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51318-10846-Comparison of critical pitting temperatures of stainless steel in different salt solutions

This paper attempts to compare the critical pitting temperature (CPT) for alloys when ASTM G150 is not applicable. By using MgCl2 as electrolyte, the boiling point is increased and the measuring zone for CPT is broader.

Product Number: 51318-10846-SG
Author: Anna Delblanc / Kristina Lund / Anna Iversen
Publication Date: 2018
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  Localized corrosion, such as pitting and crevice corrosion, is one of the most common reasons to failure in stainless steels. The standard method ASTM G150 measures the critical pitting temperature (CPT) electrochemically, and is used to rank the pitting corrosion resistance in stainless steels. However, for high-alloyed materials such as hyper-duplex and super-austenitic grades with a Pitting Resistance Equivalent (PRE) above 48, the resistance to pitting corrosion is too high to be measured in 1M NaCl, mainly because of limitations in the boiling point of NaCl. For such alloys, the critical crevice temperature (CCT) may be used for ranking these materials, but it is more difficult to rank and compare high-alloyed stainless steels with respect to their pitting resistance.

 This paper attempts to compare the CPT for alloys when ASTM G150 is not applicable. By using MgCl2 as electrolyte, the boiling point is increased and the measuring zone for CPT is broader.

The CPT values of austenitic and duplex stainless steels have been measured in 1M NaCl and in 3M MgCl2. A linear relationship between the CPT values was found. The chloride concentrations and the pH-values were measured and the solubility concept in the salt solutions has been considered.

Key words: Stainless steel, austenitic stainless steel, super-austenitic stainless steel, duplex stainless steel, super-duplex stainless steel, hyper-duplex stainless steel, pitting corrosion, sodium chloride, magnesium chloride, salt solutions, electrolyte, ASTM G150, UNS S31600, UNS N90804, UNS S31254 UNS S34565, UNS 32654, UNS 32304, UNS S32005, UNS S32750

 

 

  Localized corrosion, such as pitting and crevice corrosion, is one of the most common reasons to failure in stainless steels. The standard method ASTM G150 measures the critical pitting temperature (CPT) electrochemically, and is used to rank the pitting corrosion resistance in stainless steels. However, for high-alloyed materials such as hyper-duplex and super-austenitic grades with a Pitting Resistance Equivalent (PRE) above 48, the resistance to pitting corrosion is too high to be measured in 1M NaCl, mainly because of limitations in the boiling point of NaCl. For such alloys, the critical crevice temperature (CCT) may be used for ranking these materials, but it is more difficult to rank and compare high-alloyed stainless steels with respect to their pitting resistance.

 This paper attempts to compare the CPT for alloys when ASTM G150 is not applicable. By using MgCl2 as electrolyte, the boiling point is increased and the measuring zone for CPT is broader.

The CPT values of austenitic and duplex stainless steels have been measured in 1M NaCl and in 3M MgCl2. A linear relationship between the CPT values was found. The chloride concentrations and the pH-values were measured and the solubility concept in the salt solutions has been considered.

Key words: Stainless steel, austenitic stainless steel, super-austenitic stainless steel, duplex stainless steel, super-duplex stainless steel, hyper-duplex stainless steel, pitting corrosion, sodium chloride, magnesium chloride, salt solutions, electrolyte, ASTM G150, UNS S31600, UNS N90804, UNS S31254 UNS S34565, UNS 32654, UNS 32304, UNS S32005, UNS S32750

 

 

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