Experimental study of the impact of hydrogen embrittlement on the ductility of natural gas pipeline steels

Abstract

The mechanical integrity of low-carbon and low-alloy steels is significantly affected by hydrogen embrittlement (HE), particularly in hydrogen-rich environments. Despite extensive research on HE, investigations involving hydrogen-natural gas blends remain limited. This study addresses this gap by examining the effects of HE on the tensile properties of X52, X60, and X70 pipeline steels.

The study evaluates the reduction of area (RA) and elongation in these steels under exposure to pure hydrogen at pressures ranging from 0 to 6.9 MPa and hydrogen-natural gas blends with hydrogen concentrations between 0 % and 100 % by volume. All experiments were conducted at ambient temperature to isolate the effects of hydrogen-induced embrittlement. The susceptibility of the selected pipeline steels to HE was assessed in both pure hydrogen and mixed gas environments.

The results from pure hydrogen exposure reveal a systematic decline in ductility with increasing pressure, as evidenced by reductions in RA and elongation. This trend underscores the critical need for HE mitigation strategies in hydrogen-exposed pipeline materials. In contrast, the mixed gas experiments exhibited distinct RA and elongation variations with increasing hydrogen concentration. The highest RA value in pure hydrogen was observed at zero hydrogen pressure, whereas in the blended gas environment, the maximum RA was recorded at approximately 7.5 % hydrogen concentration.

Comparative analysis under equivalent hydrogen partial pressure conditions indicates that embrittlement is less severe in mixed gas than in pure hydrogen at low partial pressures (∼0.52 MPa). A similar trend was observed in elongation measurements. However, at hydrogen concentrations exceeding 20 %, embrittlement effects in mixed gas surpassed those observed in pure hydrogen under equivalent partial pressure conditions. These findings provide critical insights into the interaction between hydrogen exposure and tensile properties, contributing to the development of hydrogen-compatible pipeline materials.