Which is more resistant to chloride ions: 904 stainless steel, duplex steel, or titanium?
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Which is more resistant to chloride ions: 904 stainless steel, duplex steel, or titanium?
904 is an austenitic stainless steel that has strict requirements regarding chloride ions; long-term exposure to these ions can lead to intergranular corrosion, so it is not recommended for use. Both duplex steels and titanium are expensive. If the temperature of the medium is below 100°C, it is advisable to use plastic pipes or carbon steel pipes lined with PTFE, as these materials offer better corrosion resistance than duplex steels and titanium.
The principle behind stainless steel’s corrosion resistance lies in the passivation film, and the formation and breakdown of this film are influenced by the surrounding environment. 904L is a good material for sulfuric acid-based systems, but it is likely not suitable for environments with chloride ions. The MVR equipment used for wastewater treatment here is made of titanium; over time it will corrode and become damaged, so regular replacement is necessary to meet production requirements
Is it just simple chloride corrosion, or are there other factors such as temperature and pressure? If it is just chloride ions, this can be addressed with coatings, and the results are very good.
In terms of chloride resistance, duplex stainless steel is more durable than 904 stainless steel. 904 stainless steel ages and becomes brittle when exposed to chloride ions over a long period of time. However, titanium is more resistant to chloride ions than duplex stainless steel.
Materials resistant to chloride ions include titanium–duplex steel–904L. This can be reflected in the price of these materials; of course, other factors such as pressure and temperature also play a role
Is this order indicating an increasing chlorine resistance?
As I understand it, in terms of corrosion resistance to chloride ions in brine, from highest to lowest: TA2-904L-2205 (tested with coupon testing)
Stainless steel has inferior corrosion resistance to halogen elements (fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At)) compared to titanium
This depends on your specific operating conditions. For example: temperature, pressure, medium properties, and concentration, and then a selection is made based on the specific operating conditions. Non-metallic materials, composite materials, linings, spraying, and other solutions can also be chosen.