Buried carbon steel fuel transmission pipelines, protected by external coatings and cathodic protection, are known to experience transgranular stress corrosion cracking (TGSCC). Failure analysis of failed pipelines and laboratory tests have indicated that hydrogen plays an important role in the overall failure mechanism. However, the role of various groundwater constituents in TGSCC and the source of hydrogen are not well understood. The objective of this research was to further understand the mechanism of TGSCC by examining the environments in which TGSCC can occur and near-neutral pH can be maintained. Specifically, this research focuses on the production of hydrogen through the interaction of iron with carbonic acid. (H2CO3) and bicarbonate (HCO3(-)) as based on the Colwell-Leis mechanism. The Colwell and Leis mechanism attributes the hydrogen generation, in groundwater solutions, to the decomposition of bicarbonate and reaction with metal ions to form metal carbonate. Results from coupon exposure tests and slow strain rate tests indicate that TGSCC on pipeline steels can be produced in simple bicarbonate solutions. Slow strain rate tests in simple bicarbonate solutions with 5% carbon dioxide (CO2) produced cracks that have similar crack morphologies to what is found in the field. These results suggest that the environmental conditions for TGSCC and intergranular stress corrosion cracking (IGSCC) on pipeline steel surface are related and may change from one to another by changes in the applied cathodic potential.
Investigating a mechanism for transgranular stress corrosion cracking on buried pipelines in near-neutral pH environments
Untersuchung des Mechanismus der transkristallinen Spannungsrisskorrosion an erdverlegten Rohrleitungen im pH-neutralen Bereich
Corrosion, Houston ; 63 , 10 ; 932-939
2007
8 Seiten, 3 Bilder, 7 Tabellen, 19 Quellen
Aufsatz (Zeitschrift)
Englisch