Discussion on material selection for carbon dioxide compression devices
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As the title suggests, the carbon dioxide produced after compression in the low-temperature methanol washing unit is used as a raw material for urea. The pipes used to transport this carbon dioxide can be made of either stainless steel or carbon steel; what are the reasons behind choosing stainless steel?
The CO2 from low-temperature methanol washing is free of water, so carbon steel can be used for the pipelines; however, after compression, the carbon dioxide needs to undergo dehydrogenation treatment, and it is recommended to use stainless steel for the pipelines after decarburization
The corrosion of carbon dioxide pipelines is primarily caused by H2CO3 formed from CO2 + H2O. The CO2 product obtained through low-temperature methanol washing contains no water and only trace amounts of sulfur, so this aspect of corrosion can be disregarded. However, the urea plant requires dehydration (to prevent explosions in the exhaust gases), and dehydration involves introducing air into the system; oxygen will react with hydrogen, so stainless steel materials should be used for the pipelines at normal temperatures thereafter.
The operating conditions of this project do not take dehydrogenation into account. It has been questioned whether it is reasonable to opt for stainless steel due to the possibility of water not being completely removed during hydrostatic testing
Carbon steel is the usual choice, but it’s best to apply internal anti-corrosion protection