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Bridging The Gap

How ISO 28765-2022 Enhances AWWA D103-19 for Glass-Fused-to-Steel Tanks

Greatario recognizes that municipal water storage solutions must meet the highest standards for safety, durability, and efficiency. While the AWWA D103 design code has long been considered a guideline for bolted steel tanks in North America, the ISO 28765 standard has emerged as a critical benchmark for specifying glass-fused-to-steel (GFS) tanks. In this blog post, I will explore the history of ISO 28765, highlight its key quality requirements, and demonstrate the significant gaps between it and AWWA D103. For specifying engineers, we provide practical guidance on integrating ISO 28765 into their specifications for superior GFS tank performance.

Dillon Occleston
Sales Manager – Ontario

Jan 2025

Introduction to ISO 28765: Setting the Global Standard for Glass-Fused-to-Steel Tanks

The ISO 28765 standard, titled “Vitreous and Porcelain Enamels — Design of Bolted Steel Tanks for the Storage or Treatment of Water or Municipal or Industrial Effluents and Sludges,” was first published in 2008, with its latest revision released in 2022. It was developed to address the unique requirements of glass-fused-to-steel tanks, offering a more comprehensive framework for quality and performance than AWWA D103.

ISO 28765 focuses specifically on the glass coating process, detailing stringent requirements for corrosion resistance, thermal shock, abrasion, and impact resistance. It recognizes four quality classifications for glass coatings: Class AA, Class A, Class B, and Class C, each class suited to different applications and environments. This detailed approach ensures that GFS tanks meet the highest long-term durability and reliability standards.

In contrast, AWWA D103-19 provides minimum guidelines for bolted steel tanks but lacks the specificity needed for glass coating quality assurance. This gap can lead to inconsistent performance, particularly in challenging environmental conditions.

Municipal
GFS panels
GFS panels being fired

Major Gaps Between AWWA D103 and ISO 28765

AWWA D103 is a well-regarded standard in North America, but it primarily focuses on structural design and construction methods without delving deeply into the quality requirements for glass coatings. ISO 28765 fills this gap by providing comprehensive testing and quality metrics for glass-fused-to-steel tanks.

Here are some of the critical gap’s ISO 28765 covers that are absent in AWWA D103:

  1. Glass Coating Thickness: ISO 28765 specifies minimum and maximum glass thickness for both internal and external surfaces, ensuring consistent corrosion protection.
  2. Thermal Shock Resistance: ISO 28765 requires that glass coatings withstand thermal shock at 350°C, ensuring tanks can handle temperature fluctuations without damage.
  3. Chemical Resistance: ISO 28765 mandates rigorous chemical resistance testing, including exposure to citric acid, sulfuric acid, and other corrosive agents.
  4. Impact and Abrasion Resistance: ISO 28765 includes detailed impact resistance tests, ensuring that glass coatings can withstand mechanical stress. It also includes abrasion resistance standards to prevent wear over time.

Developing a Linear Specification Theory: Why Engineers Should Focus on ISO 28765

For engineers specifying GFS tanks, relying solely on AWWA D103 can result in missed opportunities to ensure optimal GFS coating performance over the design life. By incorporating ISO 28765 into your specifications, engineers will achieve a higher level of quality assurance, particularly in the following areas:

  1. Corrosion Protection: ISO 28765’s focus on glass thickness and chemical resistance ensures tanks are more resilient against corrosion, reducing maintenance costs and extending service life.
  2. Durability in Extreme Conditions: With requirements for thermal shock and impact resistance, ISO 28765 safeguards tank coating quality in order to withstand harsh environmental conditions and mechanical stresses, beneficial to cold Northern Canadian climates.
  3. Quality Consistency: The ISO standard provides clear, measurable benchmarks for glass quality, reducing the variability seen with less specific guidelines found in the AWWA standard. Holiday testing within AWWA remains comparable only to class C glass coatings, the lowest standard within ISO, and not comparable to AA, A or B class quality inspection requirements.

 

Practical Steps for Engineers

  • Reference ISO 28765 in Specifications: Instead of relying solely on AWWA D103, engineers should reference ISO 28765 within their glass coating requirements in their project specifications.
  • Specify Glass Quality Classifications: Identify the appropriate glass quality class (AA, A, B, or C) based on the tank’s intended application. Recall that AWWA standards will allow a thinner INTERIOR coating, whereas ISO specifies greater thickness and, therefore greater protection for classes AA, A, and B. (see chart below)
  • Require Certification: Ensure your tank manufacturers can provide certification demonstrating compliance with ISO 28765 standards which are current and audited.

Conclusion

While AWWA D103 remains a historic guideline for bolted steel tanks, it’s important to recognize that ISO 28765, as the prevailing global standard, offers a more robust framework for specifying glass-fused-to-steel coatings. Engineers can ensure that their water storage solutions meet the highest possible quality and performance benchmarks by bridging the gap between these two standards and requiring ISO 28765 certification.

Thanks for reading!

Greatario remains committed to expert guidance for municipalities and industries planning their design, construction, and maintenance of GFS tanks.

I’m always free by email at Doccleston@Greatario.com if you want to discuss any supplemental information when specifying and designing your next GFS storage project!

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