Asignificant limiting factor that affects tube life in fossil fired steamboilers is the growth of iron oxide scale (magnetite) on the inside and outsidetube surfaces. The oxide scale, which forms under long term exposure to veryhigh temperatures, acts as a thermal insulator. While external scale limitsheat transmission into the tube and reduces boiler efficiency, internal scalebuildup represents a potentially more serious problem. The insulating effect ofinternal scale limits heat transmission into the water vapor inside the tube,which in turn causes chronic overheating of the tube wall and promotesaccelerated metallurgical failure. Non Destructive measurement of internaloxide scale thickness is of major interest in the power generation industry andother users of fossil fuel steam boilers, since scale thickness may be used topredict remaining tube life. While very high frequency ultrasonic gagingtechniques have been available for this measurement for a number of years, theyinvolved use of cumbersome, expensive pulser/receiver and oscilloscope systems.Recent advances in instrumentation technology have made available small,hand-held ultrasonic gages with software optimized for measurement of internalscale and advanced data logging capability. Additionally, the use of normalincidence shear wave transducers improves resolution of thin scale layers,permitting measurement of scale buildup down to approximately 0.125 mm withhand-held equipment. ITE has uses Olympus 38 DL plus with suitable probes fortesting of tubes for deposition of oxide scales. We have been providing theseservices for more than a decade and have various customers across the countryin Power Sector who regularly use our services.
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