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Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water
Outokumpu Stainless AB, Avesta Research Centre, Avesta, Sweden. (Surface and corrosion science)ORCID iD: 0000-0001-8182-6530
Outokumpu Stainless AB, Avesta Research Centre, Avesta, Sweden.ORCID iD: 0000-0002-0980-0560
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.

Place, publisher, year, edition, pages
2011.
Keywords [en]
drinking water, chloride, chlorination, total residual chlorine (TRC), localised corrosion, stainless steel
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-263815OAI: oai:DiVA.org:kth-263815DiVA, id: diva2:1370290
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
In thesis
1. Localised corrosion and atmospheric corrosion of stainless steels
Open this publication in new window or tab >>Localised corrosion and atmospheric corrosion of stainless steels
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
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:nbn:se:kth:diva-263756 (URN)978-91-7873-330-9 (ISBN)
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

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