By Marco Lendi, Swan Analytical Instruments Switzerland, Dr. Heinz Wagner, Swan Analytical Instruments Switzerland, Dr. Peter Wuhrmann, Swan Analytical Instruments Switzerland, and Randy Turner, Swan Analytical USA
Proper measurement of pH is a key factor of corrosion risk surveillance in water-steam cycles. Since it still seems to be difficult to measure the sample pH directly with glass electrodes, pH calculation, using the difference of sample conductivity before and after a strong acid ion-exchanger, is a frequently used alternative. The precision and reliability of this measuring method is well known and proven in water-steam cycles containing one alkalization agent only. For applications using mixtures of alkalization agents, the pH calculation model was never verified. We present here calculation models to predict the precision and limitation of the pH calculation by differential conductivity measurement in morpholine-ammonia and ethanolamine-ammonia mixtures.