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Pitting corrosion on stainless steel with or without passivation

Karlsson, Jeanette LU (2017) KOO920 20162
Centre for Analysis and Synthesis
Abstract
The stainless steel metal includes a large group of alloys and which one should choose for a process can be difficult to determine. Despite much research on corrosion, there is still disagreement on the impact of the corrosion resistance from passivation. This master thesis was assembled together with Tetra Pak to see the influence of passivation on stainless steels used in their processes.
The goal of this master thesis was to understand whether the passivation of the two stainless steels gave a better protection against corrosion. This was supposed to be investigated at different temperatures and concentrations of chloride ions. A large part of the project however, became finding out the right method to measure with. Because of this,... (More)
The stainless steel metal includes a large group of alloys and which one should choose for a process can be difficult to determine. Despite much research on corrosion, there is still disagreement on the impact of the corrosion resistance from passivation. This master thesis was assembled together with Tetra Pak to see the influence of passivation on stainless steels used in their processes.
The goal of this master thesis was to understand whether the passivation of the two stainless steels gave a better protection against corrosion. This was supposed to be investigated at different temperatures and concentrations of chloride ions. A large part of the project however, became finding out the right method to measure with. Because of this, the master thesis has given large insight of how a project proceeds from start to finish and has brought knowledge in problem solving and planning.
In this project, stainless steel types 304 and 316 were studied using polarization and OCP measurements. The stainless steels in half of the measurements had been passivated with citric acid. From the initial measurements it was clear that the OCP measurements required more time than the project could offer - after 12 hours it had still not reached a stable value and thus could not be used to draw any conclusions. One could nevertheless see tendencies for an increased protection by passivation in the beginning of the measurements, but after some time the values tended to reach stagnation.
The polarisation measurements gave more varying results and appeared to be more sensitive against small differences in the system. From the polarisation measurements one could see that the pitting potential (Epit) ranged from 2.37E-6 mm/year to 1.44E-4 mm/year. The corrosion rate (Crate) with the estimated compositions of the steel varied between 149mV and 1235mV. The reliability of the measurements was questioned early in the process since the results differed from what was expected. The accuracy was later seen more clearly by comparing results from the same tests with each other. Since the temperature in this project differed greatly from the temperatures that are used in Tetra Pak’s processes, one cannot advise on whether to passivate or not. However, the report can lead to knowledge of methods to measure corrosion and knowledge of how materials are affected at lower temperatures. The report also contains advice on how the research should continue. (Less)
Popular Abstract (Swedish)
Korrosion (rost) är ett stort forskningsområde som hunnit komma långt, men fortfarande finns det mycket kvar att lära. Detta kan man se enbart genom att reflektera över de nästan 100 miljarder kronor som korrosionsskador kostar samhället i Sverige årligen. Rostfritt stål har ett vilseledande namn då det faktiskt rostar i vissa miljöer. I detta projekt har korrosion av rostfritt stål undersökts i olika miljöer för att se skillnaden med och utan förbehandling. Förbehandlingen gör att det rostfria stålet får ett ökat skyddande lager.
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author
Karlsson, Jeanette LU
supervisor
organization
course
KOO920 20162
year
type
H2 - Master's Degree (Two Years)
subject
keywords
materials chemistry, materialkemi
language
English
id
8903674
date added to LUP
2017-02-24 12:48:09
date last changed
2017-02-24 12:48:09
@misc{8903674,
  abstract     = {The stainless steel metal includes a large group of alloys and which one should choose for a process can be difficult to determine. Despite much research on corrosion, there is still disagreement on the impact of the corrosion resistance from passivation. This master thesis was assembled together with Tetra Pak to see the influence of passivation on stainless steels used in their processes. 
The goal of this master thesis was to understand whether the passivation of the two stainless steels gave a better protection against corrosion. This was supposed to be investigated at different temperatures and concentrations of chloride ions. A large part of the project however, became finding out the right method to measure with. Because of this, the master thesis has given large insight of how a project proceeds from start to finish and has brought knowledge in problem solving and planning. 
In this project, stainless steel types 304 and 316 were studied using polarization and OCP measurements. The stainless steels in half of the measurements had been passivated with citric acid. From the initial measurements it was clear that the OCP measurements required more time than the project could offer - after 12 hours it had still not reached a stable value and thus could not be used to draw any conclusions. One could nevertheless see tendencies for an increased protection by passivation in the beginning of the measurements, but after some time the values tended to reach stagnation. 
The polarisation measurements gave more varying results and appeared to be more sensitive against small differences in the system. From the polarisation measurements one could see that the pitting potential (Epit) ranged from 2.37E-6 mm/year to 1.44E-4 mm/year. The corrosion rate (Crate) with the estimated compositions of the steel varied between 149mV and 1235mV. The reliability of the measurements was questioned early in the process since the results differed from what was expected. The accuracy was later seen more clearly by comparing results from the same tests with each other. Since the temperature in this project differed greatly from the temperatures that are used in Tetra Pak’s processes, one cannot advise on whether to passivate or not. However, the report can lead to knowledge of methods to measure corrosion and knowledge of how materials are affected at lower temperatures. The report also contains advice on how the research should continue.},
  author       = {Karlsson, Jeanette},
  keyword      = {materials chemistry,materialkemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Pitting corrosion on stainless steel with or without passivation},
  year         = {2017},
}