Blogs

When a hydroprocessing unit is revamped to process biofuel feeds, one of the areas that needs to be analyzed for a possible increased risk of corrosion is the recycle gas system. This gas is primarily hydrogen, and in renewables units will have a much higher water content compared to the previous refinery hydroprocessing service. Even downstream of the compressor, which adds some superheat to the stream, factors such as the piping not being insulated, low flow rates in some branches, cold climates, etc., can lead to water condensation in the lines. The risk of corrosion on carbon steel due to this water formation then depends primarily on the carbon dioxide content in the gas. Recent units have required tracing and insulating of this line to avoid corrosion. A unique scenario which can lead to stress corrosion cracking of stainless steel piping sections in recycle gas quench spools close to the reactor is also described.