Research On The Initial Corrosion Behavior Of Carbon Steel In The Typical Environment Of Nuclear Power Plants

Coastal areas often become key development places because of their geographical advantages,and the regional atmosphere gradually changed from the marine to the marine-industrial environment with the increase of industries.The pumping station in nuclear power plate which often built in coastal areas with many different functions is distributed a large number of carbon steel structures and pipelines,and its inner atmosphere filled with salts because of the seawater filtration function.Many researches have been done on the corrosion behavior of carbon steel in the natural atmosphere,but these studies focus on analyzing medium and long-term results and pay less attention to corrosion behavior in the short term.The atmospheric corrosion process is complex and is influenced by many factors,such as weather conditions?temperature?humidity?rainfall?,material compositions,corrosion products,etc.Materials produce relatively light corrosion and fewer products over a short period of time,so we can see the process of corrosion occurrence and evolution more clearly and better understand the related corrosion mechanism.Therefore,we carried out a short-term exposure experiment of carbon steel in a marine-industrial atmosphere and a PX pumping station.The corrosion behavior of carbon steel was analyzed from the aspect of corrosion dynamics,macro-and micromorphology,corrosion product and electrochemical.We also discussed the effects of stress on corrosion and the effects of uniform corrosion and local corrosion on the mechanical properties of carbon steel.At the same time,the corrosion degree of other environments in nuclear power plate is analyzed quantitatively by exposing carbon steel to these environments for half a year.The following main conclusions were drawn:The thickness loss of carbon steel in the marine-industry atmosphere is almost linear with exposure time and the average corrosion rate affected by environmental factors such as temperature and humidity fluctuates.The corrosion product components are ?-FeOOH and ?-FeOOH at the early stage,and then Fe₃O₄ was detected.The amount of y-FeOOH has a trend of decreasing over exposure time,?-FeOOH is opposite,and Fe₃O₄ is relatively stable.Pitting and irregular localized corrosion can be observed on the surface of samples exposed for 10 days.The rust layer covered the entire surface of samples exposed for 60 days is uneven and has much nest structures which can weaken the protection of the layer.The thickness loss of carbon steel in the PX pumping station can be well fitted with power function,and the average corrosion rate decreases over exposure time.The corrosion product components are ?-FeOOH,y-FeOOH,?-FeOOH and Fe₃O₄.The content of ?-FeOOH is highest,and ?-FeOOH is lowest.The proportion of compositions is relatively stable after 30 days.Localized corrosion is the main type at the early stage of corrosion.Lip type corrosion and annular pitting can be observed on the surface of carbon steel specimens exposed for 20 days.The center and outer part of annular pitting are different in terms of structure and the content of chloride ion.The localized corrosion gradually transformed to the uniform corrosion.The applied stress can increase the corrosion of carbon steel by damaging the rust layer.The damage will be severe when the applied stress exceeds the yield strength.The corrosion products of all specimens are ?-FeOOH,?-FeOOH and Fe₃O₄.The amount of y-FeOOH increased when the stress was applied,?-FeOOH and/or Fe₃O₄ decreased.Uniform corrosion and local corrosion can lead to the degradation of the mechanical properties of carbon steel.The thickness loss of carbon steel in MX station is least;YA station takes the second place;PX8,PX8W and PX9W have large and similar value.