Inspection of wall thickness of the evaporator walls is usually performed from the inside of the boiler with standard ultrasonic (UT) spot testing. The costs for this type of inspection is largely determined by the cost for scaffolding and grinding and by safety measures which sometimes even include radiation control. The necessity for grinding also slightly impacts the accuracy of the readings. A new non-destructive testing application has been developed which provides the possibility to do this inspection from the outside of a boiler and thus eliminating the need for scaffolding. Windows of interest of about 10 to 120 ft2 are selected and provisions in the boiler insulation are made. The tubes in the selected areas are tested through UT scanning. The minimum wall thickness of each tube in that window is graphically presented in a report and repeat measurements enable the plant owner to compare these values in time. Trends in wall thickness reduction provide a basis for boiler life time prediction and to take preventive action. As a tool for preinspection to assess required maintenance measures (such as overlay welding or tube replacement), this test application has already shown to be very valuable. Recent applications include wall thickness assessment of refractory covered wall tubes, testing of boiler wall tubing with internal wall thickness loss at the fire sided tube face and wall thickness assessment of Inconel clad tubes at waste incinerators (EU project: NextGen Biowaste). This paper will discuss the method of non-destructive testing of wall thickness of the evaporator walls from the outside and will present examples where this method is applied.

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