What Does Methanol-Induced Corrosion Mean?
Methanol-induced corrosion is a type of corrosion induced by methanol. It is a recognized problem in the gas and oil industries, pipelines, municipal sewage treatment systems, and a variety of industrial applications. Stress-corrosion cracking has been observed in absolute methanol.
For solutions with a methanol content of 50% or more, the corrosion rate of carbon steel is significantly higher in the aerobic environment than the anaerobic environment.
Large quantities of methanol (25%-50% by volume) were found to be the most effective for inhibiting the general corrosion of carbon steel under anaerobic conditions.
Corrosionpedia Explains Methanol-Induced Corrosion
The effect of methanol on corrosion is more complicated in acidic environments; the risk of localized corrosion increases with methanol content even though the general corrosion rate appears unaffected. An associated risk with the use of methanol is that oxygen is more soluble in methanol than in water.
Pitting corrosion was observed when the methanol content was 50% or more. When present in large quantities, methanol may compete with H2S for adsorption sites on the metal surface and block the passage of H2S, resulting in the formation of an uneven iron sulfide film. A metal surface with an inconsistent protective film is more prone to localized corrosion.
Under acidic gas conditions, the presence of methanol can increase the risk of sulfide stress cracking (SSC) and stress-oriented hydrogen induced cracking. Methanol can increase the rate of vapor phase corrosion, which directly increases the risk of a top-of-the-line corrosion failure.
Industrial methanol normally contains sufficient water to provide immunity to titanium. In the past, the specification of a minimum of 2% water content has proved adequate to protect commercially pure titanium equipment for all but the most severe conditions. In such conditions, due to temperature and pressure, titanium alloys would more than likely be required. A more conservative margin of safety was established by the offshore industry at 5% minimum water content. SCC of zirconium has been found in concentrated methanol solutions containing heavy metal chlorides, even though zirconium and its alloys are free from stress-corrosion cracking in seawater and most aqueous chemical media.