Utilizing Robotic Inspection to Optimize Detection and Management of Localize Corrosion

Internal corrosion is a major integrity threat in oil and gas processing facilities, especially where carbon dioxide is present in the process stream. CO2 combines with water to form carbonic acid, which can aggressively attack carbon steel piping (up to 1000 mpy). Most often, the corrosion is highly localized either on the top of line, on the bottom of the line, or in areas of turbulence such as elbows. The top of line attack often occurs when the stream is cooled to below the dew point temperature. On the other hand, corrosion will occur at the bottom, if there is a separate water phase. Severity of CO2 is further influnced by partial pressure of CO2, pH, operating temperature, flow velocity, and the presencse of oxygen. Increasing CO2 partial pressure lowers the pH of the aqueous phase, resulting in higher corrosion rate. High flow velocities, turbulence, and impingement, particularly downstream of control valves, reducers, elbows, and tees can promote localized attack. Corrosion commonly initiates at locations where CO2 condenses from the vapor phase or where liquid water accumulates, such as low points, dead legs, and water–vapor interfaces. This form of attack produces deep, flat-bottomed pits, a type of damage often known as mesa-type CO2 corrosion. The challenge with this type of localize corrosion is that it could difficult to detected if inspection coverage is limited to widely spaced points. Traditional inspection programs for piping typically rely on periodic ultrasonic thickness (UT) measurements at defined condition monitoring locations (CMLs). While this type of inspection is useful for general loss of thickness, it could miss spots of localized corrosion, if it falls between CMLs. This was the case in a gas processing plant that experienced a minor leak due to localized CO2 corrosion in a section of pipe, where UT measurements did not reveal any significant loss of thickness. The incident highlighted the need for a comprehensive inspection approach to identify localized thinning before failure. To manage the threat of localized corrosion, the inspection team utilized a combination of Risk-Based Inspection (RBI) and robotic inspection. RBI study prioritizes inspection efforts on the high-risk piping, where localized corrosion is expected. Based on the RBI study, Remote Visual Inspection (RVI) were employed to directly observe the internal surfaces of the piping through robotic crawler cameras. Based on RVI findings, manual UT is utilized to confirm the thickness at the concerned location. The integrated approach successfully identified severe localized CO2 corrosion in a gas compression system, enabling timely repairs before a failure.