Effect of Overheating and Incorrect Material Selection on Power Plant Superheater Tube

The present investigation portrays the tube failure in the superheater used in the power plants. The failure occurred after only three months of operation, by longitudinal fish-mouth rupture. The operating pressure of the object boiler is 192 bar while the temperature of its superheater steam is 540 °C. The failed tubes were fabricated from standard Si killed carbon steel. Many longitudinal parallel fine crack-like grooves were detected at the outer surface of the rupture area. Metallurgical examinations revealed that the failed tube remained subjected to overheating for the short-term. According to the analysis of the failed tubes, the temperature reached over 600 °C by insufficient coolant flow or unpredicted operating conditions. The carbon steel emerged as an underperforming material for the applications in superheater tubes, and it is highly recommended to replace the carbon steel by a high-grade Cr-Mo steel.

3D RECONSTRUCTION OF INNER STRUCTURE OF RADIOACTIVE SAMPLES UTILIZING GAMMA TOMOGRAPHY

Unique 3D tomography apparatus was built and successfully tested in Research Centre Rez. The apparatus allows three-dimensional view into the interior of low-dimension radioactive samples with a diameter up to several tens of millimeters with a betterresolution then 1 mm3 and is designed to detect domains with different levels of radioactivity. Structural inhomogeneities such as cavities, cracks or regions with different chemical composition can be detected using this equipment. The SPECT scanner has been successfully tested on several samples composed of a 3-mm radionuclide source located eccentrically within homogeneous steel bushings. To detect fine cracks inside a small sample, an ultrafine scan of the sample was carried out in the course of 24 hours with a 0.5-mm longitudinal and transverse step and 18° angular step. The exact location and orientation of a fine crack artificially formed inside a sample has been detected.