Periodic cleaning of sales gas lines often yields large quantities of material known as black powder. This paper describes a research study that was conducted to provide estimates for corrosion rates of carbon steel in TEG-water mixtures with TEG content in the range 0.0 wt% to 99.5 wt%.

Glycol systems are widely used in gas processing plants for the removal of contaminants such as moisture from the gas. Since the majority of the piping and vessels in these plants are fabricated from carbon steel there is a high potential for corrosion. This paper provides a brief overview of some of the major corrosion mechanisms associated with Glycol regeneration unit. In addition a case study from a Try-Ethylene Glycol (TEG) regeneration system is also discussed where localized corrosion was noticed in the Glycol reboiler and surge vessel. Booster Station facility receives gas from Gathering Center for further compression and removes moisture before being exported to the refinery. This is achieved by compression of gas in multiple stages with locally provided compression equipment and processed in glycol dehydration units to remove the moisture. Water vapor removal from the gas stream is achieved by contacting the wet gas counter-currently with lean (dry) TEG in the glycol contactor column. The rich glycol having water content is routed through a pre-heating coil flash tank filters and finally comes in the Glycol reboiler. Due to the high temperature in reboiler the glycol loses its ability to hold water. Separated water is vaporized and leaves through top of the still column. The regenerated glycol flows to the surge tank and from there it is pumped to Glycol absorber. During one of the Plant Maintenance shutdowns Glycol reboiler and surge vessel were opened for internal inspection and appreciable corrosion was noticed in the top sections of the vessels. A study was initiated to find out the probable causes of the deterioration. Corrosion products were collected for XRD analyses. Also chemical analysis of lean & rich Glycol samples taken from various streams was carried out. A corrosion pattern was established along the glycol regeneration circuit which revealed mainly the low pH of Rich Glycol due to possible decomposition reaction of glycol into organic acid. Presence of Iron sulfate and various forms of iron sulfide including Pyrite Greigite and Pyrhotite (also referred to as Black Powder Derivatives) all known to expedite localized corrosion and deterioration of the metals. This paper presents the findings based on the analysis of the corrosion products and glycol samples and discusses the possible corrosion mechanisms. Recommendations are also provided to ensure the integrity and reliability of these vessels for sustainable operation. This case history demonstrates the diverse nature of the causes of Glycol related corrosion in plants and the differing approaches that have to be taken to mitigate corrosion in Glycol regeneration equipment.

Pipeline quality gas is normally dried in Triethylene Glycol (TEG).  This paper explores how TEG vapor can exist in a pipeline in a similar manner to water, and possibly lead to corrosion. TEG vapor can condense at long distances down a gas pipeline as the line cools.