In carbon steels, wet CO2 corrosion can cause a leak while leaving most of the rest of the tube/pipe untouched. A problem only for the oil and gas industry? No, CO2 corrosion is relevant to many industries.  CO2 is in water, and it is a reaction product in many industries. 

The pipe below operated for less than three years when operations personnel noted a product buildup on the outer surfaces of the horizontal line. The line carried warm, moderately alkaline water, and it was only partially filled, but it was open to the atmosphere at the discharge. This leak was the second failure of the line; the first failure had similar morphology. What happened?

The top image shows the 12 o’clock (Top) pits. The left middle image is a close-up of the Top pits on the pipe’s inside surface. The middle right image shows the pipe’s inside surface 6 o’clock side; it has some pits, but it does not have the deep pits shown on the Top side. The bottom images show the metallographic cross-sections of the Top (left) and 6 (right) o’clock sides of the pipe. The losses on the Top side are extensive.

In this instance, CO2 resulted in the localized carbon steel attack since:

  • The 12 o’clock pits are narrow, deep, undercut, and generally scale-free, typical of pitting in very low pH environments, which can develop in condensates with CO2.
  • Based on X-ray Diffraction (XRD) analyses, the ID scale is primarily siderite (FeCO3). Siderite is a common corrosion product of carbon steel in the presence of CO2 and water.

Condensation along the Top of the line does not have the same buffering compounds of the process fluid. Atmospheric oxygen in the line could have acidified the condensation as the process flow did not always clear it. Several line modifications were implemented to mitigate the damage; this included the pipe inside diameter being coated.