Fatigue Crack Growth Study of X70 Line Pipe Steel in Hydrogen Containing Natural Gas Blends

Abstract

Blending hydrogen in the natural gas transmission and distribution systems is an option for hydrogen transportation. Integrity management of the existing infrastructure requires a risk evaluation for the planned hydrogen introduction and the challenge of hydrogen embrittlement needs to be considered. The aim of the current study was to evaluate the effect of blending different percentages of hydrogen in methane on the fatigue crack growth rate (FCGR) of X70 line pipe steel. Microstructures associated with base metal, weld center line (WCL) and heat affected zone (HAZ) of girth welds, as well as WCL and HAZ of SAWL seam weld were studied using compact tension specimens based on fracture mechanics. Hydrogen concentrations of 1, 5 and 10 mole% blended in methane were studied. The data was compared to baseline Paris curves in 100% methane as well as the BS7910 in-air mean curve for steel to quantify the increase in fatigue crack growth rate relative to inert environments. In addition, the data was also compared to the ASME B31 curve for carbon steel in hydrogen, to understand the degree of conservatism associated with the ASME curves for the concentrations of H2 evaluated. An increase in FCGR relative to methane baseline was observed for all the microstructures at all concentrations of hydrogen. However, the increase in FCGR relative to the in-air values varied with ΔK. Of the microstructures studied, the base metal showed the highest susceptibility to hydrogen embrittlement for all the hydrogen blends, followed by the girth weld – HAZ location. These two microstructures also had higher hardness compared to the other three locations. A crack growth assessment was also performed for circumferential and axial flaws utilizing the FCGR generated data coupled with pressure cycling data obtained from pipeline operations.

Hydrogen Blending into Natural Gas Pipeline Infrastructure: Review of the State of Technology

“…It should be noted that Cerniauskas et al (2020) claim that pipes constructed of X70 can be suitable for operation with hydrogen because of the low susceptibility to hydrogen-induced subcritical crack growth at heat-affected zones and because fatigue crack propagation can be mitigated; however, other studies have found susceptibility of X70 to hydrogen embrittlement and cracking for both the weld (Nguyen et al 2020) and the parent material (Chandra et al 2021).…”

Challenges toward achieving a successful hydrogen economy in the US: Potential end-use and infrastructure analysis to the year 2100

“…A systematic effort to establish codes and standards for safe operation of hydrogen components and systems is already underway (Office of Energy Efficiency and Renewable Energy: Hydrogen and Fuel Cell Technologies Office, 2021), and in the area of materials compatibility, research is ongoing (Chandra et al, 2021;Nibur et al, 2010;Pluvinage, 2021) with a number of organizations and professional societies developing codes and standards. A notable example is the development of the B31.12 standard by the American Society of Mechanical Engineers (ASME) on hydrogen piping and pipelines (Code and Piping, 2011).…”