Hydrogen-Accelerated Fatigue of API X60 Pipeline Steel and Its Weld

Abstract

In this work, the hydrogen fatigue of pipeline steel X60, its girth welds and weld defects were investigated through in situ fatigue testing. A novel in situ gaseous hydrogen charging fatigue set-up was developed, which involves a sample geometry that mimics a small-scale pipeline with high internal hydrogen gas pressure. The effect of hydrogen was investigated by measuring the crack initiation and growth, using a direct current potential drop (DCPD) set-up, which probes the outer surface of the specimen. The base and weld metal specimens both experienced a reduction in fatigue life in the presence of hydrogen. For the base metal, the reduction in fatigue life manifested solely in the crack growth phase; hydrogen accelerated the crack growth by a factor of 4. The crack growth rate for the weld metal accelerated by a factor of 8. However, in contrast to the base metal, the weld metal also experienced a reduction of 57% in resistance to crack initiation. Macropores (>500 µm in size) on the notch surface reduced the fatigue life by a factor of 11. Varying the pressure from 70 barg to 150 barg of hydrogen caused no difference in the hydrogen fatigue behavior of the weld metal. The fracture path of the base and weld metal transitioned from transgranular and ductile in nature to a mixed-mode transgranular and intergranular quasi-cleavage fracture. Hydrogen accelerated the crack growth by decreasing the roughness- and plasticity-induced crack closure. The worst case scenario for pipelines was found in the case of weld defects. This work therefore highlights the necessity to re-evaluate pipelines for existing defects before they can be reused for hydrogen transport.

Assessing Hydrogen Embrittlement in Pipeline Steels for Natural Gas-Hydrogen Blends: Implications for Existing Infrastructure

“…Specifically, the specimen exhibited approximately a 70% reduction in fatigue life at 1 wppm hydrogen content. This significant decline in fatigue life due to HE aligns with the findings of Meng et al [50] and Faucon et al [51], however they employed different methodologies. Both studies utilized in-situ gaseous hydrogen charging, contrasting with the electrochemical hydrogen charging method employed in this study, and while Meng estimated fatigue life using fatigue crack growth rate models, Faucon conducted actual fatigue life tests.…”

“…Using the mentioned method for predicting the fatigue life, their findings indicated a severe reduction in fatigue life, from 24,431 cycles in nitrogen gas to 2,130 cycles in a 5 vol% hydrogen blend at 12 MPa. Among the few studies on hydrogen embrittlement (HE) of pipeline steels that perform fatigue life tests, Faucon et al [51] developed an in situ gaseous hydrogen charging fatigue setup to investigate the hydrogen-accelerated fatigue life of API X60 pipeline steel. They tested specimens at hydrogen pressures of 70 and 150 barg.…”

The Simulation of Extremely Low Cycle Fatigue Fracture Behavior for Pipeline Steel (X70) Based on Continuum Damage Model

“…In order to conduct fracture failure analysis of pipelines effectively, it is necessary to identify the fracture modes of the pipeline material that may occur during a pipeline's service [2][3][4]. Fracture modes of pipeline steel can be commonly classified into several categories, including ductile fracture, brittle fracture and fatigue fracture [5][6][7][8][9][10][11]. Pipeline steel is generally required to have high plasticity and toughness.…”

“…At low temperatures, brittle fracture of the pipeline steel may occur due to a decrease in toughness [10,13]. Fatigue fracture is also a common failure mode of pipeline steel which occurs under cyclic load [5,6,14]. According to the fatigue cycles, fatigue fracture can be further divided into low cycle fatigue fracture (LCF, N f < 10,000) and high cycle fatigue fracture (HCF, N f > 10,000).…”