成果報告書詳細
管理番号20150000000318
タイトル*平成26年度中間年報 水素利用技術研究開発事業 水素ステーション安全基盤整備に関する研究開発 高圧水素ガス用高窒素高強度ステンレス鋼配管の溶接継手に関する研究開発 (株式会社エア・リキード・ラボラトリーズ)
公開日2015/12/2
報告書年度2014 - 2015
委託先名株式会社エア・リキード・ラボラトリーズ
プロジェクト番号P13002
部署名新エネルギー部
和文要約
英文要約Title: Research and Development on Welded Joints of a High-nitrogen and High-strength Stainless Steel Tube for High-pressure Hydrogen Gas (FY2014-FY2015) FY2014 Annual Report

The purpose of this research is the implementation of welded joints for high-nitrogen and high-strength steel XM19, which is expected to be used in hydrogen refueling station.
(1) Development of welding technique for a high-nitrogen stainless steel
Butt welding of tubes were performed by an automatic TIG welding machine. Firstly, welding tests were conducted using argon as the shielding gas but continuous welding was difficult to achieve due to the high current needed to obtain complete penetration of the arc. In FY2014, welding tests using several welding gases were performed and welding conditions were investigated in order to develop a welding method with good workability. Non filler welding is normally conducted for small diameter tubes. However, it is possible that a local decrease of cross-sectional thickness (undercut) appears, especially when thick tubes are welded. In order to avoid undercut and ensure good workability, appropriate filler material and associated welding procedure were developed.
(2) Microstructure evaluation of weld metal
Microstructure of the weld metal and heat affected zone (HAZ) were observed with an optical microscope, and the hardness distribution around the HAZ was measured. It was found that the strength of this alloy was dominated by not only solid solution strengthening due to nitrogen but also grain refinement strengthening. The grain coarsening caused by welding therefore led to a significant decrease in hardness of HAZ. It was suggested that the nitrogen desorption during welding must be prevented to avoid the weakening of HAZ.
(3) Evaluation of hydrogen embrittlement of welded tubes
In practical usage of tubes for high-pressure hydrogen gas, fatigue strength should be considered. The fatigue of tubes by internal pressure is caused by circumferential stress. Hydraulic pressure cycle test or hydrogen gas pressure cycle test are frequently used for the fatigue test of tubes, however, they remain difficult to apply because of their high cost and long duration. Since the evaluation of the fatigue limit of welded tube is one of key issues in this development, these standard pressure cycle tests are not necessarily adequate for our development. In this regard, a fatigue test method simulating inner pressure cycle was developed. This new test method enables evaluation of both high cycle fatigue properties and fatigue limits of tubes. It was confirmed that the morphology of the fatigue fracture of the developed method is similar to that of hydraulic or gas pressure cycle tests. Using this new fatigue test method, S-N diagrams of non-welded tubes and welded tubes were obtained. Interpretation of the fatigue test results and fatigue fracture mechanism is ongoing.
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