Stop Methanol from Corroding Wet Gas Pipelines
- 1. Role of Methanol in Oil and Gas Production – How does methanol present a potential integrity threat to operating pipelines? David Richardson, P.Eng. Calgary, AB Canada david@corrosionmitigation.com Company Home Page: www.corrosionmitigation.com (403) 880-2835 www.linkedin.com/in/corrosionmitigation
- 2. Objective of MeOH Injection • MeOH injection “shifts” the hydrate formation curve so that hydrate formation will occur at a temperature much lower than an untreated pipeline (for a given operating pressure) • MeOH injection provides field, operations with a reduced risk of hydrate formation, line plugging, and unplanned operational shutdowns MeOH lowers the temperature at which a solid hydrate will form at a specific operating pressure Untreated MeOH Injection Example: 600 psi No MeOH Injection Hydrate Temperature: 64 F With MeOH Injection Hydrate Temperature: 44 F MeOH creates a lower risk operation
- 3. Design of MeOH Programs for Hydrate Suppression is well Understood Total MeOH injection requirement considers four separate demands: 1. MeOH that enters the vapour (gas) phase; 2. MeOH that enters the hydrocarbon condensate (condy) phase; 3. MeOH that enters the free-water phase; and, 4. MeOH that enters the condensing water phase • based upon PVT behaviour of the specific pipeline operation. Standard Industry Equation used to Calculate Injection Rate for MeOH
- 4. How does MeOH become a corrosion hazard to the pipeline? NOTE: If MeOH injection follows Hammerschmidt Equation MeOH corrosion will not occur MeOH corrosion only occurs when injection volume (greatly ) exceeds the capacity of the pipeline fluids to absorb all of the injected MeOH: • vapour / condy / water / condensed water demand • MeOH is an impure product • low levels of strong organic acid impurities • formic, hydrofluoric, hydrochloric • At regions where MeOH droplets “rain” inside the pipeline a low pH corrosion attack can occur • Corrosion will occur if gas stream is insufficient to “carry- away” the droplets and if pigging does not regularly remove the droplets from the active corrosion region MeOH Corrosion Mechanism – Top-of-the-Line Corrosion Attack from Strong Acids Where MeOH droplets condense and “rain strong organic acids from within the MeOH solution causing high-rate corrosion Mechanism is general thinning of the top-of-pipe 80-100 MPY The corrosion will be active where gas flow is insufficient to remove the droplets, and where pigging is not performed Excess MeOH acid “rain” inside the pipe MeOH corrosion is a rare event
- 5. How can MeOH corrosion be identified ? MeOH Corrosion Mechanism – Top-of-the-Line Corrosion Attack (80-100 mpy) from Strong Acids Sustained MeOH condensation and low pH corrosion occurs on the leeward-side after a moderate inclination provided over-injection of MeOH occurs, the gas flow does not remove (shear-off) the droplets, and pigging is not performed Photograph of pipeline failure where top-of-line thinned by MeOH condensation and strong acid attack Corrosion occurred because: • Massive over-injection of MeOH vs stoichiometric requirement for gas / condensate / water phases • pigging did not regularly remove condensing MeOH / organic acid droplets • shear stress of gas did not “rip” droplets and carry them down the line • the droplets remained at the “scene of the crime” MeOH corrosion is a rare event
- 6. How can MeOH corrosion be identified ? MeOH Corrosion Mechanism – Top-of-the-Line Corrosion Attack (80-100 mpy) from Strong Acids MeOH corrosion is a rare event Photograph of pipeline damage where top-of- line thinned by MeOH condensation and strong acid attack Top-of-Pipeline Wall Thinning