Hydrogen entry into pipeline steel under freely corroding conditions in two corroding media

Hydrogen permeation through API 5L X65 pipeline steel was studied under freely corroding conditions in NACE solution (simulated seawater) and poisoned 1 N H2SO4. A steady state condition with regards to permeation flux is not obtained due to the presence of corrosion product, changing sample dimension and a possible change in hydrogen availability on the corroding surface. A unique way of calculating the sub-surface hydrogen concentration (C0) under non-steady state freely corroding conditions has been developed. The C0 has been evaluated as a function of exposure time in NACE solution and poisoned H2SO4 solution. The sub-surface hydrogen concentration (C0) increased initially but then decreased with increasing exposure to the corroding solutions, after demonstrating an early maximum. The changes in C0 have been explained taking into consideration the corrosion products that developed, the possible anodic reactions, the changes in sample thickness and other issues in the dynamic system.