I am thinking about using a carbohydrazide conditioner for a cooling water circuit at approx. 160 ºC. The exposed material is a high strength steel under tensile stress. I am aware that the substance will break down to hydrazine and CO2 at the given temperature and thus introduce carbonate to the system. Acidification by carbonate will be couterbalanced with a pH conditioner and the system will run at approx. pH 9.5. Will I run into the danger of inducing carbonate SCC to the high strength steel?
I think there is a strong probability that carbonate SCC can occur. The latter has occurred in the past in comparable service conditions.
Dear Felix Lampert
Operating cooling water circuit at approx. 160 ºC is critical condition since the decomposition temperature of carbohydrazide is reported about 180C and one should consider the steel surface temperature at least 10C higher therefore it is possible to get carbonate inducing to water circuit but it is difficult to say that you run into the danger SCC as this case need to have the applied and residual stress value is about or higher than the threshold value for carbonate SCC of the running steel system that you operate. so this can be only solved by laboratory test.
Best regards
Dear Dr. Perumal and Dr. Al'Atia,
Thank your for your input. This is very valuable for me.
Kind regards
Felix Lampert
Yes. True. Carbonate SCC can occur at certain temperature. at high temperature there will be o effect in case of carbonate as molecules will loose bonding and enthalpy value will be high.
Ashish
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