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Localised corrosion and atmospheric corrosion of stainless steels
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. (Corrosion)ORCID iD: 0000-0001-8182-6530
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

Denna avhandling inriktar sig på att definiera gränser för korrosion hos rostfria stål. Syftet med den första delen (Artikel I-IV) var att förstå inverkan av legeringssammansättning och miljöparametrar på lokal korrosion i vattenlösningar. En kombination av elektrokemiska korttidsförsök och långvarig provning har utförts. Resultaten visar att kloridhalten och temperaturen är de två viktigaste faktorerna som påverkar den lokala korrosionsbeständigheten hos rostfritt stål. Närvaro av kvarvarande klor är också en betydande faktor som leder till att korrosionspotentialen ökar. Om korrosionspotentialen når genombrottspotentialen drabbas det rostfria stålet av lokal korrosion. Syreinnehåll och pH visade sig vara ytterligare faktorer som påverkar miljöns korrosivitet. Syftet med den andra delen (Artikel V-VIII) var att presentera information om hur olika legeringsämnen, yttillstånd och miljöparametrar påverkar den atmosfäriska korrosionsbeständigheten i Mellanöstern. Fälttester har utförts i kombination med korrosionstester i laboratoriet. Resultaten visar att ett högre legeringsinnehåll (i både bulkmaterialet och på ytan), samt en jämnare och rengjord yta gav en förbättring av korrosionsegenskaperna. Klorid och sulfat är de två huvudsakliga föroreningarna som finns i Mellanösterns atmosfär. Rostfria stål exponerade under skyddade förhållanden uppvisade en bättre korrosionsbeständighet än under öppna förhållanden. Tre faktorer anses bidra till denna skillnad: en mycket låg nederbörd, mer kondens som leder till korrosion under öppna förhållanden och en högre nivå av gynnsamt sulfat i avlagringar under skyddade förhållanden. Resultaten visade också en rimlig korrelation mellan laboratorietester och de atmosfäriska fälttesterna. Resultaten från forskningen ger referensdata som kan användas som stöd för materialval och för att lättare kunna välja rätt rostfri stålsort. Resultaten kan också användas för att förstå gränser för rostfritt stål gällande lokal korrosion i olika miljöer.

Place, publisher, year, edition, pages
KTH: KTH , 2019. , p. 109
Series
TRITA-CBH-FOU ; 2019:56
Keywords [en]
stainless steel, localised corrosion, atmospheric corrosion, alloy composition, surface finish, surface roughness, surface treatment, surface orientation, contamination, chloride, sulphate, temperature, chlorination, exposure conditions.
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-263756ISBN: 978-91-7873-330-9 (print)OAI: oai:DiVA.org:kth-263756DiVA, id: diva2:1369553
Public defence
2019-12-13, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 2019-11-19

Available from: 2019-11-19 Created: 2019-11-12 Last updated: 2019-11-21Bibliographically approved
List of papers
1. Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water
Open this publication in new window or tab >>Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water
2011 (English)In: Proceedings Eurocorr 2011, 2011Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

In drinking water systems, the main stainless steel grades used are the standard austenitic stainless steel grades 4307 (304L) and 4404 (316L), with the grade selection depending on the chloride and chlorine levels in the water. The lean duplex grades LDX 2101® and LDX 2404® provides attractive alternatives, with a more stable price and higher strength level, but there is little available data on their use in drinking water systems.

The European Drinking Water Directive sets a maximum limit of 250 ppm (mg/L) for chlorides in drinking water but does not contain guidelines for chlorine. Drinking water is normally treated to give a residual level of 0.2 to 0.5 ppm of chlorine to kill bacteria, but the actual concentrations added are usually higher. The WHO drinking water standard states that 2-3 ppm chlorine should be added to water in order to gain a satisfactory disinfection and adequate residual concentration. For a more effective disinfection the residual amount of free chlorine should exceed 0.5 ppm after at least 30 minutes of contact time at a pH value of 8 or less.

The residual chlorine has a significant influence on the corrosion behavior of stainless steels. The remaining of residual chlorine in drinking water is a major factor leading to the ennoblement of the natural potential of stainless steel. This oxidizing effect of chlorine may have detrimental consequences in that stainless steels may suffer from localized corrosion if an inappropriate grade is used.

The aim was to understand and determine to what extent residual chlorine levels at various chloride contents will affect the localized corrosion behaviour of the standard austenitic stainless steel grades 4307 and 4404, also the duplex grades LDX 2101®, LDX 2404® and 2205. A simulated chlorination system was created in which the specimens were immersed for 30 days at 30°C and 50°C at chloride levels of 200 ppm and 500 ppm, with residual chlorine levels of 0.2, 0.5 and 1 ppm at pH 6.5-7.5. The specimens were investigated by visual examination and microscopy.

The duplex grades LDX 2404® and 2205 perform very well in all the chlorinated environments tested. The lean duplex grade LDX 2101® performed as well as or better than 304L at both 30°C and 50°C. The results also indicated that the presence of a crevice increased the risk for localized corrosion in a chlorinated environment. This study demonstrates that duplex stainless steels are good candidates to use in water pipes or water storage tanks.

Keywords
drinking water, chloride, chlorination, total residual chlorine (TRC), localised corrosion, stainless steel
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-263815 (URN)
Conference
EUROCORR 2011, 4-8 September 2011, Stockholm, Sweden
Note

QC 20191115

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19Bibliographically approved
2. Limiting conditions for pitting corrosion of stainless steel EN 1.4404 (316L) in terms of temperature, potential and chloride concentration
Open this publication in new window or tab >>Limiting conditions for pitting corrosion of stainless steel EN 1.4404 (316L) in terms of temperature, potential and chloride concentration
2017 (English)In: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 68, no 3, p. 272-283Article in journal (Refereed) Published
Abstract [en]

The main stainless steel grades used for water applications are 1.4307 and 1.4404. The grade selection depends on the conditions: 1.4404 is a more conservative choice and has an improved corrosion resistance over 1.4307. This paper addresses the concept of defining limiting conditions for pitting corrosion of 1.4404 in terms of the environmental parameters such as temperature, potential and chloride concentration. Extensive testing has been done with a combination of short-term electrochemical measurements and long-term chlorination experiments. Results are discussed in the light of the current understanding of the critical levels of key parameters for pitting corrosion.

Place, publisher, year, edition, pages
Materials and Corrosion: , 2017
Keywords
Pitting corrosion, stainless steel, chloride ion, temperature, 316L, chlorination, pitting diagram
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-263817 (URN)10.1002/maco.201609061 (DOI)000395403000001 ()2-s2.0-84978915409 (Scopus ID)
Note

QC 20191115

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19Bibliographically approved
3. Corrosion of Stainless Steel in Sodium Chloride Brine Solutions
Open this publication in new window or tab >>Corrosion of Stainless Steel in Sodium Chloride Brine Solutions
2014 (English)Conference proceedings (editor) (Other (popular science, discussion, etc.))
Abstract [en]

With increasing environmental awareness follows demands for handling of brines that remain after use in a variety of applications. For this reason, stainless steels are being used in increasingly corrosive brine environments. The risk for corrosion in brines is associated with the chloride content, temperature, pH and oxygen level. This paper aims to explore the corrosion resistance of some stainless steels in highly concentrated sodium chloride solutions.

The resistance to localized corrosion of stainless steels in 20,000,100,000 and 200,000 ppm Cl - sodium chloride solutions was investigated at 90°C. The effects of chloride content, oxygen content and solution pH were studied on test coupons with and without welds and on U-bend specimens. Evaluation was performed for pitting and crevice corrosion, as well as for stress corrosion cracking. Long-term exposures (>1300 hours) were combined with electrochemical measurements such as cyclic polarization curves and determination of the critical pitting temperature (CPT). Investigated materials included duplex, super duplex, as well as 6Mo and 7Mo super austenitic stainless steels, which were compared to a standard austenitic grade.

A ranking of the tested stainless steel grades according to their corrosion resistance in sodium chloride brine solutions was: UNS S31603 < UNS N08904, UNS S32205 < UNS S31254, UNS S32750 < UNS S34565 < UNS S32654. Oxygen content was found to be an important factor influencing the corrosiveness of the sodium chloride brine solutions, with aerated conditions being the most corrosive ones. Also increasing chloride content and decreasing pH increased the corrosiveness of sodium chloride brine solution.

Place, publisher, year, edition, pages
NACE International, 2014. p. 12
Keywords
stainless steel, corrosion, brine, sodium chloride, pitting corrosion, crevice corrosion, stress corrosion cracking
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-263812 (URN)
Conference
Nace Corrosion Conference
Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19
4. Limiting conditions of pitting corrosion for lean duplex stainless steel as a substitute for standard austenitic grades
Open this publication in new window or tab >>Limiting conditions of pitting corrosion for lean duplex stainless steel as a substitute for standard austenitic grades
2014 (English)In: Proceedings EUROCORR Conference 2014, 2014Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

Lean duplex stainless steels such as EN 1.4162 (LDX 2101Ò) are today used in many applications where they can substitute for the standard austenitic stainless steel 304L and 316L. The advantages include higher strength, better resistance to stress corrosion cracking, good uniform corrosion resistance and better price stability due to the lower nickel content.

This paper focuses on the performance of the lean duplex stainless steel LDX 2101Ò as a substitute for type 304L and 316L in chloride containing environments ranging from potable water to seawater. A combination of short term electrochemical testing and long term exposures is used to investigate the tendency to pitting corrosion as a function of chloride concentration and temperature. This is used to define the limiting conditions for pitting corrosion and construct engineering diagrams showing the risk areas for localised corrosion as a function of environmental parameters. Results are discussed in terms of the role of alloying elements and microstructure.

 

Keywords
Lean duplex stainless steel, EN 1.4162 (LDX 2101Ò), temperature, potential, chloride concentration, pitting potential, engineering diagram.
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-263813 (URN)
Conference
EUROCORR Conference 2014, 8-12 September 2014, Pisa, Italy
Note

QC 20191115

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19Bibliographically approved
5. Atmospheric Corrosion Resistance of Stainless Steel: Results of a Field Exposure Program in the Middle-East
Open this publication in new window or tab >>Atmospheric Corrosion Resistance of Stainless Steel: Results of a Field Exposure Program in the Middle-East
2016 (English)In: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 161, no 1, p. 33-43Article in journal, Editorial material (Refereed) Published
Abstract [en]

Stainless steels have been widely used as architectural and construction materials because of their high degree of corrosion resistance, unique aesthetic quality, and stability in an unpolluted atmosphere. Although stainless steel is highly corrosion resistant, localized corrosion can occur in certain environments, especially in marine atmospheric conditions if the appropriate grade is not used. Exposure of stainless steel to an environment more aggressive than the limiting conditions may be harmful to its aesthetic appearance and ultimately even to its load-bearing capacity. Selecting a suitable stainless steel grade requires knowledge of the actual location of the application and the atmospheric conditions. In terms of materials selection, the austenitic stainless steel grade 316/316L has proved a very popular choice for architectural applications in many locations, but it is not always suitable at demanding sites such as marine environments in the Middle-East. In such cases the use of a higher-performance grade, often in combination with a good surface finish and established cleaning routines, is required to maintain pristine surfaces.

The main objective of this paper is to present information about the atmospheric corrosion resistance of a number of stainless steels in the Middle-East at a marine site. The results obtained are analysed and discussed in terms of factors affecting atmospheric corrosion of stainless steel such as the, alloying element level, surface roughness, surface treatment, and microclimate.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Atmospheric corrosion of stainless steel, marine environment
National Category
Engineering and Technology
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-263806 (URN)10.1007/s00501-016-0447-9 (DOI)
Note

QC 20191115

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19Bibliographically approved
6. Effect of surface finishes on the atmospheric corrosion of duplex grade UNS S32205: results of a field exposure program in Dubai
Open this publication in new window or tab >>Effect of surface finishes on the atmospheric corrosion of duplex grade UNS S32205: results of a field exposure program in Dubai
2016 (English)Conference proceedings (editor) (Other (popular science, discussion, etc.))
Abstract [en]

The duplex grade UNS S32205 is an excellent choice in many marine environments where UNS S31603 is on the borderline in regards to atmospheric corrosion resistance. The properties of S32205 make it well suited for construction with respect to strength, reduced maintenance, durability and long-term service. In marine environments the use of a sufficiently highly alloyed stainless steel, often in combination with a good surface finish and adequate maintenance, is required to maintain pristine surfaces.

The main objective with this paper is to present information about the effect of different surface finishes on the corrosion and aesthetic appearance of the duplex grade S32205 exposed at a marine test site in Dubai, UAE. The results obtained include the effect of characteristics such as surface roughness, surface treatment and surface orientation after several years of exposure. Results show that duplex grade UNS S32205 can be considered for architectural materials in severe marine locations such as the Dubai site. A smooth surface and an appropriate surface treatment give improved corrosion resistance. Chromium and silicon in the passive film were found to be beneficial in terms of resistance to aesthetic degradation. A correlation was observed between aqueous corrosion resistance measured in laboratory pitting corrosion tests and the atmospheric field test results.

Place, publisher, year, edition, pages
NACE International, 2016. p. 15
Keywords
duplex stainless steel UNS S32205, atmospheric corrosion, appearance, surface finish, pitting
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-263808 (URN)
Conference
Nace Corrosion Conference 2016
Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19
7. Effect of Stainless Steel Composition on Atmospheric Corrosion Resistance at a Marine Site in Dubai
Open this publication in new window or tab >>Effect of Stainless Steel Composition on Atmospheric Corrosion Resistance at a Marine Site in Dubai
2017 (English)In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 73, no 7, p. 880-891Article in journal (Refereed) Published
Abstract [en]

The influence of the composition of stainless steels on atmospheric corrosion resistance in a marine environment in Dubai was investigated after 2 y and 4 y of exposure. Different stainless steel grades with different surface finishes were included in the investigation: three ferritic stainless steels, five austenitic stainless steels, and four duplex stainless steels. The alloying elements chromium (Cr) and molybdenum (Mo) both had a beneficial influence on the corrosion resistance. The pitting resistance equivalent number (PREN =%Cr + 3.3%Mo + 16%N) and the (%Cr + 3.3%Mo) content in the surface film correlated well to the atmospheric corrosion resistance. An increased Cr content both in the bulk material and in the passive film improved the atmospheric corrosion resistance and the additional presence of Mo was effective in preventing red rust and also reduced the depth of pits. The depth of the pitting attack and the degree of aesthetic degradation were both influenced by alloying level, surface finish, and exposure conditions (open and sheltered). In the severe marine environment in Dubai, it is necessary to use Mo-bearing high-Cr stainless steel for adequate atmospheric corrosion resistance. The most resistant stainless steel grades were the high alloyed grades which ranked in the order UNS S31254 similar to UNS S3750 < UNS S34565 < UNS S32654. The duplex stainless steel grade S32205 may be considered for construction and architectural materials in Dubai but is likely to require more maintenance.

Place, publisher, year, edition, pages
National Assoc. of Corrosion Engineers International, 2017
Keywords
alloying composition, appearance rating, atmospheric corrosion, marine environment, rust and stain, surface film
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-210340 (URN)10.5006/2372 (DOI)000403213200010 ()2-s2.0-85021262110 (Scopus ID)
Note

QC 20170704

Available from: 2017-07-04 Created: 2017-07-04 Last updated: 2019-11-19Bibliographically approved
8. Atmospheric corrosion resistance of stainless steel in the Middle East: Result of a field exposure program in various environments
Open this publication in new window or tab >>Atmospheric corrosion resistance of stainless steel in the Middle East: Result of a field exposure program in various environments
2017 (English)Conference proceedings (editor) (Other (popular science, discussion, etc.))
Abstract [en]

The environmental conditions and the characteristics of the stainless steel grades used such as alloying composition and surface condition are the most significant factors affecting the atmospheric corrosion resistance of stainless steels. The environment in the Middle East is characterized by high temperature and very little rain fall which together with the distance to the sea have a huge effect on the corrosiveness. The closer the distance is to the sea the higher the corrosivity is of the atmosphere.

Selecting suitable stainless steel grades in different locations in the Middle East requires knowledge of the actual atmospheric condition at the location of the application. The aim with this paper is to present information about the effect of various environments in the Middle East on the atmospheric corrosion performance of stainless steels after 4 years exposure. Three different test sites were selected in this study: a marine site and a semi-marine site in the UAE and a rural site in Saudi Arabia. The field test results obtained are used for comparing the atmospheric corrosion resistance of eight different stainless steel grades: two ferritic, two austenitic and four duplex stainless steel grades. The atmospheric corrosion resistance of the stainless steel coupons was determined in terms of corrosion resistance and aesthetic appearance.

Place, publisher, year, edition, pages
NACE International, 2017. p. 14
Keywords
Stainless steel, atmospheric corrosion, appearance rating, marine environment, semi-marine environment, rural environment, Middle East, chloride ion in soluble deposit
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-263811 (URN)
Conference
Nace Corrosion Conference
Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2019-11-19

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