Local Perforation of Boiler Tubes

One tube in a watertube boiler developed leakage from a perforation. The external surface was covered with a dark deposit indicative of local fusion. Perforation resulted from the development of a crack from the internal surface. Microscopic examination revealed extensive intergranular penetration by molten copper. Particles of copper were seen in scale deposits on the bore of the tube. The tube in general showed a ferritic structure with partially spheroidized carbide. The fact that fusion of the copper had occurred indicated temperatures of 1100 deg C (2012 deg F) had been experienced locally, and the structural condition suggested that the tube in general had been heated at a lower temperature of the order of 600 deg C (1112 deg F) for some appreciable time. In this instance, overheating of the tube in the absence of the copper deposits may not have led to failure.