Abstract
In high pressure boilers not only caustic corrosion but also potassium phosphate corrosion is very dangerous. Subsequently to the NaOH corrosion test on which we reported last time, we made a study of the potassium phosphate corrosion. The result obtained is as follows:
1) Potassium phosphate is easily concentrated on the “hot spot” of high pressure boiler tube, and the concentration in the state of equilibrium reaches about 40% in weight, when the difference between the temperature of the internal surface of the tube and that of the water flowing in the tube is 30°C.
2) The rate of corrosion of mild steel due to potassium phosphate aqueous solution is very high at the temperature of the “hot spot” of high pressure boiler tube. For instance, the corrosion rate reaches 20-30mg/cm2·100hr at 375°C, when the concentration is 30% in weight.
