The Combined Influences of Microstructure, Strength, and Titanium Content on the Hydrogen Stress Cracking Resistance of Precipitation Hardened Nickel Alloys

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Precipitation hardenable nickel alloys N09925, N07718, N09945, N09946 and N07725 provide high strength and excellent sour service corrosion resistance for critical downhole oilfield applications. This family of alloys achieves yield strength minimums ranging from 120 to 160 KSI (827-1103 MPa) and can withstand high temperatures and partial pressures of H2S. The primary strengthening mechanism is the formation of γ’ and γ” nanometer sized particles during an age hardening heat treatment.

Product Number: 51323-19348-SG

Author: Stephen A. McCoy, E. Buddy Damm, Brian A. Baker, William MacDonald

Publication Date: 2023

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Increasingly demanding downhole and subsea environments have driven the need for improved hydrogen stress cracking resistance of age hardened nickel alloys. Deleterious phases have been shown to reduce hydrogen embrittlement resistance in field failures and in laboratory studies, but it is also known that hydrogen embrittlement performance can suffer even in the absence of deleterious phases. A series of laboratory scale VIM heats were produced, solutionized and aged to assess the influence of chemical composition on hydrogen stress cracking resistance. Laboratory results were then scaled-up and applied to mill produced and heat-treated material, and hydrogen embrittlement performance was again tested. For all variants presented, the absence of significant deleterious phases was confirmed with light and scanning electron microscopy. Results for both laboratory and production material are summarized and show that enhanced hydrogen embrittlement performance can be achieved through the reduction of Ti content. The results and data presented are considered as patent pending.