Tests to measure whether a system, part or process is performing as intended vary across industries. For example, hardness, ductility and tensile strength are key metrics for components that make up construction and infrastructure assets. Testing those metrics involves stressing parts or materials to their breaking points. But the only way to determine that breaking point is to do just that—break something.

Testing industrial coatings is different because the only way to see if a coating was applied properly and is performing as intended is to examine it after application. How do you do that without damaging a coating system?

Nondestructive testing (NDT) is the only viable option for inspecting coatings systems that are already in service. A subset of broader testing procedures, NDT does not compromise the integrity of the system or material while being conducted.

NDT procedures include using electromagnetic waves to gauge the thickness of a coating, measuring heat distribution (thermography) to determine how well a coating is bonding to its substrate, or the use of lasers to measure surface profile without physically contacting the substrate. While some NDT methods sound incredibly complex (and some are), checking a tank for leaks by filling it with water is technically an NDT method. To satisfy the definition, the test simply needs not to render the subject it’s testing unusable.

One example of NDT in the coatings industry involves the use of a permanent base coating that fluoresces under a black light. This allows inspectors to check for any imperfections in the base coating without in any way damaging it. It is a relatively quick and inexpensive NDT method sometimes used for inspections covering a large surface area.

NDT methods are as numerous and varied as the applications and industries they affect. An entire professional organization, The American Society for Nondestructive Testing (ASNT), has even sprung up to provide standards and best practices for the field.   

NDT gauges and industrial coatings
Probably the most significant contribution to NDT to industrial coatings, though, concerns electronic gauges. These devices have become standard inspection equipment for quality control and quality assurance in the industry. Made by manufacturers such as Elcometer or DeFelsko and others, these tools use ultrasonic waves to measure the dry film thickness (DFT) of an applied coating.

Because coatings are manufactured to perform at a specific DFT, accurately measuring it is one of the most important things coating inspectors can do for an asset owner. Recording DFT precisely —down to microns of thickness— helps the inspector to know that a coating was applied according to specifications and should perform as intended.

Thanks to coating thickness gauges, measuring DFT no longer has to be a destructive practice. This and other NDT techniques make smarter, more economical and less labor-intensive inspection processes possible.

While NDT techniques will change and improve as new methods and technologies are developed, one thing is certain: your coating inspector should have a bag of NDT tricks at the ready to verify that a coating application has been carried out according to the specifications provided.

About the author
Michael Harkin is a NACE and SSPC coating inspector and current President of FeO – a QP5-certified coating inspection and consulting company. Prior to FeO, Michael served as an Army soldier and a Marine Corps officer.