What is the corrosivity of H₂O₂ when injected into a process water?

In most cases, the corrosivity imparted a process water by adding H2O2 is due to dissolved oxygen which is a natural decomposition product of H2O2. Oxygen has known corrosive properties toward ferrous metals, with well documented pH, temperature, pressure and salinity effects.

For diluted solutions of H2O2 (< 1%), Perry's Chemical Engineering Handbook indicates corrosion rates of < 0.02 in. per yr (< 0.5 mpy).

• Oil field brine corrosity. In coupon tests involving oil field brine, corrosion rates on 1030 carbon steel were 6 mpy after 30 days exposure to a few hundred mg/L H2O2. Brine is known to be corrosive when oxygenated and the corrosion rate for most applications of H2O2 will be less.
• Soluble icon corrosity. The study developed a model which related corrosivity to (soluble) iron content, pH and H2O2 dose. Iron level and pH were found to be far more significant than H2O2 dose, and when the iron levels were low, there was virtually no effect attributable to H2O2. Still, it is prudent to consider corrosivity when designing injection assemblies, where H2O2 concentrations will be greatest.

Two scenarios warrant special notice:

• Applications involving H2S or Fenton's Reagent. Sulfide-laden waters are typically devoid of oxygen and often provide a protective iron sulfide coating on the submerged portions of the metal (corrosion rates < 1 mpy), while severe corrosion occurs at and above the air-water interface (corrosion rates >20 mpy). While H2O2 use in these applications may increase corrosion below the water surface, corrosion above the water surface is negligible.
• Strong catalytic H2O2 processes. These processes (especially Fenton's Reagent) are very corrosive and should be performed in stainless or lined reactors.