Investigation of corrosion resistant primers, barrier topcoats and duplex systems
What is are the best primers for preventing aqueous corrosion? What are the most effective barriers to water intrusion? Is it possible to combine these materials into a duplex system that would deliver performance and service life rivaling vinyl, coal tar, and lead based paint.
Need and Benefit
Old coatings systems such as solution vinyl resin, coal tar enamel and lead-based paint were utilized throughout the mid to late 20th century during construction of many Reclamation projects to coat equipment such as outlet works, penstocks, gates and other important equipment. Since these coatings typically exhibited a long service life, total life cycle costs have been relatively low. However, modern systems such as epoxies, have already demonstrated significantly shorter lifespans in the 20 year range while material and labor costs have continued to increase. Therefore, our aging facilities can expect to face much higher O&M costs related to controlling corrosion. Better, longer-lasting coatings are needed to help keep costs in check. This project builds on existing research to help identify longer lasting products and systems that can might modern safety standards while performing in line with facility expectations. Previously funded S&T work (Project ID 8835) examined vinyl resin coatings and compared several modern coating systems both thermos-plastic and thermoset. Testing revealed several important findings which the current proposal seeks to build on:
1. Vinyl system provide an electrolyte barrier that is superior to many epoxy systems. This could be one reason for the difference in service life.
2. Zinc-rich primer outperformed the standard vinyl systems. Zinc-rich epoxy systems are available but typically related to atmospheric service. Additional investigation is needed to evaluate zinc-rich primers in immersion.
3. Thermoplastic materials: Nylon, ECTFE, PVDF, and Polyolfefin all provide excellent barrier properties similar to vinyl in EIS testing.
4. Aromatic polyurethanes do as well but long-term adhesion is problematic with these materials.
The expected contract cost to reline a penstock is between $70 and $100 per ft2. Hence, a single penstock could cost approximately $1,000,000. Reclamation has over 492 dams with outlet works and gates and many with multiple penstocks, spiral cases, draft tubes and gates and spillway gates all of which are coated. Many of these items will require rehabilitation in the next 10 to 20 years. If we can extend the service life of a penstock or gate's coating system by a factor of 2. The organization is able to save millions of dollars in contracting and engineering costs while increasing generating time and safety by reducing the number of maintenance outages required.
Our generation has inherited a legacy of infrastructure that will be difficult or impossible to replace. Therefore, it is imperative that we continue to maintain the infrastructure to the highest standard. However, if we don't find better materials than what is currently being used, costs will increase dramatically and may become unsustainable for many of the small facilities that don't generate large revenue streams.
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