Caroline Pipeline Failure: Findings on Corrosion Mechanisms in Wet Sour Gas Systems Containing Significant CO2

Abstract

Abstract A leak occurred in the 5-32S flowline between Junction 1 and the South Compressor Station in the Canada Limited Caroline Complex gathering system near Sundre, Alberta, due to internal wet H2S (hydrogen sulphide) and CO2 (carbon dioxide) pitting corrosion at the bottom of the pipeline. The significant contributing factors to the extremely high pitting corrosion rate, approximately 30 mm/y (1200 mpy), are considered to be unexpectedly high amounts of chloride ions in the produced well fluids, settling of the produced water under low flow conditions, high condensate/water ratio, inadequate inhibition and pigging, and insufficient monitoring programs. Corrosion mechanisms in sour gas gathering systems with significant CO2 concentration were reviewed. Preliminary findings pointed to CO2 partial pressure, not H2S, as a main corrosion rate determining factor. The steps taken to prevent similar future incidents were also reviewed.