tank’s pressure. The vessel must be designed to withstand the wide range of temperature, pressure, and pH during the reaction and high heat that it may be exposed to under unexpected conditions.
When factoring in a chemical resistance range, be cautious of FRP. Straight FRP tanks, in which chemicals come in direct contact with the chemical resistance resin layer of FRP, are designed and built using a specific resin with a limited area of performance. Any deviation from anticipated conditions can cause damage or premature failure.
CPVC-Lined FRP Vessels
The solution for straight FRP is CPVC-lined FRP, which relies on the structural strength of the FRP and the broad chemical resistance of CPVC. Corzan CPVC effectively handles a wide range of chemicals, including acids, caustics and salts.
Factor #3: Fabrication Reliability
Unlike many aspects of industrial processing systems, vessel standards are not as widely available, known or regulated. For tanks storing hundreds of gallons of highly corrosive and potentially hazardous chemicals, the chance for failure must be alleviated.
One way industrial plants can increase the reliability of their tanks is by working with certified fabricators.
ASME RTP-1 is the standard for the fabrication of reinforced plastic vessels used for the “storage, accumulation, or processing of corrosive or other substances at pressure not exceeding 15 psig externally or internally. The certification is specifically for manufacturers of reinforced plastic tanks.
Certification with ASME RTP-1 gives a plant or operations manager confidence in the total fabrication and weld quality of a tank. A system is only as strong as its weakest link—or seam.
Learn about the basics of CPVC hot air welding.
Learn More About CPVC-Lined FRP
In the industrial sector, CPVC-lined FRP vessels are growing in popularity and case studies are accruing to verify their effectiveness. To learn more about how CPVC-lined FRP is being used in the industry and if it could be a use case for your next storage vessel, contact us. We’ll connect you with a product or engineering specialist to answer your questions.