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Ultrasonic Sensor System for Wall-Thickness Monitoring

Metal loss due to corrosion and erosion is a widespread issue in the O&G and Power Generation industries for tanks, high-energy piping, pressure vessels, and other critical assets. Metal loss can result in loss of pressure containment with resulting consequences that can include: loss of life, damage to assets, disruption of service, environmental harm, loss of public image, fines and others. As such, asset inspections are required by operators and are mandated in regulations and codes such as 29CFR–1910; API 570, ASME Sections V & XI, and ASTM E797. While there are many methods for measuring wall thickness, a predominant method is the use of portable ultrasonic equipment. Ultrasound is non-intrusive as it is applied to the outside of the pipe or vessel, is accurate and relatively low cost to deploy in most situations. However, it does have several shortcomings including that the ultrasonic transducer or probe needs to be applied in direct contact to the external surface of the pipe requiring scaffolding, excavation, stripping of coatings or insulation, etc. Thus, the cost of access to the structure often far exceeds the basic cost of inspection. Furthermore, a trained and certified inspector is required to operate the ultrasonic instrumentation, requiring personnel to sometimes be exposed to potentially hazardous environments. The accuracy and repeatability of ultrasonic measurements are operator-dependent and recent studies have shown that the probability-of-detection (POD) can be poor1. Finally, the measurements are only performed periodically, taking a snap-shot of plant condition. Many end users are interested in investing in new technology to overcome these concerns. In the process industries, such as in petrochemical or refineries, all critical process parameters are measured in real time. Obtaining information on flow, temperature, pressure, PH, equipment upsets or unusual conditions are monitored and reported on a continuing basis via Key Performance Indicators or KPI’s. The automation of thickness measurements would alter the paradigm from the current, manual/periodic measurements to thickness and corrosion rate as a process and plant health variables that can be used to optimize asset usage and inspections.

  1. O’Brien, J. “Chevron NDE Performance Demonstration Exams” API Inspection Summit, January 26-29, Galveston Island Convention Center, Galveston, TX.
  2. Biagiotti, S. (1997) “Effect of Temperature on Ultrasonic Velocity in Steel” NACE Corrosion 97, Paper number 259, NACE International, Houston, TX.
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