The effect of the pipe forming on the hydrogen permeation of the linepipe steel was investigated in aqueous sour environment with respect to the steel thickness and the circumferential position of the steel pipe. The hydrogen permeation data shows well the effects of the strain level and of the inclusion distribution. The HIC susceptibility increases as the ratio of the thickness (t) and pipe diameter (D) is increased since the level of strain is increased. The thickness of steel pipe affects not only the t/D ratio but also the size and distribution of the inclusion in the steel. Between the 12 mm and 18 mm thick steel pipes, the HIC susceptibility is the highest at 180o position of the steel pipe manufactured from the thicker one.
Hydrogen damages have caused many serious failures in the pipe lines used for oil and gas transportation and mostly in the environment contains hydrogen sulfide (H2S). [Bruno, 1999] Most hydrogen related problems are caused by the hydrogen atoms reduced by the electrochemical reaction on the surface of the linepipe steels when it is exposed to the aqueous sour environment. The hydrogen sulfide environment can suppress the recombination reaction of the hydrogen atoms to form hydrogen molecules and accelerate the rate of the hydrogen atoms to diffuse into the steel substrate. [Abayarathna, 1996] If the hydrogen atoms are accumulated to a certain critical level, hydrogen assisted cracking can occur and the cracks are initiated in the steel matrix. [Liou, 1993] The hydrogen assisted cracking problems such as hydrogen induced cracking (HIC) or sulfide stress cracking (SSC) have been the main issues for pipeline services in the sour environment. Numerous electrochemical permeation measurements have been conducted to investigate the characteristics of hydrogen related cracking for the non-deformed linepipe steel sheets.
