Session: MF-02-08 Materials for Hydrogen Service-Pipeline Infrastructure 1

Paper Number: 123383

123383 - Microstructure and Mechanical Performance of X120 Linepipe Steel in High-Pressure Hydrogen Gas 

To support clean hydrogen energy economy, steel pipelines are being considered as a cost-effective method for long-distance gaseous hydrogen transportation. Hydrogen-induced degradations, especially hydrogen-assisted fatigue, and fracture, must be carefully considered to maintain reliability and structure integrity of steel pipelines in gaseous hydrogen service. Additionally, the susceptibility of steels to hydrogen is well documented to be sensitive to the strength of the steel. Therefore, high strength pipeline steels with yield strength greater than 600 MPa, such as X100 and X120, must be evaluated to assess their susceptibility to hydrogen embrittlement.

In this work, microstructure and mechanical properties, including the fatigue crack growth rate and fracture toughness in high-pressure hydrogen gas (at a pressure of 1000 bar), of an as-received X120 steel were experimentally investigated. The results show the fatigue crack growth rates in gaseous hydrogen of this X120 steel follow the ASME design curves for hydrogen from the Boiler and Pressure Vessel Code Section VIII, Section 3 Code Case 2938-1. The fracture resistance in 1000 bar hydrogen gas is ~ 43 MPa×m^1/2, which is higher than ~ 30 MPa×m^1/2 reported for Cr-Mo and Ni-Cr-Mo pressure vessel steels with the similar tensile strength level (~ 950 MPa). Multi-scale metallurgical analyses were conducted to characterize the underlying microstructural features contributing to the higher fracture toughness of X120 compared to the Cr-Mo and Ni-Cr-Mo steels. The characterization shows a fine (grain size: ~ 1 mm), lower bainitic microstructure and fewer carbides, characteristics created by the thermo-mechanically controlled processing and a lower carbon content, respectively. These features likely provide a higher fracture resistance in gaseous hydrogen compared to the traditional tempered martensitic microstructure of pressure vessel steels with greater carbon contents. A fractography analysis on the tested X120 specimens was also conducted to further reveal its fracture characteristics under high-pressure hydrogen gas. Both fatigue and fracture surfaces exhibit mainly quasi-cleavage cracks. Secondary cracks propagated in a mixed intergranular and transgranular mode. The fracture surface is much coarser and has deeper secondary cracks than that in the fatigue region.  

Presenting Author: Yiyu Wang Oak Ridge National Laboratory

Presenting Author Biography: Dr. Yiyu Wang is currently a R&D Associate Staff in the Materials Science and Technology Division at Oak Ridge National Laboratory. He earned his Ph.D. degree from University of Alberta in 2018. Dr. Wang’s research focuses on advanced manufacturing (welding & joining), physical and welding metallurgy, advanced materials characterization, in-situ/ex-situ mechanical testing. Dr. Wang is an active member of many professional associations, including the AWS and ASME. Dr. Wang has authored more than 50 peer-reviewed journal papers and 40 conference papers in topics of creep-resistant steel welding, pipeline integrity, and joining dissimilar metals. He is a co-recipient of the 2017 W. H. Hobart Memorial Award, and the 2018 and 2023 Warren F. Savage Memorial Award from the American Welding Society.

Authors:

Yiyu Wang Oak Ridge National Laboratory
Zhili Feng Oak Ridge National Laboratory
Yanli Wang Oak Ridge National Laboratory
Joseph Ronevich Sandia National Laboratories
Milan Agnani Sandia National Laboratories
Chris San Marchi Sandia National Laboratory