A Nondestructive Approach to the Detection and Sizing of Diffused Carbon in Heater Tubes

The main cause of failure in furnace heater tubes is primarily related to carburization damage (i.e., residual carbon which is diffused into the material). Until recently the only reliable method of testing for carburization damage was to cut out a sample of pipe material, test it by metallurgical examination then weld the section back in. The application of a new nondestructive examination technique, developed specifi cally to detect and quantify carburization damage, negates the need to for cutting and welding of the pipe material. When used as part of a life assessment program, the information obtained from this inspection can be fed directly into life expectancy models, giving operators knowledge of future failure predictions. The new ultrasonic procedure was developed for 2-9% Chrome alloy, creep resistant heater tubes, which are prone to carburization damage. The procedure identifi es and quantifi es the amount of carburization damage present without the requirement for destructive examination. Although the test trials and procedure development were carried out on visbreaker type heater tubes, this paper relates to all heater tubes which are susceptible to the carburization damage mechanism.

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