In high purity water system design, the material used for distribution piping is not simply a construction decision. It directly impacts water quality, bacterial control strategy, maintenance procedures, sanitization compatibility, fire code compliance, fabrication method, and long-term operational stability.

While cost often drives material selection, improper material choice can introduce elevated total organic carbon, microbial risk, regulatory challenges, and extended downtime during system modifications.

At Atlas High Purity Water, material selection is based on application requirements, sanitization strategy, fabrication standards, and long-term performance, not just initial capital cost.

PVC: Cost Effective but Limited for Deionized Water

Polyvinyl chloride, or PVC, has historically been used in water distribution systems because of its low cost and ease of installation. PVC systems are assembled using solvent cement, commonly referred to as glued fittings.

Deionized water, however, is highly aggressive. Because it contains very low ionic content, it naturally seeks equilibrium and can extract residual materials from the surfaces it contacts. In PVC systems, this can result in the release of extractables and leachables such as plasticizers, stabilizers, and other manufacturing additives from the pipe wall.

This extraction can temporarily elevate total organic carbon levels within the distribution system, particularly during startup or after new piping is introduced. In some cases, elevated organics may even be noticeable at points of use. As the leachable components are stripped from the pipe, the material itself can visibly lighten in color compared to its original appearance.

While this condition typically stabilizes over time, it may persist for several weeks before TOC levels normalize.

When repairs or loop extensions are required, newly installed PVC sections must undergo the same stabilization period. During this time, facilities may experience extended downtime while waiting for TOC levels to return to acceptable limits.

Elevated organics also serve as a nutrient source for bacteria, increasing microbial risk in systems where biological control is critical.

PVC may perform adequately in reverse osmosis only applications. However, in high purity deionized water systems, more stable materials and cleaner joining methods are often preferred.

Modern Alternatives for Deionized Water Distribution

Today, higher performance piping materials are commonly selected for deionized water systems to reduce extractables, improve sanitization compatibility, enhance fire code compliance, and provide superior joint integrity.

Common materials include:

  • Polyethylene
  • Polypropylene
  • PVDF
  • Stainless Steel

Polyethylene and Polypropylene

Polyethylene and polypropylene provide improved chemical resistance and reduced extractables compared to PVC.

Polypropylene has a density of approximately 0.89 to 0.93 grams per cubic centimeter, making it lightweight and economical. However, it is a combustible polyolefin material.

From a fire code standpoint, polypropylene does not inherently meet plenum fire performance requirements. Air handling plenum spaces governed by the International Mechanical Code and NFPA 90A typically require materials to be noncombustible or to meet flame spread and smoke developed index limits of 25 and 50 respectively when tested under ASTM E84 or UL 723. Standard polypropylene piping generally does not meet these requirements unless specifically tested and listed for plenum use.

From a fabrication standpoint, polypropylene systems are joined using heat fusion methods, including socket fusion, butt fusion, or infrared fusion. These methods create a monolithic joint without adhesives, reducing the introduction of foreign materials into the system and improving long-term joint integrity.

Polypropylene is generally compatible with chemical sanitization but is not typically rated for continuous ozone exposure.

PVDF: Enhanced Fire Performance and Advanced Joining Options

Polyvinylidene fluoride, or PVDF, is a fluoropolymer with a density of approximately 1.78 grams per cubic centimeter, nearly double that of polypropylene. Its fluorinated structure contributes to improved chemical resistance, mechanical strength, and inherently better flame and smoke performance.

When tested under ASTM E84 or UL 723, certain PVDF systems can achieve flame spread and smoke developed ratings that meet plenum requirements, making them suitable for exposed installation in air handling spaces when properly listed.

From a fabrication perspective, PVDF systems can be joined using socket fusion, butt fusion, infrared fusion, and bead and crevice free fusion methods. Bead and crevice free systems are specifically designed for high purity applications where minimizing internal surface irregularities is critical to reducing bacterial harborage and improving cleanability.

PVDF is compatible with both chemical and ozone sanitization strategies, offering flexibility in microbial control programs.

Stainless Steel: Precision Fabrication and Surface Finish Control

Stainless steel is typically used in high purity and pharmaceutical applications where durability, sanitization flexibility, and mechanical strength are paramount.

Most high purity systems utilize 316L stainless steel due to its enhanced corrosion resistance. Surface finish is a critical factor, with internal roughness average values often specified to meet application requirements. Smoother surface finishes reduce the potential for biofilm formation and improve cleanability.

Stainless steel distribution systems are typically joined using orbital welding. Orbital welds provide consistent, repeatable, high integrity welds with minimal internal irregularities when properly executed.

Stainless systems can be sanitized using chemicals, ozone, or heat. However, proper passivation is required to establish the protective oxide layer that provides corrosion resistance. Facilities must also monitor and manage rouging under certain operating conditions.

When designed, fabricated, and maintained properly, stainless steel provides exceptional long-term performance in critical high purity applications.

Engineering Based on Application

Material selection should be driven by:

  • Required water purity levels
  • Total organic carbon sensitivity
  • Sanitization strategy
  • Building code and plenum requirements
  • Fabrication method and joint integrity
  • Surface finish requirements
  • Long-term operational cost

PVC may offer a low cost solution for certain RO only applications. However, in deionized water systems where organic control, microbial management, sanitization flexibility, fabrication quality, and code compliance are critical, higher performance materials provide measurable operational advantages.

Conclusion

The material used in a high purity water distribution system directly influences water quality, microbial control, fire code compliance, fabrication integrity, and system downtime.

While PVC offers a lower initial cost, its use in deionized water systems can introduce elevated TOC, extended commissioning periods, increased microbial risk, and limitations in joining methods.

Modern materials such as polypropylene, PVDF, and 316L stainless steel offer improved compatibility with high purity applications and advanced sanitization strategies. When properly selected and fabricated, these materials support long-term system stability and operational reliability.

Atlas High Purity Water evaluates each application carefully to ensure that material selection and fabrication methods align with performance requirements and regulatory expectations. The right material is selected not simply on cost, but on its ability to protect water quality and support the process it serves.