Precipitation hardened (PH) nickel alloys have been broadly used in various applications in the oil and gas industry thanks to its high strengths and outstanding corrosion resistance in several aggressive environments. Alloy 718 (UNS1 N07718), Alloy 925 (UNS N09925), Alloy K-500 (UNS N05500), Alloy 725 (UNS N07725), and others are among the most used PH nickel alloys in the oil and gas industry. Despite of their known high corrosion properties, hydrogen embrittlement is one common failure reported by the industry for this class of alloys.
Product Number:
51322-17718-SG
Author:
Julia Botinha, Bodo Gehrmann, Helena Alves
Publication Date:
2022
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Precipitation hardened (PH) nickel alloys have been extensively used in diverse applications in the oil and gas industry due to its high strengths and outstanding corrosion resistance in several aggressive environments. Despite of their known high corrosion properties, hydrogen embrittlement is one common failure reported by the industry for this class of alloys.
PH nickel alloys exhibit complex microstructures, composed by diverse secondary phases. Numerous research activities to study the mechanisms behind hydrogen embrittlement have been carried out in the last years and are still a point of debate in the oil and gas community, mainly when it comes to the interaction of these microstructural features with the hydrogen uptake provided by the service environment. Several mechanisms have been proposed to explain the role of hydrogen in the microstructure of metallic materials. Hydrogen enhanced decohesion (HEDE) has been proposed as the mechanism behind the intergranular character of some of the fracture surfaces, being explained by the presence of grain boundary decoration. However, materials having a very limited amount of precipitates in the grain boundaries still can be susceptible to hydrogen embrittlement. When presenting a transgranular failure mode, the mechanism proposes that the cohesive strength between the metal atoms is reduced by the presence of hydrogen in the bulk. In spite of these observations, limited work is available in the literature in regards to microstructure features and a complete understanding of their roles on the hydrogen embrittlement.
This work is based on a cooperation with the Max Planck Institute for Iron Research in Düsseldorf, Germany. The interaction of hydrogen with microstructure elements primarily present in nickel-based alloys was fundamentally studied using ab-initio and atomistic models, showing that the strength and hardness levels are not primarily decisive for the susceptibility to hydrogen embrittlement, but rather the microstructure.
