Hydrogen Embrittlement in Pipelines Transporting Sour Hydrocarbons

Lamination-like defects in pipeline steels can be of both metallurgical and operational origin. In pipelines transporting hydrocarbon usually such defects are not a big challenge since they do not propagate under operating conditions. Nonetheless, in presence of a corrosion phenomenon and sour gas (H2S), it is possible to observe blisters and cracks which may propagate in the steel. The observed damage mechanisms is Hydrogen Embrittlement and in spite of a huge amount of study and publications available, it is quite difficult for a pipeline owner to get practical data (crack propagation rate for instance) allowing a reliable estimate of the fitness for service of a pipeline. Taking advantage of a pipeline spool containing internal defects that was in service for more than 10 years and recently removed, a comprehensive study is underway to obtain a complete assessment of the pipeline future integrity. The program is comprehensive of study and comparison of ILI reports of the pipeline, to determine the optimum interval between inspections, assessment of inspection results via an accurate nondestructive (UT) and destructive examination of the removed section, to verify ILI results, lab tests program on specimens from the removed spool at operating conditions (75-80 bar and 30°-36° C) in presence of a small quantity of water, H2S (5%) and CO2 (7%), in order to assess defect propagation and to obtain an estimate of crack growth rate, and test in field of available methods to monitor the presence of Hydrogen and/or the growth of defects in in-service pipelines. This quite ambitious program is also expected to be able of offering a small contribution toward a better understanding of HE mechanisms and the engineering application of such complex, often mainly academic, studies.