Industrial-grade chlor-alkali production has been underway for more than 120 years, and in many ways, the principles by which these plants operate have not changed significantly. What has changed is the range of material choices available for chlor-alkali systems.
Today, chlor-alkali plants operating across the globe require pipes, tanks, headers, manifolds, storage towers and more to be fabricated with resilient materials that can stand up to some of the harshest conditions existing in any industry.
Materials used to transport acids, bases, brine or other chemicals must exhibit superior corrosion-resistance properties and the ability to function continuously at high temperatures, among other requirements. The more resilient the material, the longer the service life of chemical processing equipment, and in turn, the lower the costs required to maintain it. Choosing the right materials can also mean reduced risk of monetary loss related to system downtime and reduced risk of injury or damage related to chemical leaks.
As a result, when investigating piping system materials, it is important to understand:
Specifically, it is important to be familiar with the benefits offered by chlorinated polyvinyl chloride (CPVC), a material that, when formulated by technology leaders, offers exactly the sort of properties a chlor-alkali facility needs.
Because of the nature of the applications, materials that might usually last 25 years in other demanding industrial applications may last five to eight years at best in a chlor-alkali system—often eight to 10 years of service life is considered good. That being said, there are still some materials that work better than others, and thus, it is prudent to focus on a few key differentiators when making choices.
The foremost requirement of any chlor-alkali processing system is corrosion resistance. Frequently, the substances being transmitted through pipes and tanks in a chlor-alkali facility are corrosive to some extent, and very few materials can stand up well to these chemicals over an extended period of time.
Any material chosen for piping, chemical-resistance layers in tanks or other structures within a processing system may need to resist corrosion from a variety of strong and weak acids, strong and weak bases, salts, aliphatic compounds, oxidants and more.
Materials used in wastewater treatment applications are often useful in chlor-alkali applications as well, as wastewater treatment materials must also persevere when in contact with many of these substances over a prolonged period of time.
While some degree of corrosion over the course of a pipe or tank’s service life is inevitable, ideally you want uniform corrosion across surfaces. Localized corrosion, where penetration into vessel walls occurs more prevalently in specific areas, can lead to concentrated erosion and shortened service life of system components.
Over time, issues with localized corrosion have become associated with carbon steel components, whereas stress corrosion cracking—another risk posed to pipes and other structures in a corrosive environment—is often seen when stainless steel is chosen. It can be difficult to detect these types of subtle corrosion, but by knowing the inherent strengths and weaknesses of the materials you choose, you have a better chance of avoiding certain issues altogether.
Another key requirement of any material used in chlor-alkali systems is reliable long-term operation when exposed to high temperatures. It is frequently the case that chlor-alkali systems are transporting and storing fluids and gases that are consistently around 220ºF, and thus, system component materials must be able to not only stand up to corrosion, but do so at continuously elevated temperatures.
Because of the nature of a chlor-alkali system and the fact that the success of an oxidation / reduction process within an electrolysis cell is dependent on certain inputs being present, it is very important to ensure the purity and concentration of the various compounds.
For this reason, the leaching of elements—such as calcium, magnesium, silicon, nickel, lead or tin—out of piping or other system components as a result of chemical reactions can cause significant problems both with processing and system service life.
For instance, in the most commonly used type of electrolysis chamber—a membrane cell, a charge sensitive membrane that only allows ions with a certain charge to pass through—is crucial to the electrolysis process, but can be compromised if anything but low levels of leached minerals infiltrate the cell.
In addition to the three key properties mentioned above, it is also possible that a system, depending on its design, could require system components to demonstrate other specific properties.
In general, it is always very important to know the intricacies of your system and processing when doing any sort of material selection, such as:
By taking steps to educate yourself in this regard, you stand the best chance of choosing a material that will work best for your specific application.
While there are a number of materials that demonstrate desirable properties in some of the performance categories mentioned, such as carbon or stainless steel, there is one material specified for its universal appeal in chlor-alkali applications at an increasing rate: chlorinated polyvinyl chloride (CPVC).
The best industrial-grade CPVC products offer:
Not all CPVC is created equal, but for 30 years, Corzan CPVC has been chosen as a chemical barrier material for the transport of hot, caustic chemicals or brine because of its consistent reliability and the expert advice and research backing it up.
Also, do not neglect to consider some of the less tangible benefits of making a certain material choice over another. To create a system that will last, seek out materials from manufacturers that:
With the right approach to specification and construction, you will likely find yourself saving time, money and risk for many years to come.
Corzan CPVC is the reliable solution for the intense processes of the chlor-alkali industry. To learn more, or if you are interested in a free consultation on chemical resistance, process suitability or any technical questions, contact us.