Evaluation of Hydrogen Charging in Ni-Cr-Mo Alloys Using the Hot Extraction Method

RIP2025-00055: Nickel superalloys are widely used due to their exceptional mechanical properties at elevated temperatures and superior corrosion resistance, making them indispensable for applications such as submarine components and fasteners in the oil and gas industry. Among these alloys, Fe-Cr-Ni-Mo austenitic are the most commonly used, with nickel (Ni) as the primary alloying element. However, the harsh operational conditions in offshore environments often necessitate the implementation of cathodic protection on metallic components, a practice that may inadvertently induce hydrogen embrittlement (HE) due to hydrogen generation.

In light of this, the selection of Ni alloys that combine high mechanical strength and corrosion resistance with low susceptibility to HE is critically important. This study aims to evaluate hydrogen charging in Ni-Cr-Mo alloys using the hot extraction method.

For this purpose, three distinct high-molybdenum (Mo) austenitic alloys, previously subjected to cold rolling, were selected. The test specimens, each with an exposed area of 3 cm², underwent electrochemical hydrogen charging. The tests were conducted in a 0.5 M H₂SO₄ aqueous solution with a cathodic current density of 5 mA/cm² for durations of 24 h and 168 h to enable a comparative analysis among the studied materials. The experimental setup included a 125 mL electrolytic cell, a platinum wire counter electrode (0.5 mm diameter and 2 m in length), and an Ag/AgCl reference electrode in 3 M KCl. Additionally, the potential was continuously monitored throughout all tests.

After the specified charging periods, the samples were removed, cleaned, and immediately analyzed using a Bruker G4 PHOENIX DH device. Diffusible hydrogen content was measured using the hot extraction method, with a carrier gas in a tubular furnace coupled to a thermal conductivity detector (TCD).

This study is ongoing, with additional tests being conducted. Preliminary results indicate no significant variations in the diffusible hydrogen content comparing the two test durations. Ultimately, this research aims to provide a deeper understanding of the hydrogen behavior in different Ni-Cr-Mo alloys, contributing to their optimization for offshore applications.