Steam expansion at turbine lowers its pH. Why?

It doesn't. chemicals in the boiler water are needed to assure proper condensate ph.

dougarthur42,

You have sure about that? In your opinion, the pH doesn't lowers in the process of expansion in turbine? Is not it the physiochemical phenomenon in the expansion of steam to reduce its ph?

It's strange that we have a superheated steam at pH of around 8 and its condensate after "condensation turbine", having a condensate with a pH of around 3.

I have no sure about that, because the constants of the steam can vary in the expansion process in the turbine stages: Kp = equilibrium constant in terms of partial pressure and its relationship with Kc = equilibrium constant in terms of concentration? I think it can explain what I'm telling!

I would like to know how you take Ph of superheated steam. You may be taking a sample of steam, condensing it then taking ph of the liquid condensate. Normally a ph value is present in the steam drum of the saturated steam. Volatile chemicals are added to the boiler water before it boils, these chemical are carried out with the steam and form as ph raising element of the condensate. But it has nothing to do with the turbine blading, even if the steam goes through a pressure reducing valve it will not volatize until it turns to condensate. So depending on how much volatile chemicals you use will determine ph of turbine condensate. how ever there are other factor that contribute to ph also. You are probably right about your equilibrium formula, but there are many factor that happen when superheated steam is condensed in a steam turbine. Heat and pressure are given up, impurities settle on blading, and I am sure that ph , conductivity and alkalinity are different before and after.