The Importance of Water and Wastewater Coatings Performance Testing
Water and Wastewater Coatings & Polyurethane / Pure Polyurea Performance Testing
Whatever the linings system used in water and wastewater coatings applications, all have to withstand aggressive chemical substances, abrasion, corrosion, and in addition, provide a good level of impermeability. That being said, the success and longevity of any coating system utilised in this area ultimately depends on the stress levels it can tolerate.
To determine the performance of a polyurethane / pure polyurea coating system within the water and wastewater industry, there are a number of tests that can be carried out by testing and analytical services. For example the Australian Water Quality Centre test products that come in contact with drinking water, this standard is known as AS/NZS 4020. (Note: Ensure you use the very latest version when considering Potable Water Approval.)
However, it is important to remember that conditions in a laboratory are not the same as those in the field especially where protection from chemical substances are required. Normally when testing for chemical resistance a sample of the coating is immersed into the chemical being tested. There are times when this is not possible, that is why it is recommended that prior to the full application of any coating material that a test be carried out under real conditions, this will help determine the performance of the coating system especially when it comes to abrasion and chemical resistance. This is where Standard AS3894 Site Testing of Protective Coatings is implemented.
When it comes to protective coatings such as epoxies, polyurethanes and pure polyureas, water and wastewater coatings performance tests can include, but are not limited to:
- Abrasion Resistance – ASTM D4060
- Taber Abrasion Test is where a sample of the product is rotated under a specific weight (1kg) against a grinding wheel (CS17 or CS18) for a defined number of revolutions (1000 cycles). The sample is evaluated by measuring the weight of the sample before and after the test, the more abrasion resistant the coating is the lower the reported weight loss.
- Adhesion – AS3894 Site Testing of Protective Coatings
- The Adhesion of a protective coating system to the substrate is deemed a good indicator of the coatings ability to resist corrosion signifying longevity of the coating. The better the adhesion the longer the coating lasts, it should also be noted that durability of the lining can also be governed by the thickness of coating.
- Cathodic Disbondment – ASTM G95
- Cathodic disbondment is one measure of the undercutting resistance of a coating/lining system. Linings with better cathodic disbondment resistance have better corrosion resistance and greater longevity.
- Chemical Resistance
- Chemical resistance tests are carried out specific to the application required. A swatch of the coating is submersed into a sample of chemical, if this cannot be done tests are devised which simulate as close as possible the actual conditions.
- Flexibility – ASTM D522
- Flexibility is a good indicator of a coating/lining’s ability to withstand the cracking, disbanding, or other mechanical damage of the coating/lining that can occur.
- Impact Resistance – ASTM G14
- Impact resistance test method represents the coatings ability to withstand damage to a direct impact with another object, this methods help predict the lining performance and resistance to damage
- Water Absorption – ASTM D570
- Polyurethanes are susceptible to water absorption during its life of water and temperature exposure, this can lead to degradation, and failure of the lining, however there are certain levels that are within the acceptable range.
Some of the above U.S. based tests are included in the AS/NZ 4858 “Wet Area Membranes” which gives further indication of a coatings performance.
Factors that Affect a Coatings Performance
The performance of any coating/lining system depends on many variables, such as surface preparation, film thickness, temperature, cathodic protection, flexibility, impact resistance and so on, other factor that need to be taken into account that can affect the performance of a coating include:
- The design
- Surface preparation
- Surface profile
- Coating type
- Coating thickness
- Weather conditions
When selecting a coating system, it is imperative that you consider these performance measures in order to make the best choice. When it comes to corrosion resistance in water and wastewater coatings applications it is important to be preemptive, so understand what your objectives are, and know what long-term outcomes you require otherwise your company could end up spending a lot more than liked.