Localised corrosion and atmospheric corrosion of stainless steels
Time: Fri 2019-12-13 14.00
Subject area: Chemistry
Doctoral student: Sukanya Hägg Mameng , Yt- och korrosionsvetenskap, Corrosion
Opponent: Professor Thomas Ladwein, Aalen University
Supervisor: Professor Rachel Pettersson, Jernkontoret; Professor Christopher Leygraf, Materialvetenskap, Materialvetenskap, Kemi, Yt- och korrosionsvetenskap
This research is focused on defining limiting conditions for corrosion of stainless steels. The aim of the first part (Papers I-IV) was to understand the role of alloying level and environmental parameters on localised corrosion in aqueous conditions. Testing was done with a combination of short-term electrochemical and long-term immersion experiments. Results show that the chloride ion concentration and temperature are the main factors that affect the localised corrosion resistance. The presence of residual chlorine is also significant, since it leads to the ennoblement of the corrosion potential. If the corrosion potential exceeds the breakdown potential, the stainless steel will suffer from localised corrosion. Oxygen content and pH were identified as additional factors influencing the corrosivity of the environment.
The aim of second part (Papers V-VIII) was to present information about the effect of alloying level, surface condition and environmental conditions on atmospheric corrosion resistance in Middle-East environments. Field exposure tests were performed and supplemented by laboratory aqueous corrosion tests. Results demonstrate that a higher alloying level (in both the bulk material and the surface), plus a smoother and cleaner surface gave an improvement in the corrosion performance and resistance to aesthetic degradation. Chloride and sulphate are the main surface contaminants found in the Middle East atmosphere. Stainless steels exposed in sheltered conditions showed a better atmospheric corrosion resistance than in open conditions. Three factors are considered to contribute to this difference: a very low rainfall, more condensation leading to corrosion in the open conditions and a higher level of beneficial sulphate in the deposits in sheltered conditions. The results showed a reasonable correlation between laboratory pitting corrosion tests and atmospheric field tests.
The results from this thesis provide reference data to aid selection of appropriate stainless steel grades. Results can also be used to help understand the limits for use of stainless steels in different conditions in both aqueous environments and in the atmosphere.