Electrical Conductivity of Pipeline Deposits Under Pressure and Their Impacts on Sales-Gas Pipeline Cathodic Protection Systems

Abstract

Summary Natural gas pipelines are critical for safe and efficient energy transport across large distances. To maintain operational safety, pipelines use cathodic protection systems that minimize the rate of external corrosion. This work characterizes the effects of black powder deposits, a widely experienced operational hazard across the natural gas industry, on the failure of pipeline cathodic protection systems due to electrical “shorting” of isolation devices. Black powder sludgy deposits from coal seam gas (CSG) pipelines were analyzed, revealing electrical conductivity values within the range of 580 to 5400 µS/cm when under pipeline pressure. These values were used to calculate the internal resistances of monolithic isolation joints (MIJs), a type of electrical isolation device, to show that electrical shorting (internal resistance of < 100 Ω) can occur for black powder sludgy deposit thicknesses in the range of millimeters. To reduce the frequency of such shorting events, it is recommended that upstream dehydration systems be designed to reduce carry-over of triethylene glycol (TEG), that internal nonconductive coatings be applied to isolation devices, and that these devices are installed in ways that facilitate regular cleaning.