After more than 7,000 votes were counted in the first Readers’ Choice Corrosion Innovation of the Year Award presented by Materials Performance (MP) magazine, Tnemec’s Severe Wastewater Analysis Test, or S.W.A.T., was in the top 10 nominations selected for recognition.
S.W.A.T. was selected from 64 innovations representing groundbreaking advances in coatings and linings, cathodic protection, materials and design, instrumentation, testing, integrity assessment, chemical treatments, and other corrosion prevention and mitigation technologies. Nominations were submitted by individuals, companies, organizations and governments representing 17 countries and posted online, where MP readers were asked to select the top 10 nominations.
“This peer recognition validates S.W.A.T. as an innovative testing protocol for evaluating protective coatings and linings for severe wastewater exposures” said Vaughn O’Dea, director of sales, Water & Wastewater Treatment. “S.W.A.T. offers the wastewater industry a mechanism for determining the suitability of protective coatings and linings for these severe exposures.”
Prior to S.W.A.T., testing programs were based solely on chemical immersion in sulfuric acid (H2SO4) and did not reflect the permeation effects of gases found in sewer headspaces above the waterline in enclosed sewer pipes and structures.
“Wastewater headspace environments are very corrosive due to the presence of sewer gases and H2SO4 generated during the biogenic sulfide corrosion process,” O’Dea explained. “With the development of S.W.A.T., it is possible to simulate and accelerate corrosive conditions characteristic of municipal sewer headspaces inside an airtight glass chamber.”
The lower portion of the S.W.A.T. chamber contains a corrosive solution of sulfuric acid and sodium chloride. The upper portion of the chamber is a mixture of air containing sewer gases, including hydrogen sulfide (H2S), carbon dioxide (CO2), and methane (CH4), which are responsible for altering barrier properties of protective coatings and linings. The temperature of the test chamber is elevated higher than sewer wastewater to create accelerated conditions and reaction rates.
Coated steel and concrete specimens are positioned on a carousel and placed inside the test chamber where they are immersed into the aqueous solution three times daily for a period of 15 minutes each, then exposed to the sewer gas the balance of the time. The cyclic exposure continues for a period of 28 days or longer.
After the testing period is completed, coated specimens are evaluated on retained properties such as their ability to act as a barrier separating the substrate from the corrosive service environment. Polymers with low permeation are assumed to offer better substrate protection within severe wastewater environments.
For steel specimens, it is possible to evaluate a coating’s permeability properties using electrochemical impedance spectroscopy (EIS) analysis, a proven method using electrical current to determine the level of coating degradation after exposure to a testing environment.
By measuring the electrical resistance of a coating (referred to as impedance) before and after exposure to S.W.A.T., it is possible to evaluate its permeability properties. A coating in good condition resists penetration, or electrical current, as opposed to a coating that has degraded. The higher and more stable the retained impedance following exposure to the S.W.A.T. chamber, the better the long-term permeability resistance and coating performance.
Permeation of concrete specimens can be assessed by microscopically observing a cross section of the coating film for signs of discoloration. At 100X magnification, it is possible for a protective coatings specialist to measure the rate of permeation of the coating based on color change within the film.
Protective coatings are also evaluated on physical properties such as adhesion and tensile strength and on their ability to retain film quality without blistering, checking or cracking.
“It may also be necessary to use other data such as chemical resistance, shrinkage, thermal expansion and abrasion resistance to determine the suitability of a protective coating or lining on the service life found in a severe wastewater environment,” O’Dea added. “Results from S.W.A.T. are usually interpreted by protective coatings specialists.”
The top 10 innovations were announced by NACE International President Oliver Moghissi at CORROSION 2012, NACE International’s annual corrosion conference and exposition. Mark Thomas, vice-president of marketing, accepted the award presented on behalf of Tnemec.
Published monthly by NACE International, Materials Performance is the world’s largest circulation journal dedicated exclusively to corrosion prevention and control.