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On the Susceptibility of Precipitation Hardened Nickel Alloys to Hydrogen Assisted Cracking

Precipitation Hardened (PH) Nickel alloys have been widely used in the Oil & Gas Industry for decades as these materials offer high strength and outstanding corrosion resistance in aggressive environments. They are commonly used in high-strength components in downhole wellhead subsea and Christmas tree equipment. However high profile failures of equipment have occurred including tubing hangers cross-overs and subsea bolts with alloys such as UNS N07718 UNS N07716 or UNS N07725. In all these cases the mechanism identified was Hydrogen Assisted Cracking (HAC) as the result of the interaction between atomic hydrogen adsorbed by the alloy and its microstructure.PH Nickel alloys are all subject to precipitation of secondary and tertiary phases which if processed improperly (particularly during hot working and heat treatment) may adversely affect the material properties required for the intended application. Despite the number of scientific and technical contributions produced over the last years the interaction between these complex microstructural features and atomic hydrogen is still not understood and is further complicated by variations in testing approaches used to simulate severe hydrogen charging conditions. The present paper provides insights on the HAC failure mechanism for API 6ACRA PH Nickel alloys comparing findings from numerous studies. In addition implications for currently adopted standards and emerging specifications are also presented and discussed.

Product Number: 51319-12846-SG
Author: Roberto Morana
Publication Date: 2019
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$20.00
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51317--9655-The Effect of Hydrogen on Plain and Notched Test Specimens of PH Nickel Alloys

Product Number: 51317--9655-SG
ISBN: 9655 2017 CP
Author: Stephen McCoy
Publication Date: 2017
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This paper reviews previous work and shows laboratory results using different test techniques to demonstrate the influence of yield strength and microstructure on the resistance to Hydrogen Stress Cracking of precipitation hardenable Nickel alloys N07718, N09925, N07725, N09945 and N09946.