Experimental Study of Black Powder Formation in Field TEG Solutions

Black powder formation has been studied in laboratory experiments. The amount and type of solid particles were determined when X-65 carbon steel was exposed to 9 different types of contaminated TEG solutions (95-98 wt% TEG) from various TEG drying units and to 5 TEG solutions mixed in the laboratory. The experiments were run at 5, 25 and 40 °C respectively, the test gas was a blend of 1 bar CO₂ and 0.4 mbar H₂S and the salt content  100 to 10000 ppm. The test duration varied from 60 to 102 days. Corrosion rates were determined from weight loss and varied in the range 1-25 um/year. The experiments showed that the corrosion rate increased significantly when solid iron sulfide accumulated on the steel surface and the liquid contained high amount of dissolved salt. The accumulation of FeS particles increases the cathodic area, facilitates the cathodic reaction and increases the corrosion rate. The typical particle size was 1-2 µm and the size did not increase significantly going from 60 to 102 days exposure. The number of particles however was much larger after 102 days. The paper describes the experimental procedures and discusses the results and the formation mechanism of the particles.