Natural objects, such as granite, and man-made structures, such as bridges, cars, ships, refineries, aircraft, are all subject to the same environmental stresses. Light, temperature changes, water, and gasses in the air all play a role in the breakdown of materials. The one major difference is just how quickly that breakdown occurs.
A general term for the degradation of man-made structures is corrosion. Scientists try to understand the mechanisms by which corrosion occurs, design barriers to corrosion, find ways to monitor the progress of corrosion, and build processes for asset maintenance and systems to reduce the overall costs of corrosion to society.
The economic impact of corrosion has been researched at length. A well-known study published in 1999 by NACE (the National Association of Corrosion Engineers) titled The United States Cost of Corrosion Study indicates that the direct cost of corrosion is more than 3 percent of the Gross Domestic Product (GDP). Similar studies report direct costs ranging from 2 to 4.5 percent of the GDP. The real issue is where direct costs end and indirect costs begin.
Given these enormous costs, it is not surprising that there are large industries centered on:
- Corrosion prevention (such as additives in water systems, coating materials like paint for automobiles, etc.)
- Corrosion repair and maintenance
- Corrosion monitoring, detection, and measurement.
Regularly scheduled inspections can validate corrosion rates and allow engineers and operators to better plan for maintenance situations. While ultrasound thickness (UT) readings can be of occasional use with regularly scheduled inspections, they do not provide enough precision with the collection of manual thickness readings to adequately determine wall thickness losses from corrosion. Pitting cannot be reliably detected by conventional UT methods simply because the size of the defect is small compared to the area inspected. Phased array ultrasound (PAUT) techniques can be developed to approach the needed precision and get great coverage quickly.
The direct and indirect costs of corrosion can be staggering. With improved inspection technologies, such as digital radiography and phased array ultrasound, and maintenance schedules, equipment manufacturers and providers are helping organizations control costs and get a better handle on the health of their assets.
For more information on corrosion monitoring, detection and measurement, read Robert Ward’s article in Inspection Trends – Corrosion, Monitoring, Detection and Measurement. And, for more information on GE’s phased array flaw detectors, visit here.
By Bob Ward, Senior Product Manager, Portables, GE Measurement & Control