Mitigation of Flow-Accelerated Corrosion by Titanium Injection in PWR Secondary Systems

A useful method for the reduction of corrosion on carbon steel surfaces is chemical inhibition via injection of a mitigating agent. This agent acts to make the surface more protective by incorporation into and stabilization of the oxide layer. The set of experiments described here investigated three possible mitigating agents which all might act by incorporating Ti into the inner oxide. The root of this investigation comes after similar experiments in simulated CANDU primary coolant have proven that it is possible for Ti to aid in building a protective oxide.;The three compounds tested for transport properties and mitigating characteristics under simulated PWR feedwater conditions were titanium diboride (TiB 2), AeroxideRTM P25 (TiO2-anatase) and DuPont(TM) TyzorRTM LA (titanium lactate).;Typical chemistry conditions of the feedwater stream of a PWR were achieved in a pressurized water loop by careful chemical control of the coolant (pH 25°C = 9.2 +/-0.25 with ammonia, hydrazine to 40+/-10 ppb and temperature = 140°C) and the coolant flow rate was varied between 1.0 and 2.5 LPM (2.5 LPM normally) at key times in order to investigate flow effects. Flow-accelerated corrosion (FAC) was monitored utilizing an online measurement technique.;Additions generally up to 10 mug/L of Ti in the coolant were tested for an effect using all three compounds with the following results: (1) TiB 2: Ti transport around the loop in the coolant was possible, but deposits were slight; FAC changes were not observed. (2) DuPont(TM) TyzorRTM LA: Ti transport was again possible and deposit on the probes was sufficient to reduce FAC by ∼18%; flow dependencies of FAC were unchanged from previous work. (3) AeroxideRTM TiO2 P25: Ti transport was possible and deposits were slight; no measurement of FAC was available but the effect was expected to be similar to that of TiB2. While there is a notable and beneficial effect of the TyzorRTM additions, due to the relatively low benefit and the possible drawbacks, it is not likely that any in-plant trials will be performed.