Impact of Operating Temperature Increase on Liquid Pipeline Corrosion Management

Abstract Some liquid pipeline operators are experiencing an upward trend in operating temperatures. This trend is influenced by increasing flowrate through fixed pipeline inventory (viscous heating), hotter product entering some pipelines, and environmental warming (less heat loss to soil and atmosphere). While increasing temperature is known to increase the degradation rate of some coatings and the often-mentioned Arrhenius Equation suggests chemical reaction rate could double with every 10°C temperature increase, the true effect on pipeline corrosion is not fully understood. The real-world impact of temperature changes is a complex interaction of physical and chemical processes. To find the impact of temperature increase on pipeline external corrosion growth rate (CGR), results from laboratory studies and field case studies will be presented. Long term corrosion testing was performed under a simulated coating disbondment condition at various fixed and modulated temperatures (to simulate seasonal variation). Corrosion rates were measured gravimetrically and by measured pit depth. It was demonstrated that Arrhenius level CGR-temperature correlations could be emulated under artificially severe conditions, but more realistic conditions produced a far lower CGR. Long term case histories were conducted on liquid pipelines by investigating their temperature profiles, CGR (derived from consecutive in-line-inspections) and repair frequency before and after temperature increase. For a portion of one pipeline, an increase in maximum and average operating temperature of up to 10°C was observed starting in 2014. This line is 1960s vintage with polyethylene (PE) tape coating. After several years of operation at the increased temperature, no clear correlation was observed between operating temperature increase and corrosion degradation or repair frequency. This same trend is observed on another PE coated line. These observations align with the above laboratory testing. However, in another unique case study, a 1950s vintage coal tar coated pipeline experienced very rapid external corrosion within a cased crossing shortly after the pipeline operating temperature was increased, suggesting that operating temperature increases may still require change management consideration. Recommendations on liquid pipeline corrosion management with increased operating temperature will be presented.