How to Find the Right Industrial Pipe Material for Chlor Alkali Plants
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:
- The precise needs of chlor-alkali applications.
- The properties of the most compelling materials on the market for chlor-alkali applications.
- How to ensure you are constructing systems that offer the most service life for your investment.
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.
What Does a Chlor-Alkali Facility Need?
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.
1. Corrosion Resistance
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.
Examples of chemicals in chlor-alkali applications include:
- Sulfuric acid
- Sodium hydroxide (caustic soda)
- Concentrated sodium chloride (brine)
- Cell liquor (brine, sodium hydroxide)
- Sodium hypochlorite
- Hydrochloric acid
- Demineralized / deionized water
- Wet chlorine gase
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.
2. High-Temperature Resistance
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.
3. Non-Leaching Properties
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.
Other Possible Needs
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.
Examples of desirable material traits might include:
- A high hydrostatic pressure rating at elevated temperatures
- Simple fabrication of system components
- Easy weldability for repairs and additions
- The inclusion of flanges for secure transitions among other pipe materials
- Creep-resistance 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:
- Which transported substances might be particularly aggressive.
- How those substances might interact with different system component materials (which a supplier can often help to explain).
- What rate of corrosion is acceptable to maintain the desired lifespan of your structures.
- And so forth.
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.
The Case for CPVC in Chlor-Alkali Systems
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:
- Superior chemical resistance across a broad spectrum of substances
- Outstanding mechanical properties
- Excellent combustion properties
- Low thermal conductivity compared to metallic materials
- Low thermal expansion compared to other non-metallic materials
- Non-leaching properties
- High-pressure performance
- Global availability
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.
Know Your Process, Ask Questions and Reduce Costs
By comprehensively understanding your application and knowing what to look for in terms of certifications, approvals and specific property data, you will be in the best position to determine which chlor-alkali system material will best suit your needs.
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:
- Are material technology leaders.
- Provide a quality assurance program to guarantee certain levels of product performance.
- Have testing documentation or testing services to reassure you that products will meet application demands.
- Offer other support services, such as field assistance to ensure your system can best take advantage of product properties.
With the right approach to specification and construction, you will likely find yourself saving time, money and risk for many years to come.
The Reliable Solution
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.