On the Hydrogen Embrittlement Resistance of Additively Manufactured Alloy 625 under Cathodic Protection Conditions

Abstract

Nickel alloys, particularly UNS N06625 (Inconel 625), are commonly used in the oil and gas industry in environments unsuitable for conventional stainless steel. When used in subsea components, nickel-based alloys can be coupled with carbon and low alloy steels under cathodic protection, which can lead to the generation of atomic hydrogen at the surface. Atomic hydrogen can then diffuse into nickel alloy components and, under specific conditions, lead to hydrogen embrittlement, a significant concern for the industry. In this study, the hydrogen embrittlement (HE) resistance of Inconel 625 manufactured by Laser Powder Bed Fusion (LPBF)—also known as Selective Laser Melting (SLM)—is investigated and compared with the conventional wrought counterpart. The experiments were performed using the step-loading tensile test method based on the ASTM F1624-12 standard. The tensile samples were charged with hydrogen in 0.6M NaCl (unadjusted pH approximately 6.0) at a galvanostatic current of 50mA, equivalent to -1.4VAgACl. Samples were first pre-charged for 48 h before the in-situ Step Loading test. Charging continued during loading. Results indicated that SLM625 outperformed wrought Inconel 625 in both the grade 1 and grade 2 conditions, exhibiting an excellent HE resistance irrespective of printing direction.