Monitoring a degradation of steam generator boiler tubes

The present invention is concerned with an on-line degradation monitoring for boiler tubes (15a,15b) in large combustion facilities, in particular waste incineration plants. The degradation of the tubes, in particular corrosion or caking, is determined in a more or less continuous manner while the combustion facility is operating, and thus not restricted to optical inspection during downtimes. A rate or accumulated degradation can be related to an operation mode of the facility. Appropriate degradation sensors (4) are arranged outside of a flue gas tract (14) where the boiler tubes are exposed to noxious flue gases from the combustion process, and receive ultrasonic signals from a space or volume within the flue gas tract (14). A test tube (40) is provided exclusively for the monitoring of the degradation progress and introduced into the flue gas tract (14) at a particularly corrosion exposed location.