Session: MF-02-09 Materials for Hydrogen Service (Joint with C&S)-9

Paper Number: 153076

153076 - Fracture Toughness and Fatigue Crack Growth Characteristics of Api 5l X65 Linepipe and the Girth Welds Under High-Pressured Hydrogen Gaseous Environment 

Abstract: 

Hydrogen is considered one of the essential energy resources for a carbon-neutral society, and its demand is expected to increase in the future. Several methods have been proposed for transporting hydrogen. The appropriate transport method depends on the state of the hydrogen and the distance to be transported, but pipelines may be an efficient way to transport large quantities of gaseous hydrogen. However, carbon steel pipes, used for natural gas, are known to be susceptible to hydrogen embrittlement. Many researchers have investigated the characteristics of hydrogen embrittlement, such as strength, ductility, fracture toughness, and fatigue crack propagation characteristics. Most of these studies have focused on base materials, with a few specializing in welded joints, particularly on-site circumferential welding parts. In many cases, fractures initiate from welds due to stress concentration and initial defects, so investigating the fractures of welds is important. In this study, we evaluated the fracture toughness and fatigue crack growth characteristics of APIX65 under hydrogen gas.

For evaluating fracture toughness, JIC tests were conducted under various pressures and temperatures. Initially, the pressure was set between 0 and 90MPa at 50°C. Fracture toughness decreased due to hydrogen up to 10 MPa, after which saturation trends were observed. Next, the temperatures were set at -10 and 50 °C under a 10MPa hydrogen gas pressure. Results showed the effects of hydrogen embrittlement were significantly higher at 50°C than at -10°C. Lastly, all of the test results converted to K-value exceeded the ASME standard value, 55MPa m^(1/2).

Fatigue crack propagation tests were conducted at room temperature under a hydrogen pressure of 10 MPa. The results showed that the crack propagation rate at a hydrogen pressure of 10MPa was ten times faster than in an atmospheric environment. However, these results were slower than the fatigue crack growth specified in ASMEB31.12, making it applicable. Furthermore, fatigue crack growth analysis revealed a lifespan considerably longer than the anticipated service life.

Presenting Author: Yuki Kiyokawa NIPPON STEEL ENGINEERING CO., LTD.

Presenting Author Biography: He earned master degree at Osaka university in 2020.
He joined Nippon Steel Engineering Co., Ltd. in 2020 as a welding engineer.
He began his career in the pipeline welding construction department of Oil & Gas.
Then moved to Welding Technology Section, Engineering R&D Institute, where he is currently engaged in research and development related to welding.

Authors:

Yuki Kiyokawa NIPPON STEEL ENGINEERING CO., LTD.
Yuji Kisaka NIPPON STEEL ENGINEERING CO., LTD.
Fumiaki Kimura NIPPON STEEL ENGINEERING CO., LTD.
Yasuhiro Kawai NIPPON STEEL ENGINEERING CO., LTD.
Keigo Manabe NIPPON STEEL PIPELINE & ENGINEERING CO., LTD.
Shusuke Fujita NIPPON STEEL PIPELINE & ENGINEERING CO., LTD.
Hiroto Shoji Osaka University
Mitsuru Ohata Osaka University