Tales abound concerning operational failures in steam generating systems. In most cases, during the investigation phase of the root cause analysis, it becomes clear that the unit was not operated in the manner consistent with what the designers had in mind. To illustrate this point, several case studies are offered in this paper to demonstrate how out of design operation can lead to poor performance and possibly, tube failures.

Key Words: Deposit weight density (DWD), cation conductivity, condensate in-leakage, wick boiling, under deposit corrosion, circulation, oxygen pitting, galvanic corrosion, copper deposition, downcomers, finned tubes, gouging, departure from nucleate boiling (DNB), acid anions, spheroidization, heat affected zone (HAZ), thermal ramp rate, steam stall, pinch point, back pressure valve, header pressure sag, Widmanstatten structure, Larson-Miller parameter, creep voids.