Different effects of pure hydrogen vs. hydrogen/natural gas mixture on fracture toughness degradation of two carbon steels

Abstract

This work aims to investigate the fracture toughness of X80 and GB20# pipeline steel in hydrogen and actual natural gas/hydrogen mixture. It is found for the first time that pure hydrogen and natural gas/hydrogen mixture had different deteriorating effects on the fracture toughness of the two kinds of materials. The fracture toughness of X80 deteriorated the most in pure hydrogen gas compared with that in natural gas and the mixture. However, for GB20#, the fracture toughness degradation in the mixture was the most serious, approximately 2.5 times of that in hydrogen. The fracture surfaces observation showed that X80 evolved from ductile dimple fracture in natural gas to brittle quasi-cleavage fracture in hydrogen-containing environment, while GB20# in lower pressure was always ductile dimple fracture, resulting in its higher fracture toughness and slighter deterioration.