Material Properties & Installation Considerations with Thermoplastic Valves

Thermoplastic valves are increasingly being utilized in various industrial applications due to their lightweight nature, excellent chemical resistance, and corrosion resistance. However, the installation and maintenance of these valves require specific approaches and techniques that differ from traditional metal valve systems. This article outlines best practices for the installation and maintenance of thermoplastic valves.

Specification and Preparation

Thermoplastic materials are widely used in various applications due to their inherent flexibility, ease of processing, and favorable mechanical properties. However, the chemical resistance of these materials can vary significantly based on their composition and the specific chemicals they are exposed to.

Prior to installation, verify the compatibility of the thermoplastic materials (such as PVC, CPVC, PVDF, and PP) with the fluids being transported—reference chemical resistance charts (part of Asahi/America’s full valve chemical resistance chart is listed to the right, as an example) to ensure adequacy under operating conditions.

PVC is known for its excellent resistance to a variety of chemicals. It is particularly resistant to acids and solvents and is effective against many inorganic acids, including sulfuric acid and hydrochloric acid, at low concentrations. PVC is also resistant to alkalis and certain salts, making it suitable for water supply systems. While PVC is generally resistant to alcohols, fats, and oils, it should not be used with esters, ketones, or chlorinated hydrocarbons.

CPVC is an enhanced version of PVC with better thermal stability and chemical resistance. It exhibits superior resistance to hot water and corrosive liquids, making it ideal for industrial piping systems. CPVC is resistant to many acids, bases, and salts but has limited resistance to amines and should not be used with many chlorinated or aromatic hydrocarbons.

PVDF is favored in applications requiring high purity and chemical resilience as it offers exceptional resistance to a wide range of solvents, acids, and bases, including hydrochloric acid and nitric acid. It is also often used as a protective coating in chemical processing.

Polypropylene (PP) offers the advantages of being highly resistant to a broad range of chemicals, including mineral acids, bases, salts, and hydrocarbon solutions, making it ideal for various chemical processing applications. One of its primary benefits is its high tensile strength and rigidity, providing enhanced mechanical stability. Additionally, polypropylene pipe offers improved temperature resistance compared to other types of thermoplastics, making it suitable for demanding environments.

Handling and Installation

Handle thermoplastic valves with care to avoid impacts that could compromise the material integrity. For instance, storing valves in a dark, cool environment is recommended to prolong their lifespan, particularly if they have elastomeric seals. Ultraviolet light exposure can accelerate material degradation in products that aren’t UV stabilized or sealed. Ensure the internal parts of the valve remain clean and free from contaminants during the installation process, as residues can damage seals and impact valve performance.

Sometimes, installers overlook the specific guidelines provided by the valve manufacturer regarding installation procedures, torque values, and recommended tools. These guidelines are crucial to ensuring a proper installation. Insufficient alignment of pipes can stress the valve, causing premature wear or failure. Pipes should be properly aligned and supported to avoid any bending or twisting forces on the valve during operation. Failing to provide adequate support to the piping system can lead to sagging, which puts excessive strain on the valve, especially during thermal expansion and contraction. Proper bracing and support are essential, particularly for larger or heavier piping systems.

For valves requiring socket fusion, not achieving the correct temperatures can result in weak joints. Overheating or underheating can compromise the integrity of the fusion bond, leading to future leaks.

When using threaded types of connections, apply sealing tape or paste compound suitable to the application, starting from the second thread to prevent tape from entering the valve, ensuring the threads are aligned and properly tightened to avoid stress on the valve body.

In flanged connections, improper application of torque can lead to leaks. Over-tightening can distort the flange and damage the valve body, while under-tightening may result in insufficient sealing under pressure. It is advisable to follow a crisscross pattern for even torque distribution.

Installing a valve without properly cleaning its interfaces can lead to contamination and inadequate sealing. Impurities can prevent the valve from achieving proper sealing, leading to leaks post-installation. In retrofitting situations, failing to clean old pipes and fittings before installation can introduce contaminants that jeopardize the effectiveness of the new valve.

Proper orientation is crucial for valve operation. Installing a valve backwards or upside down can lead to operational inefficiencies and potential failure. It is essential to follow manufacturer specifications regarding flow direction.

Special Considerations

Thermoplastic materials can expand and contract significantly with temperature changes. Failing to account for this expansion can cause undue stress on joints and connections, potentially leading to leaks or structural failure. Installers should design the system with flexibility in mind, incorporating expansion joints where necessary.

Thermoplastic materials generally exhibit high coefficients of thermal expansion compared to metals. Specifically, for a 1-inch run of pipe:

• PVC = ~28.0 x 10^(-6) in/ ° F
• CPVC = ~44.0 x 10^(-6) in/ ° F
• PP (typically) = ~110 x 10^(-6) in/ ° F

In contrast, metals such as steel and brass have lower coefficients of thermal expansion, which, for a 1-inch run of pipe, are:

• Steel ranges from 10.8 to 12.5 x 10^(-6) in/ ° F
• Brass = ~11.2 x 10^(-6) in/ ° F
• Copper = ~9.8 x 10^(-6) in/ ° F

This disparity indicates that thermoplastics expand and contract more extensively with temperature changes than metals, which can significantly impact system design and performance and lead to several issues during installation and operation.

If piping systems utilize both materials without appropriate allowances for thermal expansion, thermal stresses can develop at joints, potentially leading to leaks or failures. For example, when CPVC pipes are exposed to temperature changes, the resultant thermal expansion can generate significant stresses that may compromise the integrity of the piping system.

Connections between thermoplastic valves and metal pipes may experience differential movement, risking damage to fittings and joints. This issue is particularly critical in applications where temperatures fluctuate widely, as seen in chemical processing facilities.

In light of these challenges, several strategies can be implemented to limit the effects of thermal expansion. Incorporating expansion loops or offsets allows for mitigated movement due to thermal expansion. These mechanisms help manage the stresses induced by temperature changes, ensuring long-term integrity in piping systems.

Implementing expansion joints can accommodate axial movement, providing additional flexibility in systems where space is too limited for traditional expansion loops. Proper design ensures these joints perform effectively without causing additional stress elsewhere in the system.

Conclusion

The installation and maintenance of thermoplastic valves require thoughtful consideration of the unique characteristics of thermoplastic materials. By adhering to best practices in specification, preparation, and installation, operators can enhance the reliability and longevity of thermoplastic valves in their fluid systems. These practices prevent operational failures and ensure compliance with safety and quality standards critical to industrial applications. Stay tuned for the continuation of this article and discussions on maintenance and repair operations.

Continued education and adherence to manufacturer specifications will help the end-users maximize their investment in thermoplastic valves.

EDITOR’S NOTICE: Please note, the information in this article is for educational purposes only and does not supersede any Asahi/America technical information or product specifications. Please consult Asahi/America’s technical department at 1-800-343-3618 or [email protected] on all product applications in regards to material selection based on the pressure, temperature, environmental factors, chemical, media, application, and more.