Abstract
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 degrees 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 degrees 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.