Session: MF-02-09 Pipeline Infrastructure 2

Paper Number: 123477

123477 - Comparison Between Fatigue and Fracture Behavior of Pipeline Steels in Pure and Blended Hydrogen With Equivalent Fugacity 

Existing natural gas (NG) pipeline infrastructure can be used to transport hydrogen gas or blends of NG and hydrogen as low carbon alternatives to NG. Pipeline steels exhibit accelerated fatigue crack growth rates and reduced fracture resistance in the presence of hydrogen. The hydrogen-assisted fatigue crack growth (HAFCG) rates and hydrogen assisted fracture (HAF) resistance for pipeline steels depend on the hydrogen gas pressure. Therefore, it is necessary to better understand the correlation between the HAFCG rates and HAF resistance in pure hydrogen and in blends at different pressures and blending ratios. This study aims to correlate and compare the HAFCG rates of pipeline steels tested in two different gaseous environments; high-purity hydrogen (99.9999 % H₂) and a blend of nitrogen with 3% hydrogen gas (N₂+3%H₂). High-purity H₂ gas at a pressure of 3.45 MPa (500 psi) and the blend of N₂+ 3% H₂ gas at a pressure of 73.1 MPa (10600 psi) have equivalent fugacity (thermodynamic partial pressure) of hydrogen. K-controlled FCG tests were performed using compact tension (CT) samples extracted from a vintage X52 (installed in 1962) and a modern X70 (2021) pipeline steel in the two different gaseous environments with equivalent fugacities. Subsequently, monotonic fracture tests were performed in the gaseous environment. The HAFCG rates for different load ratios (R= 0.1, 0.5 and 0.7) are compared for the different steels and gaseous environments. Both the steels contain a banded ferrite and pearlite microstructure. The vintage steel has slightly lower HAFCG rates compared to the modern steel. Nearly identical HAFCG rates were observed for the steels in different environments with equivalent fugacity. The HAF resistance of modern steel was substantially higher compared to the vintage steel. Similar HAF resistance values were obtained for a given steel in the different gaseous environments. This study confirms that fugacity parameter can be used to correlate HAFCG and HAF behavior of different hydrogen blends. The fatigue fracture surface features of the two pipeline steels, tested in the different environments are compared to rationalize the observed HAFCG behavior.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.

Presenting Author: Milan Agnani Sandia National Laboratories California

Presenting Author Biography: Milan Agnani is a postdoctoral researcher at Sandia National Laboratories California working on fatigue and fracture of metals in gaseous hydrogen environment. Previously, he has worked on microstructure development and fatigue behavior of high-carbon steels at Colorado School of Mines, and alloy design and additive manufacturing of Cu alloys for naval applications at Delft University of Technology.

Authors:

Milan Agnani Sandia National Laboratories California
Joseph Ronevich Sandia National Laboratories California
Chris San Marchi Sandia National Laboratories California