Because of the need for reliable electric power and the increasing cost of replacement power purchased on the spot market, the reliability of these tubes has taken on an increased importance. In fact, replacement power is sometimes not available and rolling brown outs or black outs are becoming increasingly frequent. The significant reductions in utility reserve capacity means that this situation will likely become worse as the competitive electric market approaches. Further, companies that purchase plants from other utilities are frequently unable to assess the metallurgical condition of the tubes and rarely have a complete operating history to use as a basis for evaluating tube remnant life.
Little effort is required to see that an accurate tube remaining life assessment tool is necessary.
The current approaches that employ internal oxide thickness measurements are commonly highly conservative. Although it is unlikely that a utility will experience tube failures using one of these methods, it is painfully true that the tubes will be replaced long before necessary. In the light of a net present value calculation, significant monies are wasted. The first topic to be discussed is the matter of deterministic versus probabilistic techniques. Clearly, a reheater or superheater is composed of many tubes.