The Case for NACE
In the desert Southwest, the sun can heat up to unbearable temperatures. These temperatures can create havoc, including killing your plants or fading the coating on your car. Any coating over a steel substrate is at risk of fading, peeling and becoming an eyesore. Just as your car’s paint job is at danger from these high temperatures and UVs that the sun can produce, the coatings that have been applied to steel ground and elevated water storage tanks are also in danger. This is where NACE International comes to the rescue.
NACE International, formerly called NACE (National Association of Corrosion Engineers), was founded in 1943 by 11 corrosion engineers. Over the decades, NACE International (now commonly referred to in the industry as simply NACE) began to expand and broaden its scope to include chemical processing and protective coatings. Headquartered in Houston, Texas, it is globally recognized as the premier authority for corrosion control solutions. NACE offers technical training and certification programs, conferences, industry standards and more to nearly 36,000 of its members.
PSC has the distinction of having three, NACE-certified employees in its El Paso office. Two of the employees — Vince Bazan and Martin Contreras — are certified as Coating Inspectors Level I. Then there is myself, certified as a Coating Inspector Level II and also a licensed engineer in Texas and New Mexico. I received my Level I and Level II certifications in 2010 and 2012, respectively. As of the publish date of this article, PSC can claim it is the only engineering firm in West Texas and Southern New Mexico with these skills under one roof.
To receive a certification in both Coating Inspection Levels I and II, one must pass a written and hands-on final exam based on multiple topics taught throughout an intense, six-day certification period.
While there are many steps in a coating application. Surface preparation is the most important. Eighty percent or more of coating failures are attributed to surface preparation or, more defined, the lack of it. With surface preparation regarded as the most important, there are other items that a coating inspector must keep a watch over: engineer-approved material delivered to the site, proper mixing procedures, weather conditions, substrate temperature, proper application procedures and the applied coating thickness.
The coating system is a barrier between the substrate (metal) and the liquid, and therefore acts as cathodic protection (CP). There are two forms of cathodic protection. The first is sacrificial, and the second is impressed current.
During inspection of a ground storage tank (GST), it is impossible to monitor the underside of the floor plates. You will not know when corrosion is present until it is too late. To help slow the corrosion in the area, you can place sacrificial anode bags or ribbons under the steel floor plates during construction. These bags or ribbons generally contain zinc or magnesium.
Impressed current is often used in applications where galvanic anodes (sacrificial) cannot deliver sufficient current to provide protection in both a ground storage and an elevated storage tank (EST). In an impressed current system, the anodes are connected to a DC power source called a rectifier. These rectifiers provide an optimized voltage/current sufficient to protect the object or structure that requires protection. This optimized output is determined by measuring the potential between a standard reference electrode and the steel that is being protected. Depending on the steel properties and the anode material employed on the project, the optimum output of the rectifier can be between 20 and 100 volts of impressed current.
If an impressed current system is used, one must remember that it will only protect the steel located below the high-water elevation. After long periods of the tank being in service, minor pitting may develop. However, if the CP system is maintained properly, this damage will be minimal and not affect the tank.
There are differences in construction between an elevated storage tank and a ground storage tank. The ground storage tank will be more susceptible to corrosion in the roof area. Approximately 95 percent of the corrosion will occur in this area. Because this corrosion is going to happen with or without cathodic protection, some engineers will not incorporate CP into the design. However, the engineer should discuss this with the Owner.
With the many things that must be monitored throughout the entire coating process, it is nearly impossible to have a coating project without issues. However, these issues can be mitigated by understanding and following the standards and guidelines from NACE International and the Society for Protective Coatings (SSPC). Proper surface preparation, oversight of the coating procedures, plus knowledge of the standards and guidelines will give owners a project they will be proud of for years to come.