Selecting a protective coating for industrial service has long been a challenge for specifying engineers and end users alike. The final purchasing decision should include, at least, these considerations:
Safety and compliance with local state and federal guidelines;
Compatible performance parameters with service conditions;
Ease of application.
Influencing factors may include references with case histories as well as warranties.
SAFETY AND COMPLIANCE
Safety and compliance with local, state and federal guidelines is a go/no-go decision. If the coating system does not meet guidelines — such as those for VOC content and toxicological exposure risk — then the product should be dropped from consideration. To bring a non-compliant system or a system with elevated toxicological hazards on site would expose the plant workers and the site itself to unnecessary risks.
VOC levels defined by the EPA
VOC levels are clearly defined by the EPA and, if two systems are being considered, it is almost always the better choice to elect the lower VOC system. This can help a plant stay under the established VOC emissions cap. At the same time, it creates a safer work environment where multiple crafts such as welding, cutting and grinding can be present in proximity to the coating application. It is also a safe bet that higher-solids (low-VOC) systems will provide longer-term performance under more aggressive conditions than a lower-solids (high-VOC) system, especially at edges, angles and when multiple coats are required to achieve a functional film.
Toxicological Hazards and Global Harmonized System (GHS)
Toxicological risks are also important to consider. This is especially so when the systems are using hazardous chemicals.
By now all coating manufacturers should be using the Global Harmonized System (GHS) to communicate the toxicological hazards associated with their product. GHS is a logical and comprehensive approach to:
Defining health, physical and environmental hazards of chemicals;
Creating classification processes that use available data on chemicals for comparison with the defined hazard criteria; and
Communicating hazard information, as well as protective measures, on labels and safety data sheets (SDS).
GHS-compliant SDSs utilize a standardized 16-part format, covering everything from composition to firefighting methods. Note, while more than 65 countries have adopted the GHS system, there is no mandate that any country comply with it.
Toxicological hazards are easily identifiable based on the pictograms adopted under GHS guidelines. Figure 1 explains the various symbols and their meanings.
Figure 1. Shown are symbols for toxicological hazards. Learn more about GHS-compliant safety data sheets: SDS 101. A wallet-sized reference card (right) with pictograms and key terms is available for download here.
COMPATIBLE PERFORMANCE PARAMETERS
Ensuring compatibility with in-service conditions means confirming that the coating systems can provide reliable service for the required duration under the anticipated service conditions. These conditions can include, but are not limited to:
Heat (maximum and minimum as well as cycling history and risk of thermal shock);
Physical forces/stresses (tensile, flexural, compressive);
Chemical attack (acid, alkali, solvent);
Permeation gradients (thermal, osmotic, pressure); and
Abrasion/erosion (velocity, percent suspended solids, particle size, shape, hardness).
Most suppliers will require some definitive service condition parameters in order to recommend protective coating products, but they will often provide data results without the test methods defined or they may claim subjective ratings, such as “excellent.” Relying solely on a manufacturer's product data sheets can make purchasing decisions difficult for the end user.
End users should, instead, provide guidance to suppliers on what performance factors are critical in the specific application. Ideally, they will include data points that conform to an industry-recognized test standard body, such as ASTM, NACE or ISO, so all recommended products can be compared using the same standard. Each qualified supplier can then review the demands and provide objective data.
Too often price is a lead factor in the coating selection process, yet the highest cost component of any coating job is typically the materials and labor associated with surface preparation and application. While an option for a low-cost coating system may be available, that system may not provide the required longevity of service. Selecting even a marginally more expensive option may provide longer-term service, saving maintenance costs over time.
EASE OF APPLICATION
Another critical factor to be considered in the selection process is the ease of application of the selected system. Certain products require specialized equipment to apply them properly. Sometimes this equipment can be quite expensive and requires a level of operational training that the applicator may not have.
Conventional airless spray is an example of a coating system that is easy to apply. The equipment required for this system is more commonly used, lower priced and requires far less maintenance and operator training than some other systems. A coating system comprised of a direct-to-metal base coat with a subsequent top coat of the same system is easier to use than a system comprised of a stand-alone primer, mid coat and top coat — each having different application characteristics and environmental concerns.
Consider the following facts:
Contractors may be incentivized to use products and systems that increase their profit margin. This may lead some contractors to use multiple-coat systems instead of single-coat systems — all other considerations being equal.
Coating companies also make more money when they specify multi-coat systems with different products. For example, a coating company will sell more paint if a three-product coating system with a predictive waste value of, say, 15 percent is specified. Three different products means three different opportunities for waste versus a single-coat system or a multi-coat system using the same product with only one opportunity for waste.
The coatings industry can be better served all around if end users count safety and health concerns as significant purchasing considerations. End users should also define critical performance parameters and required test methods that will support manufacturer claims, so suppliers can provide relevant, objective technical data to support use of these products. Finally, end users should consider ease and speed of application in the selection process, choosing a single-coat system whenever practical and always choosing the system with fewer coats over one with more coats.