High-temperature corrosion continued pressure effects

Principles and Characteristics Water is an interesting alternative for an extraction fluid because of its unique properties and nontoxic characteristics. Two states of water have so far been used in the continuous extraction mode, namely subcritical (at 100 °C < T < 374 °C and sufficient pressure to maintain water in the liquid state) and supercritical (T>374°C, p>218 bar). Unfortunately, supercritical water is highly corrosive, and the high temperatures required may lead to thermal degradation of less stable organic compounds. However, water is also an excellent medium for extraction below its critical temperature [412], Subcritical water exhibits lower corrosive effects. 

Conductivity measurement with contact electrodes is used in many different process analytical applications. In all of them the main interest is to detect the presence of ionic species in the sample. The effectiveness of distillation and demineralization units is normally controlled by continuous measurement of the conductivity of the outgoing stream. Any defect in the operation of the unit can immediately be seen in the increase in conductivity. The feeding water to steam turbines has to be as clean as possible in order to avoid corrosion in the system that operates under high pressure and at elevated temperatures. The conductivities of feeding water as well as the condensed steam are also continuously monitored by conductivity measurement. Increased conductivity is an immediate indication of corrosion in the system or leakage in the cooling system. This is of extreme importance in nuclear power plants where among other risks corrosion products may also become activated. 

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