Mechanical properties of low-carbon pipe steel under the influence of pressurized hydrogen gas

Abstract

This study investigates changes in the mechanical properties of the base metal and weld seam of strength-grade X70 electric-welded pipes, as well as their resistance to crack growth, following exposure to high-purity hydrogen at a pressure of 7 MPa. A comparison of the results of reference tests conducted in air with those conducted in hydrogen reveals a change in the tensile strength of the pipe base metal of 3–5%, and a change of 5–9% in the tensile strength of the weld seam. Hydrogen embrittlement is characterized by a degradation of plastic characteristics, including a 5% decrease in relative elongation and an 11% reduction in area in the base metal, and by 22% and 23% reductions in the weld seam, respectively. The experimental results demonstrate that pressurized gaseous hydrogen reduces ductility and causes a more pronounced degradation of the mechanical properties in the weld seam compared to the base metal. Moreover, the study determined the threshold stress-intensity factor for the material in a hydrogen environment. Notwithstanding this degradation, the findings indicate that the pipe metal, with a wall thickness of up to 37 mm and manufactured using the appropriate technology, is suitable for transporting high-purity hydrogen at pressures up to 7 MPa, in compliance with steel product qualification criteria.